Hiroshima University Doctoral Thesis

Multinuclear Coinage Metal Complexes ofBis(diphenylphosphinyl)-functionalized
Dipyrido-annulated N-heterocyclic Carbene(ࣅࢫ(ࢪࣇ࢙ࢽࣝ࣍ࢫࣇ࢕ࢽࣝ)ᐁ⬟ᇶࢆ᭷ࡍࡿࢪࣆࣜࢻ⦰⎔ N-࣊ࢸࣟࢧ࢖ࢡࣜࢵ
ࢡ࢝ࣝ࣋ࣥࡢከ᰾㈌ᖯ㔠ᒓ㘒య)

2019
Department of Chemistry,
Graduate School of Science,
Hiroshima University
Zhang, SIHAN

Table of Contents
1. Main Thesis
Multinuclear Coinage Metal Complexes of Bis(diphenylphosphinyl)functionalized Dipyrido-annulated N-heterocyclic Carbene(ࣅࢫ(ࢪࣇ࢙ࢽࣝ࣍ࢫࣇ࢕ࢽࣝ)ᐁ⬟ᇶࢆ᭷ࡍࡿࢪࣆࣜࢻ⦰⎔ N࣊ࢸࣟࢧ࢖ࢡࣜࢵࢡ࢝ࣝ࣋ࣥࡢከ᰾㈌ᖯ㔠ᒓ㘒య)   Zhang, SIHAN

2. Thesis Supplements(1) Luminescent
Diand
Tetranuclear
Gold
ComplexesofBis(diphenylphosphinyl)-functionalized Dipyrido-annulated N-heterocyclic
CarbeneS. Zhang, R. Shang, M. Nakamoto, Y. Yamamoto, Y. Adachi and J. Ohshita
Inorganic Chemistry 2019, 58(9), 6328–6335.
(2) Bis(diphenylphosphinyl)-functionalized Dipyrido-annulated N-heterocyclic
Carbene towards Silver(I) and Copper(I)S. Zhang, R. Shang, M. Nakamoto, Y. Yamamoto, Y. Adachi and J. Ohshita
Dalton Transactions 2019, accepted.

Main Thesis

Multinuclear Coinage Metal Complexes ofBis(diphenylphosphinyl)-functionalized
Dipyrido-annulated N-heterocyclic Carbene

Department of Chemistry,
Graduate School of Science,
Hiroshima University

Zhang, SIHAN

Contents
Chapter 1. General Introduction
1-1. N-heterocyclic Carbenes

2

1-2. Functionalized N-heterocyclic Carbenes

5

1-3. Polynuclear Coinage Metal NHC Complexes

6

1-4. Phosphine-functionalized N-heterocyclic Carbenes

8

1-5. Bis(diphenylphosphinyl)-functionalized

Dipyrido-annulated

N-

10

P2

heterocyclic Carbene (dpa -NHC)
1-6. Purpose of This Work

13

References

14

Chapter 2. Di- and Tetranuclear Au(I) Complexes of Bis(Diphenylphosphine)Functionalized Dipyrido-Annulated N-Heterocyclic Carbene
2-1. Introduction

20

2-2. Syntheses and Characterization of Dinuclear Au Complexes Based on

21

P2

dpa -NHC and its carbene precursor
2-3. Syntheses and Characterization of Tetranuclear Au Complexes Based28

P2

on dpa -NHC
2-4. Alternative Syntheses of Di- and Tetragold Complexes 3 and 4 from

27

Complex 2
2-5. Photophysical Properties of the Free Carbene Ligand dpa P2-NHC and

31

Complexes 1-4
2-6. Conclusion and Outlook

37

References

38

Chapter 3. Multinuclear Cu, Ag, and Bimetallic Cu-Ag Complexes ofBis(diphenylphosphinyl)-functionalized Dipyrido-annulated N-heterocyclic
Carbene3-1. Introduction

41

3-2. Syntheses of Dinuclear Silver Complex Ag2L2

43

3-3. Syntheses of Neutral Tetranuclear Copper Complex Cu4LBr452

3-4. Syntheses of Dinuclear Copper Complex Cu2L2

56

3-5. Syntheses of Tetranuclear Bimetallic Ag/Cu Complex Ag2Cu2L2 from

61

Cu2L2
3-6. Syntheses of Tetranuclear Cu(I) Complex Cu4L2·2CH3CN from Cu2L263

3-7. Syntheses of Pentanuclear Cu(I) Complex Cu5L2Br3 from Cu2L2

67

3-8. Syntheses of Homonuclear Copper Complexes Cu4 L2·2MeCN and70

Cu5L2Br3 from dpaP2-NHC and Heteronuclear Complexes Ag2Cu2L2
from Ag2L2
3-9. Photophysical Properties of the Obtained Silver and Copper Complexes

72

3-10. Conclusion and Outlook

75

References

76

Chapter 4. Conclusion and Outlook

80

Experimental Section

85

Crystal Structure Analysis

128

Reference134

List of Publications
Acknowledgement

Chapter 1

General Introduction

1-1. N-heterocyclic Carbenes
Pursuing the carbon-based species which feature unique electronic properties and concomitantreactivity has always been the active area of chemical research. The neutral compounds N-heterocycliccarbenes (NHCs), containing a divalent carbon atom with a six-electron valence shell and stabilized
by at least one neighboring nitrogen atom within the heterocycle, have attracted considerable attention
since the landmark isolation of the first stable NHC via the deprotonation of 1.3-di-1adamantylimidazolium chloride with potassium tert-butoxide or sodium hydride in the presence of
catalytic dimsyl anion by Anduengo et al. in 1991,1 due to their peculiar topology. So far, a large
number of NHCs with diverse electronic and steric properties were synthesized and structurally
characterized, in which 5-membered rings account for the largest part.2 Among them, imidazole-based
NHCs (Figure 1. A), the carbene carbon stabilized by two neighboring nitrogen atoms, are the mostrepresentative and famous species, which, to date, have received enormous interests from the worldwide chemists.
Other NHCs with 5-membered rings (Figure 1) include N-substituted (N,N’-disubstituted)
imidazolidinylidenes (B), triazolinylidenes (C), benzimidazolinylidenes (D),3 the ‘abnormal’imidazolinylidenes (E)4 and the cyclic(alkyl)(amino)carbenes (CAACs) (F) which gathered increasing
interests since its first isolation by Bertrand et al. in 2005,5 and so forth. Though the reduced
conjugated π-system, B can still stably exist at room temperature, demonstrating the unsaturation in
the imidazole ring is not required to produce a stable nitrogen-substitued carbene. D showed aenhanced thermal stability compared to A due to their widened and 10 electron conjugated π-system.
In comparison to A which exhibit strong σ-donation but weak π-acceptor properties, F showed not
only strong σ-donation but also relativey stronger π-acceptor properties so that these ligands can firmly
bind to transition metals and main group elements. Due to their enormous practical significance, manyof the NHCs are commercially available. Meanwhile, these compounds have found numerous
applications, for instance, as supporting ligands for transition metal complexes, stabilizing p-blockelements and as organocatalysts. 6 This, after all, benefits mostly from the distinct features,electronically and sterically, of NHCs.

Figure 1. Structures of some of the most classical NHCs
In detail, due to the bent and sp2-like arrangement of the carbene carbon as shown in Figure 2 of
their ground-state electronic structure, NHCs are generally considered as singlet carbenes.7 This
endows these compounds with nucleophilic ability since the lone pair in carbene carbon situates in theplane of the heterocycle of NHCs. Consequently, NHCs can serve as the strong σ-donor groups to bind2

to a broad range of (non)metallic species, which leads to the formation of metal NHC complexes withstrong metal-Ccarbene bonds. Comparatively, these bonds are generally stronger than that of their mimics,
tertiary phosphines.8 The enhanced strength and distinct features of the interactions between NHC andcoordinated metals have notable influence on the stability, structure and reactivity of the resulting
complexes.9

Figure 2. Representative ground-state electronic structure of NHCs
In general, it is fair to say that most of the NHCs can be described as fan- or umbrella-shaped with
the nitrogen-substituents flanking the carbene carbon prefering to point towards the coordinated metals(Figure 3).9,10 Therefore, any change of the nitrogen substituents could have a effect on the stericenvironment of the metal centers, thereby on the steric and electronic properties of NHCs,
independently. While, in stark contrast to NHCs, the sp3-hybridized phosphines exhibit a cone-shaped
spatial arrangement (Figure 3), such that changing the substituents of phosphines invariably
influences the steric and electronic properties.9 This is also one of the advantages why the NHCs canrival their mimics of phosphines to become mainstream of chemical research as ancillary ligands.
Furthermore, it is worth noting that thanks to decades of research on the preparation of heterocyclic
compounds,11 facile modifications of the peripheral architecture of NHCs are accessible by simple
variation of the starting materials.

Figure 3. Steric influence of NHCs and phosphines on the metals which they are coordinated to.
While one should keep in mind that although NHCs have gained such interest, their scaffolds arestill very limited, namely, the imidazole-based NHCs take up the largest part of research. The NHCs
with different scaffolds, such as those with larger ring size and increased aromaticity, are still
underexplored.12 So far, only a handful of this kind of NHCs have been reported, including theimidazo[1,5-a]pyridin-3-ylidenes,12a,dindazolin-3-ylidenes,12b,c

12e,k,l,m,o,p,r

heptyl)phenyl)-imidazol-2-ylidenes,

multicyclopentyl(or12fisoquinolin-1-ylidenes,

hexyl,

5,7-bis(1,1-dimethylethyl)-

5H-imidazo[4,5-f]-2,1,3-benzothiadiazol-6-ylidene,12g mixed amino-amido NHCs,12h,j porphyrin–
NHCs12i and phenanthro[4,5-abc]phenazino[11,12-d] or acetonaphtho[1,2-b]quinoxaline[11,12-

3

d]imidazol-2-ylidenes12n,q. Given this, as the supporting ligands NHCs have great potential to be
exploited for a long time.

41-2. Functionalized N-heterocyclic Carbenes
In principle, NHCs are considered as typical monodentate σ-donor ligands, thus the coordinationof NHCs towards transition metals leads, in most cases, to the formation of mononuclear metalcarbene complexes. These complexes are suitable in a broad applications such as catalytictransformations, medicinal and luminescent materials.9 Whereas with the rapid development ofmodern chemistry, research scope has been gradually extended from those monometallic NHC
complexes to multimetallic NHC complexes, which gained in more and more popularity recently
owing to their optoelectronic,13 catalytic, medicinal and material applications.14 Usually, two or more
donor centers, such as NHC, phosphines, oxygens or nitrogens, are required for synthesizing themultimetallic complexes. The polydentate ligands which integrate the donor centers into one ligand
seem to be a good choice as building blocks for multimetallic complexes. In this contribution,functionalized NHC ligands, as one of the polydentate ligands, attracted considerable attention.
Introducing the functional groups into the NHC ligands allows for hemilability, modification of
the bite angles, establishing a specific ligand geometry or fine-tuning the electronic or steric propertiesof the ligand.15 Hence, in a forward sense, functionalization of this class of ligands seems to benecessary. Furthermore, the functional groups of NHCs can strongly influence the reaction behaviors
between ligands and the metals and structural motifs and properties of the concomitant products: (1)functionalized NHCs serving as pincer ligands type can afford more stable coordination environment
for the metal centers of mononuclear NHC complexes since the functional groups can serve as the σdonor ligand to coordinate with the metal center such that to further stabilize it; (2) it is conceivablethat the designed functionalized NHCs are capable to precisely tune the metal coordination spherethrough their multiple donor atoms;16 (3) the multidentate NHC ligands functioning as the building
blocks can provide a broad platform for selectively constructing the polynuclear metal NHC
complexes. Meanwhile, interesting coordination chemistry of the functionalized NHC ligands towards
transition metals are usually found and has attracted considerable attention of researchers.

51-3. Polynuclear Coinage Metal NHC Complexes
Coinage metal complexes bearing NHC ligands have been widely studied for their diverse
coordination geometries and a variety of applications. For example, Ag(I)-NHC complexes have been
widely utilized as reagents of transmetallation for the synthesis of other transition metal-NHC
complexes.17 Meanwhile, they showed excellent performance as catalysts in many important organic
transformations.18 Multinuclear Ag(I)-NHC complexes usually feature attractive intramolecular AgAg interactions and diverse structures which are of current interest to researchers. Au(I)-NHC
complexes are well-defined precatalysts in some of the most important transformations. 19 Oftentimes,
multinuclear Au(I)-NHC complexes show attractive luminescence properties and metal-metalinteractions. The Cu(I)-NHC complexes can serve as catalysts in many organic transformations. 20
Recently, many researchers have focused on the exploration of the photophysical properties ofmultinuclear Cu(I)-NHC complexes, especially, featuring strong intramolecular Cu-Cu interactions.
A seminal overview by J. C. Y. Lin et al.21 in 2009 outlined comprehensively the development of
this class of complexes, including their modular syntheses, diverse structural properties, excellent
catalytic performance and medicinal applications, as well as their great potentials as luminescentmaterials. Since then, numerous coinage metal-NHC complexes have been synthesized, among whichpolynuclear coinage metal complexes based on phosphine-functionalized NHC ligands play animportant role and are gathering increasing interests due to their diverse structures, metal-metalinteractions and interersting photophysical properties (Figure 5).22

6

Figure 5. Examples of multinuclear coinage metal complexes bearing P-functionalized NHCs withdiverse structures, metal-metal interactions and interesting photophysical properties
Our group has been always interested in the design and synthesis of pincer type ligands which canserve as the supporting ligands for monomeric mononuclear transition metal complexes. 23 These
complexes showed good performance as catalysts in many organic transformations. Fortunately, theaforementioned supporting ligands that support coinage metal complexes can also be regarded as thestandard pincer type ligands. Consequently, by virtue of our accumulation in the design and synthesisof pincer type ligands before, we are determined to expand our research area to the multinuclear
coinage metal complexes.

71-4. Phosphine-functionalized N-heterocyclic Carbenes
As we have mentioned that functinalized NHC ligands attracted considerable attention and arehighly desirable. To date, much efforts have been made to introduce functional groups into NHCs andfortunately, achievements in this field are remarkably prominent. 13,24 Among these, the NHC ligands
functionalized by phosphine groups occupy the overwhelming position. Multidentate ligands
containing both N-heterocyclic carbene and phosphine moieties can offer combined, complementaryelectronic properties and coordination geometries to transition metal centers to enhance the desired
physical and chemical properties. Since the first isolation of a phosphinyl-functionalized imidazolium
iodide by Herrmann et al. in 1996,25 P-functionalized NHCs have been widely investigated as
supporting ligands to afford numerous metal-NHC complexes which have been one of the hot research
topics in the chemistry due to their great potentials in optoelectronic, medicinal and material
applications as mentioned above. To date, a variety of phosphine-functionalized NHC ligands, as wellas their modular syntheses have been developed (Figure 4, G-I).22
It is worth noting that most of these phosphine-functionalized NHC ligands are derived from theArduengo type imidazole scaffold. Meanwhile, these phosphine-functionalized NHCs can begenerally categorized into the rigid mono- and disubstituted bisphosphanyl NHC ligands (Figure 4,G), and the flexible mono- and disubstituted bisphosphanyl NHC ligands with a spacer between thephosphine and carbene moieties (Figure 4, H and I). For the former ligands, the carbene andphosphine donors align the metal cations along one axis (x axis in Figure 4), allowing intramolecular
metal-metal interactions. Although free rotation along the N-P bond (the x axis) is possible,
coordination to the metal leads to mostly rigid 2-D structures where all carbene and phosphine ligands,
and metal centers lie within the same plane. Consequently, this kind of linking mode, to a large extent,
limits their coordination geometries. In contrast, the latter ligands allow controllable degrees of
freedom in all directions depending on the spacer between the coordination sites, permitting morediversified coordination geometries. However, due to the long distance between σ donors, thecomplexes based on these ligands usually have longer metal-metal distances, which prevent
intramolecular d10-d10 interactions which are desired and important in our initial design of the target
compounds. In addition, the flexibility of ligands is known to hamper the efficiency of luminescencethrough thermal vibrations.

8

Figure 4. Selected examples of phosphine-functionalized NHC ligands
Compared to conventional chemical bonds, the metal-metal (coinage metals) interactions are
regarded as weak forces. Even that, theoretical calculations and experiments have shown that theseweak forces play an important role in the photophysical properties and electronic conductivity ofcoinage metal complexes.26
In this contribution, a structurally rigid design containing carbene and phosphine that offers
different coordination geometries and short metal-metal distance would be highly desirable.

9

1-5.

Bis(diphenylphosphinyl)-functionalized Dipyrido-annulated N-heterocyclic Carbene
P2(dpa -NHC)
Dipyridoimidazolinylidene, an electron-rich NHC with the empty carbene p-orbital additionallystabilized by a broad conjugation between which and the 14 electron conjugated π-system of thedipyrido moiety, was first reported by Weiss et al. in 1998 (Figure 6. J).27 Interests in this ligand lay
dormant for almost a decade until 2005 when it was used by Kunz group as supporting ligand toconstruct the chromium and tungsten pentacarbonyl complexes.28 Simultaneously, for increasing its
thermal stability and solubility in solution, the author introduced the tert-butyl groups into thiscompound by fixing them at the 2- and 10-positions, respectively, of the dipyrido moiety (Figure 6.
K), which was structurely characterized in the next year.29 Since then, compound K served as theancillary ligand for otherwise transition metal complexes appeared in a limited number of literaturesfrom Prof. Kunzʼs group.30
Due to our long-standing interest in the chemistry of pincer type ligands23 and the unique featuresof compound K, we attempted to introduce functional groups (-SPh) into the monodentate compound
K and fortunately as a result, two new hybrid NHC ligands (Figure 6. M) were synthesized, which
both were successfully introduced as supporting ligands into rhodium carbene complexes (Figure 6.
N).23c Shortly after this, based on compound K a new hybrid tridentate NHC ligand dpaP2-NHC
functionalized by diphenylphosphine groups (Figure 6) was synthesized by our group, which was thenintroduced as supporting tridentate ligand for monomeric mononuclear rhodium carbene complexes(Figure 6, O).23d While unfortunately, at that time this compound was just used as the transientintermediate, such that its isolation and structurally characterization were not obtained.

Figure 6. Reported dipyrido-annulated N-heterocyclic carbene ligands (top) and ortho-substituted
dipyrido-annulated NHC rhodium complexes (bottom).
10

It is not until most recently dpaP2-NHC was successfully isolated and structurally characterized
by us. The dpaP2-NHC was generated by the deprotonation of the carbene precursor L(H)I with
KOtBu in anhydrous THF for 3-4 h. After evaporation under reduced pressure of the resulting reaction
solution, the addition of anhydrous hexane and the subsequently filtration and evaporation, puredpaP2-NHC was obtained as a yellow solid in 69% yield. In stark contrast to the compound K which
can only stably exist at <-30 °C, dpaP2-NHC did not show any sign of decomposition at ambient
temperature in inert atmosphere for several months as judged by the NMR spectroscopy. The stability
will considerably favor its subsequent complexation with metals. The characterisrtic downfieldresonance at 8.3 ppm assignable to pro-carbenic proton in L(H)I in the 1H NMR spectrum is missing,suggesting the successful deprotonation. The carbene carbon gave rise to a triplet resonance at 198.3
ppm (t, 3JCP = 34 Hz, C1) in the 13C{1H} NMR spectrum which is slightly downfield shifted by 2.0
ppm in comparison to that of compound K (δ 196.3),29 which is indicative of a more stable structure
for dpaP2-NHC via phosphine groups inducively lowering the energy of the occupied σ-donor. 31P{1H}
NMR spectrum displays only one singlet at -13.86 ppm, indicating the equivalence of two phosphinegroups in dpaP2-NHC in solution.
Single crystals suitable for X-ray analysis were obtained by slow evaporation of the dpaP2-NHC
solution in the mixed solvents THF/hexane at ambient temperature. The molecular structure (Figure7) shows an almost inversion symmetry with the orientation of the lone pairs at phosphine syn to thelone pair of Ccarbene, which allows more access to the metal centers. Three cycles of the backbone arecoplanar, in which dipyrido moiety exhibits alternating single and double bonds as in the case ofcompound K.29 While the phosphine groups show slightly bend out of the backbone plane() PCCP=9.6°). The N-Ccarbene bonds lengths of 1.368(2) Å (N1-C1) and 1.378(2) Å (N2-C1) are in the
typical range for imidazoline derived NHCs. Meanwhile, the N-Ccarbene-N shows an angle of
100.15(16)˚ that is slightly bigger compared with that of compound K (99.6(2)˚).29 The N-C-N angleof 100.2(2)° is slightly larger than compound K (99.6(2)°). Furthermore, The close spatial proximity
between the donor atom sites (P and C carbene, averaged 2.971 Å) can be observed from the crystal
conformation. This, together with the high rigidity of this ligand, will be conducive to the formationof polynuclear metal complexes with strong intramolecular metal-metal interactions.

