Novel cationic and neutral Pd(II) complexes bearing imidazole based chelate ligands: Synthesis, structural characterisation and catalytic behaviour

Article abstract of DOI:10.1016/S0022-328X(00)00227-8

A variety of neutral and cationic methyl palladium(II) complexes [Pd(CH₃)(Cl)(L-L)] (3) and [Pd(CH₃)(CH₃CN)(L-L)]BF₄ (4), containing known and new N-methylimidazole-2-yl (mim) and N-methylbenzimidazole-2-yl (bmi

Full text of DOI:10.1016/S0022-328X(00)00227-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 607 (2000) 78–92
Novel cationic and neutral Pd(II) complexes bearing imidazole
based chelate ligands: synthesis, structural characterisation and
catalytic behaviour
Melanie C. Done a, Thomas Ru¨ther* a,1, Kingsley J. Cavell* a,2, Melvyn Kilner b,
Evan J. Peacock c, Nathalie Braussaud a, B.W. Skelton d, Allan White d
a Department of Chemistry, Uni6ersity of Tasmania, GPO Box 252-75, Hobart, Tasmania 7001, Australia
b Department of Chemistry, Cardiff Uni6ersity, PO Box 912, Cardiff CF10 3TB, Wales, UK
c Central Science Laboratory (CSL), Uni6ersity of Tasmania, GPO Box 252-74, Hobart, Tasmania 7001, Australia
d Department of Chemistry, Uni6ersity of Western Australia, Nedlands, WA 6907, Australia
Received 7 March 2000; received in revised form 16 April 2000
Dedicated to Professor Martin Bennett on the occasion of his retirement and in recognition of his major international contribution to
organometallic chemistry.
Abstract
A variety of neutral and cationic methyl palladium(II) complexes [Pd(CH3)(Cl)(L–L)] (3) and [Pd(CH3)(CH3CN)(L–L)]BF4 (4),
containing known and new N-methylimidazole-2-yl (mim) and N-methylbenzimidazole-2-yl (bmim) based chelate ligands (L–L)
have been synthesised. The dichloro complexes [Pd(Cl)2{(mim)2CO}] (2b) and [Pd(Cl)2(mim)PPh2] (2e) have also been synthesised.
The crystal structures of [Pd(Cl)2{(mim)2CꢀNPh}] (2d) and [Pd(CH3)(Cl){(bmim)2CO}] (3c) have been determined and show a
square planar geometry at palladium(II) with an appreciable diminished bite angle (85.6°) in 3c compared to 2d (88.5°). The
molecular structure of 2d and 3c show both bisimidazole ligands coordinated via the ring nitrogen donors and inclination of the
chelate ring bridge to the coordination plane (boat conformation). Low temperature NMR spectra indicate boat-to-boat inversion
of the chelate ring in [Pd(CH3)(CH3CN){(mim)2CO}]+ (4b). Examples of the neutral and cationic complexes were tested in the
Heck reaction and CO/ethylene copolimerisation respectively. The CꢀO bridged bisimidazole complex (3b) exhibited high activity
(TON of 100 000) in the Heck reaction whereas the closely related benzimidazole complex 3c was about half as active (TON of
53 000). Low activities were found for the cationic complex 4b in the CO/ethylene copolymerisation (TON 449). © 2000 Elsevier
Science S.A. All rights reserved.
Keywords: Palladium; Imidazole ligands; Heck reaction; CO/ethylene copolymerisation
1. Introduction
[4], olefin/CO copolymerisation [3c,5] and olefin/alkyl–
acrylate copolymerisation [6]. Previous studies have
been primarily devoted to complexes incorporating
rigid chelating diimine or bipyridine type ligands [3a–c,
f–i]. In more recent papers Jordan et al. [7] described
neutral and cationic Pd(II) complexes containing
bis(pyrazolyl)methane ligands which oligomerise ethyl-
ene to predominantly linear internal C8–C24 olefins.
Klaeui et al. [8] reported Ni complexes bearing related
tris(pyrazolyl)borata ligands which catalyse the ethyl-
ene/CO copolymerisation, and Vrieze et al. [3e] investi-
gated Pd complexes containing tridentate nitrogen
ligands with varying N-heterocycles.
Palladium alkyl complexes play an important role in
transformation reactions of unsaturated molecules. A
key step in these reactions is the insertion into the
metal–carbon bond [1]. A number of neutral and
cationic Pd complexes [PdRX(L–L)] bearing chelating
nitrogen ligands [2] were reported to undergo facile
insertion reactions [3] and hence have received signi-
ficant attention as catalysts for olefin polymerisation
1 *Corresponding author.
2 *Corresponding author. Fax: +61-3-6226-2858; e-mail: cavell-
kj@cardiff.ac.uk
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00227-8

M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
79
Imidazole and benzimidazole ligands [9] have primar-
ily been used to model the binding sites of enzymes in
order to provide insight into the nature of enzymatic
catalytic cycles [10]. However, very recently the groups
of Field and Messerle [11] have studied Rh and Ru
complexes of bisimidazole type ligands and investigated
the performance of the Rh complexes in intramolecular
cyclisation, hydroamination and hydrosilation reac-
tions. Monomethyl and dimethyl Pd(II) complexes of
bridged bisimidazole and mixed imidazole–N-heterocy-
cle (py, pz) ligands have been prepared by Canty et al.
and their dynamic behaviour has been studied by vari-
able temperature NMR [12].
The strong nucleophilic properties and the bisiimine
like structure of bridged bisimidazole chelate ligands
led us to investigate several new cationic and neutral
Pd(II) complexes of these ligands. Furthermore, the use
of complexes of this ligand type had not previously
been reported in catalytic carbon–carbon coupling re-
actions. We were interested in investigating the coordi-
nation properties of a series of imidazole based ligands
and determine how electronic and steric factors of these
ligands influence reactivity at the metal centre. Conse-
quently we have synthesised complexes in which the Pd
centre was placed in bisimidazole frameworks with
different substitution patterns. We now report the syn-
thesis and first structural characterisation of Pd(II)
halogen and methyl complexes bearing functionalised
bisimidazole ligands. Their behaviour in the ethylene/
CO copolymerisation and the Heck reaction is also
reported.
recorded by the Central Science Laboratory (CSL),
University of Tasmania, on a Carlo Erba EA 1108
elemental analyser. Gas chromatography (GC) was per-
formed on a Hewlett–Packard 5890 series II GC fitted
with a SGE 50QC3/BP1 0.5 capillary column and flame
ionisation detector (FID). GC-MS and MS were car-
ried out by the CSL, using a HP5890 GC fitted with a
25 m HP1 column (0.32 mm film) and a HP5970B mass
selective detector, and a Kratos Concept ISQ MS by
liquid secondary ion mass spectrometry (LSIMS, 10 kV
caesium ions, m-nitrobenzyl alcohol matrix) with an
accelerating voltage of 5.3 KV. ESI spectra were
recorded on a Finnigan LCQ spectrometer (direct infu-
sion 3 ml min−1, needle voltage 4.5 kV, capillary
voltage 20 V, sheath gas 30 psi). Infrared (IR) spectra
were recorded on a Bruker IFS-66 FTIR spectrometer.
2.2. Structure determinations
Full spheres of low-temperature CCD area-detector
diffractometer data were measured (Bruker AXS instru-
ment; 2qmax=58°, ꢀ-scans; T ca. 153 K; monochro-
,
matic Mo–Ka radiation, u=0.71073 A) yielding Ntotal
reflections, merging to N unique (Rint quoted) after
‘empirical’/multiscan absorption correction, No with
F\4|(F) being considered ‘observed’ and used in the
full-matrix least-squares refinement, refining anisotropic
thermal parameter forms for the non-hydrogen atoms.
(x, y, z, and Uiso)HHH were refined for 2d, and con-
strained at estimated values for 3c. Conventional resid-
uals R, Rw (reflection weights: (|2(F)+0.0004F2)−1
)
are quoted at convergence. Neutral atom complex scat-
tering factors were employed, computation using the
2. Experimental
XTAL 3.4 program system [31]. Pertinent results are
given below and in the Figure and Tables, full atom
parameters being deposited.
2.1. General
Solvents were dried and purified by standard meth-
ods and freshly distilled under N2 immediately prior to
use. All manipulations were carried out using standard
Schlenk techniques or in a nitrogen glovebox. Te-
tramethyl tin [13], [Pd(Cl)2(COD)] [14], [Pd(Me)(Cl)-
(COD)] [15], and ligands 1c [16], 1e [17] were prepared
according to published procedures. Ligands 1a,b,d,f
were prepared by modified literature procedures or by
methods developed in our laboratory. All other
reagents were used as received. Nuclear magnetic reso-
nance (NMR) spectra were recorded at ambient tem-
perature (20°C), unless otherwise indicated, on a Varian
Gemini-200 NMR spectrometer and on a Varian Unity
Inova 400 WB NMR spectrometer. Chemical shifts (l)
are reported in units of ppm relative to internal TMS
2.2.1. Crystal/refinement data
2.2.1.1. Compound 2d. C15H15Cl2N4Pd. CHCl3, M=
562.0. Monoclinic, space group P21/c (C52h, No. 14),
,
a=9.847(1), b=7.3418(8), c=29.563(3) A, i=
3
92.420(2)°, V=2135 A . Dc (Z=4)=1.748 g cm−3
;
,
F(000)=1112. vMo=15.1 cm−1; specimen: 0.15×
0.14×0.12 mm; Tmin,max=0.73, 0.88. Nt=20549, N=
5304 (Rint=0.028), No=4590; R=0.034, Rw=0.043.
nv=308, ꢀDzmaxꢀ=0.80(4) e A
−3
,
.
2.2.1.2. Compound 3c. C18H17ClN4OPd. CH2Cl2, M=
532.2. Monoclinic, space group P21/n (C52h, No. 14,
variant), a=9.853(1), b=15.111(2), c=13.885(3) A,
,
3
,
i=102.493(2)°, V=2018 A . Dc (Z=4)=1.751
g
(13C, H), or external 85% H3PO4 (31P). Coupling con-
cm−3. F(000)=1064. vMo=13.4 cm−1; specimen:
0.20×0.12×0.04 mm;Tmin,max=0.74, 0.89. Nt=
1
stants (J) are given in Hz and NMR peaks are labelled
as singlet (s), doublet (d), triplet (t), quartet (q), multi-
plet (m) and broad (br). Elemental analysis were
24062, N=5219 (Rint=0.061), No=3412; R=0.042,
Rw=0.041. nv=253, ꢀDzmaxꢀ=1.1(1) e A
−3
,
.

