Crowded diphosphinomethane ligands in catalysis: [(R2PCH 2PR′2-κ2P)-NiR″]+ cations for ethylene polymerization without activators

Article

pubs.acs.org/Organometallics

Crowded Diphosphinomethane Ligands in Catalysis: [(R₂PCH₂PR′₂-κ²P)-

NiR″]⁺Cations for Ethylene Polymerization without Activators

Madeleine Schultz,^†Frank Eisentrager, Christian Regius, Frank Rominger, Patrick Hanno-Igels, Paul Jakob,

̈

Irene Gruber, and Peter Hofmann*

Organisch-Chemisches Institut, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany

̈

S

* Supporting Information

ABSTRACT: The preparation of a series of nickel dichloride

complexes with bulky diphosphinomethane chelate ligands

R₂PCH₂PR′₂is reported. Reaction with the appropriate Grignard

reagent leads to the corresponding dimethyl and dibenzyl

complexes. Cationic monomethyl and mono-η³-benzyl complexes

are generated from these dialkyl complexes by protonation with

[H(OEt₂)₂]⁺[B(3,5-(CF₃)₂C₆H₃)₄]⁻, while the complex

[(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[B(3,5-(CF₃)₂C₆H₃)₄]⁻

is obtained from protonation of the Ni(0) olefin complex

(dtbpm-κ²P)Ni(η²-trans-stilbene). Crystal structures of exam-

ples of dichlorides, dimethyl, dibenzyl, cationic methyl, and

cationic η³-benzyl complexes are reported. Solutions of the cations polymerize ethylene under mild conditions and without the

necessity of an activating agent, to form polyethylene having high molecular weights and low degrees of chain branching. In

comparison to the Ni methyl cations, the η³-benzyl cation complexes are more stable and somewhat less active but still very

efficient in C₂H₄polymerization. The effect on the resulting polyethylene of varying the substituents R, R′ on the phosphine

ligand has been examined, and a clear trend for longer chain PE with less branching in the presence of more bulky substituents

on the diphosphine has been found. Density functional calculations have been used to examine the rapid suprafacial η³to η³

haptotropic shift processes of the [(R₂PCH₂PR′₂)Ni] fragment and the η³−η¹change of the coordination mode of the benzyl

group required for polymerization in those cations.

start a new polymer chain. Instead, either linear polymer chain

formation or chain walking can occur via reinsertion at the other

side of the double bond, leading to branched polyethylene.

During the past decade various examples of ethylene poly-

merizations by nickel complexes have been published.²⁴⁻³⁸The

nickel−indenyl systems of Zargarian polymerize ethylene when

activated with PMAO, but not with other chloride abstracting

agents. The BP system³⁹is similar to Brookhart’s, with a bulky,

neutral bidentate ligand, which inhibits chain transfer in the

same way as described above.

For quite some time research in our group has focused on

the use of the sterically bulky, electron-rich ligand bis(di(tert-

butyl)phosphino)methane (dtbpm),⁴⁰the narrow bite angle

and the steric bulk of which imposes unusual reactivity and

bonding patterns upon four-membered-ring chelated metal

centers.⁴¹⁻⁴³Relevant for the present study, neutral, three-

coordinate (dtbpm-κ²P)Rh^Ialkyl complexes (alkyl = e.g. neo-

pentyl) stabilized by γ-agostic interactions have been prepared

and investigated^44,45which do not polymerize ethylene. They

do, however, bind C₂H₄to form Rh(I) η²-ethylene complexes

of highly unusual structures, being potential models for alkyl

olefin intermediates preceding the olefin insertion step.⁴⁶It was

INTRODUCTION

■

The immense volume and commercial value of industrial oligo-

mer and polymer production from α-olefins, in particular from

ethylene and propylene, are the impetus for continual research

into new types of transition-metal catalysts with improved acti-

vities and selectivity patterns.¹Catalyst research is increasingly

guided by the detailed mechanistic understanding obtained

from sophisticated experimental²and theoretical studies.³⁻⁵

Well-defined, single-component systems are most suitable for

such studies, and metallocenes of d⁰metals are by far the most

extensively investigated homogeneous polymerization catalysts.

A groundbreaking discovery in the field of homogeneous

catalysis was the report by Brookhart et al. in 1995 that square-

planar nickel and palladium alkyl cations with bulky diimine

ligands can catalyze the polymerization of α-olefins.⁶This was

the first report of the use of late transition metals for polymeri-

zation rather than oligomerization as intended and observed for

typical SHOP catalysts,⁷and Brookhart-type systems have since

been studied extensively, both experimentally⁸⁻²⁰and theoret-

ically.²¹⁻²³The specific feature of the ligand system that leads

to polymerization rather than chain termination is the pair of

bulky, substituted aryl rings oriented perpendicular to, and at

the front of, the ligand chelate ring. The steric bulk of these aryl

rings prevents monomer association at an axial coordination

site after β-H elimination from the growing chain, which could

Received: August 15, 2011

Published: December 27, 2011

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Article

expected that iso(valence)electronic (dtbpm-κ²P)Ni^IIalkyl cations

could be active catalysts for ethylene polymerization, because

the steric crowding provided by the tert-butyl groups, potentially

also protecting against chain termination, is similar to that in

Brookhart’s (and the BP) systems, as shown in Figure 1.

η³-benzyl complex [(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[B(3,5-

(CF₃)₂C₆H₃)₄]⁻.

To the best of our knowledge, the solid-state structures of

cationic monomethyl complexes [(R₂PCH₂PR′₂-κ²P)Ni(CH₃)-

(S)]⁺[B(3,5-(CF₃)₂C₆H₃)₄]⁻(S = solvent) disclosed here are

so far the only cases of isolated and structurally characterized

monomethyl Ni(II) cations active in C₂H₄polymerization,

although such species have been multiply studied by NMR at

low temperature in solution.^16,49,50

The polymerization capability for ethylene using these

methyl and η³-benzyl cations has been tested under stand-

ardized conditions. The properties of the resulting polymers

are presented and correlated with the substitution (steric bulk)

of the phosphine ligands, similar to the studies with sterically

varying heterocyclic imine ligands.⁵¹The type of well-defined

single-site cationic Ni polymerization catalysts described in

detail here has been disclosed in 2002.⁵²The only closely

related study of cationic η³-benzyl nickel compounds with diphos-

phine ligands as catalyst precursors for ethylene ologomerization/

polymerization by Cam

̀

pora et al. appeared 2 years later.⁵³These

authors investigated the bite-angle dependence of cationic p-CF₃-

substituted η³-benzyl nickel complexes carrying bisphosphines

ⁱPr₂P(CH₂)_nPⁱPr₂(n = 1−3) in ethylene oligo- and polymeriza-

tion. Their synthesis of the [(P−P)κ²-P)Ni(p-CF₃-η³-benzyl)]⁺

cations is less generally applicable and straightforward than

the synthesis we had reported earlier and we refer to here. A

cationic η³-benzyl Ni diimine complex was reported in 2003⁵⁴

by Monteiro et al., which is only moderately active in ethylene

polymerization when MAO is applied as an activator. A zwitter-

ionic η³-benzyl Ni complex has been used by Bazan et al. for

C₂H₄polymerization.⁵⁵Brookhart et al. have tested the dibro-

mide (dtbpm-κ²P)NiBr₂using standard activating cocatalysts,

as disclosed in a patent.^41b

Figure 1. Comparison of ball-and-stick (front view toward Ni) and

space-filling (top view upon the chelate ring planes) representations of

metal fragments taken from the X-ray structures of a typical Brookhart

diazadiene Ni dichloride (with two o,o′-diisopropyl-substituted N-phenyl

groups, top structures) and of (dtbpm-κ²P)NiCl₂(bottom structures,

vide infra). Only the metal centers with their chelate rings in two orien-

tations are shown; the two chlorides have been omitted for a clearer

picture in both cases.

If steric effects play the same role as in Brookhart’s bulky

diazadiene ligands, the positive charge of the bisphosphine

Ni(II) systems should lead to distinctly higher polymerization

reactivity than in the neutral rhodium(I) case because of weaker

back-bonding from the metal center to coordinated olefins. We

have already shown that, in contrast to smaller ligands such as

dppm,⁴⁷the use of the dtbpm ligand with Pd(II) leads to very

efficient catalysts for CO/ethylene copolymerization, yielding

high-molecular-weight polyketones.⁴⁸

Varying the substituents on the phosphorus atoms while

retaining the small bite angle caused by the methylene bridge

was expected to allow for variable steric and electronic environ-

ments at the metal center. The effect of this alteration on the

resulting metal complex should be manifested in its structure

and reactivity and in the physical characteristics of the polyethy-

lene produced. Similar ligand variations have been studied in

the Brookhart and the BP systems and have been found to

affect the chain branching and molecular weight; it was found

by Brookhart that a sterically less bulky ligand led to less bran-

ched and lower molecular weight polyethylene.⁶In studies on

the BP system, the less bulky ligands led to shorter chains but

with higher levels of branching than with the bulkiest ligands

studied.²⁶

RESULTS AND DISCUSSION

■

Synthesis and Structures. Deep red nickel dichloride

complexes of the bidentate phosphine ligands R₂PCH₂PR′₂

(R = R′ = ^tBu, dtbpm; R = Ph, R′ = ^tBu, ptbpm; R = Cy, R′ = ^tBu,

i

t

ctbpm; R = Pr, R′ = Bu, iptbpm; R = R′ = Cy, dcpm) can be

prepared easily by direct reaction of the respective bisphosphine

ligands with anhydrous NiCl₂in refluxing ethanol (Scheme 1),

as reported for dtbpm.^41a

Scheme 1. Synthesis of the Ni(II) Dichloride Complexes

In this paper we report the preparation of thermally sensitive

dimethyl and dibenzyl nickel(II) complexes containing a series

of bidentate, bulky, electron-rich diphosphinomethane ligands

R₂PCH₂PR′₂. Protonation with [H(OEt₂)₂]⁺[B(3,5-(CF₃)₂-

C₆H₃)₄]⁻leads to loss of methane or toluene to give the

well-defined methyl or η³-benzyl cations; the latter are ther-

mally quite stable compounds. The nickel(0) stilbene complex

(dtbpm-κ²P)Ni(η²-trans-PhCHCHPh), easily accessible from

trans-stilbene by in situ reduction of [(dtbpm-κ²P)NiCl₂,^41acan

also be protonated with this acid to give the benzyl-substituted

These air-stable complexes are very soluble in halo-

genated hydrocarbons and slightly soluble in hot ethanol.

They, and all of the other complexes prepared in this work, are

diamagnetic red, orange, or yellow square-planar nickel(II)

complexes.

The molecular structures of the dichloride compounds have

been determined in order to study the effect of the change

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in phosphine substituents on the geometry in the solid state.

Important bond distances and angles are presented in Table 1,

Table 1. Selected Bond Distances (Å) and Angles (deg) of

(L)NiCl₂in the Solid State

a

L

dtbpm

ctbpm

iptbpm

dcpm

Ni−P

2.1745(6) 2.1763(6),

2.1674(6)

2.1833(6),

2.1510(6)

2.1542(7),

2.1524(7)

Ni−Cl

2.2060(6) 2.2171(6),

2.2161(6)

2.2262(6),

2.1961(7)

2.2180(7),

2.2174(7)

P−Ni−P

P−C−P

mean deviation

from P−P−Ni−

Cl−Cl plane

77.85(3)

95.1(1)

0.019

76.40(2)

93.5(1)

0.040

76.09(2)

93.0(1)

0.040

75.70(2)

91.7(1)

0.148

a

Figure 2. ORTEP diagram (50% probability displacement ellipsoids)

of (dtbpm-κ²P)NiCl₂. Hydrogen atoms and cocrystallized solvent

CH₂Cl₂have been omitted for clarity.

The first value of Ni−P is the distance to the phosphorus atom

bearing tert-butyl substituents (if applicable), and the first value of

Ni−Cl is that trans to that phosphorus atom.

Supporting Information. The core of each structure is a P−P−

Ni−Cl−Cl square plane, and the narrow bite angle of these

methylene-bridged diphosphine ligands is manifested in P−

Ni−P angles of around 76°, compared to 87° in the analogous

and Table 2 contains important data collection and structure

solution parameters for all structures other than (ptbpm-κ²P)-

NiCl₂(the single-crystal structure of which could not be solved

satisfactorily, although the connectivity is clear from the data

obtained). Full crystallographic details for the four struc-

tures are provided in the Experimental Section. The structure

of (dcpm-κ²P)NiCl₂has been reported independently else-

where,⁵⁶in a modification without cocrystallized solvent. The

structure of the solvate (dcpm-κ²P)NiCl₂·CHCl₃reported here

is similar to the reported structure, and details are provided for

comparison.

57

ethylene-bridged diphosphine complex (dppe-κ²P)NiCl₂and

91° in (dtbpe-κ²P)NiCl₂.⁵⁸

The core of (dcpm-κ²P)NiCl₂·CHCl₃is very slightly dis-

torted from an ideal square plane toward a tetrahedral struc-

ture; the angle between the Cl−Ni−Cl plane and the P−Ni−P

plane is 14°. This is not a pyramidal distortion, as shown by the

torsion angle defined by one of the phosphorus atoms, the

midpoint between the two phosphorus atoms, the midpoint

between the two chlorine atoms, and one of the chlorine atoms

of 14°. The analogous torsion angles in the other three di-

chloride structures are below 4°. There is no obvious cause for

Figure 2 shows the solid-state structure of (dtbpm-κ²P)-

NiCl₂·3CH₂Cl₂. Because the structures with other phos-

phine ligands are similar, ORTEP diagrams are given in the

Table 2. Selected Crystal Data and Data Collection Parameters for (dtbpm-κ²P)NiCl₂·3CH₂Cl₂, (ctbpm-κ²P)NiCl₂, (iptbpm-κ²P)-

NiCl₂, and (dcpm-κ²P)NiCl₂·CHCl₃

(dtbpm-κ²P)NiCl₂·3CH₂Cl₂

(ctbpm-κ²P)NiCl₂

(iptbpm-κ²P)NiCl₂

(dcpm-κ²P)NiCl₂·CHCl₃

formula

C₂₀H₄₄Cl₈NiP₂

688.80

C₂₁H₄₂Cl₂NiP₂

486.10

C₁₅H₃₄Cl₂NiP₂

405.97

C₂₆H₄₇Cl₅NiP₂

657.54

fw

color

red

space group (No.)

a (Å)

C2/c (15)

15.1240(3)

12.0207(3)

17.9892(3)

94.486(1)

3260.4(1)

4

P2₁/c (14)

9.7401(2)

17.1283(4)

14.5481(3)

99.398(1)

2394.5(1)

4

P2₁/c (14)

17.9811(2)

8.3568(1)

14.1060(1)

108.869(1)

2005.7

P2₁/n (14)

11.2757(2)

12.4752(2)

22.8363(1)

102.322(1)

3138.3

b (Å)

c (Å)

β (deg)

V (Å³)

Z

4

d_calcd(g/cm³)

μ(Mo Kα)_calcd(mm⁻¹

size (mm)

transmissn range

2θ range (deg)

no. of rflns collected

1.403

1.348

1.344

1.392

)

1.358

1.172

1.384

1.161

0.31 × 0.25 × 0.22

0.49−0.78

4.3−55.0

5948

0.40 × 0.11 × 0.08

0.65−0.91

3.7−50.0

20 419

0.27 × 0.20 × 0.13

0.71−0.84

2.4−51.0

14 466

0.40 × 0.10 × 0.08

0.65−0.91

3.7−51.1

22 909

no. of unique rflns

3546

4238

3459

5446

2

no. of rflns, F_o> 2σ(F_o)

2977

3473

3114

4370

no. of variables

157

266

191

307

a

R1

0.037

0.029

0.032

b

wR2

0.086

0.065

0.067

0.066

GOF

1.04

1.06

1.08

1.04

max/min residual electron density (e/Å³)

0.47 and −0.48

0.48 and −0.33

0.58 and −0.56

0.34 and −0.28

a

b

R1 = ∑||F_o| − |F_c||/∑||F_o|. wR2 = [∑w(F_o− F_c²)²/∑w(F_o)²]^1/2

.

2

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this distortion, which is also observed in the reported structure

without cocrystallized solvent.⁵⁶The two nickel−phosphorus

distances in the complexes containing the unsymmetrical

ligands ptbpm, ctbpm, and iptbpm are different; the Ni−P

distance to the phosphorus atom bearing the tert-butyl groups

is slightly longer than the distance to the other phosphorus

atom in each structure. This may be a superposition of a steric

effect, caused by the bulkiest groups on the phosphorus atom in

the strained four-membered ring, and an electronic effectthe

electron rich metal atom binds the less electron rich P atom

more closely. The difference between the two phosphorus atoms

is also apparent in the ³¹P{¹H} NMR spectra of these

compounds, which each display two doublets. The chemical

shift of the phosphorus atom bearing two tert-butyl groups is

similar in each case, at around δ −5, while the chemical shift of

decomposition points in the range of 92−128 °C, which might

be an indication of a solvent-assisted reductive elimination.

The X-ray crystal structures of the four dimethyl complexes

prepared have been also determined; an ORTEP diagram

of (dtbpm-κ²P)NiMe₂is presented in Figure 3, while Table 3

2

the other phosphorus atom varies significantly. The J_PP

coupling constants are similar and relatively large (ca. 140 Hz)

(see Experimental Section for full characterization details).

The yellow dimethyl and the red dibenzyl complexes can

be prepared from the dichloride complexes by reaction of the

appropriate Grignard reagent with the dichloride complex in

cold THF or pentane (Scheme 2).

