Synthesis of nickel(II) complexes containing neutral N,N- and anionic N,O- bidentate ligands, and their behaviour as chain-growth catalysts; Structural characterisation of complexes containing (mim) 2CO, mimCO2-, and mimCPh2O- (mim = 1-methylimidazol-2-yl)

Inorganica Chimica Acta 359 (2006) 1710–1724

www.elsevier.com/locate/ica

Synthesis of nickel(II) complexes containing neutral N,N^ꢀ

and anionic N,O^ꢀbidentate ligands, and their behaviour as

chain-growth catalysts; structural characteris_ꢀation of

complexes containing (mim)₂CO, mimCO₂, and

mimCPh₂O^ꢀ(mim = 1-methylimidazol-2-yl)

a

a,

a,b,

c

a

Michael P. Batten , Allan J. Canty ^*, Kingsley J. Cavell

^*, Thomas Ruther ,

¨

c

Brian W. Skelton , Allan H. White

a

School of Chemistry, University of Tasmania, G.P.O. Box 252-75, Hobart, Tasmania 7001, Australia

b

Department of Chemistry, Cardiﬀ University, P.O. Box 912, Cardiﬀ CF10 3TB, Wales, UK

c

Department of Chemistry M313, University of Western Australia, 35 Stirling Highway, Crawley, W.A. 6009, Australia

Received 18 June 2004; accepted 22 June 2004

Available online 9 March 2005

Dedicated to Professor Gerard van Koten.

Abstract

The complexes NiBr₂(L₂) [L₂= (mim)₂CO (7a), (bim)_ꢀ₂CO (7b), py(mim)CO (8), PhN@CHbim (9)], NiBr(o-Tol){(mim)₂CO}

(10), Ni(L₂)(o-Tol)(PPh₃) [L₂¼ mimCO ð11aÞ; bmCO₂ð11bÞ, mimCPh₂O^ꢀ(12), mimC₆H₄O^ꢀ(13)], and [Ni{(mim)₂CO}₃][B-

ꢀ

2

F₄]₂Æ 0.25H₂O (16) have been synthesised from nickel(II) salts (7–9, 16) or NiBr(o-Tol)(PPh₃)₂[10–13], where mim = 1-meth-

ylimidazol-2-yl, bim = 1-benzylimidazol-2-yl, and py = pyridin-2-yl. The square-planar complexes (11a, 12) and octahedral 16

have been characterised by X-ray diﬀraction studies, together with octahedral cis-[Ni{(mim)₂CO}₂Br(OH₂)]Br Æ CD₃CN (14) and

cis-[Ni{(mim)₂CO}₂(OH₂)₂]Br₂Æ 3CD₃CN (15). Preliminary catalytic studies have been undertaken with a number of the nickel

complexes. Complexes 11–13 form single component catalysts for the oligomerization or polymerization of ethylene and the

bromo-complexes (7–9) form active catalysts for the oligomerization or polymerization of ethylene when activated with MMAO.

Keywords: Nickel; Catalysis; Imidazole; Structure; X-ray; Bidentate

1. Introduction

prominent applications of nickel in homogeneous catal-

ysis [2]. The SHOP catalysts contain a bidentate [P–O]^ꢀ

ligand coordinated to nickel(II) and show exceptionally

high selectivities for linear a-oleﬁns. Interest in nickel

based catalysts has been renewed by Brookhart and

co-workerꢀs [3–6] discovery that bulky a-diimine–Ni(II)

[and Pd(II)] complexes are capable of oligomerising or

polymerising ethylene and higher oleﬁns. In these sys-

tems the molecular weight of the polymer formed is

dependent on the steric bulk of the ligand, since increas-

Following the pioneering work by Reppe, Wilke and

Keim [1], nickel complexes have found widespread

application in industrial catalysis [1–6]. Notably, the

shell higher oleﬁns process (SHOP) is one of the most

*

Corresponding authors. Tel.: +61 3 6226 2162; fax: +61 3 6226

2858 (A.J. Canty); Tel.: +44 29 2087 5899 (K.J. Cavell).

E-mail address: Allan.Canty@utas.edu.au (A.J. Canty).

doi:10.1016/j.ica.2004.06.069

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

1711

ing bulk hinders associative displacement (b elimina-

tion) of the growing polymer chain. Another important

feature of this class of nickel catalysts is their tolerance

for heteroatoms, which allows copolymerisation of ole-

ﬁns with substrates such as acrylate, vinylacetate and

pyrimidone functionalised oleﬁns [7]. In contrast, early

transition metal catalysts tend to be limited to non-polar

oleﬁns due to the oxophilic nature of these metals.

The transition metal organometallic chemistry of N-

heterocyclic, and in particular imidazole containing li-

gands has been developed more recently [8–22]. In view

of the close relationship between the imidazole group

and a-diimine and related ligands, we have commenced

studies on the coordination chemistry and of the poten-

tial application in catalysis of such ligands. We recently

reported preliminary studies of Pd(II) and Cr(III) sys-

tems [16,17,21], and have now extended our investiga-

tions to Ni(II) and included a wider range of ligand

systems (Scheme 1). The ligands were selected to contain

two imidazole groups (1), an imidazole and a pyridine

group (2), or an imidazole and an imine group (3) allow-

ing comparison with diimine chemistry; or an imidazole

and anionic oxygen donor groups (4–6) to provide com-

parisons with the SHOP system and the more recently

reported pyridine-2-carboxylate [18], pyrazine-2-carbox-

ylate [19] and salicylaldimine systems [23]. We report

here nickel imidazole-carboxylate complexes that are in-

ert to atmospheric moisture and are stable in ethanol.

RN

N

MeN

BnN

N

O

N

RN

Ph

2: py(mim)CO

3: PhN=CHbim

1a: R = Me, (mim)₂CO

1b: R = Bn, (bim)₂CO

-

O

Ph

O

Ph

N

MeN

RN

5: R = mimCPh₂O^-

6: mimC₆H₄O^-

-

4a: R = Me, mimCO₂

-

4b: R = Bn, bimCO₂

MeN

RN

MeN

BnN

N

Br

N

Br

Me

Ni

O

Ni

O

Ni

N

Ph

7a: R = Me

7b: R = Bn

9

10

8

Ph

O

PPh₃

Me

O

N

O

N

PPh₃

Me

Ph

O

N

PPh₃

Me

Ni

MeN

RN

MeN

12

11a: R = Me

11b: R = Bn

13

Scheme 1. Bidentate ligands containing imidazole groups and four-coordinate nickel complexes.

1712

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

Preliminary catalytic studies on examples of Ni(II) com-

plexes containing imidazole-based ligands illustrate their

ability to oligomerise and polymerise lower oleﬁns.

ments were measured by Prof. K.S. Murray at Monash

University. GC-FID was carried out using an HP 5890

series II GC ﬁtted with a 25 m SGE 50QC3/BP1 column.

GC-MS were measured on an HP 5890 GC ﬁtted with a

25, HP1 capillary column and an HP 5970 mass selective

detector. Electrospray ionisation mass spectrometry

(ESMS) were recorded on a Finnigan MAT LCQ mass

spectrometer using continuous infusion of the sample.

Electron impact (EI) and liquid secondary ion (LSI)

mass spectra were recorded at the Central Science Lab-

oratory, University of Tasmania on a Kratos Concept

ISQ. Microanalyses were performed by Dr. Graham

Rowbottom at the Central Science Laboratory, Univer-

sity of Tasmania, using a Carlo Erba EA1108 Elemental

Analyser.

2. Experimental

All manipulations were carried out using Schlenk

techniques and dry nitrogen as an inert atmosphere un-

less speciﬁcally noted. Celite was stirred with concen-

trated hydrochloric acid for 12 h and washed with

deionised water until the washings were neutral and free

of chloride ions, then washed consecutively with metha-

nol and dichloromethane, dried at 100^oC in vacuo and

degassed with nitrogen. Solvents were puriﬁed and dried

in the usual manner [24]. Sodium tetraphenylborate,

nickel(II) tetraﬂuoroborate solution and 1-benzylimi-

dazole were purchased from Aldrich and used without

further puriﬁcation. Ethylene (polymer grade) was sup-

plied by Matheson. MAO was obtained as a 10% w/w

toluene solution from Schering and MMAO was sup-

plied as a 1.82 M heptane solution from Akzo Nobel.

