Synthetic and structural studies of [AuCl3(NHC)] complexes

Article abstract of DOI:10.1021/om900814e

A series of N-heterocyclic carbene complexes [AuCl(NHC)] 1 [NHC: IPr, a; SIPr, b; IPr^Mc, c; IPr^cl, d; IMes, e; SIMes, f; I'Bu, g; IAd, h; and ICy, i] were reacted with chlorine gas or PhICl₂ to afford [AuCl₃(IPr)], 2a; [AuCl₃(SIPr)], 2b; [AuCl ₃(IPr^CI], 2c; [AuCl₃(IPr^CI)], 2d; [AuCl₃(IMeS)], 2e; [AuCl₃(SIMeS)], 2f; [AuCl ₃(FBu)], 2g; [AuCl₃(IAd)], 2h; and [AuCl ₃(ICy)], 2i, respectively. Complete characterization by ¹H and ¹³C NMR spectroscopies as well as by single-crystal X-ray diffraction was performed in order to discern electronic and structural differences between organogold(I/III) congeners. Calculations of the buried volume of the NHC ligand in complexes [AuCl₃(NHC)] 2 were also performed in order to evaluate the steric hindrance of the NHC. These data permit comparisons with the related complexes [AuCl(NHC)] 1 and [AuBr ₃(NHC)].

Full text of DOI:10.1021/om900814e

394 Organometallics 2010, 29, 394–402
DOI: 10.1021/om900814e
Synthetic and Structural Studies of [AuCl3(NHC)] Complexes
Sylvain Gaillard,† Alexandra M. Z. Slawin,† Allen T. Bonura,‡ Edwin D. Stevens,‡ and
Steven P. Nolan*,†
‡
†School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, United Kingdom and Department
of Chemistry, University of New Orleans, 2000 Lakeshore Drive, New Orleans, Louisiana 70148
Received September 17, 2009
A series of N-heterocyclic carbene complexes [AuCl(NHC)] 1 [NHC: IPr, a; SIPr, b; IPrMe, c; IPrCl,
d; IMes, e; SIMes, f; ItBu, g; IAd, h; and ICy, i] were reacted with chlorine gas or PhICl2 to afford
[AuCl3(IPr)], 2a; [AuCl3(SIPr)], 2b; [AuCl3(IPrMe)], 2c; [AuCl3(IPrCl)], 2d; [AuCl3(IMes)], 2e; [Au-
Cl3(SIMes)], 2f; [AuCl3(ItBu)], 2g; [AuCl3(IAd)], 2h; and [AuCl3(ICy)], 2i, respectively. Complete
characterization by 1H and 13C NMR spectroscopies as well as by single-crystal X-ray diffraction was
performed in order to discern electronic and structural differences between organogold(I/III)
congeners. Calculations of the buried volume of the NHC ligand in complexes [AuCl3(NHC)] 2
were also performed in order to evaluate the steric hindrance of the NHC. These data permit
comparisons with the related complexes [AuCl(NHC)] 1 and [AuBr3(NHC)].
Introduction
catalytic mediators.3 Moreover, in the past few years, gold(I/
III) complexes have found renewed interest as anti-
cancer drugs4 and have also been investigated for their
photoluminescence properties.5 In spite of this recent atten-
tion, a limited number of reports have highlighted the
synthesis and characterization of well-defined neutral gold-
(III) trihalide complexes. To the best of our knowledge,
[AuCl3(Py)] and [AuBr3(Py)] (Py = pyridine) were the first
gold(III) complexes, reported by Gibson and Colles in 1931.6
Since then, the synthesis of [AuI3(arsine)],7 [AuX3(phos-
phine)] (X=Cl and I),7,8 [AuX3(Rphen)] (Rphen=2,9-dialkyl-
1,10-phenanthroline) (X=Cl and Br),9 and [AuX3(NHC)]10
During the past decade, organogold chemistry and cata-
lysis have undergone a veritable rebirth. The most commonly
used species in gold catalysis are gold(I/III) salts or gold(I)
complexes with ligands such as phosphines and NHCs
(N-heterocyclic carbenes).1 Among the wide range of appli-
cations of gold, gold(I) complexes have proven to be
particularly efficient in natural product synthesis.2 In com-
parison, organogold(III) complexes are rarely described as
*Corresponding author. Fax: (þ) 44(0)1334463808. E-mail: snolan@
st-andrews.ac.uk.