Figure 3. ORTEP diagram (50% probability displacement ellipsoids)

of (dtbpm-κ²P)NiMe₂. Hydrogen atoms have been omitted for clarity.

Scheme 2. Preparation of Dimethyl and Dibenzyl Complexes

Table 3. Selected Bond Distances (Å) and Angles (deg) of

(L)NiMe₂in the Solid State

a

L

dtbpm

ptbpm

iptbpm

dcpm

Ni−P

2.2382(7), 2.2298(5), 2.230(1), 2.1806(6),

2.2377(7) 2.2056(4) 2.197(1) 2.2135(6)

Ni−C(methyl)

1.957(3),

1.953(3)

1.958(2),

1.959(2)

1.968(3), 1.969(2),

1.960(3) 1.956(2)

P−Ni−P

P−C−P

mean deviation from

76.93(2)

96.8(1)

0.037

75.75(2)

94.57(7)

0.018

75.86(2) 76.002

94.6(1)

0.021

93.5(1)

0.077

P−P−Ni−C−C plane

Optimal conditions for the syntheses vary according to the

ligand set, and full details are provided in the Experimental

Section. The stability of these compounds in solution varies

from extreme thermal sensitivity, decomposing at −78 °C, to

stability up to 55 °C and is clearly related to the steric bulk of

the phosphine ligands, with the bulkiest ligands (dtbpm and

ctbpm) leading to the least stable molecules. After extensive

screening, cold THF was found to be the best solvent for the

synthesis of the dimethyl complexes. The complex (dtbpm-

κ²P)NiMe₂reductively eliminates ethane with a half-life of less

than 30 min in solution at room temperature, generating the

unstable [(dtbpm-κ²P)Ni⁰] fragment which, in the presence

of additional appropriate ligands, can be trapped and forms

adducts.⁵⁹⁻⁶¹This is consistent with the reported facile thermal

elimination of neopentane and neosilane from (dtbpm-κ²P)Pt-

(Np)(H) and (dtbpm-κ²P)Pt(Ns)(H), respectively,⁶²and the

elimination of ethane or Me₃Si(CH₂)₂SiMe₃, respectively, from

(dtbpm-κ²P)PdMe₂and (more facile) (dtbpm-κ²P)Pd(CH₂-

SiMe₃)₂.⁶³While in the cases of platinum and palladium, in the

absence of other ligands the eight-membered cyclic d¹⁰−d¹⁰

dimer (μ-dtbpm)₂M₂⁶²⁻⁶⁴is formed with bridging dtbpm ligands,

in the nickel case, in the absence of additional ligands, thermal

decomposition leads to precipitation of black elemental nickel and

free ligand, which is observed for all of the dimethyl compounds

reported here. Remarkably, in the solid state rather than in

solution, the dimethyl complexes are thermally stable with

a

The first value of Ni−P is the distance to the phosphorus atom

bearing tert-butyl substituents (if applicable), and the first value of

Ni−C(methyl) is that trans to that phosphorus atom.

contains selected bond distances and angles and Table 4 provides

important data collection and structure solution parameters.

Again, because the structures are similar, ORTEP diagrams

of the remainder of the dimethyl complexes appear in the

Supporting Information. As for the dichloride complexes, the

dimethyl molecules have a square-planar geometry about the

nickel center. As was observed above, the greatest distortion

from planarity is observed in the dcpm case; the angle between

the C−Ni−C and P−Ni−P planes for (dcpm-κ²P)NiMe₂is

8°, which is only a very slight distortion; the torsion angle

described for the dichloride structures in this case is also 8°.

The Ni−P distances for the dimethyl complexes are slightly

longer than those for the dichloride complexes, while the angles

around nickel are unchanged. The bond lengthening to the

phosphorus atoms is obviously related to the increased electron

donor properties of the methyl groups in comparison to the

chloride ligands. As observed in the dichloride cases, the

nickel−phosphorus distances of the molecules with unsym-

metrical diphosphine ligands are somewhat different, with the

distance to the phosphorus atom bearing the tert-butyl groups

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Table 4. Selected Crystal Data and Data Collection Parameters for (L)NiMe₂

L

dtbpm

ptbpm

iptbpm

dcpm

formula

fw

C₁₉H₄₄NiP₂

393.19

C₂₃H₃₆NiP₂

433.17

C₁₇H₄₀NiP₂

365.14

C₂₇H₅₂NiP₂

497.34

color

yellow

space group (No.)

a (Å)

P2₁/c (14)

17.9363(3)

8.5024(2)

14.8549(3)

92.437(1)

2263.3(1)

4

P2₁/c (14)

18.48480(1)

9.85510(1)

13.2549(2)

102.944(1)

2353.28(4)

4

P2₁/c (14)

18.5285(2)

8.0957(1)

14.8617(2)

110.879(1)

2082.89(4)

4

P2₁/c (14)

11.4633(4)

12.6493(5)

19.6646(7)

102.983(1)

2778.5(2)

4

b (Å)

c (Å)

β (deg)

V (Å³)

Z

d_calcd(g/cm³)

μ(Mo Kα)_calcd(mm⁻¹

1.154

1.223

1.164

1.189

)

0.996

0.965

1.077

0.825

size (mm)

0.42 × 0.20 × 0.08

0.68−0.92

4.5−51.2

16 162

0.44 × 0.34 × 0.22

0.68−0.82

2.2−51.2

17 255

0.26 × 0.16 × 0.11

0.77−0.89

2.6−51.3

14 935

0.34 × 0.20 × 0.16

0.77−0.88

3.6−51.1

20 323

transmissn range

2θ range (deg)

no. of rflns collected

no. of unique rflns

3927

4091

3614

4817

2

no. of rflns, F_o> 2σ(F_o)

3049

3630

3060

4008

no. of variables

213

249

194

273

a

R1

0.033

0.023

0.033

0.032

b

wR2

0.073

0.060

0.075

GOF

1.03

1.02

1.09

1.03

max/min residual electron density (e/Å³)

0.41 and −0.30

0.36 and −0.16

0.49 and −0.22

0.48 and −0.33

a

b

R1 = ∑||F_o| − |F_c||/∑||F_o|. wR2 = [∑w(F_o− F_c²)²/∑w(F_o)²]^1/2

.

2

again being slightly longer. In addition, as observed for the

dichlorides, the chemical shifts in the ³¹P{¹H} NMR spectra are

very similar for those phosphorus atoms, and to the singlet of

(dtbpm-κ²P)NiMe₂, at δ 19, but the coupling constants are

much smaller (around 10 Hz).

The dibenzyl complexes are thermally less stable than the

dimethyl complexes, presumably due to the increased steric bulk

of two benzyl groups compared with two methyl groups around

the metal center. Neither (dtbpm-κ²P)NiBz₂nor (ctbpm-κ²P)-

NiBz₂could be prepared in THF; precipitation of black nickel

was observed even at −78 °C. In those two cases, the dibenzyl

complex was generated in a heterogeneous reaction in pentane

at −78 °C, extracted into diethyl ether, and added directly to a

flask containing [H(OEt₂)₂]⁺[B(3,5-(CF₃)₂C₆H₃)₄]⁻to gen-

erate the benzyl cation. The steric bulk of the ligands ptbpm

and iptbpm is less, and the dibenzyl complexes bearing these

ligands can be prepared in THF at −35 °C and isolated

by crystallization from toluene. The dibenzyl complex (dcpm-

κ²P)NiBz₂can be prepared in pentane at room temperature and

crystallized from toluene. Thus, some measure of the relative

bulkiness of the diphosphine ligands is implied by the varying

decomposition reactivity of their nickel dibenzyl complexes.

The structures of (ptbpm-κ²P)NiBz₂and (iptbpm-κ²P)NiBz₂

were determined crystallographically. ORTEP diagrams of the

complexes are shown in Figures 4 and 5, while Table 5 contains

selected bond distances and angles for the two complexes

and Table 6 contains data collection and structure solution

parameters.

Figure 4. ORTEP diagram (50% probability displacement ellipsoids)

of (ptbpm-κ²P)NiBz₂. Hydrogen atoms have been omitted for clarity.

Important features of these structures are that the benzylic

carbon atoms do not lie in the plane of the Ni−diphosphine

fragment; they are shifted toward a tetrahedral geometry,

particularly in the case of (ptbpm-κ²P)NiBz₂, in which the

P−Ni−P and C−Ni−C planes intersect at an angle of 26°. The

torsion angle, described for the dichloride complexes above, in

Figure 5. ORTEP diagram (50% probability displacement ellipsoids)

of (iptbpm-κ²P)NiBz₂. Hydrogen atoms have been omitted for clarity.

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Organometallics

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by a torsion angle of 16° between one phosphorus atom, the

midpoint between the phosphorus atoms, the midpoint be-

tween the benzylic carbon atoms, and one of the benzylic carbon

atoms. The nickel−phosphorus distances in both complexes are

unequal, again due to the asymmetrical diphosphine ligands

(Table 5). The Ni−C distances to the benzyl CH₂carbon

atoms are similar to those to the methyl carbon atoms in the

structures of the dimethyl complexes. The Ni−P bond lengths

are also similar to those observed in the dimethyl structures.

The chemical shifts of the phosphorus atoms bearing tert-butyl

groups for the dibenzyl complexes are once again observed at

around δ 20, while the ²J_PPcoupling constants in the complexes

with asymmetric ligands are all around 30 Hz. Interestingly, the

chemical shifts of the two phosphorus atoms of (ctbpm-κ²P)-

NiBz₂are the same as for the free ligand ctbpm,⁶⁵and only the

large difference in coupling constants (30 vs 108 Hz) distin-

guishes the ³¹P{¹H} NMR spectra.

Reaction of the dimethyl or dibenzyl complexes with

[H(OEt₂)₂]⁺[B(3,5-(CF₃)₂C₆H₃)₄]⁻in diethyl ether leads to

loss of one of the carbon ligands as methane or toluene, respec-

tively, and to the formation of the yellow to orange cationic salts

with the noncoordinating counterion [B(3,5-(CF₃)₂C₆H₃)₄]⁻

(=[BAr_f]⁻). The benzyl-substituted η³-benzyl cation complex

[(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻was also prepared,

in that case by reaction of the known Ni(0) stilbene complex

(dtbpm-κ²P)Ni(trans-PhCHCHPh)⁴¹with [H(OEt₂)₂]⁺[BAr_f]⁻.

In an NMR tube, addition of 1 equiv of [H(OEt₂)₂]⁺[BAr_f]⁻

to a solution of any of the dimethyl complexes at room tem-

perature leads to quantitative formation of the corresponding

cation; gas bubbles, presumably of methane, can be observed.

Table 5. Selected Bond Distances (Å) and Angles (deg) of

(ptbpm-κ²P)NiBz₂and (iptbpm-κ²P)NiBz₂and of the

Cations of [(dtbpm-κ²P)Ni(Me)(THF)]⁺[BAr_f]⁻·2THF and

[(ptbpm-κ²P)Ni(Me)(THF)]⁺[BAr_f]⁻in the Solid State

[(dtbpm- κ²P) [(ptbpm- κ²P)

(ptbpm-κ²P) (iptbpm- κ²P)

Ni(Me)

a

b

NiBz₂

(THF)]⁺

(THF)]^+,

a

Ni−P

2.2653(7),

2.2079(7)

1.993(2),

1.993(2)

74.19(2)

93.9(1)

2.2641(8),

2.2250(8)

1.996(3),

1.990(3)

75.42(3)

95.9(1)

17

2.3082(9),

2.1402(9)

1.941(3)

78.33(3)

98.3(2)

11

2.292(2),

2.101(2)

1.941(8)

77.01(8)

95.9(3)

9

Ni−C

P−Ni−P

P−C−P

intersection of 26

planes

mean

0.249

0.165

0.106

0.091

deviation

from plane

Ni−O_THF

1.989(2)

1.991(5)

a

The first value of Ni−P is the distance to the phosphorus atom

bearing tert-butyl substituents, and the first value of Ni−C(benzyl) is

b

that trans to that phosphorus atom. The first Ni−P distance given is

to the phosphorus atom trans to the methyl ligand, which in the

ptbpm case is the phosphorus atom bearing the tert-butyl substituents.

this case measures 26°, indicating that the distortion is again

not toward pyramidal. In (ptbpm-κ²P)NiBz₂, the phenyl resi-

dues of the benzyl ligands point in opposite directions in the

solid state, presumably for steric reasons, while in (iptbpm-κ²P)

NiBz₂they lie on the same side of the chelate plane but

point outward; again, a distortion toward tetrahedral is shown

Table 6. Selected Crystal Data and Data Collection Parameters for (ptbpm-κ²P)NiBz₂, (iptbpm-κ²P)NiBz₂, [(dtbpm-κ²P)-

NiMe(THF)]⁺[BAr_f]⁻·2THF, and [(ptbpm-κ²P)NiMe(THF)]⁺[BAr_f]⁻in the Solid State

(iptbpm- κ²P)

[(dtbpm- κ²P)

[(ptbpm- κ²P)

(ptbpm-κ²P)NiBz₂

NiBz₂

NiMe(THF)]⁺[BAr_f]⁻·2THF

NiMe(THF)]⁺[BAr_f]⁻

formula

C₃₅H₄₄NiP₂

585.35

C₂₉H₄₈NiP₂

517.32

C₆₂H₇₇BF₂₄NiO₃P₂

1457.70

yellow

C₅₈H₅₃BF₂₄NiOP₂

1353.46

fw

color

red

yellow-orange

space group (No.)

a (Å)

P2₁/n (14)

12.1364(7)

15.6573(9)

16.700(1)

90

P2₁/c (14)

13.3737(7)

11.5980(6)

18.7372(9)

90

C2/c (15)

20.5704(1)

17.3468(2)

39.5515(1)

90

P1 (2)

̅

12.962(1)

14.146(1)

17.793(1)

96.491(2)

108.742(1)

91.243(2)

3064.0(4)

2

b (Å)

c (Å)

α (deg)

β (deg)

95.757(1)

90

90.607(1)

90

100.352(1)

90

γ (deg)

V (Å³)

3157.5(3)

4

2906.1(3)

4

13883.5(2)

8

Z

d_calcd(g/cm³)

μ(Mo Kα)_calcd(mm⁻¹

size (mm)

transmissn range

2θ range (deg)

no. of rflns collected

1.231

1.182

1.395

1.467

)

0.737

0.792

0.432

0.481

0.17 × 0.16 × 0.16

0.88−0.89

3.6−51.1

23 117

0.50 × 0.26 × 0.14

0.69−0.90

3.0−51.1

20 983

0.44 × 0.39 × 0.38

0.83−0.85

2.1−51.3

51 766

0.38 × 0.19 × 0.16

0.84−0.93

3.32−45.0

11 660

no. of unique rflns

5444

5024

12 085

7857

2

no. of rflns, F_o> 2σ(F_o)

3693

4208

9277

4362

no. of variables

349

299

1048

946

a

R1

0.036

0.041

0.049

0.066

b

wR2

0.066

0.109

0.115

0.134

GOF

1.01

1.04

1.07

1.02

max/min residual electron density

0.29 and −0.22

1.09 and −0.39

0.44 and −0.37

0.42 and −0.44

(e⁻/Å³)

a

b

2

R1 = ∑||F_o| − |F_c||/∑||F_o|. wR2 = [∑w(F_o− F_c²)²/∑w(F_o)²]^1/2

.

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The vacant coordination site of each Ni(II) methyl cation com-

plex is occupied by the solvent (THF in these experiments),

and the two phosphorus atoms are inequivalent, resulting in

two doublets in the ³¹P{¹H} spectra for the complexes with

symmetric ligands (dtbpm and dcpm). In the cases of the com-

plexes bearing unsymmetric phosphine ligands, ptbpm and

iptbpm, both possible isomers A and B of the methyl cations

are formed (Figure 6), and two sets of two doublets are ob-

served in the ³¹P{¹H} spectra.

Figure 7. ORTEP diagram (50% probability displacement ellipsoids)

of the cation of [(dtbpm-κ²P)Ni(Me)(THF)]⁺[BAr_f]⁻·2THF. Hydro-

gen atoms and a noncoordinated THF have been omitted for clarity.

the cations are, as expected, somewhat shorter than for their

dimethyl precursors. The distortion away from planarity for the

methyl cations is greater than in the dimethyl complexes but

much less than in the dibenzyl complexes.

Figure 6. The two possible stereoisomers A and B of [(L)NiMe-

(THF)]⁺formed from protonation of the corresponding dimethyl

complex in THF with L = ptbpm (R = tBu, R′ = Ph) and L = iptbpm

(R = tBu, R′ = iPr).

The η³-benzyl cations are far more stable, both oxidatively

and thermally, than the methyl cations, due to the η³-coor-

dination mode of the benzyl ligand. These orange salts can be

handled briefly in air in the solid state and melt at over 150 °C.

As in the case of the methyl cations, the two possible isomers

for each of the compounds with unsymmetric diphosphine

ligands depicted in Figure 8 are formed. In all cases, they are

Spectra were assigned by two-dimensional NMR spectros-

copy, by redissolution of structurally determined crystals, and

by comparison between the compounds (complete spectral data

and assignments are given in the Experimental Section). Not

surprisingly, the two isomers are not produced in a 1:1 ratio. In

the case of ptbpm, a ratio of 1.7:1 of the two isomers was formed

(determined by integration of ³¹P{¹H} NMR spectra), with iso-

mer A in slight excess. In the case of iptbpm, the ratio of the two

isomers was almost 1:6, with the favored isomer being that with

the methyl ligand trans to the tert-butyl-substituted phosphorus

atom, isomer B. This assignment is based on comparison with

the ³¹P{¹H} spectra of the benzyl cations described below. It is

not clear why this isomer should be favored to such a large

extent. The isomers A and B do not interconvert on the NMR

time scale at room temperature, as evidenced by sharp signals in

the NMR spectra for each isomer, although dissociation of the

solvent ligand is expected to be facile. This is not surprising,

because the inversion of a T-shaped three-coordinate d⁸metal

complex through a Y-shaped geometry is electronically dis-

favored.⁴³The predominance of B could be caused by kinetic

control through the protolysis reaction.

