# Cis-Chelating Diphosphanes for Intracavity Nickel(II)-Catalyzed Ethylene Oligomerization

Yang Li, Sara Figueirêdo de Alcântara Morais, Mingyang Han, Tuan-anh Phan, Geordie Creste, Matthieu Jouffroy, Dominique Matt, Jean-pierre Djukic, Yann Cornaton, Pierre Braunstein, et al.

<figure><img src="image_1.png" /></figure>

► To cite this version:

Yang Li, Sara Figueirêdo de Alcântara Morais, Mingyang Han, Tuan-anh Phan, Geordie Creste, et al., Cis-Chelating Diphosphanes for Intracavity Nickel(II)-Catalyzed Ethylene Oligomerization. Chemistry - A European Journal, 2025, 31 (34), pp.e202501188. 10.1002/chem.202501188. hal-05118365

HAL Id: hal-05118365

https://hal.science/hal-05118365v1

Submitted on 25 Nov 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>
<figure><img src="image_3.png" /></figure>

# Cis-Chelating Diphosphanes for Intracavity Nickel(II)-Catalyzed Ethylene Oligomerization

Yang Li,[a] Sara Figueirêdo de Alcântara Morais,[b] Mingyang Han,[a] Tuan-Anh Phan,[a] Geordie Creste,[a] Matthieu Jouffroy,[c] Dominique Matt,[c] Jean-Pierre Djukic,[b] Yann Cornaton,[b] Pierre Braunstein,[a] Katrin Pelzer,[*a] and Dominique Armspach*[a]

*Dedicated to the memory of Sir Fraser Stoddart*

Four cis-chelating diphosphanes derived from cyclodextrins (CDs), each featuring a distinct intracavity environment, compel NiII or PdII metal centers to reside within α- or β-CD cavities. Nickel(II) complexes of these metal-confining ligands act as active catalysts in ethylene oligomerization upon activation with modified methylaluminoxane (MMAO). The size of the cavity and the position of the P₂Ni fragment relative to the cavity affect both the activity and selectivity of the reaction. In all

instances, 1-butene is the major product (up to 98% C4 products and 90% 1-butene within the C₄ fraction). Extensive theoretical studies with state-of-the-art methods carried out on the most selective system suggest that the CD cavity restricts isomerization pathways by limiting the mobility of the coordinated olefin in this constrained supramolecular environment, thereby enhancing α-olefin formation.

## 1. Introduction

Performing metal-catalyzed reactions in confined spaces, whether in solids[1] or in molecular systems[2] is increasingly attractive because of the possibility of achieving unusual and high selectivities with minimal catalyst deactivation.[3] It is widely accepted that confining a catalytic center within a restricted or enclosed space can provide more effective steric control over a catalytic reaction than simply grafting flexible, bulky entities onto the main ligand(s). However, substrate acces-

sibility to the catalytically active site remains a prerequisite for catalytic activity. Nickel-catalyzed ethylene oligomerization/polymerization is a perfect example of an industrial reaction in which steric hindrance around the catalytic center can significantly influence catalyst properties (chain length selectivity, double bond regioselectivity, branching, activity, and stability).[1a,4] In particular, introducing steric bulk in the axial positions of nickel complexes incorporating dimines[5] and other chelating ligands[6] disfavors chain transfer and termination reactions[7] and strongly influences chain walking mechanisms, which are responsible for branching and alkene isomerization reactions.[8] Steric bulk can be positioned above and/or below the metal chelate plane, typically using semi-rigid substituents containing aromatic units. To date, only one example of a macrocyclic ligand has been reported to achieve this feature, but in none of the corresponding complexes is the metal center fully encapsulated.[4c,9] Although diphosphane ligands equipped with bulky substituents are not as commonly used for ethylene oligomerization/polymerization[10] as the ubiquitous diimines, they have recently been shown to exhibit similar catalytic behavior in the case of their palladium complexes.[11]

Cavity-shaped ligands based on cyclodextrins (CDs) displaying metal-confining ability have demonstrated great potential in highly selective catalytic processes; however, their capacity to catalyze selective ethylene oligomerization/polymerization remains largely unexplored.[12] Very recently, a cis-chelating P*N* ligand derived from a permethylated α-CD was found to induce very high selectivity in nickel-catalyzed ethylene dimerization yielding up to 91% 1-butene.[13] This remarkable result motivated us to explore other CD-based metal-confining bidentate ligands for this reaction.

<footnote>[a] Dr. Y. Li, Dr. M. Han, Dr. T.-A. Phan, G. Creste, Dr. P. Braunstein, Dr. K. Pelzer, Prof. D. Armspach
Équipe Confinement Moléculaire et Catalyse, Institut de Chimie de Strasbourg, UMR 7177 CNRS, Université de Strasbourg, 4, rue Blaise Pascal, CS90032, 67081 Strasbourg cedex, France
E-mail: kpelzer@unistra.fr
d.armspach@unistra.fr</footnote>

<footnote>[b] Dr. S. Figueirêdo de Alcântara Morais, Dr. J.-P. Djukic, Dr. Y. Cornaton
Laboratoire de Chimie et Systémique Organo-Métalliques, Institut de Chimie de Strasbourg, UMR 7177 CNRS, Université de Strasbourg, 4, rue Blaise Pascal, CS90032, 67081 Strasbourg cedex, France</footnote>

<footnote>[c] Dr. M. Jouffroy, Dr. D. Matt
Laboratoire de Chimie Inorganique Moléculaire et Catalyse, Institut de Chimie de Strasbourg, UMR 7177 CNRS, Université de Strasbourg, 4, rue Blaise Pascal, CS90032, 67081 Strasbourg cedex, France</footnote>

<footnote>Supporting information for this article is available on the WWW under https://doi.org/10.1002/chem.202501188</footnote>

<footnote>© 2025 The Author(s). Chemistry – A European Journal published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.</footnote>
<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>[NiBr₂(DPPE)]</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>[NiBr₂(L⁵)]</figcaption></figure>

We report here the use of four cavity-shaped *cis*-chelating diphosphanes (*L*¹-*L*⁴), each with a unique inner space capable of encapsulating via chelation catalytically relevant NiII and PdII metal centers. Some of the resulting complexes ([NiBr₂(*L*¹-*L*³)], [NiCl₂(*L*⁴)], 6a,b and 7a,b), along with cavity-free analogs [NiBr₂(DPPE)] (DPPE = 1,2-bis(diphenylphosphano)ethane) and [NiBr₂(*L*⁵)], were tested in ethylene oligomerization to evaluate the influence of the cavity on the catalytic outcome.

## 2. Results and Discussion

### 2.1. Synthesis and coordination properties

Nickel complexes [NiBr₂(L¹)] and [NiBr₂(L³)] (Scheme 1) were synthesized in 68% and 86% yield, respectively from [NiBr₂(DME)] (DME = 1,2-dimethoxyethane) and the previously reported α-CD-based diphosphanes L¹ and L³, which were themselves obtained from dimesylate 1.[14] Complexes [NiBr₂(L²)] and [NiCl₂(L⁴)], featuring a larger β-CD cavity were not obtained from the pure ligands L² and L⁴, but from their crude mixtures. In the case of ligand L², reacting dimesylate 2 with bis(phosphide) 4 – formed via a Smiles-like rearrangement of diphosphane 3 upon treatment with excess n-BuLi in THF (Scheme 2)[14,15] – yielded a mixture of three diastereomeric diphosphanes[15] with the desired *cis*-chelating bidentate ligand L² being the major product. Heating this mixture in mesitylene increased the proportion of L², and subsequent treatment with [NiBr₂(DME)] enabled the desired chelate complex [NiBr₂(L²)] to be separated from non-chelate complexes by column chromatography. As with complexes [NiBr₂(L¹)] and [NiBr₂(L³)] partial halide metathesis occurred during chromatographic purification, leading to a mixture of bromido and chlorido complexes. Treating this mixture with excess LiBr in MeOH quantitatively yielded the pure dibromido complex [NiBr₂(L²)] in 31% yield starting from dimesylate 2.

Ligand L⁴ was synthesized by reacting dimesylate 2 with monophosphide 5, which was obtained by treating diphosphane 3 with excess LDA (LDA = lithium diisopropylamide) (Scheme 2).[14] Under these conditions, the previously observed Smiles-like rearrangement did not occur. In stark contrast to the α-CD analog L³, pure ligand L⁴ could not be isolated, as the P-bridging reaction in this case was not 100% stereoselective. Instead, an inseparable mixture of L⁴ and its diastereomer (Figure S1) was obtained in an approximate 2:1 ratio. To prevent halide exchange during chromatographic purification, the chlorido complex was synthesized instead of its bromido analog by reacting the mixture of diasteromers containing L⁴ with

<figure><img src="image_7.png" /><figcaption>1, α, n = 1</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>2, β, n = 2</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Scheme 1. Synthesis of diphosphanes L¹-L⁴ and d⁸ complexes [NiBr₂(L¹-L³)], [NiCl₂(L⁴)] and [PdCl₂(L¹-L⁴)] i) 4 (1.5 equiv.), THF, 25 °C, 8 h, then mesitylene, 160 °C, 4 h; ii) 5 (1.2 equiv.), THF, 12 h; iii) [NiBr₂(DME)] or [NiCl₂(DME)] (1 equiv.), CH₂Cl₂, 25 °C; iv) [PdCl₂(COD)], (1 equiv.), CH₂Cl₂, 25 °C.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Scheme 2. Reactivity of phosphane 3 in the presence of excess n-BuLi or LDA.</figcaption></figure>

[NiCl₂(DME)] (Scheme 1). The desired complex [NiCl₂(L⁴)] was stable enough to be purified via column chromatography, yielding 16% starting from dimesylate 2.