Bis(1-methylimidazol-2-yl)methanone [25], bis(1-ben-

zylimidazol-2-yl)methanone [26], (pyridin-2-yl)(1-meth-

ylimidazol-2-yl)methanone [9,27], 1-methylimidazol-2-

diphenylmethanol [28], 1-methylimidazol-2-ylphenol

[29], potassium 1-benzylimidazole-2-carboxylate.2/3hy-

drate [30] trans-[NiBr(o-tolyl)(PPh₃)₂] [18], dibromo-

The synthesis of 1-benzyl-2-hydroxymethylimidazole

is presented here as it involves signiﬁcant improvement

on the published report [34] and provides full character-

isation data.

2.1. Synthesis of reagents

2.1.1. 1-Benzyl-2-hydroxymethylimidazole

1-Benzylimidazole (5.97 g, 37.8 mmol) and parafor-

maldehyde (4.42 g, 150 mmol) were placed in an auto-

clave and heated at 120 ꢁC for 18 h. The resulting

clear syrup was distilled, the product being collected at

l

250 ꢁC and 0.2 mm. Yield: 6.70 g, 94%. H NMR

(dimethoxyethane)nickel(II)

[31],

dibromo(bipyri-

(CDC1₃): d 7.38–7.27 (2H, m, H3⁰5⁰), 7.17–7.13 (2H,

m, H2⁰6⁰), 6.80 (1H, s, H4⁰), 6.56 (1H, s, H5), 5.23

(1H, s, CH₂OH), 4.63 (1H, s, CH₂Ph). ¹³C NMR

(CDC1₃): d 148.6 (C2), 136.8, 129.4, 128.5, 127.8,

127.1, 121.1, 56.1 (CH₂OH), 50.2 (CH₂Ph).

dine)nickel(II) [5], dibromo(dioxane)nickel(II) [32], and

bis(1-methylimidazole-2-carboxylato)(1-methylimidazole)

zinc(II) [33] were prepared as reported.

Electronic spectra were recorded using a Cary 5E

UV–Vis double beam spectrophotometer ﬁtted with a

low temperature platform. Solid state spectra were ob-

tained from KBr discs using a diﬀraction grating as ref-

erence; CH₂Cl₂solutions were made up in oven dried

volumetric ﬂasks under a nitrogen atmosphere, and a

Dewar ﬂask ﬁtted with a vacuum chamber, thermocou-

ple and quartz windows was used for variable tempera-

ture solution phase experiments. Quartz cells were oven

dried, cooled in a vacuum, and ﬁlled and sealed under

nitrogen. IR spectra were measured on a Bruker IFS

66 FT-IR spectrometer as KBr mulls prepared in a glove

box or in air. Polymer IR spectra were measured using

the same instrument, as ﬁlms or on an FT-IR micros-

copy stage. Polymer melting points were measured using

a Settaram DSC-92 using a temperature program suit-

able for polyethylene samples. NMR spectra were re-

corded on a Varian Gemini-200 spectrometer at 199.98

MHz (¹H), 161.80 MHz (³¹P) or 50.00 MHz (¹³C); var-

iable temperature experiments were performed on a Var-

ian Unity Inova 400 WB spectrometer at the Central

Science Laboratory, University of Tasmania, and chem-

ical shifts are given in ppm relative to internal SiMe₄

(¹H, ¹³C), or external 85% H₃PO₄(³¹P). Magnetic mo-

2.1.2. 1-Benzyl-2-1-phenylaldiminoimidazole,

PhN@ CHbim (3)

1-Benzyl-2-hydroxymethylimidazole (1.88 g, l0

mmol) was dissolved in chloroform (50 mL) and stirred

with activated manganese dioxide (8.5 g). After 48 h the

suspension was ﬁltered and the solvent removed in a

vacuum. The residue was distilled, giving 1-benzyl-2-

formylimidazole (1.50 g) at 135 ꢁC and 0.2 mm. 1-Ben-

zyl-2-formylimidazole (0.50 g, 2.7 mmol) was stirred

with aniline (1.02 g, 11.0 mmol) for 15 min, toluene

(42 mL) was added resulting in a cream solid that dis-

solved as toluene addition was completed. The solution

was stirred (15 min) before being distilled to give the

product at >250 ꢁC and at 0.2 mm. Yield: 0.70 g, quan-

l

titative. H NMR (CDC1₃): d 8.58 (1H, s, H C=N),

7.44–7.19 (11H, m, Ph), 7.08 (1H, s, H4), 5.88 (2H, s,

CH₂Ph). ¹³C NMR (CDC1₃): d 151.7, 151.4, 143.6,

137.6, 131.1, 129.8, 129.3, 128.4, 128.1, 127.0, 125.2,

121.4, 51.6 (CH₂Ph). EI-MS m/z: 261(M⁺, 30%),

245(12), 193(14), 169(100), 157(20), 91(52), 77(25)

(C₁₇H_l5N₃requires C, 78.14; H, 5.79; N, 16.08. Found:

C, 78.20; H, 5.52; N, 16.09%).

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

1713

2.2. Synthesis of complexes

tracts were evaporated in a vacuum to give a pale

yellow powder. Yield: 0.311 g, 83%. Insuﬃciently soluble

for NMR spectroscopy. LSI-MS in mnba m/z: 326

(MH⁺ꢀ HBr, 100%), 245 (48), 188 (LH⁺, 17). Electronic

spectrum (KBr disc): k 703, 749, 1167 nm. IR (KBr disk):

1623 (m), 1581 (m), 1533 (m), 1443 (w), 1484 (m), 1453

(m, sh), 1437 (s), 1385 (w), 1359 (w), 1329 (w), 1207

(w), 1134 (w), 969 (m), 916 (w), 895 (m), 769 (m), 718

(m), 696 (m), 599 (w), 555 (w) cm^ꢀ1. Magnetic moment

2.53 BM (C₁₀H₉N₃OBr₂Ni requires C, 29.60; H, 2.36;

N, 10.36. Found: C, 29.72; H, 2.27; N, 10.25%).

2.2.1. Dibromo{bis(1-methylimidazol-2-

yl)methanone}nickel(II), NiBr₂{(mim)₂CO} (7a)

A solution of bis(1-methylimidazol-2-yl)methanone

(0.500 g, 2.63 mmol) in CH₂Cl₂(9 mL) was added to a

stirred

suspension

of

dibromo(dimethoxye-

thane)nickel(II) (0.812 g, 2.63 mmol) in CH₂Cl₂(13

mL). After 25 min the suspension was ﬁltered, the solid

washed with CH₂Cl₂(3 · 4 mL) and dried in a vacuum

to give the product as a green solid. Yield: 1.075 g, quan-

titative. Insuﬃciently soluble for NMR spectroscopy.

LSI-MS in mnba m/z: 519 [Ni{(mim)₂CO}₂Br, 47%],

438 [Ni{(mim)₂CO}₂, 52%], 329 (MH⁺ꢀ HBr, 45), 248

[{(mim)₂CO}Ni, 100]. EI-MS: m/z 408 (M⁺-distorted

isotope pattern, 2%), 329 (100), 248 (50), 190 (14). Elec-

tronic spectrum, KBr disc ꢀ180 ꢁC, k: 511, 683 (sh), 716,

759, 1404. IR (KBr disc): 3107 (w,b), 2360 (w,b), 1641

(1632 free ligand, m), 1487 (w), 1421 (s), 1292 (w),

1169 (w), 952 (w), 900 (s), 790 (w), 653 (w), 607 (w)

cm^ꢀ1. Magnetic moment 3.00 BM (C₉H₁₀N₄NiBr₂re-

quires C, 26.45; H, 2.47; N, 13.71. Found: C, 26.50;

H, 2.65; N, 13.58%).

2.2.4. Dibromo{1-benzylimidazol-2-yl(1-phenylaldimine)}

nickel(II), NiBr₂(PhN@CHbim) (9)

1-Benzylimidazol-2-yl(1-phenylaldimine) (0.157 g,

0.602 mmol) in CH₂Cl₂(8 mL) was added to a stirred

suspension of dibromo(dimethoxyethane)nickel(II)

(0.185 g, 0.599 mmol) in CH₂Cl₂(20 mL). After 1.5 h

the olive green mixture was ﬁltered and the solid prod-

uct washed with CH₂Cl₂(3 · 5 mL) and light petroleum

(bp 40–60 ꢁC) (2 · 5 mL), and dried to give a pale green

powder. Yield: 0.202 g, 70%. Insuﬃciently soluble for

NMR spectroscopy. LSI-MS in mnba m/z: 661(100%),

580(26), 400(M ꢀ Br,100), 319(70), 260(35). Electronic

spectrum (KBr disc): k 679(sh), 707, 757, 1001 nm. IR

(KBr disk): 1607 (m, sh), 1584 (m), 1531 (w), 1484 (s),

1454 (sh), 1437 (s), 1386 (w), 1357 (w), 1329 (w), 1207

(w), 1134 (w), 969 (m), 916 (w), 895 (m), 717 (s), 697

(s), 600 (w), 555 (w) cm^ꢀ1. Magnetic moment 3.21 BM

(C₁₇H₁₅N₃NiBr₂requires C, 42.55; H, 3.15; N, 8.76.