Ligands such as PPh₃, for example, readily displace THF

from [(L)NiMe(THF)]⁺, and the X-ray structure of [(dtbpm-

κ²P)NiMe(PPh)₃]⁺is displayed in the Supporting Information.

The methyl cation salts are extremely air sensitive. None-

theless, it was possible to determine crystallographically the

solid-state structures of two of these compounds as the first

representatives of this class. An ORTEP diagram of the cation

of [(dtbpm-κ²P)Ni(Me)(THF)]⁺[BAr_f]⁻·2THF is shown in

Figure 7, while Table 5 contains important bond distances and

angles of that structure as well as those for [(ptbpm-κ²P)Ni-

(Me)(THF)]⁺[BAr_f]⁻, an ORTEP diagram of which is included

in the Supporting Information.

Figure 8. The two possible isomers C and D of [(L)Ni(η³-Bz)]⁺

formed from protonation of the corresponding dibenzyl complex for

L = ptbpm, ctbpm, and iptbpm (R = tBu).

observed in the ³¹P{¹H} NMR spectra in approximately equal

amounts.

These isomers are not expected to interconvert for the same

reasons the methyl cations do not.⁴³Isomer C is analogous to

the methyl cation isomer A, because the benzylic carbon is cis

to the tert-butyl-substituted phosphorus atom, while isomer

D is similarly analogous to isomer B. Suprafacial haptotropic

fluxionality of the benzyl ligand, shown in Scheme 3, is fast on

the NMR time scale, as evidenced by the observation of only

1

one set of phenyl resonances in the H and ¹³C{¹H} NMR

spectra of the benzyl cations.

A transition state for this process was calculated using density

functional theory (B3LYP/SDD,6-31G(d)) for a simplified model

having dhpm (=H₂PCH₂PH₂) as the diphosphine ligand. The

energy of the transition state is only 5.0 kJ/mol higher than that

of the two degenerate (enantiomeric) η³ground states; thus, it is

not surprising that the process is fast on the NMR time scale and

could not be frozen out. This is comparable with the value calcu-

lated for the neutral rhodium system [(H₂PCH₂PH₂κ²-P)Rh(η³-

Bz)] (B3LYP/LANL2DZ) of 6.7 kJ/mol.^66aIn the unsubstituted

The isomer of the cation [(ptbpm-κ²P)NiMe(THF)]⁺for

which the structure could be determined is that with the tert-

butyl groups on the phosphorus atom trans to the methyl

ligand, isomer B, which is the minor isomer formed from the

synthesis but crystallizes preferentially. Important data

collection and structure solution parameters for both structures

are provided in Table 6. The bond distances about the metal in

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Scheme 3. Schematic Illustration of the Suprafacial

Haptotropic η³to η³Shift of the Benzyl Ligand, Keeping the

Two P Atoms Inequivalent (for both R = R′ and R ≠ R′)

Scheme 5. Overlap Situation between the b₂-Type Frontier

MO of a Ni Bisphosphine and the Relevant Frontier MO π₄

of the Benzyl Ligand along the η³to η³Rearrangement

Pathway, Viewed from the Side of the Ni Fragment

of the benzyl residue with respect to the metal. The syn geo-

metry is observed in the crystal structure (see below).

The crystal structures of the two symmetric benzyl cations

as well as that of [(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻

have been determined by X-ray crystallography. Figure 9 shows

benzyl systems and for R = R′, the geometries before and after

suprafacial shift are identical. It should be noted, however, that for

frontier orbital overlap reasons the two P atoms do not inter-

change during this dynamic process: i.e., the benzyl ligand dis-

plays a symmetric spectrum, while the ³¹P signals remain as two

doublets even for the symmetrical diphosphinomethanes. The

metal fragment undergoes what has been called a “windshield-

wiper motion”.

In monocationic η³-benzyl complexes such as [(dtbpm-κ²P)-

Ni(η³-benzyl)]⁺or one of its congeners carrying other diphos-

phinomethanes, the Ni fragment can be formally counted either

as a neutral d¹⁰ML₂unit interacting with a benzyl cation or a

dicationic d⁸ML₂moiety interacting with a benzyl anion. In

either representation, the dominant frontier MO interaction is

between the π₄-MO of the benzyl unit (empty or filled) and the

b₂-type MO of the bisphosphine Ni fragment (filled or empty),

as shown in Scheme 4.^66b

Figure 9. ORTEP diagram (50% probability displacement ellipsoids)

of the cation of [(dtbpm-κ²P)NiBz]⁺[BAr_f]⁻·THF. Hydrogen atoms

have been omitted.

an ORTEP diagram of the cation of [(dtbpm-κ²P)Ni(η³-Bz)]⁺-

[BAr_f]⁻·THF and Figure 10 one isomer of the cation of

Scheme 4. Dominant Frontier MO Interaction between a

Bent Bisphosphine Ni Fragment (Arbitrarily Taken as a

Dicationic d⁸ML₂) and a Benzyl Anion Unit

Figure 10. ORTEP diagram (50% probability displacement ellipsoids)

of the cation of [(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻. Hydro-

gen atoms have been omitted.

[(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻, and Table 7 con-

tains selected bond distances and angles of the three structures.

Table 8 provides important data collection and structure solution

parameters.

Details of the crystallographic studies as well as an ORTEP

diagram of the cation of [(dcpm-κ²P)Ni(η³-Bz)]⁺[BAr_f]⁻•THF

are presented in the Supporting Information. The crystal struc-

tures of [(ptbpm-κ²P)Ni(η³-Bz)]⁺[BAr_f]⁻and [(ctbpm-κ²P)-

Ni(η³-Bz)]⁺[BAr_f]⁻were also determined but are severely dis-

ordered; thus, no bond distances could be extracted. The whole

In the η³to η³metal shift process, the change of the overlap

situation while passing the C_stransition state is indicated in

Scheme 5. In the transition state, there is still appreciable

frontier MO overlap, provided the metal moves without inter-

change of P_aand P_b.

In the protonated stilbene system, this suprafacial shift of the

benzylic part of the ligand leads to a syn and anti conformation

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Table 7. Selected Bond Distances (Å) and Angles (deg) of

the Molecular Structures of the Cations of [(dtbpm-κ²P)-

NiBz]⁺[BAr_f]⁻·THF, [(dcpm-κ²P)NiBz]⁺[BAr_f]⁻, and

[(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻in the Solid

State

Table 8. Selected Crystal Data and Data Collection

Parameters for [(dtbpm-κ²P)NiBz]⁺[BAr_f]⁻·THF, [(dcpm-

κ²P)NiBz]⁺[BAr_f]⁻, and [(dtbpm-κ²P)Ni(η³-

CH(CH₂Ph)Ph]⁺[BAr_f]⁻

[(dtbpm-κ²P)

Ni(η³-CH-

[(dtbpm-κ²P)

[(dcpm-κ²P)

(CH₂Ph)Ph)]⁺-

[BAr_f]⁻

[(dtbpm-

[(dcpm-κ²P)NiBz]⁺

Ni(η³-CH-

a

NiBz]⁺[BAr_f]⁻·THF

NiBz]⁺[BAr_f]⁻

κ²P)NiBz]⁺(2 unique molecules) (CH₂Ph)Ph]⁺

toluene⁶⁷

b

formula

fw

C₆₀H₆₅BF₂₄NiOP₂C₆₄H₆₅BF₂₄NiP₂

C₆₃H₆₃BF₂₄NiP₂

1407.59

red

Ni−P

2.254(1), 2.205(2), 2.242(3), 2.276(1),

1389.58

orange

1421.62

orange

2.181(1)

2.152(2) 2.141(2) 2.205(1)

color

Ni−C1 1.999(6)

Ni−C2 2.055(4)

Ni−C3 2.183(6)

P−Ni−P 79.24(5)

P−C−P 98.4(2)

C1−C2 1.430(9)

C2−C3 1.403(8)

C3−C4 1.39(1)

C4−C5 1.33(1)

C5−C6 1.42(1)

C6−C7 1.37(1)

C7−C2 1.417(8)

2.001(8) 2.06(1)

2.009(3)

space group (No.) P2₁(4)

P1 (2)

̅

P2₁/c (14)

12.7881(3)

18.7788(4)

27.1176(6)

90

2.017(7) 2.054(8) 2.062(3)

2.169(7) 2.136(8) 2.202(3)

77.79(7) 77.44(8) 78.9(1)

a (Å)

13.3717(2)

17.6494(1)

19.3171(2)

21.0416(3)

113.020(1)

92.120(1)

94.502(1)

6564.3(1)

4

b (Å)

17.6205(2)

13.7480(2)

90

c (Å)

95.0(3)

1.42(1)

1.41(1)

1.40(1)

1.35(1)

1.42(1)

1.37(1)

1.44(1)

96.1(3)

1.49(1)

1.35(1)

1.40(1)

1.37(1)

1.44(1)

1.35(1)

1.41(1)

99.3(1)

α (deg)

β (deg)

γ (deg)

V (Å³)

Z

d_calcd(g/cm³)

μ (mm⁻¹

1.444(5)

1.408(5)

1.431(5)

1.368(7)

1.384(7)

1.346(6)

1.422(5)

1.5024(17)

1.3929(18)

1.389(2)

98.526(1)

90

93.422(1)

90

3203.45(8)

2

6500.5(3)

4

1.380(2)

1.3795(19)

1.3861(18)

1.3906(16)

1.441

1.438

)

0.462

0.451

0.455

size (mm)

0.26 × 0.17 × 0.14 0.52 × 0.25 × 0.25 0.45 × 0.29 × 0.25

a

The labeling of the carbon atoms in this structure is different, but the

distances around the equivalent positions of the benzyl ligand have

been given: i.e. C1 = C37, C2 = C36, C3 = C35, C4 = C34, C5 = C33,

transmissn range

2θ range (deg)

0.89−0.94

3.8−55.0

0.80−0.90

2.4−46.5

35 555

0.82−0.89

2.6−51.2

29 792

no. of rflns collected 32 890

b

C6 = C32, C7 = C31. The first Ni−P distance given is to the

no. of unique rflns 14 525

18 629

11 007

phosphorus atom trans to the benzylic carbon, while the second Ni−P

2

no. of rflns, F_o

2σ(F_o)

>

9945

11 643

8170

distance is to the phosphorus atom trans to the ring.

2

no. of variables

910

1823

1040

a

cation in each case is disordered over two orientations, with

the bulky alkyl residues of the diphosphine ligand being in

the same region for both orientations, while the nickel atom

and the benzyl groups are located on both sides of this

region, resulting in a crystallographic mixture of the two

isomers.

R1

0.062

0.088

0.041

b

wR2

0.115

0.212

0.089

GOF

1.09

1.07

1.03

max/min residual

electron density

(e⁻/Å³)

0.39 and −0.26

1.11 and −0.41

0.31 and −0.30

a

b

R1 = ∑||F_o| − |F_c||/∑|F_o|. wR2 = [∑w(F_o− F_c²)²/∑w(F_o)²]^1/2

.

2

The Ni−P and Ni−C bond distances in the benzyl cations

are within the normal range, as observed in the structures of the

dibenzyl complexes. The bond distances in the phenyl rings of

the benzyl ligands are unequal, indicating some loss of

aromaticity. The contribution of the cyclohexadiene resonance

structure F depicted in Scheme 6 is apparent in the pattern of

lengthening and shortening of bonds. Thus, the bonds C³−C⁴,

C⁵−C⁶, and C⁷−C²in a benzyl ligand are expected to lengthen

and the bonds C¹−C², C⁴−C⁵, and C⁶−C⁷are expected to

shorten relative to toluene. This is observed (see Table 7),

especially for the dtbpm structure. The electron density of the

bond C2−C3 is directly involved in binding to the metal, which

is expected to increase the bond distance. The bond length is

observed (at 1.403 Å) to be slightly longer than the related

bonds in toluene⁶⁷(1.393 Å) in each structure. The resolution

of the dcpm structure is not as good, but the trend is none-

theless present.

Scheme 6. Resonance Forms of the Benzyl Ligand Showing

a

Aromatic and Nonaromatic Contributing Structures

a

Benzyl hydrogens are omitted.

Ethylene Polymerization. Pressurizing a solution of the

cation [(dtbpm-κ²P)Ni(Me)(THF)]⁺[BAr_f]⁻in diethyl ether at

0 °C with 7 bar of ethylene causes the solution to become

cloudy within minutes as a white precipitate is formed. The

polymer can be isolated and has been characterized by

differential scanning calorimetry (DSC) and gel permeation

chromatography (GPC). The molecular weight curve is narrow,

showing the single-site nature of the catalyst, and the mean

molecular weight of 470 000 g/mol corresponds to a long-chain

polymer. The melting point of 136 °C is typical for a long,

unbranched polyethylene chain; the low degree of branching

(6.2 methyl branches/1000 carbon atoms as determined by IR)

is presumably because the insertion step is more rapid than

potential chain-walking steps.

The other methyl cations were generated in situ by

dissolution of the respective dimethyl complex and 1 equiv of

[H(OEt₂)₂]⁺[BAr_f]⁻in diethyl ether at room temperature.

This is more practical due to the extreme thermal, oxygen, and

water sensitivity of the methyl cations. In each case, poly-

merization begins immediately upon pressurization with

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ethylene (10 bar) and leads to a white powder of polyethylene

being precipitated. The melting points and molecular weights

of the polymers produced by the different ligand systems are

shown in Table 9. In each case, single-site catalysis is observed

at 25 °C.

Scheme 7. Associative Initiation of Ethylene Polymerization

for Ni(II) η³-Benzyl Cations

Table 9. Comparison of Melting Points of Polyethylene

Produced by Methyl Cations Generated in Situ from

(L)NiMe₂and [H(OEt₂)₂]⁺[BAr_f]⁻at 25 °C and 10 bar in

Diethyl Ether

These results support the hypothesis that the coordination

change in the nickel cation only occurs in the presence of the

incoming ligand, which effectively pushes the phenyl ring of

the benzyl ligand out of the coordination sphere. The energy

for coordination of ethylene to the η³-benzyl complex to

form an η¹-benzyl ethylene complex as shown in Scheme 7 was

calculated to be endothermic by 30.1 kJ/mol.⁶⁸

Three polymerization experiments were conducted with the

stilbenyl cation [(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻

at different temperatures with 7 bar of ethylene pressure.

L

melting pt of polymer (°C)

M_w(g/mol)

dtbpm

ptbpm

iptbpm

dcpm

134.3

124.5

120.4

109.5

101 316

28 904

11 939

5885

GPC analysis (Figure 11) also shows the polymer character-

istics as a function of the bisphosphine ligand systems and the

monomodal nature of the polyethylene formed.

The trend in melting points of the polyethylene reflects the

trend in molecular weights; only dtbpm as auxiliary ligand leads

to long-chain polyethylene. The difference is presumably due to

the steric effects of the substituents on the diphosphine ligand,

which shield the growing polymer chain from termination in a

manner similar to that proposed by Brookhart.^6,8

Table 10. Polymerization Activity of [(dtbpm-κ²P)Ni-

(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻with 7 bar of Ethylene at

0 °C in Et₂O

concn

(mmol/L) solvent

temp

(°C)

yield

(mg)

activity

The benzyl cations were expected to be more stable and

more easily handled, which indeed they are, in comparison with

the corresponding methyl cations. For an η³-benzyl complex

to polymerize ethylene, however, the ligand must change co-

ordination mode to η¹, in order to generate a vacant coor-

dination site for ethylene to bind (Scheme 7). This process has

been studied theoretically using density functional theory.

Despite extensive searching, no minimum was found for an

η¹-coordinated benzyl in the absence of another ligand. This

contrasts with the situation for the analogous, neutral rhodium

complex, for which a minimum was found for (dtbpm-κ²P)-

Rh(η¹-CH₂C₆H₅), 47.7 kJ/mol higher in energy than the η³

ground state.⁶⁶We note that the neutral ethylene adduct

(kg/((mol of Ni) h)) TON

4.4

2.7

2.6

Et₂O

THF

28

44

70

205

665

3.4

18.5

36.8

121

660

1300

1314

Table 10 summarizes the results of those experiments, and

Figure 11 displays the GPC traces of polyethylenes obtained

with cationic benzyl complexes and dtbpm, itbpm, ptbpm, and

dcpm as ligands.

In the case of [(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻

at the two lower temperatures (28 and 44 °C), unreacted

[(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻was observed by

³¹P{¹H} NMR spectroscopy in the solution after the polymer-

ization reaction, and the solutions were still active in catalysis

(dtbpm-κ²P)Rh(CH₂Bu-κC)(η²-C₂H₄) could be isolated but

t

does not have the expected square-planar structure.⁴⁶

Figure 11. GPC traces of polymers produced from the methyl cations generated in situ from (L)NiMe₂and [H(OEt₂)₂]⁺[BAr_f]⁻at 25 °C and 10

bar in diethyl ether (L = dcpm, itbpm, ptbpm, dtbpm).

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when further ethylene was added. At 70 °C, this was no longer

the case, which implies that all of the η³ligand moves to η¹

coordination at that temperature and pressure. The reaction at

higher temperature also resulted in the production of liquid

oligomers (butene to decene), which were identified by GC/

MS but not included in the yield. The polymer produced at

44 °C was analyzed and has an average molecular weight of

182 137 g/mol and one methyl branch per 1000 carbon atoms.