The PdCl₂ complexes [PdCl₂(L¹-L⁴)] were also synthesized by reaction of [PdCl₂(COD)] (COD = cyclooctadiene) with their respective ligands, whether pure or not (Scheme 1). As observed for their nickel and cavity-shaped P'N counterparts,[13] only *cis*-complexes with a 1:1 metal/CD ligand ratio were formed, even in the presence of excess ligand. Encapsulation of the MX₂ units in the square planar complexes [NiBr₂(L¹)], [NiBr₂(L²)], [PdCl₂(L¹)], and [PdCl₂(L³)] was confirmed by X-ray diffraction analysis (Figure 1).[16] In each case, the MX₂ unit is directed toward the
<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /><figcaption>**Figure 1.** Molecular structures of complexes [NiBr₂(L¹)], [NiBr₂(L²)], [PdCl₂(L¹)], and [PdCl₂(L³)] featuring an encapsulated MX₂ unit. Solvent molecules are omitted for clarity; C: fawn, O: red; P: orange, Cl: light green, Br: dark red, Ni: dark green, Pd: cyan.</figcaption></figure>

cavity interior. In complex [PdCl₂(L³)], the PdCl₂ moiety is nearly
perpendicular to the mean O(4) plane of the CD with α angles
between the P₂MX₂ unit and the O(4) plane of 86.5° and 86.1°
for the two CD complexes present in the unit cell. In contrast,
the MX₂ units in complexes [NiBr₂(L¹)], [NiBr₂(L²)], and [PdCl₂(L¹)]
tend to lie more parallel to the corresponding O(4) plane (α =
17.3° in [NiBr₂(L¹)]; 24.8° and 32.5° in the two complexes present
in the unit cell of [NiBr₂(L²)] and 24.3° in [PdCl₂(L¹)]). The rela-
tively small α angle of 17.3° in the complex [NiBr₂(L¹)] is best
explained by the presence of the small α-CD cavity, unsuited to
accommodate the large NiBr₂ unit, whereas the smaller PdCl₂
unit fits better within the α-CD cavity of complex [PdCl₂(L¹)].
The two M-P bonds have approximately the same length
in complexes [NiBr₂(L¹)], [NiBr₂(L²)], and [PdCl₂(L¹)]. The same
trend is observed for M-X bonds with the bond closer to the
CD inner wall always being shorter than the other. This effect
is particularly pronounced in the more constrained complex
[NiBr₂(L¹)] (2.3098(5) Å and 2.3291(5) Å, respectively). Surprisingly,
in complex [PdCl₂(L³)], both Pd-Cl and Pd-P bond lengths are
nearly identical, even though, contrary to complexes [NiBr₂(L¹)],
[NiBr₂(L²)], and [PdCl₂(L¹)], the two phosphorus atoms are not
electronically equivalent. Additionally, the two cis-positioned
chlorido ligands are located in very different steric environments
in [PdCl₂(L³)], a rare feature in cavity-shaped complexes.[17] In
all the aforementioned complexes, the CD unit retains an
undistorted circular shape, with all glucose units adopting the
standard ⁴C₁ conformation.

The solution behavior of complexes [NiBr₂(L¹)], [NiBr₂(L²)], [PdCl₂(L¹)], and [PdCl₂(L³)] aligns with their solid-state struc- tural features. Close examination of the ¹H NMR spectra of [NiBr₂(L³)], [NiCl₂(L⁴)], [PdCl₂(L³)], and [PdCl₂(L⁴)] revealed a sig- nificant downfield shift of the H-5 proton in the bridged unit A upon metal complexation (δ ranging from 5.21 to 5.34 ppm, compared to 4.21 ppm for ligand L³). This shift is character- istic of the presence of an M-X bond inside the CD cavity and is further supported by the short distance between the H- 5 proton of the bridged glucose unit A and the encapsulated chloride in the molecular structure of complex [PdCl₂(L³)] (2.74 and 2.84 Å).[¹⁸] Similar but less pronounced downfield shifts of other H-5 protons (Δδ ~0.5 ppm) were observed for complexes [NiBr₂(L¹)], [PdCl₂(L¹)], [NiBr₂(L²)], and [PdCl₂(L²)] indicating a shal- lower metal inclusion. This observation is consistent with the molecular structures of [NiBr₂(L¹)], [NiBr₂(L²)], and [PdCl₂(L¹)].

<figure><img src="image_13.png" /></figure>

To obtain palladium complexes capable of function-
ing as precatalysts for ethylene oligomerization, the
[PdCl(Me)(diphosphane)] complexes 6 and 7 were synthesized
by reaction of [PdCl(Me)(COD)] with diphosphanes L³ and L¹,
respectively in THF. Each reaction yielded an inseparable mixture
of isomeric complexes, 6a,b and 7a,b, differing in the position of
the Pd-Cl bond. For comparison, the Pd complex [PdCl(Me)(L⁶)]
derived from a previously reported P^N cavity-shaped ligand
(L⁶), was also prepared.[13]

Careful analysis of the ¹H and ³¹P{¹H} NMR spectra (C₆D₆) of the 6a,b mixture clearly confirmed the presence of two isomers. The ³¹P{¹H} NMR spectrum displays two distinct AB patterns, each corresponding to one isomer. In 6a, the two doublets of the AB pattern are closely spaced (δ₃₁p = 41.0 and 41.7 ppm, with 3 + 2Jp,p = 23.6 Hz), whereas in 6b, they are significantly farther
<figure><img src="image_14.png" /></figure>

<table><caption>**Table 1.** Isomeric ratios of 6a to 6b and 7a to 7b resulting from the metal complexation of cavity-shaped diphosphanes 1 and 2 with [PdClMe(COD)] at different reaction conditions.</caption><thead><tr><th>Solvent, temperature</th><th>6a:6b</th><th>7a:7b</th></tr></thead><tbody><tr><td>THF, 25 °C</td><td>23:77</td><td>60:40</td></tr><tr><td>THF, -78 °C</td><td>23:77</td><td>60:40</td></tr><tr><td>CH<sub>2</sub>Cl<sub>2</sub>, 25 °C</td><td>68:32</td><td>47:53</td></tr><tr><td>CH<sub>2</sub>Cl<sub>2</sub>, -78 °C</td><td>80:20</td><td>42:58</td></tr></tbody></table>

apart (δ<sub>31P</sub> = 29.1 and 57.1 ppm, with 3 + 2J<sub>P,P</sub> = 25.7 Hz). An HMQC (¹H–³¹P) experiment (Figure S92) enabled the assignment of the more basic bridging phosphorus atom to the more upfield-shifted doublets (41.0 ppm for 6a and 29.1 ppm for 6b). Clearly, the PdMeCl complexes 6a,b adopt a cis-chelate configuration similar to the PdCl<sub>2</sub> analog [PdCl<sub>2</sub>(L<sup>3</sup>)]. However, since the two exogenous ligands (chlorido and methyl) are no longer identical, two distinct isomers can form upon complexation. Each isomer was readily distinguished by 2D ROESY NMR. The ROESY spectrum of the mixture revealed a strong correlation between the Pd-methyl protons of 6a and the inner cavity H-5 protons of several glucose units (Figure S94), confirming their location inside the CD cavity. In contrast, no such correlations were observed for 6b but only between Pd-methyl protons and the H-6 protons, consistent with the methyl group being positioned outside the cavity. Additionally, in the ¹H–³¹P HMQC NMR spectrum, the bridging phosphorus atom in 6b exhibits a strong correlation with the trans-disposed palladium-bound methyl protons (Figure S92), whereas the correlation between the same methyl group and the cis-disposed PAr<sub>2</sub>Ar' atom appears significantly weaker. As expected, the opposite trend was observed for 6a, consistent with the methyl group being trans to the PAr<sub>2</sub>Ar' atom and therefore positioned inside the CD cavity. This reflects the larger orbital overlap between the methyl group and the phosphorus atom via the metal d<sub>x<sup>2</sup>-y<sup>2</sup></sub> orbital when the donor atoms are trans-disposed. Indeed, the methyl groups in both 6a and 6b resonate as doublets of doublets (δ<sub>1H</sub> = 1.13 ppm with ³J<sub>PtransH</sub> = 7.3 Hz and ³J<sub>PcisH</sub> = 2.5 Hz for 6a, and δ<sub>1H</sub> = 1.23 ppm ³J<sub>PtransH</sub> = 8.7 Hz and ³J<sub>PcisH</sub> = 3.2 Hz for 6b). In both cases, as expected, the coupling constant is significantly larger for the trans-disposed P(III) and methyl groups.[19] Further evidence supporting the location of the chlorido ligand inside the CD cavity in 6b is the presence of a strongly downfield-shifted H-5 signal (δ<sub>1H</sub> = 5.31 ppm) corresponding to one of the capped glucose units. In contrast, no such downfield shift is observed for 6a (δ<sub>1H</sub> = 4.77 ppm), where the methyl ligand is included in the cavity. The ¹H NMR spectrum recorded in CD<sub>2</sub>Cl<sub>2</sub> revealed a 6a:6b ratio of approximately 23:77 at room temperature (Table 1). Knowing that the reaction temperature could influence this isomeric ratio[20] the complexation was then conducted in the same solvent (THF) at low temperature (–78 °C). However, no change in the isomeric ratio was observed at this temperature. Changing the NMR solvent (CD<sub>2</sub>Cl<sub>2</sub> instead of C<sub>6</sub>D<sub>6</sub>) also did not affect the isomeric ratio. Surprisingly, the 6a:6b ratio varied significantly when the complexation was carried out in different solvents. When CH<sub>2</sub>Cl<sub>2</sub> was used as the reaction solvent instead of THF, 6a was found

