Metal-Metal Bonds Using
Redox-Active Ligands
2021. 6. 3
Literature Seminar #2
M1 Yuri Katayama
1

Contents
1. Introduction
2. Catalysis of [NDI]Ni2 complexes
I. Hydrosilylation
II. Alkyne cyclotrimerization
III. Carbene and vinylidene transfer
IV. C(sp2)-H amination
3. Summary
2

Metal—metal bond in biology• redox transformations• Ni-Fe hydrogenase

Powers, I. G. and Uyeda, C., ACS Catal. 2017, 7, 936.
3

Group 10 dinuclear complexes
Ni, Pd, Pt : M(I)-M(I), M(III)-M(III) dimer
2010 Agapie
Ni(I)-Ni(I) dimer

2009 RitterPd(III)-Pd(III) intermediates

Agapie, T. et al., J. Am. Chem. Soc. 2010, 132, 6296.
Ritter, T et al., Nat. Chem. 2009, 1, 132.
4Uyeda, C. et al., Synlett 2016, 27, 814.

Group 10 dinuclear complexes2+MeN
MeNC

Ni

P

CNMe

Ni

P PP

­2e2e-P

P
MeNC

MeNC

Ni
P

Ni
C
NP
Me

Ni(dppm)2

Kubiak, C. P. et al., J. Am. Chem. Soc. 1987, 109, 754.

Agapie, T. et al., Chem. Commun. 2014, 50, 4427.

There are few examples of Ni(I)-Ni(I) complexes which are redox active.
Most dinuclear Ni2 complexes … nonredox-active, strong field ligands
5Christopher Uyeda• Associate Professor at Department of Chemistry,Purdue University, US• Research theme : Catalysis at metal-metal bonds• Dinuclear nickel complexes using redox-active ligands• The Uyeda group :https://www.chem.purdue.edu/uyeda/index.html
6Redox-active ligands
One example of redox-active ligands
act as electron reservoirs in redox processes

from mononuclear complexes
to dinuclear complexes

NDI = naphthyridine diimine
Luca, O. R. et al., New J. Chem., 2012, 36, 1149.
Uyeda, C. et al., Inorg. Chem. 2014, 53, 11770.

7

Ni2 complexes using NDI ligand

NDI : redox-active ligands→ redox flexibility[iPrNDI]Ni2(C6H6)・HOMO : ligand-centered π orbital
・LUMO : Ni-Ni σ* orbital
・NDI2- & Ni(I)-Ni(I)Uyeda, C. et al., Inorg. Chem. 2014, 53, 11770.
Uyeda, C. et al., Synlett 2016, 27, 814.

8

Five oxidation states[iPrNDI]Ni2(C6H6)
2

1 e- reduction

2 e- oxidation
1 eoxidation

1 ereduction

1 eoxidation

Uyeda, C. et al., Inorg. Chem. 2014, 53, 11770.

9

MO diagrams
morereduced

3 : metalloradical character5 : ligand radical character

Uyeda, C. et al., Inorg. Chem. 2014, 53, 11770.

10

Contents
1. Introduction
2. Catalysis of [NDI]Ni2 complexes
I. Hydrosilylation
II. Alkyne cyclotrimerization
III. Carbene and vinylidene transfer
IV. C(sp2)-H amination
3. Summary
11

Redox process in transition-metal
Prototypical two-electron redox processes in transition-metal catalysis

Mn+2

LX

2
oxidative
couplingXMnLY

oxidativeaddition

Mn+2

LY

Dinuclear reactions coupled to ligand-centered redox activity
m+2 LMn

LMn

2oxidativecouplingm L

Mn

LMn

XYoxidativeaddition

m+2 LMn

XLMn

YMetal-centered redox - two-electron oxidative additioncleavage of M-M bond (σ-bond) formation of M-M bond (σ-bond)
X

Y

Mn

X

Mn+1

Mn

Mn

Y

Mn+1

Mn

X

YX

Mn+1

Y

Mn+1

Two-electron oxidative addition
at metal-metal bonds

change in bond order (π/δ-bond)
Mn
Mn

X

Y

X

Mn+1

Y

Mn+1

Powers, I. G. and Uyeda, C., ACS Catal. 2017, 7, 936.
Uyeda, C. et al., Synlett 2016, 27, 814.
12

Two type reactions

oxidative addition… hydrosilylation,reactions involving carbenes,
vinylidenes, and C-C bondactivationoxidative crosscoupling… alkyne
cyclotrimerization,
Pauson-Khand reaction
Powers, I. G. and Uyeda, C., ACS Catal. 2017, 7, 936.13

Catalysis at an intact M-M bond
explored

Stoichiometric redox
reactions,Precatalysts ortransient intermediates

unexplored

Challenges for catalysis
・Instability of metal-metal bondtoward redox processes
however, …
・Lack of redox flexibility

2010. Agapiemononuclear complexes
under turnover conditions

2005. BarderSuzuki-Miyaura coupling

6 : Pd(I)-Pd(I)as precatalysts

Agapie, T. et al., J. Am. Chem. Soc. 2010, 132, 6Barder, T. E. J. Am. Chem. Soc. 2005, 128, 898.
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First M-M catalysis
Catalytic hydrosilylation reaction
reversible

R2SiH2
H-Si-H activation• Back-donation from the Ni-Ni dxy-dxy π
orbital into the LUMO of the silane• Charge transfer from the reduced NDI
ligand π system affords a sufficiently
electron-rich Ni(I)-Ni(I) bond.