80
M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
2.3. Synthesis of the ligands
Found: C, 36.30; H, 4.37; N, 16.74%. MS (LSIMS)
m/z: 317, [M–CH3]+ (11%); 297, [M–Cl]+ (41%); 282,
[M–CH3–Cl]+ (97%); 177, [Ligand]+ (100%). 1H-
NMR (400 MHz, DMSO): l 7.32 (s, 1H, ImH); 7.17 (s,
1H, ImH); 7.14 (s, 1H, ImH); 6.92 (s, 1H, ImH); 3.76
(s, 3H, N–CH3); 3.70 (s, 3H, N–CH3); 0.46 (s, 3H,
Pd–CH3).
The synthesis of bisimidazole ligands 1a,b,d,f and
methods employed for the synthesis of other related
mixed donor ligands will be reported elsewhere.
2.4. General procedure for the preparation of neutral
complexes
2.4.5. [Pd(Me)(Cl){(mim)2CO}] (3b)
Compound 3b was isolated as a yellow solid: Anal.
Calc. for C10H13ON4ClPd: C, 34.60; H, 3.77; N, 16.14.
Found: C, 34.73; H, 3.71; N, 15.98%. MS (ESI in
CH3CN) m/z: 352, [M–Cl+CH3CN]+ (100%); 337,
The complexes were prepared by standard methods
[15]. Thus, 1.03 equivalents of the ligand were added to
a
suspension or solution of [Pd(Cl)2(COD)] and
[Pd(Me)(Cl)(COD)] in CH2Cl2 and the reaction mixture
was allowed to stir overnight. In the cases where the
product precipitated from the reaction mixture (2b,e,
3a,b,e) the suspension was allowed to settle and the
solution removed via a syringe. The crude product was
washed with CH2Cl2 (3×ca. 10 ml) followed by hex-
anes (3×ca. 10 ml) and dried under vacuum. In the
cases of CH2Cl2 soluble products (3c,d,f) the solution
was filtered through Celite and the solvent removed in
vacuo. The solid was washed with ether or hexanes
(3×ca. 10 ml) and dried under vacuum. Yields for all
complexes were \90%.
1
[M–Cl–CH3+CH3CN]+ (54%). H-NMR (200 MHz,
DMSO): l 7.83 (s (br), 1H, ImH); 7.75 (s(br), 1H,
ImH); 7.67 (s(br), 1H, ImH); 7.34 (s(br), 1H, ImH);
4.05 (s, 3H, N–CH3); 0.68 (s, 3H, Pd–CH3). IR (KBr):
1633 cm−1
.
2.4.6. [Pd(Me)(Cl){(bmim)2CO}] (3c)
Compound 3c was isolated as a yellow solid: Anal.
Calc. for C18H17N4OClPd: C, 48.34; H, 3.83; N, 12.53.
Found: C, 47.99; H, 4.03; N, 11.86%. MS (LSIMS)
m/z: 411, [M–Cl]+ (30%); 431, [M]+ (11%); 396, [M–
Cl–CH3]+ (100%); 291, [Ligand]+ (57%). 1H-NMR
2
(200 MHz, CDCl3): l 8.62 (d(br), 1H, JH–H=12.5 Hz,
2.4.1. [Pd(Cl)2{(mim)2CO}] (2b)
2
ArH), 8.07 (d(br), 1H, JH–H=10 Hz, ArH), 7.6–7.4
Compound 2b was isolated as a light brown solid:
Anal. Calc. for C9H10N4OCl2Pd: C, 29.41; H, 2.74; N,
15.24. Found: C, 29.58; H, 2.56; N, 14.96%. MS
(m, 6H, ArH) 4.25 (s, 3H, N–CH3); 4.23 (s, 3H,
N–CH3); 1.12 (s, 3H, Pd–CH3). IR (KBr): w (CꢀO)=
1662 cm−1. Crystals suitable for X-ray analyses were
obtained by slow diffusion of petrol ether (60/80) into a
CH2Cl2 solution of the complex.
1
(LSIMS) m/z: 332.7, [M–Cl]+ (100%); H-NMR (200
MHz, DMSO): l 7.88 (s, 1H, ImH); 7.34 (s, 1H, ImH);
4.05 (s, 3H, N–CH3). IR (KBr): w (CꢀO) 1639 cm−1
.
2.4.7. [Pd(Me)(Cl){(mim)2CꢀNPh2}] (3d)
2.4.2. [Pd(Cl)2{(mim)2C=NPh}] (2d)
Compound 3d was isolated as a yellow solid: Anal.
Calc. for C16H18N5ClPd: C, 45.52; H, 4.29; N, 16.59.
Found: C, 44.65; H, 4.41; N, 15.86%. MS (LSIMS)
m/z: 406, [M–CH3]+ (8%); 386, [M–Cl]+ (26%); 371,
[M–Cl–CH3]+ (100%); 264, [Ligand]+ (53%). 1H-
NMR (200 MHz, CDCl3): l 7.7–7.15 (m, 5H, ArH)
7.1–6.7 (m, 4H, ImH), 4.12 (s (br), 3H, N–CH3), three
isomers (cis–trans{major}/cis–trans{minor}/imidazole-
imine) 2.87/2.79/2.91 (each: s, 3H, N–CH3), 1.01/0.89/
0.96 (each: s, 3H, Pd–CH3).
Compound 2d was isolated as orange needles from a
chloroform solution of 3d: 1H-NMR (200 MHz,
4
DMSO): l 7.58 (d, 1H, JH–H=1.3 Hz, ImH), 7.54 (d,
1H, 4JH–H=1.9 Hz, ImH), 7.36 (d, 1H, 4JH–H=1.1
4
Hz, ImH), 7.32 (s(br), 1H, ImH), 7.22 (d, 1H, JH–H
=
1.5 Hz, ImH), 7.02 (s(br), 1H, ImH), 6.9 (s(br), 1H,
4
ImH), 6.86 (d, 1H, JH–H=1 Hz, ImH), 4.09 (s, 3H,
N–CH3), 2.8 (s, 3H, N–CH3).
2.4.3. [Pd(Cl)2{(mim)PPh2}] (2e)
Compound 2e was isolated as a brown–orange solid:
Anal. Calc. for C16H15N2PCl2Pd: C, 43.32; H, 3.41; N,
6.32. Found: C, 43.06; H, 3.44; N, 6.25%. MS (ESI in
CH3CN) m/z: 852.7, [2MH–Cl]+ (100%); 448, [M–
2.4.8. [Pd(Me)(Cl){(mim)PPh2}] (3e)
Compound 3e was isolated as a green–yellow solid:
Anal. Calc. for C17H18N2PClPd: C, 48.25; H, 4.29; N,
6.62. Found: C, 47.42; H, 4.58; N, 6.67%. MS (LSIMS)
m/z: 811, [2MH–Cl]+ (100%); 781, [2MH–Cl–2CH3]+
(24%); 443, [MH–CH3+Cl]+ (31%); 372, [M–Cl-
1
Cl+CH3CN]+ (27%). H-NMR (200 MHz, DMSO): l
3
7.9–7.2 (m, 10H, ArH), 7.12 (d, 2H, JH–H=2.28 Hz,
ImH), 3.68 (s, 3H, N–CH3); 31P-NMR (400 MHz,
DMSO): l 89 (s).
CH3]+ (19%). H-NMR (200 MHz, DMSO): l 7.9–7.3
1
(m, 12H, ArH+ImH), two isomers (major/minor)
3.13/2.78 (each: s, 3H, N–CH3), 0.94/0.85 (each: d, 3H,
3JP–H=3.8/4.4 Hz, Pd–CH3); 31P-NMR (400 MHz,
DMSO): two isomers (major/minor) l 23.9/16.6 (each:
s).
2.4.4. [Pd(Me)(Cl){(mim)2CH2}] (3a)
Compound 3a was isolated as a white solid: Anal.
Calc. for C10H15N4ClPd: C, 36.06; H, 4.53; N, 16.82.