to be the major isomer (6a:6b = 68:32, at a reaction temperature of 25 °C), and the 6a:6b ratio even increased slightly when the reaction was conducted at low temperature (6a:6b = 80:20, at –78 °C). Moreover, to determine whether isomers 6a and 6b are in equilibrium, three different reaction mixtures – obtained in CH<sub>2</sub>Cl<sub>2</sub> at either 25 °C or –78 °C and in THF at 25 °C – were analyzed by NMR spectroscopy over an extended period of time at 25 °C. Their ¹H and ³¹P{¹H} NMR spectra recorded in CD<sub>2</sub>Cl<sub>2</sub> remained unchanged over seven days, indicating the absence of any equilibrium, at least at room temperature. Note that this contrasts with the solution behavior previously reported for PdMeCl complexes derived from heterodiphosphanes.[19,21] Clearly, the formation of 6b over 6a is kinetically favored in THF, whereas the opposite is true in CH<sub>2</sub>Cl<sub>2</sub>. Determining which factors – electronic or steric – influence most the isomeric ratio is challenging, given the complexity of the ligand and the small energy differences involved. As for the PdMeCl complexes of L<sup>3</sup>, metal complexation of L<sup>1</sup> with [PdCl(Me)(COD)] in THF produced two different isomers (7a,b) in a 7a:7b ratio of 60:40. In the ³¹P{¹H} NMR spectrum of the mixture, the two phosphorus atoms in each compound resonate as a pair of doublets (δ<sup>31P</sup> = 41.8 and 54.5 ppm with 3 + 2J<sub>P,P</sub> = 25.9 Hz for the major isomer 7a, and δ<sub>31P</sub> = 34.6 and 63.7 ppm with 3 + 2J<sub>P,P</sub> = 26.6 Hz for the minor isomer 7b). Given the complexity of the ¹H NMR spectra of the 7a,b mixture, full assignment for each isomer could not be achieved, and the exact position of the methyl group within the cavity in both isomers could not be determined from NMR studies (see X-ray studies below for the assignment of 7a and 7b).[22] However, the ¹H–³¹P HMQC spectrum (Figure S99), as for 6a,b, shows clearly that the phosphorus atom belonging to one of the bridged units in either 7a or 7b correlates strongly with the trans-disposed palladium-bound methyl protons, whereas the cross-peaks are much less intense for correlations between the same methyl group and the second P(III) atom, which is cis to the methyl group. This methyl group resonates as a doublet of doublets at δ<sub>1H</sub> = 0.39 ppm (³J<sub>PtransH</sub> = 8.3 Hz and ³J<sub>PcisH</sub> = 3.9 Hz) for 7a and 0.47 ppm (³J<sub>PtransH</sub> = 8.5 Hz and ³J<sub>PcisH</sub> = 3.4 Hz) for 7b with in both cases a much larger coupling constant for the mutually trans P(III) and methyl groups compared to the cis ones. As in the case of L<sup>3</sup>, metal complexation was carried out in different solvents and at different temperatures (Table 1). Similar to 6a,b, the same proportion of the two isomers (7a:7b ratio = 60:40) was observed when the reaction was performed in THF at either room or low temperature (–78 °C). In contrast, the ratios were 47:53 and 42:58 at room temperature and –78 °C, respectively, when metal complexation was conducted in CH<sub>2</sub>Cl<sub>2</sub>. A 6:4 mixture of 7a and 7b was monitored by ³¹P and ¹H NMR spectroscopy in CD<sub>2</sub>Cl<sub>2</sub> at 25 °C over an extended period. During the first few days, the proportion of 7a and 7b remained largely unchanged, but after seven days, some decomposition occurred, with the 7a:7b ratio shifting to approximately 2:8. This observation suggests that isomer 7a decomposes faster than 7b. However, a slow equilibrium between the two isomers cannot be entirely ruled out.[19,7b]

Single crystals suitable for X-ray diffraction analysis[16] were obtained by slow diffusion of n-pentane into a solution of 7a,b in CH<sub>2</sub>Cl<sub>2</sub>. Both geometrical isomers, 7a and 7b, are present in the single crystal in a 3:7 ratio, respectively. Only the major
<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /><figcaption>**Figure 2.** Molecular structure of complexes **7a,b** (70% Cl1/C78 (**7b**), 30% Cl1A/C78A (**7a**)). The C78/Cl1A and C78A/Cl1 atoms are located at the same positions. The Pd-Cl1/Pd-C78 and Pd-Cl1A/Pd-C78A distances are therefore averaged. Only the major isomer (**7b**) is depicted. Hydrogen atoms and solvent molecules are omitted for clarity; C: fawn, O: red, P: orange, Cl: light green, Pd: cyan).</figcaption></figure>

isomer (**7b**) is depicted in Figure 2. The single crystals used for X-ray diffraction analysis were redissolved in CD₂Cl₂, and the ¹H and ³¹P NMR spectra were quickly recorded. The same isomeric ratio as in the solid state (3:7) was observed in CD₂Cl₂ solution, allowing for the identification of both isomers in the NMR spectra.[23] X-ray crystal structure analysis of **7a,b** confirmed the chelating behavior of the diphosphane as well as the square planar geometry of the complexes. The angle between the PPPd plane and the CD O(4) atoms plane is 21.76°, a value nearly identical to that observed in [PdCl₂(L¹)]. Therefore, complexes **7a,b** and [PdCl₂(L¹)] experience a very similar steric environment within the CD cavity.

In the case of complex [PdCl(Me)(L⁶)], only one isomer was observed. Because the H-5 proton of unit B is hardly downfield-shifted upon complexation (δH = 4.41 ppm versus 4.31 ppm for the P'N ligand), the chlorido ligand is likely located outside the cavity.

The position of the Pd-methyl fragment inside the CD was inferred from a ROESY experiment. Thus, the PdMe signal of [PdCl(Me)(L⁶)], which resonates as a doublet at 0.78 ppm, gave rise to cross-peaks corresponding to through-space correlations involving all inner cavity H-5 protons (Figure S108). The orientation of the methyl ligand does not result from its affinity for the α-CD inner space but rather from the relative trans influence of the individual ligands present in [PdCl(Me)(L⁶)].[24] Consistent with the experimentally established orienting series (trans-influence order: CH₃⁻ >> PR₃ > Cl⁻ > NR₃), the methyl group can only be cis to phosphorus and inside the CD cavity, whereas the chlorido ligand has to be trans to the phosphorus donor atom and outside the cavity.

## 2.2. Catalysis

All cavity-shaped Ni complexes [NiBr₂(L¹⁻L³)] and [NiCl₂(L⁴)] were tested for their ability to catalyze the oligomerization of ethylene