11

dpaP2-NHC, front viewdpaP2-NHC, side view

Figure 7. Molecular structure of compound dpaP2-NHC. Ellipsoids are shown at the 50% probability
level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles [˚]: N1-C1
1.368(2), N2-C1 1.378(2), N1-C6 1.416(2), N2-C7 1.409(2), C6-C5 1.419(3), C7-C8 1.420(3), C5C4 1.361(3), C8-C9 1.362(3), C4-C3 1.442(3), C9-C10 1.443(3), C3-C2 1.350(3), C10-C11 1.352(3),C2-N1 1.404(2), C11-N2 1.400(2), C2-P1 1.839(2), C11-P2 1.830(2); N1-C1-N2 100.15(16); torsion
angle ) P1C2C11P2 = 9.6.
However, although the NHC ligand dpaP2-NHC has been designed and synthesized by us before,
deeply exploring this interesting compound as the supporting ligand of polynuclear metal complexes
remains dormant.

12

1-6. Purpose of This Work
With dpaP2-NHC in hand and our interest in the research area of the polynuclear coinage metal
complexes, we are determined to investigate the coordination chemistry of dpaP2-NHC towards
coinage metals as well as the photophysical properties of the concomitant products. In this thesis, thesyntheses, spectroscopically and structurally characterization, interesting coordination chemistry andphotophysical properties of the multinuclear coinage metal complexes based on dpaP2-NHC will be
discussed.
Chapter 2 described the synthesis and photophysical properties of three dinuclear and one
tetranuclear gold(I) complexes based on dpaP2-NHC and its imidazolium salt precursor. All of thesecomplexes are structurally characterized by X-ray diffraction analysis and investigated with NMR
spectroscopy.
Chapter 3 described the synthesis and photophysical properties of five homonuclear copper(I) andsilver(I) complexes and one heteronuclear bimetallic Ag-Cu complexes based on dpaP2-NHC. These
complexes have been investigated with NMR spectroscopy and X-ray diffraction study.
Chapter 4 summarized the work of Chapter 1-3 and brought forward the outlook towards our
future work.

13

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18

Chapter 2

Di- and Tetranuclear Au(I) Complexes ofBis(Diphenylphosphine)-Functionalized Dipyrido-Annulated
N-Heterocyclic Carbene

2-1. Introduction
Gold(I)-NHC complexes have been the active area of research in the past three decades owing totheir numerous applications, for instance, in catalysis,1 medicine2 and luminescence materials.3 These
compounds usually display remarkable luminescence properties, as the gold metal centers are capableof enhancing intersystem crossing and providing an effective means for the access of the spinforbidden triplet states upon photoexcitation to the singlet excited states. 4 Since the first report ofluminescent AuI-NHC complex by Lin et al. in 1999,5 this class of compounds has been considerablyenriched with numerous NHC AuI complexes featuring interesting optical properties being prepared.
With the increasing understanding of this family of complexes, researchers have a high propensity tothe polynuclear AuI-NHC complexes with aurophilic interaction, since most of which exhibit morevarious and excellent luminescence properties in comparison to the mononuclear ones which generally
show excellent catalytic performance in some of the most important transformations. That is mainly
due to the ease and characters of electron communications of polynuclear AuI-NHC complexes notjust between ligands, ligand and metal centers, but also between the metal centers which are normallyabsent in the mononuclear AuI-NHC complexes. More importantly, recent experimental andtheoretical studies have shown that the aurophilic interactions have a crucial impact on theluminescence properties of gold complexes, as well as favor the formation of polymetallic structures. 6
On the other hand, multidentate NHC ligands provide great opportunities for the research ofcoordination chemistry with metals and construction of metal complexes with diverse structures,
oftentimes some of which are unexpected. For instance, Danopoulos and Braunstein group7 hasrecently prepared a series of gold(I) NHC complexes with novel coordination sphere (Figure 1) basedon their new developed tridentate P-functionalized NHC ligand, N,N’-diphosphanyl-imidazol-2ylidene. These unexpected coordination behaviors and structures can considerably promote
fundamental understanding of the nature of coordination chemistry between σ-donor ligands andmetals.
Therefore, in this chapter, we aim to investigate the coordination chemistry of dpaP2-NHC towards
gold(I), establish the solid state structures of concomitant complexes and conduct the preliminary
investigation on their luminescence properties.

Figure 1. Selected examples of Au complexes based on N,N’-diphosphanyl-imidazol-2-ylidene
reported by Danopoulos and Braunstein group.

20

2-2. Syntheses and Characterization of Dinuclear Au Complexes Based on dpaP2-NHC
As mentioned above, aurophilic interaction has a crucial impact on the luminescence properties ofgold complexes. Thus, for taking a glimpse of the influence of intramolecular d10-d10 interaction to theluminescence properties of gold complexes, we were first to aim to synthesize a dinuclear AuI-carbene
complex without intramolecular d10-d10 interaction, that is, a complex without activation of the carbene
function. So the starting material should be the carbene precursor L(H)I rather than the free carbene
dpaP2-NHC. To avoid the potential substitution of chloride associated with AuI (AuCl·SMe2 chosen
to be the gold precursor in next complexation reaction) by iodide, an anion, such as PF6ˉ, that will not
adopt strong coordination with AuI atom needs to be introduced instead of the iodide anion before
complexation. Concerning the cost and the convenience of reagent acquisition, the PF6ˉ was eventuallychosen as the counter anion which replaces the iodide ion in subsequent anion metathesis.
Eventually, salt metathesis reaction was carried out by the combination of L(H)I and KPF6 in
CH2Cl2, generating the compound L(H)PF6 (Scheme 1). A multiplet resonance centered at δ -143.2
in 31P NMR spectrum suggests the success of this anion metathesis.
With L(H)PF6 in hand, we are going to synthesize the dinuclear gold complex without the
intramolecular aurophilic interactions as we designed before. Given the stability of the starting
materials and the designed product to air and moisture, the next complexation was thus carried out atambient atmosphere and the reaction solvent CH2Cl2 did not undergo rigorous drying procedure. The
combination of [AuCl(SMe2)] and L(H)PF6 in a ratio of 2:1 in CH2Cl2 gave rise to the desired digold
complex 1 as bright yellow solid in excellent yield (90%) (Scheme 1). As predicted before, complex
1 is water tolerant and notably stable towards the air. In comparison to the phosphorous resonance of
L(H)PF6 at δ -13.6, complex 1 shows a significant downfield shift by 48.0 ppm (δP 27.2 for 1),
indicating the formation of gold(I) coordinated phosphines. This, together with the upfield shift of the
pro-carbenic proton resonance [1: δH 8.3 vs L(H)PF6: δH 8.6], demonstrates the formation of the digold
complex 1, with two gold atoms respectively ligated to the phosphine groups. It is of note that the pcarbon resonance signal of phenyl groups cannot be found in the 13C NMR spectrum, whereas which
was detected at δ 134.6 (d, 4JPC = 2 Hz) in DEPT (135) NMR measurements. Meanwhile, ESI-MS
spectrum shows an ion peak at m/z = 1113.1609 a.u. expected for the [(AuCl)21(H)]+ cation.

Scheme 1. Syntheses of digold complex 1.
Further characterization for complex 1 was performed by X-ray diffraction analysis. Slow
diffusion of diethyl ether into the solution of 1 in dimethylformamide (DMF) grew suitable single
21

crystals for structure analysis. Molecular structure (Figure 2) shows that complex 1 is C2 symmetrical,
with each gold nearly linearly coordinating with one phosphine and chloride atoms (P-Au-Cl
176.35(4)q). Presumably due to the steric repulsion from the diphenylphosphine groups, two Au-Cl
bonds point towards the opposite orientations. The P-Au bond length of 2.2290(11) Å and Au-Cl bondlength of 2.2984(12) Å are both in the typical range for gold(I) phosphine complexes 8 and AuCl
complexes.9 In agreement with our initial design, no intramolecular Au-Au interaction was observed
based on their long distance of 7.006 Å.10 In the crystal lattice, the AuCl moieties are aligned withintermolecular Au-Cl distance of 3.55 Å, and Au-Au distance of 4.219 Å, indicating no intermolecular
metal-metal interactions.

front viewside view

Figure 2. Molecular structure of the cation of 1 in 1·4DMF. Ellipsoids are shown at the 50%
probability level. Solvent molecules and dissociated anion are omitted for clarity. Selected bondlengths (Å) and angles [˚]: Au1-P1 2.2290(11), Au1-Cl1 2.2984(12); P1-Au1-Cl1 176.35(4).
Next, we aimed to afford the multinuclear gold complexes with intramolecular aurophilicinteractions. Generally, gold(I)-carbene complexes can be produced either from the free carbene11 orby transmetallation from their corresponding silver(I)-carbene complexes.12 Considering the cost andtime factors, we temporarily choose the former method. While unfortunately, one-pot reaction of
dpaP2-NHC with the gold precursor [AuCl(SMe2)] in THF failed to generate the desired goldcomplexes, with ill-defined mixture formed. Changing the reaction conditions, such as reaction solvent,gold precursor and reactions temperature, did not make any progress for the reaction outcome.
Given the strong σ-donation and coordination abilities of carbene13 and the Au atom weakly
coordinated by SMe2,14 we surmise that the metalation between dpaP2-NHC and gold precursor[AuCl(SMe2)] would rapidly proceed. Thus, an optimized procedure different from the one-pot
reaction was developed. Under the argon protection, an approximately saturated solution of
AuCl·SMe2 in anhydrous CH2Cl2 was added dropwise to the solution of dpaP2-NHC in hexane, with22

yellow solid instantly precipitating (Scheme 2). After filtration, a novel dimeric digold complex 2 was
obtained in a 72% isolated yield. Its molecular structure was established by X-ray diffraction analysis.

Scheme 2. Syntheses of dinuclear gold(I) complex 2.
Complex 2 is asymmetric (Figure 3), in which two gold centers are both three-coordinate but
exhibiting different arrangement, i.e., Au1 is ligated by one CNHC donor and one P donor which arefrom two hybrid ligands dpaP2-NHC, with the coordination sphere being completed by theneighboring AuI atom, and Au2 is ligated by one CNHC and one chloride, with the third coordinationsite being occupied by the adjacent AuI. Two identical carbene ligands dpaP2-NHC are respectively
nearly planar, and significantly twisted into each other by 28.4q from a 90q angle, which can be
attributed to the strong intramolecular AuI-AuI interaction. Both gold(I) atoms feature an almost linear
arrangement with respect to C44-Au1-P4 angle of 178.48(12)q and C1-Au2-Cl1 angle of 178.27(13)q.
The bond lengths for CNHC-Au (C44-Au1 = 2.026(4) Å, C1-Au2 = 1.995(4) Å), P4-Au1 of 2.2914(12)Å and Au2-Cl1 of 2.3087(13) Å lie in the expected range for gold(I)-NHC,15 gold(I)-phosphine and
AuCl complexes.8,9 Nevertheless, the P2-Au1 (2.8944(12) Å) and P3-Au2 (2.9374(14) Å) bonddistances are significantly longer than the typical P-Au bond distance. In spite of that, these distances
are still much shorter than the sum of van der Waals radii of 3.44 Å for P-Au, indicating the weakinteraction between them. This probably results from the strain and reduced orbital overlap within the
AuI-contained five-membered rings due to the acute bite angle of 78.13(14)q (C1-Au2-P3) and
77.09(12)q (C44-Au1-P2), respectively. An intramolecular aurophilic d10-d10 interaction is present
judging by the short bond length between two gold(I) atoms (Au1-Au2 = 2.9557(3) Å).1023

Figure 3. Molecular structure of complex 2 in 2·2DMF. Ellipsoids are shown at the 50% probability
level. Hydrogen atoms, dissociated chloride anion and solvent molecules are omitted for clarity.
Selected bond lengths (Å) and angles [˚]: Au1-Au2 2.9557(3), Au1-P4 2.2914(12), Au1-C44 2.026(4),Au2-Cl1 2.3087(13), Au2-C1 1.995(4); C1-Au2-Au1 88.11(13), C1-Au2-Cl1 178.27(13), C44-Au1Au2 105.60(13), C44-Au1-P4 178.48(12), P4-Au1-Au2 75.42(3).
Although crystals of 2·2DMF can be obtained reproducibly in good yield, the solid state structure
cannot be maintained in solution. Specifically, the NMR spectra at ambient temperature did not show
any discernible signal for complex 2, while cooling down to -10 °C gave rise to four singlets at δ 26.2,
27.3, 28.5, 30.3, respectively, in 31P NMR spectrum with slightly different intensity. Correspondingly,
1

H NMR spectrum displays a base peak (singlet) at δ 1.20 neighbored by four less intense peaks, bothof which can be assigned to the proton signals of tert-butyl groups. Together, these NMR data suggest
an arguably fluxional process for 2 in solution.
To investigate further this dynamic behavior, VT (variable temperature) NMR experiments werethus conducted for complex 2 (Figure 4). With the temperature cooling down from -10 to -40 °C, thesinglet at δ 28.5 in 31P NMR spectrum became more intense, while simultaneously the intensity ofother three signals correspondingly decreased, finally this process averaged out at -40 °C. In themeantime, the base peak at δ 1.20 became slightly less intense with the neighboring small peaks
correspondingly becoming more intense. This phenomenon can be tentatively explained by the rapid
interconversion of the mixture of monomer, dimer or oligomers, which resulted from the presence of
three dangling phosphine ligands as well as the lability of chloride that may dissociate or coordinate
to the gold center in solution. Unfortunately, numerous attempts to grow suitable crystals of themonomer or oligomers at low temperature (below 0 °C) for X-ray analysis failed due to theconsistently identical results that only the crystals of complex 2 can be obtained. Thus, proof is not
sufficient enough to support the hypothesis above and more efforts for affording the crystals of the24monomer and oligomers is underway.

Figure 4. VT 1H (top) and 31P (bottom) NMR spectra of complex 2 in CDCl3 from -10 to -40 ºC.
The complexation behavior of gold(I) precursors often depends on their ligands. The presence orabsence of halide (X ligand), and the coordination strength of Lewis base (L ligand) have been reported
to provide structurally different products. For instance, in 2016 P. Ai et al.16 reported that reactions ofphosphine-functionalized NHC with different gold(I) precursors yielded completely different gold(I)carbene complexes (Scheme 3). Through the reaction of dpaP2-NHC with AuCl(SMe2), the digold
complex 2 has been formed as described above. Thus, we were curious about the outcome of thereaction of dpaP2-NHC with [Au(tht) 2(OTf)]. Surprisingly, combination of the free carbene dpaP2NHC with 1 equiv [Au(tht)2(OTf)] in THF resulted in the formation of a new dinuclear gold(I)-carbene
complex, the complex 3 (Scheme 4), in an 83% isolated yield. Two triplets at δ 29.65 (virtual triplet(vt), JPP = 31.5 Hz) and 6.75 (vt, JPP = 30.7 Hz), respectively, in 31P{1H} NMR spectrum suggest thepresence of two different kinds of gold coordinated phosphine groups in 3. Correspondingly, two
singlets in the 1H NMR spectrum at δ 1.04 and δ 1.20, respectively, that can be ascribed to the protonsof tert-butyl groups, indicates the presence of two sets of tert-butyl groups. Both the NMR spectra arein good agreement with the observation of its solid state structure as shown in Figure 5. Meanwhile,
ESI-MS spectrum shows a signal at m/z = 845.2486 expected for the ion peak of the dication of 3,25

revealing its persistence in solution.

Scheme 3. Syntheses of two different gold(I) complexes starting from the same NHC by changing theanions of gold precursors (P. Ai et al. in 2015)

Scheme 4. Syntheses of digold complex 3 from dpaP2-NHC.
Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl
ether into the solution of complex 3 in dimethylformamide (DMF). Its molecular structure iscentrosymmetric and the planes of the two carbene heterocycles are not coplanar but at 122.55q. Twogold(I) atoms are three-coordinate and display identical coordination sphere with each metal ligatedby one P donor and one NHC from two dpaP2-NHC ligands, and the neighboring AuI. Interestingly,
the P1-Au1-Au2-P3 chain shows a nearly linear arrangement in terms of the P1-Au1-Au2 angle of
176.56(2)q and Au1-Au2-P3 angle of 174.52(3)q, respectively. Comparing with complex 2, the bonddistances of Au-P (Au1-P4 2.3072(13), Au2-P2 2.3015(13)) and Au-CNHC (Au1-C1 2.048(5), Au2C44 2.041(5) Å) in 3 show negligible deviations (maximum average deviation 0.034 Å for CNHC-Au),
while the Au-Au bond length of 3.0173(3) Å is 0.0616 Å longer but still implies a strong
intramolecular d10-d10 interaction.10 This change can be ascribed to the strain of the metallocycles,
especially the internal ten-membered ring, in 3. Furthermore, this novel arrangement is reminiscent of
a dinuclear Pd(I) complex with phosphine-functionalized tridentate NHC ligand.17 Directed byhydrogen bonding between triflate and phenyl hydrogen atoms, the two rigid dpaP2-NHC forms a bowl
shape with phosphines orientated outwards (Figure 5, side view).

26

front viewside view

Figure 5. Molecular structure of complex 3 in 3·2DMF·Et2O. Ellipsoids are shown at the 50%
probability level. Hydrogen atoms, counter anions, and solvent molecules are omitted for clarity.
Selected bond lengths (Å) and angles [˚]: Au1-Au2 3.0173(3), Au1-P4 2.3072(13), Au1-C1 2.048(5),Au2-P2 2.3015(13), Au2-C44 2.041(5); C1-Au1-Au2 106.22(13), C1-Au1-P4 174.50(14), C44-Au2Au1 106.53(14), C44-Au2-P2 176.07(14), P2-Au2-Au1 77.39(3), P3-Au2-Au1 174.52(3), P4-Au1Au2 78.10(3).
Given the two nuclear Au(I) complexes, namely 2 and 3, obtained above, we can make aconclusion that the products of the reactions of free carbene dpaP2-NHC with gold(I) precursors
depend on the nature of the anions associated with latter. Compared with triflate anion, chloride anion
is a better ligand in terms of their abilities to coordinate to metals. Thus, in complex 2 one of thechlorides is prone to serve as a ligand coordinating to one Au(I), instead of a free anion which is like
triflate anions in complex 3. Consequently, two different dinuclear complexes 2 and 3 were achieved
when dpaP2-NHC reacted with equimolar amounts of two different gold(I) precursors, namely[AuCl(SMe2)] and [Au(tht)2(OTf)], respectively.

27

2-3. Syntheses and Characterization of Tetranuclear Au Complexes Based on dpaP2-NHC
The successful syntheses of complex 1 has proven that two phosphine donors in dpaP2-NHC arecapable of coordinating metal cations independently. Thus, both 2 and 3, the two dinuclear gold(I)complexes, can be considered to be coordinatively unsaturated since each tridentate dpaP2-NHC
captured only one metal center and the phosphine donors (three in 2 and two in 3) are found to be nonmetallated, which can be activated for coordination to metal center. In other words, these complexes
have the potential to capture more metals. Meanwhile, recent reports have shown that diphosphinefunctionalized NHC ligands are able to capture three, five and even six transition-metal cations in theform of dimeric species (Figure 6).3e,7a

Figure 6. reported tri-, tetra- and pentanuclear complexes supported by diphosphine-functionalized
NHC ligands.
To complete the series of gold complexes of P-functionalized NHC ligand dpaP2-NHC, we thus
aimed to synthesize the multinuclear gold(I)-carbene complexes such as those reported in recent
literature.7a Considering the synthetic method for gold dpa P2-NHC complexes containing more than
two metals, there are currently two choices, coordination of the free carbene dpaP2-NHC to a labilegold precursor (in this case [Au(tht)2(OTf)]) in a ratio of <1:1 or reaction of dinuclear gold complex 2(or 3) containing non-metallated phosphine donors with gold precursor. Both seem to be reasonable
and applicable and will be utilized in the next study.
To our excitement, a tetranuclear gold(I) complex 4 was afforded through the reaction of dpaP2NHC with either 1.5 equiv or 2 equiv [Au(tht) 2(OTf)] in 71.3% isolated yield (Scheme 5).
Interestingly, increasing the amount of gold precursor [Au(tht)2(OTf)] did not lead to the formation of
new complexes with higher metal content but 4. The 31P NMR singlets at δ 36.3 suggests equivalenceof all the phosphine groups. Meanwhile, the protons on the tert-butyl groups gave rise to only one
singlet at δ 1.12 in the 1H NMR spectrum, indicating the highly symmetric structure of 4 in solution.
Both NMR data are in line with the observation of molecular structure as shown in Figure 7.