M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
81
2.4.9. [Pd(Me)(Cl){(mim)CHCH2PPh2}] (3f)
2.5.3. [Pd(Me)(CH3CN){(mim)2CO}]BARF (4b/BARF)
Compound 3f was isolated as a white solid: Anal.
Calc. for C23H26N4PClPd: C, 51.99; H, 4.93; N, 10.54.
Found: C, 51.87; H, 4.71; N, 10.27%. MS (LSIMS)
m/z: 1027, [2MH–Cl]+ (17%); 495, [M–Cl]+ (100%);
295, [Ligand–C6H5]+ (68%). 1H-NMR (400 MHz,
CDCl3): l 7.66 (s(br), 2H, ArH) 7.57 (s(br), 2H, ArH),
7.4 (s(br), 7H, 6 ArH+1 ImH), 6.88 (s(br), 2H, ImH)
6.42 (s(br), 1H, ImH), 5.46 (m (br), 1H, CH), 3.60
(m(br), 1H, CH2), 3.28 (s(br), 3H, N–CH3), 3.16 (s(br),
3H, N–CH3), 2.95 (m(br), 1H, CH2), 0.61 (d(br), 3H,
3JP–H=3.2 Hz, Pd–CH3); 31P-NMR (400 MHz,
CD2Cl2) l 29.4 (s(br)).
Compound 4b/BARF was isolated as a white solid:
Anal. Calc. for C44H28ON5BF24Pd: C, 43.46; H, 2.32;
N, 5.76. Found: C, 43.80; H, 2.00; N, 5.50%. MS (ESI
in CH3CN) m/z: 352, [M–BF4]+ (51%); 337, [M–BF4–
CH3]+ (100%); 296, [M–BF4–CH3–CH3CN]+ (15%).
1H-NMR (200 MHz, CD2Cl2): l 7.73 (m(br), 8H, o-
3
ArH), 7.57 (s(br), 4H, p-ArH), 7.3 (d, 1H, JH–H=1.8
Hz, ImH), 7.27 (d, 2H, 3JH–H=1.4 Hz, ImH), 7.14
(s(br), 1H, ImH), 4.09 (s, 6H, N–CH3), 2.41 (s, 3H,
CH3CN), 0.98 (s, 3H, Pd–CH3); IR (KBr) w(CꢀO) 1651
cm−1, w(CꢁN) 2300 cm−1
.
2.5.4. [Pd(Me)(CH3CN){(mim)2CO}]BARF (4b/BPh4)
Compound 4b/BPh4 was isolated as a light brown
solid: Anal. Calc. for C36H36ON5BPd: C, 64.35; H,
5.40; N, 10.42. Found: C, 64.54; H, 4.30; N, 9.61%.
1H-NMR (200 MHz, CDCl3): l 7.7–6.8 (m, 24H,
ArH+ImH), 4.13 (s, 3H, N–CH3), 4.10 (s, 3H, N–
CH3), 2.01 (s, 3H, CH3CN), 0.98 (s, 3H, Pd–CH3); IR
2.5. General procedure for the preparation of cationic
complexes
The complexes were prepared according to the fol-
lowing general procedure [15]. A solution of AgBF4 (or
NaBARF (BARF=[3,5-(CF3)2C6H3]4B−), NaBPh4) in
CH3CN/CH2Cl2 was added to a well-stirred solution or
suspension of the methyl chloro Pd-complex in the
same solvent (except for 4d which was prepared in
CH3CN only). After 1 h at room temperature (r.t.) the
solution was separated from the white precipitate by
filtration through Celite and the filtrate was evaporated
to dryness. The solid was washed with hexanes (3×5
ml) and dried under vacuum. Yields in all reactions
were \90%.
(KBr) w(CꢀO) 1643 cm−1
.
2.5.5. [Pd(Me)(CH3CN){(bmim)2CO}]BF4 (4c)
Compound 4c was isolated as a yellow solid: Anal.
Calc. for C20H20ON5BF4Pd: C, 44.52; H, 3.73; N,
12.98. Found: C, 43.76; H, 3.53; N, 12.80%. MS
(LSIMS) m/z: 452, [M–BF4]+ (26%); 411, [M–BF4–
CH3CN]+ (84%); 396, [M–BF4–CH3CN–CH3]+
1
(100%). H-NMR (200 MHz, CD2Cl2): l 7.93 (pseudo
triplet, 2H, o-ArH), 7.78 (m, 6H, ArH), 4.34 (s, 3H,
N–CH3), 4.25 (s, 3H, N–CH3), 2.31 (s, 3H, CH3CN),
1.12 (s, 3H, Pd–CH3); IR (KBr) w (CꢀO) 1669 cm−1, w
2.5.1. [Pd(Me)(CH3CN){(mim)2CH2}]BF4 (4a)
(CꢁN) 2314 cm−1
.
Compound 4a was isolated as a white solid: Anal.
Calc. for C12H18N5BF4Pd: C, 33.87; H, 4.26; N, 16.46.
Found: C, 33.88; H, 4.13; N, 16.40%. MS (LSIMS)
m/z: 338, [M–BF4]+ (10%); 297, [M–BF4–CH3CN]+
2.5.6. [Pd(Me)(CH3CN){(mim)2CꢀNPh}]BF4 (4d)
Compound 4d was isolated as a yellow solid: Anal.
Calc. for C18H21N6BF4Pd: C, 42.0; H, 4.12; N, 16.33.
Found: C, 39.24; H, 4.27; N, 15.04%. MS (LSIMS)
m/z: 427, [M–BF4]+ (6%); 386, [M–BF4–CH3CN]+
1
(41%); 282, [M–BF4–CH3CN–CH3]+ (49%). H-NMR
(400 MHz, CDCl3): l 6.98 (s, 1H, ImH), 6.76 (s, 1H,
ImH), 6.62 (s, 1H, ImH) 6.59 (s, 1H, ImH), 3.49 (s,
3H, N–CH3), 3.44 (s, 3H, N–CH3), 2.19 (s, 3H,
CH3CN), 0.61 (s, 3H, Pd–CH3). IR (KBr): w (CꢁN)
1
(18%); 371, [M–BF4–CH3CN–CH3]+ (37%). H-NMR
(200 MHz, CD2Cl2): l 7.7–6.8 (m, 9H, ArH), three
isomers (cis–trans {major} /cis–trans {minor}/imida-
zole-imine) each: 4.16/4.12/4.08 (s, 3H, N–CH3), 2.88/
2.84/2.92 (s, 3H, N–CH3), 2.42/2.46/2.49 (s, 3H
CH3CN), 1.0/0.89/0.97 (s, 3H, Pd–CH3).
2314 cm−1
.
2.5.2. [Pd(Me)(CH3CN){(mim)2CO}]BF4 (4b/BF4)
Compound 4b/BF4 was isolated as a yellow solid:
Anal. Calc. for C12H16ON5BF4Pd: C, 32.79; H, 3.67;
N, 15.93. Found: C, 33.12; H, 3.23; N, 15.42%. MS
(ESI in MeOH/CH3CN) m/z: 352, [M–BF4]+ (100%);
337, [M–BF4–CH3]+ (77%); 296, [M–BF4–CH3–
2.5.7. [Pd(Me)(CH3CN){(mim)PPh2}]BF4 (4e)
Compound 4e was isolated as a yellow solid: Anal.
Calc. for C19H21N3PBF4Pd: C, 44.26; H, 4.10; N, 8.15.
Found: C, 43.79; H, 3.68; N, 8.07%. MS (LSIMS) m/z:
943, [2M–BF4]+ (50%); 811, [2MH–CH3–CH3CN–
1
CH3CN]+ (9%). H-NMR (400 MHz, CH2Cl2/DMSO):
l 7.63 (d, 1H, ImHd), 7.54 (d, 1H, ImHa), 7.40 (d,
1H, ImHc), 7.54 (d, 1H, ImHb), 3.97 (s, 3H, N–
CH3i), 3.96 (s, 3H, N–CH3h), 1.93 (s, 3H, CH3CN),
0.61 (s, 3H, Pd–CH3); IR (KBr) w (CꢀO) 1663
1
C6H5]+ (17%). H-NMR (200 MHz, CD2Cl2): l 7.63
(m, 10H, ArH), 7.57 (s, 1H, ImH), 7.53 (s, 1H, ImH),
4.34 (s, 3H, N–CH3), 3.24 (s, 3H, N–CH3), 1.77 (s, 3H,
3
cm−1
.
CH3CN), 1.32 (d, 3H, JP–H=3.6 Hz, Pd–CH3).