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pubs.acs.org/Organometallics
Published on Web 12/18/2009
2009 American Chemical Society

Article
Organometallics, Vol. 29, No. 2, 2010 395
Figure 1. NHC ligands a-i used in this study.
Scheme 1. Oxidative Addition of Chlorine on [AuCl(IPrMe)], 1c
(X=Cl, Br, and I) have been achieved. Among [AuX3(NHC)]
complexes, only one study has appeared on the synthesis of
complexes bearing imidazolyl as NHC and chloride as halide
atoms.10a In this context, the development of new [AuCl3-
(NHC)] complexes and novel, straightforward strategies to syn-
thesize them continue to be an area of great activity and interest.
Recently, we have reported the synthesis and characteriza-
tion of a series of [AuBr3(NHC)] complexes.10b Catalytic
activity of such complexes was also investigated and compared
to gold(III) salts in alkyne hydration and in the polymerization
of styrene.11 It is suspected that the active gold species in this
chemistry is in fact a (NHC)Au(I) species generated by reduc-
tive elimination of the halogen. As the Au-Cl bond should be
stronger than the analogous Au-Br bond, the synthesis of
[AuCl3(NHC)] 2 complexes was next targeted. In a previous
study, we reported preliminary results on (NHC)gold(III)
chloride synthesis bearing 4,5-dimethyl-N,N0-bis(2,6-diisopro-
pylphenyl)imidazol-2-ylidene (IPrMe) c (Figure 1) by oxida-
tive addition of chlorine gas on the corresponding gold(I)
complexes.10f In this instance, an interesting mixture of two
products with one resulting from C-H bond activation of a
backbone methyl group was obtained (Scheme 1).
Scheme 2. Oxidative Addition of Chlorine Gas on [AuCl(IPr)], 1a
dinegold(III)12 complex with the free carbene IPr a (N,N0-
bis(2,6-diisopropylphenyl)imidazol-2-ylidene). This proce-
dure led to the formation of the expected complex 2a, with
concomitant formation of [AuCl(IPr)], 1a, as the major
product resulting from gold reduction.10b An alternative
route, based on earlier work of Raubenheimer et al.,10a,13
and by analogy with our previous study on the [AuBr3(NHC)]
synthesis,10b was envisaged where chlorine gas14 is used as an
oxidative reagent enabling the synthesis of [AuCl3(NHC)] 2.
Bubbling chlorine gas in a solution of commercially available
[AuCl(IPr)],15 1a, in dichloromethane at room temperature
resulted in significant decomposition of 1a. Nevertheless,
when the reaction was carried out at -78 °C and slowly
warmed to room temperature over 5 h, the expected [AuCl3-
(IPr)], 2a, was obtained as a pale yellow powder in 95% yield
(Scheme 2). The use of low temperature at the beginning
of the reaction caused the chlorine gas condensation (bp =
-34 °C) and ultimately diminishes its oxidative activity.
1H NMR spectroscopic analysis provided similar chemical
shifts to those found for [AuBr3(IPr)]. The most significant
Here we report on the oxidation of [AuCl(NHC)] 1 com-
plexes with chlorine gas or PhICl2 as chlorinating agent
leading to [AuCl3(NHC)] 2 complexes (Figure 1). We also
present an analysis of the steric hindrance of different NHCs
coordinated around the gold center (Figure 1), by calculating
the buried volume (%VBur) value for these ligands in the
present relatively unencumbered gold systems.
Results
(12) Gibson, C. S.; Colles, W. M. J. Chem. Soc. 1931, 2407–2416.
€
(13) Kuhlkamp, P.; Raubenheimer, H. G.; Field, J. S.; Desmet, M.
Initially, the synthesis of [AuCl3(IPr)], 2a, was attempted
via a substitution reaction involving the trichloropyri-
J. Organomet. Chem. 1998, 552, 69–74.
(14) CAUTION: the use of chlorine gas should be conducted in a well-
ventilated hood.
ꢀ
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396 Organometallics, Vol. 29, No. 2, 2010
Gaillard et al.
Scheme 3. Synthesis of [AuCl(IPrCl)], 1d
by NaH in the presence of a catalytic amount of KOtBu to
generate the free carbene IPr, a. Then, CCl4 wasaddedtoafford
the free carbene IPrCl d. Finally, following the strategy of
Sadighi,22 [(Me2S)AuCl] was added to the solution of d to
furnish directly [AuCl(IPrCl)], 1d, after 2 days with a 56% yield
(Scheme 3).