<table><caption>**Table 2.** Ethylene oligomerization with nickel complexes [NiBr₂(DPPE)], [NiBr₂(L¹⁻L³)], [NiCl₂(L⁴)], [NiBr₂(L⁵)], and [NiBr₂(L⁶)] as precatalysts in the presence of MMAO[ª].</caption><thead><tr><th rowspan="2">Entry</th><th rowspan="2">Precatalyst</th><th rowspan="2">Time</th><th rowspan="2">TOF<sup>[b]</sup></th><th colspan="3">Products weight distribution [%]<sup>[c]</sup></th></tr><tr><th>C<sub>4</sub> [α]<sup>[d]</sup></th><th>C<sub>6</sub> [α]<sup>[e]</sup></th><th>C<sub>8</sub></th></tr></thead><tbody><tr><td>1</td><td>[NiBr<sub>2</sub>(DPPE)]</td><td>35 min</td><td>17 871</td><td>93(20)</td><td>7(8)</td><td>&lt;1</td></tr><tr><td>2</td><td>[NiBr<sub>2</sub>(DPPE)]</td><td>24 h</td><td>8760</td><td>90(6)</td><td>9(2)</td><td>&lt;1</td></tr><tr><td>3</td><td>[NiBr<sub>2</sub>(L<sup>5</sup>)]</td><td>35 min</td><td>80 816</td><td>88(84)</td><td>11(99)</td><td>&lt;1</td></tr><tr><td>4</td><td>[NiBr<sub>2</sub>(L<sup>5</sup>)]</td><td>3 h</td><td>25 141</td><td>87(60)</td><td>12(15)</td><td>&lt;1</td></tr><tr><td>5</td><td>[NiBr<sub>2</sub>(L<sup>1</sup>)]</td><td>35 min</td><td>21 824</td><td>87(72)</td><td>11(59)</td><td>&lt;2</td></tr><tr><td>6</td><td>[NiBr<sub>2</sub>(L<sup>1</sup>)]</td><td>24 h</td><td>2432</td><td>76(66)</td><td>19(56)</td><td>4</td></tr><tr><td>7</td><td>[NiBr<sub>2</sub>(L<sup>2</sup>)]</td><td>35 min</td><td>7405</td><td>89(63)</td><td>10(75)</td><td>&lt;1</td></tr><tr><td>8</td><td>[NiBr<sub>2</sub>(L<sup>2</sup>)]</td><td>3 h</td><td>5445</td><td>83(62)</td><td>11(44)</td><td>4</td></tr><tr><td>9</td><td>[NiBr<sub>2</sub>(L<sup>2</sup>)]</td><td>24 h</td><td>2661</td><td>87(73)</td><td>8(72)</td><td>5</td></tr><tr><td>10</td><td>[NiBr<sub>2</sub>(L<sup>3</sup>)]</td><td>35 min</td><td>2115</td><td>98(88)</td><td>2(100)</td><td>0</td></tr><tr><td>11</td><td>[NiBr<sub>2</sub>(L<sup>3</sup>)]</td><td>24 h</td><td>1050</td><td>91(82)</td><td>8(38)</td><td>&lt;1</td></tr><tr><td>12</td><td>[NiCl<sub>2</sub>(L<sup>4</sup>)]</td><td>35 min</td><td>24 137</td><td>92(90)</td><td>5(80)</td><td>3</td></tr><tr><td>13</td><td>[NiCl<sub>2</sub>(L<sup>4</sup>)]</td><td>3 h</td><td>20 948</td><td>91(85)</td><td>8(72)</td><td>1</td></tr><tr><td>14<sup>[13]</sup></td><td>[NiBr<sub>2</sub>(L<sup>6</sup>)]</td><td>35 min</td><td>5780</td><td>92(95)</td><td>6(70)</td><td>2</td></tr><tr><td>15<sup>[13]</sup></td><td>[NiBr<sub>2</sub>(L<sup>6</sup>)]</td><td>24 h</td><td>4000</td><td>85(92)</td><td>12(65)</td><td>3</td></tr></tbody></table>

[ª] Conditions: amount of catalyst: 1 × 10⁻⁵ mol, amount of cocatalyst (MMAO-12): 4 × 10⁻³ mol (400 equiv.), T = 30–35 °C, solvent: toluene, total volume: 20 mL, 10 bar C₂H₄, every test was repeated at least twice;

[ᵇ] turnover frequency ([mol(C₂H₄) mol(Ni)⁻¹ h⁻¹]);

[ᶜ] % calculated by GC analysis;

[d] 1-butene vs total butenes formed;

[e] 1-hexene vs total hexenes formed.

after activation with modified methylaluminoxane (MMAO). Their catalytic properties were compared to those of cavity-free analogs [NiBr₂(DPPE)][25] and [NiBr₂(L⁵)][26] and P'N complex [NiBr₂(L⁶)][13] (Table 2 and Figure 3). Complexes [NiBr₂(L³)] and [NiCl₂(L⁴)] primarily produced C₄ olefins (up to 98%) and 1-butene (up to 90%), similar to the analogous cavity-shaped P'N complex [NiBr₂(L⁶)], albeit with slightly lower α-olefin selectivity (Table 2, entries 10–15). Unsurprisingly, the larger β-CD analog [NiCl₂(L⁴)] is much more active than its α-CD counterpart [NiBr₂(L³)] with nearly identical selectivities (Table 2, entries 10–13). Compared to their cavity-free analog [NiBr₂(L⁵)], both complexes [NiBr₂(L³)] and [NiCl₂(L⁴)] are significantly more selective with only minor loss of activity in the case of complex [NiCl₂(L⁴)] after prolonged reaction times. Again, as for the P'N complex [NiBr₂(L⁶)], the α-olefin content is high for both complexes [NiBr₂(L³)] and [NiCl₂(L⁴)] (Table 2, entries 10–13), but not for cavity-free [NiBr₂(DPPE)] and [NiBr₂(L⁵)] (Table 2, entries 1–4) for prolonged reaction times, pointing to a scenario where chain-walking and post-isomerization processes are disfavored within the CD cavity. Complex [NiBr₂(L¹)] which displays an α-CD cavity-shaped environment very different from [NiBr₂(L³)] is much more active (Table 2, entries 5, 6, 10 and 11) than the latter but tends to deactivate over prolonged reaction times. Surprisingly, the β-CD-based precatalyst [NiBr₂(L²)] is less active than its smaller counterpart [NiBr₂(L¹)] and also tends to deactivate over time (Table 2, entries 7–9). Moreover, the α-olefin
<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /><figcaption>**Figure 3.** Selectivities of complexes [NiBr₂(DPPE)], [NiBr₂(L¹-L³)], [NiCl₂(L⁴)] and [NiBr₂(L⁵-L⁶)] for C4 compounds and α-olefins using MMAO as cocatalyst.</figcaption></figure>

selectivity for [NiBr₂(L¹)] and [NiBr₂(L²)] is somewhat lower than that of [NiBr₂(L³)], [NiCl₂(L⁴)] and the P^N complex [NiBr₂(L⁶)], (Table 2, entries 5–9) and is closer to the selectivity observed for the cavity-free complex [NiBr₂(L⁵)] (Table 2, entries 3 and 4), but much higher than the electronically similar complex [NiBr₂(DPPE)] (Table 2, entries 1 and 2).

All attempts to oligomerize ethylene with PdMeCl complexes **6a,b**, **7a,b** and [PdCl(Me)(L⁶)][²⁴] upon activation with NaBArF₄ failed, whether in toluene or in the more polar solvent CH₂Cl₂, with only trace amounts of butenes observed.

## 2.3. Theoretical studies

To investigate the reactivity of cis-chelating diphosphanes, as well as the influence of the CD cavity on the Ni¹¹-catalyzed ethylene dimerization, a computational study was performed on the key steps of the reaction by adopting a seldom-used methodology for very large molecules based on the GFN2-xTB density functional tight binding method.[27] The complex selected for this study was the one with the highest α-olefin selectivity in the α-CD series, namely the cavity-shaped complex [NiBr₂(L³)], along with its cavity-free analog [NiBr₂(L⁵)]. The key atoms involved in the reactions catalyzed by Ni¹¹-complexes [NiBr₂(L⁵)] (with P^P ligand) and [NiBr₂(L³)] (with P^P^CD ligand) after MMAO activation are shown in Figure 4. This scheme illustrates the two possible modes of ethylene coordination: *trans* to P² (with the ethyl group *trans* to P¹) or *trans* to P¹ (with the ethyl group *trans* to P²). Goldman et al.[28] emphasized the importance of *trans*-influence in ethylene insertion into nickel-alkyl bonds catalyzed by X^Y bidentate ligands. Their work demonstrated the roles of strong *trans*-influence (STI) and weak *trans*-influence (WTI) in stabilizing intermediates such as π-complexes and agostic interactions, as well as their impact on system reactivity, particularly in the case of SHOP-type P^O ligands. They showed that ethylene insertion occurs with lower energy barriers in the presence

<figure><img src="image_19.png" /></figure>

less stable but
more reactive

P¹ = STI

P² = WTI

<figure><img src="image_20.png" /></figure>

more stable but
less reactive

<caption>**Figure 4.** Atom labeling in a generic P^P complex with the ethylene group coordinated *trans* to P² (a) or *trans* to P¹ (b). In this scheme, P¹ is the P with strong *trans*-influence (STI) and P² is the P with the weak *trans*-influence (WTI).</caption>

of STI^WTI bidentate ligands (such as P^O) compared to STI^STI ones (e.g., P^P). STI^WTI ligands stabilize the π-complex, leading to an overall decrease in the ethylene insertion energy barrier. However, the present study reveals that functional groups bonded to the phosphorus atoms in a nonsymmetric diphosphane (P^P) ligand can alter the system's reactivity, mimicking STI^WTI behavior.