Found: C, 42.36; H, 3.32; N, 8.68%).

2.2.2. Dibromo{bis(1-benzylimidazol-2-

yl)methanone}nickel(II), NiBr₂{(bim)₂CO} (7b)

A solution of bis(l-benzylimidazol-2-yl)methanone

(0.226 g, 0.661 mmol) in CH₂Cl₂(15 mL) was added

to a stirred suspension of dibromo(dioxane)nickel(II)

(0.203 g, 0.661 mmol) in CH₂Cl₂(10 mL). After 18 hr

the red-brown suspension was collected and extracted

with CH₂Cl₂. The ﬁltrate was treated with diethyl ether

(15 mL) to precipitate a green solid that was collected,

washed with diethyl ether (3 · 5 mL) and dried in a vac-

uum to give a green solid. Yield: 0.292 g, 79%. ESMS in

CH₃CN m/z: 1041(20%), 823(100), 521(M + l-Br with

coordinated MeCN 58). Electronic spectrum (KBr disc):

k 662(sh), 705, 760, 942; (CH₂Cl₂solution at 18 ꢁC): k

510, 644, 864, 976; (CH₂Cl₂solution 0 ꢁC): k 510, 655,

2.2.5. Bromo(ortho-tolyl){bis(1-methylimidazol-2-yl)

methanone}nickel(II), NiBr(o-Tol){(mim)₂CO} (10)

A solution of bis(1-methylimidazol-2-yl)methanone

(0.042 g, 0.221 mmol) in CH₂Cl₂(4.2 mL) was added

to a well stirred solution of trans-[NiBr(o-Tol)(PPh₃)₂]

(0.167 g, 0.221 mmol) in CH₂Cl₂at ꢀ14 ꢁC. After 45

min the blood red solution had warmed to 4 ꢁC, it was

frozen and petroleum ether (8 mL) added. The mixture

was allowed to melt and diﬀuse with the aid of gentle

stirring, further diethyl ether/petroleum ether (3 · 5

mL) were then added and the precipitated red solid

dried in vacuo. Yield: 0.71 g, 80%. Electronic spectrum

(KBr disc) k : 508; (CH₂Cl₂solution at 18 ꢁC) k(e) :

508 (1550). LSI-MS of an MeCN solution in mnba m/

z: 519(7%), 473(14), 438(33), 339(M ꢀ Br, 12), 327(M-

Tol), 283(M-Br₂+ Cl, 18), 248(100). EI-MS in CH₂Cl₂

m/z: 329(M-Tol, 7%), 283(12), 248(5), 190(29), 162(44),

l

821(sh), 976. H NMR (CD₂Cl₂, 20 ꢁC): d 7.41 and

6.98 (12H, m, Ph+H4,5), 6.3 (2H, s, CH₂Ph); (CD₂Cl₂,

ꢀ10 ꢁC) d 7.42, 7.07, 6.99, 6.36 (s, CH₂Ph). IR (KBr

disc): 1653 (s, br), 1436 (s, br), 1296 (m), 1180 (s), 901

(s), 798 (m), 775 (m), 668 (m), 647 (m), 612 (w), 592

(w) cm^ꢀ1. Magnetic moment 2.48 BM (C₂₁H₁₈N₄O-

NiBr₂requires C, 44.97; H, 3.23; N, 9.99. Found: C,

44.87; H, 3.23; N, 10.05%).

2.2.3. Dibromo{(pyridin-2-yl)(1-methylimidazol-2-yl)

methanone}nickel(II), NiBr₂{py(mim)CO} (8)

1

109(54), 82(100). H NMR (CD₂Cl₂): d at 18⁰C: 8.00

A solution of 1-methylimidazol-2-yl(pyridin-2-yl)

methanone (0.173 g, 0.925 mmol) in CH₂Cl₂(15 mL)

was added to a stirred suspension of dibromo(dimeth-

oxyethane)nickel(II) (0.286 g, 0.926 mmol) in CH₂Cl₂

(15 mL). The brown suspension was ﬁltered and the sol-

ids extracted with CH₂Cl₂(20 · 5 mL). The ﬁltered ex-

(1H,s (br), mim), 7.47 (1H, m, H5-Tol). 7.17 (1H, s

(br), mim), 6.85 (1H, s (br), mim), 6.70 (3H, m, H2,3-

Tol), 5.88 (1H, mim), 4.02 (6H, m, mim-CH₃), 3.03

(3H, s, Tol-CH₃); d at ꢀ50⁰C: 7.90 (1H, s, mim), 7.44

(1H, m, H5-Tol), 7.19 (1H, s, mim), 6.86 (1H, s, mim),

6.69 (3H, m, H2,3-Tol), 5.78 (1H, s, mim), 4.02 (3H, s,

1714

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

mim-CH₃), 3.95 (1H, s, mim-CH₃), 3.03 (3H, s, Tol-

CH₃). ¹³C NMR (CD₂Cl₂): d 204.8, 156.0, 149.1,

145.0, 140.5, 134.3, 133.3, 131.7, 127.5, 43.2, 29.6

(C₁₆H₁₇N₄OBrNi requires C, 45.76; H, 4.08; N, 13.34.

Found: C, 46.16; H, 4.17; N, 13.71%).

(53). IR (KBr disk): 1667 (s), 1634 (s), 1591 (m), 1488

(m), 1443 (m), 1412 (s), 1384 (m), 1276 (w), 1251 (w),

1173 (w), 1161 (w), 1060 (w), 1020 (w), 927 (s), 777

(m), 723 (w), 703 (m), 656 (m), 642 (w), 623 (w) cm^ꢀ1

.

¹H NMR (CD₂Cl₂) d 7.51–7.26 (21H, m), 7.18–7.15

(1H, m), 6.77 (1H, m), 6.61–6.48 (3H, m), 5.62 (2H, s,

CH₂Ph), 2.53 (3H, s, Tol-CH₃). ¹³C NMR (CD₂Cl₂) d

143.0, 136.2, 135.9, 134.4, 134.3, 130.6, 130.4, 130.1,

129.1, 128.5, 128.3, 128.2, 127.6, 125.1, 122.9, 122.6.

³¹P–{¹H} NMR (CD₂Cl₂) d 29.2 (C₃₆H₃₁N₂O₂PNi re-

quires C, 70.50; H, 5.09; N, 4.57. Found: C, 70.68; H,

5.08; N, 4.75%).

2.2.6. (ortho-Tolyl)(1-methylimidazol-2-carboxylato)

(triphenylphosphine)nickel(II), Ni(mimCO₂)(o-Tol)

(PPh₃) (11a)

A solution of bis(1-methylimidazol-2-carboxylato)(1-

methylimidazole)zinc(II) (0.13 g, 0.33 mmol) in tetrahy-

drofuran (10 mL) was added to a stirred solution of

trans-[NiBr(o-Tol)(PPh₃)₂] (0.57 g, 0.76 mmol) in tetra-

hydrofuran (10 mL). After 7 h the dark orange suspen-

sion had faded to pale yellow, the solvent was removed

in a vacuum at 40 ꢁC to give a solid that was taken up in

dichloromethane (10 mL), ﬁltered through celite and

washed with further dichloromethane (3 · 5 mL).

