N-Functionalised heterocyclic carbcne complexes of silver

Article abstract of DOI:10.1039/b007504n

W-Functionalised imidazol-2-ylidene carbene complexes of Ag1 have been prepared by interaction of the corresponding imidazolium salt with Ag2O in dichloromethane or 1,2-dichloroethane in the presence of molecular sieves or with Ag2CO3 in 1,2-dichloroethane. In an analogous way disilver(i) complexes of o-phenylenedimethylenebis(imidazol-2ylidene) have been obtained. Their structures, as determined by X-ray crystallography, indicate that the carbene ligand ' ' acts as monodentate from the carbene end or as a bridge between two different metal atoms. In one case the silver is coordinated by two carbene ligands. In the majority of the structurally characterised complexes the metal centres adopt linear geometries with M-C(carbene) bond lengths in the range of 207-210 pm characteristic of a single bond. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b007504n

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N-Functionalised heterocyclic carbene complexes of silver
Arran A. D. Tulloch,a Andreas A. Danopoulos,*a Scott Winston,a Sven Kleinhenza and
Graham Easthamb
a Department of Chemistry, University of Southampton, Highfield, Southampton,
UK SO17 1BJ
b Ineos Acrylics, Wilton, PO Box 90, Middlesbrough, Cleveland, UK TS90 8JE
Received 15th September 2000, Accepted 27th October 2000
First published as an Advance Article on the web 1st December 2000
N-Functionalised imidazol-2-ylidene carbene complexes of AgI have been prepared by interaction of the corresponding
imidazolium salt with Ag2O in dichloromethane or 1,2-dichloroethane in the presence of molecular sieves or with
Ag2CO3 in 1,2-dichloroethane. In an analogous way disilver() complexes of o-phenylenedimethylenebis(imidazol-2-
ylidene) have been obtained. Their structures, as determined by X-ray crystallography, indicate that the carbene ligand
acts as monodentate from the carbene end or as a bridge between two different metal atoms. In one case the silver is
coordinated by two carbene ligands. In the majority of the structurally characterised complexes the metal centres
adopt linear geometries with M–C(carbene) bond lengths in the range of 207–210 pm characteristic of a single bond.
There is growing interest in the use of nucleophilic Arduengo
type carbenes as ligands on transition metals.1 This stems
from recent reports describing unprecedented catalytic activity
of nucleophilic carbene complexes in important reactions
such as Pd-catalysed Heck and Suzuki couplings, CO-ethylene
copolymerisations, Ru-catalysed olefin metathesis and Rh-
catalysed hydrosilylations.2 The electronic characteristics of
nucleophilic carbenes as ligands have been compared to those
of the well studied phosphines.3 The thermodynamic stability
of the resulting complexes, in combination with the vast
opportunities of ligand design, show immense potential for
new catalysts. The synthesis of mixed donor carbene com-
plexes has been the topic of recent reports by us4 and others.5
Potentially hemilabile carbene ligands could prove useful
in stabilising catalytic centres while creating a degree of co-
ordinative and electronic unsaturation, in the presence of sub-
strates. In the first of a series of papers in this topic we describe
the synthesis and the full characterisation of mixed donor
N-functionalised imidazolium salts and their conversion into
silver() carbene complexes. Silver carbene complexes are
well known and some of them are structurally characterised.6,7
However, the compounds described here are the first struc-
turally characterised examples with mixed donor carbene
ligands.
N-Functionalised carbene complexes of silver
Silver carbene complexes were prepared by modification and
extension of the method reported by Wang and Lin,6 i.e. by
interaction of the imidazolium salts with Ag2O or Ag2CO3
as shown in Scheme 2. We found that: (i) with the relatively
unreactive bulky imidazolium salts (6a–6c) the reaction took
place only in refluxing 1,2-dichloroethane, whereas for all other
imidazolium salts it was faster; (ii) under these conditions
substantial exchange of bromide for chloride was observed;
(iii) when complexes 7c and 8 were synthesized at higher tem-
peratures in 1,2-dichloroethane the formation of by-products
was increased (see below); (iv) the purity of the products is
improved by addition of activated 4 Å molecular sieves to the
reaction medium; (v) Ag2CO3 in refluxing chlorinated solvents
could be used instead of Ag2O although the reaction times were
usually longer. We have been unable to prepare the carbene
complexes from silver halides and base under phase transfer
catalysis as reported by Wang and Lin.6 The identity of the
silver carbene complexes was established by a combination
of analytical and spectroscopic techniques. Electrospray mass
spectroscopy in acetonitrile solution was of low diagnostic
value, because conversion of Ag(ligand)Br into [Ag(ligand)2]ϩ
was observed under the sampling conditions employed. This
was further confirmed by using an acetonitrile solution of
a crystal of 9b, which by X-ray diffraction was shown to be
Ag(ligand)Br; the molecular ion observed in this case corre-
sponded to [Ag(ligand)2]ϩ.
The formation of the carbene complexes was established by
a weak peak below δ 165 in the 13C-{1H} NMR spectra
which was assigned to the 2C-imidazol-2-ylidene (carbene)
carbon, and by the absence of the downfield peak for the
2H-imidazolium proton in the 1H NMR spectra (usually
observed in non-protic solvents below δ 9).
The structures of the isolated silver carbene complexes in
the solid state as determined by X-ray diffraction show con-
siderable variety. Figs. 1 and 2 show the structures of 7c and
8 respectively, important bond lengths and angles are given in
Table 1. As shown, 7c contains one silver atom coordinated by
two carbene moieties and the second silver atom coordinated
by two bromides and one pyridine group. The geometry around
Ag(1) is linear and around Ag(2) is trigonal planar. The twist
Results and discussion
N-Functionalised imidazolium salts
The new functionalised imidazolium salts were prepared by
quaternisation of substituted alkyl and aryl imidazoles (see
Scheme 1). The use of bulky substituents is expected to dif-
ferentiate the reactivity of the resulting carbene complexes from
the known, easily available 1-methylimidazolium analogues. In
addition the crystallinity of the isolated compounds is generally
expected to be better. The quaternisation reactions proceed
selectively and at good rate in polar solvents like methanol,
ethanol and 1,4-dioxane. The white solids obtained were
characterised by analytical and spectroscopic methods. The
majority of them crystallised as hydrates and the crystal
structure of 1a shows an interaction of the water molecule with
the bromine.8
DOI: 10.1039/b007504n
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This journal is © The Royal Society of Chemistry 2000
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Scheme 1 Reagents and conditions: (i) 2-BrCH2py, EtOH; (ii) 2-Brpy, 150 ЊC; (iii) α,αЈ-dibromoxylene, 1,4-dioxane; (iv) BrCH2NEt2, 1,4-dioxane;
(v) 2-(BrCH2)-4,6-But2C6H2NO2 followed by N2H4ؒH2O/Pd/C; (vi) PhCHO, HCO2H.