The reaction mechanism follows the established pathway outlined in Scheme 3, based on the general mechanism for oligomerization reactions.[29] Since CD-based diphosphanes are large ligands with around 200 atoms, it is challenging if not impossible to fully optimize these cavity-shaped Ni¹¹ complexes using density functional theory (DFT) methods. Therefore, the semiempirical tight-binding method GFN2-xTB[27] was selected to model the Ni¹¹-catalyzed ethylene dimerization using CD-based ligands. The GFN2-xTB method enables rapid calculations of molecular systems containing up to 1000 atoms and has been successfully applied in studies of organometallic complexes, although it does have limitations when it comes to accurately modeling the coordination geometries of transition metal
<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /><figcaption>**Scheme 3.** Ni(II)-catalyzed ethylene oligomerization with the ethyl group coordinated in the active complex I *trans* to P¹ (*a*, in black) or *trans* to P² (*b*, in red). Not all intermediates are drawn.</figcaption></figure>

complexes.[27,30] In this study, the steps of ethylene insertion into the Ni-C bond catalyzed by the cavity-free complex [NiBr₂(L⁵)] after MMAO activation (Figures S119–S122) were first calculated using both the PBE[31]-D3(BJ)[32]/def2-TZVP[33]/COSMO[34] (toluene) level of theory and the GFN2-xTB/ALPB[35] (toluene) level of theory. Furthermore, the enthalpy profile of the reaction was calculated for the cavity-free system for the *a*-type and *b*-type intermediates. The optimized geometries and energies obtained from both methods were compared to validate the results from the GFN2-xTB method before applying it to the CD-based Ni¹¹ complexes. Enthalpy, rather than Gibbs free energy, was used to construct the comparative reaction coordinate energy profile. Enthalpies were also used in the final GFN2-xTB calculations to provide a clearer visualization of the reaction energy profiles.

This initial benchmarking study demonstrated that GFN2-xTB is well-suited for investigating Ni¹¹-catalyzed ethylene dimerization, offering a good balance between computational cost and result quality. The energy difference between the activation barriers (ΔH‡) calculated using DFT and GFN2-xTB methods was only of around 1 kcal/mol (Figures S119–S122, Tables S1–S5). Our calculations also revealed that the PPh₂ coordinating unit acts as a weaker *trans*-influencer (WTI) than the P¹Pr₂ unit, which means that the L⁵-IIIa intermediate is less stable but more reactive than L⁵-IIIb, with the *a*-type intermediates driving the catalytic cycle (Figures S121–S122, Table S1). Details of this benchmarking study are provided in the Supporting Information.

Thus, the GFN2-xTB method was applied to study the reaction pathways involving complexes [NiBr₂(L⁵)], (P^P ligand) and [NiBr₂(L³)] (P^P^CD ligand). The dimerization and isomerization steps follow the pathway outlined in Scheme 3. The reaction coordinate for ethylene dimerization was computed with the ethyl group coordinated *trans* to P¹ (*a*-type intermediate) (Figure 5) and *trans* to P² (*b*-type intermediate) (Figure S124).

<table><caption>**Table 3.** Relative enthalpy (ΔH) in kcal/mol of the stationary points of ethylene insertion in the Ni-C1 bond catalyzed by complex [NiBr₂(L⁵)] (P^P^P ligand) and complex [NiBr₂(L³)] (P^P^P^CD ligand) after MMAO activation with the ethyl group coordinated in the active complex *trans* to P¹ (*a*) and *trans* to P² (*b*) computed at the GFN2-xTB/ALPB (toluene) level of theory.</caption><thead><tr><th rowspan="2">Intermediate [Y]</th><th colspan="4">ΔH [kcal/mol]</th></tr><tr><th>L<sup>5</sup>-Y<sub>a</sub><sup>[a]</sup></th><th>L<sup>5</sup>-Y<sub>b</sub><sup>[a]</sup></th><th>L<sup>3</sup>-Y<sub>a</sub><sup>[b]</sup></th><th>L<sup>3</sup>-Y<sub>b</sub><sup>[b]</sup></th></tr></thead><tbody><tr><td>I</td><td>0.0</td><td>0.9</td><td>0.0</td><td>3.5</td></tr><tr><td>II</td><td>-9.3</td><td>-13.4</td><td>-1.5</td><td>-4.9</td></tr><tr><td>III</td><td>-1.4</td><td>-0.4</td><td>-2.5</td><td>8.6</td></tr><tr><td>TSII-IV</td><td>3.1</td><td>4.5</td><td>6.0</td><td>8.1</td></tr><tr><td>IV</td><td>-22.6</td><td>-23.3</td><td>-21.0</td><td>-26.4</td></tr><tr><td>V</td><td>-33.0</td><td>-32.5</td><td>-31.2</td><td>-34.8</td></tr><tr><td>TSV-VI</td><td>-26.2</td><td>-31.3</td><td>-29.7</td><td>-29.2</td></tr><tr><td>VI</td><td>-26.1</td><td>-32.5</td><td>-29.5</td><td>-28.6</td></tr><tr><td>VII</td><td>-30.3</td><td>-32.9</td><td>-30.0</td><td>-30.9</td></tr><tr><td>TSVII-VIII</td><td>-29.6</td><td>-32.5</td><td>-24.2</td><td>-31.5</td></tr><tr><td>VIII</td><td>-29.9</td><td>-35.4</td><td>-28.9</td><td>-37.6</td></tr><tr><td>IX</td><td>-31.8</td><td>-35.8</td><td>-36.8</td><td>-35.3</td></tr><tr><td>TSIX-X</td><td>-29.2</td><td>-32.6</td><td>-34.0</td><td>-31.1</td></tr><tr><td>X</td><td>-33.7</td><td>-32.9</td><td>-33.5</td><td>-31.0</td></tr></tbody></table>

[a] Enthalpy relative to complex L⁵-IIIa + ethylene;

[b] Enthalpy relative to complex L³-IIIa + ethylene.

the following discussion, the distinction between the *a* and *b* isomers will not always be made, especially when referring to the general steps. The reaction coordinate enthalpy profiles, shown in Figures 5, and S123, with enthalpies for all the steps listed in Table 3, indicate that ethylene coordination is more stabilized in the P^P^ system than in the P^P^CD one, particularly for the L⁵/L³-III pairs (Figures S125, and S127). The reaction profile begins with
<figure><img src="image_23.png" /></figure>

<figure><img src="image_24.png" /><figcaption>**Figure 5.** Enthalpy profiles for ethylene dimerization catalyzed by complex [NiBr₂(L⁵)] (P·P ligand) in light blue and by complex [NiBr₂(L⁵)] (P·P⁴ ligand) in dark blue after MMAO activation. Relative enthalpy values are given in kcal/mol relative to the respective active species (P·P-la for complex [NiBr₂(L⁵)] and P·P⁴-la for complex [NiBr₂(L⁵)]) obtained from geometry optimizations at the GFN2-xTB/ALPB(toluene) level of theory.</figcaption></figure>

the active species L⁵/L³⁻I, followed by ethylene coordination, which yields the π-complex L³/L⁵⁻II. The π-complexes in the presence of cyclodextrin, L³-IIa (ΔH = -1 kcal/mol) and L³-IIIb (ΔH = -5 kcal/mol), are significantly less stabilized than the corresponding cavity-free complexes L⁵-IIa (ΔH = -9 kcal/mol) and L⁵-IIIb (ΔH = -14 kcal/mol), respectively. However, the ligands have first to position themselves in a favorable conformation (syn coplanar to the metal-alkyl bond), through a 90° rotation about the Ni-olefin η² bond, leading to structures L³/L⁵⁻III (Figures S126, and S128). This rotation of the olefin from L³/L⁵⁻II to L³/L⁵⁻III is barrierless. The difference of enthalpy between these two rotamers in the a- and b-type intermediates is significantly increased by the presence of the CD, L³-IIIa (ΔH = -1 kcal/mol) versus L³-IIIb (ΔH = 14 kcal/mol) and L⁵-IIa (ΔH = 8 kcal/mol) vs L⁵-IIIb (ΔH = 13 kcal/mol). Overall, L³/L⁵⁻II intermediate is more stable than L³/L⁵⁻III. After the formation of the L³/L⁵⁻III intermediate (syn coplanar with the metal-alkyl bond), the system passes through a transition state for ethylene insertion. This process has an activation enthalpy of ΔH⁺ = 5 kcal/mol from L⁵-IIa and L⁵-IIIb, ΔH⁺ = 8 kcal/mol from L³-IIIa and is nearly barrierless from L³-IIIb. The overall payload of the insertion of the ethylene into the Ni-C1 bond should be considered as being the sum of the rotational enthalpy payload and the activation barrier of the insertion reaction. The energy barriers of ethylene insertion into the Ni-C1 bond are lower for L³-TSII-IVa (ΔH⁺ = 7 kcal/mol) and L³-TSII-IVb (ΔH⁺ = 13 kcal/mol) than for L⁵-TSII-IVa (ΔH⁺ = 13 kcal/mol) and L⁵-TSII-IVb (ΔH⁺ = 18 kcal/mol), indicating that the environment conferred by the CD cavity lowers the activation barrier. Following TSII-IV, the butyl group is formed with a β-agostic interaction (L³/L⁵⁻IV). The L³-IVa intermediate is stabilized by approximately 1 kcal/mol more than the L⁵-IVa intermediate, which lacks the CD ligand, while L³-IVb is approximately 7 kcal/mol more stable than L⁵-IVb (Figure S124). The butyl group in L⁵/L³⁻IV subsequently rotates

to form a more stabilizing interaction, specifically a β-agostic one with the C4-H (See Figure 4 for labeling) bond (L⁵/L³⁻V). In this case, L³-Va is approximately 1 kcal/mol less stable than L⁵-Va (Figure 5), while L³-Vb is about 5 kcal/mol more stable than L⁵-Vb (Figure S124). From L³/L⁵⁻V, the reaction can proceed along two possible pathways: a second ethylene insertion leading to chain growth (which is not explored in this study), or a β-H elimination via TSV-VI, forming the hydrido-π-complex L³/L⁵⁻VI. Once L³/L⁵⁻VI formed, 1-butene can either undergo chain transfer, where a new ethylene molecule coordinates and 1-butene is released, thereby restarting the catalytic cycle at L³/L⁵⁻I, or the Ni-bound olefin in L³/L⁵⁻VI can rotate, in order to orient the olefin syn coplanar to the hydride to form L⁵-VII (ΔH = -4 kcal/mol for L⁵-VIIa and ΔH = 0 kcal/mol for L⁵-VIIb) or L³-VII (ΔH = 0 kcal/mol for L³-VIIa and ΔH = -2 kcal/mol for L³-VIIb). Similar to the rotation seen for coordinated ethylene, the rotation of 1-butene is expected to proceed in a barrierless fashion. However, in the presence of a CD, steric hindrance imposed by the cavity makes this rotation energetically demanding, as the cavity must undergo conformational changes to make the rotation possible. The transition state of this rotation remained elusive despite efforts to locate it.