82
M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
2.5.8. [Pd(Me){(mim)2CHCH2PPh2}]BF4 (4f)
which was dried at 100°C and cooled to r.t. under
vacuum.
Compound 4f was isolated as a white solid: Anal.
Calc. for C23H26N4PBF4Pd: C, 47.4; H, 4.51; N, 9.62.
Found: C, 47.22; H, 4.82; N, 9.36%. MS (LSIMS) m/z:
495, [M–BF4]+ (100%); 295, [Ligand–C6H6]+ (56%).
1H-NMR (200 MHz, DMSO): l 7.7–7.3 (m, 10H,
ArH), 7.05 (m, 3H, ImH), 6.86 (s, 1H, ImH), 4.82
(q(br), 3JH–H=12.8 Hz 1H, CH), 3.92 (s, 3H, N–
CH3), 3.2 (s(br), 5H, CH2+N–CH3), −0.55 (d, 3H,
3JP–H=3.4 Hz, Pd–CH3).
2.8.1. General procedure
A solution of the complex in CH2Cl2 (40 ml) was
transferred into the autoclave under nitrogen. The au-
toclave was weighed then charged with 20 bar of ethyl-
ene followed by 20 bar of carbon monoxide at r.t. The
vessel was then placed into an oil bath at 90°C and
allowed to equilibrate at 50°C, at which point timing
was started. The mixture was stirred for 1 h at 50°C
then cooled to r.t. in an ice bath. The pressure was
slowly released and the autoclave reweighed. The reac-
tion mixture was filtered and the filtrate analysed by
GC. The solid was washed with CH2Cl2 and dried in
air. Values typically found for the grey–white solids:
Anal. Calc. for C3H4O: C, 64.26; H, 7.21. Found: C,
2.6. Variable temperature NMR studies of CO and
ethylene insertions into cationic methyl complexes
CD2Cl2 was added to a NMR tube charged with the
desired complex under a nitrogen atmosphere. For the
less soluble complexes d6-DMSO was added dropwise
until complete dissolution was obtained. The tube was
closed with a septum fitted with two needles, one
reaching into the solution. The tube was immersed into
a cooling bath set to the desired temperature and a
gentle stream of CO or ethylene was bubbled through
the solution for approximately 3 min.
63.14; H, 7.38%. IR (KBr): w(CꢀO) 1694 cm−1
.
3. Results and discussion
3.1. Preparation and characterisation of neutral and
cationic complexes
2.6.1. [Pd(Me)(CH3CN){(mim)2CO}]BARF (5b),
[Pd(Me)(CO){(mim)2CO}]BARF (5b%) (obser6ed in situ
(NMR) at −60°C)
The imidazole chelate ligands 1a and 1b [11,12a] (Fig.
1) have been synthesised by modified literature proce-
dures. Thus, lithiation of N-methylimidazole and subse-
quent reaction with diethylcarbonate at low tem-
perature in THF afforded the keto bridged 1b. The
methylene bridged bis-imidazole 1a was obtained by
Wolff–Kishner reduction of 1b. These compounds
served as precursors for the new ligands 1d and 1f.
Treatment of a CH2Cl2 solution of 1b with a slight
excess of aniline in the presence of TiCl4 gave the imine
derivative 1d. Deprotonation at the bridging methylene
group in 1a with BuLi followed by reaction with
Ph2CH2Cl [18] at low temperature in THF afforded 1f.
A paper describing synthetic details for these and other
related ligands will be published elsewhere. Compound
1c was prepared as previously reported [16] and 1e
following a procedure given for the N-benzyl derivative
[17].
Reaction of [PdCl2(COD)] or [PdMeCl(COD)] with
1.05 equivalents of the respective ligand in CH2Cl2
afforded the neutral dichloro and chloro, methyl com-
plexes in yields \90% (Scheme 1). Generally the
methyl, chloro complexes appear to be lighter in colour
than their dichloro counterparts. Complexes 2b–d and
3a–c are relatively air and temperature stable com-
pounds, whereas 2e, 3e,f are air sensitive due to facile
oxidation of the phosphorus. In chloroform solution
the imine complex 3d undergoes elimination of the
methyl group, even at r.t. Within 1 or 2 days orange
needles, which were identified by crystal structure deter-
mination (see below) as the respective dichloro complex
1H-NMR (400 MHz, CD2Cl2): l 7.3, 7.27, 7.24, 7,
7.02, 6.97, 6.90, 6.86 (each: s, 1H, ImH (5b, 5b%)), 4.02,
4.01, 3.99, 3.97 (each: s)(6H, N–CH3), 2.67 (s, 3H,
Pd–C(O)CH3 (5b%)), 2.47 (s, 3H, Pd–C(O)CH3 (5b)),
2.36 (s, 3H, CH3–CN (5b)).
2.7. Catalytic Heck coupling of n-butyl acrylate and
4-bromoacetophenone
In a typical run, a 100 ml Schlenk flask was charged
with 4-bromoacetophenone (4.98 g, 25 mmol) and an-
hydrous sodium acetate (2.29 g, 27.92 mmol), and
degassed by successive vacuum-nitrogen cycles. N,N-
Dimethylacetamide (25 ml) and n-butyl acrylate (5 ml,
27.5 mmol) were then added. The complex (2.5×10−5
mmol) was dissolved in N,N-dimethylacetamide (10 ml)
and 0.1 ml of this solution injected into the reaction
mixture which was then heated to 120°C. After 24 h the
mixture was allowed to cool and di(ethylene gly-
col)butyl ether (500 ml) added. A sample of the solution
(500 ml) was taken, injected into a sample vial
containing 5% HCl (5 ml) and extracted with 2.5 ml of
CH2Cl2. The CH2Cl2 extracts were analysed by gas
chromatography.
2.8. Catalytic copolymerisation of CO and ethylene
Catalytic copolymerisation of CO and ethylene was
carried out in a 75 ml stainless steal test autoclave

M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
83
Fig. 1. 1,1-Methylimidazole based chelate ligands used in the preparation of palladium complexes.
Scheme 1.

84
M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
Table 1
Selected 1H-NMR data for neutral complexes
Complex
Solvent
Pd–CH3
N–CH3
2b
2d
2e
3a
3b
3c
DMSO
DMSO/CDCl3
DMSO
DMSO
DMSO
–
–
–
0.46
0.68
1.12
4.05
2.79/4.09
3.68
3.70/3.76
4.05
4.23/4.25
CDCl3
a
3d
CDCl3
1.01, 0.89, 0.96
DMSO
CDCl3
2.87/4.12 (br), 2.79/4.12 (br), 2.91/4.12 (br)
0.85/0.94
0.61
3e b
3f
2.78/3.13
3.16/3.28
a Three isomers.
b Two isomers.
Table 2
Selected 1H-NMR data for cationic complexes
Complex
Solvent
Pd–CH3
N–CH3
NC–CH3
4a
CDCl3
0.31
3.44/3.49
2.19
4b/BF4
4b/BF4
4b/BARF
4c
DMSO
CD2Cl2/DMSO
CD2Cl2
0.76
0.0/0.73
0.98
4.04
4.06
4.09
4.25/4.34
–
2.05/(1.94)
2.41
2.31
CD2Cl2
1.12
4c
4d
4e
4f
CD2Cl2/DMSO
CD2Cl2
CD2Cl2
0.79/0.94
1.0, 0.89, 0.97
1.31
4.11
2.26/(1.99)
2.42, 2.46, 2.49
1.77
–
a
2.88/4.16, 2.84/4.12, 2.92/4.08
3.24
3.2/3.92
DMSO
−0.55
a Three isomers.
2d, crystallised from the CDCl3 solution. Complexes 2d,
3c,d,f are soluble in CH2Cl2 and CHCl3 whereas 2b,
3a,b require DMSO as a solvent. Complexes 2e and 3e
are only sparingly soluble in DMSO.
Full characterisation of the complexes was accom-
1
plished by H-NMR, MS, IR, and microanalysis. Se-
lected 1H-NMR data are shown in Table 1 (neutral
complexes) and Table 2 (cationic complexes).
The cationic acetonitrile complexes 4a–e were pre-
pared in \90% yields from the respective chloro com-
plexes in CH3CN or CH3CN/CH2Cl2 solution by halide
abstraction with silver or sodium salts (Scheme 1). The
complex 4f contains no ancillary solvent ligand and
hence the remaining coordination site is occupied by
the third donor function of the ligand 1f (see discussion
below). The cationic complexes are unstable in solution
over extended periods at r.t. Decomposition in solution
was significantly more rapid for 4d and precipitation of
a brown black solid from CH2Cl2 solutions occurred
within a few minutes. The cationic complexes 4b/BARF
(BARF=[3,5-(CF3)2C6H3]4B−) [19] and 4b/BPh4 were
prepared by treatment with the sodium salts of the
anions. Stabilities were found to decrease in the order
BF−4 \BARF−\BPh−4 . A similar trend in stabilities
was observed by Macchioni et al. [18] who investigated
the counterion effect on the ethylene/CO copolymerisa-
tion for cationic Pd(II) bipy complexes. The com-
pounds can be kept over weeks without decomposition
when stored as solids at –20°C.
A downfield shift of the Pd–CH3 resonance is ob-
served for the complexes 3b–d and 4b–d compared to
3a and 4a which reflects the influence of the electron
withdrawing CꢀO and CꢀN–Ph groups present in the
ligand backbone, on the metal centre.
Mass spectra analysis of the imidazole phosphine
complexes 2e, 3e and 4e provided evidence for the
expected dimeric structures. For an analogous ligand,
diphenylphosphine(1-benzylimidazol-2yl),
a
dimeric
gold complex was reported [17], and the related pyri-
dine ligand has been shown to act as a bridging ligand
1
in Rh and Pd complexes [21]. The H- and 31P-NMR
spectra of 2e display one singlet for the CH3–N group
(l=3.68 ppm) and for phosphorus (l=89 ppm), re-
spectively, indicating the presence of one isomer, the
exact structure of which is uncertain (whether head-to-
tail or head-to-head; Fig. 2). For 3e evidence for the
formation of two of the four possible isomers (Fig. 2)
was detected. The 31P-NMR spectrum displays singlets
at l=23.9 and 16.6 ppm. The Pd methyl resonances
of 3e (l=0.94 ppm, 3JP–H=3.8 Hz, and 0.85 ppm,