LUMO

HOMO

Steiman, T. J. and Uyeda, C. J. Am. Chem. Soc. 2015, 137, 6104.
Powers, I. G. and Uyeda, C., ACS Catal. 2017, 7, 936.

five-center four-electroninteraction

Ni-Ni
dxy-dxy π orbital
15

Contents
1. Introduction
2. Catalysis of [NDI]Ni2 complexes
I. Hydrosilylation
II. Alkyne cyclotrimerization
III. Carbene and vinylidene transfer
IV. C(sp2)-H amination
3. Summary
16

Alkyne cyclotrimerization

A comparison of catalyst reactivity*5 = Ni(COD)2
ü Rapid and selective cyclotrimerization
ü Major 1, 2, 4- trisubstituted arenes
17Pal, S. and Uyeda, C. J. Am. Chem. Soc. 2015, 137, 8042.

Stoichiometric reactivity studies[4+2] cycloadditiontransition structure

HOMO-1the metallacycle intermediate

Regioselectivity• Head-to-tail coupling (12) because of steric hindrance of iPr• 𝜂 2 interaction : the second Ni & one double bond of diene→ Asymmetry results in a steric preference (C1-C6)
18

Pal, S. and Uyeda, C. J. Am. Chem. Soc. 2015, 137, 8042.

Other cyclotrimerization
Co2(CO)8 catalyzed cyclotrimerization

71 : dicobaltacyclopentadiene intermediate
𝜂 4 interaction : the second Co & dienyl π system↔ 𝜂 2 interaction : the second Ni & one double bond of diene (Uyeda’s complex)→ Higher regioselectivity
Powers, I. G. and Uyeda, C., ACS Catal. 2017, 7, 936.

19

Spin crossover mechanism
DFT calculations considering multiple spin states revealed another mechanism –a spin crossover mechanism.
・Regioselectivity
・Cyclotrimerization vs cyclotetramerization selectivity

Uyeda, C. and Ess, D. H. et al., ACS Catal. 2017, 7, 4796.

20

Ligand coordination① Ligand coordination
1→ 2/3 spin-state intersystem crossing

1

Uyeda, C. and Ess, D. H. et al., ACS Catal. 2017, 7, 4796.

21

Metallacyclopentadiene② Formation of metallacyclopentadiene
Bimetallacyclohexadiene
Stepwise zwitterionic and diradical pathway → unfavored intermediate → unstable

One-step oxidative coupling← observed instoichiometric reactionin the previous study

triplettriplettripletUyeda, C. and Ess, D. H. et al., ACS Catal. 2017, 7, 4796.

22

Reaction with the third alkyne③ Metallacyclopentadiene intermediates + alkynes
3 proposed mechanisms

6.3 kcal/mol higher
Uyeda, C. and Ess, D. H. et al., ACS Catal. 2017, 7, 4796.

23

Other cyclotrimerization
Tsai reported

Key intermediates
65 : [2+2+] cycloaddition
66 : [2+2+2] cycloaddition
dimetallacyclopentadiene• Dinuclear molybdenum complexes
Mashima, K. et al., Dalton Trans. 2016, 45, 17072.
Tsai, Y. C. et al., Angew. Chem., Int, Ed. 2012, 51, 10342.
• 1, 3, 5-trisubstituted arene• Different cycloheptatriene intermediates
24

Outline of the cyclotrimerization

Uyeda, C. and Ess, D. H. et al., ACS Catal. 2017, 7, 4796.

25

Cyclotrimerization selectivity
cyclotrimerization vs cyclotetramerization selectivity

TS2trans

TS2cisb) Mononuclear Ni complexes favors TS of trans.
→ Migratory insertion instead of reductive elimination
occurs to form to metallacyclononatetraene.
This dinickel complex favors TS ofcis (4→5).
Reductive elimination is morefavorable than migratory insertion(5→1).
→ cyclotrimerization selectivity
26

Uyeda, C. and Ess, D. H. et al., ACS Catal. 2017, 7, 4796.

Mononuclear Ni-cyclotetramerization
Reppe reported• Mononuclear Ni-catalyzed cyclotetramerization• Favorable trans metallacycloheptatriene intermediates• Another migratory insertion → metallacyclononatetraene
Straub, B. F. et al., Chem. Eur. J. 2004, 10, 3081.

27

Regioselectivity
regioselectivity controlled by TS1 and TS2
Oxidative CC coupling

Migratory insertion

Lower by 1-3 kcal/mol

Uyeda, C. and Ess, D. H. et al., ACS Catal. 2017, 7, 4796.