28

Scheme 5. Syntheses of tetranuclear gold complex 4 from dpaP2-NHC.
Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl
ether into the solution of complex 4 in dimethylformamide (DMF). Complex 4 crystallized in thetriclinic space group PῙ with two molecules in the asymmetric unit, which differ slightly with regard
to their bond lengths and angles. Only one of the two molecules is discussed here. The structure of 4
shows a centrosymmetry with two identical Au2(dpaP2-NHC)-2OTf subunits, and two dpaP2-NHC
ligands are not coplanar but parallel and pointing precisely in opposite direction, which are bridged
by a four-membered planar gold(I) ring connected by strong aurophilic interactions (Au4-Au3
3.0341(7), Au4-Au3# 3.1630(7) Å), although these Au-Au bond lengths are slightly longer than thosein complexes 2 and 3. Each outer AuI displays a deviation from the linear P4-Au3-P3# arrangement(157.02(10)q) toward the central gold(I) atoms, which is likely attributed to the attractive
intermolecular AuI-AuI interaction with the central golds. Regardless of the Au-Au interactions, all thefour gold atoms are two-coordinate. Unlike the trinuclear AuI bis(NHC) complexes7a in which all thethree metals are respectively coordinated by either the two CNHC donors (central gold) or two of the P
donors (two outer golds) that belong to two hybrid carbene ligands, each of the two central golds in 4
is identically coordinated by one CNHC donor and one DMF molecule, while the two outer AuI atoms
are respectively bound to two P donors from different ligands. This dimeric molecular 3D latticearrangement is unique from all previously reported heteroleptic phosphine/carbene multinuclear
complexes because the three donors are restricted to one plane with only rotation possible at thephosphines (Figure 7. side view). To the best of our knowledge, a similar structure with 4 has not beenreported to date.

29

front viewside view

Figure 7. Molecular structure of complex 4·2DMF in 4·4DMF. Ellipsoids are shown at the 50%
probability level. Hydrogen atoms, counter anions, and disassociated solvent molecules (DMF) areomitted for clarity. Selected bond lengths (Å) and angles [˚]: Au3-Au4 3.0341(7), Au3#-Au4 3.1630(7),Au4-C2 1.970(10), Au3-P4 2.302(3), Au3-P3 2.301(3); Au3-Au4-Au3# 113.284(16), Au4-Au3-Au4#
66.719(16), P4-Au3-P3# 157.02(10), C2-Au4-Au3 102.0(3), C2-Au4-Au3# 102.0(3).

302-4. Alternative Syntheses of Di- and Tetragold Complexes 3 and 4 from Complex 2
Looking more closely to the formulas of complexes 2 and 3, it is easy to find that the only
distinction between them is their counter anions, namely, complexes 2 and 3 possess two chlorides(one is coordinated to gold atom, another is serving as free counter anion) and two disassociatedtriflates, respectively, as their counter anions, regardless of their steric configurations. Thus, we
wonder if it is possible to generate 3 starting from 2 by chloride abstraction. In view of that, reactionof complex 2 with 2 equiv AgOTf in CH2Cl2 in the absence of light was carried out and fortunately,complex 3 was expectedly formed as the only product in an 64% isolated yield as judged by the NMR
spectroscopy (Scheme 6).
Most recently, in a landmark paper O. Rivada-Wheelaghan et al.18 reported the controlled stepwise
growth of linear copper (I) chains in their specially designed ligands. In detail, the author can easily
increase the nuclearity (from one to four) of the complex by the stepwise addition of copper precursor
and in the meantime, stepwise nuclearity reducing (from four to one) of the complex can also be
achieved by changing the reaction solvent. Even though the author stressed that the ligand scaffolds
are the key factor for achieving the metal growth, we hold the opinion that ligand transfer seems toplay a more important role in these metal growth reactions. In other words, the quantitatively equal orexcess σ-donors for supporting additional metals are likely responsible for accessing the metal growth.
For example, in the dinuclear gold(I) complex 2, it is conceivable that one, two, three even four
additional metals can be introduced into this compound, since complex 2 owns totally six σ-donors(four phosphines and two NHCs) and two of the phosphine donors are non-metallated which arecapable of coordinating to metal centers. Thus, we wonder if it is really feasible to implement themetal growth in our ligand system. As expected, this idea was successfully realized after the additionof 2 equiv [Au(tht) 2(OTf)] into the solution of complex 3 in THF, with 4 being afforded as the only
product in a yield of 51% (Scheme 6). Despite the unclear mechanism of the formation of 4, it isplausible that the phosphine ligands transfer from the coordinated AuI and the coordination of dangling
phosphine donors to new added Au ions (simultaneously or sequentially) led to the formation of 4.

Scheme 6. Syntheses of complexes 3 and 4 starting from complex 2.
Consequently, the above two reactions clearly demonstrate that complex 2 is able to function as31

the precursor on the way to complexes 3 and 4. More importantly, it also provides alternative method
for the syntheses of multimetallic gold-NHC complexes, which not only is suitable to our ligand(dpaP2-NHC), but also is highly likely to be applicable to other similar ligand systems. By the way,these discoveries inspire us to explore further the coordination chemistry of dpaP2-NHC towards othertransition metals, especially the other two group 11 metals, silver and copper.

32

2-5. Photophysical Properties of the Free Carbene Ligand dpaP2-NHC and Complexes 1-4
As mentioned above, interesting photophysical properties most often can be found in gold NHC
complexes. This, together with the novel structures of the complexes 1-4, prompted us to investigate
their luminescence in solution.
The obtained absorption spectra for free carbene dpaP2-NHC and complexes 1-4 in dilute 2methyl-THF are depicted in Figure 8. All the measured compounds absorbed in the visible region withthe absorption maxima ranging from 320 to 420 nm, and these absorption bands can be tentatively
attributed to the ligand-centered (LC) transitions and metal-to-ligand charge transfer (MLCT)
transitions.19 In comparison to the analogous multinuclear coinage metal complexes bearing Pfunctionalized imidazole-2-ylidene ligand (absorption maxima ranging from 260 to 350 nm), 7a,b theabsorption bands of complexes 1-4 are dramatically red-shifted, which can be rationalized by the
expansion of the π-system from the dipyrido-annulated NHC ligand dpaP2-NHC which leads to alower lying LUMO energy than that of imidazole-based ligands.20 Interestingly, 1 exhibits a low
energy absorption band relative to complexes 2 and 3 (1: λmax = 394 nm versus 2: λmax = 366 nm and3: λmax = 388 nm), which is probably associated with (σ + Cl)-π* charge transfer from the Au-Cl bondto the LUMO in complex 1.21 Nevertheless, the significantly red-shifted absorption band was observed
for complex 4 (λmax = 431 nm) relative to complex 1, which is most likely due to the presence of
intramolecular aurophilic interactions.

Figure 8. UV-vis absorption spectra of compounds dpaP2-NHC and 1-4 in 2-methyl-THF solution(2.0 × 10-5 M) at room temperature.
Upon excitation at Oexc = 345 nm, complexes 2-4 exhibit broad, structureless emission bands withthe emission maxima in the sequence 3˘2˘4 (complexes 3, 2 and 4 of 510, 522 and 550 nm,
respectively) (Figure 9), tentatively pointing towards a greater contribution of an excited state wherestrong intramolecular AuI-AuI interaction is involved.22 Given their low-energy emission, we thus
tentativey assigned these luminescence to MMLCT excited states. In sharp contrast, complex 1
without the intramolecular AuI-AuI contact displays a higher energy emission band at Oem = 486 nm,
33

in comparison to that of complexes 2-4 with intramolecular aurophilic interactions. While thisphenomenon is in good agreement with the observation that an aurophilic contact can cause theemission band red-shifted.22 Furthermore, the excitation spectra recorded by monitoring emission
bands display excitation bands with almost same wavelength centered at Oexc = 375 nm for all thecomplexes, which correspond nicely to their UV-vis absorption spectra, indicating that the origin of
the photoluminescence process is same in both cases.

Figure 9. Normalized excitation (dash line) and emission (solid line) spectra of complexes 1-4 in
CH2Cl2 solution at room temperature (2.0 × 10-5 M). Samples were excited at 345 nm.
Photoluminescence excitation spectra were recorded by monitoring emissions at 485 nm (1), 510 nm(3), 520 nm (2) and 550 nm (4).
In the meantime, the measurement of luminescence properties of complexes 1-4 and free carbene
dpaP2-NHC in a different solvent, degassed 2-methyl-THF, was also conducted, and the result isshown in Figure 10. Judging from the obtained emission spectrum, we can find that variation of thesolvent did not have any impact on their photoluminescence excitations as the excitation bands in bothsolvents are almost identical. This clearly suggests that the change of the solvent has approximately
negligible influence on the photoluminescence excitation process of the studied complexes.
Nevertheless, the emission spectrum shows a significant change compared to that in CH 2Cl2 solution.
In detail, all the investigated complexes 1-4 in degassed 2-methyl-THF display almost identicalemission bands with the maximum centered at 500 nm, which are obviously different from that inCH2Cl2 as mentioned above. While it is worth noting that comparing with complexes 2-4, 1 exhibits
a blue shifted emission wavelength, which fits to the observation of these complexes in CH 2Cl2.
Compared to the emission band of the ligand dpa P2-NHC, all the obtained gold complexes 1-4 showed
negligible shift in terms of their emission bands, indicating these electronic transitions can be
attributed to the ligand-centered transitions.

34

Figure 10. Photoluminescence excitation (dash line, normalized) and emission (solid line, normalized)
spectra of complexes 1-4 in degassed 2-Me-THF at ambient temperature. Samples were excited at 375
nm (complexes 1-3) and 420 nm (dpaP2-NHC and 4). Photoluminescence excitation spectra wererecorded by monitoring emissions at 485 nm (1 and 2) and 500 nm (complexes dpaP2-NHC, 3 and 4).
All complexes are not phosphorescent at room temperature, but emit intense phosphorescence at
77K in glassy 2-methyl-THF. As shown in Figure 11, complexes 1-3 exhibit broad and structured
phosphorescence spectra, in which both 1 and 2 show dual emissions at 579 and 617 nm, 603 and 659
nm, respectively. While 3 consists of three emission bands at 613, 639 and 667 nm, respectively, incontrast to which a broad phosphorescence at 648 nm was observed for complex 4. Looking moreclosely to the spectrum, we can find that the phosphorescence bands of complexes 2-4 were slightly
red-shifted from that of the free carbene dpaP2-NHC, which was indicative of electronic perturbationof the gold cation to the triplet state of the carbene to a limited extent. Moreover, it is most likely thatthe two triplet states arising from different orbital parentages do not readily interconvert leading to theformation of two phosphorescent bands for 1 and 2.23

35

Figure 11. Normalized phosphorescence spectra of free carbene dpaP2-NHC and gold complexes 1-4
at 77K in degassed glassy 2-methyl-THF (2.0 × 10-5 M). Samples were excited at 345 nm.
The phosphorescence decay profiles are depicted in Figure 12, from which the lifetimes of thefree carbene dpaP2-NHC and gold complexes 1-4 are calculated to be 772.0, 259.3, 89.1, 85.1 and
478.3 μs, respectively. Most likely, the long luminescence lifetimes for complexes 1 and 4 can be
explained to originate from the lowest triplet states, while complexes 2 and 3 can be assigned as thelowest singlet state, based on their relatively long and short lifetimes.

Figure 12. Phosphorescence decay traces for free carbene ligand dpaP2-NHC and complexes 1-4 in
2-methyl-THF solution (2.0 × 10-5 M) at 77 K. The spectra were recorded by monitoring
phosphorescence at 602 nm (dpaP2-NHC and 2), 615 nm (1 and 3) and 645 nm (4). The calculated

lifetimes of dpaP2-NHC and 1-4 are 771.97, 259.29, 89.14, 85.11 and 478.32 μs, respectively.

36

2-6. Conclusion and Outlook
In conclusion, di- and tetranuclear gold(I) complexes (complexes 2-4) bearing diphenylphosphinefunctionalized dipyrido-annulated NHC ligand were selectively synthesized from dpaP2-NHC bychanging the molar ratio between the gold(I) precursors and NHC ligand, as well as the anion
associated with the former. Moreover, an interesting synthetic route has been developed together, thatis, chloride abstraction of complex 2 with AgOTf gave rise to complex 3, which subsequently reactedwith Au(tht) 2OTf affording complex 4 by the possible phosphine ligand transfer. Note that thisalternative synthetic route provides nothing but an additional option for the syntheses of multinuclear
metal NHC complexes. The room temperature NMR spectroscopy displaying possible coalescenceindicated that complexes 2 and 4 underwent dynamic behavior in solution. X-ray analysis shows thatcomplexes 3 and 4 display interesting coordination geometry: in 3, both two gold centers are twocoordinate (neglecting the Au-Au interaction) and feature identical coordination sphere comprising an
NHC and a phosphine donors belonging to two dpaP2-NHC ligands; in 4, the four gold(I) centersformed a planar ring which bridged two dpaP2-NHC ligands in parallel.
All the gold complexes (1-4) show a variety of photoluminescence properties; in particular, thesecomplexes exhibit totally different emission spectra when measured in different solvents. In 2-methylTHF, complexes 1-4 exhibited almost same fluorescence bands with the free carbene ligand dpaP2NHC, suggesting that the electronic transmissions of these gold complexes are likely attributed to theligand-centered (LC) transmissions. Furthermore, all the gold complexes are found to provide
phosphorescence in degassed glassy 2-methyl-THF at 77 K, with the lifetime ranging from 89.1 μs to772.0 μs. Since the investigation of gold part has been finished, we next turn our attention toinvestigating the coordination chemistry of dpaP2-NHC towards silver(I) and copper(I) as well we thephotophysical properties of concomitant complexes.

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39

Chapter 3

Multinuclear Cu, Ag, and Bimetallic Cu-Ag Complexes ofBis(diphenylphosphinyl)-functionalized Dipyrido-annulated
N-heterocyclic Carbene

3-1.

Introduction

Ag(I)-NHC complexes have been an active area of research for decades due to their multiple
applications, for example, in NHC transfer reactions,1 in catalysis2 and in material science. 3 As
excellent NHC transfer reagents, Ag(I)-NHC complexes have been utilized to successfully synthesize
other transition metal-NHC complexes, in particular, those of the other two group 11 metals, Au andCu, which largely benefits from the widespread nature that the coinage metal-NHC bond strength
follows the order Au(I) > Cu(I) > Ag(I).4 Meanwhile, along with the increasing interest in thefunctionalized NHCs that serve as the supporting ligands, multinuclear Ag(I) complexes bearing
functionalized NHC ligands are also being intensively investigated owing to their diverse structures,
as well as the concomitant interesting photoluminescence properties.5 Many polynuclear silver
complexes bearing functionalized NHC ligands with novel structures and metal-metal interactions
have been reported recently.
Thanks to their excellent performance and great potential in some important catalytictransformations6 and material science,7 Cu(I)-NHC complexes are gathering increasing popularity inthe recent past and particularly, an increasing number of groups recently start to investigate theluminescence properties of Cu(I)-NHC complexes.8 In particular, the complexes featuring multi
metals and strong inter- or intramolecular cuprophilic interactions have been experimentally andtheoretically demonstrated to be able to provide a design methodology for highly efficient Cu(I)-based
emitters.9 Furthermore, owing to the cost and supply advantages, copper-based NHC complexes
showing excellent luminescent properties seems to be the promising candidates of cyclometallated
iridium complexes in terms of their application in organic light-emitting diodes (OLEDs).
Heterobimetallic complexes have gained increasing interest recently due to their distinct characterof featuring two catalytically active sites.10 While, the site-selective metallation seems to be a hugechallenge that is hard to meet for achieving the heterobimetallic complexes. Few synthetic strategies
which are not generally applicable have been used for the preparation of heterometallic complexes;
for example, the stepwise deprotonation and metalation of the corresponding azolium salts, 11 thetransmetallation from corresponding Ag(I)-NHC complexes benefiting from the difference incoordination chemistry of silver and the employed metals,12 as well as the recently developed siteselective metallation based on the difference in reactivity of benzimidazole C2-Cl and imidazolium
C2-H bonds.13 While preparing heterobimetallic NHC complexes by taking advantage of thedifference of coordination chemistry of the employed metals and the transmetallation aptitude ofphosphine and NHC donors is extremely rare.14
Theoretical study15 has shown that the coordination number of coinage metal ions is practicallydetermined by the interaction energy and the energy of deformation of the metal coordination sphere.
Accordingly, the gold complexes, having larger deformation energy in comparison with copper andsilver ones, show an obvious predominance of dicoordination, compared to CuI and AgI. This notion
41was also further corroborated by the synthesis of a series of dpa P2-NHC AuI complexes (Chapter 2),
in which all the gold ions displayed dicoordination (neglecting the metal-metal interactions).
Nonetheless, the dominant dicoordination, due to its relatively simple coordination mode, limits the
structural diversity of Au complexes, to a large extent. In contrast, CuI and AgI, most commonly foundas three- or four-coordinated species,15 are expected to form complexes with more diversified
structures for a given combination of metal ion and ligands.
In this chapter, we describe the coordination chemistry of bis(diphenylphosphinyl)-functionalized
dipyrido-annulated N-heterocyclic carbene, dpaP2-NHC, towards silver(I) and copper(I). Based on
dpaP2-NHC, two dinuclear silver (Ag2L2) and copper (Cu2L2) complexes, two tetranuclear copper
complexes (Cu4LBr4 and Cu4L2·2CH3CN), a tetranuclear bimetallic silver/copper complex[Ag2Cu2L2(O)] and a pentanuclear copper complex (Cu5L2Br3) were achieved and characterized.
NMR spectroscopy indicated that all the obtained complexes underwent dynamic behavior in solution
at room temperature, which will be discussed in detail below. Furthermore, investigation into thephotophysical properties of all the complexes showed that they are luminescent at room temperature,in which Cu4LBr4, Cu4L2·2CH3CN and Cu5L2Br3 provided phosphorescence at 77 K with relatively
long lifetimes ranging from 268.7 μs to 655.6 μs.

42

3-2.

Syntheses of Dinuclear Silver Complex Ag2L2

As mentioned above, silver-NHC complexes can serve as the versatile carbene transfer reagentsowing to their weaker Ag-NHC bond strength compared to those of gold and copper, thereby fromwhich Au-NHC complexes can be synthesized. In contrast, the synthesis of Ag-NHC complexes fromtheir gold analogues have never been reported. In this contribution, silver-NHC complexes are
generally accessible via two synthetic methods: the reaction of the carbene precursor (usually
imidazolium salt) with Ag2O,1a or the coordination of the preformed free carbene to a labile silver
precursor.16 Considering the easy handle of dpaP2-NHC (easy preparation and storage, stable for along time), we choose the latter method. Meanwhile, ordinary silver salt AgOTf (OTf = triflate) for
preparative purpose was chosen for this study. In view of this, a reaction of dpaP2-NHC with AgOTf
in a ratio of 1:1 in the absence of light was carried out, which led to the formation of a dinuclear silver
complex Ag2L2 as orange solid in a 79% isolated yield (Scheme 1). This compound is stable at ambient
atmosphere for several hours and does not show any sign of decomposition.