To assess the impact of the CD cavity on 1-butene rotation, we then conducted a study (See Supporting Information, section 6.3) where we calculated the energy of complexes L³/L⁵⁻VI with rotated 1-butene, but without relaxing the geometry. As expected, no significant hindrance was observed for complex L⁵⁻VI. However, in complex L³-VI, rotation of 1-butene resulted in structural clashes and high energy, indicating that the CD cavity restricts 1-butene rotation towards L³-VII. A third pathway passes back through TSVI-V via a 1,2-insertion, thereby returning to L³/L⁵⁻V with minimal activation energy.

Additionally, L³/L⁵⁻VII can undergo a 2,1-insertion via TSVII-VIII, with ΔH⁺ = 1 kcal/mol for L⁵-TSVII-VIIIa, ΔH⁺ = 0 kcal/mol
<figure><img src="image_25.png" /></figure>

for L³-TSVII-VIIIb, and ΔH⁺ = 6 kcal/mol for L³-TSVII-VIIIa and ΔH⁺ = -1 kcal/mol for L³-TSVII-VIIIb forming L³-VIIIa and L³-VIIIb, respectively. This result indicates that the hydride insertion is barrierless in the b path in stark contrast to the a path. In L³-VIIIb, where the chain is positioned outside the CD cavity, the olefin is already syn coplanar oriented to the hydride, closely resembling the geometry of L³-TSVII-VIIIb. Conversely, in L³-TSVII-VIIIa, where the chain is inside the CD cavity, the olefin is perpendicular to the hydride due to the steric constraints imposed by the CD cavity, thereby requiring more energy to reach L³-TSVII-VIIIa. L³/L⁵-VIII exhibit a β-agostic interaction involving the C3–H bond (See Figure 4 for labeling), where H is the hydrogen atom originally bonded to C4, which underwent β-H elimination, and was subsequently inserted into the C3 carbon via L³/L⁵-TSVII-VIII. The more active pathway via L³-TSVII-VIIIa is approximately 5 kcal/mol higher in energy than L⁵-TSVII-VIIIa indicating that isomerization is less favored within the CD cavity. The enthalpy profile suggests that once the L³/L⁵-VI intermediate has rotated to form L³/L⁵-VII, the barrier to 2,1-insertion is considerably low. This very small difference in enthalpy does not explain the higher yield of α-C4 olefin observed for the P^P^CD system. On the other hand, the restricted 1-butene rotation on going from complex L³-VI to L³-VII is clearly inhibiting 1-butene isomerization within the CD cavity. After the formation of intermediates L³/L⁵-VIII, the butyl group can rotate to establish a β-agostic interaction between H1 and the nickel center (Figure 4), yielding L³/L⁵-IX. These intermediates then undergo β-H elimination via TSIX-X, with an energy barrier of approximately 3 kcal/mol for both the cavity-free and cavity-shaped complexes, ultimately leading to the formation of the coordinated isomerized product, namely 2-butene (L³/L⁵-X).

To investigate the effect of the CD ligand and its inter-
actions with both the substrate and the Ni metal center, an
electron density-based analysis was performed using the Indep-
pendent Gradient Model (IGM).[36] The local descriptor Δginter
which quantifies electron density (ED) sharing between two
user-specified fragments was computed to assess the interac-
tion strength between the L⁵ or L³ ligand and the substrate. IGM
analysis was carried out for both cavity-free and cavity-shaped
complexes. Throughout the reaction, the substrates coordinated
to the metal vary (e.g., ethyl + ethylene in L³/L⁵-II, L³/L⁵-TSII-IV,
or butyl in L³/L⁵-V). The C2 substrates are referred to as Et or C₂H₄
while the C4 substrate is named Bu throughout the reaction. On
the other hand, the ligand (L³ or L⁵) is denoted as L. Figure 6
illustrates the two defined fragments in the Δginter analysis for
the L⁵ ligand only.

The interaction between the diphosphane, whether cavity-
shaped or cavity-free, and Ni (Δginter<sub>Ni-L</sub>) was also evaluated
(Table S18). The Δginter analysis revealed that intermediate
L<sup>3</sup>-II exhibits weaker interactions between Ni and the C4 sub-
strate (Δginter<sub>Ni-Bu</sub> = 2.082 a<sub>0</sub><sup>-1</sup> (a<sub>0</sub> = Bohr radius) for L<sup>3</sup>-IIa and
Δginter<sub>Ni-Bu</sub> = 1.655 a<sub>0</sub><sup>-1</sup> for L<sup>3</sup>-IIb) compared to intermediate L<sup>5</sup>-II
(Δginter<sub>Ni-Bu</sub> = 2.169 a<sub>0</sub><sup>-1</sup> for L<sup>5</sup>-IIa and Δginter<sub>Ni-Bu</sub> = 2.131 a<sub>0</sub><sup>-1</sup>
for L<sup>5</sup>-IIb). In contrast, the Δginter for the interaction between
Ni and ethylene was found to be stronger in the presence of
the P^P^CD ligand in intermediate L<sup>3</sup>-II (Δginter<sub>Ni-C2H4</sub> = 0.925 a<sub>0</sub><sup>-1</sup>
for L<sup>3</sup>-IIa and Δginter<sub>Ni-C2H4</sub> = 0.722 a<sub>0</sub><sup>-1</sup> for L<sup>3</sup>-IIb) compared

<figure><img src="image_26.png" /><figcaption>**Figure 6.** Fragments used for the IGM-Δginter analysis of L⁵-IIa and L⁵-Va. For Δginter<sub>Bu-L</sub> (right), the first fragment is the C4 substrate in red and the second one is the ligand in blue. In grey are the not interacting atoms in the respective Δginter score. L is the ligand (L³ or L⁵), and Bu is the C4 substrate, which in L⁵-Va is 1-butyl. The Δginter score for the interaction between the C4 substrate and ligand is referred to as Δginter<sub>Bu-L</sub>.</figcaption></figure>

to intermediate L⁵-II (Δginter<sub>Ni-C2H4</sub> = 0.737 a₀⁻¹ for L⁵-IIa and Δginter<sub>Ni-C2H4</sub> = 0.711 a₀⁻¹ for L⁵-IIb). The interaction involving ethylene coordinated inside the CD cavity (L⁵-IIa) is particularly strong (Figure 7 and Figure S137). These results indicate that ethylene is more strongly activated through its interaction with Ni when it is located inside the CD cavity. This activation is promoting ethylene insertion by strengthening the interaction with the ethyl ligand.

The interaction between the ethyl and ethylene ligands was also investigated for complexes L³/L⁵-II. The ethyl-C₂H₄ interaction is stronger for the cavity-shaped complex (Δginter<sub>Et-C2H4</sub> = 0.150 a₀⁻¹ for L³-IIa (Figure 8 and Figure S138) and Δginter<sub>Et-C2H4</sub> = 0.113 a₀⁻¹ for L³-IIb, Figure S139) compared to the cavity-free complex (Δginter<sub>Et-C2H4</sub> = 0.127 a₀⁻¹ for L⁵-IIa, Figure S138, and Δginter<sub>Et-C2H4</sub> = 0.107 a₀⁻¹ for L⁵-IIb, Figure S139). This demonstrates that the confined environment provided by the CD enhances the ethylene-Ni interaction consequently strengthening the interaction between ethylene and the alkyl group, which facilitates ethylene insertion and reduces the corresponding activation barrier.

Additionally, the interaction between the C4 substrate (Bu) and the P^P^CD ligand (Δginter<sub>Bu-L</sub> = 1.483a<sub>0</sub><sup>-1</sup> for L³-IIa) is nearly twice as strong as that of the CD-free P^P^ ligand (Δginter<sub>Bu-L</sub> = 0.845 a<sub>0</sub><sup>-1</sup> for L⁵-IIa). These larger Δginter values are, at least in part, due to the bigger size of the P^P^CD ligand compared to the P^P^ ligand, offering a larger "contact surface" between the two fragments at stake.