Figure 2. Ball-and-stick representation of [AuCl3(IPr)], 2a. H
atoms are omitted for clarity.
The slow transmetalation of IPrCl d from 6 to [(Me2S)-
AuCl] may very well be caused by the electronic and struc-
tural properties of 6. In the 13C NMR, the coupling constants
difference is an upfield shift in the septet assigned to the
isopropyl proton (2a: 2.85 ppm; [AuBr3(IPr)]: 2.99 ppm) due
to the difference in electronegativity of the halogen atoms. In
the 13C NMR spectrum, the chemical shift of the carbenic
carbon of the IPr in 2a is similar to the analogous bro-
mide complexes (2a: 145.7 ppm; [AuBr3(IPr)]: 146.2 ppm).
X-ray-quality crystals of complex 2a were grown by slow
evaporation of a saturated solution of the crude product in
dichloromethane/hexane (Figure 2).16 The gold atom is four-
coordinate, as usual for gold(III) complexes, and exhibits a
square-planar geometry. Selected bond distances and angles
are summarized in Tables 3 and 4.
J
109/107Ag-13C for 6, which depend on the magnetogyric ratio
of these nuclei,23 were resolved at 273.8 and 236.9 Hz,
respectively. These important values of J109/107Ag-13C indi-
cate a relatively strong Ag-Ccarbene bond.24 To unambigu-
ously characterize 6 and 1d, X-ray-quality crystals of both
complexes were grown by slow evaporation of mixtures of
chloroform/hexane.16 Ball-and-stick representations are
provided in Figure 3.
From these data, the Ag-Ccarbene bond length of 6 was
˚
In an effort to extend our methodology to other NHCs, we
synthesized a series of [AuCl(NHC)] [NHC = N,N0-bis(2,6-
diisopropylphenyl)imidazolin-2-ylidene (SIPr), 1b; 4,5-di-
methyl-N,N0-bis(2,6-diisopropylphenyl)imidazol-2-ylidene
(IPrMe), 1c; 4,5-dichloro-N,N0-bis(2,6-diisopropylphenyl)imi-
dazol-2-ylidene (IPrCl), 1d; N,N0-bis(2,4,6-trimethylphenyl)-
imidazol-2-ylidene (IMes), 1e; N,N0-bis(2,4,6-trimethylphenyl)-
imidazolin-2-ylidene (SIMes), 1f; N,N0-di-tert-butylimidazol-
2-ylidene (ItBu), 1g;N,N0-diadamantylimidazol-2-ylidene (IAd),
1h; N,N0-dicyclohexylimidazol-2-ylidene (ICy), 1i] (Figure 1).17
For the new complex 1d, 5 was first synthesized from 4 by
modification of the Arduengo procedure.18 The silver NHC
complexes are often employed as NHC transfer agents, and the
related [AgCl(IPrCl)], 6, can be synthesized in low yield (28%)
using the procedure involving silver(I) oxide and 5.19 Finally,
complex 1d was prepared in 31% yield by a transmetalation
reaction of IPrCl d from [AgCl(IPrCl)] (6) to [(Me2S)AuCl]20
(Scheme 3).10b,19,21 Due to the low overall yield (7.3%) of 6
from 3 and the long time reaction (1 week) of this route, a one-
pot multistep reaction was attempted. Initially following the
calculated as 2.064(12) A and revealed a very short Ag-
Ccarbene bond compared to previously reported bond dis-
24,25
˚
tances (between 2.056 and 2.095 A).
It thus confirmed
the strong interaction between the ligand and the silver atom,
which was suspected as the cause for the extremely slow
transmetalation of d. The particularity of ligand d is also
evident in [AuCl(IPrCl)], 1d. The Au-Ccarbene bond is one of
the shortest observed in the [AuCl(NHC)] 1 series, with a
˚
bond length of 1.91(2) A, which typically range from 1.942 to
˚
2.018 A for Au-Ccarbene in 1. Nevertheless, the chemical shift
of the carbene in 13C NMR was found at 175.1 ppm, which is
very close to that found for 1a (175.5 ppm) (Table 2). All
structural and spectroscopic data indicate that the substi-
tution at the backbone may very well influence the metal-
ligand interaction and possibly also catalytic activity.