Scheme 1. Syntheses of dinuclear silver complex Ag2L2 from dpaP2-NHC.
Single crystals of Ag2L2 suitable for X-ray diffraction analysis were obtained from a DMF solution
overlayered with diethyl ether at -30 ˚C. Molecular structure of Ag2L2 (Figure 1) shows a dimericsaddle-like structure. Actually, Ag2L2 can be structurally regarded as two identical [Ag(dpaP2NHC)](OTf) monomers condensed together. Both two silver centers are three-coordinate (neglecting
the Ag-Ag interaction) and exhibiting an identical coordination sphere comprising two phosphinedonors from two dpaP2-NHC ligands and one NHC donor. Different with its dinuclear Au analogue inwhich two of the phosphine donors remain dangling, all of the six σ-donors (two NHC and four
phosphine donors) are respectively coordinating to one of the silver atoms. The bond distances
between Ag(I) and CNHC (C1-Ag1 2.166(3) Å, C44-Ag2 2.188(3) Å) lie in the typical range for silverNHC complexes.17 While interestingly, categorized by the bond length, two type of Ag-P bonds in
Ag2L2 were identified, that is, Ag1-P4 (2.4288(8) Å) and Ag2-P2 (2.4547(8) Å) with comparable bondlengths for typical silver-phosphine complexes,14,16c, Ag2-P3 (2.6694(9) Å) and Ag1-P1(2.6668(9) Å)with significant longer bond lengths compared to typical silver-phosphine complexes, respectively.
These elongated bonds are most likely resulting from the strain and reduced orbital overlap within the43four-membered ring coming from the acute bite angle of 78.14(8)° (C44-Ag2-P3) and 77.80(9)° (C1Ag1-P1), respectively. A strong d10-d10 interaction is present based on the short distance between twosilver atoms (Ag1-Ag2 2.8363(4) Å).17,18

Figure 1. Thermal ellipsoid representation (50% probability level) of the structure of the cation in
Ag2L2. Hydrogen atoms, two triflate anions and molecules of solvent of crystallization((CH3)2NCHO) are omitted for clarity. Selected bond lengths (Å) and angles [°]:Ag1-Ag2 2.8363(4),Ag1-P1 2.6668(9), Ag1-P4 2.4288(8), Ag1-C1 2.166(3), Ag2-P2 2.4547(8), Ag2-P3 2.6694(9), Ag2C44 2.188(3); P1-Ag1-Ag2 135.53(2), P2-Ag2-Ag1 76.77(2), P2-Ag2-P3 122.68(3), P3-Ag2-Ag1
142.02(2), P4-Ag1-Ag2 78.28(2), P4-Ag1-P1 118.54(3), C1-Ag1-Ag2 84.02(8), C1-Ag1-P4
161.66(9), C1-Ag1-P1 77.80(9), C44-Ag2-Ag1 82.13(8), C44-Ag2-P2 158.10(9), C44-Ag2-P3
78.14(8).
Room temperature NMR spectra of Ag2L2 showed a single and symmetrical dpaP2-NHC ligand
environment. In detail, three singlets at 8.71, 6.83 and 1.13 ppm corresponding to two kinds of pyridyl
protons and tert-butyl protons, respectively, were detected; correspondingly, 13C NMR spectrum
shows only one set of resonance signals and only a broad singlet at -10.0 ppm was observed in 31P
NMR spectrum. Apparently, these solution data were inconsistent with the observation of its solidstate structure since molecular structure of Ag2L2 showed that two identical dpaP2-NHC ligands areasymmetrical, that is, the four protons of dipyridyl groups and the two tert-butyl groups in each dpaP2NHC ligand are inequivalent. It is likely that these presumable NMR coalescences are the result of afast fluxional behavior for Ag2L2 in solution.
In order to explore the dynamic behavior of Ag2L2 in solution, VT 1H NMR study was performed.
To our excitement, notable differences were observed between the 1H NMR resonance of hightemperature and low temperature. In other words, when the temperature was cooled down to below
203 K, the 1H NMR spectrum of Ag2L2 exhibited discernible decoalescence (Figure 2). In detail, uponcooling to 203 K, the singlet at 1.13 ppm assignable to the tert-butyl groups was split into two singlets.
44

Likewise, the pyridyl protons adjacent to the phosphine-substituted pyridyl carbons resonating as
singlet at 8.71 ppm were found to give rise to two singlets starting from 203 K. Thus, at thistemperature range, the resonance signals can be well resolved on the 1H NMR timescale. And it isworth noting that those low temperature 1H NMR spectra are in good agreement with the solid state
structure.

Figure 2. VT 1H NMR spectrum of Ag2L2 in THF-d8 from 293 K to 173 K.
Meanwhile, we also conducted the VT 31P NMR experiment for Ag2L2 from 293 K to 178 K.
Before our discussion, it is necessary to point out that a discernible room temperature 31P NMR
resonance for Ag2L2 can be detected only after an overnight measurement or even longer. Due to ourlimited measuring condition, the VT NMR experiments at each set temperature can be running for nolonger than 1 h. In other word, as shown in Figure 3, within 1 h no recognizable 31P NMR resonance
was observed from 293 K to 218 K, whereas discernible 31P NMR resonance was detected below 218
K. On the other hand, owing to the silver element having two NMR active spin I = 1/2 isotopes (109Ag
and 107Ag) with natural abundances of 48.18% and 51.82% respectively, after P-Ag coupling thestandard 31P NMR spectrum for P-NHC Ag complexes generally displays two close doublets with thecoupling values ranging from 450-700 Hz.14,16a,c,19
A broad resonance signal at -10.0 ppm was observed for Ag2L2 in the room temperature 31P NMR
spectrum, which is indicative of a possible coalescence and apparently inconsistent with the solid state
structure which showed two different types of phosphine. While cooling down the temperature to 208
45

K led to decoalescence, where two multiplets at 5.1 ppm and 16.8 ppm, respectively, were observed(Figure 3). The ratio of these two multiplets in terms of their intensity are approximately 1:1; thedownfield resonance and upfield resonance can be assigned to the inner two and outer two phosphines,
respectively. Consequently, though the obtained low temperature 31P NMR resonance were not wellresolved likely due to the fast dynamic behavior of Ag2L2 in solution, the conclusion can still be madethat these spectral characteristics are roughly consistent with the solid state structure of Ag2L2.

Figure 3. VT 31P NMR spectrum of Ag2L2 in THF-d8 from 293 K to 173 K.
Given the obtained room temperature NMR spectroscopy of Ag2L2, two possibilities could
describe its activities in solution. One is the dimeric species Ag2L2 existing as a monomericmononuclear species with symmetrical structure. The other one is the fast interconversion between
two isomers (including Ag2L2). While the former one was less likely since a fairly broad room
temperature 31P {1H} NMR resonance was observed: the postulated monomeric mononuclear silver
species, likely featuring no interactions between the phosphine donors and silver center, is on thepropensity to give rise to a sharp 31P {1H} NMR singlet. Furthermore, the latter hypothesis was
eventually confirmed by the subsequent low temperature NMR experiments for Ag2L2. Careful
simulation and kinetic analysis (Kinetic Study of Ag2L2, shown below) lead to a large positive entropy46

(ΔS‡ = 68.6 cal mol−1 K–1), indicative of a dissociative process with an energy barrio of ca. 25.3 kcal
mol−1. In addition, we proposed this dynamic behavior as shown below in Scheme 2.

Kinetic Study of Ag2L2A JEOL JNM-ECA 600 NMR spectrometer was used for Variable Temperature (VT)-NMR
studies of the solution behaviour of Ag2L2. The probe temperature was calibrated using standard
methanol solution purchased from Sigma-Aldridge. The spectra were recorded at set temperatures,the corresponding probe temperatures from calibration curve were used for calculations. The
gNMR Spectral Simulation Program (version 4.1) was used to simulate the obtained spectra.
From the calibration curve of our instrument, the real probe temperatures were calculatedusing the calibration equation: y = 0.0014x2 + 1.6451x 63.72
where x = Set Temperature, y = real probe temperatures.
Table 1. Temperature calibration: correlations between the set and real probe temperatures.
Set Temp /°C

Set Temp /K

Real Probe Temp /°CReal Probe Temp /K

65.0

208.2

55.1

218.1

70.0

203.2

60.4

212.8

75.0

198.2

65.9

207.3

80.0

193.2

71.3

201.9

85.0

188.2

76.9

196.3

The hydrogen resonances corresponding to dipyridyl groups of Ag2L2 are shifting dependingon the temperature. We plotted chemical shifts against temperatures, and used the best
approximation curve to assist the modeling of the chemical shifts (Hz) and half-width (Hz) of theresonances using gNMR. The simulated values for δ1, δ2 (in ppm) and half-width of signals (inHz) as well as the rate constant k are listed below (the observed and simulated signals are attachedat the end of this section).

47

Table 2. Simulated parameters from gNMR for an Eyring plot.
Temp. Calibration

gNMR Simulation

Set Temp

Real Probeδ1 /ν1/2 (δ1)/°C

Temp /K

ppm

/Hz

65.0

218.1

8.732

48.00

8.720

70.0

212.8

8.780

12.90

75.0

207.3

8.809

80.0

201.9

85.0

196.3

Eyring Plot

ν1/2 (δ2)

k / s1

1/T

ln(k/T)

48.00

205.600.00458

0.06

8.704

12.00

54.90

0.00470

1.35

25.80

8.695

24.00

10.98

0.00482

2.94

8.823

19.80

8.698

19.20

1.92

0.00495

4.66

8.836

12.20

8.708

12.00

0.30

0.00509

6.48

δ2 / ppm/Hz

With the simulated k values at different temperatures, an Eyring plot (ln(k/T) v.s.1/T) was
created to estimate the ΔG‡, ΔS‡ and ΔH‡ values according to the equation:௱ு ș ଵ௞௱ௌ ș

௞ln(୘) = ( ୖ )୘ + ( ୖ ) + ln( ୦ಳ )
௱ு ș

௱ௌ ș

௞

where the slope of the plot = ( ୖ ), and the intercept = ( ୖ ) + ln( ୦ಳ )From the Eyring plot:
Slope = 12705, y-intercept = 58.282
Standard error and standard deviation of intercept: σM = 0.958, σ = 2.143
Standard error and standard deviation of X variable 1 (1/T): σ M = 198.238, σ = 443.274
ΔS‡ = 68.60 cal mol1K1 = 287.03 J mol1K1, ΔH‡ = 25.30 kcal mol1 = 105.64 kJ mol1

σM (standard error) = 0.0798

Figure 4. Eyring plot
To verify our simulation, the ΔG‡ value at each temperature was calculated from the obtained
ΔS‡ and ΔH‡ values, from which the corresponding k is also calculated according to the rearranged48

equation:
௞ ்

ష೩ಸș

k = ( ಳ ሻ݁ ೃ೅௛The difference between the calculated k from the Eyring plot and the initial simulated k iswithin 10%.
Table 3. Calculated and simulated parameters for k at different temperatures.
Set Temp

Real ProbeᇞG‡ / kJ mol1

Calculated k

Simulated k
1(gNMR)/s1/°C

Temp /K

65.0

218.1

43.03

224.72205.60

70.0

212.8

44.56

50.73

54.90

75.0

207.3

46.12

10.39

10.98

80.0

201.9

47.69

1.91

1.92

85.0

196.3

49.29

0.31

0.30

49

(Eyring plot) /s

gNMR simulation:
Measured NMR Spectra

Simulated Spectra (gNMR)

Figure 5. Comparison between measured and simulated spectra
50Scheme 2. Possible dynamic behavior of Ag2L2 in solution

51

3-3.

Syntheses of Neutral Tetranuclear Copper Complex Cu4LBr4Generally, the Cu(I)-NHC complexes can be prepared via two commonly applied synthetic routes,
that is, transmetallation from the corresponding Ag(I) complexes and the direct reaction of the (preformed) free carbene with labile Cu(I) precursor. Considering the cost and time factors, as well as thefacile preparation and notable stability of dpaP2-NHC, we prefer to use the latter method in thesubsequent reactions.
As we have mentioned in chapter 2 that the products of the reactions of dpaP2-NHC with gold(I)precursors are determined by the nature of the anions associated with the latter. Thus, we are curious
about the outcome of the reactions between dpaP2-NHC and copper(I) precursors with different
associated anions.
Given the easy handle of [CuBr(tht)] (tht = tetrahydrothiophene) which is stable at ambient
atmosphere, we preferred to carry out the reaction of dpaP2-NHC with [CuBr(tht)]. And fortunately,a tetracopper complex Cu4LBr4 with a novel and rare arrangement was produced when dpaP2-NHC
reacted with [CuBr(tht)] in the ratio of 1: 2.5 (Scheme 3). Cu4LBr4, existing as yellow solid, is stable
at ambient atmosphere and shows good solubility in normal solvents, such as benzene, acetonitrile anddichloromethane; the reaction yield is 72% calculated based on the amount of [CuBr(tht)]. A single
set of NMR signals indicates the highly symmetrical structure of Cu4LBr4 in solution; in detail, theprotons of dipyrido moiety and tert-butyl groups gave rise to three singlets at 8.55, 6.66 and 1.15 ppm,
respectively, in 1H NMR spectrum and simultaneously, 31P{1H} NMR spectrum showed only one
resonance at 19.7 ppm as a broad singlet. These NMR data are broadly in agreement with the solidstate structure of Cu4LBr4. While one should keep in mind that the diphenylphosphinyl groups gave
rise to a broad resonance ranging from 7.00 ppm to 7.60 ppm in the 1H NMR spectrum, indicating a
possible fluxional behavior of Cu4LBr4 in solution. Cooling down the temperature to 233 K (40˚C)
did not lead to any decoalescence of these resonance but more broadening.

Scheme 3. Syntheses of the tetranuclear copper(I) complex Cu4L-Br4.
Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl
ether into the DMF solution of Cu4LBr4. Molecular structure (Figure 6) shows an inversion symmetryof complex Cu4LBr4 which consists of a tetrahedral CuI core unit supported by one dpaP2-NHC ligand
and decorated by four bridging bromides in an μ2 fashion with Cu-Br distances falling within the range52

of 2.2579(8)-2.4422(8) Å; in the meantime, weak CuI-CuI interaction can be found between adjacent
CuI atoms (Cu1-Cu2 2.6762(8) Å, Cu1-Cu3 2.6847 (9) Å, Cu2-Cu4 2.7074(9) Å, Cu3-Cu4 2.6849(9)Å), but not between the opposing CuI atoms (Cu1-Cu4 3.144 Å, Cu2-Cu3 3.165 Å).7 It is most likelythat the interaction between bromide and CuI results in the weak metal-metal interaction, as describedin the literature: a stronger interaction between the anion or solvent and CuI atoms leads to theweakening of the metal-metal interaction.20 The Ccarbene-Cu bond distance of 1.886(5) Å is slightly
shortened compared with the typical bond lengths in NHC-Cu complexes, indicating a stronger
interaction between them. 21 That is tentatively due to the strong π donation from bromine which
increasing the Cu-to-Ccarbene backdonation to strengthen the Cu-Ccarbene bond.22 Moreover, the P-Cu
bond distances of 2.2364(13) Å (P1-Cu2) and 2.2257(13) Å (P2-Cu3) are comparable to those fortypical CuI-phosphine complexes.21 Generally, for multinuclear coinage metal (+1 oxidation state)complexes bearing NHC ligands, the σ-donor groups from NHCs are essential for stabilizing the metal
centers by direct interaction with them, situation like Cu4 that is stabilized without interacting withthe σ-donors of NHC is extremely rare with only one example being described in which two of thefour silver(I) metals are stabilized by their adjacent atoms (silver and iodide) in the Ag(I)-NHC
complex.23
Cu4

Br2

Br3

Br4

Cu1
C
P1

Cu3

Cu2
Br1
N1

P2
C1
N2

Figure 6. Molecular structure of complex Cu4LBr4. Ellipsoids are shown at the 50% probability level.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles [˚]: Br1-Cu1 2.2579(8),Br1-Cu4 2.4150(11), Br2-Cu2 2.4422(8), Br2-Cu4 2.3556(8), Br3-Cu3 2.4282(8), Br3-Cu4 2.3526(8),Br4-Cu2 2.4344(8), Br4-Cu3 2.4305(8), Cu1-Cu2 2.6762(8), Cu1-Cu3 2.6847(9), Cu2-Cu4 2.7074(9),Cu3-Cu4 2.6849(9), Cu1-C1 1.886(5), Cu2-P1 2.2364(13), Cu3-P2 2.2257(13); Cu1-Br1-Cu4
85.19(3), Cu4-Br2-Cu2 68.68(3), Cu4-Br3-Cu3 68.31(3), Cu3-Br4-Cu2 80.51(3), Cu1-Cu2-Cu4
72.01(3), Cu1-Cu3-Cu4 72.23(3), Cu2-Cu1-Cu3 71.81(2), Cu3-Cu4-Cu2 71.33(3).
Looking more closely to the coordination sphere around the metal centers, it is easy to find thatthree of the CuI atoms are bridged by the dpaP2-NHC ligand in a κP,κC,κP bonding mode which is anormal coordination sphere for polynuclear coinage metal NHC complexes, while the fourth one is53

fixed, in a rare way, by two adjacent CuI atoms through metal-metal interaction together with threeneighboring bromide ligands. In detail, the penta-coordinated CuI atom (Cu4) is in a trigonal-planar
environment (ΣaCu4 = 357.5°) formed by its three adjacent bromides (Br1, Br2, Br3), simultaneously
by which two adjacent CuI centers (Cu2 and Cu3) are capped with cuprophilic interaction as discussed
above. These two planes (Br1-Br2-Br3 plane and Cu2-Cu3-Cu4 plane) are at 54.5° and coincidently,
in which Cu4 is the intersection. This special coordination environment leads to Cu4 being steadily
fixed by virtue of its five adjacent atoms without the direct participation of σ-donors from dpaP2-NHC
ligand.
While it is worth noting that the ratio of copper(I) atoms to dpaP2-NHC ligand (4:1) in complex
Cu4LBr4 is inconsistent with that of the copper(I) precursor to dpaP2-NHC ligand (2.5:1), which wereused as the starting materials in the reaction mentioned above. This thus prompted us to investigate
what the product will be when dpaP2-NHC reacts with [CuBr(tht)] under the same reaction condition
as mentioned above except the ratio of the starting materials changed from 2.5:1 to 4:1. Interestingly,
the combination of dpaP2-NHC with copper(I) precursor [CuBr(tht)] in a ratio of 1:4 led to theformation of a pure species different from Cu4LBr4 judging from the NMR spectroscopy (Figure 7).
Similar to Cu4LBr4, the new obtained compound was found with only one set of NMR signals, which,however, show some slight chemical shifts compared with those of Cu4LBr4. In detail, the 1H NMR
resonances at 8.55 and 6.66 ppm assigned to the two sets of protons at dipyrido moiety for Cu4LBr4are down- and upfield shifted, respectively, to 8.60 and 6.58 ppm for the new obtained compound.
Furthermore, the 31P NMR singlet at 19.7 ppm for Cu4 LBr4 is downfield shifted to -18.5 ppm forthe new compound.

54Figure 7. Comparison of 1H (top) and 31P (bottom) NMR spectra between the obtained pure species
and Cu4LBr4.
Given the above mentioned NMR spectroscopy, a highly symmetrical structure for the new
obtained compound is expected since only one set of NMR signals can be observed, which is similar
to that of Cu4LBr4. To further prove this hypothesis, much efforts have been made to structurally
characterize this compound. While unfortunately, attempts to obtain its solid-state structure by X-ray
diffraction analysis failed due to its extremely poor solubility in normal solvents, such as THF, DMF
and MeCN. Meanwhile, though it showed a good solubility in DMSO, single crystals suitable for Xray study were not yet obtained after numerous recrystallization using DMSO/ether as the solvent.

55

3-4. Syntheses of Dinuclear Copper Complex Cu2L2
As mentioned in Chapter 2 that the products of the reaction of dpaP2-NHC with gold(I) precursors
depend on the nature of the anions associated with the later, we were wondering if different outcomes
will be generated when dpaP2-NHC reacts with copper(I) precursors associated with different counter
anions. The neutral tetranuclear copper(I) complex Cu4L-Br4 has been produced from the reaction of
dpaP2-NHC with [CuBr(tht)], we next turned our attention to a different copper precursor,[Cu(MeCN)4(OTf)]. The reason why we choose [Cu(MeCN)4(OTf)] here is because that different withthe associated anion Br- which has been proved to possess a stronger coordination ability towards themetals, OTf would prefer to serve as disassociated counter anion in the formed metal complexes,
which thereby will probably result in the formation of copper complexes with entirely different
coordination geometry from Cu4L-Br4.
As expected, when dpaP2-NHC reacted with [Cu(MeCN)4(OTf)] in a ratio of 1:1 in THF, adinuclear copper(I) complex Cu2L2 was generated in a good yield (72%) as brown solid (Scheme 4).
Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl ether
into the solution of Cu2L2 in DMF (dimethylformamide) at room temperature. Molecular structure of
Cu2L2 (Figure 8) shows an unsymmetrical dimeric structure, with an extremely rare coordination
sphere. In detail, two carbene carbons adopt entirely distinct bonding modes, with one (C1)simultaneously bound to two copper(I) atoms, yet the other one (C44) coordinating to only one (Cu2).
Thus as expected, the C44-Cu2 bond length of 1.954(2) Å is comparable to the typical length for theterminal CuI-NHC complexes, whereas the C1-Cu1 and C1-Cu2 distances of 2.153(2) and 2.236(2) Å,
respectively, are significantly longer. Meanwhile, both two copper(I) atoms are five-coordinate but indifferent coordination sphere: Cu1 is coordinated by two phosphine atoms belonging to two dpaP2NHC ligands, one carbene carbon (C1) and the neighboring copper atom Cu2 through intermetallic
interaction, whose coordination sphere is completed by a DMF molecule; Cu2 is coordinated by two
phosphine atoms and two carbene carbons belonging to two dpaP2-NHC ligands, respectively, and theneighboring copper atom Cu1. A strong intramolecular CuI-CuI interaction is present based on the
short distance between Cu1 and Cu2 (Cu1-Cu2 2.5182(5) Å).24

Scheme 4. Syntheses of dinuclear copper(I) complex Cu2 L2 from dpaP2-NHC.