Scheme 2 The synthesis of silver complexes. See Experimental section for details. Compounds in bold have been structurally characterised.
angle between the two planes, defined by the carbene rings,
is 33.5Њ. The dihedral angle formed between the plane of the
picolyl and carbene rings is 89Њ. The molecule adopts a con-
formation which keeps the picolyl rings away from each other.
There is no evidence of Ag ؒ ؒ ؒ Ag interaction. The Ag–C bond
length is 206.9 pm, similar to those observed by Wang and Lin6
and Arduengo et al.7 In contrast, the solid state structure of
8 comprises a silver atom coordinated by a carbene carbon and
a bromide in a linear geometry. There are no close contacts to
the pyridyl nitrogen. The Ag–C bond lengths in both structures
are similar. Why 7c and 8 adopt different structures is not clear.
The ligand with the carbene moiety directly linked to the
pyridine (as in 8) is more rigid than the one with a methylene
linker between the two rings (7c). Although the introduction
of a second ligand to 8 would have increased unfavourable
steric interligand interactions, these do not seem to inhibit
the formation of [Ag(ligand)2][AgBr2]. In depth NMR studies
involving 7c and 8 show many interesting features. The
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Table 1 Selected bond lengths (pm) and angles (Њ) for structurally characterised compounds
7b
7c
8
9b
10
11b
Ag–C(1)/Ag–C(2)
Ag–X(1)/Ag–X(2)
C(1)–Ag(1)–X(1)/C(2)–Ag–Ag(2)
C(1)–Ag–C(2)
Ag–N(1)
Ag ؒ ؒ ؒ Ag
X–Ag–X
N–Ag–X
Twist of R against imidazole ring
Twist of imidazole against imidazole
Angle imidazole–pyridine
207(2)
206.9(5)/207.4(5)
207.5(7)
242.1(1)
176.1(2)
—
—
—
—
—
84.8(3)
—
31.5(3)
209.9(3)
241.0(1)/290.7(1)
157.3(1)/110.3(1)
—
—
—
90.14(3)
—
80.8(1)
—
209.8(2)
237.1(1)
162.92(7)
206.1(7)/209.2(8)
234.2(2)/238.9(2)
177.4(2)/163.3(2)
237.3(4)/295.2(4) 249.1(1)/250.9(1)
162.5(5)/94.6(5)
—
—
336.7(5)
102.4(2)
—
—
—
—
175.9(2)
246.7(4)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
154.5(1)
108.8(1)/95.8(1)
88.8(2)/89.5(2)
33.5(1)
—
77.8(2)/86.5(2)
—
Fig. 3 An ORTEP diagram of the crystal structure of the dimeric
silver carbene complex 7b; see text for details.
Fig. 1 An ORTEP9 diagram of the crystal structure of silver carbene
complex 7c (50% probability thermal ellipsoids, as in all cases shown).
formed (as shown by NMR spectroscopy) which we were
unable to isolate. The 1H NMR spectra of these mixtures show
two sets of peaks, which are assignable to two different silver
carbene complexes; their 1H NMR spectra have the same sym-
metry but are slightly shifted. The major component is identical
to that obtained from the low temperature preparations
(see Experimental section). The presence of these two species
persists within the range Ϫ80 to ϩ50 (for 7c) and Ϫ80 to
Ϫ10 ЊC (for 8), showing no indication of interconversion.
Furthermore, analytical data for both impure (by NMR) and
pure 7c and 8 support the presence of compounds with the
same stoichiometry. Crystals of 7c and 8 suitable for X-ray
diffraction were grown from solutions containing only one
species. The crystal structures show that the isolated 7c is [Ag-
(ligand)2][AgBr2] and 8 is Ag(ligand)Br. Therefore, we think
that plausible formulations for the observed by-products are
the isostoichiometric Ag(ligand)Br (in the case of 7c) and
[Ag(ligand)2][AgBr2] (in the case of 8).
It is interesting that the structure of compound 7b has also
been determined.† Although twinned crystals were reproducibly
obtained, and therefore did not allow refinement of the data
to a level acceptable for publication, the connectivity can be
deduced unequivocally; (Fig. 3). Here the molecule comprises
two silver atoms bridged by bromides while the ligand acts as
Fig. 2 An ORTEP diagram of the crystal structure of silver carbene
complex 8.
appearance of the spectra is dependent on the concentration
of the sample, probably due to intermolecular interactions in
solution. Dilute samples display sharp spectra, as given in the
Experimental section, whereas concentrated samples display
broad spectra. Furthermore, the spectra are temperature
dependent. Pure (by NMR) 7c and 8 are obtained when the
preparations are carried out at lower temperatures (40 ЊC).
However, in refluxing 1,2-dichloroethane by-products were
† Crystal data: C18H19Ag1Br1N3, M = 465.14, monoclinic, space group
P2/n, a = 977.52, b = 1686.7, c = 1090.9 pm, β = 95.11Њ, V = 1.7915(5)
nm3, Z = 4, T = 150 K, µ = 3.358 mmϪ1, no. of data collected = 3686,
No. unique data = 1916, R1 with Fo2 > 2σ(Fo)2 = 0.206.
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Interaction of compounds 3a, 3b or 5 with Ag2O gave the
corresponding silver carbene complexes. The 1H NMR spectra
of 9a, 9b and 10 in chlorinated solvents show the presence
of only one species. The structures of 9b and 10 are shown in
Figs. 4 and 5; important bond lengths and angles are given in
Table 1. In both, the coordination sphere of silver comprises
one carbene moiety and one halide. There is no intra- or inter-
molecular interaction of the amide or imine functionalities with
silver atoms. The bond lengths and angles are in the normal
range for this type of compound. The partial occupation of the
halide positions by chloride has no effect on the geometrical
parameters of the metal centre while it improves the R1 of the
structures. Support for the incorporation of chloride is given
from analytical data (see Experimental section). The chlorine
atoms possibly originate from the chlorinated solvents used.
Hydrochloric acid washed glassware, used during the work up,
is a less likely alternative.
Finally, interaction of the bis-imidazolium salts 6a–6c with
an excess of Ag2O leads to isolation of the disilver dicarbene
complexes 11a–11c. The structure of 11b was determined by
X-ray diffraction study and is shown in Fig. 6; important bond
lengths and angles are given in Table 1. In 11c both silver atoms
adopt a linear geometry, with one carbene moiety and one
halide per silver. In the conformation observed the silver atoms
are ‘anti’. All other geometrical parameters are comparable to
those of the compounds described above.
Fig. 4 An ORTEP diagram of the crystal structure of silver carbene
complex 9b.