Once all [AuCl(NHC)] complexes 1a-i were on hand, we
explored the compatibility of the reaction shown in Scheme 3
with other NHC ligands presented in Figure 1. The results of
the oxidative addition of chlorine [using either Cl2 gas
(method A) or PhICl2 (method B)] onto gold(I) precursors
to furnish (NHC)gold(III) are summarized in Table 1.
Method A. Carefully bubbling chlorine gas in a solution of
[AuCl(NHC)] 1 furnished the expected [AuCl3(NHC)] 2 as
pale yellow air-stable powders with yields ranging from 79%
Arduengo procedure18 for d, IPr HBF4 (4) was deprotonated
3
(16) CCDC 743930-743940 for compounds 1d, 2a-i, and 6 contain
the supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
ꢀ
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(22) Akana, J. A.; Bhattacharyya, K. X.; Muller, P.; Sadighi, J. P.
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F. Organometallics 1993, 12, 3405–3409.
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I. D.; Gay, I. D.; Clyburne, J. A. C. Inorg. Chem. 2003, 42, 1391–1393.
(b) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005, 105, 3978–4008.
(18) Arduengo, A. J.III; Krafczyk, R.; Schumutzler, R.; Craig, H. A.;
Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55,
14523–14534.
(19) (a) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972–
975. (b) Schneider, S. K.; Hermann, W. A.; Herdtweck, E. Z. Anorg. Allg.
Chem. 2003, 629, 2363–2370. (c) Hu, X.; Castro-Rodriguez, I.; Olsen, K.;
Meyer, K. Organometallics 2004, 23, 755–764.
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Article
Organometallics, Vol. 29, No. 2, 2010 397
Figure 3. Ball-and-stick representation of [AgCl(IPrCl)] (6) (left) and [AuCl(IPrCl)] (1d) (right). H atoms are omitted for clarity.
˚
Selected bond distances (A) and angles (deg), for 6: Ag1-C1 2.064(12), Ag1-Cl1 2.278(4), C1-Ag1-Cl1 180.000(1). For 1d:
Au1-Ccarbene 1.91(2), Au1-Cl1 2.280(6), Ccarbene-Au1-Cl1 178.1(7).
chlorinating agent. The use of the chlorine-based oxidant
Table 1. Synthesis of [AuCl3(NHC)] Complexes
iodobenzene dichloride (PhICl2),26 already reported for the
oxidation of Pt(II),27 Pd(II),28 and Mo(II),29 metals of
group V,30 group VI,31 and Au(I)8a,d was explored. Fortu-
nately, in the presence of 1.1 equiv of PhICl2 in dichloro-
methane at room temperature, all (NHC)gold(I) precursors
1a-i were quantitatively and cleanly oxidized into the
expected [AuCl3(NHC)] complexes 2a-i with yields ranging
from 90% to 96% (Table 1). By this method, all yields were
generally improved. Due to these softer conditions, the
selectivity of the reaction was also improved, especially in
the case of [AuCl(IPrMe)] 1c (Table 1, entry 3), where no
byproduct 3 was observed (Scheme 1).
Finally, among the two methods, the second with the use
of PhICl2 presents several advantages. This chlorinating
reagent is easily handled and can be quickly prepared on a
large scale.26b The use of PhICl2 also permits conducting the
reactions at room temperature, which is more economical
and practical than the protocol of method A.
AuClðNHCÞ
AuCl3ðNHCÞ
method A or B
1
2
CH2Cl2,T,t
yield of 2 (%)a
entry
AuCl(NHC)
method A
method B
1
2
3
4
5
6
7
8
9
IPr 1a
95
90
88b
80
79c
0d
96
91
0d
95
92
90
92
94
95
96
92
91
SIPr 1b
IPrMe 1c
IPrCl 1d
IMes 1e
SIMes 1f
ItBu 1g
IAd 1h
ICy 1i
a Isolated yield. Method A: excess of chlorine was bubbled at -78 °C
in a solution of (NHC)gold(I) 1 in dichloromethane, and the reaction
mixture was slowly warmed to room temperature in 5 h under stirring
(except for 1e, 1f, and 1i, which ran at -78 °C during 7 h). Method B:
In a vial, (NHC)gold(I) 1 (1 equiv) and PhICl2 (1.1 equiv) were
dissolved in dichloromethane and stirred at room temperature over-
night. b Mixture of 2c and 3 was obtained in the ratio 1.5:1. c Reac-
tion carried out at -78 °C during 7 h. d Product detected among
decomposition.