56

Figure 8. Molecular structures of the cation in Cu2L2·DMF. Hydrogen atoms, two dissociated triflateanions and molecules of crystallization solvent (CH3CH2OCH2CH3) are omitted for clarity. Selectedbond lengths (Å) and angles [˚]: Cu1-Cu2 2.5812(5), Cu1-P1 2.3049(7), Cu1-P4 2.2873(7), Cu1-C1
2.154(2), Cu2-P2 2.2889(7), Cu2-P3 2.4006(7), Cu2-C1 2.236(2), Cu2-C44 1.954(2); P1-Cu1-Cu2
109.15(2), P2-Cu2-Cu1 99.19(2), P2-Cu2-P3 104.54(2), P3-Cu2-Cu1 141.29(2), P4-Cu1-Cu2
86.38(2), P4-Cu1-P1 117.50(3), C1-Cu1-Cu2 56.55(6), C1-Cu1-P1 87.20(6), C1-Cu1-P4 141.51(6),C1-Cu2-Cu1 53.47(6), C1-Cu2-P3 98.39(6), C1-Cu2-P2 85.04(6), C44-Cu2-Cu1 90.04(7), C44-Cu2P3 86.42(7), C44-Cu2-P2 147.03(7), C44-Cu2-C1 124.67(9).
It is worth noting that the μ-bridging carbene in CuI-NHC complexes is extremely rare, and to thebest of our knowledge, only two examples have been described to date. 25 Normally, in NHC-metal
complexes presented as dimer or oligomer, the NHC ligands are in same coordination mode, that is,
terminal carbene or bridging carbene. Structures like the dimer Cu2L2, in which two NHC ligands
adopt totally different coordination sphere, that is, one is terminal carbene and the other one is bridging
carbene, is unprecedented as we are aware of. Two possibilities seem to be reasonable to describe thisnovel binding mode. One is that one of the dpaP2-NHC ligands (containing C1) was reduced togenerate a bridging carbene carbon with sp3 hybridization, which coordinates to two copper(II) atoms.
Unfortunately, no literature has yet reported this situation to date. The other possibility involves an
sp2-hybridized μ2-CNHC and two copper(I) centers, namely, a σ–bonding interaction between μ2-CNHCand one of the two copper centers (in this case C1-Cu1) and an unconventional π-interaction between
μ2-CNHC and another one (in this case C1-Cu2).25a,26 According to the distances between μ2-CNHC andtwo copper atoms mentioned in the last paragraph, this description is quite reasonable.
While 1H NMR spectrum of Cu2L2 at room temperature shows a symmetrical and single dpaP2NHC ligand environment, namely, the protons of pyridyl and tert-butyl groups appear as three singlets57

at δ 8.50, 6.99 and 1.20, respectively, which is inconsistent with the observation of its solid-state
structure since, for instance, the four tert-butyl groups are obviously nonequivalent judging from its
molecular structure. Correspondingly, only one 31P NMR singlet was detected at δ -16.3, and the 13C
NMR spectrum shows only one set of resonance at ambient temperature. These NMR spectra datasuggest that Cu2L2 is likely to undergo a fast dynamic behavior in solution, or convert to a highly
symmetric species once dissolved in solution.
If the former hypothesis which Cu2L2 undergoes a dynamic process in solution is the fact, it isvery possible that its NMR spectra or UV-vis spectrum will show some obvious or characteristic
difference from those at ambient temperature, as long as the measuring temperature is low enough.
Thus, to give an accurate explanation, variable temperature (VT) UV-Vis absorption experiment was
first to be conducted. The VT UV-vis absorption spectrum (Figure 9) at ambient temperature in THF
exhibits a broad band ranging from 360 nm to 550 nm with the maximum at 415 nm, which showedalmost no any change when the temperature was gradually cooled to 183 K, except the slightly
increasing intensity.

Figure 9. VT UV-vis absorption spectrum of Cu2L2 in THF from 293 K to 183 K.
Thus, according to the obtained VT UV-vis spectrum, it seems like Cu2L2 exists as a symmetrical
species in solution in the temperature regime of 293 K-178 K. But we still can not exclude thepossibility of Cu2L2 undergoing a fast fluxional behavior in solution. To study further the behavior of
Cu2L2 in solution, we simultaneously conducted a VT 1H NMR experiment. Gradually cooling down
the temperature of 1H NMR experiment from 293 K to 178 K for Cu2L2 did not lead to any
decoalescence of the NMR resonance (Figure 10), namely, the 1H NMR spectrum of Cu2L2 displays
no significant change. Likewise, no obvious change was observed for the VT 31P {1H} NMR spectrumof Cu2L2 from 293 K-178 K. Therefore, though a variety of experimental attempts have been
conducted, the obtained results are not sufficient enough to support us to make a conclusion about theaccurate state of Cu2L2 in solution in the temperature range of 293 K-178 K.
58

Figure 10. VT 1H NMR spectrum of Cu2L2 from 293 K to 178 K in THF-d8.
While given the obtained solution data, there are two possibilities that could describe the state of
Cu2L2 in solution. The first possibility is that Cu2L2 exists as a symmetrical species in solution. Here,
we proposed this very symmetrical species to be a monomeric complex, CuL (Scheme 5), in which
the only metal atom (Cu) is connected to the carbene carbon. The reasons why we provide this proposal
here include: 1) the molecular structure of CuL is in good agreement with the observation of its NMR
spectroscopy mentioned above; 2) the NMR resonance found in 13C NMR spectrum at 198.3 ppm
which corresponds to the carbene carbon of dpaP2-NHC shifted significantly towards upfield to 153.5
ppm, indicating the existence of metal (Cu)-coordinated carbene carbon in CuL. The other possibility
involves the fast interconversion between two dimeric species (Scheme 5), Cu2L2 and Cu2L2'. For
this hypothesis, the symmetrical NMR spectroscopy can be the result of the possible NMR coalescence.
The origin of this dynamic behavior is likely involving the rapid μ2-Carbene-Cu and P-Cu bonds
breaking/formation.

59

Scheme 5. Two possible fluxional behavior of Cu2L2 in solution.
Even though the obtained solution data (VT NMR spectroscopy and VT UV-vis spectra) seem tobe (in our view) reasonable for supporting the hypothesis of the fluxional behavior of Cu2L2 in solution(ķ and ĸ) as mentioned above, this evidence is still not sufficient and convincible enough to enable
us to conclude that these two proposed dynamic behavior are existing 100 percent, unless the precise
structural assignment for CuL and Cu2L2' is performed. Thus, to achieve the rigorous proof, it seems
to be necessary to establish the molecular structures of CuL and/or Cu2L2'. We made some attempts
to grow single crystals of CuL or Cu2L2' suitable for X-ray diffraction analysis by a DMF solution of
Cu2L2 overlayered by diethyl ether, at low temperature (below 30 ˚C). Unfortunately, rather than the
expected molecular structure of CuL or Cu2L2', the obtained crystals were consistently proved to be
the dimeric species, Cu2L2. While in turn, these unsuccessful attempts demonstrate the stable
existence of Cu2L2 in the form of solid state.

60

3-5. Syntheses of Tetranuclear Bimetallic Ag-Cu Complex Ag2Cu2L2 from Cu2L2
In Chapter 2, we have described the syntheses of tetranuclear gold complex 4 from the dinuclear
gold complex 3. Actually, both Cu2L2 and Cu2L2' can be considered as the analogues of 3. In thiscontext, dpaP2-NHC complexes containing higher metal nuclei than 2 are likely to be accessible from
Cu2L2. On the other hand, according to our previous hypothesis, the monomeric mononuclear complex
CuL features two non-metallated phosphine donors, which implies the possibility of capturing extra
metal centers. Therefore, it is very possible that multinuclear complexes (the number of metal beyond2) can be afforded by reactions of the Cu2L2 solution with metal precursors. Considering our researchscope, the coinage metals (gold, silver and copper) will be checked in the next study.
In light of the synthesis of gold complexes 2-4, trinuclear complexes based on dpaP2-NHC are
unlikely to be achieved. Therefore, we seek to achieve dpa P2-NHC supported complexes with 4 ormore metal nuclei instead of 3. Reaction of Cu2L2 with two equivalents of AgOTf in THF under theprotection of N2 in the absence of light (Scheme 6) was carried out, which, after approximately 3 h, aheterobimetallic complex, Ag2Cu2L2, was isolated as the only product in the form of orange solid ina modest yield (47%).

Scheme 6. Syntheses of heterobimetallic complex Ag2Cu2L2 from Cu2L2.
The 1H NMR spectrum of Ag2Cu2L2 showed a single and symmetrical dpaP2-NHC ligand
environment. In detail, the protons of pyridyl groups give rise to only two singlets at 8.50 and 7.00
ppm, respectively; the protons of tBu groups resonate as one singlet at 1.20 ppm. Correspondingly,
only one set of signals was clearly observed in 13C NMR spectrum, in which, unfortunately, thecarbene carbon resonance signal was not detected, even after a three days’ measurement in the solutionof DMSO-d6 at ambient temperature. Meanwhile, 31P NMR spectrum shows a broad doublet at 2.6 and4.2 ppm (JP-107/109Ag ≈ 273.8 Hz), respectively, at 233 K, which is likely to be the result of a possible
fluxional process.
Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl
ether into the solution of Ag2Cu2L2 in dimethylformamide (DMF). Interestingly, the obtained crystal
structure showed an oxygenated species, Ag2Cu2L2(O), which is different from our proposed structure.
It is likely that in the course of crystallization, Ag2Cu2L2 was oxygenated by water contained in61

solvents DMF/ether. While, satisfactory refinement of the structure was persistently unavailable. Eventhen, the connectivity of Ag2Cu2L2(O) and its composition can be clearly deduced (Figure 11), but adetailed discussion of metrical data on this complex is impossible. Molecular structure of this complex
shows a dimeric and roof-like structure with two dpaP2-NHC ligands being bridged by a fourmembered metallocycle (Ag-Cu-Ag-Cu) which is connected by intramolecular metal-metalinteractions. Two outer Ag atoms are respectively coordinated by two phosphine donors from two
dpaP2-NHC ligands, while each of the two inner Cu atoms featuring an identical coordination sphereis bound to only one carbene carbon. Furthermore, two Cu atoms are capped by an oxygen atom
located in the vertex of the geometry. The source of the oxygen atom of Ag2Cu2L2(O) is arguably
water contained in organic solvents which were used in the workup procedure. One of two counter
anions, OTf, is dissociated from the cation and the other one is connected to an outer silver atom.

Figure 11. Thermal ellipsoid representation (50% probability level) of the structure of the cation in
Ag2Cu2L2(O). Hydrogen atoms, phenyl groups and dissociated triflate anion are omitted for clarity.
The successful synthesis of Ag2Cu2L2 is important because it clearly demonstrates the existenceof the dynamic behavior of Cu2L2 in solution as we expected, although we cannot make sure whichķ and ĸ) the process is. Meanwhile, it also inspired us to check the reactions of Cu2L2 withone (ķ
other two group 11 metals (Cu and Au).

62

3-6.

Syntheses of Tetranuclear Cu(I) Complex Cu4L2·2CH3CN from Cu2L2

Encouraged by the successful syntheses of the tetranuclear bimetallic Ag/Cu complex Ag2Cu2L2
from Cu2L2, we therefore sought to synthesize tetranuclear bimetallic Au/Cu complex and tetranuclear
copper complex by treatment of Cu2L2 with suitable gold and copper precursors, respectively.
We first conducted a reaction of Cu2L2 with 2 equiv [Au(tht)2(OTf)] in inert atmosphere,
unfortunately resulting in the formation of ill-defined mixture as judged by NMR spectroscopy. Thisis most likely due to the scrambling of the transmetallation from copper to gold of the NHC donor27
and the coordination of gold directly by phosphine donors, which generate the admixture of goldcoordinated NHC and phosphine complexes. However, to be honest, the interpretation for the failed
experiment cannot be currently identified since there is no pure product from the mixture that can beisolated yet.
Subsequently, a reaction of Cu2L2 with 2 equiv [Cu(MeCN)4(OTf)] in the absence of light was
performed (Scheme 7), which resulted in the formation of a tetranuclear copper complex
Cu4L2·2CH3CN after a reaction time of approximately 3 h. The product was collected after work-up
as a yellow solid and pure enough for the next analysis.

Scheme 7. Syntheses of tetranuclear copper(I) complex Cu4L2·2CH3CN from Cu2L2.
The 31P NMR spectrum of Cu4L2·2CH3CN at room temperature showed only one singlet at 14.3
ppm, indicating the equivalence of all the phosphine ligands. Correspondingly, the 1H NMR spectrum
displays one set of resonance signals, which suggested a symmetrical and single ligand environment.
In detail, the protons of dipyridyl groups adjacent to phosphine donors and tert-butyl groups gave rise
to a downfield doublet at 8.09 nm ( 3JHP = 1.8 Hz) and an upfield singlet at 1.22 ppm, respectively.
Simultaneously, three kinds of phenyl protons appeared as three resonance signals, respectively, in thedownfield (6.8-7.3 ppm). However, the left dipyridyl protons cannot be found in the room temperature
1

H NMR spectrum. This can be attributed to the overlap with the signals of phenyl protons. To

ascertain our postulation such that achieving well-resolved 1H NMR spectrum, VT 1H NMR
experiment for Cu4L2·2CH3CN was performed (Figure 12). Fortunately, cooling down thetemperature to 253 K led to the appearance of the very dipyridyl protons, presenting as a singlet at637.08 ppm. These spectral characteristics are indicative of a highly symmetrical structure of
Cu4L2·2CH3CN.

Figure 12. VT 1H NMR spectrum of Cu4L2·2CH3CN in CD3CN from 293 K to 233 K.
Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl
ether into the solution of Cu4L2·2CH3CN in DMF. While interestingly, instead of our proposed
structure for Cu4L2·2CH3CN, X-ray diffraction analysis suggested an oxygenated tetranuclear
Cu4L2(O) structure as shown in Figure 13, similar to Ag2Cu2L2(O). It is worth noting that satisfactoryrefinement of this structure was persistently unavailable due to the heavy disorder of the molecule,however, the connectivity of Cu4L2(O) and its composition can be clearly deduced, and a detailed
discussion of metrical data on this complex is impossible. Molecular structure of Cu4L2(O) shows analmost same geometry with Ag2Cu2L2(O). The main difference between these two complexes is their
two outer metal atoms, that is, in Ag2Cu2L2(O) two silvers, in Cu4L2(O) two coppers.

64Figure 13. Thermal ellipsoid representation (50% probability level) of the structure of the cation in
Cu4L2(O). Hydrogen atoms, phenyl groups and a dissociated triflate anion are omitted for clarity.
Actually, the structure of Cu4L2(O) showed also consistency with the aforementioned NMR
spectroscopy. Therefore, a question arises: is the bulk sample Cu4L2·2CH3CN or Cu4L2(O) (crystals
has been identified as Cu4L2(O))? To verify this, we performed a 19F NMR experiment, since thefluorine content of equimolar amount of Cu4L2·2CH3CN and Cu4L2(O) are different. Here, we usedthe dinuclear gold complex 1 (Chapter 2) featuring a PF6 anion as the standard sample and the sample
for NMR experiment was the mixture of equimolar amount of 1 and bulk sample (bulk sample waspresumed as Cu4L2·2CH3CN). The obtained 19F NMR spectrum (Figure 14) displayed a doublet for
1 at 68.8 and 70.7 ppm with same intensity and a singlet for bulk sample at 77.4 ppm, whose ratio
is 1:1:4. This revealed that the fluorine content of bulk sample is one time more than that of equimolar
amount of 1, suggesting that the bulk sample has four triflate anions. Consequently, we affirm that thebulk sample is Cu4L2·2CH3CN. The source of the oxygen atom of Cu4L2(O) is arguably watercontained in recrystallization solvent DMF or diethyl ether.

65

Figure 14. 19F NMR spectrum of equimolar amount of complex 1 and bulk sample in DMSO-d6 atroom temperature.

66

3-7.

Syntheses of Pentanuclear Cu(I) Complex Cu5L2 Br3 from Cu2L2

As described above, using the dinuclear species Cu2L2 as the starting material, two tetranuclear
species, Ag2Cu2L2 and Cu4L2, have been cleanly achieved. We wonder if it is possible to generate
multinuclear metal complexes, from Cu2L2, whose number of nuclei is above 4. Keeping this in mind,
we carried out a reaction of Cu2L2 with 3 or 4 equivalents of [Cu(MeCN)4(OTf)] in THF in the absenceof light, which, unfortunately and consistently, led to the isolation of Cu4L2 as the only product as
judged by the obtained NMR spectra. In this context, four metals seem to be the highest metal content
that dpaP2-NHC is capable of capturing.
Nonetheless in 2016, Ai, P. et al.8c reported the syntheses of a hexanuclear copper(I) complex basedon a diphhosphine-functionalized NHC ligand (N,N’-diphosphanyl-imidazol-2-ylidene), in which two
adjacent copper(I) atoms connected by intramolecular cuprophilic interactions were capped by one or
two iodides. With this arrangement, six coppers were captured and framed by two NHC ligands,
together with five iodides. Triflate, as the sixth counter anion, is dissociative and does not show any
obvious interactions with those six coppers. In this very compound, halides are likely playing animportant role for stabilizing those six coppers. Accordingly, we attempted to introduce halide into thereaction so as to achieve multinuclear copper complex with a higher metal content in comparison to4.

Scheme 8. Syntheses of pentanuclear copper(I) complex Cu5L2Br3 from Cu2L2.
Considering the resource what we have at hand in our lab, bromide which is fixed in [CuBr(tht)]
was chosen as the halide source. Subsequent reaction was carried out at ambient atmosphere sinceboth reactants are air stable. Excitingly and expectedly, a pentanuclear copper complex Cu5L2Br3 wasachieved as a yellow solid in a 52.5% yield when Cu2L2 reacted with 3 equiv [CuBr(tht)] (Scheme 8),
which shows no sign of decomposition when exposed, in the form of solid, to ambient atmosphere.
NMR data implied a symmetrical ligand environment of Cu5L2Br3 in solution. In detail, two
downfield singlets at 8.60 and 6.62 ppm, respectively, in the 1H NMR spectrum were detected,
corresponding to two type of dipyridyl protons. Meanwhile, only one upfield 1H NMR singlet at 1.15
ppm assignable to the tert-butyl protons was detected. Correspondingly, the 31P NMR spectrum of
Cu5L2Br3 displayed a broad singlet at 18.7 ppm, indicating the equivalence of the phosphine groups.
67

The broadening of this copper-coordinated 31P NMR singlet can be attributed to the fast quadrupole
relaxation of the 63Cu nucleus (I = 3/2).28 While unfortunately, these solution data are inconsistent withthe observation of its solid state structure (Figure 15). Cooling down the temperature to 193 K (80˚C)
had no effect for obtaining well resolved NMR spectra. We proposed the coalescence to be the resultof dynamic behavior of Cu5L2Br3 in solution.
Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl
ether into a DMF solution of Cu5L2Br3. Note that the obtained molecular structure Cu5L2Br3·2DMF
is solvated by two DMF molecules. While the comparison of the NMR spectra between Cu5L2Br andCu5L2Br3·2DMF which showed almost identical chemical shifts suggested that these two compounds
are supposed to adopt the same coordination geometry in solution. In other words, the coordination
sphere of Cu5L2Br3·2DMF shown in Figure represents the structural assignment of Cu5L2Br3.
Molecular structure reveals that Cu5L2Br3·2DMF contains two identical [Cu3(dpaP2-NHC)Br·DMF]
subunits that are sharing one of five copper atoms (Cu3) and bridged by one of three bromides (Br3)through the interactions with two coppers (Br3-Cu4, Br3-Cu5), whereas pointing in the opposite
directions. Five copper atoms found in a six-member metallocycle are connected via the Cu-Cu
interactions (average Cu-Cu distance 2.5918 Å), which are slightly stronger in comparison to thetypical cuprophilic interactions.21 In each [Cu3(dpaP2-NHC)Br·DMF] subunit, three copper atoms
connected through Cu-Cu interactions are spanned by one μ3-dpaP2-NHC,κP,κC,κP ligand and cappedby one bromide. As a result, the interactions between bromide and respective three copper atoms arepresent and can be roughly grouped into two types based on the bond length, that is, Br1-Cu1 with astrong interaction (2.2789(11) Å), Br1-Cu4 and Br1-Cu3 with relatively weak interactions (2.6223(12)and 2.6947 (12) Å). This strong interaction can be attributed to the strong Br-to-Cu π-backdonation.
Furthermore, it is worth noting that the bond lengths between Cu and CNHC (Cu1-C1 1.883(7) Å and
Cu2-C44 1.884(6) Å) are slightly shorter in comparison to the typical CuI-NHC complexes (>1.9 Å),21
which is likely due to the strong copper-to-CNHC π-backdonation. Furthermore, in comparison totetranuclear gold complexes 4 (Chapter 2), there is one additional CuBr inserted between a metalphosphine interaction.