Experimental
Elemental analyses were carried out by the University College
London Microanalytical Laboratory. NMR data were recorded
on Bruker AMX-300 and AM 360 spectrometers, operating at
300 and 360 MHz (1H), respectively. The spectra were refer-
enced internally using the signal from the residual protio-
solvent (1H) or the signals of the solvent (13C). Mass spectra
(electrospray ionisation) were obtained from acetonitrile
solutions on a VG Biotec platform. The calculated isotopic
envelopes agree well with the experimentally observed pattern.
Commercial chemicals were from Acros, Aldrich and Avocado;
the light petroleum had bp 40–60 ЊC. The following starting
materials were prepared following literature methods: 1-tert-
butylimidazole,10 1-mesitylimidazole and 1-(2,6-diisopropyl-
phenyl)imidazole,11 2-bromomethylpyridine hydrobromide,12
2,6-bis(bromomethyl)pyridine hydrobromide,13 2-bromo-N,N-
Fig. 5 An ORTEP diagram of the crystal structure of silver carbene
complex 10.
diethylacetamide,14
benzene.15
2-bromomethyl-4,6-di(tert-butyl)nitro-
Preparations
3-tert-butyl-1-(2-pyridylmethyl)imidazolium bromide hydrate
1a. 2-(Bromomethyl)pyridine hydrobromide (4 g, 1.6 mmol)
was neutralised using a saturated aqueous solution of sodium
carbonate. The liberated 2-bromomethylpyridine was extracted
into diethyl ether (3 × 50 cm3) at 0 ЊC, dried with magnesium
sulfate and filtered. The filtrate was concentrated to ca. 100 cm3.
1-tert-Butylimidazole (1.95 g, 1.6 mmol) in methanol (100 cm3)
at 0 ЊC was added, the ether removed under reduced pressure
and the solution stirred at room temperature overnight.
Evaporation of the volatiles under reduced pressure left
compound 1a as a white solid. Yield: 3.80 g, 80%. mp 65 ЊC.
MS (ES): m/z 216 (Mϩ). δH(DMSO-d6) 1.6 (9H, s, (CH3)3C),
5.6 (2H, s, CH2), 7.5 (1H, m, 5-CH of py), 7.6 (1H, d, 3-CH of
py), 7.9 and 8.1 (2 × 1H, s, 4,5-imidazolium CH), 8.0 (1H, t,
4-CH of py), 8.6 (1H, d, 6-CH of py) and 9.6 (1H, s, 2-
imidazolium CH) (Found: C, 49.68; H, 6.43; N, 13.88. C13H20-
BrN3O requires C, 49.69; H, 6.42; N, 13.37%).
Fig. 6 An ORTEP diagram of the crystal structure of silver carbene
complex 11b.
monodentate from the carbene end (see also the structure
of 9b). The geometry of the chelate ring is rhombic and the
Ag ؒ ؒ ؒ Ag distance 334 pm, indicating a weak metal–metal
interaction. The C–Ag–Br vector is almost linear.
3-Mesityl-1-(2-pyridylmethyl)imidazolium bromide hydrate
1b. This was obtained following a procedure similar to that
described for compound 1a, using 2-bromomethylpyridine
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J. Chem. Soc., Dalton Trans., 2000, 4499–4506

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hydrobromide (3 g, 1.2 mmol) and 1-mesitylimidazole (2.2 g,
1.2 mmol). Yield: 2.9 g, 70%. mp 210 ЊC (decomp). MS (ES):
m/z 278 (Mϩ). δH(CDCl3) 2.0 (6H, s, o-mesityl CH3), 2.3 (3H, s,
p-mesityl CH3), 6.1 (2H, s, CH2), 6.9 (2H, s, mesityl CH), 7.0
and 8.0 (2 × 1H, s, 4,5-imidazolium CH), 7.2 (1H, m, 5-CH
of py), 7.7 (1H, t, 4-CH of py), 7.9 (1H, d, 3-CH of py),
8.5 (1H, m, 6-CH of py) and 10.4 (1H, s, 2-imidazolium CH)
(Found: C, 56.42; H, 5.42; N, 11.03. C18H22BrN3O requires C,
57.45; H, 5.89; N, 11.17%).
3 hours. After cooling to room temperature the volatiles were
evaporated under reduced pressure and the residue was tri-
turated with ether until it solidified. The yield of the white solid
nitro compound was quantitative. MS (ES): m/z 372 (Mϩ).
mp 184 ЊC. δH(CDCl3) 1.3 and 1.4 {2 × 9H, s, C6H2[C(CH3)3]2},
1.7 [9H, s, NC(CH3)3], 5.6 (1H, s, CH2), 7.3 and 7.6 (2 × 1H, s,
4,5-imidazolium H), 7.5 and 8.2 {2 × 1H, s, C6H2[C(CH3)3]2}
and 10.9 (1H, s, 2-imidazolium H). This compound (1 g, 2.2
mmol) was dissolved in degassed absolute ethanol (100 cm3),
and Pd/C (0.3 g, 10% PdC) and hydrazine hydrate (10 cm3) were
then added. The mixture was refluxed under nitrogen for 12
hours and, after cooling to room temperature, filtered. The
volatile components were evaporated under reduced pressure,
and the oily residue was washed with ether (3 × 30 cm3) and
dissolved in chloroform. The chloroform solution was dried
with MgSO4 and the product crystallised by addition of ether
and then cooling to Ϫ20 ЊC. Yield: 0.60 g, 65%. mp 184 ЊC.
MS (ES): m/z 342 (Mϩ). δH(CDCl3) 1.3 and 1.4 {2 × 9H, s,
C6H2[C(CH3)3]2}, 1.7 [9H, s, NC(CH3)3], 4.2 (2H, br s, NH2),
5.8 (2H, s, CH2), 7.3 and 7.6 (2 × 1H, s, 4,5-imidazolium H),
7.5 and 8.2 {2 × 1H, s, C6H2[C(CH3)3]2} and 10.7 (1H, s,
2-imidazolium H).
3-(2,6-Diisopropylphenyl)-1-(2-pyridylmethyl)imidazolium
bromide hydrate 1c. This was obtained following a similar
procedure using 2-bromomethylpyridine hydrobromide
(3 g, 1.2 mmol) and 1-(2,6-diisopropylphenyl)imidazole (2.75 g,
1.2 mmol). Yield: 3.4 g, 70%. mp 220 ЊC (decomp). MS (ES):
m/z 320 (Mϩ). δH(CDCl3) 1.1 and 1.2 (2 × 6H, d, CH(CH3)2),
2.3 [2H, septet, CH(CH3)2], 6.2 (2H, s, CH2), 7.1 and 8.3
(2 × 1H, s, 4,5-imidazolium CH), 7.3 (2H, d, 3,5-Pri2C6H2H),
7.3 (1H, m, 5-CH of py), 7.5 (1H, t, 4-Pri2C6H2H), 7.8 (1H, t,
4-CH of py), 8.0 (1H, d, 3-CH of py), 8.5 (1H, d, 6-CH of py)
and 10.1 (1H, s, 2-imidazolium CH).