Diethyl ether (60 mL) was added to the ﬁltrate, the pre-

cipitated solid removed by ﬁltration through celite and

the pale yellow solution was evaporated in vacuo. The

resulting solid was recrystallised from dichlorometh-

ane/pentane to give the product as a yellow microcrys-

talline solid. Yield: 0.163 g, 91%. LSI-MS of an

acetonitrile solution in mnba m/z: 537 (MH⁺, 7%), 445

(6), 353 (100). IR (KBr disk): 1655 (s), 1570 (w), 1495

(m), 1434 (s), 1309 (m), 1287 (m), 1183 (m), 1097 (m),

1022 (w), 827 (w), 802 (w), 744 (m), 694 (m), 650 (w),

2.2.8. (ortho-Tolyl)(1-methylimidazol-2-diphenylmet

hanolato)(triphenylphosphine)nickel(II), Ni(mim-CPh₂O)

(o-Tol)(PPh₃) (12)

1-Methylimidazol-2-diphenylmethanol (2.11 g, 7.54

mmol) in tetrahydrofuran (20 mL) was added to solid

potassium methoxide (0.437 g, 7.52 mmol) and the sus-

pension stirred for 12 h. The solvent was evaporated in a

vacuum to give a white solid. A solution of trans-[Ni-

Br(o-Tol)(PPh₃)₂] (0.83 g, 1.10 mmol) in tetrahydrofu-

ran (25 mL) was added to the white solid (0.349 g)

and stirred to form a red-brown suspension. After 24

h the suspension had faded to yellow and a ﬁne precip-

itate had formed. The suspension was ﬁltered and the

solvent removed in vacuo, the remaining solid dissolved

in dichloromethane (5 mL), ﬁltered through celite and

the celite washed with solvent (2 · 2 mL). Pentane was

added and the orange crystals that formed were col-

lected and washed with pentane (2 · 2.5 mL) and dried

in a vacuum. Yield: 0.59 g, 79%. LSI-MS acetonitrile

solution in mnba m/z: 675 (MH⁺, 30%), 583 (MH⁺ꢀ tol-

uene, 53), 353 (100), 305 (58), 247 (42). ¹H NMR

(CD₂Cl₂): d 7.50–7.07 (27H, m), 6.66–6.39 (4H, m),

3.09 (3H, s, mim-CH₃), 2.51 (3H, 3,Tol-CH₃). ¹³C

NMR (CD₂Cl₂) d 147.8, 144.1, 137.2, 134.7, 134.6,

132.4, 132.0, 129.4, 128.5, 128.3, 127.8, 127.6, 127.5,

126.6, 123.8, 122.3, 121.8, 121.6, 34.6, 25.6. ³¹P–{¹H}

NMR (CD₂Cl₂) d 30.2 (C₄₂H₃₇N₂OPNi requires C,

74.69; H, 5.52; N, 4.15. Found: C, 74.39; H, 5.63; N,

4.07%).

624 (w), 532 (m), 506 (m), 435 (w) cm^ꢀ^{1 1}H NMR

.

(CD₂Cl₂): d 7.57–7.36 (18H, m, H3,4,5-Tol and mim),

6.78–6.52 (3H, H3,4,5-Tol and mim), 3.97 (3H, s,

mim-CH₃), 2.65 (3H, s, Tol-CH₃). ¹³C NMR (CD₂Cl₂):

d 238.7, 164.3, 149.7, 143.7, 138.1, 136.7, 135.5, 135.4,

135.1, 134.9, 134.8, 134.4, 132.9, 132.7, 131.6, 131.1,

130.6, 130.5, 129.7, 129.4, 129.0, 128.7, 128.6, 128.3,

125.3, 124.9, 123.7, 123.4, 34.3, 26.3. ³¹P–{¹H} NMR

(CH₂Cl₂) d 29.3. (C₅₀H₂₇N₂O₂NiP requires C, 67.07;

H, 5.07; N, 5.21. Found: C, 67.17; H, 5.06; N, 5.19%.)

LSI-MS of acetonitrile solution in mnba m/z:

537(MH⁺, 7%), 445(6), 353 (100).

2.2.7. (ortho-Tolyl)(l-benzylimidazol-2-carboxylato)

(triphenylphosphine)nickel(II), Ni(bimCO₂)(o-Tol)

(PPh₃) (11b)

2.2.9. (ortho-Tolyl)(1-methylimidazol-2-phenoxo)

(triphenylphosphine)nickel(II), Ni(mimC₆H₄O)(o-Tol)

(PPh₃) (13)

trans-[NiBr(o-Tol)(PPh₃)₂] (0.88 g, 1.17 mmol) in tet-

rahydrofuran (30 mL) was added to potassium 1-meth-

ylimidazol-2-carboxylate.2/3hydrate (0.24 g, 1.19 mmol)

and the red-brown mixture stirred at 26 ꢁC for 5 h. The

solvent was removed in a vacuum and the solid residue

was dissolved in CH₂Cl₂, ﬁltered through Celite and the

solvent removed in a vacuum to give a yellow solid. The

crude product was dissolved in CH₂Cl₂(10 mL) and

diethyl ether added to precipitate a pale yellow solid.

The ﬁltrate was concentrated and hexanes added to af-

ford a second crop of pale yellow solid. Yield: 0.40 g,

85%. LSI-MS in m/z: 613 (MH⁺, 100%), 521 (20), 353

1-Methylimidazol-2-phenol (0.046 g, 0.264 mmol) in

tetrahydrofuran (4 mL) was treated with potassium

methoxide (1.2 mL of 0.219 M solution, 0.26 mmol) in

methanol and stirred for 2 h. The solvent was evapo-

rated in a vacuum to give a white solid. A solution of

trans-[NiBr(o-Tol)(PPh₃)₂] (0.199 g, 0.264 mmol) in tet-

rahydrofuran (75 mL) was added, and the suspension

stirred for 12 h and the solvent removed to give an am-

ber solid. The solid was dissolved in dichloromethane (7

mL), ﬁltered, diethyl ether added and the resulting sus-

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

1715

pension ﬁltered and the ﬁltrate evaporated in a vacuum

to give a yellow solid which was recrystallised from

diethyl ether/light petroleum. Yield: 0.075 g, 48%. LSI-

MS in mnba m/z: 584 (M⁺, 7%), 493 (M⁺ꢀ C₇H₇, 17),

353 (M⁺ꢀ PPh₃, 100), 322 (10), 263 (PPh₃, 5) 231 [Ni-

(mimC₆H₄O)⁺, 12]. ¹H NMR (CD₂Cl₂): d 7.00 (7H,

m), 6.89 (5H, m), 6.77 (7H, m), 6.42 (1H, m), 6.16

(1H, m), 6.10–5.95 (4H), 3.13 (3H, s, mim-CH₃),

2.10(3H, s, Tol-CH₃). ¹³C NMR (CD₂Cl₂) d 144.1,

137.1, 134.5, 134.4, 131.7, 131.3, 130.0, 129.7, 128.0,

127.9, 127.2, 127.0, 126.6, 122.8, 122.7, 122.2, 121.4,

115.2, 112.5, 37.5, 25.8. ³¹P–{¹H} NMR (CD₂Cl₂) d

27.9 (C₃₅H₃₁N₂OPNi requires C, 71.82; H, 5.34; N,

4.79. Found: C, 71.91; H, 5.28; N, 4.89%).

1294 (w), 1168 (w), 1051 (m, br), 953 (w), 900 (s), 771

(w), 724 (w), 656 (w), 606 (w) cm^ꢀ1. Magnetic

moment 3.09 BM (C₂₇H_30.5B₂F₈N₁₂NiO_3.25requires C,

40.16; H, 3.81; N, 20.82. Found: C, 40.08; H, 3.83; N,

20.84%).

2.3. X-ray structure determinations

Full spheres of low-temperature CCD area-detector

diﬀractometer data were measured (Bruker AXS instru-

ment, x-scans, monochromatic Mo Ka radiation,

˚

k = 0.7107 A; T ca. 153 K) yielding N_treﬂections, merg-

ing to N unique (R_intquoted) after ꢁempiricalꢀ/multiscan

absorption correction (proprietary software), N_owith

F > 4r(F) being considered ꢁobservedꢀ and used in the

full matrix least squares reﬁnements, reﬁning aniso-

tropic displacement parameter forms for the non-hydro-

2.2.10. cis-Di{bis(1-methylimidazol-2-yl)methanone}

(bromo)aquanickel(II) bromide.acetonitrile, [Ni

{(mim)₂CO}₂Br(OH₂)]Br Æ MeCN (14)

gen atoms, (x,y,z,U_iso)_Hbeing reﬁned for the hydrogen

A solution of bis(1-methylimidazol-2-yl)methanone

(0.251 g, 1.32 mmol) in MeCN (21 mL) was added to

a solution of NiBr₂.3H₂O (0.367 g, 1.34 mmol) in MeCN

(20 mL), and a blue precipitate rapidly formed. The

solution was decanted and a second equivalent of solid

ligand was added to the solution. The solution changed

from blue to blue-green and a blue crystalline solid

deposited. Yield: 0.152 g, 17%. Electronic spectrum

(KBr disc): k 561 nm. IR (KBr disc): 3700–2750 (b),

1647 (m), 1489 (m), 1424 (s), 1176 (w), 1090 (w), 957

(w), 901 (s), 798 (w), 653 (w), 604 (w) cm^ꢀ1. Magnetic

moment 3.09 BM.

atoms. Conventional residuals R, R_w(weights:

((r²F) + 0.0004F²)^ꢀ1) are quoted on |F| at convergence,

neutral atom complex scattering factors being employed

within the ^XTAL-3.7 program system [35]. Pertinent re-

sults are given below and in Tables 1–3 and Figs. 1–3,

the latter displaying 50% probability displacement enve-

lopes for the non-hydrogen atoms, hydrogen atoms hav-

˚

ing arbitrary radii of 0.1 A. Individual diﬃculties,

variations in procedure, abnormalities, etc., are cited

as Variata.