Discussion
1
1H and 13C NMR Data. The H NMR spectra of com-
plexes bearing unsaturated NHCs without substitution on
the backbone, 2a, 2e, 2g, 2h, and 2i, displayed a low-field
singlet between 7.30 and 7.50 ppm assigned to the two
protons of the imidazole backbone, versus the range of
to 96% (Table 1, entries 1-5 and 7, 8). In the case of 1c
(Table 1, entry 3), we previously reported a concomitant
formation of 3 with [AuCl3(IPrMe)] (2c), resulting from a CH
insertion on the methyl framework of the backbone
(Scheme 1).10f Another precedent has been reported by
Ghosh et al. with bromine, which reacted with a framework
of the ligand after the oxidation of the metal center.10d It is
noteworthy that no addition of chlorine to the double bond
of the unsaturated carbenes was detected. Under these
conditions, attempts to synthesize [AuCl3(IMes)] (1e) and
[AuCl3(SIMes)] (1f) failed and led only to decomposition
products. Nevertheless, when the reactions were carried
out at -78 °C during 7 h, 1e was obtained with 79% yield
and 1f was also observed but was surprisingly unstable under
these conditions (Table 1, entries 5 and 6). In the case
of [AuCl3(ICy)] (1i), only decomposition was obtained
even if the reaction mixture was kept at -78 °C (Table 1,
entry 9).
(26) (a) Zielinska, A.; Skulski, L. Tetrahedron Lett. 2004, 45, 1087–
1089. (b) Zhao, X.-F.; Zhang, C. Synthesis 2007, 4, 551–557.
(27) (a) Baxter, L. A. M.; Heath, G. A.; Raptis, R. G.; Willis, A. C.
J. Am. Chem. Soc. 1992, 114, 6944–6946. (b) Bennett, M. A.; Bhargava,
ꢀ
S. K.; Bond, A. M.; Edwards, A. J.; Guo, S.-X.; Priver, S. H.; Rae, A. D.; Willis,
A. C. Inorg. Chem. 2004, 43, 7752–7763. (c) Bennett, M. A.; Bhargava, S. K.;
€
ꢀ
Messelhausser, J.; Priver, S. H.; Welling, L. L.; Willis, A. C. Dalton Trans.
2007, 3158–3169. (d) Whitfield, S. R.; Sanford, M. S. Organometallics 2008,
27, 1683–1689. (e) Mamtora, J.; Crosby, S. H.; Newman, C. P.; Clarkson, G. J.;
Rourke, J. P. Organometallics 2008, 27, 5559–5565.
(28) (a) Cotton, F. A.; Koshevoy, I. O.; Lahuerta, P.; Murillo, C. A.;
ꢀ
Sanau, M.; Ubeda, M. A.; Zhao, Q. J. Am. Chem. Soc. 2006, 128, 13674–
13675. (b) Whitfield, S. R.; Sandford, M. S. J. Am. Chem. Soc. 2007, 129,
15142–15143.
(29) Baya, M.; Houghton, J.; Daran, J.-C.; Poli, R.; Male, M.;
Albinati, A.; Gutman, M. Chem.-Eur. J. 2007, 13, 5347–5359.
(30) (a) Witte, P. T.; Meetsma, A.; Hessen, B. Organometallics 1999,
18, 2944–2946. (b) Hayton, T. W.; Legzdins, P.; Patrick, B. O. Inorg. Chem.
2002, 41, 5388–5396.
Method B. To improve and generalize the syntheses of
[AuCl3(NHC)] 2, we turned our attention to an alternative
€
(31) Filippou, A. C.; Winter, J. G.; Kociok-Kohn, G.; Troll, C.; Hinz,
I. Organometallics 1999, 18, 2649–2659.

398 Organometallics, Vol. 29, No. 2, 2010
Gaillard et al.