68

Figure 15. Thermal ellipsoid representation (50% probability level) of the structure of the cation in
Cu5L2Br3·2DMF. Hydrogen atoms and two triflate anions are omitted for clarity. Selected bondlengths (Å): Br1-Cu3 2.6947 (12), Br1-Cu1 2.2789(11), Br1-Cu4 2.6223(12), Br2-Cu3 2.6432(11),
Br2-Cu2 2.2907(11), Br2-Cu5 2.6165(12), Br3-Cu4 2.4527(13), Br3-Cu5 2.4448(14), Cu1-Cu4
2.5752(13), Cu1-C1 1.883(7), Cu2-Cu5 2.5347(13), Cu2-C44 1.884(6), Cu2-Cu3 2.6333(12), Cu3Cu1 2.6240(12), Cu3-P4 2.2618(19), Cu3-P2 2.2590(19), Cu4-P1 2.206(2), Cu5-P3 2.194(2).
We also made attempts to achieve hexanuclear complexes of dpaP2-NHC by treatment of Cu2L2
with 4 equiv [CuBr(tht)] but failed, with only Cu5L2Br3 being isolated from these reactions. This
probably resulted from the combined effects of steric and electronic properties of dpaP2-NHC.

69

3-8.

Syntheses of Homonuclear Copper Complexes Cu4L2·2MeCN and Cu5L2Br3 from dpaP2-

NHC and Heteronuclear Complexes Ag2Cu2L2(O) from Ag2L2
To be honest, it is unexpected and intriguing to have developed the synthetic routes to
Cu4L2·2MeCN, Cu5L2Br3 and Ag2Cu2L2 from Cu2L2, since part of our initial plan was to achievethese multinuclear complexes straightforwardly from the free carbene ligand dpa P2-NHC. We suspectthat these established synthetic routes provide nothing but alternative syntheses of Cu4L2·2MeCN,
Cu5L2Br3 and Ag2Cu2L2 (successful syntheses of Cu4L2·2MeCN and Cu5L2Br3 directly from dpaP2NHC and Ag2Cu2L2 from Ag2L2 will be introduced in the following paragraph) and proof of Cu2L2
undergoing fluxional process in solution. While in view of the efficiency of syntheses, one-stepreaction is definitely more efficient comparing to two-step reaction when starting materials and target
compounds are respectively same. Given this and in continuation of our initial objective, we next
attempt to prepare Cu4L2·2MeCN, Cu5L2Br3 and Ag2Cu2L2 from dpaP2-NHC by one-pot reaction.
Reaction of dpaP2-NHC with two equivalents of [Cu(MeCN) 4(OTf)] was prior to be carried out,
leading to formation of the expected tetracopper complex Cu4L2·2MeCN as the only product in 73%
yield (Scheme 9). Meanwhile, the pentanuclear copper complex Cu5L2Br3 was successfully generated
by treatment of dpaP2-NHC with [Cu(MeCN)4(OTf)] and [CuBr(tht)] in a ratio of 2:2:3, in 60% yield.
Thus obviously, these two homonuclear copper complexes are accessible from dpaP2-NHC in one step
as we expected. Furthermore, the yield of one step reactions (73% for Cu4L2·2MeCN and 60% for
Cu5L2Br3) are significantly higher than those of two step reactions (50% for Cu4L2·2MeCN and 38%
for Cu5L2Br3).

Scheme 9. Syntheses of homonuclear copper complexes Cu4L2·2CH3CN and Cu5L2Br3
from dpaP2-NHC.
While unfortunately, treatment of dpaP2-NHC with [Cu(MeCN)4(OTf)] and AgOTf in a ratio of
1:1:1 did not give the desirable heteronuclear complex Ag2Cu2L2 but ill-defined mixture, as judged
by NMR spectroscopy (Scheme 10). According to the analysis of proposed reaction mechanism,
formation of Ag2Cu2L2 from dpaP2-NHC by one pot reaction seems reasonable: NHC donor and oneof two phosphine donors in dpa P2-NHC coordinate to copper and silver ions, respectively, leading to
the formation of AgCuL moiety, which is put together to give Ag2Cu2L2. In addition, there should be
no scrambling of the coordination of NHC or phosphine towards metals since we and others14 have70

proven that the NHC shows superior transmetallation aptitude to phosphine, and silver coordinated by
NHC or phosphine tends to be substituted by other transition metals, including copper. Moreexperiments and careful analysis are underway for figuring out the reason of the failure of this reaction.

Scheme 10. Attempt to synthesize bimetallic Ag/Cu complex Ag2Cu2L2 from dpaP2-NHC.
Nonetheless, things are always unexpected. When the dinuclear silver complex Ag2L2 reacted withequimolar amount of [Cu(MeCN)4(OTf)] (Scheme 11), Ag2Cu2L2 was isolated as the only product in
64% yield after workup at ambient atmosphere. Concerning the process of the formation of Ag2Cu2L2,
we proposed two steps, that is, prior CNHC donors transmetallation from Ag to Cu and subsequently,
an outward “sliding” movement of Ag. This reaction is significant because it corroborates that, incomparison to the phosphine ligand Ph2PCpyridyl, the NHC features superior transmetallation aptitude.14

Scheme 11. Syntheses of heteronuclear bimetallic Ag/Cu complex Ag2Cu2L2 from Ag2L2.

71

3-9. Photophysical Properties of the Obtained Silver, Copper and Bimetallic Silver/Copper
Complexes
As described previously, luminescence properties of coinage metal complexes supported by NHC
ligands have always been an interesting research subject. 29 With the silver and copper complexes inhand, we start to investigate their photophysical properties in degassed 2-methyl-THF, at room
temperature (UV-vis absorption, photoluminescence excitation and emission) and 77 K
(phosphorescence).
Figure 16 shows the obtained UV-vis absorption spectra of Cu4LBr4, Cu2L2, Ag2Cu2L2,
Cu4L2·2CH3CN, Cu5L2Br3 and Ag2L2 at room temperature, whose absorption bands were found in
the UV spectral range from 320 nm to 450 nm. These absorption bands compared well to those of goldcomplexes 1-4 (Chapter 2), which therefore can mainly be attributed to the ligand-centered (LC)transitions and metal-to-ligand charge transfer (MLCT) transitions.

Figure 16. UV-vis absorption spectra of complexes Cu4 LBr4, Cu2L2, Ag2Cu2L2, Cu4L2·2CH3CN,
Cu5L2Br3 and Ag2L2 at room temperature in degassed 2-methyl-THF (2×10-5 M).
Photoluminescence excitation spectra (dash line) and emission spectra (solid line) acquired atroom temperature were combined in Figure 17. All the obtained complexes are luminescent anddisplay unstructured and almost same emission bands centered at about 500 nm. These emission bands
are comparable to those of gold complexes 1-4 (Chapter 2), as well as, in particular, the free carbene
ligand dpaP2-NHC. Therefore, it suggests that the electronic transitions of these silver and copper
complexes can be mostly attributed to the ligand-centered (LC) transitions. Meanwhile, once excited
at 505 and 500 nm for Ag2L2 and Cu4LBr4, Cu2L2, Ag2Cu2L2, Cu4L2·2CH3CN, Cu5L2Br3,
respectively, all the complexes provided single excitation band centered at about 375 nm. The
excitation spectra showed identical profiles to the corresponding UV-vis absorption spectra.

72

Figure 17. Normalized Excitation (dashed lines) and emission (solid line) spectra of complexes
Cu4LBr4, Cu2L2, Ag2Cu2L2, Cu4L2·2CH3CN, Cu5L2Br3 and Ag2L2 at room temperature in degassed
2-methyl-THF (2×10-5 M). Samples were excited at 420 nm (Cu4LBr4, Cu2L2, Ag2Cu2L2,
Cu4L2·2CH3CN and Ag2L2) and 395 nm (Cu5L2Br3). Photoluminescence excitation spectra wererecorded by monitoring emissions at 505 nm (Ag2L2) and 500 nm (Cu4LBr4, Cu2L2, Ag2Cu2L2,
Cu4L2·2CH3CN and Cu5L2Br3).
All the complexes have been investigated concerned with their phosphorescence at 77 K and only
Cu4LBr4, Cu4L2·2CH3CN and Cu5L2Br3 were found to exhibit phosphorescence under this condition(Figure 18). Both Cu4L2·2CH3CN and Cu5L2Br3 showed a single phosphorescence band at about
640 nm; while interestingly, Cu4LBr4 showed a dual phosphorescence at about 640 and 725 nm, which
is likely stemming from the difficult interconversion of two triplet states arising from different orbital
parentages. Compared with the free carbene ligand dpaP2-NHC (Chapter 2), the phosphorescencebands of Cu4LBr4, Cu4L2·2CH3CN and Cu5L2Br3 were red-shifted, suggesting electronic
perturbation of the copper cation to the triplet state of the carbene to a limited extent.

73

Figure 18. Normalized phosphorescence spectra of Cu4LBr4, Cu4L2·2CH3CN and Cu5L2Br3 indegassed 2-methyl-THF (2×10-5 M) at 77 K. Samples were excited at 420 nm (Cu4LBr4 andCu4L2·2CH3CN) and 395 nm (Cu5L2Br3).
The phosphorescence decay profiles are depicted in Figure 19, from which the lifetimes of
Cu4LBr4, Cu4L2·2CH3CN and Cu5L2Br3 are calculated to be 268.7, 571.9 and 655.6 μs, respectively.
Most likely, these long luminescence lifetimes can be explained to originate from the lowest triplet
states.

Figure 19. Phosphorescence decay traces for Cu4LBr4, Cu4L2·2CH3CN and Cu5L2Br3 in degassed
2-methyl-THF (2×10-5 M) monitoring at 640 nm at 77 K. The lifetimes of complexes Cu4LBr4,
Cu4L2·2CH3CN and Cu5L2Br3 are 268.7, 571.9 and 655.6 μs, respectively.

74

3-10.

Conclusion and Outlook

In conclusion, we have investigated the coordination chemistry of bis(diphenylphosphinyl)functionalized dipyrido-annulated NHC (dpaP2-NHC) towards silver(I) and copper(I). Based on dpaP2NHC, a series of multinuclear complexes featuring intramolecular d10-d10 interactions have beenachieved and characterized, including two dinuclear silver and copper complexes (Ag2L2 and Cu2L2),
a bimetallic tetranuclear complex (Ag2Cu2L2), two tetranuclear copper complexes (Cu4LBr4 andCu4L2·2CH3CN) and a pentanuclear copper complex (Cu5L2Br3). Judging by the obtained NMR
spectra, all of the complexes underwent dynamic behavior in solution at room temperature. In
particular, the room temperature NMR spectra of Ag2L2 displaying a coalescence were well resolved
at low temperature (below 208 K) and a dissociative process for Ag2L2 was observed based on thecalculated Eyring plot. In contrast, the possible coalesced NMR spectra of Cu2L2 did not show any
significant change with the temperature varying from 293 K to 173 K, indicating extremely low barrierof the fluxional process of Cu2L2 in solution. Ag2L2 showed a similar coordination sphere with its
gold analogue 3 (Chapter 2). While differently, the dicopper complex Cu2L2 contained two distinct
carbenes, namely a terminal carbene and a bridging carbene. Cu4LBr4 is neutral and monomeric, inwhich four copper centers were rigidly fixed by the tridentate ligand dpaP2-NHC and additional
bromide anions. Cu5L2Br3 showed a similar coordination sphere with the tetranuclear gold complex
4 (Chapter 2), except that one additional CuBr was inserted between a metal-phosphine interaction
for Cu5L2Br3.
All complexes obtained are luminescent, in which Cu4L2 ·2CH3CN, Cu4LBr4 and Cu5L2Br3 arephosphorescent at 77 K. The metal centers and the different solid-state structures did not seem tochange the solution photoluminescence properties of these dpa P2-NHC complexes. This may be dueto the dynamic processes in solution because of the rigidity of the ligand. Earlier group metal centersthat prefer higher coordination numbers maybe more suitable for stronger non-dissociative
coordination. This and their photophysical properties of the resulting complexes are our next research
focus.

75

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78

Chapter 4

Conclusion and Outlook

Since the spectroscopically and structurally characterization of the first isolable N-heterocycliccarbene by Arduengo and co-workers in 1991, NHCs have attracted considerable attention due to theirnumerous applications across a variety of fields. As part of our long-standing interests in the chemistryof pincer ligands, we designed and synthesized a diphosphine-functionalized hybrid NHC,
bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC (dpaP2-NHC). Closely following
this, the coordination chemistry of dpaP2-NHC towards coinage metal ions was investigated, fromwhich exciting results were obtained.
Apprehensive of the potential experimental challenges to be met when dealing with the possible
air- or light-sensitive silver carbene complexes, we were first to be focus on the coordination chemistryof dpaP2-NHC towards AuI.
At first, an air- and water-stable, monomeric dinuclear gold complex 1, with two gold-coordinatedphosphines and unactivated carbene, was achieved starting from the carbene precursor L(H)I via a
two step reaction (Scheme 1). Considering the subsequent synthetic convenience, we attempted toisolate the free NHC dpaP2-NHC at room temperature, which was successfully realized through thedehydrogenation reaction of L(H)I with tBuOK. dpaP2-NHC is stable at inert atmosphere at room
temperature for months, which is, to some extent, in favor of our next experimental work.
Shortly afterward, starting from the free carbene dpaP2-NHC, we afforded two dinuclear goldcomplexes (2-3) and one tetranuclear gold complex (4) via respective one-step reactions (Scheme 1).
While it is worth noting that two totally different digold complexes 2 and 3 were respectively generated
from dpaP2-NHC, when subjected to two different gold precursor (AuCl(SMe2) and Au(tht)2OTf).
Alternatively, complex 2 can serve as the precursor on the way to complexes 3 and 4 (Scheme 1)
through the reactions of halide (chloride) abstraction and likely phosphine transfer, respectively. The
obtained NMR spectra indicated that complexes 1 and 3 showed consistency in solid state and solution,
while complexes 2 and 4 underwent possible dynamic behavior in solution.
The free carbene dpaP2-NHC and complexes 1-4 were structurally characterized by X-ray
diffraction analysis. Strong Au-Au interactions were found in complexes 2-4. Especially, molecular
structure of tetragold species 4 showed a novel and unprecedented coordination sphere, in which fourgold cations connected by aurophilic interactions formed a planar metallocycle bridging two dpaP2NHC ligands, which are parallel to each other and point in the opposite direction. In the meantime,each of the central golds (NHC coordinated) lies in the plane of three σ-donors in each NHC ligand
owing to the hindered rotation at the phosphines.

80

Scheme 1. Syntheses of di- and tetranuclear gold complexes (1-4) from L(H)I.
After finishing the gold part, we turned our attention to investigating the coordination chemistryof dpaP2-NHC towards silver and copper. As a result, a series of homonuclear silver(I) and copper(I)complexes based on dpaP2-NHC were synthesized and spectroscopically and structurally
characterized, including two dinuclear complexes Ag2L2 and Cu2L2, two tetranuclear copper
complexes Cu4LBr4 and Cu4L2·2CH3CN, and a pentanuclear copper(I) complex Cu5L2Br3 (Scheme
2).

Scheme 2. Syntheses of homonulcear silver and copper complexes from dpaP2-NHC

81

The two dinuclear complexes (Ag2L2 and Cu2L2) were found to undergo fluxional behavior insolution judging from the obtained NMR spectroscopy, since both the room temperature NMR spectraof these two complexes showed a single and symmetric dpa P2-NHC environment that contrasts withthe observation of their solid state structure. For Cu2L2, cooling temperature to 193 K did not lead tothe decoalescence of the NMR spectra. While the fluxional behavior can be directly corroborated by
the successful synthesis of Cu4L2·2CH3CN, Ag2Cu2L2 and Cu5L2Br3 from Cu2L2 via one step
reaction (Scheme 3). For Ag2L2, well resolved NMR spectra can be observed on the 1H and 31P NMR
timescale when the temperature is at <208 K. At this temperature range, the NMR spectra are inagreement with the solid state structure and a dissociative process was observed according to thecalculated Eyring plot.

Scheme 3. Syntheses of homonulcear copper and heteronuclear silver/copper complexes from Cu2L2
Meanwhile, it is interesting to find that the bimetallic Ag/Cu complex Ag2Cu2L2 can be generated
by reaction of Cu2L2 with two equivalent of [Cu(MeCN)4(OTf)] (Scheme 4). This reaction is likely
to proceed via the transmetallation of the NHC donor from Ag(I) to Cu(I) and the following outward
sliding movement of Ag(I) which is captured by two phosphine ligands from two dpaP2-NHC ligands.
This reaction is also significant because it corroborates that the NHC transmetallation aptitude issuperior to that of the triarylphosphine.

82

Scheme 4. Syntheses of heteronulcear silver/copper complexes Ag2Cu2L2 from Ag2L2
The dicopper complex Cu2L2 showed a novel coordination mode with two carbene carbons
adopting two different bonding modes, namely one bound to only one copper atom and the othersimultaneously bound to two copper atoms. Thus, two types of carbene carbons in terms of thehybridization can be expected, that is, the terminal carbene carbon in sp2 hybridization and the bridging
carbene carbon in sp3 hybridization. Ag2L2 displayed an entirely same coordination sphere comparedto the obtained digold complex 3. Interestingly, the tetranuclear copper complex Cu4L2·2CH3CN thatare expected to adopt similar coordination sphere with the tetragold complex 4 likely underwent
reactions with water contained in solvent (DMF) in the course of crystallization, resulting in theinsertion of the oxygen atom in a form of bridging two central copper atoms. The neutral andmonomeric complex Cu4LBr4 showed a novel coordination mode with four copper centers of which
are rigidly fixed by three σ donors (two phosphines and one NHC) and adjacent bromide anions. To
our best knowledge, this coordination mode is unprecedented for phosphine-functionalized NHC
supported coinage metal complexes. The pentanuclear copper complex Cu5L2Br3 comprised two same
[Cu3Br(dpaP2-NHC)(DMF)] subunits sharing a hexacoordinated copper and bridged by one of thebromides through interactions with two phosphine-coordinated coppers, which point in opposite
directions.
All the obtained complexes are luminescent in solution at room temperature. Of these, the goldcomplexes (1-4) and homonuclear copper complexes (Cu4 LBr4, Cu4L2·2CH3CN and Cu5L2Br3) emit
phosphorescence at 77 K with long lifetimes ranging from 85.1 to 772.0 μs. While to be honest, thephotoluminescence properties of these complexes were determined with no spectacular results, namely,
all the complexes showed almost the same emission bands lying in the range of 450-600 nm. Given
the comparison with the free carbene dpaP2-NHC, we can attribute the luminescence of thesecomplexes to the ligand-centered (LC) transitions. In other words, the metal-metal interactions haveno significant contribution to the enhancement of the photophysical properties of the obtainedcomplexes in solution. This could be tentatively associated with the dynamic behavior of thesecomplexes in solution, which lead to the possible disappearance of metal-metal interactions. Our next
work is mainly focused on improving the stability of these complexes by replacing the dissociated83anion triflate with the anions with stronger coordinating ability, like halide anions, which are able tocoordinate with the metal centers so that to stabilize the metal-metal interactions and keep the integrityof complexes in solution, to some extent.
The luminescence of complexes in solid state has been always an important parameter formeasuring the physical properties of complexes. According to our original design, the strong metalmetal interactions and wide π-electron conjugation of the backbone as our obtained coinage metal
dpaP2-NHC complexes feature would contribute significantly to enhance the photophysical propertiesof the complexes. While unfortunately, due to the limited laboratory condition, measuring theluminescence of the obtained complexes in solid state cannot be carried out. We will do this work in
the near future.
Given the reported excellent performance of gold- and copper-NHC complexes in a variety ofchemical transformations as catalysts, we will also attempt to explore the catalytic uses of goldcomplexes (2-4) in cycloisomerization and C-H bond activation and copper complexes in crosscoupling reactions.

84Experimental Section
General Procedure
Unless otherwise noted, all the manipulations were carried out using standard Schlenk techniques
under an argon atmosphere. THF and hexane were purified by passing through a Glass Contour solvent
dispensing system under an N2 atmosphere; other solvents used were purified and dried by standard
methods. The starting material L(H)I was prepared according to the literature procedure.1-3 1H (400
MHz, 600 MHz), 13C (100 MHz, 150 Hz), and 31P (162 MHz, 243MHz) NMR spectra were recorded
on JEOL AL-400S spectrometer and were referenced to CDCl3 (1H: δ=7.26 ppm; 13C: δ=77.1 ppm),
C6D6 (1H: δ=7.16 ppm; 13C: δ=128.0 ppm), DMSO-d6 (1H: δ=2.50 ppm; 13C: δ=39.5 ppm) or CD3CN(1H: δ=1.94 ppm; 13C: δ=118.26 ppm) as external standards. 31P NMR spectra are referenced to 85%
H3PO4 (δ=0.0 ppm) as external standards. UV-vis absorption spectra were recorded with a Shimadzu
UV-1650PC spectrophotometer. Photoluminescence spectra were measured with a HORIBA
FluoroMax-4 spectrophotometer.