2.3.1. Crystal/reﬁnement data

Complex 11a. Ni(mimCO₂)(o-Tol)(PPh₃) Æ 1/3CH₂Cl₂

„C₃₀H₂₇N₂NiO₂P Æ 1/3CH₂Cl₂, M = 565.5, triclinic,

2.2.11. Di{bis(1-methylimidazol-2-yl)methanone}

diaquanickel(II) bromide tris(acetonitrile), [Ni{(mim)₂CO}₂

(OH₂)₂]Br₂Æ 3MeCN (15)

ꢀ

˚

space group P1, a = 11.291(1) A, b = 19.375(2) A, c =

˚

20.051(2) A, a = 82.311(3)ꢁ, b = 85.098(3)ꢁ, c =

3

75.897(3)ꢁ, V = 4210 A , D_c(Z = 6) = 1.33₈g cm^ꢀ3

,

˚

A solution of bis(1-methylimidazol-2-yl)methanone

(0.188 g, 0.989 mmol) in MeCN (8 mL) was added to

a solution of NiBr₂.3H₂O (0.135 g, 0.495 mmol) in

MeCN (10 mL). A blue precipitate rapidly formed,

and after 19 d the solution had become green. The solu-

tion was decanted and the solids washed with CH₂Cl₂(4

mL). The combined solvents were allowed to stand for a

week, and a single green crystal of the product was

isolated.

l

_Mo= 8.4 cm^ꢀ1

,

specimen: 0.45 · 0.13 · 0.10 mm,

T_min,max= 0.71, 0.86, 2h_max= 50ꢁ, N_t= 47025, N =

14482 (R_int= 0.069),_ꢀN₃_o= 8538, R = 0.049, R_w= 0.048,

˚

|Dq_max| = 0.80(7) e A

Variata. (x,y,z,U_{iso H}

.

)

were included in the

reﬁnement, constrained at estimated values. The

dichloromethane solvent molecule was modelled as

disordered over two sets of sites, occupancies reﬁning,

within a total constraint set at unity after trial

reﬁnement, to x = 0.608(3), 1 ꢀ x. Similarly, each o-tolyl

ring was modelled as disordered over two sets of

sites, occupancies 0.848(7), 0.77(1), 0.65(1) and

complements.

2.2.12. Tri{bis(1-methylimidazol-2-yl)methanone}nickel

(II) tetraﬂuoroborate quadrantishydrate, [Ni{(mim)₂-

CO}₃] [BF₄]₂Æ 0.25H₂O (16)

A solution of nickel(II) tetraﬂuoroborate (0.34 mL,

50% wt, 0.74 mmol) was added to a solution of bis(1-

methylimidazol-2-yl)methanone (0.43 g, 2.3 mmol) in

water (5.6 mL). A thick pink suspension immediately

formed, acetone (10 mL) was added and the resulting

purple solution gave purple crystals on standing for 6

days. Yield: 0.60 g, quantitative. Electronic spectrum

(single crystal): k 541, 768 (sh), 876 nm. IR (KBr disc):

3416 (m, br), 1643 (s), 1487 (m), 1463 (m), 1419 (s),

Complex 12. Ni(mimCPh₂O)(o-Tol)(PPh₃)„C₄₂H₃₇

N₂NiOP, M = 675.4, monoclinic, space group P2₁,

˚

a = 8.884(1) A, b = 15.201(3) A, c = 12.918(2) A, b =

104.115(4)ꢁ, V = 1692 A , D_c(Z = 2) = 1.33₅g cm^ꢀ3

,

3

˚

l

_Mo= 6.6 cm^ꢀ1

,

specimen: 0.32 · 0.27 · 0.14 mm,

T_min,max= 0.73, 0.86, 2h_max= 75ꢁ, N_t= 34564, N =

8351 (R_int= 0.031), N_o= 7168, R = 0.033, R_w= 0.039,

ꢀ3

˚

|Dq_max| = 0.64(6) e A

.

1716

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

Table 1

(a) Selected geometries for Ni(L-N,O)(o-Tol)(PPh₃) (11a, 12) L ¼ L⁰¼ mimCO ð11aÞ; L ¼ L⁰⁰¼ mimCPh₂O^ꢀð12Þ

L/molecule

ꢀ

2

L⁰/1

L⁰/2

L⁰/3

L⁰⁰(/1)^a

˚

Distances (A)

Ni–N(1)

Ni–O(21)

1.907(4)

1.910(4)

1.894(4)

1.895(2)

1.961(3)

2.150(1)

1.861(7)

1.294(6)

1.502(7)

0.73(4)

1.964(3)

2.152(2)

1.87(1)

1.960(3)

2.152(2)

1.93(1)

1.923(2)

2.1536(6)

1.896(2)

1.408(2)

1.509(3)

Ni–P

Ni–C(01)^b

C(20)–O(21)

C(2)–C(20)

C(01)–C(01⁰)

N(1)ꢁ ꢁ ꢁO(21)

1.284(7)

1.491(7)

0.48(3)

1.281(6)

1.497(7)

0.69(2)

2.581(5)

2.586(5)

2.583(5)

2.568(3)

Angles (ꢁ)

N(1)–Ni–O(21)

83.7(2)

173.7(1)

91.4(2)

83.8(2)

174.8(1)

91.6(4)

84.2(1)

173.7(1)

91.4(4)

84.55(8)

178.56(6)

89.18(9)

96.19(5)

168.49(9)

90.30(7)

113.2(2)

115.9(1)

118.5(2)

107.1(2)

N(1)–Ni–P

N(1)–Ni–C(01)

O(21)–Ni–P

92.79(9)

170.7(2)

92.8(2)

93.7(1)

172.0(4)

91.4(3)

91.8(1)

174.6(3)

92.3(3)

O(21)–Ni–C(01)

P–Ni–C(01)

Ni–N(1)–C(2)

Ni–O(21)–C(20)

N(1)–C(2)–C(20)

C(2)–C(20)–O(21)

111.5(3)

115.3(3)

118.1(4)

110.7(5)

111.5(3)

114.9(3)

118.2(5)

111.6(4)

111.4(3)

115.1(3)

118.0(4)

111.1(4)

Interplanar dihedral angles (ꢁ) (ꢁPCNOꢀ is the coordination environment of the nickel)

PCNO/C₃N₂

PCNO/CCO₍₂₎

PCNO/C₆

13.5(2)

19.86(8)

87.3(2)

6.3(2)

5.4(1)

17.57(8)

87.6(3)

12.2(1)

5.5(1)

15.4(1)

88.6(3)

10.8(2)

12.06(7)

2.5(2)

82.93(9)

10.0(1)

C₃N₂/CCO

˚

Out-of-plane deviations, d (A)

d Ni/PCNO

d Ni/C₃N₂

d Ni/CCO₍₂₎

d Ni/C₆

0.035(2)

0.305(8)

0.469(5)

0.249(10)

0.056(2)

0.062(7)

0.517(5)

0.16(2)

0.084(7)

0.080(7)

0.233(5)

0.03(2)

0.047(1)

0.421(4)

0.039(6)

0.331(4)

Torsion angles (ꢁ)

O(21)–Ni–O–C(11)

C(01)–Ni–P–C(11)

Ni–P–C(11)–C(16)

Ni–P–C(21)–C(26)

Ni–P–C(31)–C(36)

159.8(2)

ꢀ27.7(3)

65.7(4)

157.8(2)

ꢀ28.5(4)

77.7(4)

169.0(2)

ꢀ7.4(4)

68.1(5)

20.8(5)

34.2(4)

169.9(1)

ꢀ19.7(1)

80.3(2)

19.4(5)

40.8(4)

23.5(4)

35.0(5)

23.2(2)

ꢀ5.2(2)

(b) Comparative [Ni(ar-N,O)R (phosphine)] arrays ‘‘py’’ = pyridine, ꢁquinꢀ = quinoline

˚

Ligands

Chelate

Distances (A)

Ni–N

Phosphine

Hydrocarbyl

Ref.