Table 2. Chemical Shift (ppm) of the Carbenic Carbon (δC) of Free NHCs, NHC Salts, and [AuCl(NHC)] 1, [AuCl3(NHC)] 2,
and [AuBr3(NHC)] Complexes10b,f,17,18,25,33
ΔδC (ppm)
between
NHC salt and 2
δC of free
NHC
δ
C of
δ
C of
[AuBr3(NHC)]a
ΔδC (ppm)
between 2 and 1
ΔδC (ppm) between
[AuBr3(NHC)] and 2
NHC
NHC HCl salt
δ
C of 1a
δ
C of 2a
3
IPr a
220.6c
244.0c
132.2e
160.0e
136.0f
140.2g
134.8e
160.2e
132.7e
132.1e
134.9a
175.5
196.1
171.4
175.1
173.4
195.0
168.2
166.3b
168.0
145.7
172.8
141.4b
148.3
144.7
171.2b
135.7
134.2
138.7
146.2
174.1
13.5
12.8
5.4
8.1
9.9
11.0
3.0
2.1
3.8
29.4
23.3
24.6
25.7
28.7
23.8
32.5
32.1
29.3
-0.5
-1.3
SIPr b
IPrMe c
IPrCl d
IMes e
SIMes f
ItBu g
IAd h
ICy i
220.6c
219.7d
243.8c
213.2d
211.4d
210.1d
144.4
172.3
134.2
132.9
136.8
0.3
-1.1
1.5
1.3
1.9
a NMR recorded in CDCl3. b NMR recorded in CD2Cl2. c NMR recorded in d6-benzene. d NMR recorded in d8-tetrahydrofuran (d8-THF). e NMR
recorded in d6-dimethylsulfoxide (d6-DMSO). f NMR recorded in d2-water (D2O). g NMR recorded in d4-methanol (d4-MeOD).
˚
Table 3. Selected Au-Ccarbene and Au-Cl Bond Distances (A) for
Complexes 2a-i
imidazolium salt (ΔδC) were calculated to be between 2.1
and 13.5 ppm. Among organometallic complexes bearing
NHC, the δC values of complexes 2 present the most upfield
Au-
Ccarbene
Au-
Cl(trans)
Au-
Cl(cis)
Au-
Cl(cis)
resonances, close to that of the NHC HCl salt. This is also in
complex
3
good agreement with our previous study on [AuBr3(NHC)]
complexes (Table 2).10b These data highlight the strong
Lewis acidity of the AuCl3 moiety in complexes 2a-i. Dif-
ferences of the carbenic carbon signal (ΔδC) between
[AuCl(NHC)] 1a-i and [AuCl3(NHC)] 2a-i were found to
range between 23.3 and 32.5 ppm (ΔδC were included
between 24.9 and 38.2 ppm for [AuBr(NHC)] and their
analogous [AuBr3(NHC)]). This trend results from the
change in oxidation state of the gold center as observed by
Raubenheimer and co-workers.10a When the δC values of [Au-
Cl3(NHC)] 2a-i and [AuBr3(NHC)] complexes were com-
pared, no significant differences appeared (-1.5 to 1.3 ppm),
implying that the chemical property was independent of the
nature of the halide.34
[AuCl3(IPr)], 2a
2.013(9)
2.002(9)
2.010(8)
1.975(13)
1.998(10)
1.977(6)
2.013(11)
2.006(4)
2.009(10)
1.986(18)
2.306(3)
2.303(3)
2.311(2)
2.315(3)
2.298(3)
2.306(2)
2.315(3)
2.320(13)
2.325(3)
2.307(5)
2.270(3)
2.272(3)
2.272(2)
2.284(4)
2.258(3)
2.276(2)
2.278(3)
2.2872(9)
2.284(3)
2.281(5)
2.259(3)
2.255(3)
2.270(2)
2.250(4)
2.274(4)
2.268(2)
2.258(3)
2.2864(9)
2.295(3)
2.274(1)
[AuCl3(SIPr)], 2b
[AuCl3(IPrMe)], 2c
[AuCl3(IPrCl)], 2d
[AuCl3(IMes)], 2e
[AuCl3(SIMes)], 2f
[AuCl3(ItBu)], 2g
[AuCl3(IAd)], 2h
[AuCl3(ICy)], 2i
7.04 and 7.24 ppm for 1a, 1e, 1g, 1h, and 1i. This significant
variation already observed for the [Au(NHC)Br3] complexes
family indicated an important decrease of the electron
density of the double bond. The consequence could be an
increase of the acidic character of the gold center due to the
presence of two more halides as ligands. For the same reason,
saturated NHCs possessing a singlet correspond to the four
protons of the backbone with a signal at 4.28 ppm for 2b and
4.24 ppm for 2f versus 4.06 and 3.98 ppm in [AuCl(SIPr)] (1b)
and [AuCl(SIMes)] (1f), respectively.