M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
85
3JPꢂH=4.3 Hz) appear as doublets with coupling con-
stants indicating cis arrangements for the phosphorus
and methyl group. Similar values were found by Vrieze
et al. [22] for Pd and Pt complexes with P–N ligands.
Since both Pd–CH3 resonances appear as doublets the
possibility of the second isomer being the head-to-head
isomer can be excluded and therefore the formation of
head-to-tail isomers with the methyl groups either trans
or cis to each other is very likely. For the complex 4e,
one singlet at 17.4 ppm in the 31P-NMR spectrum and
1
one doublet at 1.32 ppm (3JP–H=3.8 Hz) in the H-
NMR spectrum indicate the presence of one isomer
only.
The imino function in the ligand backbone of 3d
1
gives rise to two sets of signals in the H-NMR spec-
trum due to the formation of the two possible isomers
(Fig. 3) in a ratio of approximately 1.7:1. A third set of
signals of low intensity, with similar shift values, pre-
sumably belongs to a third isomer in which the ligand
is coordinated via one imidazole ring and the imino
function. The 1H-NMR spectrum of 4d exhibits the
expected sets of resonances for the three possible iso-
mers of 4d (Table 2). In addition a singlet for free
CH3CN and other signals belonging to unidentified
decomposition products are present owing to the lim-
ited stability of 4d.
Complexes 3f and 4f are particular interesting since
they contain the new tridentate mixed donor ligand 1f.
A doublet for the Pd–CH3 group in 3f at l=0.61 ppm
(3JP–H=3.2 Hz) reveals N–P coordination in which the
soft Pd centre prefers the soft P donor. All signals are
broad at r.t. indicating a slow dynamic process, which
involves exchange between coordinated and uncoordi-
nated groups. Canty et al. has reported similar fluxional
behaviour for the symmetrical and unsymmetrical tri-
Fig. 2. Possible ‘head-to-tail’ and ‘head-to-head’ isomers of 2e and 3e.
dentate
ligands
[(pz)2(mim)CH],
[(pz)2(py)CH],
[(py)2(mim)CH] and [(py)(mim)2CH] when coordinated
to PdMe2 and PdMeI fragments [12b].
Surprisingly, no coordinated CH3CN could be de-
tected in the NMR spectrum of 4f after removal of the
solvent under reduced pressure and microanalysis confi-
rmed the absence of the solvent ligand. The compound
was only soluble in hot DMSO but remained in solu-
tion on cooling to r.t. No signs of decomposition were
observed. Removal of the solvent under reduced pres-
sure and a second addition of DMSO led to the same
observation. The 1H-NMR (d6-DMSO) of 4f shows
bidentate coordination by two of the three donor atoms
and coordination by DMSO. The appearance of a
3
doublet for the Pd–CH3 group (l= −0.55 ppm, JP–H
=3.4 Hz) and two singlets for the CH3–N group
(l=3.19 and 3.92 ppm) indicate P–N coordination of
the ligand. The coordination of the |-donor DMSO
gives rise to a large upfield shift of the Pd–CH3 group
compared to 3f. It is apparent that the ligand in 4f
displays hemilabile behaviour with one imidazole ring
dangling in the presence of coordinating solvents and
becoming coordinating when the solvent is removed.
We therefore conclude that coordination of all three
Fig. 3. Isomers of 3d and 4d.

86
M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
donors occurs in solid, desolvated 4f. Although there is
no evidence for the presence of a dimeric species in the
mass spectrum of 4f ([M]=495 (100%)), we are unable
to unambiguously decide whether the complex adopts a
dimeric structure in which 1f acts as a bridging ligand
or whether it has a monomeric structure with a trigonal
pyramidal geometry around the Pd centre (Fig. 4). The
insolubility of 4f in common non-coordinating solvents
prevented the growth of crystals. Vrieze et al. [3c,15]
reported cationic PdMe complexes bearing tridentate
nitrogen ligands, which coordinate via all three donor
atoms. Because of the flexibility of the ligands Pd
adopts a square planar geometry in these complexes.
Interestingly, for the related neutral PdMeCl complexes
they observed that only one of the ligands, containing a
imidazole ring, has a strong tendency to coordinate in a
tridentate fashion whereas the other closely related
ligands prefer bidentate coordination [3c].
Fig. 4. Possible structures for 4f.
3.2. Crystal structures of the complexes
[PdCl2{(mim)2NPh}] (2d) and [PdMeCl{bmim)2CO}]
(3c)
Complexes 2d and 3c were characterised by X–ray
crystallography (Fig. 5). Selected bond distances and
angles are given in Table 3. The results of the low-tem-
perature single-crystal X-ray structure determinations
are in accord with the stoichiometries, connectivities
and stereochemistries proposed/implied above. In each
case, a single molecule of complex, accompanied by a
single molecule of hydrogen-bonded solvent—chloro-
form and dichloromethane, respectively, comprise the
asymmetric unit of the structure.
The palladium atoms, as might be expected, are
found in the common, four-coordinate ‘square-planar’
environment, comprising a pair of essentially equivalent
chelating Pd–N (bidentate) interactions, opposed by a
pair of unidentate trans interactions. However, in com-
plex 3c containing the ‘fused’ benzimidazole ligand the
narrow bite angle [N(11)–Pd–N(21)=85.6(1)°] causes
distortion of the square planar structure. In comparison
the bite angle in 2d [N(11)–Pd–N(21)=88.5(1)°] devi-
ates only slightly from the ideal value. A similar obser-
vation was made by Jordan et al. for the bispyrazolyl
complexes [PdCl2{Ph2C(3-tBu-pz)2}] [83.62(8)°] and
[PdCl2{Ph2C(pz)2}] [89.51(8)°] [7] and Canty et al. re-
ported similar bite angles for tris pyrazolata Pd(IV)
complexes [23].
Fig. 5. Projection of 2d and 3c with their associated solvent
molecules. Fifty percent displacement ellipsoids are shown for ther
,
non-hydrogen atoms having arbitrary radii of 0.1 A.
One Pd–Cl interaction is common to both 2d and 3c;
,
Pd–Cl(1) differ appreciably, longer in 3c by ca. 0.03 A,
in keeping with the considerable diminution in biden-
tate ligand bite, presumably consequent on substitution
of CNPh in 2d by CO in 3c. The Pd–N interaction,
Pd–N(21), reflects the differing trans-effects of methyl
versus Cl(2), an effect which presumably also correlates
with the change in bite of the bidentate ligand, and also
Fig. 6. Annotation of protons of (mim)2CO in 4b, assigned by COSY
NMR experiments.

M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
87
in the cis N–Pd–X angles, which, symmetrical in 2d,
become appreciably different in 3c. The Pd–N(21)
the significant differences in Pd–N–C(2,5) angles, con-
sequent upon the change in coordinating entity from a
simple imidazole to a benzimidazole (Table 3). Other
angular parameters of the C3N2 array remain similar
for the two complexes, except insofar as the arrays are
bound together by CO or CNPh, where significant
differences, again perhaps attributable to benzimidazole
fusion, are found in C–C(n2)–N(n3).
,
bond [2.156(3) A] trans to the methyl group in 3c is
significantly longer than the Pd–N(11) bond [2.042(3)
,
A] trans to the chloride group which is in keeping with
the greater trans effect of the methyl group and similar
values have been reported for other nitrogen chelate Pd
complexes [3a,d,i,24].
While N(coordinated)–C distances are identical be-
tween the two compounds, it is of interest to observe
At the fusion of the two rings, the N,O:CC2 arrays
are effectively planar. Dihedral angles between
Table 3
Selected molecular geometries (2d, 3c) a
Atoms
Parameter
Atoms
Parameter
,
Distances (A)
Pd–Cl(1)
Pd–N(11)
2.2916(8), 2.323(1)
2.020(3), 2.042(3)
1.331(4), 1.338(5)
1.385(4), 1.389(5)
1.359(4), 1.364(5)
1.376(4), 1.378(5)
1.341(5), 1.393(6)
1.481(4), 1.489(6)
1.284(4), 1.212(5)
2.48(3), 2.66(est.)
Pd–Cl(2)/C(0)
Pd–N(21)
2.2964(9), 2.030(4)
2.031(2), 2.156(3)
1.324(1), 1.323(5)
1.372(4), 1.374(5)
1.353(3), 1.367(5)
1.361(4), 1.374(5)
1.363(5), 1.414(5)
1.461(4), 1.489(6)
3.374(4), 3.597(5)
N(11)–C(12)
N(11)–C(15)
C(12)–N(13)
N(13)–C(14)
C(14)–C(15)
C(12)–C
N(21)–C(22)
N(21)–C(25)
C(22)–N(23)
N(23)–C(24)
C(24)–C(25)
C(22)–C
C–N/O
H(1)···Cl(1)
Cl(1)···C(1)
Angles (°)
N(11)–Pd–N(21)
N(11)–Pd–Cl(2)/C(0)
N(11)–Pd–Cl(1)
Pd–N(11)–C(12)
Pd–N(11)–C(15)
C(12)–N(11)–C(15)
N(11)–C(12)–C
N(11)–C(12)–N(13)
C–C(12)–N(13)
C(12)–N(13)–C(14)
N(13)–C(14)–C(15)
C(14)–C(15)–N(11)
C(12)–C–C(22)
88.5(1), 85.6(1)
91.03(7), 90.6(1)
177.50(7), 176.8(1)
124.0(2), 119.6(3)
129.5(2), 131.1(3)
106.0(3), 105.7(3)
124.1(3), 125.3(4)
110.5(2), 111.9(3)
125.4(3), 122.7(3)
106.7(3), 106.7(3)
107.5(3), 130.7(4)
109.2(3), 108.8(4)
114.5(2), 117.5(4)
126.7(3), 121.4(4)
152(3), 163(est.)
Cl(1)–Pd–Cl(2)/C(0)
N(21)–Pd–Cl(1)
N(21)–Pd–Cl(2)/C(0)
Pd–N(21)–C(22)
Pd–N(21)–C(25)
C(22)–N(21)–C(25)
N(21)–C(22)–C
N(21)–C(22)–N(23)
C–C(22)–N(23)
C(22)–N(23)–C(24)
N(23)–C(24)–C(25)
C(24)–C(25)–N(21)
C–N–C(01)
90.57(3), 87.9(1)
89.95(7), 95.65(9)
176.93(6), 173.2(2)
125.6(2), 119.3(3)
126.9(2), 132.6(2)
107.4(2), 105.7(3)
123.2(2), 124.9(4)
109.9(3), 112.7(4)
126.9(3), 122.3(3)
107.4(2), 106.6(3)
107.4(3), 135.9(4)
107.9(3), 109.1(3)
123.0(2), –
C(12)–C–N/O
Cl(1)···H(1)–C(1)
C(22)–C–N/O
118.7(2), 121.0(4)
,
Plane parameters (de6iations l (A); dihedrals q (°))
(a) The N2Cl(1)Cl(2)/C(0) array ( 1340, 134)
2
lN(11)
lCl(1)
lPd
0.085(3), 0.027(4)
0.010(1), 0.003(1)
0.014(1), 0.071(2)
22.4(1), 45.6(1)
lN(21)
−0.073(3), −0.023(4)
−0.010(1), −0.043(5)
57.69(8), 61.3(1)
lCl(2)/C(0)
q/O,NC3
q/im(2)
q/im(1)
28.5(1), 39.7(1)
(b) The (benz)imidazole C3N2/C7N2 planes
2(1)
22, 159
2(2)
13, 32
q1/O,NC3
q(1/2)
lPd1
49.1(1), 24.3(2)
39.0(1), 28.9(1)
0.247(5), 0.647(5)
0.100(6), 0.153(6)
q2/O,NC3
39.3(1), 25.9(1)
lPd2
lC2
0.137(5), 0.517(5)
−0.003(5), 0.054(6)
lC1
2
(c) The central ring N(11,21)C(12,22) plane ( 387, 92)
q/im(1)
lPd
22.5(1), 15.6(1)
0.509(4), 0.955(5)
q/im(2)
lC
lN/O
16.9(1), 13.3(1)
0.442(4), 0.289(6)
1.195(6), 0.690(8)
a The two values in each entry are for 2d, 3c, respectively, the latter italicized. In 2d, the dihedral angle between the phenyl C6 plane and the
NC3 plane is 42.1(1)°; it is also at 39.8(1)° to the coordination plane and 51.8(1), 12.9(1)° to the C3N2(im) planes.