Further investigation into the interaction between the P^P^CD
ligand and the substrate (Bu) was carried out using the δginter<sub>Bu-L</sub>
isosurface plot (Figure 9 and Figures S131–S136) and the Δginter<sub>Ni-L</sub>
attractive and repulsive scores (Table S19). The δginter isosurface
plot revealed that the P^P^CD ligand displays larger non-bonding
interaction areas with the substrate than the P^P^ ligand. These
interactions are likely to be responsible for the constrained,
and thus less favorable, rotation of the olefin in the CD-system
(L³-VI to L³-VII) than in the cavity-free one (L⁵-VI to L⁵-VII). These
analyses indicate that the attractive interactions between the
substrate and the ligands are stronger than the repulsive inter-
actions in the cavity-shaped complexes. The δginter isosurface
plot shows that attractive interactions between the P^P^CD ligand
and C1-H and C2-H bonds (See Figure 4 for labeling) are notably
stronger (evidenced by the blue color parts in the isosurface
<figure><img src="image_27.png" /></figure>

<figure><img src="image_28.png" /><figcaption>**Figure 7.** Zoomed-in view of the δg^inter^ isosurface plot (cutoff: δg^inter^ = 0.04 a₀⁻⁴ and Blue Green Red color scale in the range 0.1 < sign(λ₂)ρ < 0.1 a₀⁻³) displaying the interaction between Ni and C₂H₄ for (a) L⁵-IIa, (b) L⁵-IIIb, (c) L³-IIla, and (d) L³-IIIb. Electron density was computed at the PBE-D3(BJ)/def2-TZVP/CPCM(toluene) level of theory from geometry optimized at the GFN2-xTB/ALPB(toluene) level of theory. Surface color code: blue = attractive interaction, green = nonbonding interactions, red = repulsive interactions. Atom color code: hydrogen (white), carbon (silver), phosphorus (orange), and nickel (ice blue).</figcaption></figure>

<figure><img src="image_29.png" /><figcaption>**Figure 8.** δg^inter^ isosurface plot (cutoff: δg^inter^ = 0.005 a₀⁻⁴ and Blue Green Red color scale in the range 0.1 < sign(λ₂)ρ < 0.1 a₀⁻³) displaying the interaction between ethyl and C₂H₄ in L³-IIa. Electron density was computed at the PBE-D3(BJ)/def2-TZVP/CPCM(toluene) level of theory from geometry optimized at the GFN2-xTB/ALPB(toluene) level of theory. Surface color code: blue = attractive interaction, green = nonbonding interactions, red = repulsive interactions. Atom color code: hydrogen (white), carbon (silver), phosphorus (orange), and nickel (ice blue).</figcaption></figure>

<caption>**Figure 9.** δg^inter^ isosurface plot (cutoff: δg^inter^ = 0.005 a₀⁻⁴ and Blue Green Red color scale in the range 0.04 < sign(λ₂)ρ < 0.04 a₀⁻³) displaying the interaction between (a) Bu and P^P^ ligand in intermediate L⁵-VIIa and (b) between Bu and P^P^CD ligand in intermediate L³-VIIa. Electron density was computed at the PBE-D3(BJ)/def2-TZVP/CPCM(toluene) level of theory from geometry optimized at the GFN2-xTB/ALPB(toluene) level of theory. Surface color code: blue = attractive interaction, green = nonbonding interactions, red = repulsive interactions. Atom color code: hydrogen (white), carbon (silver), phosphorus (orange), and nickel (ice blue).</caption>

plot) than in the case of the P^P^ ligand. This behavior suggests that these attractive interactions, which stabilize the substrate, play a crucial role in inhibiting isomerization within the CD cavity.

The IGM analysis indicates that the CD environment not only influences isomerization through steric hindrance, but also affects electron density distribution in the system, thereby modifying Ni reactivity, its interactions with the substrates, and ligand-substrate interactions. These effects are reflected in the energy profile, which aligns with the experimental results.
<figure><img src="image_30.png" /></figure>

### 3. Conclusion

Four *cis*-chelating, CD-based diphosphanes have been shown to exhibit unique coordination behavior with various *d*⁸ cations within their well-defined cavity. The study of the ligands' coordination properties was facilitated by the fact that CD cavities are lined with protons, which can serve as NMR probes for the encapsulated metal center. The ability to easily modulate stericities in these cavity-shaped ligands enabled us to investigate the impact of metal confinement on nickel-catalyzed ethylene oligomerization. In this context, it was demonstrated that metal confinement, as seen in a previously studied cavity-shaped P*N* Ni¹¹ complex, positively affects catalyst robustness and α-olefin selectivity by inhibiting olefin isomerization. Theoretical studies have shown that the restricted rotation of the olefinic substrate within the confined environment of the CD cavity is responsible for the high α-olefin selectivity observed in the most selective cavity-shaped systems. Additionally, it was found that activity can remain reasonably high without compromising selectivity if the cavity is large enough, as exemplified by the *β*-CD complex [NiCl₂(L⁴)]. Further catalytic studies involving metal-confining and *cis*-chelating ligands with various donor atoms are currently underway.

### 4. Experimental Section

Detailed experimental materials and methods as well as theoretical data can be found in the Supporting Information. The authors have cited additional references within the *Supporting Information*. [37]

#### Acknowledgements

We thank the China Scholarship Council for a PhD studentship awarded to Y.L. (CSC201808420261) and the University of Chinese Academy of Sciences for providing a visiting PhD scholarship to M.H. S.F.d.A.M. gratefully acknowledges the International Center for Frontier Research in Chemistry (ICFRC)/ Fondation Jean-Marie Lehn (project "Quantified Noncovalent Interactions for the prediction of reactivity") for financially supporting her associate research position. The computational work was performed using HPC resources from CCUS (grant g2024a282c) and GENCI-IDRIS (grant 2024-AD010812469R3).

#### Conflict of Interests

The authors declare no conflict of interest.

#### Data Availability Statement

The data that support the findings of this study are available in the supplementary material of this article.

**Keywords:** cyclodextrin · ethylene oligomerization · nickel · palladium · phosphane

[1] a) E. D. Metzger, C. K. Brozek, R. J. Comito, M. Dinca, ACS Cent. Sci. **2016**, *2*, 148; b) E. D. Metzger, R. J. Comito, C. H. Hendon, M. Dinca, *J. Am. Chem. Soc.* **2017**, *139*, 757; c) E. D. Metzger, R. J. Comito, Z. W. Wu, G. H. Zhang, R. C. Dubey, W. Xu, J. T. Miller, M. Dinca, ACS Sustainable Chem. Eng. **2019**, *7*, 6654; d) Z. H. Yu, N. Ji, X. Y. Li, R. Zhang, Y. A. Qiao, J. Xiong, J. Liu, X. B. Lu, *Angew. Chem., Int. Ed.* **2023**, *62*, e202213612.

[2] a) D. Fiedler, D. H. Leung, R. G. Bergman, K. N. Raymond, *Acc. Chem. Res.* **2005**, *38*, 349; b) T. S. Koblenz, J. Wassenaar, J. N. H. Reek, *Chem. Soc. Rev.* **2008**, *37*, 247; c) H. Amouri, C. Desmarets, J. Moussa, *Chem. Rev.* **2015**, *112*, 2015; d) C. Deraedt, D. Astruc, *Coord. Chem. Rev.* **2016**, *324*, 106; e) L. Catti, Q. Zhang, K. Tiefenbacher, *Chem.-Eur. J.* **2016**, *22*, 9060; f) J. Yang, B. Chatelet, D. Hérault, J. P. Dutasta, A. Martinez, *Eur. J. Org. Chem.* **2018**, *2018*, 5618; g) A. Molnár, *ChemCatChem.* **2021**, *13*, 1424; h) Z. Kaya, E. Bentouhami, K. Pelzer, D. Armspach, *Coord. Chem. Rev.* **2021**, *445*, 214066; i) D. Matt, J. Harrowfield, *ChemCatChem.* **2021**, *13*, 153; j) D. L. Diao, A. J. Simaan, A. Martinez, C. Colomban, *Chem. Commun.* **2023**, *59*, 4288; k) J. E. Smart, J. Emerson-King, R. J. Jeans, T. M. Hood, S. Lau, A. Bara-Estaún, U. Hintermair, P. G. Pringle, A. B. Chaplin, *ACS Catal.* **2024**, *14*, 11803.

[3] a) S. H. A. M. Leenders, R. Gramage-Doria, B. de Bruin, J. N. H. Reek, *Chem. Soc. Rev.* **2015**, *44*, 433; b) V. Mouarrawis, R. Plessius, J. I. van der Vlugt, J. N. H. Reek, *Front. Chem.* **2018**, *6*, 623.

[4] a) D. Zhang, E. T. Nadres, M. Brookhart, O. Daugulis, *Organometallics*, **2013**, *32*, 5136; b) Z. Chen, K. E. Allen, P. S. White, O. Daugulis, M. Brookhart, *Organometallics*, **2016**, *35*, 1756; c) C. S. Popeney, Z. B. Guan, *J. Am. Chem. Soc.* **2009**, *131*, 12384; d) Q. H. Tran, X. Q. Wang, M. Brookhart, O. Daugulis, *Organometallics* **2020**, *39*, 4704.

[5] L. K. Johnson, C. M. Killian, M. Brookhart, *J. Am. Chem. Soc.* **1995**, *117*, 6414.