The molecular weight curve could be deconvoluted into two

components, each with a narrow distribution, and averaged

masses of 104 664 and 253 441 g/mol.

Table 12. Physical Properties of Polyethylene Produced at

Room Temperature (25 °C) by [(L)NiBz]⁺[BAr_f]⁻with 10

bar of Ethylene in Et₂O

melting pt

(°C)

mol wt

(g/mol)

total Me branches per 1000 C

atoms

L

dtbpm

ptbpm

ctbpm

iptbpm

dcpm

137.7

126.0

133.5

129.2

125.1

167 917

12 303

30 260

26 177

10 825

1

4.6

2.8

2.6

6

Clearly, the sterically bulky dtbpm, while leading to slower

catalysis, also gives much longer chains with less branching than

the other diphosphine ligands. Note that the unsymmetric ligands

nonetheless gave single-site catalysis, presumably because the

growing polymer chain moves from one side of the ligand to

the other at each insertion step.

Polymerization with the series of benzyl cations [(L)NiBz]⁺

[BAr_f]⁻was tested at 40 °C and 10 bar of ethylene pressure in

Table 11. Polymerization Activity of [(L)NiBz]⁺[BAr_f]⁻at

40 °C with 10 bar of Ethylene in Et₂O

The trend in molecular weight for the polymers produced

by the benzyl cations parallels the trend observed for the much

more active methyl cations, except that the ordering of the

ligands ptbpm and iptbpm is inverted. However, unlike in

Brookhart’s system, the bulkier ligands lead to not only longer

chains but also less branching.^6,7

L

concn (mmol/L) time (h) yield (mg) activity (kg/(mol h))

dtbpm

ptbpm

ctbpm

iptbpm

dcpm

0.50

1.08

2.63

1.34

1.04

6

84

355

200

157

129

5.6

22

3

5.1

11.6

7.8

2

3.5

Copolymerization of ethylene with 1-hexene is possible. If

[(dtbpm-κ²P)Ni(Me)(Solv)]⁺[BAr_f]⁻is used as a catalyst in Et₂O

at ambient temperature, the polymerization activity amounts to

62.5 kg/(mol h). It should be noted that is close to twice as

efficient as ethylene polymerization, a phenomenon which has

been observed before.⁶⁹The melting point of the copolymer

is 125.4 °C, significantly lower than without 1-hexene. GPC

shows an M_wvalue of 144 000 with PDI = 2.73, indicating again

single-site catalysis. ¹³C NMR analysis reveals that 1-hexene is

incorporated into the polyethylene chain with around 81

molecules per 1000 C atoms (2 mol %) and that the expected

n-butyl side chains are formed. A typical ¹³C NMR spectrum is

given in the Supporting Information.

Et₂O, and the results are summarized in Table 11. See also the

GPC traces in Figure 12.

Unreacted benzyl cations can be observed by ³¹P{¹H} NMR

spectroscopy after the reaction. In a separate experiment, a

solution of a benzyl cation in an NMR tube was placed under 1

bar of ethylene pressure at −78 °C and gradually warmed to

room temperature. Although the precipitation of a white solid

was observed in the NMR tube, no change in the ³¹P{¹H}

NMR spectrum was observed. These results indicate that not all

of the catalyst is active up to 40 °C, presumably due to the

barrier to associative η³−η¹conversion described above, imply-

ing that the activity of each catalytic center is higher than is

indicated by the data. For comparison of the polymers pro-

duced by the catalysis, the experiment was repeated at room

temperature for each cation. Table 12 shows the characteristics

of the resulting polymers.

It should also be mentioned parenthetically that the Ni

dichlorides, if activated with MAO (1:1000), are polymerization

catalysts if at 70 °C an ethylene pressure of 40 bar is used.

Lower pressures and temperatures only lead to oily oligomers.

For (dtbpm-κ²P)NiCl₂polyethylene is produced with

Figure 12. GPC traces of polymers produced from the η³-benzyl cations at room temperature with 10 bar of ethylene in Et₂O and dtbpm, itbpm,

ptbpm, and dcpm as ligands. See Table 12 for characterization.

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darkened significantly. The reaction flask was then sealed under

nitrogen and cooled to −20 °C overnight, which led to the

precipitation of a large quantity of a deep red solid. The product

was extracted into CH₂Cl₂, filtered, and recrystallized at −60 °C.

Yield: 0.83 g (60%). Mp: 280 °C dec. Anal. Calcd for C₂₁H₃₀NiCl₂:

C, 53.2; H, 6.38; P, 13.1; Cl, 15.0. Found: C, 53.1; H, 6.16; P, 12.8; Cl,

M_w= 170 000 g/mol but a PDI of 16.8, because there is a second,

small low-molecular-weight minimum visible by GPC. As men-

tioned earlier and disclosed in their patent,^41bBrookhart et al.

have tested the dibromide (dtbpm-κ²P)NiBr₂with MMAO

(26−28 °C, 6.9 bar), obtaining a wax-type polymer (M_w= 7860,

M_n= 3410, PDI = 2.3).

1

3

14.7. H NMR (CD₂Cl₂, 298 K, 300 MHz): δ 1.50 (d, 18H, J_HP

=

15.6 Hz, C(CH₃)₃), 2.85 (t, 2H, ²J_HP= 8.9 Hz, PCH₂P), 7.52 (m, 6H,

m/p-C₆H₅), 8.22 (q, 4H, o-C₆H₅). ³¹P{¹H} NMR (CD₂Cl₂, 298 K,

202.5 MHz): δ −53.5 (d, ²J_PP= 166.5 Hz, PPh₂), −4.4 (d, ²J_PP= 166.5

Hz, P(C(CH₃)₃)₂. ¹³C{¹H} NMR (CD₂Cl₂, 298 K, 125.8 MHz): δ

CONCLUSIONS

■

Stable dichloro nickel(II) complexes bearing bulky methylene-

bridged diphosphine ligands (diphosphinomethanes) of the type

R₂PCH₂PR′₂are readily prepared. They physically resemble

the archetypal nickel complexes with ethylene- or propylene-

bridged diphosphine ligands. These dichlorides can be

transformed to thermally rather sensitive but fully characterized

dimethyl or dibenzyl derivatives, which by protonolysis and

methane or toluene loss, respectively, lead to highly sensitive

cationic monomethyl and much more stable, fluxional cationic

mono-η³-benzyl complexes. In reactions with ethylene, the new

nickel methyl cations bearing these bulky diphosphine ligands,

as either isolated compounds or generated in situ, are very

active ethylene polymerization catalysts. Rather than oligomers,

solid polyethylene is produced at room temperature and low

pressure, in the absence of an activating agent. The solid-state

structure of highly active THF ligated cationic monomethyl

complexes of Ni(II) could be determined. For the cationic

η³-benzyl complexes bearing the members of the sterically

crowded diphosphinomethane series we also find high catalytic

activity for polyethylene formation without a need for acti-

vators. The change from η³-benzyl to η¹-benzyl coordination,

necessary for initiating the polymer formation, does not occur

by itself but is induced by ethylene association. As shown for

an η²-stilbene complex of a diphosphine-ligated Ni(0), cationic

η³-benzyl type Ni(II) catalysts can also be easily prepared by

protonation of appropriate Ni(0) olefin complexes. As to the

dependence of catalyst activity and polymer structure on di-

phosphinomethane ligand structure, the greater the steric bulk

of the diphosphine, the longer the polymer chains that are

produced but the lower the catalytic activity.

1

2

24.2 (d, J_CP= 19.2 Hz, PCH₂P), 28.2 (d, J_CP= 3.0 Hz, C(CH₃)₃),

1

37.2 (d, J_CP= 8.1 Hz, C(CH₃)₃), 128.0 (d, J_CP= 42.4 Hz, i-C₆H₅),

129.4 (d, ²J_CP= 11.1 Hz, o-C₆H₅), 132.3 (s, p-C₆H₅), 133.2 (d, ³J_CP

=

10.1 Hz, m-C₆H₅). MS (FD+): m/z 472.0 [M]⁺with correct isotope

pattern. IR (KBr): ν [cm⁻¹] 3048 w, 2966 m, 2947 m, 2899 w, 2366 w,

1686 m, 1542 w, 1467 s, 1434 s, 1374 m, 1336 m, 1258 w, 1177 m,

1097 s, 1021 m, 809 w, 744 s, 720 s, 690 s, 523 m, 486 m, 476 m.

(ctbpm-κ²P)NiCl₂. This was prepared in a manner analogous to

that for (ptbpm-κ²P)NiCl₂with a yield of 1.38 g (98%). Mp: 319−320

°C. Anal. Calcd for C₂₁H₄₂NiCl₂: C, 51.9; H, 8.71; P, 12.7. Found: C,

1

51.7; H, 8.55; P, 12.7. H NMR (CD₂Cl₂, 298 K, 500 MHz): δ 1.40

(m, 10H, C₆H₁₁), 1.57 (d, 18H, ³J_HP= 15 Hz, C(CH₃)₃), 1.75 (m, 2H,

C₆H₁₁), 1.85 (m, 4H, C₆H₁₁), 2.19 (t, 2H, ²J_HP= 9 Hz, PCH₂P), 2.42

(m, 6H, C₆H₁₁). ³¹P{¹H} NMR (CD₂Cl₂, 298 K, 202.5 MHz): δ

2

−30.41 (d, J_PP= 140 Hz, PCy₂), −6.11 (d, J_PP= 140 Hz,

P(C(CH₃)₃)₂). ¹³C{¹H} NMR (CD₂Cl₂, 298 K, 125.8 MHz): δ 15.51

1

(overlapping dd, J_CP= 20 Hz, PCH₂P), 25.9 (s, p-C₆H₁₁), 26.9 (d,

²J_CP= 11.5 Hz, o-C₆H₁₁), 27.5 (d, J_CP= 11.5 Hz, o-C₆H₁₁), 28.4 (d,

2

³J_CP= 4 Hz, m-C₆H₁₁), 29.1 (s, C(CH₃)₃), 29.5 (d, J_CP= 4 Hz,

3

1

m-C₆H₁₁), 35.77 (d, J_CP= 14 Hz, i-C₆H₁₁), 37.09 (d, J_CP= 8.5 Hz,

C(CH₃)₃). MS (FAB): m/z 935.3 [2M − Cl]⁺, 486.2 [M]⁺, 449.2 [M

− Cl]⁺with correct isotope patterns. IR (KBr): ν [cm⁻¹] 2930 s, 2853

s, 1473 m, 1447 m, 1392 w, 1373 m, 1341 w, 1273 w, 1209 w, 1178 m,

1120 w, 1081 m, 1019 m, 889 m, 852 w, 809 m, 754 m, 718 w, 682 m,

466 w.

(iptbpm-κ²P)NiCl₂. This was prepared in a manner analogous to

that for (ptbpm-κ²P)NiCl₂with a yield of 47%. Mp: 309 °C dec. Anal.

Calcd for C₁₅H₃₄P₂NiCl₂: C, 44.4; H, 8.44; Cl, 17.5; P, 15.3. Found: C,

44.2; H, 8.20; Cl, 17.5; P, 15.3. ¹H NMR (300 MHz, CD₂Cl₂, 298 K):

δ 1.37 (dd, 6H, ³J_PH= 15.4 Hz, ³J_HH= 7.2 Hz, CH(CH₃)₂), 1.49 (dd,

3

6H, J_PH= 17.0 Hz, J_HH= 7.2 Hz, CH(CH₃)₂), 1.58 (d, 18H, J_PH

=

2

15.1 Hz, C(CH₃)₃), 2.21 (t, 2H, J_PH= 9.2 Hz, PCH₂P), 2.73 (6-line

m, 2H, CH(CH₃)₂). ³¹P{¹H} NMR (122 MHz, CD₂Cl₂, 298 K):

δ −5.2 (d, ²J_PP= 140.8 Hz, P(C(CH₃)₃)₂), −21.7 (d, ²J_PP= 140.8 Hz,

P(ⁱPr)₂). ¹³C{¹H} NMR (75 MHz, CD₂Cl₂, 298 K): δ 16.6

A density functional study of the complete catalytic cycle has

been performed, which will be published separately.⁶⁸

2

EXPERIMENTAL SECTION

(overlapping dd, J_CP= 19.3 Hz, PCH₂P), 18.1 (s, CH(CH₃)₂), 19.7

■

2

(s, CH(CH₃)₂), 25.6 (d, J_CP= 16.0 Hz, CH(CH₃)₂), 29.4 (d, J_CP

=

General Comments. All reactions and product manipulations

were carried out under dry argon using standard Schlenk and glovebox

(Braun instruments) techniques unless otherwise indicated. Dry,

oxygen-free solvents were employed throughout, except where noted.

The elemental analyses were performed by the Mikroanalytisches

Laboratorium der Chemischen Institute of Heidelberg University. The

following compounds were prepared by literature procedures: (dtbpm-

κ²P)NiCl₂,^41a[H(OEt₂)₂]⁺[BAr_f]⁻,⁷⁰and the ligands dtbpm, ptbpm,

ctbpm, iptbpm, and dcpm.⁶⁵Methyl and benzyl Grignard reagents

were purchased as THF and diethyl ether solutions, respectively, from

Fluka, and their concentrations were determined by titration.

Anhydrous nickel dichloride was purchased from Fluka and used

without further purification. Ethylene for polymerization was of grade

2.7 and was not further purified before use.

2.2 Hz, C(CH₃)₃), 37.4 (d, ¹J_CP= 8.7 Hz, C(CH₃)₃). MS (FAB): m/z

773.2 [2M − Cl]⁺, 404.1 [M]⁺, 369.1 [M − Cl]⁺with correct isotope

patterns. IR (KBr): ν [cm⁻¹] 2959 m, 2871 m, 2359 w, 2340 w, 1634

w, 1470 s, 1374 m, 1258 w, 1179 m, 1091 m, 1050 m, 1023 m, 887 w,

811 w, 767 m, 708 m, 696 m, 574 w, 482 w.

(dcpm-κ²P)NiCl₂. This was prepared in a manner analogous to

that for (ptbpm-κ²P)NiCl₂in 70% yield. Mp: 347 °C dec. Anal. Calcd

for C₂₅H₄₆P₂NiCl₂: C, 55.79; H, 8.62; Cl, 13.18; P, 11.51. Found: C,

1

55.62; H, 8.74; Cl, 13.19; P, 11.54. H NMR (300 MHz, CDCl₃, 298

K): δ 1.2−2.6 (m, C₆H₁₁and PCH₂P). ³¹P{¹H} NMR (122 MHz,

CDCl₃, 298 K): δ −24.06; note that this differs from the reported

value of δ −32.5.⁵⁶¹³C{¹H} NMR (75 MHz, CDCl_3,298 K): δ 13.6 (t,

¹J_PC= 20.3 Hz, PCH₂P), 25.7 (C₆H₁₁), 26.6 (C₆H₁₁), 27.0 (C₆H₁₁),

27.8 (C₆H₁₁), 29.0 (C₆H₁₁), 34.9 (C₆H₁₁). MS (FAB): m/z 536 [M]⁺,

501 [M − Cl]⁺with correct isotope patterns. IR (KBr): ν [cm⁻¹] 2921

s 2854 s, 2358 w, 1449 m, 1326 w, 1294 w, 1264 w, 1204 w, 1179 w,

1111 w, 1069 m, 1046 w, 1026 w, 996 w, 915 w, 885 w, 850 w, 820 w,

774 w, 746 w, 708 w, 684 w, 655 w, 530 w, 510 w, 462 w.

(ptbpm-κ²P)NiCl₂. In a manner analogous to that reported for

(dtbpm-κ²P)NiCl₂, anhydrous NiCl₂(0.37 g, 2.83 mmol) was weighed

into a Schlenk flask equipped with a magnetic stirrer and the ligand

ptbpm (1.00 g, 2.90 mmol) was weighed into a separate Schlenk flask.

Ethanol was added to both flasks (30 mL), which were then both

warmed to reflux. The colorless ctbpm solution was transferred via

cannula through the reflux condenser into the nickel dichloride

solution, and the yellow slurry immediately became pale orange. The

mixture was heated to reflux for 2.5 h, during which time the color

(dtbpm-κ²P)NiMe₂. In a Schlenk tube, 1.0 g (2.31 mmol) of

(dtbpm-κ²P)NiCl₂was suspended in 25 mL of THF and the

suspension stirred overnight at room temperature. The mixture was

then cooled to −78 °C, and a dropping addition funnel was added to

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the flask. The methyl Grignard solution (1.6 mL of 2.9 M in THF,

4.64 mmol) was diluted with 25 mL of THF, transferred to the

addition funnel, and then added to the cooled suspension over 4 h

with stirring. After the addition was complete, the suspension was

stirred at −20 °C for 1 h. The solvent was then removed under

dynamic vacuum, and the yellow-gray residue was extracted into

toluene (3 × 10 mL) and filtered through Celite. The filtrate was

cooled to −30 °C to avoid decomposition. The volume of toluene was

reduced by half at 0 °C under dynamic vacuum and cooled to −30 °C,

which resulted in the precipitation of yellow crystals. These were

washed with cold toluene and dried under vacuum. A second crop of

crystals was also obtained from the mother liquor. The compound is

thermally sensitive in solution and in the solid state, with a half-life at

room temperature of less than 1 h in solution and 1 week in the solid

state.

12.81 Hz, ³J_HH= 7.18 Hz, CH(CH₃)₂), 1.07 (dd, 6H, ³J_PH= 12.99 Hz,

³J_HH= 7.35 Hz, CH(CH₃)₂), 1.20 (d, 18H, ³J_PH= 12.0 Hz, C(CH₃)₃),

2

1.85 (“t”, 2H, J_PH= 7.14 Hz, PCH₂P), 1.98 (m, 2H, CH(CH₃)₂).