Figure S1. Atom numbering used for the assignment of the NMR resonances
Syntheses of L(H)IThe carbene precursor L(H)I was afforded via a seven-step reaction according to the literaturefrom us and other groups.1-3

85

Syntheses of dpaP2-NHC

The solution of L(H)I (400.0 mg, 0.515 mmol) and t-BuOK (69.3 mg, 0.618 mmol) in THF (40mL) was stirred at room temperature for 2 h and volatiles were then removed under reduced pressure.
Hexane (60 mL) was added and the solution was filtered through Celite. After removal of the solvent,dpaP2-NHC was obtained as a yellow solid. Yield: 68.7% (230.1 mg, 0.354 mmol). 1H NMR (600
MHz, C6D6): δ 1.08 (s, 18H, CH3), 6.54 (s, 2H, Ha), 6.93-7.06 (m, 12H, m-/p-CHPh), 7.42 (m, 8H, oCHPh), 7.53 (s, 2H, Hb). 31P{1H} NMR (243 MHz, C6D6): δ -13.8. 13C{1H} NMR (150 MHz, C6D6):
δ 30.3 (CH3), 34.7 (C(CH3)), 111.5 (C1/C9), 121.1 (C3/C7), 122.7 (d, 1JPC = 2 Hz, C4/C6), 128.5 (d,3

JPC = 8 Hz, m-CPh), 128.8 (p-CPh), 134.7 (d, 1JPC = 21 Hz, o-CPh), 136.9 (d, 2JPC = 12 Hz, i-CPh), 140.3(C10/C11), 142.0 (d, 3JPC = 14 Hz, C2/C8), 198.3 (t, 3JPC = 33 Hz, Ccarbene). Element analysis calcd for
C43H42N2P2 (648.77): C 79.61, H 6.53, N 4.32; found: C 79.37, H 6.20, N 4.84.
Syntheses of L(H)PF6

The solution of L(H)I (100 mg, 0.129 mmol) and KPF6 (47.4 mg, 0.258 mmol) in CH2Cl2 (20 mL)
was stirred at room temperature for 24 h. After the reaction solution being concentrated to 2-3 mLunder reduced pressure, hexane (10 mL) was added to precipitate the yellow solid L(H)PF6 that wascollected by filtration. Yield: 85.7% (87.8 mg, 0.111 mmol). 1H NMR (400 MHz, DMSO-d6): δ 1.23
(s, 18H, CH3), 6.97 (dd, 4JHH = 2.0 Hz, 3JPH = 2.4 Hz, 2H, Ha), 7.21-7.38 (m, 8H, o-CHPh), 7.39-7.67(m, 12H, m-/p-CHPh), 8.64 (s, H, NCHN), 8.91 (d, 4JHH = 2.0 Hz, 2H, Hb). 31P{1H} NMR (162 MHz,DMSO-d6): δ -13.6 (s), -143.2 (sept, 1JPF = 720.9 Hz, PF6). 13C{1H} NMR (100 MHz, DMSO-d6): δ
29.9 (CH3), 35.1 (C(CH3)), 110.2 (t, 3JPC = 16 Hz, NCHN), 114.8 (C1/ C9), 123.9 (C10/C11), 126.9(d, 2JPC = 6 Hz, C6/C4), 129.0 (d, 1JPC = 6 Hz, C7/C3), 129.9 (d, 3JPC = 8 Hz, m-CPh), 131.2 (p-CPh),
133.1 (d, 1JPC = 25 Hz, i-CPh), 133.9 (d, 2JPC = 21 Hz, o-CPh), 146.0 (C2/C8). HRMS (ESI) m/z [MPF6]+ 649.290. Element analysis calcd for C43H43F6N2P3 (794.74): C 64.99, H 5.45, N 3.52; found: C
65.10, H 5.70, N 3.64.

86

Syntheses of complex 1

To a solution of L(H)PF6 (20.0 mg, 0.025 mmol) in CH2Cl2 (10 mL) was added [AuCl(SMe2)](14.8 mg, 0.051 mmol) and the resulting solution was stirred at room temperature for 1 h. After being
concentrated to 2-3 mL under reduced pressure, hexane (15 mL) was added to precipitate the yellow
solid complex 1 that was collected by filtration. Yield: 90.5% (28.5 mg, 0.023 mmol). Suitable crystals
for X-ray analysis were obtained by slow diffusion of diethyl ether into the solution of 1 indimethylformamide.

1

H NMR (400 MHz, DMSO-d6): δ 1.24 (s, 18H, CH3), 7.14 (d, 3JPH= 10.4 Hz,

2H, Ha), 7.59-7.89 (m, 20H, CHPh), 8.30 (s, H, NCHN), 9.23 (s, 2H, Hb). 31P{1H} NMR (162 MHz,DMSO-d6): δ 27.2 (s), -143.2 (sept, 1JPF = 720.9 Hz, PF6). 13C{1H} NMR (100 MHz, DMSO-d6): δ
29.9 (CH3), 35.3 (C(CH3)), 110.0 (br s, 110.0), 118.1 (C1/C9), 122.7 (d, 1JPC = 65 Hz, C4/C6), 123.5(d, 1JPC = 62 Hz, i-CPh), 125.1 (d, 3JPC = 2 Hz, C10/C11), 130.0 (d, 2JPC = 10 Hz, C3/C7), 131.0 (d,3JPC = 13 Hz, m-CPh), 134.6 (d, 4JPC = 2 Hz, p-CPh), 134.8 (d, 2JPC = 10 Hz, o-CPh), 146.7 (C2/C8).

HRMS (ESI) m/z [M-PF6]+ 1113.1609. Element analysis calcd for C43H43Au2Cl2F6N2P3 (1259.58): C
41.00, H 3.44, N 2.22; found: C 40.58, H 3.24, N 2.13.
Syntheses of complex 2

The approximately saturate solution of [AuCl(SMe2)] (74.8 mg, 0.254 mmol) in CH2Cl2 (6 mL)
was slowly added dropwise to a solution of free carbene dpaP2-NHC (150.0 mg, 0.231 mmol) in
hexane (80 mL) and the instantly formed yellow precipitate was collected by filtration. After
recrystallization with THF at -18°C, desired product was collected as light yellow solid by filtration.
Yield: 72.3% (147.2 mg, 0.084 mmol). Suitable crystals for X-ray analysis were obtained by slow
diffusion of diethyl ether into the solution of 2 in dimethylformamide. Due to the fluxional process insolution, the proton resonance in 1H NMR spectrum can not be clearly ascribed; 13C{1H} NMR
spectrum could not be obtained due to the poor solubility and harsh measurement condition: long time
(more than 1 days) and low temperature (around -10 qC). 31P{1H} NMR (243 MHz, CDCl3): δ26.2 (s),8727.3 (s), 28.5 (s), 30.3 (s). HRMS (ESI) m/z [M-2Cl]2+ 845.2498. Element analysis calcd for
C86H84Au2Cl2N4P4 (1762.37): C 58.61, H 4.80, N 3.18; found: C 58.37, H 4.99, N 3.18.
Syntheses of complex 3

Method A: The solution of complex 2 (100.0 mg, 0.057 mmol) and AgOTf (29.3 mg, 0.114 mmol)in CH2Cl2 (15 mL) was stirred at room temperature over 1 h in the absence of light. Then the resulting
solution was filtered through Celite and the filtrate was concentrated to 2-3 mL under reduced pressure;hexane (15 mL) was added to precipitate complex 3 that was collected as an orange solid by filtration.
Yield: 64.3% (73.0 mg, 0.0367 mmol). Method B: The solution of free carbene dpaP2-NHC (50.0 mg,
0.077 mmol) and [Au(tht)2(OTf)] (40.2 mg, 0.077 mmol) in THF (10 mL) was stirred at room
temperature for 2 h and then concentrated to 2-3 mL under reduced pressure; hexane (15 mL) was
added to precipitate complex 3 that was collected as an orange solid by filtration. Yield: 82.6% (63.3
mg, 0.0318 mmol). Suitable crystals for X-ray analysis were obtained by slow diffusion of diethyl
ether into the solution of 3 in dimethylformamide. 1H NMR (400 MHz, DMSO-d6): δ 1.04 (s, 18H,
CH3), 1.20 (s, 18H, CH3), 6.76 (br s, 8H, CHPh), 6.88 (s, 4H, Hb), 7.10-7.70 (m, 32H, CHPh), 8.82 (s,2H, Ha), 8.97 (s, 2H, Ha). 31P{1H} NMR (162 MHz, DMSO-d6): δ 29.7 (virtual triplet, JPP = 31.5 Hz),
6.8 (virtual triplet, JPP = 30.7 Hz). 13C{1H} NMR (100 MHz, DMSO-d6): δ 29.7 (CH3), 29.8 (CH3),
34.7 (C(CH3)), 34.9 (C(CH3)), 114.8 (C1), 118.1 (C9), 119.6 (q, 1JCF = 345.1 Hz, CF3), 125.5 (C4),126.2 (C6), 126.9 (C3), 128.8 (d, 1JPC = 7 Hz, i'-CPh), 129.2 (m'-CPh), 129.6 (br, p'-/m-CPh), 130.2 (C7),130.8 (p-CPh),131.8 (d, 1JPC = 7 Hz, i-CPh), 132.7 (o-/o'-CPh), 135.4 (C10/C11), 142.5 (C2), 145.0 (C8),the carbene carbon could not be detected. HRMS (ESI) m/z [M-2O3SCF3] 2+ 845.2486. Element
analysis calcd for C88H84Au2F6N4O6P4S2 (1989.60): C 53.12, H 4.26, N 2.82; found: C 54.24, H 4.12,
N 2.87.

88

Syntheses of complex 4

Method A: The solution of free carbene dpaP2-NHC (25.0 mg, 0.0385 mmol) and [Au(tht)2(OTf)](40.2 mg, 0.077 mmol) in THF (10 mL) was stirred at room temperature for 2 h and concentrated to
2-3 mL under reduced pressure; hexane (15 mL) was added to precipitate complex 4 that was collected
as an orange solid by filtration. Yield: 71.3% (36.7 mg, 0.0137 mmol). Method B: The solution ofcomplex 3 (25.0 mg, 0.0126 mmol) and [Au(tht)2(OTf)] (13.1 mg, 0.0252 mmol) in THF (15 mL) was
stirred at room temperature for 3 h and concentrated to 2-3 mL under reduced pressure; hexane (15mL) was added to precipitate complex 4 that was collected as an orange solid by filtration. Yield:
51.3% (16.1 mg, 0.006 mmol). Suitable crystals for X-ray analysis were obtained by slow diffusion ofdiethyl ether into the solution of 4 in dimethylformamide. 1H NMR (400 MHz, DMSO-d6): δ 1.12 (s,36H, CH3), 6.65 (s, 4H, Hb), 6.91-8.21(m, 40H, CHPh), 9.06 (d, 3JPH = 22.0 Hz, 4H, Ha). 31P{1H} NMR(162 MHz, DMSO-d6): δ 36.3 (s). 13C{1H} NMR (100 MHz, DMSO-d6): δ 29.7 (CH3), 34.7(C(CH3)),
118.2 (C1/C9), 119.1 (C4/C6), 122.4 (C10/C11), 125.9 (C3/C7), 129.5 (i-CPh), 130.2 (m-CPh), 132.0(p-CPh), 133.2 (o-CPh), 143.4 (C2/C8), the carbene carbon and carbons of triflates could not be detected.
HRMS (ESI) m/z [M-4O3SCF3] 4+ 521.1086. Element analysis calcd for C88H84Au2F6N4O6P4S 2(2681.66): C 40.31, H 3.16, N 2.09; found: C 39.87, H 3.32, N 1.77.
Syntheses of Ag2L2

The solution of dpaP2-NHC (50.0 mg, 0.077 mmol) and AgOTf (19.8 mg, 0.077 mmol) in THF(10 mL) was stirred at room temperature in the absence of light for 2 h and then concentrated to 2-3
mL; hexane (15 mL) was added to precipitate Ag2L2 that was collected as a yellow solid by filtration.
Yield: 78.9% (55.0 mg, 0.030 mmol). X-ray quality crystals were obtained by slow diffusion of diethyl
89

ether into the DMF solution of Ag2L2. Anal. Calcd. for C88H84Ag2F6N4O6P4S2: C 58.35, H 4.67, N
3.09. Found: C 58.29, H 4.71, N 3.15. 1H NMR (600 MHz, DMSO-d6, 293K): δ 8.71 (s, 4H, Ha),
7.40-7.50, (m, 8H, p-CHPh), 7.20-7.35 (m, 16H, m-CHPh), 7.02 (br s, 16H, o-CHPh), 1.13 (s, 36H,
C(CH3)3); 1H NMR (600 MHz, THF-d8, 188 K): δ 8.87 (s, 2H, Ha), 8.74 (s, 2H, Ha), 8.15-6.88 (m,40H, CHPh), 6.68 (s, 4H, Hb), 1.25 (s, 18H, C(CH3)3), 1.07 (s, 18H, C(CH3)3). 31P{1H} NMR (243MHz, DMSO-d6, 293 K): δ -10.0 (br m); 31P{1H} NMR (243 MHz, THF-d8, 188 K): δ –16.76 (m), 5.11 (br d, 1Jp-107/109Ag ≈ 527Hz). 13C{1H} NMR (150 MHz, DMSO-d6): δ 142.6 (C2/C8), 133.1 (oCPh), 131.2 (p-CPh), 129.8 (C10/C11), 129.3 (m-CPh), 129.1 (i-CPh), 127.0 (C3/C7), 125.2 (C4/C6),
121.8 (q, 1JCF = 214 Hz, CF3), 116.0 (C1/C9), 34.7 (C(CH3)3), 29.8 (CH3), the carbene carbon C5 can
not be detected.
Syntheses of Cu4LBr4The solution of dpaP2-NHC (20 mg, 0.031 mmol) and CuBr·tht (17.8 mg, 0.077 mmol) in THF (4mL) was vigorously stirred at ambient temperature. After 3 h, hexane (15 mL) was added to precipitate
the desired product Cu4LBr4 as a bright yellow solid, which was collected by filtration. Yield: 72.3%(17 mg, 0.014 mmol) (yield was calculated based on CuBr·tht). X-ray quality crystals were obtainedby slow diffusion of diethyl ether into the DMF solution of Cu4LBr4. Anal. Calcd. for
C43H42Br4Cu4N2P2: C 42.24, H 3.46, N 2.29; found: C 42.68, H 3.09, N 2.56. 1H NMR (400 MHz,DMSO-d6) δ 8.55 (s, 2H, Ha), 6.98-7.78 (br m, 20H, CHPh), 6.66 (s, 2H, Hb), 1.15 (s, 18H, C(CH3)3).
31

P{1H} NMR (162 MHz, DMSO-d6) δ -19.7 (s). 13C{1H} NMR (100 MHz, DMSO-d6) δ142.5(C2/C8), 133.8 (d, 2JPC = 16 Hz, o-CPh), 132.2 (i-CPh), 131.1 (p-CPh), 129.3 (d, 3JPC = 8 Hz, m-CPh),
125.8 (C3/C7), 123.6 (C4/C6), 115.1 (C1/C9), 34.7 (C(CH3)3), 29.9 (C(CH3)3), the carbene carbon C5
and C10/C11 can not be detected.

90

Syntheses of Cu2L2

The solution of dpaP2-NHC (50.0 mg, 0.077 mmol) and [Cu(MeCN)4(OTf)] (29.0 mg, 0.077mmol) in THF (10 mL) was stirred at room temperature in the absence of light. Two hours later,
reaction solution was concentrated to 2-3 mL; hexane (15 mL) was added to precipitate Cu2L2 thatwas collected as a brown solid by filtration. Yield: 71.5% (47.4 mg, 0.027 mmol). X-ray quality
crystals were obtained by slow diffusion of diethyl ether into the DMF solution of Cu2L2. Anal. Calcd.
for C88H86Cu2F6N4O7P4S2: C 60.72, H 4.98, N 3.22. Found: C 60.28, H 5.18, N 3.18. 1H NMR (600
MHz, DMSO-d6): δ 8.50 (s, 4H, Ha), 7.38-7.28 (m, 8H, p-CHPh), 7.20-7.10 (m, 16H, m-CHPh), 6.99(s, 4H, Hb), 6.88 (br s, 16H, o-CHPh), 1.20 (s, 36H, C(CH3)3). 31P{1H} NMR (243 MHz, DMSO-d6):
δ -13.6. 13C{1H} NMR (150 MHz, DMSO-d6): δ 153.5 (C5), 143.1 (C2/C8), 132.9 (C10/C11), 131.9(o-CPh), 130.4 (p-CPh), 129.7 (i-CPh), 128.9 (m-CPh), 127.1 (C3/C7), 125.5 (C4/C6), 121.7 (q, 1JCF =214.0 Hz, CF3), 116.1 (C1/C9), 34.8 (C(CH3)3), 29.9 (CH3).
Syntheses of Ag2Cu2L2

Method A: To the solution of Ag2L2 (40.0 mg, 0.022 mmol) in CH2Cl2 (10 mL) was added[Cu(MeCN)4(OTf)] (17.0 mg, 0.045 mmol) at room temperature and the resulting mixture was stirred
for 2 h in the absence of light. After removal of the volatiles under reduced pressure, THF (3 mL) was
added to dissolve the residual; desired product Ag2Cu2L2 was precipitated by the addition of hexane(did not undergo drying procedure) and collected as an orange solid by filtration. Yield: 63.9% (29.8
mg, 0.014 mmol); Method B: The solution of Cu2L2 (24 mg, 0.015 mmol) and AgOTf (7.7 mg, 0.03mmol) in THF (5 mL) was stirred at room temperature. Two hours later, hexane (15 mL) was added91

to precipitate the desired product Ag2Cu2L2 as a yellow solid collected by filtration. Yield: 46.7% (15mg, 0.007 mmol). X-ray quality crystals were obtained by slow diffusion of diethyl ether into the DMF
solution of Ag2Cu2L2. Anal. Calcd. for C88H84Ag2OCu2F6N4O7P4S2[Ag2Cu2L2(O)]: C 54.08, H 4.33,
N 2.87. Found: C 54.54, H 4.55, N 3.13. 1H NMR (600 MHz, DMSO-d6): δ 8.50 (s, 4H, Ha), 7.387.28 (m, 8H, p-CHPh), 7.20-7.08 (m, 16H, m-CHPh), 7.00 (s, 4H, Hb), 6.88 (br s, 16H, o-CHPh), 1.20
(s, 36H, C(CH3)3). 31P{1H} NMR (243 MHz, DMSO-d6): δ -4.24 (br d, JP-107Ag/109Ag ≈ 273.8 Hz).
13

C{1H} NMR (150 MHz, DMSO-d6): δ 143.0 (C2/C8), 131.8 (o-CPh), 130.3 (p-CPh), 129.6 (C10/C11),

128.8 (m-CPh), 128.5 (i-CPh), 127.1 (C3/C7), 125.4 (C4/C6), 121.6 (q, 1JCF = 213.0 Hz, CF3), 116.0(C1/C9), 34.7 (C(CH3)3), 29.8 (CH3), the carbene carbon C5 can not be detected.
Syntheses of Cu4L2·2CH3CN

Method A: The solution of dpaP2-NHC (20.0 mg, 0.031 mmol) and [Cu(MeCN)4(OTf)] (22.7 mg,
0.062 mmol) in CH2Cl2 (10 mL) was stirred at room temperature in the absence of light for 2 h. Afterthe removal of volatiles, desired product Cu4L2·2CH3CN was obtained as an orange solid, Yield:
73.2% (23.1 mg, 0.011 mmol); Method B: The solution of Cu2L2 (20.0 mg, 0.012 mmol) and[Cu(MeCN)4(OTf)] (9.1 mg, 0.024 mmol) in CH2Cl2 (10 mL) was stirred at room temperature in theabsence of light for 2 h. After the removal of volatiles, desired product Cu4L2·2CH3CN was obtained
as an orange solid, Yield: 69.9% (15.9 mg, 0.008 mmol). X-ray quality crystals were obtained by slow
diffusion of diethyl ether into the DMF solution of Cu4L2·2CH3CN. Anal. Calcd. for
C88H84OCu4F6N4O7P4S2 [Cu4L2(O)]: C 56.65, H 4.54, N 3.00. Found: C 56.84, H 4.20, N 2.89. 1H
NMR (600 MHz, CD3CN): δ 8.09 (d, 3JHP = 1.8 Hz, 4H, Ha), 7.30-7.24 (m, 8H, p-CHPh), 7.08 (s, 4H,
Hb), 7.07-7.01 (m, 16H, m-CHPh), 6.85 (br s, 16H, o-CHPh), 1.96 (s, 6H, CH3CN), 1.22 (s, 36H,
C(CH3)3). 31P{1H} NMR (243 MHz, CD3CN): δ -14.4. 13C{1H} NMR (150 MHz, CD3CN): δ 144.5(C2/C8), 133.3 (o-CPh), 131.4 (p-CPh), 129.7 (m-CPh), 128.6 (C3/C7), 126.8 (C10/C11), 125.3 (C4/C6),
121.1 (q, 1JCF = 212.0 Hz, CF3), 116.5 (C1/C9), 35.7 (C(CH3)3), 30.3 (CH3), the carbene carbon C5
and i-CPh can not be detected.