3-(2,6-Diisopropylphenyl)-1-(2-pyridyl)imidazolium bromide 2.
A 100 cm3 Schlenk flask equipped with a small stirrer bar,
charged with 2-bromopyridine (2.2 g, 7.8 mmol) and 1-(2,6-
diisopropylphenyl)imidazole (2.23 g, 9.75 mmol), was evacu-
ated and then heated in an oil bath at 150 ЊC for 3–4 days.
During the heating period the imidazole which sublimed
onto the colder parts of the apparatus was melted back into
the reaction mixture. After cooling to room temperature the
brown residue was washed three times with ether and the
insoluble solid product isolated by filtration and dried in vacuo
at room temperature. Yield: 2.26 g, 95%. mp >220 ЊC. MS (ES):
m/z 306 (Mϩ). δH(CDCl3) 1.2 and 1.3 [2 × 6H, d, CH(CH3)2],
2.4 [2H, septet, CH(CH3)2], 7.3 (2H, d, Pri2C6H2H), 7.5 (1H, t,
Pri2C6H2H), 7.5, 8.1, 8.5 and 9.1 (4 × 1H, pyridyl H), 7.4
and 9.3 (2 × 1H, d, 4,5-imidazolium H) and 10.9 (1H, s,
2-imidazolium H).
1-(2-Benzylideneamino-3,5-di-tert-butylbenzyl)-3-tert-butyl-
imidazolium bromide 5. A solution of compound 4 (1.5 g,
4.4 mmol), benzaldehyde (2.2 g, 20 mmol) and HCO2H
(0.5 cm3) in absolute ethanol was refluxed until the con-
1
sumption of 4 was complete according to H NMR. Removal
of the volatiles under reduced pressure and trituration of
the residue with ether gave crude 5 as an off-white powder.
This was dissolved in chloroform, dried with MgSO4 and then
concentrated. Addition of ether followed by cooling to Ϫ20 ЊC
gave analytically pure 5 as white crystals. Yield: 1.1 g, 60%.
mp > 220 ЊC. MS (ES): m/z 430 (Mϩ). δH(CDCl3) 1.3 {18H, s,
C6H2[C(CH3)3]2}, 1.6 [9H, s, NC(CH3)3], 5.7 (2H, s, CH2), 7.3
and 7.6 (2 × 1H, s, 4, 5-imidazolium H), 7.3–7.4 and 7.8–7.9
(5H, m, C H CH᎐N), 7.5 and 8.2 {2 × 1H, s, [(CH ) C] C H },
᎐
6
5
3
3
2
6
2
8.4 (1H, s, C H CH᎐N) and 10.4 (1H, s, 2-imidazolium H).
᎐
6
5
1-tert-Butyl-3-(N,N-diethylcarbamoylmethyl)imidazolium
bromide 3a. 2-Bromo-N,N-diethylacetamide (2 g, 10 mmol)
and 1-tert-butylimidazole (1.9 g, 15 mmol) were dissolved in
1,4-dioxane (50 cm3) and the solution was heated at 100 ЊC
overnight. After cooling to room temperature a colourless oil
separated. The supernatant was decanted and the oil triturated
with ether until it solidified. The white solid product was
separated by filtration and dried in vacuo. Yield: 2.4 g, 75%.
mp 118 ЊC. MS (ES): m/z 238 (Mϩ). δH(CDCl3) 1.1 and 1.3 (2 ×
3H, t, diastereotopic CH2CH3), 1.7 [9H, s, C(CH3)3], 3.2 and
3.5 (2 × 2H, q, diastereotopic CH2CH3), 5.7 (2H, s, CH2), 7.3
and 7.6 (2 × 1H, s, 4,5-imidazolium H) and 10.3 (1H, s,
2-imidazolium H).
3,3Ј-Di-tert-butyl-1,1Ј-o-phenylenedimethylenebis(imida-
zolium) dibromide 6a. A solution of 2,2Ј-dibromo-o-xylene
(1.0 g, 3.8 mmol) and 1-tert-butylimidazole (2.00 g, 8.3 mmol)
in 1,4-dioxane (100 cm3) was heated at 100 ЊC overnight. After
cooling to room temperature compound 6a precipitated as a
white powder which was collected by filtration. Additional
product was isolated from the supernatant by removal of the
volatiles under reduced pressure and trituration of the resultant
oil with ether. Yield: 1.92 g, 92%. mp 247 ЊC (decomp). MS
(ES): m/z 176.3 (¹ M2ϩ). δH(D2O) 1.5 [18H, s, C(CH3)3], 5.5
¯
²
(4H, s, CH2), 7.2 and 7.6 (2 × 2H, s, 4,5-imidazolium H), 7.3
and 7.5 (2 × 2H, m, xylyl) and 8.8 (2H, s, 2-imidazolium H).
δC(D2O) 31.5 [C(CH3)3], 52.8 (CH2), 63.0 [C(CH3)3], 123.2,
124.9, 133.3, 133.6, 134.3 and 136.4 (xylene and imidazolium C)
(Found: C, 50.85; H, 5.99; N, 10.48. C22H34Br2N4O requires C,
49.82; H, 6.46; N, 10.56%).
3-(N,N-Diethylcarbamoylmethyl)-1-mesitylimidazolium bro-
mide 3b. This was obtained following a procedure similar to
the one described for compound 3a using 2-bromo-N,N-
diethylacetamide (2 g, 10 mmol) and 1-mesitylimidazole (2.3 g,
12.5 mmol). After cooling to room temperature the white solid
product was isolated by filtration, washed with ether and dried
in vacuo. Yield: 3.0 g, 80%. mp 175 ЊC. MS (ES): m/z 300 (Mϩ).
δH(CDCl3) 1.1 and 1.3 (2 × 3H, t, diastereotopic CH2CH3),
2.1 (6H, s, o-mesityl CH3), 2.3 (3H, s, p-mesityl CH3), 3.4 and
3.6 (2 × 2H, q, diastereotopic CH2CH3), 6.0 (2H, s, CH2), 6.9
[2H, s, m-mesityl H], 7.2 and 7.9 (2 × 1H, s, 4,5-imidazolium H)
and 10.3 (1H, s, 2-imidazolium H).
3,3Ј-Dimesityl-1,1Ј-o-phenylenedimethylenebis(imidazolium)
dibromide 6b. This was obtained by following the same pro-
cedure as for compound 6a using 2,2Ј-dibromo-o-xylene (1.0 g,
3.8 mmol) and 1-mesitylimidazole (1.55 g, 8.3 mmol). Yield:
2.2 g, 92%. mp 254 ЊC (decomp.). MS (ES): m/z 238.4 (¹ M2ϩ).