2

³¹P{¹H} NMR (122 MHz, C₆D₆, 298 K): δ 1.0 (d, J_PP= 13.36 Hz,

2

P(ⁱPr)₂, 19.1 (d, J_PP= 13.36 Hz, P(C(CH₃)₃)₂). ¹³C{¹H} NMR

2

(75 MHz, C₆D₆, 298 K): δ 0.0 (dd, J_cis‑PC= 6.63 Hz, J_trans‑PC= 9.50

2

Hz, NiCH₃), 0.6 (dd, J_cis‑PC= 4.03 Hz, J_trans‑PC= 8.63 Hz, NiCH₃),

19.5 (d, J_PC= 17.86 Hz, CH(CH₃)₂), 22.1 (“t”, J_PC= 6.05 Hz,

2

1

3

PCH₂P), 24.5 (dd, J_PC= 4.61 Hz, J_PC= 1.15 Hz, CH(CH₃)₂), 29.6

(d, ²J_PC= 3.46 Hz, C(CH₃)₃), 34.6 (dd, ¹J_PC= 4.60 Hz, ³J_PC= 2.30 Hz,

C(CH₃)₃). IR (KBr): ν [cm⁻¹] = 2951 s, 2867 s, 1469 s, 1386 w, 1367

m, 1178 m, 1093 m, 1043 w, 1020 m, 939 w, 884 w, 912 m, 746 m,

688 m, 593 w, 485 w.

(dcpm-κ²P)NiMe₂. The dichloride (dcpm-κ²P)NiCl₂(523 mg,

0.88 mmol) was weighed into a Schlenk tube, dissolved in 30 mL of

THF, and cooled to −50 °C, and 0.61 mL (1.76 mmol) of a methyl

Grignard solution (2.9 M in THF) was added with stirring. The

reaction mixture was stirred for 1 h at −40 °C, during which time the

solution remained red. Gradual warming to +10 °C led to a color

change to yellow. The solvent was then removed under dynamic

vacuum, leaving a pale yellow solid, which was extracted into toluene

(3 × 10 mL) and filtered through Celite. The volume was reduced by

half under dynamic vacuum, and the yellow-brown solution was cooled

to −78 °C. This led to X-ray-quality crystals, which were washed with

cold pentane and dried under vacuum.

Yield: 560 mg (62%). Mp: 92−94 °C dec. Anal. Calcd for C₁₉H₄₄-

NiP₂: C, 58.1; H, 11.2; Ni, 14.9; P, 15.8. Found: C, 57.7; H, 11.3; Ni,

1

15.0; P, 15.3. H NMR (270 MHz, C₆D₆, 278 K): δ 0.57 (“t”, 6H,

3

5

³J_cis‑PH+ J_trans‑PH= 7.32 Hz, Ni(CH₃)₂), 1.25 (“t”, 36H, J_PH+ J_PH

=

11.7 Hz, C(CH₃)₃), 2.15 (t, 2H, J_PH= 6.35 Hz, PCH₂P). ³¹P{¹H}

2

NMR (109 MHz, toluene-d₈, 273 K): δ 17.9 (s). ¹³C{¹H} NMR (75.5

2

MHz, toluene-d₈, 273 K): δ 0.16 (d, J_PC= 59.7 Hz, Ni(CH₃)₂), 25.2

(t, ¹J_PC= 4.85 Hz, PCH₂P), 31.1 (“t”, ²J_PC+ ⁴J_PC= 2.29 Hz, C(CH₃)₃),

35.1 (dd, J_PC= 1.84 Hz, C(CH₃)₃). IR (KBr): ν [cm⁻¹]: 2990 vs,

3

2950 vs, 2865 vs, 1636 vs, 1479 s, 1390 m, 1365 m, 1260 w, 1165 s,

1104 m, 1019 m, 934 w, 813 s, 736 m, 676 m, 567 m.

(ptbpm-κ²P)NiMe₂. In a Schlenk flask, 1 g (2.1 mmol) (ptbpm-

κ²P)NiCl₂was suspended in 25 mL of THF and the suspension cooled

to −35 °C. In a dropping addition funnel, 1.77 mL (4.2 mmol) of

methyl Grignard solution (2.38 M in THF) was diluted with 25 mL of

THF and added to the suspension at −35 °C, which resulted in a

yellow solution. The solvent was removed under vacuum at room tem-

perature, and the product was extracted into diethyl ether and

decanted from the MgCl₂. Upon cooling to −40 °C, a small amount of

precipitate formed (MgCl₂) and the solution was once more decanted.

The volume was reduced to 15 mL under dynamic vacuum and the

product crystallized at −40 °C. The crystals were collected and washed

twice with cold diethyl ether to remove the faint black discoloration.

Yield: 720 mg (79%) Mp: 104 °C dec. Anal. Calcd for C₂₃H₃₆P₂Ni:

Yield: 363 mg (83%). Mp: 128 °C dec. Anal. Calcd for C₂₇H₅₂P₂Ni:

1

C, 65.21; H, 10.54; P, 12.46. Found: C, 65.28; H, 10.70; P, 12.21. H

3

NMR (300 MHz, CDCl₃, 298 K): δ 0.68 (dd, 6H, J_cis‑PH= 4.2 Hz,

³J_trans‑PH= 11.1 Hz, Ni(CH₃)₂), 1.1−2.4 (m, 44H, C₆H₁₁). ³¹P{¹H}

NMR (122 MHz, C₆D₆, 298 K): δ −4.50 (s). ¹³C{¹H} NMR (75

2

MHz, C₆D₆, 298 K): δ 0.26 (dd, J_trans‑PC= 75 Hz, J_cis‑PC= 15.5 Hz,

Ni(CH₃)₂), 20.69 (t, ¹J_PC= 12.2 Hz, PCH₂P), 26.57 (s, C₆H₁₁), 27.44

(d, ²J_PC= 8.8 Hz, o-C₆H₁₁), 27.62 (d, ²J_PC= 11.0 Hz, o-C₆H₁₁), 29.29

(s, C₆H₁₁), 29.63 (d, ³J_PC= 3.3 Hz, m-C₆H₁₁), 35.15 (d, ¹J_PC= 11 Hz,

i-C₆H₁₁). IR (KBr): ν [cm⁻¹] = 2919 s, 2849 s, 1447 m, 1341 w, 1265

w, 1176 w, 1103 w, 1066 w, 997 w, 915 w, 890 w, 850 w, 819 w, 755 w.

[(dtbpm-κ²P)NiMe(THF)]⁺[BAr_f]⁻. The isolated dimethyl com-

plex (dtbpm-κ²P)NiMe₂(15 mg, 38.1 μmol) was weighed into a

Schlenk flask with 38.6 mg (38.1 μmol) of [H(OEt₂)₂]⁺[BAr_f]⁻. At

room temperature, 5 mL of diethyl ether and 1 mL of THF were

added and the mixture was stirred. Gas evolution was observed. After

10 min the solvent volume was reduced to ca. 1 mL under dynamic

vacuum and 5 mL of pentane was carefully added. Within 2 h, yellow

crystals formed on the walls of the flask. These crystals were of X-ray

quality.

1

C, 63.77; H, 8.38; P, 14.30. Found: C, 62.96; H, 8.16; P, 14.02. H

NMR (300 MHz, d₈-toluene, 298 K): δ 0.83 (dd, 3H, ³J_cis‑PH= 4.4 Hz,

3

³J_trans‑PH= 10.9 Hz, NiCH₃), 0.94 (dd, 3H, J_cis‑PH= 3.7 Hz, ³J_trans‑PH

=

3

11.7 Hz, NiCH₃), 1.32 (d, 18H, J_PH= 12.4 Hz, C(CH₃)₃), 2.79 (“t”,

2H, ²J_PH= 4.4 Hz, ²J_PH= 10.9 Hz, PCH₂P), 7.26 (m, o/p-C₆H₅), 8.02

(t, J_HH= 7.86 Hz, m-C₆H₅). ³¹P{¹H} NMR (122 MHz, d₈-toluene,

3

2

298 K): δ −20.5 (d, J_PP= 8.9 Hz, PPh₂), 19.6 (d, J_PP= 8.9 Hz,

P(C(CH₃)₃)₂). ¹³C{¹H} NMR (75 MHz, d₈-THF, 298 K): δ 1.1 (dd,

Yield: 45.8 mg (71%) (quantitative by NMR) Mp: 125 °C dec.

Anal. Calcd for C₅₄H₆₁P₂NiOBF₂₄: C, 49.38; H, 4.68; P, 4.72. Found:

²J_cis‑PC= 13.81 Hz, J_trans‑PC= 80.3 Hz, NiCH₃), 2.3 (dd, J_cis‑PC= 15.2

2

1

Hz, J_trans‑PC= 73.35 Hz, NiCH₃), 29.2 (d, J_PC= 5.5 Hz, C(CH₃)₃,

C, 49.50; H, 4.55; P, 4.79. H NMR (500 MHz, d₈-THF, 298 K): δ

1

30.5 (dd, J_PC= 9.69 Hz, J_PC= 17.99 Hz, PCH₂P), 34.1 (dd, J_PC

=

−0.33 (dd, 3H, ³J_PH= 3.00 Hz, ³J_PH= 4.35 Hz, NiCH₃), 1.53 (d, 18H,

9.00 Hz, ³J_PC= 3.46 Hz, C(CH₃), 128.7 (s, m-C₆H₅), 129.9 (s, p-C₆H₅),

³J_PH= 13.05 Hz, C(CH₃)₃), 1.61 (d, 18H, ³J_PH= 14.05 Hz, C(CH₃)₃),

133.1 (d, J_PC= 12.45 Hz, o-C₆H₅), 134.9 (dd, ¹J_PC= 16.51 Hz, ³J_PC

=

2

2.72 (dd, 2H, J_PH= 10 Hz, J_PH= 6.4 Hz, PCH₂P), 7.58 (s, 4H,

p-C₆H₃(CF₃)₂), 7.80 (s, 8H, o-C₆H₃(CF₃)₂). ³¹P{¹H} NMR (300

9.69 Hz, i-C₆H₅). IR (KBr): ν [cm⁻¹] 3054 w, 2953 s, 2899 s, 2867 m,

2361 w, 2342 w, 1636 w, 1592 w, 1473 m, 1437 m, 1369 w, 1168 s,

1125 s, 1096 s, 1024 s, 936 m, 814 m, 739 m, 721 s, 697 s, 510 m.

(iptbpm-κ²P)NiMe₂. In a Schlenk flask, 395 mg (0.97 mmol) of

(iptbpm-κ²P)NiCl₂was suspended in 20 mL of THF and the sus-

pension cooled to −35 °C. At this temperature, a solution of 0.65 mL

(1.95 mmol) methyl Grignard (3 M in THF), diluted with 10 mL of

THF, was added over several hours. The suspension dissolved to an

orange solution, which was stirred for 30 min at −10 °C, following

which the solvent was completely removed under dynamic vacuum.

The solid was extracted into diethyl ether, filtered through Celite,

and then cooled to −40 °C to crystallize. X-ray-quality crystals were

obtained. A second crop of crystals was obtained by reducing the

volume of the mother liquor.

2

MHz, d₈-THF, 298 K): δ 9.7 (d, J_PP= 22.1 Hz), 37.8 (d, J_PP= 22.1

Hz). ¹³C{¹H} NMR (126 MHz, d₈-THF, 298 K): δ −9.37 (dd, ²J_PC

=

2

1

40.1 Hz, J_PC= 59.4 Hz, NiCH₃), 22.62 (dd, J_PC= 10.4 Hz, J_PC

13.7 Hz, PCH₂P), 31.19 (d, ²J_PC= 6.1 Hz, C(CH₃)₃), 31.34 (d, ²J_PC

2.8 Hz, C(CH₃)₃), 36.47 (dd, ¹J_PC= 3.8 Hz, ³J_PC= 1.4 Hz, C(CH₃)₃),

1

3

38.72 (dd, J_PC= 13.7 Hz, J_PC= 5.2 Hz, C(CH₃)₃), 118.35 (m, p-

C₆H₃(CF₃)₂), 125.68 (q, J_CF= 272.3 Hz, CF₃), 130.32 (qm, J_CF

1

2

=

31.6 Hz, M − C₆H₃(CF₃)₂), 135.88 (s, o-C₆H₃(CF₃)₂), 163.13 (q,

¹J_BC= 49.5 Hz, i-C₆H₃(CF₃)₂). MS (FAB): m/z 377.2 [(dtbpm)-

NiMe]⁺, 1617.5 [2*[(dtbpm)NiMe]⁺+ [BAr_f]⁻]⁺with correct isotope

patterns. IR (KBr): ν [cm⁻¹] 2965 w, 1612 w, 1481 w, 1356 s, 1167 s,

1135 s, 1026 w, 887 w, 839 w, 808 w, 715 m, 683 m, 670 m.

[(ptbpm-κ²P)NiMe(THF-d₈)]⁺[BAr_f]⁻. The isolated dimethyl

complex (ptbpm)NiMe₂(5.7 mg, 13.2 μmol) and 13.3 mg (13.2

μmol) of [H(OEt₂)₂]⁺[BAr_f]⁻were weighed into an NMR tube and

dissolved in 0.4 mL of d₈-THF. Gas evolution was observed, and the

Yield: 300 mg (85%) Mp: 110 °C dec. Anal. Calcd for C₁₇H₄₀P₂Ni:

1

C, 55.92; H, 11.04; P, 16.97. Found: C, 55.00; H, 11.19; P, 16.46. H

3

NMR (300 MHz, C₆D₆, 298 K): δ 0.50 (“t”, 3H, J_PH= 4.8 Hz,

3

NiCH₃), 0.54 (“t”, 3H, J_PH= 4.53 Hz, NiCH₃), 1.06 (dd, 6H, J_PH

=

219

dx.doi.org/10.1021/om200715w | Organometallics 2012, 31, 207−224

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Article

solution became yellow-orange. Ratio of isomers: 1.7:1 A:B (Figure 6)

on the basis of an integration of the ³¹P{¹H} NMR spectrum.

¹H NMR (300 MHz, d₈-THF, 298 K): δ −0.15 (dd, 3H, ³J_PH= 4.52

orange solution was cooled to −78 °C and used in the subsequent

reaction. A small fraction of the solid was extracted into C₆D₆, and the

¹H and ³¹P{¹H} NMR spectra were measured. The product was not

isolated, and no yield was determined.

3

Hz, J_PH= 2.83 Hz, NiCH₃), −0.08 (dd, 3H, J_PH= 5.27 Hz, J_PH

=

3

¹H NMR (C₆D₆, 300K, 300 MHz): δ 1.17 (m, 8H, C₆H₁₁), 1.28

2.45 Hz, NiCH₃), 1.39 (d, 18H, J_PH= 13.75 Hz, C(CH₃)₃), 1.47 (d,

3

18H, J_PH= 14.69 Hz, C(CH₃)₃), 7.57 (s, 8H, p-C₆H₃(CF₃)₂), 7.60

(d, 18H, J_HP= 12 Hz, C(CH₃)₃), 1.7 (br m, 8H, C₆H₁₁), 1.81 (“t”,

2H, ²J_HP= 7 Hz, PCH₂P), 1.95 (br, C₆H₁₁), 2.03 (br, C₆H₁₁), 2.70 (s,

(m, 12H, o,p-C₆H₅), 7.79 (s, 16H, o-C₆H₃(CF₃)₂), 7.90 (m, 8H, m-

C₆H₅). ³¹P{¹H} NMR (122 MHz, d₈-THF, 298 K): δ −29.2 (d, ²J_PP

=

3

4H, CH₂C₆H₅), 7.12 (t, 2H, J_HH= 7.14 Hz, C₆H₅), 7.31 (m, 4H,

2

3

C₆H₅), 7.58 (d, 4H, J_HH= 7.35 Hz, C₆H₅). ³¹P{¹H} NMR (C₆D₆,

26.6 Hz, PPh₂, A), 4.9 (d, J_PP= 28.8 Hz, PPh₂, B), 17.2 (d, J_PP

28.9 Hz, P(C(CH₃)₃)₂, B), 43.3 (d, ²J_PP= 26.5 Hz, P(C(CH₃)₃)₂, A).

[(iptbpm-κ²P)NiMe(THF-d₈)]⁺[BAr_f]⁻. The reaction was con-

ducted in a manner exactly analogous to that for the ptbpm analogue.

Isomer B is formed in a 6-fold excess (determined by ³¹P{¹H} NMR

spectroscopy).

2

300K, 121.5 MHz): δ −6.24 (d, J_PP= 30 Hz, PCy₂), 18.8 (d, J_PP

=

30 Hz, P(C(CH₃)₃)₂).

(iptbpm-κ²P)NiBz₂. The dichloride complex (iptbpm-κ²P)NiCl₂

(164 mg, 0.405 mmol) was suspended in 10 mL of THF and cooled to

−25 °C. While the suspension was stirred, 2 equiv of a benzyl

Grignard solution (0.81 mL of a 1.0 M solution in diethyl ether diluted

with 10 mL of THF) was added. The solution became red. After

addition of the Grignard reagent the reaction was stirred at the same

temperature for a further 30 min. The solvent was then removed under

dynamic vacuum, and the residue was extracted into toluene and the

extract filtered through Celite. Careful addition of pentane and cooling

to −40 °C led to the precipitation of the product.