[6] a) Q. H. Tran, M. Brookhart, O. Daugulis, *J. Am. Chem. Soc.* **2020**, *142*, 7198; b) M. Janeta, J. X. Heidlas, O. Daugulis, M. Brookhart, *Angew. Chem., Int. Ed.* **2021**, *60*, 4566; c) I. Göttker-Schnetmann, P. Wehrmann, C. Röhr, S. Mecking, *Organometallics* **2007**, *26*, 2348.

[7] a) H. L. Mu, L. Pan, D. P. Song, Y. S. Li, *Chem. Rev.* **2015**, *115*, 12091; b) S. D. Ittel, L. K. Johnson, M. Brookhart, *Chem. Rev.* **2000**, *100*, 1169; c) M. D. Doherty, S. Trudeau, P. S. White, J. P. Morken, M. Brookhart, *Organometallics* **2007**, *26*, 1261; d) V. C. Gibson, S. K. Spitzmesser, *Chem. Rev.* **2003**, *103*, 283.

[8] H. Sommer, F. Juliá-Hernández, R. Martin, I. Marek, *ACS Cent. Sci.* **2018**, *4*, 153.

[9] a) D. H. Camacho, E. V. Salo, J. W. Ziller, Z. Guan, *Angew. Chem., Int. Ed.* **2004**, *43*, 1821; b) C. S. Popeney, D. H. Camacho, Z. B. Guan, *J. Am. Chem. Soc.* **2007**, *129*, 10062; c) C. S. Popeney, C. M. Levins, Z. B. Guan, *Organometallics* **2011**, *30*, 2432; d) D. A. C. Ferreira, S. F. D. Morais, S. M. P. Meneghetti, M. R. Meneghetti, *J. Mol. Catal. A Chem.* **2012**, *363*, 1.

[10] H. J. Shao, Y. Zhang, X. D. Yang, M. F. Tan, Y. T. Wang, T. Jiang, *Appl. Organomet. Chem.* **2024**, *38*, e7689.

[11] D. Bézier, O. Daugulis, M. Brookhart, *Organometallics* **2017**, *36*, 443.

[12] a) D. Armspach, D. Matt, F. Peruch, P. Lutz, *Eur. J. Inorg. Chem.* **2003**, *805*; b) L. Poorters, D. Armspach, D. Matt, L. Toupet, S. Choua, P. Turek, *Chem.-Eur. J.* **2007**, *13*, 9448.

[13] Y. Li, K. Pelzer, D. Sechet, G. Creste, D. Matt, P. Braunstein, D. Armspach, *Dalton Trans.* **2022**, *51*, 11226.

[14] T. A. Phan, M. Jouffroy, D. Matt, N. Armaroli, A. S. Moncada, E. Bandini, B. Delavaux-Nicot, J. F. Nierengarten, D. Armspach, *Chem.-Eur. J.* **2024**, *30*, e202302750.

[15] T. A. Phan, N. Armaroli, A. S. Moncada, E. Bandini, B. Delavaux-Nicot, J. F. Nierengarten, D. Armspach, *Angew. Chem., Int. Ed.* **2023**, *62*, e202214638.

[16] Deposition Number(s) 2352345 (for NiBr₂(L¹)), 2352351 (for [NiBr₂(L²)], 2352375 (for [PdCl₂(L¹)]), 2352366 (for [PdCl₂(L³)]), 2352367 (for 7a,b) contain(s) = http://www.ccdc.cam.ac.uk/structures

[17] J. Gout, S. Rat, O. Bistri, O. Reinaud, *Eur. J. Inorg. Chem.* **2014**, 2819.

[18] E. Engeldinger, D. Armspach, D. Matt, P. G. Jones, R. Welter, *Angew. Chem., Int. Ed.* **2002**, *41*, 2593.

[19] T. Fanjul, G. Eastham, J. Floure, S. J. K. Forrest, M. F. Haddow, A. Hamilton, P. G. Pringle, A. G. Orpen, M. Waugh, *Dalton Trans.* **2013**, *42*, 100.

[20] P. F. Ai, A. A. Danopoulos, P. Braunstein, *Dalton Trans.* **2014**, *43*, 1957.
<figure><img src="image_31.png" /></figure>

[21] a) T. Fanjul, G. Eastham, N. Fey, A. Hamilton, A. G. Orpen, P. G. Pringle, M. Waugh, *Organometallics*. **2010**, *29*, 2292; b) T. Fanjul, G. Eastham, M. F. Haddow, A. Hamilton, P. G. Pringle, A. G. Orpen, T. P. W. Turner, M. Waugh, *Catal. Sci. Technol.* **2012**, *2*, 937.

[22] The complexity of the different NMR spectra and overlapping signals prevented the full assignment of the CD H-5 protons, which is necessary for localizing the methyl group in both complexes by ROESY.

[23] Such an assignment should be taken with caution since isomeric ratios can vary on going from the solid state to solution if the two isomers are in equilibrium in solution.

[24] a) K. R. Reddy, K. Surekha, G. H. Lee, S. M. Peng, J. T. Chen, S. T. Liu, *Organometallics*. **2001**, *20*, 1292; b) M. Agostinho, P. Braunstein, *Chem. Commun.* **2007**, 58.

[25] M. Lejeune, D. Sémeril, C. Jeunesse, D. Matt, F. Peruch, P. L. Lutz, L. Ricard, *Chem.-Eur. J.* **2004**, *10*, 5354.

[26] Y. M. Li, S. Chakrabarty, C. Mück-Lichtenfeld, A. Studer, *Angew. Chem., Int. Ed.* **2016**, *55*, 802.

[27] C. Bannwarth, S. Ehlert, S. Grimme, *J. Chem. Theory Comput.* **2019**, *15*, 1652.

[28] F. Hasanayn, P. Achord, P. Braunstein, H. J. Magnier, K. Krogh-Jespersen, A. S. Goldman, *Organometallics*. **2012**, *31*, 4680.

[29] F. Speiser, P. Braunstein, L. Saussine, *Acc. Chem. Res.* **2005**, *38*, 784.

[30] a) S. Spicher, S. Grimme, *J. Phys. Chem. Lett.* **2020**, *11*, 6606; b) S. Dohm, M. Bursch, A. Hansen, S. Grimme, *J. Chem. Theory Comput.* **2020**, *16*, 2002; c) S. Spicher, S. Grimme, *Angew. Chem., Int. Ed.* **2020**, *59*, 15665; d) J. P. Menzel, M. Kloppenburg, J. Belic, H. J. M. de Groot, L. Visscher, F. Buda, *J. Comput. Chem.* **2021**, *42*, 1885; e) C. Bannwarth, E. Caldeweyher, S. Ehlert, A. Hansen, P. Pracht, J. Seibert, S. Spicher, S. Grimme, *W. Interdiscip. Rev. Comput. Mol. Sci.* **2021**, *11*, e1493.

[31] J. P. Perdew, K. Burke, M. Ernzerhof, *Phys. Rev. Lett.* **1996**, *77*, 3865.

[32] a) S. Grimme, J. Antony, S. Ehrlich, H. Krieg, *J. Chem. Phys.* **2010**, *132*, 154104; b) S. Grimme, S. Ehrlich, L. Goerigk, *J. Comput. Chem.* **2011**, *32*, 1456.

[33] F. Weigend, R. Ahlrichs, *Phys. Chem. Chem. Phys.* **2005**, *7*, 3297.

[34] V. Barone, M. Cossi, *J. Phys. Chem. A.*, **1998**, *102*, 1995.

[35] S. Ehlert, M. Stahn, S. Spicher, S. Grimme, *J. Chem. Theory Comput.* **2021**, *17*, 4250.

[36] a) C. Lefebvre, G. Rubez, H. Khartabil, J. C. Boisson, J. Contreras-García, E. Hénon, *Phys. Chem. Chem. Phys.* **2017**, *19*, 17928; b) C. Lefebvre, J. Klein, H. Khartabil, J. C. Boisson, E. Hénon, *J. Computat. Chem.* **2023**, *44*, 1750.

[37] a) G. A. Zhurko, *Chemcraft, Version 1.8* https://www.chemcraftprog.com; b) W. Humphrey, A. Dalke, K. Schulten, *J. Mol. Graph.* **1996**, *14*, 33; c) T. K. Woo, T. Ziegler, *J. Organomet. Chem.* **1999**, *591*, 204; d) E. Engeldinger, L. Poorters, D. Armspach, D. Matt, L. Toupet, *Chem. Commun.* **2004**, 634; e) D. Armspach, L. Poorters, D. Matt, B. Benmerad, F. Balegroune, L. Toupet, *Org. Biomol. Chem.* **2005**, *3*, 2588; f) F. Weigend, *Phys. Chem. Chem. Phys.* **2006**, *8*, 1057; g) G. M. Sheldrick, *Acta Crystallogr.* **2008**, *A64*, 112; h) A. L. Spek, *Acta Crystallogr.* **2009**, *D65*, 148; i) M. Bursch, A. Hansen, S. Grimme, *Inorg. Chem.* **2017**, *56*, 12485; j) F. Neese, *WIREs Comput. Mol. Sci.* **2022**, *12*, e1606.

Manuscript received: March 26, 2025

Revised manuscript received: May 1, 2025

Version of record online: May 24, 2025