88
M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
blets (3JC–H=1.6 Hz) for the two inequivalent imida-
zole rings. COSY-NMR experiments at −50°C
revealed two independent sets of coupled imidazole
olefin peaks (3JH–H=1.2 Hz). One at low field (7.63
and 7.40 ppm) and the other at 7.54 and 7.17 ppm. The
coupling constants are small even for a cis configura-
Fig. 7. Fluxional boat-to-boat inversion of the chelate ring in 4b.
4
tion, in fact they are in the order of JH–H long range
couplings between the N–CH3 groups and Ha and Hc
in the ring (numbering scheme Fig. 6). Long range
COSY experiments revealed that the low field imidazole
coupled olefins are associated with the higher field
N–CH3 (3.96 ppm CH3a). Ha was therefore assigned
the resonance at 7.54 ppm and Hb at 7.17 ppm. Hc has
a resonance at 7.40 ppm while Hd is downfield at 7.63
ppm and CH3b at 3.97 ppm. The significant difference
in the chemical shift of Hb (at highest field) and Hd
(lowest field) reflects their proximity to the asymmetric
Pd centre.
Signals for uncoordinated (l=1.93 ppm) and coor-
dinated (l=2.04 ppm) CH3CN in a ca. 2.5:1 ratio
indicate partial exchange of coordinated CH3CN for
DMSO. The spectrum displays two singlets (0.7 and 0.0
ppm) for the Pd–CH3 protons. The imidazole signals
broaden on warming to −10°C. Between 0 and 10°C
the signal for the N–CH3 protons sharpens whereas the
signals for the olefinic imidazole ring protons have
almost vanished and the ratio of uncoordinated to
coordinated CH3CN is significantly lowered to ca.
1.3:1. Warming to 30°C gives rise to one broad signal in
the olefinic region and a sharp singlet for the N-CH3
protons. The ratio of uncoordinated to coordinated
CH3CN diminishes to 0.4:1. The disappearance of the
olefinic signals between 0 and 10°C, their broadening at
30°C and the changing ratio of uncoordinated to coor-
dinated CH3CN can be explained by a slow exchange
process between CH3CN and DMSO. Similarly, addi-
tion of d6-DMSO to a solution of 4b/BARF in CD2Cl2
(at r.t.) resulted in an upfield shift (0.4 ppm) of the
CH3CN signal and caused the three doublets of the
olefinic protons to merge into a broad singlet, indicat-
ing exchange of CH3CN for DMSO.
The four doublets and two singlets observed for 4b at
−60°C and their broadening at −10°C can be as-
cribed to a fluxional process involving the slow inver-
sion of the chelate ring (Fig. 7) which adopts a boat
conformation in the solid state as shown by the crystal
structures of 2d and 3c. Similar behaviour was observed
for the related complexes [PdCl2{(pz)2CMe2}] [25],
[PdMeX{(pz)2CHR}] [PdMeX{(py)2CHR}] (R=H,
Me; X=Me, I) [12a] and more recently [PdCl2-
{(pz)2Ph2C}] [7]. The slower ring inversion in 4b com-
pared to the methylene bridged [PdMeI{(mim)2CH2}]
[12a] which gives a singlet for the methylene protons
down to −70°C may be ascribed to a more rigid bridge
containing sp2 hybridised carbon. We cannot com-
pletely rule out a donor induced dissociative exchange
N,O:CC2 and the co-ordination planes differ by only a
few degrees (Table 3). Significant differences are found
between the pitches of the individual planes within each
complex (taking for example the co-ordination plane as
the reference in each case), of ca. 6°, with even greater
differences between the pitches of counterpart planes of
the two complexes. Those for 3c are much more steeply
inclined than those for 2d, relative to the co-ordination
plane, with the consequence that C(0) deviates much
more from the coordination plane in 3c than C(N) in
2d. It may be that in 3c, contacts between the methyl
ligand and the neighbouring benzimidazole group influ-
ence moiety dispositions. The resultant chelate rings,
Pd(NC)2C, formed by the ligands, may be described in
terms of a ‘boat’ conformation. Taking the (NC)2 array
as a datum’plane’ in each case, the palladium atom
deviates by appreciably more in 3c than 2d; by contrast,
the deviation of the bridging carbon is less in 3c, cf. 2d,
both deviations being to the same side of the plane.
Similar six-membered boat conformations have been
reported for the related bis pyrazolyl complexes [Pd
Cl2{(R-pz)2CPh2}], R=3-H, 3-tBu [7] and [Pd
Cl2{(pz)2CMe2}] [25] in which chelate ligands bond via
heterocyclic donors. Analogous structural features had
also been described earlier by Canty et al. for related
bisimidazole and mixed imidazole/heterocyclic Pd(II)
complexes on the basis of variable temperature NMR
experiments [12a]. Specific bonding parameters about
the metal in the present array are comparable with
those established in various other systems. The Pd–
CH3 distance is similar to those found for other sp3
carbons in bipy and phen ligated Pd(II) complexes
[3b,d,i,18,24] but slightly elongated compared to a
Pd(II) complex bearing a pyridine-imine chelate ligand
,
[2.01(1) A] reported by Vrieze et al. [3f].
3.3. Variable temperature NMR studies
Variable temperature NMR studies were carried out
on the cationic complexes 4b BF4/BARF and 4c/BF4 to
investigate fluxional processes in the complexes. Vari-
able temperature NMR was also used to study insertion
of CO/ethylene into the Pd alkyl bond.
Fluxional boat-to-boat inversion for the chelate ring
and exchange of the weakly coordinated CH3CN are
observed in 4b. The 1H-NMR spectrum of 4b/BF4,
dissolved in CD2Cl2/d6-DMSO at −60°C exhibits two
singlets for the N–CH3 group and four resolved dou-