¹H NMR (300 MHz, d₈-THF, 298 K): δ −0.39 (dd, 3H, ³J_PH= 2.60

Hz, ³J_PH= 4.34 Hz, NiCH₃, B), −0.31 (br s, NiCH₃, A), 1.30 (dd, 6H,

3

²J_HH= 7.06 Hz, J_PH= 15.04 Hz, CH(CH₃)₂), 1.46 (d, 18H, J_PH

=

13.54 Hz, C(CH₃)₃), 2.4 (m, 2H, PCH₂P), 2.6 (m, 2H, CH(CH₃)₂).

³¹P{¹H} NMR (122 MHz, d₈-THF, 298 K): δ −9.6 (d, ²J_PP= 20.9 Hz,

2

P(ⁱPr)₂, A), 14.1 (d, J_PP= 21.4 Hz, P(ⁱPr)₂, B), 27.7 (d, J_PP= 21.3

2

Hz, P(C(CH₃)₃)₂, B), 41.3 (d, J_PP= 20.9 Hz, P(C(CH₃)₃)₂, A).

[(dcpm-κ²P)NiMe(THF)]⁺[BAr_f]⁻. The reaction was conducted in

a manner identical to that for the ptbpm analogue.

Yield: 119.2 mg (57%). Mp: 83 °C dec. Anal. Calcd for C₂₉H₄₈P₂Ni:

1

C, 67.33; H, 9.35. Found: C, 67.20; H, 9.37. H NMR (300 MHz,

¹H NMR (300 MHz, d₈-THF, 298 K): δ −0.44 (dd, 3H, ³J_PH= 2.64

3

2

C₆D₆, 298 K): δ 0.91 (dd, 6H, J_PH= 11.7 Hz, J_HH= 7.1 Hz, CH-

3

2

Hz, J_PH= 4.52 Hz, NiCH₃), 1.20 − 2.41 (br m, 44H, C₆H₁₁), 2.46

(CH₃)₂), 1.05 (dd, 6H, J_PH= 14.0 Hz, J_HH= 7.2 Hz, CH(CH₃)₂),

1.20 (d, 18H, J_PH= 12.0 Hz, C(CH₃)₃), 1.66 (t, 2H, J_PH= 7.2 Hz,

PCH₂P) 1.82 (dsept, 2H, J_PH= 2.4 Hz, J_HH= 7.2 Hz, CH(CH₃)₂),

2

3

2

(dd, 2H, J_PH= 8.10 Hz, J_PH= 11.11 Hz, PCH₂P), 7.57 (s, 4H, p-

C₆H₃(CF₃)₂), 7.79 (s, 8H, o-C₆H₃(CF₃)₂). ³¹P{¹H} NMR (122 MHz,

d₈-THF, 298 K): δ −13.1 (d, ²J_PP= 34.0 Hz), 23.0 (d, ²J_PP= 34.0 Hz).

(dtbpm-κ²P)NiBz₂. The dichloride complex (dtbpm-κ²P)NiCl₂

(60 mg, 138.6 μmol) was suspended in 15 mL of pentane and cooled

to −40 °C, the benzyl Grignard solution (0.28 mL of 1.0 M in diethyl

ether, 280 μmol) was added, and the reaction mixture was stirred for 4

h at that temperature. The pentane solution became pale red. The

solvent was decanted, and the solid product was washed twice with

pentane. Finally, the product was extracted into diethyl ether, and the

extract was filtered through a cold Celite pad and used directly in the

synthesis of [(dtbpm-κ²P)NiBz]⁺[BAr_f]⁻. The ³¹P{¹H} NMR spec-

trum of a part of the product was collected after filtration, upon

removing the diethyl ether under vacuum. No yield was determined

because of the product’s high instability.

2

3

7.07 (t, 2H, J_HH= 7.2 Hz, p-C₆H₅), 7.26 (“t”, 4H, J_HH= 7.5 Hz, m-

C₆H₅), 7.52 (d, 4H, J_HH= 7.5 Hz, o-C₆H₅). ³¹P{¹H} NMR (122

3

MHz, C₆D₆, 298 K): δ 1.71 (d, J_PP= 27.8 Hz, P(ⁱPr)₂), 17.60 (d,

2

²J_PP= 27.8 Hz, P(C(CH₃)₃)₂). ¹³C{¹H} NMR (75 MHz, C₆D₆, 298

K): δ 18.9 (s, CH(CH₃)₂), 20.6 (s, CH(CH₃)₂), 24.7 (d, ¹J_PC= 8.3 Hz,

CH(CH₃)), 29.9 (d, ²J_PC= 5.5 Hz, C(CH₃)₃), 30.15 (m, N = 13.2 Hz,

2

PCH₂P), 34.8 (dd, J_PC= 7.3 Hz, J_PC= 5.3 Hz, CH₂C₆H₅), 38.2 (s,

C(CH₃)₃), 121.18 (s, o-C₆H₅), 126.22 (s, p-C₆H₅), 128.74 (s, m-

C₆H₅), 154.5 (s, i-C₆H₅). MS (FAB): m/z 516 [M]⁺(isotope pattern

not completely correct due to overlap), 425 [M + H − toluene]⁺

(correct isotope pattern). IR (KBr): ν [cm⁻¹] 3061 w, 3027 m, 2957 s,

2869 s, 1602 w, 1494 w, 1468 m, 1454 m, 1385 m, 1365 m, 1262 m,

1178 s, 1163 s, 1095 s, 1022 m, 941 m, 885 w, 815 s, 794 w, 752 s, 698

s, 641 w, 591 w, 520 w, 483 w.

³¹P{¹H} NMR (122 MHz, d₈-THF, 228 K): δ 11.1 (s).

(ptbpm-κ²P)NiBz₂. The dichloride complex (ptbpm-κ²P)NiCl₂

(200 mg, 0.42 mmol) was suspended in 10 mL of THF and cooled

to −25 °C. Over a period of 45 min, 0.84 mL (0.84 mmol) of a benzyl

Grignard solution (1 M in diethyl ether) diluted with 10 mL of THF

was added. The reaction mixture was then stirred for another 45 min

at that temperature, following which the THF was removed under

dynamic vacuum and the product was extracted into toluene. Filtration

through Celite led to a red solution. The volume of toluene was

reduced by half under dynamic vacuum, and the solution was cooled

to −40 °C, which resulted in crystallization of the product. The

crystals were washed in pentane and dried under vacuum.

(dcpm-κ²P)NiBz₂. The dichloride complex (dcpm-κ²P)NiCl₂

(200 mg, 0.37 mmol) was suspended in pentane (10 mL). At room

temperature, 0.74 mL (0.74 mmol) of a benzyl Grignard solution (1 M

in diethyl ether) was added. After 30 min, the solution was pale red,

and the solid had changed color slightly. The product was extracted

into toluene and the extract filtered through Celite. Pentane was

carefully added to the flask and the product crystallized at −40 °C.

Yield: 175.2 mg (73%). Mp: 96 °C dec. Anal. Calcd for C₃₉₁H₆₀P₂Ni:

C, 72.1; H, 9.31; P, 9.54. Found: C, 72.3; H, 9.48; P, 9.39. H NMR

(500 MHz, C₆D₆, 298 K): δ 1.16 (m, 16H, C₆H₁₁), 1.36 (m, 8H,

C₆H₁₁), 1.74 (m, 16H, C₆H₁₁), 2.10 (m, 6H, C₆H₁₁and PCH₂P), 2.69

Yield: 152 mg (62%). Mp: 49 °C dec. Anal. Calcd for C₃₅H₄₄P₂Ni:

3

1

(s, 4H, CH₂C₆H₅), 7.04 (t, 2H, J_HH= 7.35 Hz, p-C₆H₅), 7.24 (“t”,

C, 71.82; H, 7.58; P, 10.58. Found: C, 71.64; H, 7.73; P, 10.34. H

3

4H, J_HH= 7.70 Hz, m-C₆H₅), 7.49 (d, 4H, J_HH= 7.70 Hz, o-C₆H₅).

NMR (300 MHz, C₆D₆, 298 K): δ 1.06 (d, 18H, J_PH= 12.5 Hz,

³¹P NMR (122 MHz, C₆D₆, 298 K): δ −4.13 (s). ¹³C NMR (126

MHz, C₆D₆, 298 K): δ 17.03 (t, J_PC= 14.2 Hz, PCH₂P), 26.73 (s,

C(CH₃)₃), 2.39 (dd, 2H, ²J_PH= 8.16 Hz, ²J_PH= 6.66 Hz, PCH₂P), 2.89

(s, 4H, CH₂C₆H₅), 7.10 (br m, 16H, C₆H₅), 7.55 (m, 4H, C₆H₅).

1

2

³¹P{¹H} NMR (122 MHz, C₆D₆, 298 K): δ −11.5 (d, J_PP= 28.6 Hz,

C₆H₁₁), 27.59 (s, C₆H₁₁), 27.80 (m, C₆H₁₁), 29.28 (s, C₆H₁₁), 30.41

(s, C₆H₁₁), 34.83 (m, CH₂C₆H₅), 120.95 (s, o-C₆H₅), 128.94 (s, m-

C₆H₅), 129.47 (s, p-C₆H₅), 155.35 (s, i-C₆H₅). MS (FAB): m/z 557

[M + H − toluene]⁺with correct isotope pattern. IR (KBr): ν [cm⁻¹]

3061 w, 3027 w, 2927 s, 2825 m, 2361 s, 2342 m, 1449 w, 1262 m,

1217 w, 1161 m, 1098 s, 1022 s, 889 w, 855 w, 800 s, 698 m, 669 w.

[(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph)]⁺[BAr_f]⁻. In a Schlenk flask,

200 mg (0.37 mmol) of (η²-trans-stilbene)[(dtbpm-κ²P)Ni⁰] and

372.5 mg (0.37 mmol) of [H(OEt₂)₂]⁺[BAr_f]⁻were dissolved at 0 °C

in 20 mL of diethyl ether. After the mixture was stirred for 25 min,

20 mL of pentane was added, which led to the precipitation of a pale

brown solid. The solution was removed via cannula, and the solid was

washed twice with pentane (5 mL each) and dried under vacuum.

2

PPh₂), 22.3 (d, J_PP= 28.6 Hz, P(C(CH₃)₃)₂).

(ctbpm-κ²P)NiBz₂. The dichloride complex (ctbpm-κ²P)NiCl₂

(0.44 g, 0.9 mmol) was weighed in the box into a round-bottomed

flask equipped with a magnetic stirrer. Pentane (40 mL) was added,

and the slurry was cooled to −60 °C. Benzyl Grignard (2.6 mL of

0.71 M solution in diethyl ether, 1.8 mmol) was added, and the slurry

was stirred at a temperature between −60 and −40 °C for 4 h. During

this time, the solid observed on the walls of the flask changed from red

to orange in color. After 4 h, stirring was stopped and the slurry was

allowed to settle for 1 h. Decantation was attempted; however, a

significant amount of solid was transferred as well. The residue was

dried in vacuo and then extracted into diethyl ether, and the resulting

220

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Yield: 476 mg (0.34 mmol, 91%). Mp: 158 °C dec. Anal. Calcd for

C₄₃H₆₃P₂NiBF₂₄: C, 53.76; H, 4.51; P, 4.40. Found: C, 53.67; H, 4.60;

7.51 (m, 4H, p-C₆H₅on P, C + D), 7.62 (m, 1H, p-C₆H₅on Ni, D),

7.63 (m, 8H, m-C₆H₅on P, C + D), 7.66 (s, 8H, p-C₆H₃(CF₃)₂, C + D),

7.78 (s, 16H, o-C₆H₃(CF₃)₂, C + D), 7.84 (m, 4H, m-C₆H₅on Ni,

C + D), 7.90 (m, 8H, m-C₆H₅on P, C + D). ³¹P{¹H} NMR (300

MHz, d₆-acetone, 298 K): δ −18.1 (d, ²J_PP= 33.5 Hz, PPh₂, C), −6.1

P, 4.31. ¹H NMR (500 MHz, d₆-acetone, 298 K): δ 1.26 (d, 9H, ³J_PH

=

3

13.8 Hz, C(CH₃)₃), 1.43 (d, 9H, J_PH= 13.8 Hz, C(CH₃)₃), 1.61

(d, 9H, ³J_PH= 14.2 Hz, C(CH₃)₃), 1.63 (d, 9H, ³J_PH= 14.2 Hz, C(CH₃)₃),

3.13 (m, 2H, CH₂C₆H₅), 3.27 (m, 2H, PCH₂P), 3.83 (m, 1H,

NiCHCH₂), 6.86 (d, 1H, o-C₆H₅on Ni), 7.13 (m, N = 44.9 Hz, 6H,

2

(d, J_PP= 30.4 Hz, PPh₂, D), 26.1 (d, J_PP= 30.4 Hz, P(C(CH₃)₃)₂,

2

D), 43.0 (d, J_PP= 33.5 Hz, P(C(CH₃)₃)₂, C). ¹³C{¹H} NMR (126

3

2

C₆H₅and o-C₆H₅on Ni), 7.52 (“t”, J_HH= 7.5 Hz, 1H, m-C₆H₅on

MHz, d₆-acetone, 298 K): δ 29.02 (d, J_CP= 4.7 Hz, C(CH₃)₃, C),

Ni), 7.52 (s, 4H, p-C₆H₃(CF₃)₂), 7.58 (“t”, ³J_HH= 7.5 Hz, 1H, m-C₆H₅

on Ni), 7.74 (m, 1H, p-C₆H₅on Ni), 7.79 (s, 8H, o-C₆H₃(CF₃)₂).

³¹P{¹H} NMR (122 MHz, d₈-THF, 298 K): δ 16.8 (d, ²J_PP= 20.9 Hz),

29.14 (d, J_CP= 5.5 Hz, C(CH₃)₃, D), 29.75 (m, CH₂C₆H₅, C + D),

2

35.96 (“t”, ¹J_CP= 6.13 Hz, C(CH₃)₃, C + D), 37.19 (dd, ²J_trans‑CP= 33.9

Hz, ²J_cis‑CP= 3.3 Hz, PCH₂P, C), 39.57 (d, ²J_trans‑CP= 25.5 Hz, PCH₂P,

D), 114.12 (dd, ²J_trans‑CP= 6.1 Hz, ²J_cis‑CP= 1.4 Hz, o-Ph-C, D), 114.77

2

29.6 (d, J_PP= 20.9 Hz). ¹³C{¹H} NMR (75 MHz, d₈-THF, 298 K):

2

(dd, J_trans‑CP= 5.6 Hz, J_trans‑CP= 1.9 Hz, o-C₆H₅, C), 117.93 (m, i-

C₆H₅), 118.65 (m, p-C₆H₃(CF₃)₂), 118.68 (m, i-C₆H₅), 125.80 (q,

δ 24.8 (m, PCH₂P), 30.7−31.6 (m, C(CH₃)₃), 37.0 (m, C(CH₃)₃),

37.7 (s, NiCHCH₂C₆H₅), 38.6 (m, C(CH₃)₃), 53.9 (d, ²J_PC= 26.1 Hz,

NiCH), 109.1 (m, o-C₆H₅on Ni), 118.1 (s, p-C₆H₃(CF₃)₂), 125.4 (q,

¹J_CF= 273 Hz, CF₃), 127.2 (s, o-C₆H₅), 128.6 (s, m-C₆H₅), 129.3 (s,

p-C₆H₅), 129.9 (q, ²J_CF= 31 Hz, M − C₆H₃(CF₃)₂), 135.5 (s, o-C₆H₃-

(CF₃)₂), 136.2 (s, m-C₆H₅on Ni), 136.8 (s, m-C₆H₅on Ni), 162.7 (q,

¹J_CB= 50 Hz, i-C₆H₃(CF₃)₂]. MS (FAB): m/z = 543.4 [cation]⁺with

correct isotope pattern. IR (KBr): ν [cm⁻¹] 2966 w, 1611 w, 1473 w,

1355 m, 1279 s, 1163 m, 1128 s, 885 w, 839 w, 744 w, 716 w, 682 w,

669 w.

2

¹J_CF= 272.3 Hz, CF₃), 130.2 (qm, J_CF= 31.6 Hz, m-C₆H₃(CF₃)₂),

130.48 (s, p-C₆H₅), 130.56 (s, p-C₆H₅), 130.74 (s, m-C₆H₅), 130.83 (s,

4

m-C₆H₅), 133.20 (d, J_CP= 1.8 Hz, p-C₆H₅on Ni), 133.47 (d, J_CP

=

2

2.8 Hz, p-C₆H₅on Ni), 133.93 (d, J_CP= 3.8 Hz, o-C₆H₅), 134,03 (d,

²J_CP= 3.8 Hz, o-C₆H₅), 135.76 (s, o-C₆H₃(CF₃)₂), 137.34 (br, m-C₆H₅

on Ni), 137.75 (d, ³J_CP= 1.9 Hz, m-C₆H₅on Ni), 162.81 (q, ¹J_BC= 49.5

Hz, i-C₆H₃(CF₃)₂), i-C of benzyl not observed. IR (KBr): ν [cm⁻¹]

2966 w, 1611 w, 1470 w, 1439 w, 1355 s, 1279 s, 1124 s, 1019 w, 929 w,

887 m, 838 m, 808 w, 762 w, 744 w, 715 m, 682 m, 669 m, 521 w,

485 w. MS (FAB): m/z 493.2 [cation]⁺with correct isotope pattern.

[(ctbpm-κ²P)NiBz]⁺[BAr_f]⁻. The cold ethereal extract from the

synthesis of (ctbpm-κ²P)NiBz₂was filtered directly into a flask con-

taining solid [H(OEt₂)₂]⁺[BAr_f]⁻, which was precooled to −78 °C.

The color of the solution lightened, and after all of the ether solution

had been added some unidentified white precipitate was observed in

the bottom of the flask. The solution was warmed to room tempera-

ture at that point and filtered into a clean Schlenk flask. The volume of

solvent was reduced under dynamic vacuum, and the dark orange solu-

tion was cooled to −60 °C. A small amount of flaky solid precipitated.