¯
²
δH(D2O) 2.0 (12H, s, o-mesityl CH3), 2.2 (6H, s, p-mesityl CH3),
6.3 (4H, s, CH2), 6.9 (4H, s, m-mesityl H), 7.2 and 8.3 (2 × 2H,
s, 4,5-imidazolium H), 7.2 and 7.3 (2 × 2H, m, xylyl) and 10.1
(2H, s, 2-imidazolium H). δC(CDCl3) 18.2 and 21.5 (mesityl
CH3), 50.5 (CH2), 123.8, 124.9, 129.7, 130.2, 130.4, 131.1,
133.1, 134.7, 138.0 and 141.6 (xylene, mesityl and imidazolium
C) (Found: C, 58.16; H, 5.86; N, 7.36. C32H38Br2N4O requires
C, 58.73; H, 5.85; N, 8.56%).
1-(2-Amino-3,5-di-tert-butylbenzyl)-3-tert-butylimidazolium
bromide 4. A solution of 2-bromomethyl-4,6-di-tert-butyl-
nitrobenzene (2 g, 6.1 mmol) and 1-tert-butylimidazole (1.15 g,
9.1 mmol) in 1,4-dioxane (50 cm3) was heated at 70 ЊC for
J. Chem. Soc., Dalton Trans., 2000, 4499–4506
4503

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3,3Ј-Bis[(2,6-diisopropylphenyl)-1,1Ј-o-phenylenedimethylene-
bis(imidazolium) dibromide 6c. This was obtained by following
the same procedure as for compound 6a using 2,2Ј-dibromo-
o-xylene (1.0 g, 3.8 mmol) and 1-(2,6-diisopropyl-
phenyl)imidazole (1.90 g, 8.3 mmol). Yield: 2.13 g 78%. MS
(ES): m/z 280.5 (¹ M2ϩ). δH(CDCl3) 1.1 and 1.2 [2 × 12H,
d, diastereotopic CH(CH3)2], 2.2 [4H, septet, CH(CH3)2], 6.1
(4H, s, CH2), 7.1 and 8.7 (2 × 2H, s, 4,5-imidazolium H),
7.2 (2H, m, xylyl), 7.2 (4H, d, m-Pri2C6H2H), 7.5 (2H, t, p-
Pri2C6H2H), 7.8 (2H, d, xylyl) and 10.7 (2H, s, 2-imidazolium
H). δC(CDCl3) 24.2 and 24.6 [CH(CH3)2)], 28.8 [CH(CH3)2],
53. 7 (CH2), 124.25, 124.39, 124.82, 130.38, 132.04, 138.61,
139.19, 145.36 and 153.54 (xylene, phenyl and 4,5-imidazolium
C); 2-imidazolium-CH not observed (Found: C, 59.52; H,
6.46; N, 7.60. C19H26BrN2O requires C, 60.32; H, 6.93; N,
7.40%).
THF–ether (1:1) to 4 ЊC. MS (ES): m/z 469, [Ag(ligand)-
MeCN]ϩ; 748, [Ag(ligand)2]ϩ. δH(CDCl3) 1.1 and 1.2 [2 × 6H,
d, CH(CH3)2], 2.4 [2H, septet, CH(CH3)2], 5.5 (2H, s, CH2), 7.0
and 7.3 (2 × 1H, d, 4,5-imidazol-2-ylidene H), 7.2–7.4 (4H, m,
3,5-H of py, H of m-Pri2C6H3), 7.5 (1H, t, H of p-Pri2C6H3),
7.8 (1H, dt, 4-H of py) and 8.6 (1H, d, 6-H of py). δC(CDCl3)
24.2 and 24.6 (CH(CH3)2), 28.3 (CH(CH3)2), 56.9 (CH2), 122.1,
122.2, 123.3, 124.1, 124.2, 130.3, 134.6, 137.3, 145.6, 149.7
and 154.9 (Pri2C6H3, pyridyl, 4,5-imidazol-2-ylidene C). The
carbene carbon was not observed.
¯
²
1-(2,6-Diisopropylphenyl)-3-(2-pyridyl)imidazol-2-ylidene]-
silver bromide 8. Prepared by method B using compound 2
(2.0 g, 4.78 mmol) and Ag2CO3 (0.99 g, 3.58 mmol) in dichloro-
methane (50 cm3), heating at 40 ЊC for two days. Yield quanti-
tative. X-Ray diffraction quality crystals were grown by layering
a dichloromethane solution with ether. MS (ES): m/z 455,
[Ag(ligand)MeCN]ϩ; 719, [Ag(ligand)2]ϩ. δH(CDCl3) 1.0 and
1.3 [2 × 6H, d, CH(CH3)], 2.5 (2H, septet, CH(CH3)2), 6.3 and
7.8 (2 × 1H, d, 4,5-imidazol-2-ylidene H), 7.0–7.2 (5H, m,
m, p-H of Pri2C6H3, 3,5-H of py), 8.1 (1H, d, 6-H of py),
8.5 (1H, dt, 4-H of py). δC(CDCl3) 24.4 [CH(CH3)], 28.2
[CH(CH3)], 115.6, 119.9, 123.9, 124.3, 130.6, 134.9, 139.6,
145.5, 148.9 and 150.4 (Pri2C6H3, pyridyl, 4,5-imidazol-2-
ylidene C). The carbene carbon was not observed (Found:
C, 49.35; H, 4.78; N, 8.52. C20H23AgBrN3 requires C, 48.71;
H, 4.70; N, 8.52%).
[1-tert-Butyl-3-(N,N-diethylcarbamoylmethyl)imidazol-2-
ylidene]silver bromide 9a. Prepared by method A using com-
pound 3a (1 g, 3.2 mmol) and Ag2O (1.139 g, 4.9 mmol) in
1,2-dichloroethane at 105 ЊC for 12 hours in the presence of
molecular sieves. After filtration the solvent was removed
in vacuo. The resulting solid was washed with ether, yielding
a hygroscopic solid. Yield 0.542 g, 49.6%. MS (ES): m/z 584,
[Ag(ligand)2]ϩ. δH(CDCl3) 1.1 and 1.3 (2 × 3H, t, diastereotopic
CH2CH3), 1.7 [9H, s, C(CH3)3], 3.35 and 3.45 (2 × 2H, q,
diastereotopic CH2CH3), 5.6 (2H, s, CH2), 7.08 and 7.12
(2 × 1H, s, 4,5-imidazol-2-ylidene H). δC(CDCl3) 12.9, 13.0,
14.4 and 14.6 (CH2CH3) 30.0 and 31.9 [C(CH3)3], 41.0, 41.1,
41.9 and 42.0 (CH2CH3), 57.9 and 60.2 [C(CH3)3], 65.8 (CH2)
118.3, 118.9, 121.6 and 124.5 (4,5-imidazol-2-ylidene C),
Silver complexes. In method A a substituted imidazolium
salt was refluxed with an excess of Ag2O in dichloromethane or
1,2-dichloroethane for 3–48 hours. In some cases, addition of
activated 4 Å molecular sieves to the reaction mixture improved
the yield and purity of the product. After completion, the
reaction mixture was filtered, dried over MgSO4 (if sieves had
not been used), the volatiles were removed under reduced
pressure and the solid product was washed with ether and dried
in vacuo. In most cases the products obtained at this stage were
spectroscopically and analytically pure. If not, purification
is possible by recrystallisation. In Method B a substituted imi-
dazolium salt was refluxed with an excess of Ag2CO3 in
dichlomethane or 1,2-dichloroethane for 3–48 hours. Isolation
and purification of the product was accomplished as described
in method A.