92

Syntheses of Cu5L2Br3

Method A: The solution of dpaP2-NHC (50 mg, 0.077 mmol) in CH2Cl2 (5 mL) was added to asolution of CuBr·tht (23.7 mg, 0.115 mmol) and [Cu(MeCN)4(OTf)] (29.0 mg, 0.077 mmol) in CH2Cl2(5 mL) and the resulting mixture was stirred for 3 h at room temperature in the absence of light. Afterremoval of the volatiles under reduced pressure, the residue was dissolved with THF (10mL) andhexane (20 mL) was added to precipitate the desired product Cu5L2Br3 as a yellow solid collected byfiltration. Yield: 60.3% (49.9 mg, 0.023 mmol); Method B: The solution of Cu2L2 (15 mg, 0.0087mmol) and CuBr·tht (6.1 mg, 0.0261 mmol) in CH2Cl2 was stirred at room temperature for 4 h. Afterremoving the volatiles, the residual was dissolved with THF and hexane was added to precipitate thedesired product Cu5L2Br3 as a yellow solid collected by filtration. Yield: 52.5% (10 mg, 0.00457
mmol). X-ray quality crystals were obtained by slow diffusion of diethyl ether into the DMF solutionof Cu5L2Br3. Anal. Calcd. for C88H84Br3Cu5F6N4O6P4S2: C 49.09, H 3.93, N 2.60. Found: C 44.81, H
3.84, N 2.46. Element analysis were consistently found to be low in carbon. 1H NMR (600 MHz,DMSO-d6): δ 8.68 (s, 4H, Ha), 7.74-6.92 (m, 40H, CHPh), 6.56 (s, 4H, Hb), 1.14 (s, 36H, C(CH3)3).
31

P{1H} NMR (243 MHz, DMSO-d6): δ 16.8 (br s). 13C{1H} NMR (150 MHz, DMSO-d6): δ 142.8(C2/C8), 133.7 (o-CPh), 131.7 (p-CPh), 129.51 (m-CPh), 129.45 (i-CPh), 126.3 (C3/C7), 123.7(C10/C11), 121.7 (q, 1JCF = 213.0 Hz, CF3), 118.1 (C4/C6), 115.6 (C1/C9), 34.7 (C(CH3)3), 29.8 (CH3),
the carbene carbon C5 can not be detected.

93

NMR Spectra
NMR Spectra of dpaP2-NHC

Figure S2. 1H NMR spectrum (600 MHz) of dpaP2-NHC in C6D6.

94

Figure S3. 13C NMR spectrum (150 MHz) of dpaP2-NHC in C6D6 (* = hexane).

Figure S4. 31P NMR spectrum (243 MHz) of dpaP2-NHC in C6D6.
95

Figure S5. H-C HSQC spectrum of the free carbene dpaP2-NHC (C6D6)

Figure S6. DEPT 135 spectrum of free carbene dpaP2-NHC

96

CH3

CH3

Figure S7. Selected region (part 1) of H-C HSQC spectrum of the free carbene dpaP2-NHC

Hb

o-CHPhC6D6m-/p-CHPh

Ha

C1/C9

C3/C7

m-/p-CPho-CPhFigure S8. Selected region (part 2) of H-C HSQC spectrum of the free carbene dpaP2-NHC

97

NMR Spectra of L(H)PF6

Figure S9. 1H NMR spectrum (400 MHz) of L(H)PF6 in DMSO-d6 (* = acetone)

Figure S10. 13C{1H} NMR spectrum (100 MHz) of L(H)PF6 in DMSO-d6

98

Figure S11. 31P{1H} NMR spectrum (162 MHz) of L(H)PF6 in DMSO-d6
NMR Spectra of complex 1

Figure S12. 1H NMR spectrum (400 MHz) of complex 1 in DMSO-d6
99

Figure S13. 13C{1H} NMR spectrum (100 MHz) of complex 1 in DMSO-d6 (* = hexane)

Figure S14. 31P{1H} NMR spectrum (162 MHz) of complex 1 in DMSO-d6
100

Figure S15. H-C HMBC spectrum of complex 1 in DMSO-d6

Figure S16. DEPT(135) spectrum of complex 1 in DMSO-d6

101

Hb

Ha

CH3

C(CH3)3

Figure S17. Selected region (part 1) of H-C HMBC spectrum of complex 1 in DMSO-d6

CH3

CH3
C(CH3)3

Figure S18. Selected region (part 2) of H-C HMBC spectrum of complex 1 in DMSO-d6
102

H-Ph

Hb

Ha

C1/C9

i-CPh
C10/C11

C3/C7

Figure S19. Selected region (part 3) of H-C HMBC spectrum of complex 1 in DMSO-d6

CH3

C2/C8

Figure S20. Selected region (part 4) of H-C HMBC spectrum of complex 1 in DMSO-d6
103

Variable temperature (VT) NMR spectra of complex 2 in CDCl3

Figure S21. VT 1H NMR spectra (600 MHz) of complex 2 in CDCl3 from -10ć to -40ć104

Figure S22. 31P{1H} NMR spectrum (243 MHz) of complex 2 in CDCl3 at -10ć

Figure S23. VT 31P{1H} NMR spectrum (243 MHz) of complex 2 in CDCl3 from -10ć to -40ć105

NMR spectra of complex 3

Figure S24. 1H NMR spectrum (400 MHz) of complex 3 in DMSO-d6 (* = THF)

Figure S25. 13C{1H} NMR spectrum (100 MHz) of complex 3 in DMSO-d6 (* = THF)

106

Figure S26. DEPT(135) spectrum of complex 3 in DMSO-d6

Figure S27. 31P{1H} NMR spectrum (162 MHz) of complex 3 in DMSO-d6

107

NMR spectra of complex 4

Figure S28. 1H NMR spectrum (400 MHz) of complex 4 in DMSO-d6 (* = THF, # = tht)

Figure S29. 31P{1H} NMR spectrum (162 MHz) of complex 4 in DMSO-d6

108

Figure S30. 13C{1H} NMR spectrum (100 MHz) of complex 4 in DMSO-d6
NMR Spectra of Ag2L2

Figure S31. 1H NMR spectrum (600 MHz) of Ag2L2 in DMSO-d6

109

Figure S32. 13C{1H} NMR spectrum (150 MHz) of Ag2L2 in DMSO-d6 (* = hexane)

110Figure S33. DEPT (135) spectrum of Ag2L2 in DMSO-d6

Figure S34. 31P{1H} NMR spectrum (243 MHz) of Ag2L2 in DMSO-d6

111

Figure S35. VT UV-Vis spectra of complex Ag2L2 in THF from 293 K to 178 K at concentration of
2.0×10-5 M

112

NMR Spectra of Cu4LBr4Figure S36. 1H NMR spectrum (400 MHz) of Cu4LBr4 in DMSO-d6

Figure S37. 13C{1H} NMR spectrum (150 MHz) of Cu4LBr4 in DMSO-d6 (* = hexane, # = tht)

113

Figure S38. DEPT (135) spectrum of Cu4LBr4 in DMSO-d6

Figure S39. 31P{1H} NMR spectrum (243 MHz) of Cu4LBr4 in DMSO-d6

114

NMR Spectra of Cu2L2

Figure S40. 1H NMR spectra (600 MHz) of Cu2L2 (bulk sample, top) and Cu2L2·DMF (crystals,
bottom) in DMSO-d6

115

Figure S41. 13C{1H} NMR spectrum (150 MHz) of Cu2L2 in DMSO-d6 (* = hexane)

Figure S42. DEPT (135) spectrum of Cu2L2 in DMSO-d6

116

Figure S43. 31P{1H} NMR spectrum (243 MHz) of Cu2L2 in DMSO-d6

Figure S44. VT 1H NMR spectra (600 MHz) of Cu2L2 in THF-d8

117

Figure S45. VT 31P{1H} NMR spectra (243 MHz) of Cu2 L2 in THF-d8

118

Figure S46. VT UV-Vis spectra of complex Cu2L2 in THF from 293 K to 183 K at concentration of
2.0×10-5 M

119

NMR Spectra of Ag2Cu2L2(O)Figure S47. 1H NMR spectrum (600 MHz) of Ag2Cu2L2(O) in DMSO-d6

Figure S48. 13C{1H} NMR spectrum (150 MHz) of Ag2Cu2L2(O) in DMSO-d6 (* = hexane)120

Figure S49. 31P{1H} NMR spectrum (243 MHz) of Ag2Cu2L2(O) in DMSO-d6

121

NMR Spectra of Cu4L2·2CH3CN

Figure S50. 1H NMR spectra (600 MHz) at 253 K (top) and VT 1H NMR spectra from 293 to 233 K(bottom) of Cu4L2·2CH3CN in CD3CN
122

Figure S51. 13C{1H} NMR spectrum (150 MHz) of Cu4L2·2CH3CN in CD3CN (* = hexane)

Figure S52. DEPT (135) spectrum of Cu4L2·2CH3CN in DMSO-d6
123

Figure S53. 31P{1H} NMR spectrum (243 MHz) of Cu4L2·2CH3CN in CD3CN

124

NMR Spectra of Cu5L2-Br3

Figure S54. 1H NMR spectrum (600 MHz) of Cu5L2Br3 (bulk sample, top) and Cu5L2Br3·2DMF(crystals, bottom) in DMSO-d6 (* = THF, # = tht, & = hexane)

125Figure S55. 13C{1H} NMR spectrum (150 MHz) of Cu5L2Br3 in DMSO-d6 (* = hexane)

Figure S56. DEPT (135) spectrum of Cu5L2Br3 in DMSO-d6
126

Figure S57.

31

P{1H} NMR spectrum (243 MHz) of Cu5L2Br3 (bulk sample, top) andCu5L2Br3·2DMF (crystals, bottom) in DMSO-d6

127

Crystal Structure Determination
Crystals suitable for X-ray structural determination were mounted on a Bruker SMART APEXII
CCD diffractometer. Samples were irradiated with graphite monochromated Mo-Kα radiation (λ=0.71073 Å) at 173 K for data collection. The data were processed using the APEX program suite. Using
Olex2,4 the structures were solved with the ShelXT5 structure solution program using Intrinsic Phasing
and refined with the ShelXL6 refinement package using Least Squares minimization. Refinement was
performed on F2 anisotropically for all the non-hydrogen atoms by the full-matrix least-squares
method. The hydrogen atoms were assigned to idealized geometric positions and included in therefinement with isotropic thermal parameters. The pictures of molecules were prepared using Pov-Ray
3.7.0.7 The crystallographic data are summarized in Table S1-S5.
Table S1. Crystallographic data for compound dpaP2-NHC
CompounddpaP2-NHC

FormulaC43H42N2P2

Molecular weight648.72Crystal system

orthorhombic

Space group

Pbca

Color

brown

Habit

plate

Crystal dimens, mm

0.50×0.16×0.08

a, Å

14.093(2)b, Å

16.545(2)c, Å

30.850(5)α, deg90β, deg90γ, deg

90

V, Å

3

7193.3(18)

Z

8
-3

Dcalc, g cm

1.198

Abs coeff, mm-1

0.153

F(000)

2752

Radiation; λ, Å

Mo KD, 0.71073

Temp, K

123(2)

Reflections

32784

Independent

6331

128

Data/restraints/parameters6331 / 0 / 430

Rint

0.0829R1 [I > 2σ(I)]0.0429wR2 (all data)

0.1005

GOF

0.957

solv.

THF / hexane

for crystallization

CCDC-1894301 (dpaP2-NHC) contains the supplementary crystallographic data. The data can beobtainedfreeofchargefromtheCambridge

Crystallographic

Datawww.ccdc.cam.ac.uk/data_request/cif
Table S2. Crystal data for complexes 1 and 2.
Compound

1

2

C43H43Au2Cl2F6N2O

C86H84Au2Cl2N4P4·2

6P3·4(CH3)2NCHO(CH3)2NCHO

Molecular weight1551.92

1908.47

Crystal system

Monoclinic

Monoclinic

Space group

C2/c

P21/n

Color

yellowyellow

Habit

block

block

Crystal dimens, mm

0.06×0.06×0.05

0.13×0.13×0.075

a, Å

22.392(5)14.259(11)b, Å

16.519(4)31.08(2)c, Å

16.628(4)20.805(16)α, deg90

90

β, deg98.342(3)99.714(13)γ, deg90

90

6086(2)9088(12)Z

4

4

Dcalc, g cm-3

1.694

1.395

Abs coeff, mm-1

5.049

3.402

F(000)

3064

3840

Radiation; λ, Å

Mo KD, 0.71073

Mo KD, 0.71073

Formula

V, Å

3

129

Centrevia

Temp, K173(2)

123(2)

Reflections

15774

54785

Independent

6215

22722

Data/restraints/parameters6215/0/361

19462/150/1067

Rint

0.02740.0311R1 [I > 2σ(I)]0.03510.0384wR2 (all data)

0.1005

0.0930

GOF

1.087

1.019

DMF/ether

DMF/ethersolv.
for crystallization

CCDC-1894302 (1) and 1894303 (2) contain the supplementary crystallographic data. The data canbe obtained free of charge

from the Cambridge

Crystallographic Data

Centre via

www.ccdc.cam.ac.uk/data_request/cif
Table S3. Crystal data for complexes 3 and 4.
Compound

3

4

C88H84Au2F6N4O6P4S2·(CH3)2NC

C90H84Au4F12N4O12P4S4·

HO·CH3CH2OCH2CH3

4(CH3)2NCHO

Molecular weight2135.732964.90

Crystal system

Monoclinic

Triclinic

Space group

P21/c

P-1

Color

brown

yellow

Habit

block

plate

Crystal dimens, mm

0.10×0.10×0.08

0.05×0.05×0.02

a, Å

15.779(12)15.762(2)b, Å

25.547(19)15.767(2)c, Å

24.151(19)23.977(4)α, deg9082.204(2)β, deg97.082(15)78.435(2)γ, deg9085.067(2)9662(13)5773.2(15)

4

2

1.519

1.620

Formula

V, Å

3

Z
-3

Dcalc, g cm

130

Abs coeff, mm-1

3.213

5.270

F(000)

4456

2744

Radiation; λ, Å

Mo KD, 0.71073

Mo KD, 0.71073

Temp, K

123(2)

123(2)

Reflections

58187

30206

Independent

24011

22790

Data/restraints/parameters

19652/9/1116

19890/99/1368

Rint

0.02400.0287R1 [I > 2σ(I)]0.0341

0.0612wR2 (all data)

0.0921

0. 1975

GOF

1.016

1.033

DMF/ether

DMF/ethersolv.
for crystallization

CCDC-1894304 (3) and 1894305 (4) contain the supplementary crystallographic data. The data canbe obtained free of charge

from the Cambridge Crystallographic Data

Centre via

www.ccdc.cam.ac.uk/data_request/cif
Table S4. Crystal data for complexes Cu4LBr4 and Cu2L2·DMF.
CompoundFormulaCu4LBr4

Cu2L2·DMF

C43H42N2P2Br4Cu4

C88H84Cu2F6N4O6P4S2·[(CH3)2NC
HO+2CH3CH2OCH2CH3]

Molecular weight1222.57

1906.94

Crystal system

Monoclinic

Monoclinic

Space group

P21/c

P21/c

Color

yellow

brown

Habit

block

block

Crystal dimens, mm

0.38×0.25×0.06

0.194×0.118×0.071

a, Å

9.3808(6)13.0789(17)b, Å25.6046(17)20.410(3)c, Å18.5364(12)34.694(5)α, deg90

90

β, deg97.090(1)92.526(2)γ, deg

90

90

131

V, Å34418.2(5)9252(2)

Z

2

4

1.838

1.369

Abs coeff, mm

5.622

0.645

F(000)

2400

3980

Radiation; λ, Å

Mo KD, 0.71073

Mo KD, 0.71073

Temp, K

123(2)

123(2)

Reflections

23849

48648

Independent

9337

18706

Data/restraints/parameters9337/6/502

18706/0/1162

Rint

0.11180.0573R1 [I > 2σ(I)]0.05560.0444wR2 (all data)

0.16740.1242

GOF

1.022

1.021

DMF/ether

DMF/ether

Dcalc, g cm-3
-1

solv.
for crystallization

CCDC-1920385 (Cu4LBr4) and 1920383 (Cu2L2·DMF) contain the supplementary crystallographic
data. The data can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif
Table S5. Crystal data for complexes Ag2L2 and Cu5L2Br3·2DMF.
CompoundAg2L2

Cu5L2Br3·2DMF

C88H84Ag2F6N4O6P4S2·

C88H84Br3Cu2F6N4O6P4S2(CH3)2NCHO·2(CH3)2NCHO

Molecular weight

1884.422299.21

Crystal system

Monoclinic

Monoclinic

Space group

P21/c

P21/c

Color

brown

yellow

Habit

block

plate

Crystal dimens, mm

0.234×0.202×0.056

0.160×0.160×0.073

a, Å

14.6842(8)29.878(2)b, Å

28.1889(16)13.1902(10)c, Å

21.6554(12)28.148(2)α, deg90

90

Formula132

β, deg

106.563(1)117.060(1)γ, deg

90

90

V, Å3

8591.9(8)9878.7(12)44Dcalc, g cm

1.457

1.546

Abs coeff, mm-1

0.650

2.447

F(000)

3872

4656

Radiation; λ, Å

Mo KD, 0.71073

Mo KD, 0.71073

Temp, K

123(2)

123(2)

Reflections

45485

51294

Independent

17532

20103

Data/restraints/parameters

17532/360/1142

20103/0/1169

Rint

0.02820.0393R1 [I > 2σ(I)]0.04410.0795wR2 (all data)

0.12330.2276

GOF

1.025

1.093

DMF/ether

DMF/ether

Z
-3

solv.
for crystallization
CCDC-1920382(Ag2L2)

and

1920384(Cu5L2Br3·2DMF)

containthesupplementary

crystallographic data. The data can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif

133

References[1].

S. Fuku-en, J. Yamamoto, M. Minoura, S. Kojima, Y. Yamamoto, Inorg. Chem. 2013, 52,
11700-11702.

[2].

S. Fuku-en, J. Yamamoto, S. Kojima, Y. Yamamoto, Chem. Lett. 2014, 43, 468-470.

[3].

M. Nonnenmacher, D. Kunz, F. Rominger, T. Oser, Chem. Commun. 2006, 1378-1380.

[4].

O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Puschmann. J. Appl. Cryst.
2009, 42, 339-341.

[5].

G. M. Sheldrick. Acta Cryst. A 2015, 71, 3-8.

[6].

G. M. Sheldrick. Acta Cryst. C 2015, 71, 3-8.

[7].

Persistence of Vision Raytracer (ver. 3.7.0); Persistence of Vision Pty. Ltd., 2016; Retrieved
from http://www.povray.org/download/134

Publications

Publications(1) Luminescent Di- and Tetranuclear Gold Complexes of Bis(diphenylphosphinyl)functionalized Dipyrido-annulated N-heterocyclic Carbene
S. Zhang, R. Shang, M. Nakamoto, Y. Yamamoto, Y. Adachi and J. Ohshita
Inorganic Chemistry 2019, 58(9), 6328–6335.

(2) Bis(diphenylphosphinyl)-functionalized

Dipyrido-annulated

N-heterocyclic

Carbene towards Silver(I) and Copper(I)S. Zhang, R. Shang, M. Nakamoto, Y. Yamamoto, Y. Adachi and J. Ohshita
Dalton Transactions 2019, accepted.

Acknowledgements

The studies described in this dissertation have been carried out under the direction of Prof.
Yohsuke Yamamoto and Assist. Prof. Rong Shang at the Department of Chemistry, Graduate Schoolof Science, Hiroshima University.
The author sincerely wishes to express his appreciation to Prof. Yohsuke Yamamoto for his
continuing guidance, valuable discussions and encouragement throughout the course of studies.
Grateful acknowledgment is made to Associate Prof. Masaaki Nakamoto and Assist. Prof. Dr. Rong
Shang for their helpful discussions and suggestions.
The author is grateful to Prof. Joji Ohshita (Hiroshima University) and Assist. Prof. Yohei
Adachi (Hiroshima University) for their helpful discussions and valuable suggestions.
The author appreciates the kindly help and professional guidance from Prof. Tsutomu
Mizuta and Prof. Manabu Abe.
The author also thanks all the members of Prof. Yamamoto’s group, past and present, whohave provided author great help, not only in research but also in life, in the last three and half years at
Hiroshima University.
The author also would like to express appreciations to some of the staff at Hiroshima
University. Without their help, the author can not carry out his research such smoothly. In particular,
thanks to the NMR staff, Fujikata san, the X-ray staff, Kawata san, and the MS staff, Amimoto san,for their kindly and professional help.

July, 2019
Sihan Zhang

Department of Chemistry, Graduate School of Science
Hiroshima University