Ni–O

Ni–P

Ni–C

c

2-CO₂-py

PPh₃

PPhMe₂

o-tolyl

mesityl

1.945(4)

1.926(6)

1.919(3)

1.911(5)

2.163(2)

2.148(2)

1.884(5)

1.865(8)

d

c

f

4NO₂-2-CO₂-py

8-O-quin

2-O₂CCH₂-py

PPh₃

PMe₃

PPh₂Me

o-tolyl

Me

mesityl

1.940(4)

1.953(3)

1.951(6)

1.931(3)

1.924(3)

1.932(3)

2.163(2)

2.125(1)

2.162(2)

1.851(7)^e

1.917(5)

1.890(4)

d

a

In the chelate ring, torsions successively in the bonds Ni–N(1), N(1)–C(2), et seq. are 7.0(2)ꢁ, ꢀ10.0(3)ꢁ, 7.4(3)ꢁ, ꢀ1.3(2), ꢀ2.9(2)ꢁ.

b

c

d

e

f

Major component, where appropriate.

From [19].

From [18].

Disordered, as in the present arrays.

From [36].

3

˚

Variata. (x,y,z,U_iso)_H

were included in the reﬁne-

c = 13.091(1) A, b = 94.615(2)ꢁ, V = 2513 A , D_c

ment, constrained at estimated values. ꢁFriedel pairꢀ data

were retained distinct, ꢁx_absꢀ reﬁning to ꢀ0.006(8).

Complex 14. cis-[Ni{(mim)₂CO}₂Br(OH₂)]Br Æ CD₃CN„

C₁₈H₂₂Br₂N₈NiO₃Æ CD₃CN, M = 661.0, monoclinic,

(Z = 4) = 1.74₇

g

cm^ꢀ3

,

l

_Mo= 39.9

cm^ꢀ1

,

specimen: 0.40 · 0.08 · 0.08 mm, T_min,max= 0.54, 0.86,

2h_max= 65ꢁ, N_t= 38716, N = 9986 (R_int= 0.073),

N_o_ꢀ3= 6202, R = 0.041, R_w= 0.041, |Dq_max| = 1.4(1) e

˚

space group P2₁/c, a = 14.484(1) A, b = 13.296(1) A,

A

.

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

1717

Table 2

˚

Selected geometries, for cis-[Ni{(mim)₂CO}₂XY] in 14 (X = Br, Y = OH₂) and 15 (X = Y = OH₂); r (A) are the nickel–donor distances, the other

entries in the matrix being the angles (ꢁ) subtended by the relevant atoms at the head of the row and column values for 15 are given below those for 14

Atom

r

N(121)

N(211)

N(221)

X

Y

N(111)

2.074(2)

2.061(2)

87.3(1)

87.22(6)

177.3(1)

178.7(1)

91.8(1)

93.91(6)

87.55(7)

92.17(6)

87.6(1)

87.25(6)

N(121)

N(211)

N(221)

2.055(3)

2.084(2)

95.5(1)

92.93(6)

91.7(1)

98.87(6)

93.01(8)

89.29(6)

173.6(1)

171.67(6)

2.082(2)

2.060(2)

88.2(1)

87.37(6)

92.24(7)

86.51(6)

89.6(1)

92.46(6)

2.056(3)

2.076(1)

175.23(8)

170.04(6)

92.4(1)

87.72(6)

X(Br)

(O(2))

2.6479(5)

2.101(2)

82.89(8)

84.70(6)

Y(=O(1))

(both)

2.146(2)

2.101(2)

C₂CO/im dihedral angles are 19.1(1)ꢁ, 16.1(1)ꢁ; 14.2(1)ꢁ, 16.8(1)ꢁ (14), 6.58(9)ꢁ, 1.95(9)ꢁ; 7.98(8)ꢁ, 3.31(8)ꢁ (15); im/im dihedral angles are 21.6(1)ꢁ,

12.5(1)ꢁ (14), 8.53(9)ꢁ, 11.20(8)ꢁ (15). Ni deviations from the C₃N₂im planes are 0.031(5), 0.258(5); 0.067(5), 0.069(5) (14), 0.045(3), 0.370(3);

0.134(3), 0.414(3) A (15).

˚

Table 3

The [Ni{(mim)₂CO₃}]²⁺cation geometry of 16

Atom

r

N(121)

87.5(1)

N(211)

N(221)

N(311)

N(321)

N(111)

N(121)

N(211)

N(221)

N(311)

N(321)

2.078(3)

2.099(3)

2.089(2)

2.115(2)

2.106(2)

2.081(2)

93.3(1)

177.4(1)

89.4(1)

91.4(1)

86.1(1)

89.9(1)

90.6(1)

91.9(1)

177.87(9)

175.1(1)

88.9(1)

90.4(1)

94.0(1)

86.8(1)

˚

Metal atom environment; r (A) are the nickel–donor distances, the other entries in the matrix being the angles (ꢁ) subtended by the relevant atoms at

the head of the row and column.

Within the three ligands, C₂CO/im dihedral angles are: 1.5(1)ꢁ, 4.3(1)ꢁ; 9.0(1)ꢁ, 4.9(1)ꢁ; 6.4(1)ꢁ, 5.3(1)ꢁ; im/im angles are: 3.6(2)ꢁ, 10.6(1)ꢁ, 11.7(1)ꢁ; Ni

deviate from the im C₃N₂planes by 0.118(5), 0.013(5); 0.077(5), 0.275(5); 0.032(5), 0.556(5) A.

˚

Complex 15. cis-[Ni{(mim)₂CO}₂(OH₂)₂]Br₂Æ 3CD₃CN„

C₁₈H₂₄Br₂N₈NiO₃Æ 3CD₃CN, M = 767.2, monoclinic,

2.4. Catalysis

˚

space group P2₁/n, a = 8.5382(7) A, b = 24.308(2) A,

˚

2.4.1. Dibromonickel precatalysts

3

˚

c = 15.766(1) A, b = 92.256(2)ꢁ, V = 3270 A , D_c

In a typical procedure the precatalyst (0.02–0.03

mmol) was suspended in toluene (25 mL) at 50 ꢁC

in a dry 75 mL autoclave. The autoclave was purged

with ethylene and MMAO in heptane (0.4–0.6 mmol,

20 eq.) was injected. After stirring for 3 min, ethylene

(40 bar) was added, and after 1 h the autoclave was

rapidly cooled to approximately ꢀ25 ꢁC, brought to

1 bar and nonane (0.1 g) added. The autoclave was

sealed, the contents mixed, brought to 1 bar and a li-

quid sample taken. The contents of the autoclave were

treated with methanol (200 mL) and allowed to stand

for 2 h. The solids were collected by ﬁltration, washed

with methanol, acetone, cyclohexane, and treated with

conc. HCl (4 · 150 mL), where each treatment with

solvent or acid involved standing for 30 min. The

material remaining after acid leaching was washed

with water, methanol, and acetone and dried to give

a white polymer.

(Z = 4) = 1.55₈g cm^ꢀ3, l_Mo= 30.8 cm^ꢀ1, specimen:

0.45 · 0.40 · 0.35 mm, T_min,max= 0.42, 0.70, 2h_max

=

68ꢁ; N_t= 49317, N = 12774 (R_int= 0.042), _ꢀN_{3 o}= 8322,

˚

R = 0.033, R_w= 0.034, |Dq_max| = 0.84(8) e A

Complex 16. [Ni{(mim)₂CO}₃][BF₄]₂Æ 0.236-

H₂O„C₂₇H₃₀B₂F₈N₁₂NiO₃Æ 0.236H₂O, M = 807.4,

orthorhombic, space group Pbca, a = 15.240(1) A,

.

˚

3

˚

b = 11.728(2) A, c = 37.283(4) A, V = 6664 A , D_c

(Z = 8) = 1.60₉g cm^ꢀ3, l_Mo= 6.8 cm^ꢀ1, specimen:

0.1 · 0.1 · 0.05 mm, T_min,max= 0.68, 0.82, 2h_max= 58ꢁ,

N_t= 77863,

N = 8908 (R_int= 0.016),

R = 0.043, R_w= 0.034, |Dq_max| = 0.64(9) e A

N_o= 4473,

ꢀ3

˚

.

Variata. BF₄(ꢁ2ꢀ) was modelled as disordered over

two sets of sites, occupancies 0.736(4) and comple-

ment, the water molecule oxygen fragment concerted

with the latter, associated hydrogen atoms not being

located.