1, 2, 4-isomer
major products

1, 3, 5-isomerminor products
28

Short summary• A unique spin crossover mechanism
nonclassical bridging metallacyclopentadiene andmetallacycloheptatriene intermediates• Cyclotrimerization selectivitythe metallacycloheptatriene of cis configuration• Regioselectivity
Oxidative C-C coupling TS& migratory insertion TS to the metallacycloheptatrieneintermediate29

Contents
1. Introduction
2. Catalysis of [NDI]Ni2 complexes
I. Hydrosilylation
II. Alkyne cyclotrimerization
III. Carbene and vinylidene transfer
IV. C(sp2)-H amination
3. Summary30

Cyclopropanation
Alkene + Carbene → Cyclopropane

reductive carbene transfer(a) Diazoalkane : requirement of EWG
substituents
Zhou, Y. and Uyeda, C. Angew. Chem. Int. Ed. 2016, 55, 3→ diazoacetates …
(b) Low generality(c) This work : reductive carbene transformations
from CH2Cl2, [M] = [iPrNDI]Ni2(C6H6)
31

Vinylidene transfer
Vinylidene transfer
vs Fritsch-Buttenburg-Wiechell
rearrangements

Reductive vinylidene transfer

ü No FBW rearrangement
ü No vinylidene transfer wasobserved using mononickel
complexes bearing related Ndonor ligands.

Uyeda, C. et al., J. Am. Chem. Soc. 2017, 139, 11686.

32

Mechanism and dinuclear effects

・Reversible reduction of 4 are exploited
to close the catalytic cycle by using Zn asa reductant.

・47 : 𝜂 2 – coordination of the alkenyl system
to the second Ni→ 𝛽-hydrogen constrained, no FBWrearrangement

Uyeda, C. et al., J. Am. Chem. Soc. 2017, 139, 11686.

33

Catalytic [4+1]-cycloaddition• A : 1, 3-dienes + vinylidene from
1,1-dichloroalkenes [4+1]cycloaddition
this work• B : Challenging synthesis of fivemembered rings (background)• C : dinickel catalysts L4 with bulky
NDI ligands afforded the productsin the highest yield.

Zhou, Y. Y. and Uyeda, C., Science 2019, 363, 857.

34

Mechanism analysis• B : Chiral dinickel catalysts (S, S)-L10
high diastereoselectivity• A : A direct [4+1] cycloaddition ora tandem [2+1] cycloaddition followed by
1, 3-rearrangement

Zhou, Y. Y. and Uyeda, C., Science 2019, 363, 857.

35

Mechanism and dinuclear effects• Proposed mechanism
Ni2 cooperatively stabilize
π systems in the diene
and vinylidene

Zhou, Y. Y. and Uyeda, C., Science 2019, 363, 857.

36

Contents
1. Introduction
2. Catalysis of [NDI]Ni2 complexes
I. Hydrosilylation
II. Alkyne cyclotrimerization
III. Carbene and vinylidene transferIV. C(sp2)-H amination
3. Summary37

C (sp2) – H amination

Electrocyclization / 1, 2-shift
Driver, T. G. et al., J. Org. Chem. 2009, 74, 6442.
Uyeda, C. et al., Chem. Eur. J. 2017, 23, 7694.

38

C (sp2) – H amination

C-H bond activated by addition of an exogenous ligand→ C-N reductive elimination
Uyeda, C. et al., Chem. Eur. J. 2017, 23, 7694.39

Oxidation states of imido complexes
oxidized

Ni-centered radicaloxidized

formed by H abstraction

Oxidized (NDI)Ni2complexes may serve as
more viable platforms forcatalytic C-H amination.

Uyeda, C. et al., Organometallics 2020, 39, 3794.

40

Catalytic C-H amination reactions• 8 → 1 via H atom abstraction by
amides to generate free aniline 10• 5 : Generation of (NDI)Ni2Br2 bydisproportionation is a limiting
factor.
• 4 : halide-free cationic imido
complex→ highest yield

Uyeda, C. et al., Organometallics 2020, 39, 3794.

41

Mechanism analysis
Kinetic isotope effectElectrocyclization or 1, 2-addition• KIE → C-H cleavage is slow.
• Inaccessibility of an electrocyclization
mechanism• A – The ester blocks the position ofC(sp2)-H activation• B – E / Z difference of C-H bondorientations
Uyeda, C. et al., Organometallics 2020, 39, 3794.

42

DFT models

Uyeda, C. et al., Organometallics 2020, 39, 3794.

43C (sp2) – H bond chemoselectivity

Catalytic cycle
Ni2(μ-NAr) 4
Ni-Ni bond cleavage
C-N
reductive
amination

4B
1, 2-addition
metalacyclic intermediates

High selective nitrene insertions into
olefinic C-H bonds

Uyeda, C. et al., Organometallics 2020, 39, 3794.

44

Contents
1. Introduction
2. Catalysis of [NDI]Ni2 complexes
I. Hydrosilylation
II. Alkyne cyclotrimerization
III. Carbene and vinylidene transfer
IV. C(sp2)-H amination
3. Summary
45

Summary• NDI ligands supports coordinately unsaturated Ni-Nibonds across a broad range of formal oxidation states.
• Ligand-centered redox activity enables various
catalytic transformations.
• The electronic properties of M-M bonds are exploitedfor controlling regioselectivity.

46