Crystallographic Data. To unambiguously characterize all
new complexes 2a-i, X-ray-quality crystals were grown by
slow evaporation of a solution of complexes 2a-i in chlori-
nated solvent (dichloromethane or chloroform with hexane)
or by slow diffusion of pentane in dichloromethane.16 Ball-
and-stick representations are provided in Figure 5. The
Au-Cl(trans) bond lengths were found to range between
13C NMR is commonly accepted as one of the most
powerful analytical tools for the study of NHCs.25 The 13
C
˚
2.298 and 2.325 A and are longer than the Au-Cl(cis),
NMR spectra of complexes 2a-i displayed signals for the
carbenic carbon ranging between 134.2 and 148.3 ppm for
unsaturated NHC and around 172 ppm for saturated NHC
(Table 2). The carbenic carbon chemical shift (δC) of
[AuCl3(NHC)] 2a-i were also compared to their analogous
[AuBr3(NHC)] and [AuCl(NHC)] complexes 1a-i (Figure 4
and Table 2). Herrmann et al. have postulated a correlation
between the δC of the NHC and the acidity of the coordi-
nated metal center.32 The carbenic carbon of [AuCl3(NHC)]
complexes 2g-i with an N-alkyl-substituent displayed sig-
nals below 140 ppm and indicated an increase of the Lewis
acidity of the gold center. With regard to complexes 2a, 2c,
and 2d, a chloride substituent (148.3 ppm) decreased the
Lewis acidity of the metal center compared to unsubstituted
IPr (145.7 ppm), whereas methyl groups (141.4 ppm) in-
creased the latter. Free NHCs have a δC usually above
200 ppm and NHC salts around 130 ppm for unsaturated
NHCs and 160 ppm for saturated NHCs (Figure 4). The
differences in δC between [AuCl3(NHC)] 2a-i and the
˚
measured as 2.258 to 2.295 A. All Au-Ccarbene bond dis-
tances range from 1.975 to 2.013 A (Table 3). Usually,
˚
Au-Ccarbene bond lengths in (NHC)gold(III) complexes
10a,d,36
˚
are between 2.00 and 2.13 A,
whereas in the N,S-
heterocyclic carbene gold(III) complexes they are 1.97 and
10c
˚
2.02 A.
Noteworthy, the 2c and 2d have shorter Au-
Ccarbene bond lengths than 2a. This is in perfect agreement
with the bond length trends observed for these NHCs in the
silver(I) and gold(I) series. In all cases, the Ccarbene-Au-Cl-
(trans) and Cl(cis)-Au-Cl(cis) bonds are nearly linear, with
(33) Baker, M. V.; Barnard, P. J.; Brayshaw, S. K.; Hickey, J. L.;
Skelton, B. W.; White, A. H. Dalton Trans. 2005, 37–43.
(34) (a) Arduengo, A. J.III; Harlow, R. L.; Kline, M. J. J. Am. Chem.
Soc. 1991, 113, 361–363. (b) Arduengo, A. J.III; Dias, H. V. R.; Harlow,
R. L.; Kline, M. J. Am. Chem. Soc. 1992, 114, 5530–5534. (c) Arduengo,
A. J., III; Bock, H.; Chen, H.; Denk, M.; Dixon, A. D.; Green, J. C.;
Herrmann, W. A.; Jones, N. L.; Wagner, M.; West, R. J. Am. Chem. Soc.
1994, 116, 6641–6649. (d) Arduengo, A. J.III; Goerlich, J. R.; Marshall, W. J.
€
J. Am. Chem. Soc. 1995, 117, 11027–11028. (e) Herrmann, W. A.; Kocher,
C.; Goossen, L. J.; Artus, G. R. Chem.;Eur. J. 1996, 2, 1627–1636.
ꢀ
(35) Manojlovic-Muir, L. J. Organomet. Chem. 1974, 73, C45–C46.
(36) The Web-based free-access SambVca software is available online
at http://www.molnac.unisa.it/OMtools/sambvca.php.
(32) Herrmann, W. A.; Runte, O.; Artus, G. J. Organomet. Chem.
1995, 501, C1–C4.