1718

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

Fig. 1. Projections of single molecules of (a) Ni(mimCO₂)(o-Tol)(PPh₃) (11a, molecule 1) and (b) Ni(mimCPh₂O)(o-Tol)(PPh₃) (12) normal to their

coordination planes.

2.4.2. Single component, cationic catalyst

1 h the autoclave was rapidly cooled to approximately

ꢀ25 ꢁC and the reaction solution worked up as de-

scribed in Section 2.1.

In a typical procedure, [Ni{(mim)₂CO}{o-tolyl}Br]

(0.018 g, 0.043 mmol) was suspended in toluene (16

mL) at 50 ꢁC in a dry, 75 mL autoclave. The autoclave

was purged with ethylene and a suspension of NaBAF

[BAF = tetra(3,5-di(triﬂuoromethyl)phenyl)borate] (0.038

g, 0.043 mmol, 1 eq.) in toluene (9 mL) was added. After

stirring for 5 min, ethylene (40 bar) was added, and after

2.4.3. Neutral, single component catalyst

In a typical procedure, the precatalyst (0.02–0.08

mmol) was dissolved in the solvent (40 mL) and placed

in a dry, N₂-purged 75 mL autoclave. The autoclave was

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

1719

Fig. 2. Projections of the cations (a) cis-[Ni{(mim)₂CO}₂Br(OH₂)]⁺and (b) cis-[Ni{(mim)₂CO}₂(OH₂)₂]²⁺in 14 and 15, respectively, normal to their

quasi 2 axes, showing close contacts to associated anions (see text).

equilibrated with ethylene (40 bar), sealed and heated to

80 ꢁC for 15 hours, timed from thermal equilibrium. On

completion the autoclave was rapidly cooled to approx-

imately ꢀ25 ꢁC and the reaction solution worked up as

described in Section 2.1.

methane involving displacement of dimethoxyethane

(DME) or dioxane (Eq. (1)), or triphenylphosphine

(Eq. (2)). The complex Ni(mimCO₂)(o-Tol)(PPh₃)₂

(11a) was obtained from the reaction of NiBr(o-

Tol)(PPh₃)₂with Zn(mimCO₂)₂(mimH), and related

complexes 11b–13 were obtained, using the potassium

salts of the [N–O]^ꢀligands (Eq. (3)).

NiðLÞBr₂þ L²! NiBr₂ðL²Þ þ L

ð1Þ

3. Results and discussion

7a L²¼ ðmimÞ CO; L ¼ DME

3.1. Synthesis and characterisation of reagents and

complexes

2

7b L²¼ ðbimÞ CO; L ¼ dioxane

2

The square-planar nickel(II) complexes (Scheme 1)

were obtained by substitution reactions in dichloro-

8 L²¼ pyðmimÞCO; L ¼ DME

1720

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

Fig. 3. Projection of the cation of [Ni{(mim)₂CO}₃]²⁺in 16, down its putative 3-axis.

9 L²¼ PhN@CHbim; L ¼ DME

X-ray diﬀraction, but we were unable to exploit this syn-

thetic method to devise improved routes to complexes 14

and 15, e.g. reactions of Ni(II) tetraﬂuoroborate with

ligand and NaBr in water or acetonitrile.

NiBrðo-TolÞðPPh₃Þ þ ðmimÞ COð1aÞ

2

! NiBrðo-TolÞfðmimÞ COgð10Þ þ 2PPh₃

ð2Þ

ð3Þ

2

All of the complexes, except 14 and 15, were charac-

terised by microanalysis. Mass spectra of complexes 7a,

11a, 11b, 12 and 13 are readily interpreted as showing

parent ions as the highest m/z value; complexes 8 and

10 show the highest ion as [MH ꢀ HBr]⁺and [M ꢀ o-

Tol]⁺; and complex 9 shows higher ions together with

NiBrðo-TolÞðPPh₃Þ þ ½L²ꢂ^ꢀ

2

! NiðL²Þðo-TolÞðPPh₃Þ þ Br^ꢀþ PPh₃

11b L²¼ bimCO₂^ꢀ; 12 L²¼ mimCPh₂O^ꢀ;

1

[M ꢀ Br]⁺. H NMR spectra of o-tolylnickel(II) com-

13 L²¼ mimC₆H₄O^ꢀ

plexes exhibit spectra with integration consistent with

the formulations presented, and of the dibromo-

nickel(II) complexes only 7b was suﬃciently soluble

for ¹H NMR spectroscopy. Complexes 11–13 in CD₂Cl₂

exhibit ³¹P resonances within the range 27–30 ppm, sim-

ilar to that reported for related pyridine-2-carboxylate

and pyrazine-2-carboxylate complexes Ni(N–O)(o-

Tol)(PPh₃) in C₆D₆(24–27 ppm) [18].

Although initial studies of the reactivity of nickel(II)

bromide toward (mim)₂CO in acetonitrile in attempts to

synthesize 7a were unsuccessful, the reactions did give

small quantities of blue (14) and green crystals (15)

depending upon the stoichiometry used in the reactions.

The crystals were characterised by X-ray diﬀraction as

cis-[Ni{(mim)₂CO}₂Br(OH₂)]Br Æ MeCN (14) and cis-

[Ni{(mim)₂CO}₂(OH₂)₂]Br₂Æ 3MeCN (15) (Scheme 2),

but reliable syntheses for these complexes could not be

developed. A high yield synthesis of [Ni{(mim)₂CO}₃]-

[BF₄]₂Æ 0.25H₂O (16) was subsequently developed from

the reaction of nickel(II) tetraﬂuoroborate with the

ligand in water and the complex characterised by

3.2. X-ray structural studies

The complexes Ni(mimCO₂)(o-Tol)(PPh₃) (11a) and

Ni(mimCPh₂O)(o-Tol)(PPh₃) (12) have similar struc-

tures involving square-planar geometry with the o-Tol

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

1721

+

2+

N

Ni

N

Ni

N

Ni

N

Br

N

OH₂

N

OH₂

14: [Ni{(mim)₂CO}₂Br(OH₂)]Br.MeCN 15: [Ni{(mim)₂CO}₂(OH₂)₂]Br₂.3MeCN 16: [Ni{(mim)₂CO}₃][BF₄]₂.0.25H₂O

Scheme 2. Octahedral nickel(II) cations containing bis(1-methylimidazol-2-yl)methanone (1a). Both enantiomers are present in crystal structures

determined for 14–16 (Figs. 1 and 2).

group trans to the oxygen donor atom of the bidentate

ligands (Fig. 1). Three molecules of 11a comprise its

asymmetric unit, there being no evidence of a superlat-

tice in the structure. The o-tolyl group is rotationally

disordered in both structures, the component occupan-

cies being ca. 0.5 in 12 and 0.85, 0.77, 0.65 in 11a where

the latter may be in concert with solvent disorder. There

is almost no signiﬁcant diﬀerence in the ꢁbiteꢀ of the che-

late rings, although the ring is puckered in 12; there is a

gles within the ligands in 14 are greater than in 15, while

a considerable diﬀerence between the two is found in the

interligand angle N(121)–Ni–N(221) trans to the uniden-

tate ligands, and in the (cis-)X(1)–Ni–N(n11) angles.

The cation [Ni{(mim)₂CO}₃]²⁺in 16 (Fig. 3) is the ﬁrst

structurally characterised example of a tris-{(mim)₂-

CO} complex, and the quasi-threefold axes of the cation

are approximately directed along the crystallographic b-

direction. Each ligand is non-planar, the overall array

having signiﬁcant perturbations from ideal 32 geometry

(Table 3), perhaps most evident in departures of the

metal atom from coplanarity with various ligand

planes. There is a dearth of structural data available

for tris(symmetrical N,N⁰-bidentate)nickel(II) arrays,

˚

van der Waals contact of 2.3₅A between H(216) and

H(3a). Counterpart geometries of other ꢁNi(aryl-

N,O)R(P trans to N)ꢀ square planar Ni(II) arrays are

tabulated in Table 1(b) for comparison, the chelate rings

being ﬁve-membered with the exception of the six-mem-

bered pyridylacetate complex. The present Ni–N(im)

˚

the only accessible values (ca. 2.14 A) for six-membered

˚

distances, closely ranged at 1.902(8) A, are appreciably

shorter than those of the N–N(py) systems [1.926(6)–

chelate systems being tris(propane-1,3-diamine)nicke-

l(II) complexes [37,38], while data available for tris(sym-

metrical N,N⁰-biimidazolyl)nickel(II) species involve

ﬁve-membered chelates, Ni–N varying widely around

˚

1.953(3) A]. It is of interest to note the occurrence of aryl

substituent disorder similar to 11a and 12 in the 4-nitro-

2-picolinate complex [19].