Yield: 0.4 g, 32% based on (ctbpm-κ²P)NiCl₂. Mp: 190−195 °C. The

NMR spectra contain the two isomers C and D in a 1:1.25 ratio

(Figure 8).

[(dtbpm-κ²P)NiBz]⁺[BAr_f]⁻. The synthesis proceeded directly

from the preparation of the dibenzyl complex, which was extracted

into diethyl ether (6 × 3 mL) at −78 °C. The ethereal solution was fil-

tered through Celite directly onto 100 mg (99 μmol) of [H(OEt₂)₂]⁺-

[BAr_f]⁻at 0 °C, which led to an orange solution. During the reaction,

a small amount of an unidentified colorless solid precipitated. The

orange solution was then warmed to room temperature and decanted

from the precipitate. The volume of solvent was reduced under dyna-

mic vacuum, and addition of pentane led to the precipitation of the

orange product, which was recrystallized from ether/pentane.

Yield: 46 mg (25%). Mp: 195 °C. Anal. Calcd for C₅₆H₅₇F₂₄P₂NiB:

C, 51.05; H, 4.36; P, 4.70. Found: C, 50.98; H, 4.19; P, 4.73. ¹H NMR

3

(300 MHz, d₆-acetone, 298 K): δ 1.33 (d, 18H, J_PH= 13.9 Hz,

3

C(CH₃)₃), 1.58 (d, 18H, J_PH= 14.5 Hz, C(CH₃)₃), 2.60 (dd, 2H,

3

¹H NMR (THF-d₈, 300 K, 300 MHz): δ 1.23 (d, J_HP= 14.2 Hz,

2

3

²J_PH= 6.0 Hz, J_PH= 3.2 Hz, PCH₂P), 3.39 (dd, 2H, J_PH= 9.21 Hz,

3

³J_PH= 1.5 Hz, CH₂C₆H₅), 6.77 (d, 2H, J_HH= 6.8 Hz, o-C₆H₅), 7.52

3

18H, C(CH₃)₃, D), 1.36 (br, 12H, C₆H₁₁), 1.46 (d, J_HP= 14.6 Hz,

3

18H, C(CH₃)₃, C), 1.60 (br, 2H, C₆H₁₁), 1.91 (br, 8H, C₆H₁₁), 2.05

(t, 1H, J_HH= 7.35, p-C₆H₅), 7.66 (s, 4H, p-C₆H₃(CF₃)₂), 7.77 (m,

3

10H, o-C₆H₃(CF₃)₂+ m-C₆H₅). ³¹P{¹H} NMR (122 MHz, C₆D₆, 298

K): δ 20.0 (d, ²J_PP= 13.0 Hz), 36.0 (d, ²J_PP= 13.0 Hz). ¹³C{¹H} NMR

(126 MHz, d₆-acetone, 298 K): δ = 26.61 (t, ¹J_PC= 13.7 Hz, PCH₂P),

31.11 (d, ²J_PC= 2.4 Hz, C(CH₃)₃), 31.19 (d, ²J_PC₁= 7.6 Hz, C(CH₃)₃),

(br, 4H, C₆H₁₁), 2.26 (br, 2H, C₆H₁₁), 2.43 (d, J_HP= 5.9 Hz, 2H,

3

CH₂C₆H₅, D), 2.49 (d, J_HP= 5.9 Hz, 2H, CH₂C₆H₅, C), 2.95 (“t”,

4H, ²J_HP= 8.7 Hz, PCH₂P, C + D), 6.50 (d, 2H, ³J_HH= 7.3 Hz, C₆H₅,

D), 6.54 (d, 2H, ³J_HH= 7.3 Hz, C₆H₅, C), 7.40 (m, 4H, C₆H₅, C + D),

7.57 (8H, p-C₆H₃(CF₃)₂, C + D), 7.67 (pseudo q, 4H, C₆H₅, C + D),

7.79 (16H, o-C₆H₃(CF₃)₂, C + D). ³¹P{¹H} NMR (THF-d₈, 300 K,

1

3

37.02 (d, J_PC= 5.2 Hz, C(CH₃)₃), 37.49 (dd, J_PC= 10.4 Hz, J_PC

=

4.7 Hz, C(CH₃)₃), 54.88 (m, N = 75.5 Hz, CH₂C₆H₅), 114.17 (d, ³J_PC

2

121.5 MHz): δ −7.6 (d, ²J_PP= 23 Hz, PCy₂, C), 9.5 (d, J_PP= 21 Hz,

= 4.7 Hz, o-C₆H₅), 118.48 (s, p-C₆H₃(CF₃)₂), 125.42 (q, ¹J_CF= 271.82

2

PCy₂, D), 24.2 (d, ²J_PP= 21 Hz, P(C(CH₃)₃)₂, D), 40.0 (d, J_PP= 23

2

Hz, CF₃), 128.66 (p-C₆H₅), 129.98 (qm, J_CF= 31 Hz, m-

Hz, P(C(CH₃)₃)₂, C).

C₆H₃(CF₃)₂), 135.58 (s, o-C₆H₃(CF₃)₂), 136.64 (d, J = 1.9 Hz, m-

[(iptbpm-κ²P)NiBz]⁺[BAr_f]⁻. The dibenzyl complex (iptbpm-κ²P)-

NiBz₂(60 mg, 116 μmol) was weighed into a Schlenk tube with

[H(OEt₂)₂]⁺[BAr_f]⁻(117.5 mg, 116 μmol) and dissolved in 15 mL of

diethyl ether. The solution became red and was stirred for an hour at

room temperature. The volume of solvent was then reduced by half

under dynamic vacuum. Addition of pentane (10 mL) led to preci-

pitation of the product, which was then recrystallized from diethyl

ether and washed with pentane.

1

C₆H₅), 162.64 (q, J_CB= 49.9 Hz, i-C₆H₃(CF₃)₂). MS (FAB): m/z

453.2 [cation⁺] with correct isotope pattern. IR (KBr): ν [cm⁻¹] 2966

w, 1611 w, 1476 w, 1355 m, 1277 s, 1168 m, 1131 s, 888 w, 839 w, 807

w, 757 w, 745 w, 716 w, 682 m, 670 m.

[(ptbpm-κ²P)NiBz]⁺[BAr_f]⁻. The dibenzyl complex (ptbpm-κ²P)-

NiBz₂(24 mg, 41 μmol) was dissolved in 5 mL of diethyl ether, and

[H(OEt₂)₂]⁺[BAr_f]⁻(41.5 mg, 41 μmol) in 5 mL of diethyl ether was

added. The red solution was stirred for 1 h, and the volume of solvent

was reduced by half under dynamic vacuum. Addition of pentane led

to the precipitation of the product, which was then recrystallized, from

2 mL of diethyl ether.

Yield: 93 mg (72%). Mp: 208 °C dec. Isomer ratio: 1:1.5 = C:D

(Figure 8). Anal. Calcd for C₄₆H₄₇F₂₄₁P₂NiB: C, 50.30; H, 4.14; P, 4.80.

Found: C, 50.60; H, 4.18; P, 4.91. H NMR (300 MHz, d₆-acetone,

3

298 K): δ 1.09 (dd, 6H, J_PH= 15.4 Hz, J_HH= 7.26 Hz, CH(CH₃)₂,

Yield: 47 mg (84%). Mp: 171 °C dec. Ratio of isomers C:D = 1.6:1

(from integration of the ³¹P resonances) (Figure 8). Anal. Calcd for

C₆₀H₄₉F₂₄P₂BNi: C, 53.09; H, 3.64; P, 4.56. Found: C, 53.24; H, 3.78;

C), 1.19 (dd, 6H, ³J_PH= 16.2 Hz, ³J_HH= 7.26 Hz, CH(CH₃)₂, C), 1.27

3

(d, J_PH= 14.4 Hz, 18H, C(CH₃)₃, D), 1.37 (dd, 6H, J_PH= 2.3 Hz,

³J_HH= 7.26 Hz, CH(CH₃)₂, D), 1.43 (dd, 6H, J_PH= 2.8 Hz, J_HH

=

3

1

P, 4.49. H NMR (500 MHz, d₆-acetone, 298 K): δ 1.19 (d, 18H,

7.23 Hz, CH(CH₃)₂, D), 1.49 (d, 18H, ³J_PH= 14.9 Hz, C(CH₃)₃, C),

2.35 (m, 2H, CH(CH₃)₂, C), 2.72 (m, 2H, CH(CH₃)₂, D), 2.57 (dd,

³J_PH= 14.9 Hz, C(CH₃)₃, D), 1.41 (d, 18H, ³J_PH= 15.2 Hz, C(CH₃)₃,

C), 2.89 (dd, 2H, ²J_PH= 7.0 Hz, ²J_PH= 1.55 Hz, PCH₂P, C), 2.92 (dd,

2

3

2H, J_PH= 6.0 Hz, J_PH= 2.25 Hz, PCH₂P, D), 2.60 (dd, 2H, J_PH

=

2H, J_PH= 6.1 Hz, J_PH= 1.85 Hz, PCH₂P, D), 3.76 (dd, 2H, J_PH

=

2

3

6.4 Hz, J_PH= 2.1 Hz, PCH₂P, C), 3.10 (t, 2H, J_PH= 8.1 Hz,

11.3 Hz, J_PH= 7.9 Hz, CH₂C₆H₅, D), 3.80 (t, 2H, J_PH= 9.4 Hz,

CH₂C₆H₅, D), 3.11 (t, 2H, ³J_PH= 9.2 Hz, CH₂C₆H₅, C), 6.63 (d, 1H,

3

CH₂C₆H₅, C), 6.88 (d, 4H, J_HH= 6.3 Hz, o-C₆H₅on P, D), 6.93 (d,

4H, ³J_HH= 7.15 Hz, o-C₆H₅on P, C), 7.49 (m, 1H, p-C₆H₅on Ni, C),

³J_HH= 7.4 Hz, o-C₆H₅, D), 6.69 (d, 1H, J_HH= 7.2 Hz, o-C₆H₅, C),

3

221

dx.doi.org/10.1021/om200715w | Organometallics 2012, 31, 207−224

Organometallics

Article

7.45 (m, 1H, C₆H₅), 7.66 (s, 8H, p-C₆H₃(CF₃)₂, C + D), 7.73 (m, 1H,

C₆H₅), 7.78 (s, 16H, o-C₆H₃(CF₃)₂, C + D). ³¹P{¹H} NMR (122

absences of hkl values using XPREP.⁷³The structures were solved by

direct methods unless otherwise specified and expanded using Fourier

techniques. All non-hydrogen atoms were refined anisotropically;

hydrogen atoms were included in calculated positions and not refined

unless otherwise specified. The final cycle of full-matrix least-squares

refinement was based on all reflections, and converged. The function

minimized was ∑w((F_o)²− (F_c)²)². All calculations were performed

using the SHELXTL crystallographic software package of Bruker.⁷⁴All

of the complexes containing the BAr_fanion have some disordered

CF₃groups, which have been modeled using sensible geometric con-

trainsts. Further details are only provided for structures for which

other techniques were used or disorder was modeled.

2

MHz, C₆D₆, 298 K): δ 1.4 (d, J_PP= 24.7 Hz, P(ⁱPr)₂, C), 18.4 (d,

²J_PP= 23.2 Hz, P(ⁱPr)₂, D), 24.1 (d, ²J_PP= 22.9 Hz, P(C(CH₃)₃)₂, D),

40.0 (d, ²J_PP= 24.6 Hz, P(C(CH₃)₃)₂, C). ¹³C{¹H} NMR (126 MHz,

2

d₈-THF, 298 K): δ 19.35 (d, J_PC= 10.8 Hz, CH(CH₃)₂), 19.54 (d,

1

²J_PC= 6.6 Hz, CH(CH₃)₂), 22.58 (d, J_PC= 17.4 Hz, CH(CH₃)₂),

1

22.87 (d, ¹J_PC= 17.7 Hz, CH(CH₃)₂), 27.14 (dd, J_PC= 16.5 Hz, J_PC

= 6.1 Hz, PCH₂P), 29.40 (d, ²J_PC= 4.7 Hz, C(CH₃)₃), 29.51 (d, ²J_PC

5.6 Hz, C(CH₃)₃), 35.17 (dd, ¹J_PC= 25.0 Hz, ³J_PC= 4.3 Hz, C(CH₃)₃),

35.97 (dd, ¹J_PC= 24.0 Hz, ³J_PC= 4.2 Hz, C(CH₃)₃), 36.39 (dd, ²J_PC

=

2

4.2 Hz, J_PC= 5.7 Hz, CH₂C₆H₅), 36.79 (dd, J_PC= 5.7 Hz, J_PC₂= 9.9

(dtbpm-κ²P)NiCl₂·3CH₂Cl₂. The structure was solved by Patterson

methods. The nickel atom lies on a special position, as does the carbon

atom of one CH₂Cl₂; therefore, the asymmetric unit consists of half

the molecule and one and a half methylene chloride units. One of

the methylene chloride units is disordered, and the disorder has been

modeled as two positions.

2

Hz, CH₂C₆H₅), 113.74 (d, J_PC= 5.6 Hz, o-C₆H₅), 114.08 (d, J_PC

=

5.2 Hz, o-C₆H₅), 117.32 (m, i-C₆H₅), 117.77 (m, i-C₆H₅), 118.40

1

(m, p-C₆H₃(CF₃)₂), 125.72 (q, J_CF= 272.2 Hz, CF₃), 128.54 (m, p-

2

C₆H₅), 128.84 (m, p-C₆H₅), 130.24 (qm, J_CF= 31.6 Hz, m-C₆H₃-

(CF₃)₂), 135.81 (s, o-C₆H₃(CF₃)₂), 136.72 (s, m-C₆H₅), 136.94 (s, m-

C₆H₅), 163.02 (q, ¹J_BC= 49.9 Hz, i-C₆H₃(CF₃)₂). IR (KBr): ν [cm⁻¹]

2968 w, 1611w, 1473 w, 1355 s, 1279 s, 1164 s, 1127 s, 888 m, 839 w,

760 w, 744 w, 715 m, 682 m, 670 m.

(ctbpm-κ²P)NiCl₂. There is some disorder in the cyclohexyl rings;

however, the second chair position is not completely visible in the

difference map.

[(dcpm-κ²P)NiBz]⁺[BAr_f]⁻. The dibenzyl complex (dcpm-

κ²P)NiBz₂(20 mg, 30.8 μmol) was suspended in 10 mL of diethyl

ether and the suspension cooled to −60 °C, and [H(OEt₂)₂]⁺[BAr_f]⁻

(31.2 mg, 30.8 mol) dissolved in 5 mLof diethyl ether was added. The

reaction mixture was gradually warmed to room temperature, and no

visible reaction occurred. After stirring for 24 h at room temperature,

the solution was orange, and addition of pentane led to crystallization

of the product, which was recrystallized from diethyl ether/pentane.

Yield: 24 mg (55%). Mp: 167 °C dec. Anal. Calcd for C₆₄H₆₅-

P₂F₂₄BNi: C, 54.07; H, 4.61; P, 4.36. Found: C, 53.86; H, 4.96; P,

4.38. ¹H NMR (500 MHz, CD₂Cl₂, 298 K): δ 1.0−2.1 (m, 44H,

C₆H₁₁), 2.30 (d, 2H, ³J_PH= 4.7 Hz, CH₂C₆H₅), 2.59 (t, 2H, ²J_PH= 9.0

(ptbpm-κ²P)NiMe₂. The methyl protons were refined. One

reflection was omitted from the refinement as it was in the beam stop.

[(dtbpm-κ²P)NiMe(THF)]⁺[BAr_f]⁻·2THF. The geometries of the two

THF molecules of crystallization were coupled for refinement.

[(ptbpm-κ²P)NiMe(THF)]⁺[BAr_f]⁻. The structure was solved with

ESEL-1 and transformed into P1.

̅

[(dcpm-κ²P)NiBz]⁺[BAr_f]⁻·THF. The two unique molecules in the

asymmetric unit have been refined as separate blocks.

[(dtbpm-κ²P)Ni(η³-CH(CH₂Ph)Ph]⁺[BAr_f]⁻. The structure was

solved using Patterson methods. The hydrogen atoms were observed

in the difference map; those bound to dtbpm were included in cal-

culated positions, while the remainder of the hydrogens were freely

refined.

3

Hz, PCH₂P), 6.33 (d, 2H, J_HH= 7.3 Hz, o-C₆H₅), 7.30 (m, 1H,

3

p-C₆H₅), 7.56 (s, 4H, p-C₆H₃(CF₃)₂), 7.61 (t, 2H, J_HH= 7.7 Hz, m-

C₆H₅), 7.72 (s, 8H, o-C₆H₃(CF₃)₂). ³¹P{¹H} NMR (122 MHz, d₆-

acetone, 298 K): δ −3.5 (d, ²J_PP= 37.9 Hz), 12.6 (d, ²J_PP= 37.9 Hz).

GPC Analysis. The polyethylene samples obtained were analyzed

by high-temperature GPC, using a Waters-150C instrument with an IR

detector device (λ 3.5 mm). The solvent used was 1,2,4-trichloro-

benzene at 135 °C. Calibration was achieved by using linear polyethyl-

ene standards with narrow and broad molecular weight distribution.

Calculations. The DFT calculations were carried out using the

B3LYP functional in the Gaussian 98 package.⁷⁵Basis sets used were

SDD on Ni and 6-31G(d) for the remainder of the heavy atoms.