[1-tert-butyl-3-(2-pyridylmethyl)imidazol-2-ylidene]silver
bromide 7a. Prepared by method A using compound 1a (0.24 g,
0.77 mmol) and Ag2O (0.16 g, 0.58 mmol) in dichloromethane
(30 cm3) and heating to 40 ЊC for two days. The solid obtained
was dissolved in toluene, the solution filtered and the solvent
removed under reduced pressure. The resulting yellow powder
was washed with ether and dried in vacuo. Yield: 0.28 g, 90%.
δH(CDCl3) 1.6 (9H, s, C(CH3)3), 5.4 (2H, s, CH2), 7.1 and 7.2
(2 × 1H, d, 4,5-imidazol-2-ylidene H), 7.2 (2H, d, 3,5-H of py),
7.6 (1H, dt, 4-pyridyl H of py), 8.5 (1H, dd, 6-H of py).
δC(CDCl3) 31.6 [C(CH3)3], 53.6 [C(CH3)3)], 57.9 (CH2), 119.1,
120.2, 122.2 and 123.2 (pyridyl and 4,5-imidazol-2-ylidene
C), 137.1, 149.6 and 154.9 (pyridyl C) and 178.6 (2-imidazol-2-
ylidene C).
163.9 and 165.2 (C᎐O) and 179.0 (2-imidazol-2-ylidene C).
᎐
1-(N,N-Diethylcarbamoylmethyl)-3-mesitylimidazol-2-
ylidene]silver chloride 9b. Prepared by method A using com-
pound 3b (2 g, 5.3 mmol) and Ag2O (1.8 g, 7.9 mmol) in 1,2-
dichloroethane at 90 ЊC for 4 hours in the presence of molecular
sieves. Work up as for 9a. Yield quantitative. X-Ray diffraction
quality crystals were obtained by layering of a dichloromethane
[1-Mesityl-3-(2-pyridylmethyl)imidazol-2-ylidene]silver
bromide 7b. Prepared by method B, using compound 1b (0.4 g,
1.07 mmol) and Ag2CO3 (0.17 g, 0.64 mmol) in dichloro-
methane (30 cm3) and heating to 40 ЊC for two days. Work up
as described for 7a gave a pale yellow solid. Yield: quantitative.
X-Ray diffraction quality crystals were obtained by cooling
solution with ether. MS (ES): m/z 707, [Ag(ligand)2]ϩ
.
δH(CDCl3) 1.2 and 1.4 (2 × 3H, t, N(CH2CH3)2], 2.1 (6H, s,
o-mesityl CH3), 2.4 (3H, s, p-mesityl CH3), 3.5 [4H, q,
N(CH2CH3)2], 5.2 (2H, s, CH2) and 6.9 (2H, s, m-mesityl
H). δC(CDCl3) 13.9 and 14.7 [N(CH2CH3)2], 17.8 and 21.2
[o,p-mesityl CH3], 41.0 and 41.8 [N(CH2CH3)2], 52.8 (CH2),
123.2, 129.5, 135.0 and 139.6 (mesityl, 4,5-imidazol-2-ylidene
CH) and 167 (2-imidazol-2-ylidene C) (Found: C, 48.37;
H, 5.59; N, 9.28, C18H25AgBr0.08Cl0.92N3O requires C, 48.44; H,
5.65; N, 9.42%).
a
saturated solution of dichloromethane-light petroleum
(bp 40–60 ЊC) (1:1) to 4 ЊC. MS (ES): m/z 427, [Ag(ligand)-
MeCN]ϩ; 663, [Ag(ligand)2]ϩ. δH(CDCl3) 1.9 (6H, s, o-mesityl
CH3), 2.3 (3H, s, p-mesityl CH3), 5.4 (2H, m, CH2), 6.9 (2H, s,
m-mesityl H), 7.2 and 7.3 (2 × 1H, d, 4,5-imidazol-2-ylidene
H), 7.2 (2H, m, 3,5-H of py), 7.7 (1H, dt, 4-H of py), and
8.6 (1H, d, 6-H of py). δC(CDCl3) 17.8 (o-mesityl CH3), 21.2
(p-mesityl CH3), 57.4 (CH2), 121.9, 122.5, 123.1, 123.7,
129.6, 134.8, 137.7, 140.1 and 150.1 (mesityl, pyridyl and
4,5-imidazol-2-ylidene C) and 173.9 (2-imidazol-2-ylidene C)
(Found: C, 47.70; H, 4.22; N, 8.94. C18H19AgBrN3 requires C,
46.48; H, 4.12; N, 9.03%).
1-(2,6-Diisopropylphenyl)-3-(2-pyridylmethyl)imidazol-2-
ylidene]silver bromide 7c. Prepared by method B using com-
pound 1c (2.0 g, 5.17 mmol) and Ag2CO3 (1.06 g, 3.88 mmol)
in dichloromethane (50 cm3) and heating to 40 ЊC for two days,
quantitative yield of a white solid. X-Ray diffraction quality
crystals were obtained by cooling a saturated solution of
1-(2-Benzylideneamino-3,5-di-tert-butylbenzyl)-3-tert-
butylimidazol-2-ylidene] silver bromide 10. Prepared by method
A using compound 5 (0.15 g, 0.3 mmol) and Ag2O (0.04 g,
0.13 mmol) in dichloromethane (30 cm3) by heating at 40 ЊC
overnight. X-Ray diffraction quality crystals were grown by
cooling a saturated solution of THF–ether (1:1) to 4 ЊC.
Yield 90%. MS (ES): m/z 579, [Ag(ligand)MeCN]ϩ; 967,
[Ag(ligand)2]ϩ. δH(CDCl3) 1.3 [9H, s, CC(CH3)3], 1.3 [9H, s,
CC(CH3)3], 1.6 [9H, s, NC(CH3)3], 5.1 (2H, s, CH2), 6.8 and 7.1
(2 × 1H, d, 4,5-imidazol-2-ylidene H), 7.0 and 7.4 (2 × 1H, d,
3,5-H of C6H2), 7.2 (1H, d, p-H of phenyl), 7.5 (2H, m, o-H of
phenyl), 7.8 (2H, dd, m-H of phenyl) and 8.1 (1H, s, PhCH᎐N).