˚

2.1 A [39].

Complexes 14 and 15, isolated from similar prepara-

tive procedures and crystallised in NMR tubes from

solution in CD₃CN, involve six-coordinate Ni(II) in

the pair of isomers cis-[Ni{(mim)₂CO}₂Br(OH₂)]-

Br Æ CD₃CN (14) and cis-[Ni{(mim)₂CO}₂(OH₂)₂]-

Br₂Æ 3CD₃CN (15) (Table 2 and Fig. 2). In both

complexes one formula unit devoid of crystallographic

symmetry comprises the asymmetric unit; hydrogen

bonding is limited but signiﬁcant involving short con-

3.3. Catalytic studies

When activated with MMAO in the presence of mod-

erate pressures of ethylene the four-coordinate nickel

complexes, 7–10, give moderate to low yields of mainly

polyethylene along with some oligomers. The polymers

generated are, in general, high melting (118–120 ꢁC)

with a high degree of branching, as indicated by FT-IR

(polymer samples were too insoluble for NMR studies),

which is in contrast with the relatively linear products

generated by the Ni–diimine type catalysts reported by

Feldman et al. [40]. The oligomers generated by these

catalysts show high linearity, as demonstrated in Table

4 by the analysis of the C6 fraction.

The catalyst generated from 10/NaBAF (BAF = te-

tra(3,5-di(triﬂuoromethyl)phenyl)borate) produced only

oligomers (mainly linear), no nickel black being ob-

served. Precatalyst 9 produced oligomers with very small

amounts of linear polymer, similar to the behaviour pre-

viously noted for the bipyridine–Ni catalyst and low ste-

ric bulk a-diimine–Ni systems [3–6]. Bipyridine–Ni

catalysts were reported, by Brookhart and co-workers

[3–6] to produce oligomers and by Pakkanen and

˚

tacts (Brꢁ ꢁ ꢁH < 2.6 A) between bromide ions and water

˚

molecules,

Br(2)ꢁ ꢁ ꢁH(1a)

2.31(6)

˚

A

in

14,

Br(1)ꢁ ꢁ ꢁH(2a,1b) 2.36(3), 2.38(2) A, Br(2)ꢁ ꢁ ꢁH(2b),

˚

H(1a) (1/2 ꢀ x,1/2 ꢀ y,1/2 ꢀ z) 2.42(3), 2.34(3) A in

15. The cation of 15 has quasi 2 symmetry (Table 2).

Nickel–nitrogen distances trans to the water molecules

are slightly elongated within each ligand, with the nickel

atom lying considerably out of the associated imidazole

planes. Nickel-O(H₂) distances in the complexes

˚

[2.101(2), 2.146(2) A] are longer than the diverse values

found in [Ni(OH₂)₆]²⁺arrays, typically ca. 2.05 A, while

˚

Ni–N trans to each other are generally shorter than in

[Ni{(mim)₂CO}₃]²⁺(see below). Replacement of one of

the water molecules in 15 by a bromine atom impacts lit-

tle by way of any ꢁtransꢀ eﬀect. Interplanar dihedral an-

1722

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

Table 4

Ethylene oligomerisation/polymerisation [Ni-complex/MMAO] catalyst systems

Precatalyst

Cocatalyst

Polymer productivity

(gmmol Ni^ꢀ1h^ꢀ1

Tm

Oligomer productivity

(gmmol Ni^ꢀ1h^ꢀ1

)

Oligomer dist. C6 fraction

TON

)

Linear C6 (%)

a (%)

Bipy-NiBr₂

9

MMAO

NaBArF

trace

2.3

6.3

5.3

0.82

1.7

33

91

>99

87

38

82

62

56

66

230

193

8

126

122

132

92

107

223

7b

7a

10

4.5

10

>99

1550

1140

trace

32

co-workers [41] to produce HDPE in small quantities. In

comparative studies, we also found that the bipyridine–

Ni catalyst produces both oligomers as well as traces of

linear polymer. For the catalyst systems reported here,

the overall shape of the ligand appears to exert a major

inﬂuence on both activity and product distribution. Li-

gands forming ﬁve-membered chelates generate catalysts

that behave like typical low steric bulk a-diimine systems

and yield predominantly oligomeric products. The

bis(heterocyle)methanone catalysts, which possess stron-

ger r-donor ligands, form six-membered chelates and

generate a mixture of oligomers and signiﬁcant amounts

of high polymer. Within the series of bis(heteroc-

yle)methanone precatalysts overall activity appears to

decrease while the ratio of polymer to oligomer increases

with increasing p-acidity of the chelating ligand.

The neutral organometallic complexes 11–13 react

with ethylene under moderate pressures, without the

need for cocatalyst, to form oligomers or polymer (Ta-

ble 5). Catalysts formed from 11a/b generate a mixture

of oligomer and polymer with 11b having a slightly low-

er selectivity for polymer. This follows the behaviour of

previously reported substituted pyridine, pyrazine and

salicylaldimine ligated catalysts in that the stronger do-

nor 1-methylimidazole function results in a greater pro-

portion of lower molecular weight products when the

reaction is performed in chlorobenzene. The oligomers

are predominantly linear with a high-content (see analy-

sis of C6 fraction, Table 5). The robust nature of neutral

Ni(II) catalysts is demonstrated by complex 11a which

retains activity in neat ethanol, the product distribution

is shifted to oligomers. Changing the carboxylate group

of 11a/b to alkoxy (12) or phenoxy (13) groups lowers

the activity of the catalysts and changes the product dis-

tribution to oligomer (12) and polymer (13),

respectively.

Interestingly, a linear inverse relationship is observed

between the ³¹P chemical shifts of the catalyst precursors

and the percentage of polymer product generated, and a

reasonably linear positive correlation exists between ³¹P

chemical shifts and the linearity of the C6 oligomer frac-

tion (Fig. 4). The ³¹P chemical shift of the phosphine li-

gand may reﬂect the properties of the N–O ligands in

these systems. Very recently two further reports on Ni-

based systems in oleﬁn polymerisation reactions have

appeared, which also demonstrate the signiﬁcance of

chelate ring size and ligand bulk on catalytic perfor-

mance [42,43].

Table 5

Ethylene oligomerisation/polymerisation single component catalysts^a

Precatalyst

Solvent

Polymer (%)

Tm

Oligomer dist. C6 fraction

Linear C6 (%)

TON

a (%)

11a

11a^b

11a

11a^c

11b

12

Toluene

53

54

44

0

83

85

73

96

98

87

99^d

97

91

99

90^f

56

70

58

85

55

56

41

57

3160

142

Chlorobenzene

Ethanol

Toluene

2980

914

40

45

2

84

78

85^e

113

3930

1950

417

Chlorobenzene

Toluene

13

96

168

a

Catalytic runs were carried out at 80 ꢁC unless otherwise indicated.

30 ꢁC.

60 ꢁC.

No branched C₆materials observed.

Melting point, insuﬃcient material for DSC.

Traces of branched materials observed.

b

c

d

e

f

M.P. Batten et al. / Inorganica Chimica Acta 359 (2006) 1710–1724

1723

Fig. 4. Relationship between ³¹P chemical shifts of catalyst precursors and (a) percentage of polymer product, and (b) linearity of the C6 oligomer

fraction.

[6] S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000)

1169.

4. Supplementary material

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(1996) 2475.

[8] P.K. Byers, A.J. Canty, L.M. Engelhardt, J.M. Patrick, A.H.

Crystallographic data for the structural analyses have

been deposited with the Cambridge Crystallographic

Data Centre, CCDC Nos. 224050–224054. Copies of

this information may be obtained free of charge from

the Director, CCDC, 12 Union Road, Cambridge,

CB2 1EZ, UK (fax: +44 1223 336 033; e-mail:

deposit@ccdc.cam.ac.uk or www: http://www.ccdc.

cam.ac.uk).

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Article Doi

Synthesis of nickel(II) complexes containing neutral N,N- and anionic N,O- bidentate ligands, and their behaviour as chain-growth catalysts; Structural characterisation of complexes containing (mim) 2CO, mimCO2-, and mimCPh2O- (mim = 1-methylimidazol-2-yl)

DOI: 10.1016/j.ica.2004.06.069

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