1

¹³C{¹H} NMR (75 MHz, d₆-acetone, 298 K): δ 19.56 (t, J_PC= 20.9

Hz, PCH₂P), 25.20 (s, C₆H₁₁), 25.34 (br, C₆H₁₁), 26.40 (m, C₆H₁₁),

1

3

28.55 (m, C₆H₁₁), 33.80 (dd, J_PC= 12.6 Hz, J_PC= 4.4 Hz, CH-

2

(CH₂)₅), 34.94 (dd, J_PC= 24.7 Hz, J_PC= 3.3 Hz, CH₂C₆H₅), 35.45

(dd, ¹J_PC= 16.5 Hz, ³J_PC= 5.5 Hz, i-C₆H₁₁), 112.22 (d, ²J_PC= 7.7 Hz,

o-C₆H₅), 117.12 (m, i-C₆H₅), 117.45 (m, p-C₆H₃(CF₃)₂), 126.82 (m,

p-C₆H₅), 134.57 (s, o-C₆H₃(CF₃)₂), 135.68 (s, m-C₆H₅).

Polymerization of Ethylene. In a typical experiment, [(dtbpm-

κ²P)NiMe(THF)]⁺[BAr_f]⁻(5.0 mg) was weighed into a 10 mL thick-

walled glass autoclave (provided by BASF, pressure tolerance ≤10 bar)

equipped with a magnetic stirrer, and diethyl ether (5 mL) was added.

The autoclave was then cooled to 0 °C with stirring and pressurized

with ethylene (7 bar). After approximately 15 min, the orange solution

became cloudy and the pressure dropped slightly. Repressurization

with ethylene to maintain a pressure of 7 bar was required four times

in the first 1 h but not thereafter. After 3 h, the reaction was stopped

and the ethylene pressure released. The polyethylene was collected by

filtration, washed many times with acetone and diethyl ether, and dried

at 80 °C, resulting in an off-white powder.

ASSOCIATED CONTENT

■

S

* Supporting Information

Text, tables, figures, and CIF files giving ORTEP representa-

tions of the Ni complexes mentioned in the paper but not dis-

played as figures, a ¹³C NMR spectrum of a copolymer ob-

tained from ethylene and 1-hexene, and crystallographic data

for all complexes studied. This material is available free of

charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

■

Corresponding Author

*E-mail: ph@oci.uni-heidelberg.de.

For ethylene polymerization reactions at pressures higher than 10

bar steel autoclaves of appropriate size were used.

Crystallographic Studies. General Considerations. For each

compound studied by X-ray diffraction, a crystal was mounted on a

glass fiber with perfluoropolyether. All measurements were made on a

Bruker SMART diffractometer with graphite-monochromated Mo Kα

radiation using a CCD detector. Cell constants and an orientation

matrix for data collection were obtained from a least-squares refine-

ment of reflections from 45 0.3° frames collected for 10 s each. Frames

corresponding to a sphere of data were then collected using the ω-scan

technique; in each case, 20 s exposures of 0.3° in ω were taken. The

reflections were integrated using SAINT,⁷¹and equivalent reflections

were merged. An absorption correction was applied to each structure

using SADABS,⁷²and the data were corrected for Lorentz and polari-

zation effects. The space groups were determined by the systematic

Present Address

^†Chemistry, Queensland University of Technology, Gardens

Point, Brisbane QLD 4001, Australia.

ACKNOWLEDGMENTS

■

This research has been supported by the Polymer Department

of BASF SE, Ludwigshafen, Germany, by the University of

Heidelberg, and by the Fonds of the Chemical Industry. We are

grateful to Dr. Dieter Lilge (now LyondellBasell) and Dr.

Stephan Lehmann at BASF for carrying out the polymer charac-

terizations. We thank the Alexander von Humboldt Foundation

222

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Organometallics

Article

(33) Camacho, D. H.; Salo, E. V.; Ziller, J. W.; Guan, Z. Angew.

Chem., Int. Ed. 2004, 43, 1821.

for a postdoc fellowship (M.S.) and Dr. Marc O. Kristen from

BASF (now LyondellBasell) for valuable discussions and advice.

(34) Santi, R.; Romano, A. M.; Sommazzi, A.; Grande, M.; Bianchini,

C.; Mantovani, G. J. Mol. Catal. A: Chem. 2005, 229, 191.

(35) Zhang, J.; Wang, X.; Jin, G.-X. Coord. Chem. Rev. 2006, 250, 95.

(36) Guan, Z.; Popeney, C. S. Organomet. Chem. 2009, 26, 179.

(37) Nakamura, A.; Ito, S.; Nozaki, K. Chem. Rev. 2009, 109, 5215.

(38) Abbo, H. S.; Titinchi, S. J. J. Catal. Lett. 2010, 139, 90.

(39) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P.

J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem.

Commun. 1998, 7, 849.

REFERENCES

■

(1) Britovsek, G. J. P; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.

Ed. Engl. 1999, 38, 428.

(2) Shultz, C. S.; DeSimone, J. M.; Brookhart, M. Organometallics

2001, 20, 16.

(3) Senn, H. M.; Blochl, P. E.; Togni, A. J. Am. Chem. Soc. 2000, 122,

4098.

̈

(4) Vyboishchikov, S. F.; Musaev, D. G.; Froese, R. D. J.; Morokuma,

K. Organometallics 2001, 20, 309.

(40) (a) Hofmann, P.; Heiss, H.; Muller, G. Z. Naturforsch. 1987,

̈

42b, 395. (b) For dtbpm, the first preparation of a small, spectro-

scopically identified sample, which could not be purified, was reported

by Karsch in 1983: Karsch, H. H. Z. Naturforsch., B: Anorg. Chem. Org.

Chem. 1983, 38, 1027. The need in our group to easily access reason-

able quantities of dtbpm resulted in the development of a convenient

preparative procedure, which was disclosed in a patent in 1991, and

which allowed the synthesis of this pure bisphosphine on a 50−100 g

scale in one run: Hofmann, P.; Heiss, H. Ger. Pat. DE 41 34 772,

1991 (BASF AG). Interestingly, a slightly modified version of this syn-

thesis was included in a polyolefin patent disclosed by Brookhart et al.

in 1997 (viz. ref 41b). An updated optimized version of our procedure

developed in our group is described in ref 65 as a representative case of

a general, high-yield route to R₂PCH₂PR′₂ligand systems, as they are

used here.

(5) Tognetti, V.; Le Floch, P.; Adamo, C. J. Comput. Chem. 2009, 31,

1053.

(6) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.

1995, 117, 6414.

(7) Keim, W.; Kowaldt, F. H.; Goddard, R.; Kruger, C. Angew. Chem.,

̈

Int. Ed. 1978, 17, 466.

(8) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc.

1996, 118, 267.

(9) McLain, A. J.; Feldman, J.; McCord, A. F.; Gardner, K. H.;

Teasley, M. F.; Coughlin, E. B.; Sweetman, K. J.; Johnson, L. K.;

Brookhart, M. Macromolecules 1998, 31, 6705.

(10) Killian, C. M.; Tempel, D. J.; Johnson, L. K.; Brookhart, M.

J. Am. Chem. Soc. 1996, 118, 11664.

(11) Tempel, D. J.; Brookhart, M. Organometallics 1998, 17, 2290.

(12) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am.

Chem. Soc. 1998, 120, 888.

(13) Svejda, S. A.; Johnson, L. K.; Brookhart, M. J. Am. Chem. Soc.

1999, 121, 10634.

(14) Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson, L.

K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320.

(15) Shultz, C. S.; DeSimone, J. M.; Brookhart, M. J. Am. Chem. Soc.

2001, 123, 9172.

(41) (a) For the dichloride (dtbpm-κ²P)NiCl₂see: Hofmann, P.;

Perez-Moya, L. A.; Krause, M. E.; Kumberger, O.; Muller, G. Z.

̈

Naturforsch. 1990, 45b, 897. (b) The analogous dibromide (dtbpm-

κ²P)NiBr₂has been described, and its behavior in MMOA cocatalyzed

ethylene polymerization has been investigated: Feldman, J.; Hauptman,

E.; McCord, E.; Brookhart, M. WO98/47934, 1998 (Du Pont).

(42) (a) Hofmann, P.; Perez-Moya, L. A.; Steigelmann, O.; Riede, J.

Organometallics 1992, 11, 1167. (b) Hofmann, P; Heiss, H.; Muller, G.

̈

(16) Shultz, C. S.; DeSimone, J. M.; Brookhart, M. Organometallics

2001, 20, 16.

Z. Naturforsch. 1987, 42b, 395. (c) Hofmann, P.; Unfried, G. Chem.

Ber. 1992, 125, 659. (d) Hofmann, P.; Perez-Moya, L.-A.; Steigelmann,

O.; Riede, J. Organometallics 1992, 11, 1197. (e) Straub, B. F.;

Rominger, F.; Hofmann, P. Inorg. Chem. 2000, 39, 2113. (f) Urtel, H.;

Bikzhanova, G. A.; Grotjahn, D. B. Organometallics 2001, 20, 3938.

(g) Volland, M. A. O.; Hansen, S. M; Rominger, F.; Hofmann, P.

Organometallics 2004, 23, 800.

(17) Leatherman, M. D.; Svejda, S. A.; Johnson, L. K.; Brookhart, M.

J. Am. Chem. Soc. 2003, 125, 3068.

(18) Britovsek, G. J. P.; Baugh, S. P. D; Hoarau, O.; Gibson, V. C.;

Wass, D. F.; White, A. J. P.; Williams, D. J. Inorg. Chim. Acta 2003,

345, 279.

(19) McCord, E. F.; McLain, S. J.; Nelson, L. T. J.; Ittel, S. D.;

Tempel, D.; Killian, C. M.; Johnson, L. K.; Brookhart, M. Macro-

molecules 2007, 40, 410.

(20) Domski, G. J.; Rose, J. M.; Coates, G. W.; Bolig, A. D.;

Brookhart, M. Prog. Polym. Sci. 2007, 32, 30.

(21) Deng, L.; Margl, P. M.; Ziegler, T. J. Am. Chem. Soc. 1997, 119,

1094.

(22) Deng, L.; Woo, T. K.; Cavallo, L.; Margl, P. M.; Ziegler, T.

J. Am. Chem. Soc. 1997, 119, 6177.

(43) Hofmann, P.; Meier, C.; Englert, U.; Schmidt, M. U. Chem. Ber.

1992, 125, 353.

(44) Hofmann, P.; Meier, C.; Hiller, W.; Heckel, M.; Riede, J.;

Schmidt, M. U. J. Organomet. Chem. 1995, 490, 51.

(45) Urtel, H.; Meier, C.; Eisentrager, F.; Rominger, F.; Joschek, J.;

̈

Hofmann, P. Angew. Chem., Int. Ed. Engl. 2001, 40, 781.

(46) Urtel, H.; Meier, C.; Rominger, F.; Hofmann, P. Organometallics

2010, 29, 5496.

(47) Drent, E.; van Broekhoven, J. A. M.; Doyle, M. J. Organomet.

Chem. 1991, 417, 235.

(23) Musaev, D. G.; Froese, R. D. J.; Svensson, M.; Morokuma, K.

J. Am. Chem. Soc. 1997, 119, 367.

(24) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,

(48) (a) Lippert, F.; Hohn, A.; Hofmann, P. WO 9503353 A1 1995

̈

(BASF SE). (b) Lippert, F.; Hohn, A.; Hofmann, P. WO 9637537 A1

1996 (BASF SE).

̈

1169.

(25) Dubois, M.-A.; Wang, R.; Zargarian, D.; Tian, J.; Vollmerhaus,

R.; Li, Z.; Collins, S. Organometallics 2001, 20, 663.

(26) Cooley, N. A.; Green, S. M.; Wass, D. F.; Heslop, K.; Orpen, A.

G.; Pringle, P. G. Organometallics 2001, 20, 4769.

(27) Carter, A.; Cooley, N. A.; Pringle, P. G.; Scutt, J.; Wass, D.

Polym. Mater.: Sci. Eng. 2002, 86, 314.

(28) Daugulis, O.; Brookhart, M. Organometallics 2002, 21, 5926.

(29) Liu, W.; Malinoski, J. M.; Brookhart, M. Organometallics 2002,

21, 2836.

(49) Brookhart, M. S.; Johnson, L. K.; Killian, C. M.; McCord, E. F.;

McLain, S. J.; Kreutzer, K. A.; Ittel, S. D.; Tempel, D. J. US5880241A,

1999.

(50) Shultz, C. S.; DeSimone, J. M.; Brookhart, M. Organometallics

2001, 20, 16.

(51) Britovsek, G. J. P.; Baugh, S. P. D; Hoarau, O.; Gibson, V. C.;

Wass, D. F.; White, A. J. P.; Williams, D. J. Inorg. Chim. Acta 2003,

345, 279.

(52) Kristen, M. O.; Hofmann, P.; Eisentrager, F. WO 0202573A1

̈

(30) Malinoski, J. M.; Brookhart, M. Organometallics 2003, 22, 5324.

́

2002 (BASF SE).

(53) Albers, I.; Alvarez, E.; Cam

́

(31) Albers, I.; Alvarez, E.; Cam

́

pora, J.; Maya, C. M.; Palma, P.;

́

pora, J.; Maya, C. M.; Palma, P.;

Sanchez, L. J.; Passaglia, E. J. Organomet. Chem. 2003, 689, 833.

(54) Fassina, V.; Ramminger, C.; Seferin, M.; Mauler, R. S.; de Souza,

́

Sanchez, L. J.; Passaglia, E. J. Organomet. Chem. 2003, 689, 833.

(32) Dennett, J. N. L.; Gillon, A. L.; Heslop, K.; Hyett, D. J.;

Fleming, J. S.; Lloyd-Jones, C. E.; Orpen, A. G.; Pringle, P. G.; Wass,

D. F.; Scutt, J. N.; Weatherhead, R. H. Organometallics 2004, 23, 6077.

R. F.; Monteiro, A. L. Macromol. Rapid Commun. 2003, 24, 667.

223

dx.doi.org/10.1021/om200715w | Organometallics 2012, 31, 207−224

Organometallics

Article

(55) Lee, B. Y.; Bazan, G. C.; Vela, J.; Komon, Z. J. A.; Bu, X. J. Am.

Chem. Soc. 2001, 123, 5352.

(56) Kriley, C. E.; Woolley, C. J.; Krepps, M. K.; Popa, E. M.;

Fanwick, P. E.; Rothwell, I. P. Inorg. Chim. Acta 2000, 300−302, 200.

(57) Spek, A. L.; van Eijck, B. P.; Jans, R. J. F.; van Koten, G. Acta

Crystallogr. 1987, C43, 1878.

(58) Schultz, M.; Rominger, F.; Hofmann, P. Unpublished results.

(59) Ficker, R.; Hiller, W.; Regius, C. T.; Hofmann, P. Z. Kristallogr.

1996, 211, 60.

(60) Ficker, R.; Hiller, W.; Regius, C. T.; Hofmann, P. Z. Kristallogr.

1996, 211, 62.

(61) Ficker, R.; Hiller, W.; Regius, C. T.; Hofmann, P. Z. Kristallogr.

1996, 211, 58.

(62) Hofmann, P.; Heiss, H.; Neiteler, P.; Muller, G.; Lachmann, J.

̈

Angew. Chem. 1990, 102, 935; Angew. Chem., Int. Ed. Engl. 1990, 29,

880.

(63) Reid, S. M.; Mague, J. T.; Fink, M. J. J. Am. Chem. Soc. 2001,

123, 4081.

(64) Simhai, N.; Iverson, C. N.; Edelbach, B. L.; Jones, W. D.

Organometallics 2001, 20, 2759.

(65) Eisentrager, F.; Gothlich, A.; Gruber, I.; Heiss, H.; Kiener, C. A.;

̈

Kruger, C.; Notheis, J. U.; Rominger, F.; Scherhag, G.; Schultz, M.;

̈

Straub, B. F.; Volland, M. A. O.; Hofmann, P. New J. Chem. 2003, 27,

540.

This paper summarizes the literature on the synthesis of

R₂PCH₂PR′₂ligand systems.

(66) (a) Joschek, J. Dissertation; Ruprecht-Karls Universitat

̈

Heidelberg: Heidelberg, Germany, 1999. (b) Albright, T. A.;

Burdett, J. K.; Whangbo, M. H. Orbital Interactions in Chemistry;

Wiley: New York, 1985.

(67) Nayak, S. K.; Sathiskumar, R.; Guru Row, T. N. Cryst. Eng.

Commun. 2010, 12, 3112.

(68) Schultz, M.; Hanno-Igels, P.; Hofmann, P. To be submitted for

publication in Organometallics.

(69) Ha, J. W.; Chu, K. J J. Ind. Eng. Chem. 1997, 3, 113.

(70) Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992, 11,

3920.

(71) SAINT, 4.024 ed.; Siemens Industrial Automation, Inc.,

Madison, WI, 1995.

(72) Sheldrick, G. M. SADABS; Bruker AXS, Inc., Madison, WI,

1996.

(73) Sheldrick, G. M. XPREP; 5.03 ed.; Siemens Industrial

Automation, Inc: Madison, WI, 1995.

(74) Sheldrick, G. M. SHELXTL Crystal Structure Determination

Package; Bruker AXS, Inc., Madison, WI, 1997.

(75) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.;

Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.

D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.;

Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford,

S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.;

Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;

Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.;

Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;

Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;

Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.;

Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.;

Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.9; Gaussian, Inc.,

Pittsburgh, PA, 1998.

NOTE ADDED AFTER ASAP PUBLICATION

■

In the version of this paper published December 27, 2011, the

author name Paul Jakob was given incorrectly. The version of

this paper that appears on the web as of January 9, 2012, has

the name given correctly.

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Crowded diphosphinomethane ligands in catalysis: [(R2PCH 2PR′2-κ2P)-NiR″]+ cations for ethylene polymerization without activators

DOI: 10.1021/om200715w

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