᎐
δC(CDCl3) 30.4, 31.3 and 31.5 [C(CH3)3], 34.4, 35.7 and 54.2
4504
J. Chem. Soc., Dalton Trans., 2000, 4499–4506

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Table 2 Crystallographic data for complexes 7c, 8, 9b 10 and 11b
7c
8
9b
10
11b
Chemical formula
Formula weight
C42H50Ag2Br2N6
1014.44
C20H23AgBrN3
493.19
C18H25AgBr0.08Cl0.92N3O
446.34
C29H39AgClN3
572.95
C32.5H35Ag2Cl3N4
803.73
Crystal system
Space group
Orthorhombic
P21nb
Monoclinic
P21/n
Monoclinic
C2/c
Triclinic
P1
Monoclinic
P21/a
¯
a/pm
b/pm
c/pm
α/Њ
1277.37(1)
1655.30(1)
2013.44(2)
1088.37(4)
1641.54(6)
1141.27(4)
2653.98(2)
1044.89(1)
1688.53(2)
968.84(2)
1147.09(2)
1377.50(2)
71.937(1)
85.779(1)
76.949(1)
1.41783(4)
2
1728.53(3)
1270.79(3)
1858.79(4)
β/Њ
103.155(2)
125.90(1)
117.407(1)
γ/Њ
V/nm3
4.25728(6)
4
1.9855(2)
4
3.79301(6)
8
3.6247(1)
4
Z
T/K
150
150
3.035
2801
150
150
0.826
14216
7942
0.0375
0.0403
0.0626
150
µ/mmϪ1
2.833
37682
8211
0.0660
0.0386
0.0504
1.373
21107
5526
0.0362
0.0542
0.0678
1.327
35356
9486
0.0821
0.0734
0.1598
No. data collected
No. unique data
Rint
2167
0.0331
0.0454
0.0519
Final R(|F|) for Fo > 2σ(Fo)
Final R(F2) for all data
[C(CH3)3], 57.4 (CH2), 118.5, 119.5, 123.2, 124.1, 124.2, 128.1,
128.8, 129.0, 131.9, 135.5, 139.8, 146.3 and 149.1 (phenyl,
benzyl, 4,5-imidazol-2-ylidene C) and 163.2 (2-imidazol-2-
ylidene C) (Found: C, 58.31; H, 6.66; N, 6.78. C29H39Ag-
Br0.5Cl0.5N3 requires C, 58.52; H, 6.60; N, 7.06%).
[CH(CH3)2], 28.43 [CH(CH3)2], 56.88 (CH2), 121.72, 122.80,
123.91, 124.38, 130.69, 135.89, 138.88, 145.72 and 155.80
(phenyl, xylyl, 4,5-imidazol-2-ylidene C). Carbene carbon not
observed. The isolated product contains half a molecule of
dichloromethane per formula unit (Found: C, 52.00; H,
5.56; N, 7.58. C38.5H47Ag2Cll3N4 requires C, 52.08 ; H, 5.34;
N, 6.31%).
[3,3Ј-Di-tert-butyl-1,1Ј-o-phenylenedimethylenebis(imidazol-
2-ylidene)]dichlorodisilver 11a. Prepared by method A using
compound 6a (1.0 g, 1.6 mmol) and Ag2O (0.555 g, 2.4 mmol)
in 1,2-dichloroethane (30 cm3) in the presence of molecular
sieves. After refluxing overnight the reaction mixture was
filtered, the filtrate pumped to dryness and the resulting
solid washed with light petroleum giving the product as a pale
brown solid. The solid was precipitated by layering a saturated
solution of dichloromethane with ether, filtered and dried
in vacuo. Yield: 0.892 g, 71%. mp 152 ЊC (decomp). MS (ES):
m/z 458, [Ag(ligand)]ϩ. δH(CDCl3) 1.6 [18H, s, C(CH3)3],
5.4 (4H, s, CH2), 6.8 and 7.3 (2 × 2H, dd, xylene H), 7.0 and
7.2 (2 × 2H, d, 4,5-imidazol-2-ylidene H). δC(CDCl3) 31.6
[C(CH3)3], 53.6 (CH2), 57.7 [C(CH3)3], 119.5 and 120.1 (4,5-
imidazol-2-ylidene C) 128.3, 128.8 and 133.9 (xylene C) and
179.6 (2-imidazol-2-ylidene C).
[3,3Ј-Dimesityl-1,1Ј-o-phenylenedimethylenebis(imidazol-2-
ylidene)]disilver 11b. Prepared by method A using compound
6b (1.0 g, 1.6 mmol) and Ag2O (0.56 g, 2.4 mmol) in 1,2-
dichloroethane (30 cm3) in the presence of molecular sieves.
Work up as for 11a. X-Ray diffraction quality crystals were
grown by layering a saturated solution of dichloromethane
with ether. Yield 0.80 g, 66%. mp 158 ЊC. MS (ES): m/z 582,
[Ag(ligand)]ϩ. δH(CDCl3) 1.9 (12H, s, o-mesityl CH3), 2.3 (6H,
s, p-mesityl CH3), 5.6 (4H, s, CH2), 6.9 (4H, s, m-H of mesityl),
6.9 and 7.4 (2 × 2H, s, 4,5-imidazol-2-ylidene H) and 7.3 (4H,
m, xylyl H). δC(CDCl3) 17.6, 20.9 (o,p-mesityl CH3), 52.4 (CH2),
122.4 and 122.9 (4,5-imidazol-2-ylidene C), 127.4, 128.7 and
129.1 (xylyl C), 134.2, 134.4, 135.3 and 139.1 (mesityl C).
Carbene carbon not observed. The isolated product contains
half a molecule of dichloromethane per formula unit (Found:
C, 48.23; H, 4.33; N, 6.55. C32.5H35Ag2Cl3N4 requires C, 48.57;
H, 4.39; N, 6.97%).
Crystal structure determinations of compounds 7b, 7c, 8, 9b, 10
and 11b
A summary of the crystal data, data collection and refinement
for compounds 7c, 8, 9b, 10 and 11b is given in Table 2. All
data sets were collected on a Enraf Nonius KappaCCD
area detector diffractometer with rotating anode FR591 and
an Oxford Cryosystems low-temperature device operating
in omega scanning mode with phi scans to fill the Ewald
sphere. The programs used for control and integration were
COLLECT, SCALEPACK and DENZO.16 The crystals were
mounted on a glass fibre with silicon grease. Accurate lattice
parameters were determined from least-squares refinement of
all reflections F2 > 4σ(F2). An empirical absorption correction
was made by the SORTAV17 method from symmetry-related
measurements. The structures were solved by heavy-atom
Patterson methods (SHELXS 97).18 Refinement was carried
out by full-matrix least squares techniques (SHELXL 97).19
Non-hydrogen atoms were refined with anisotropic thermal
parameters. Hydrogen atoms were included using a riding
model.