M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
89
process (presence of DMSO) for 4b/BF4, which has also
been proposed [20]. However, the broadened reso-
nances of 4b/BARF observed at r.t. in pure CD2Cl2,
were completely resolved at −80°C. Similarly, in com-
plex 4c exchange of CH3CN for DMSO is observed
above 0°C, however boat-to-boat inversion of the
and 5b%, support a dissociative mechanism for the car-
bonylation of 4b, i.e. insertion occurring from a four-
coordinated intermediate [5b,c,20,26]. However,
a
carbonylation pathway which occurs from a five-coor-
dinated intermediate [3g,18,27] cannot be completely
ruled out.
1
chelate ring was not observed. The r.t. H-NMR spec-
Insertion of CO into the Pd–CH3 bond in 4b is
complete at −60°C. The shift values for the acyl
methyl group (l=2.67 (CO adduct) and 2.47 ppm
(CH3CN adduct) are similar to those reported for other
Pd–acyl complexes containing chelating nitrogen lig-
ands [3a–c,e,j]. The CH3CN signals broaden at −20°C
and almost disappear at 0°C indicating a slow exchange
of free and coordinated CH3CN at this temperature.
Warming to r.t. causes broadening of both acyl singlets
accompanied by coalescence of the CH3CN signals.
By contrast, carbonylation of the benzimidazole
complex 4c required higher temperatures. Insertion of
CO was complete only above −10°C (CH3(O)C–Pd:
l=2.39 ppm). Presumably steric crowding caused by
the benzimidazole rings retards the CO insertion [3a].
trum (CD2Cl2) shows two singlets for the N–CH3
groups. Down to −60°C (CD2Cl2/DMSO) only one set
of signals is observed for the ortho (doublet) and meta
(triplet) protons of the benzimidazole ring. Presumably
the sterically more demanding benzimidazole rings re-
tard ring inversion in 4c. A similar observation was
t
made for [PdCl2{(R3-pz)2Ph2C}] (R=H, Bu) [7].
3.4. CO insertion studies
In a study of the reaction of 4b/BARF with CO, at
−90°C the 1H-NMR spectrum exhibits signals for
unreacted 4b/BARF, displaced CH3CN (l=1.97 ppm),
and three other species. These species are two insertion
products 5b and 5b%, which are present as the CH3CN
(l=2.35 ppm) and CO adducts (Scheme 2), and a
species believed to be a palladium methyl, carbonyl
complex, which has a singlet at 1.07 ppm downfield
from the Pd–CH3 resonance. Consistent with our pro-
posals van Asselt et al. have reported the formation of
two Pd–acyl complexes in the reaction of cationic
[Pd(Me)(CH3CN)(p-An-BIAN)]+ with carbon monox-
ide [3a], and Brookhart et al. have reported the isola-
tion and characterisation of a related methyl, carbonyl
complex [Pd(Me)(CO)(phen)]+ along with the respec-
tive insertion product [Pd{C(O)Me}(CO)(phen)]+ in a
carbonylation reaction at −78°C [3c,5b]. The signal at
1.07 ppm disappears on warming to −70°C, and no
signal for coordinated CH3CN in this species could be
detected. These observations, the presence of uncoordi-
nated CH3CN, and the weak coordination of CH3CN,
reflected in the formation of two insertion products 5b
3.5. Ethylene insertion studies
Ethylene insertion into the Pd–acyl bond has been
studied for 5b but the formation of various intermedi-
ates which occur in this reaction [3c] and the presence
of CH3CN leading to exchange processes hampers the
unambiguous assignment of the observed signals. How-
ever, at −90°C the two acyl signals, the N–CH3
resonance and the signal for coordinated CH3CN for 5b
and 5b% are broad indicating a slow exchange process.
Coalescence is observed at −60°C giving rise to new
broadened resonances for Pd–C(O)CH3 (l=2.53 ppm)
and N–CH3 (l=4 ppm) which can be ascribed to the
formation of the expected ethylene, acyl complex
[Pd{C(O)Me}(C2H4){(mim)2CO}]+. Consistent with
ethylene CH3CN exchange a broad signal is observed
for CH3CN at 2.0 ppm. Due to the formation of
Scheme 2.

90
M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
Scheme 3.
various intermediates a series of new signals appears
between −40 and +20°C. The presence of expected
triplets between 3.1 and 2 ppm provides clear evidence
for the formation of insertion products in which either
carbon monoxide, ethylene and/or CH3CN occupy the
fourth coordination side (Scheme 3).
2, 5, 6). Early catalyst decomposition might be the
reason for the inactivity of 4d which appeared to be
unstable in chlorinated solvents. Surprisingly complex
4f containing the tridentate ligand 1f which might be
Table 4
Heck coupling reactions with 4-bromoacetophenone/butylacrylate a
3.6. Catalysis
b
Entry
Catalyst
Mol%
TON
TOF c
The results obtained from catalytic experiments (Ta-
bles 4 and 5) with these new imidazole based Pd
complexes provides information on ligand influences
and hence the catalytic behaviour of the respective
complexes.
1
2
3
3a
3b
3c
1.0×10−3
1.0×10−3
1.0×10−3
n.d. d
100 000
56 308
n.d.
4167
1513
a Reaction conditions: NaOAc (2.29 g), DMA (25 ml), 120°C, 24 h.
b Moles product per mole catalyst.
c TON per hour.
Heck coupling reactions [28,29] were carried out
using bromoacetophenone/n-butylacrylate as a test sys-
tem. TONs of up to 5 750 000 and 1 700 000 have been
reported in this reaction for phosphine palladacycles
[29b] and palladium complexes of chelating carbene
based ligands [29e] respectively. Reports on Heck-cou-
pling reactions, involving nitrogen-ligated complexes
are scarce [30]. For the keto bridged bisimidazole com-
plex 3b (entry 2, Table 4) high turnover numbers,
comparable to those reported for monodentate carbene
complexes [PdMe(carbene)(b-diketone)] [29c] were ob-
tained. In comparison, 3c is about half as active as 3b,
whereas 3a shows very little activity at all and gives
unidentified brominated products.
A similar behaviour is observed when the complexes
were tested for ethylene/CO copolymerisation (Table
5). Only 4b (entries 2–4, 6) catalysed the production of
polyketone. Activities however are low compared to
those reported for bisphosphine coordinated palladium
complexes (106 mol C2H4/mol Pd) [5d,e]. Catalysis is
accompanied by decomposition (grey polymer from Pd
deposition). The catalytic performance reflects the ex-
pected dependence on the counterion employed (entries
d Five unidentified brominated products.
Table 5
Ethylene/CO copolymerisation a
Entry
Catalyst
mmol
Time (h)
TON b Activity c
1
2
3
4a
0.035
0.126
0.055
0.035
0.079
0.074
0.089
0.099
0.1
1
1
18.5
2
1
1
1
1
3
1
–
–
4b/BF4
4b/BF4
4b/BF4
4b/BPh4
4b/BARF
4c
213
449
133
–
222
–
–
–
–
–
116
13
35
4 d
5
–
6
7
8
88
–
–
–
–
–
4d
4d
4e
4f
9 e
10
11 f
0.07
0.076
1
a Reaction conditions: CH2Cl2 (40 ml), 20 bar ethylene+20 bar
CO, 50°C.
b Moles product per mole catalyst.
c TON per hour.
d 20 bar CO+20 bar ethylene.
e 20°C.
f In methanol.

M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
91
expected to show hemilabile behaviour was inactive.
This is possibly due to rapid decomposition in MeOH
(4f is insoluble in CH2Cl2) — a common feature of all
cationic complexes studied in this work. However, un-
favourable ligand influences cannot be excluded in this
case. The precursor complex 3f is P–N coordinated
which suggests the same coordination mode is likely to
be adopted throughout the catalytic steps. Vrieze et al.
have compared reaction rates for the carbonylation of
several N–N, P–P, and P–N coordinated Pd– and
Pt–CH3 complexes and reported the rates to decrease
in the order N–N\P–P\P–N [22]. Consistent with
this comment the P–N coordinated complex 4e was
also found to be inactive in the catalytic reactions
(entry 10, Table 5).
Differences in electronic and steric influences of the
ligands employed may explain the catalytic behaviour
observed for these complexes. The strong electron with-
drawing nature of the bridging carbonyl function in 3b
and 4b, which is also reflected in the Pd–CH3 NMR
shifts, may reduce the strong s-donor capacity [9] of
the imidazole system and therefore render the metal
centre more electrophilic than in the methylene bridged
counterparts 3a and 4a. Hence the metal centre is better
able to coordinate and activate nucleophilic substrates,
e.g. CO and olefins. By contrast, the keto bridged
benzimidazole complexes 3c and 4c showed low or no
reactivity, which is probably due to steric congestion.
The crystal structures of 2d and 3c reveal a more
hindered environment at the metal centre for the benz-
imidazole complex 3c compared to the imidazole com-
plexes. This feature would hamper the entry of
substrate molecules [3a]. Low temperature NMR stud-
ies consistently showed a higher energy barrier for the
CO insertion for 4c compared to 4b.
Data Centre, CCDC reference numbers 141341 and
141684. 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).
Acknowledgements
We are indebted to the Australian Research Council
and the SPIRT scheme for financial support for T.R.
We also acknowledge the generosity of Johnson–
Matthey for providing a loan of palladium chloride.
The staff of the Central Science Laboratory (University
of Tasmania) are gratefully acknowledged for their
assistance in a number of instrumental techniques.
References
[1] (a) A. Yamamoto, Organotransition Metal Chemistry; J. Wiley
& Sons, New York, 1986. (b) D. Milstein, Acc. Chem. Res. 21
(1988) 428. (c) I. Tkatchenko, In: G. Wilkinson, F.G.A. Stone,
E.W. Abel (Eds.), Comprehensive Organometallic Chemistry,
Vol. 8, Pergamon Press, Oxford, 1982. (d) R.F. Heck, Organ-
otransition Metal Chemistry; Academic Press, New York, 1974.
[2] For a review on nitrogen donor ligands see: A. Togni, L.M.
Venanzi Angew. Chem. Int. Ed. Engl. 33 (1984) 497.
[3] (a) R. van Asselt, E.C.C.G. Gielens, R.E. Ruelke, K. Vrieze, C.J.
Elsevier, J. Am. Chem. Soc. 116 (1994) 977. (b) B.A. Markies, D.
Kruis, M.H.P. Rietveld, K.A.N. Verkerk, J. Boersma, H. Kooij-
man, M.T. Lakin, A.L. Spek, G. van Koten, J. Am. Chem. Soc.
117 (1995) 5263. (c) F.C. Rix, M. Brookhart, P.S. White, J. Am.
Chem. Soc. 118 (1996) 4746. (d) F.C. Rix, M. Brookhart, P.S.
White, J. Am. Chem. Soc. 118 (1996) 2436. (e) R. Ruelke, V.E.
Kaasjager, D. Kliphuis, C. J. Elsevier, P.W.N.M. van Leeuwen,
K. Vrieze, Organometallics 15 (1996) 668. (f) J.H. Groen, C.J.
Elsevier, K. Vrieze, Organometallics 15 (1996) 3445. (g) J. H.
Groen, J.G.P. Delis, P.W.N.M. van Leeuwen, K. Vrieze,
Organometallics 16 (1997) 68. (h) J.G.P. Delis, P.G. Aubel, K.
Vrieze, P.W.N.M. van Leeuwen, N. Veldman, A.L. Spek, F.J.R.
van Neer, Organometallics 16 (1997) 2948. (i) J.G.P. Delis, P.G.
Aubel, K. Vrieze, P.W.N.M. van Leeuwen, Organometallics 16
(1997) 4150. (j) J.H. Groen, M.J.M. Vlaar, P.W.N.M. van
Leeuwen, K. Vrieze, H. Kooijman, A.L. Spek, J. Organomet.
Chem. 551 (1998) 67.
[4] (a) L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem.
Soc. 117 (1995) 6414. (b) J. Feldman, S.J. McLain, A.
Pathasarathy, W.J. Marshall, J.C. Calabrese, S.D. Arthur,
Organometallics 16 (1997) 1514. (c) T. Schleis, J. Heinemann,
T.P. Spaniol, R. Muelhaupt, J. Okuda, Inorg. Chem. Commun.
1 (1998) 431.
[5] (a) M. Brookhart, F.C. Rix, J.M. DeSimone, J.C. Barborak, J.
Am. Chem. Soc. 114 (1992) 5894. (b) F.C. Rix, M. Brookhart, J.
Am. Chem. Soc. 117 (1995) 1137. (c) A. Sen, Acc. Chem. Res. 26
(1993) 303. (d) E. Drent, P.H.M. Budzelar, Chem. Rev. 96
(1996) 663. (e) E. Drent, J.A.M. van Broekhoven, M.J. Doyle, J.
Organomet. Chem. 417 (1998) 235.
4. Conclusion
Novel cationic methyl and neutral methyl, chloro
Pd(II) complexes have been synthesised with various
functionalised imidazole ligands. For the first time
structurally characterised examples, 2d and 3c, of this
type of Pd complex could be obtained. The chelate
ligand is shown to adopt a boat conformation. Inver-
sion of the chelate ring in 4b was established by NMR
spectroscopy. Depending on electronic and steric fea-
tures of the ligand the complexes can act as catalysts in
the CO/ethylene as well as the Heck reaction and
therefore contribute to the growing number of nitrogen
ligated transition metal catalysts.
[6] (a) S. Mecking, L.K. Johnson, L. Wang, M. Brookhart, J. Am.
Chem. Soc. 120 (1998) 888. (b) L.K. Johnson, S. Mecking, M.
Brookhart, J. Am. Chem. Soc. 118 (1996) 267.
[7] S. Tsuji, D.C. Swenson, R.F. Jordan, Organometallics 18 (1999)
4758.
5. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic

92
M.C. Done et al. / Journal of Organometallic Chemistry 607 (2000) 78–92
[21] J.P. Farr, M.M. Olmstead, A.L. Balch, J. Am. Chem. Soc. 102
[8] B. Domhoever, W. Klaeui, A. Kremer-Aach, R. Bell, D. Mootz,
Angew. Chem. Int. Ed. Engl. 37 (1998) 3050.
(1980) 6654.
[22] G.P.C. Decker, A. Buijs, C.J. Elsevier, K. Vrieze, P.W.N.M. van
Leeuwen, W.J.J. Smeets, A.L. Spek, Y.F. Wang, C.H. Stam,
Organometallics 11 (1992) 1937.
[23] P.K. Beyers, A.J. Canty, B.W. Skelton, A.H. White, J.
Organomet. 9 (1990) 826.
[24] P.K. Beyers, A.J. Canty, B.W. Skelton, A.H. White, J.
Organomet. Chem 393 (1990) 299.
[25] G. Mingetti, M.A. Cinellu, A.L. Bandini, G. Banditelli, F.
Demartin, M. Manasssero, J. Organomet. Chem 315 (1986) 387.
[26] J.S. Brumbaugh, R.R. Whittle, M.A. Parvez, A. Sen,
Organometallics 9 (1990) 1735.
[27] (a) P.W.N.M.van Leeuwen, C.F. Roobeek, J.H.G. Frijns,
Organometallics 9 (1990) 1211. (b) V.G. Albano, D. Braga, V.
De Felice, A. Panunci, A. Vitagliano, Organometallics 6 (1987)
517. (c) V.G. Albano, C. Castellari, M.E. Cucciolito, A. Panunci,
A. Vitagliano, Organometallics 9 (1990) 1269. (d) V. De Felice,
V.G. Albano, C. Castellari, M.E. Cucciolito, A. de Renzi, J.
Organomet. Chem 403 (1991) 269.
[28] (a) R.F. Heck, J. Am. Chem. Soc. 90 (1968) 5518. (b) B.A. Patel,
L.-C. Kao, A. Cortese, J.V. Minkiewicz, R.F. Heck, J. Org.
Chem. 44 (1979) 918.
[29] (a) W.A. Herrmann, M. Elison, J. Fischer, C. Koecher, G.R.J.
Artus, Angew. Chem. Int. Ed. Engl. 34 (1995) 2371. (b) W.A.
Herrmann, C. Brossmer, K. Oefele, C.-P. Reisinger, T.
Priemeier, M. Beller,J. Fischer, Angew. Chem. Int. Ed. Engl. 34
(1995) 1844. (c) D.S. McGuiness, M.J. Green, K.J. Cavell, B.W.
Skelton, A.H. White, J. Organomet. Chem. 565 (1998) 165. (d)
D.S. McGuiness, K.J. Cavell, B.W. Skelton, A.H. White,
Organometallics 18 (1999) 1596. (e) D.S. McGuiness, K.J. Cav-
ell, Organometallics 19 (2000) 741.
[30] (a) W. Cabri, I. Candiani, A. Bedeschi, J. Org. Chem. 58 (1993)
7421. (b) W. Cabri, I. Candiani, A. Bedeschi, R. Santi, Synlett
(1993) 871. (b) R. van Asselt, C. J. Elsevier, Tetrahedron 50
(1994) 323.
[9] For a comarison of of properties of (im), (pz) and (py) ligands
see: A.J. Canty, C.V. Lee, Organometallics 1 (1982) 1063.
[10] For recent reports on imidazole based model compounds for
enzymatic reactions see (and literature cited therein): (a) C.
Place, J.-L. Zimmermann, E. Mulliez, G. Guillot, C. Bois, J.-P.
Chottard, Inorg. Chem. 37 (1998) 4030. (b) G. Guillot, E.
Mulliez, P. Leduc, J.-P. Chottard, Inorg. Chem. 29 (1990) 579.
(c) C. Kimblin, V.J. Murphy, G. Parkin, J. Chem. Soc. Chem.
Commun. (1996) 235. (d) F.-J. Wu, D.M. Kurz Jr., K.S. Hagen,
P.D. Nyman, P.G. Debrunner, V.A. Vanki, Inorg. Chem. 29
(1990) 5174.
[11] (a) S. Burling, L. D. Field, B.A. Messerle, Organometallics 19
(2000) 87. (b) S. Elgafi, L.D. Field, B.A. Messerle, P. Turner,
T.W. Hambley, J. Organomet. Chem. 588 (1999) 69. (c) S. Elgafi,
L.D. Field, B.A. Messerle, T. W. Hambley, P. Turner, J. Chem.
Soc. Dalton Trans. (1997) 2341.
[12] (a) P.K. Byers, A.J. Canty, Organometallics 9 (1990) 210. (b)
P.K. Byers, A.J. Canty, R. Honeyman, J. Organomet. Chem.
385 (1990) 417.
[13] W.F. Edgell, C.H. Ward, J. Am. Chem. Soc. 76 (1954) 1169.
[14] D. Drew, J.R. Doyle, Inorg. Synth. 28 (1990) 384.
[15] R. Ruelke, J.M. Ernsting, A.L. Spek, C.J. Elsevier, P.W.N.M.
van Leeuwen, K. Vrieze, Inorg. Chem. 32 (1993) 5769.
[16] S.M. Gorun, R.T. Stilbrany, A.R. Katritzky, J.J. Slawinski, H.
Faid-Allah, F. Brunner, Inorg. Chem. 35 (1996) 3.
[17] A. Burini, B.R. Pietroni, R. Galassi, G. Valle, S. Calogero,
Inorg. Chim. Acta 229 (1995) 299.
[18] K.-P. Langhans, O. Stelzer, N. Weferling, Chem. Ber. 123 (1990)
995.
[19] (a) H. Nishida, N. Takada, M. Yoshimura, T. Sonoda,
Kobayashi, Bull. Chem. Soc. Jpn. 57 (1984) 2600. (b) W.E.
Buschmann, J.S. Miller, Chem. Eur. J. 4 (1998) 1731.
[20] A. Macchioni, G. Bellachioma, G. Cardaci, M. Travaglia, C.
Zuccaccia, Organometallics 18 (1999) 3061.
[31] S.R. Hall, G.S.D. King, J.M. Stewart, The XTAL 3.4 Reference
Manual, University of Western Australia, Lamb, Perth, 1995.
.