The chemical identity of the halogen atoms in the three com-
plexes 9b, 10 and 11b was investigated carefully considering
all possible combinations between chlorine and bromine.
Therefore, the molecular formulation presented in each case
corresponds to the combination with low R values and low
anisotropic thermal parameters for chlorine and/or bromine
atoms. The molecular formulations found by X-ray diffraction
for all complexes are consistent with the other experimental
data.
Dichloro[3,3Ј-bis(2,6-diisopropylphenyl)-1,1Ј-o-phenylene-
dimethylenebis(imidazol-2-ylidene)]disilver 11c. Prepared by
method A using compound 6c (1.0 g, 1.4 mmol) and Ag2O
(0.48 g, 2.1 mmol) in 1,2-dichloroethane (30 cm3) in the presence
of molecular sieves. Work up as for 11a. Yield 0.92 g, 62%.
mp 170 ЊC. MS (ES): m/z 667.6, [Ag(ligand)]ϩ. δH(CDCl3)
1.1 and 1.2 [2 × 12H, s, CH(CH3)2], 2.3 [4H, septet, CH(CH3)2],
5.5 (4H, s, CH2), 7.0 and 7.2 (2 × 2H, s, 4,5-imidazol-2-ylidene
H), 7.2 and 7.7 (2 × 2H, m, xylyl), 7.4 (4H, m, m-H of Pri2C6H3)
and 7.5 (2H, m, p-H of Pri2C6H3). δC(CDCl3) 24.39 and 24.80
Compound 7b was also investigated by X-ray single crystal
diffraction. Unfortunately, it repeatedly showed a very poor
diffraction pattern. The pictures taken indicated at all times a
partly amorphous or twinned system. However, it was possible
to solve the structure without problems and all non-hydrogen
atoms have been located unambiguously and their positions
refined with anisotropic thermal parameters. In spite of this
final quality it is not enough for publication; the dimensions
associated with the metal co-ordination spheres are accurate
enough to be included in Table 1.
J. Chem. Soc., Dalton Trans., 2000, 4499–4506
4505

View Online
3 J. C. Green, R. G. Scurr, P. L. Arnold and F. G. N. Cloke,
Chem. Commun., 1997, 1963; C. Boehme and G. Frenking,
Organometallics, 1998, 17, 5801.
4 A. A. D. Tulloch, A. A. Danopoulos, R. P. Tooze, S. M. Cafferkey,
S. Kleinhenz and M. B. Hursthouse, Chem. Commun., 2000,
1247.
5 W. A. Herrmann, C. Køcher, L. Goossen and G. R. J. Artus, Chem.
Eur. J., 1996, 2, 1627; W. A. Herrmann, L. Goossen and M. Spiegler,
Organometallics, 1998, 17, 2162; D. S. McGuinness and K. J. Cavell,
Organometallics, 2000, 19, 741; B. Cetinkaya, I. Ozdemir and
P. H. Dixneuf, J. Organomet. Chem., 1997, 534, 153.
6 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, 972.
7 A. J. Arduengo III, H. V. R. Dias, J. C. Calabrese and F. Davidson,
Organometallics, 1993, 12, 3405.
The crystals of compound 11b were of particularly poor
quality. The structure contains 0.5 molecule of highly dis-
ordered solvent CH2Cl2 and was treated in the manner
described by Sluis and Spec (228 e cellϪ1).20 The total potential
solvent accessible volume was found to be 496.6 × 106 pm3
cellϪ1. Recrystallisation from other solvents was unsuccessful.
CCDC reference number 186/2257.
See http://www.rsc.org/suppdata/dt/b0/b007504n/ for crystal-
lographic files in .cif format.
Acknowledgements
8 S. Kleinhenz, A. A. D. Tulloch and A. A. Danopoulos, Acta
Crystallogr., Sect. C, 2000, 56, e476.
9 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
We thank Ineos Acrylics, EPSRC and University of
Southampton for support and Dr Robert P. Tooze (Ineos
Acrylics) for helpful discussions.
10 R. Scarr, personal communication.
11 A. L. Johnson (E. I. DuPont), U.S. Pat., 3637731, 1972.
12 B. R. Brown and J. Humphreys, J. Am. Chem. Soc., 1959, 81, 2040.
13 M. E. Haeg, B. J. Whitlock and H. W. Whitlock, Jr., J. Am. Chem.
Soc., 1989, 111, 692.
14 C. Loeber, C. Wieser, D. Matt, A. DeCian, J. Fischer and L. Toupet,
Bull. Soc. Chim. Fr., 1995, 132, 166.
References
1 See for example: W. A. Herrmann and C. Køcher, Angew. Chem.,
Int. Ed. Engl., 1997, 36, 2162; D. Bourissou, O. Guerret, F. P. Gabbai
and G. Bertrand, Chem. Rev., 2000, 100, 39.
2 For Heck and Suzuki coupling reactions see: W. A. Herrmann, in
Applied Homogeneous Catalysis with Organometallic Compounds,
eds. B. Cornils and W. A. Herrmann, Wiley-VCH, Weinheim,
2000, p. 725; C. Zhang, J. Huang, M. L. Trudell and S. P. Nolan,
J. Org. Chem., 1999, 64, 3804. For CO–ethylene copolymerisations
see: M. G. Gardiner, W. A. Herrmann, C.-P. Reisinger, J. Schwarz
and M. Spiegler, J. Organomet. Chem., 1999, 572, 239. For olefin
metathesis reactions see: T. Weskamp, W. C. Schattenmann,
W. C. Spiegler and W. A. Herrmann, Angew. Chem., Int. Ed.
Engl., 1998, 37, 2490; M. Scholl, T. M. Trnka, J. P. Morgan and
R. H. Grubbs, Tetrahedron Lett., 1999, 40, 2247. For catalytic
hydrosilylations see: W. A. Herrmann, L. J. Goossen, C. Køcher and
G. R. J. Artus, Angew. Chem., Int. Ed. Engl., 1996, 35, 2805.
15 K. Yang, R. J. Lachicotte and R. Eisenberg, Organometallics, 1998,
17, 5102.
16 R. Hooft, COLLECT, Nonius BV, 1998; Z. Otwinowski and W.
Minor, SCALEPACK, DENZO, Methods Enzymol., 1997, 276, 307.
17 R. H. Blessing, SORTAV, Acta Crystallogr., Sect. A, 1995, 51, 33;
R. H. Blessing, J. Appl. Crystallogr., 1997, 30, 421.
18 G. M. Sheldrick, SHELXS 97, Program for crystal structure
solution, University of Göttingen, 1997.
19 G. M. Sheldrick, SHELXL 97, Program for crystal structure
refinement, University of Göttingen, 1997, Release 97–2.
20 P. van der Sluis and A. L. Spek, Acta Crystallogr., Sect. A, 1990, 46,
194.
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