Article
Organometallics, Vol. 29, No. 2, 2010 399
Table 4. Selected Angle Values and Torsion Angles of N-Ccarbene-Au-Cl(cis) (deg) for Complexes 2a-i
N1-Ccarbene-Au-Cl(cis)
torsion angle
complex
Ccarbene-Au-Cl(trans)
Ccarbene-Au-Cl(cis)
Cl(trans)-Au-Cl(cis)
Cl(cis)-Au-Cl(cis)
[AuCl3(IPr)], 2a
178.2(3)
178.1(3)
175.2(2)
177.3(3)
178.6(3)
178.10(18)
176.6(3)
177.53(13)
178.6(3)
179.1(5)
90.3(3)
88.9(3)
88.2(2)
87.6(3)
91.1(3)
88.50(18)
90.2(3)
87.00(13)
87.5(3)
88.5(5)
89.43(12)
89.06(12)
90.25(9)
89.82(14)
90.44(13)
90.01(10)
89.86(12)
91.20(5)
179.70(11)
179.46(13)
178.58(9)
179.48(16)
179.18(10)
178.53(7)
177.26(12)
177.94(5)
174.06(11)
176.87(18)
74.6
74.6
69.7
82.8
86.4
73.9
70.8
85.0
86.5
77.0
[AuCl3(SIPr)], 2b
[AuCl3(IPrMe)], 2c
[AuCl3(IPrCl)], 2d
[AuCl3(IMes)], 2e
[AuCl3(SIMes)], 2f
[AuCl3(ItBu)], 2g
[AuCl3(IAd)], 2h
[AuCl3(ICy)], 2i
93.06(11)
91.01(18)
and 19.6°, respectively (Table 5, entries 2 and 6). This torsion
angle in the imidazole ring affects the proximity of N-sub-
stituents of the aromatic rings to the metal.
The NHC buried volume for ligands a-i in the [AuBr3-
(NHC)] and [AuCl(NHC)] 1a-i complexes were also calcu-
lated to evaluate the influence of the halide and complex
geometry on the %VBur (Table 5). In the series of [AuBr3-
(NHC)], the buried volume ranges between 26.8% (for ICy i)
and 37.6% (for SIPr b) (Table 1, entries 2 and 9). These
values are similar to those found for the [AuBr3(NHC)]
complexes. These results permit us to conclude that the
nature of the halide does not influence the conformation of
the NHC ligand a-i in the present complexes. In the case of
[AuCl(NHC)], %VBur values fall between 27.6% (for ICy i)
and 47.4% (for SIPr b) (Table 1, entries 2 and 9). The buried
volumes of NHC a-i between gold(I) chloride and gold(III)
chloride complexes were compared, and an increase of the
values was observed in gold(I) complexes (Table 5). This
observation is related to the geometry of the complexes,
linear for gold(I) and square planar for gold(III). In the case
of linear gold(I) complexes, more space is available to the
NHC in the absence of the two halides and generally the %
VBur values are larger. Interestingly, for small NHCs such as
ICy i, no interaction between the ligand and the halides
appeared in gold(III) complexes 2i, where the buried volume
was found to be the same as in 1i.
Figure 4. Range of NHC species function of their carbenic
carbon chemical shift (δ in ppm) in 13C NMR.
angles between 175.2° and 179.7° (Table 4). These data
confirm the expected square-planar geometry for all com-
plexes. Interestingly, the plane defined by the AuCl3 moiety
and the plane defined by the imidazole ring are not perfectly
perpendicular. The Cl(cis)-Au-Ccarbene-N torsion angles
measured for complexes 2a-i are between 69.7° and 86.5°
(Table 4). The most twisted complexes were 2b and 2f, with a
torsion angle around 70° due to the flexibility of the un-
saturated imidazole ring. With bulky N-substituents on the
NHC such as IAd h (86.5°) and ItBu g (84.9°) the torsion
angles in the complexes were closer to 90° due to the steric
hindrance of the substituents that surround the metal center.
When the backbone of the imidazole ring was substituted
such as in IPrMe c (86.4°) and IPrCl d (82.8°), the 2,6-
diisopropylphenyl substituents of the NHC were “pushed”
toward the metal center and the torsion angles found were
nearly 90°.
Percent Buried Volume (%VBur). For a more in-depth
understanding of the structural properties of NHC ligands
a-i, we examined the steric hindrance brought about by this
ligand family around the metal center. To quantify this steric
influence, the percent buried volume (%VBur) of each of
these ligands was calculated using the SambVca method
developed by Cavallo and co-workers.36 The calculation
procedure has already been reported.37 In this model, the
%VBur value represents the portion of a sphere, centered
around the metal atom, occupied by the ligand (Figure 6). All
calculated buried volumes range from 27.7% (for ICy i) to
38.8% (for SIPr b) (Table 5, entries 2 and 9). Surprisingly,
IAd h and ItBu g, which are commonly accepted as the
bulkiest ligands in the studied series, revealed a large but not
largest value of 36% (Table 5, entries 7 and 8). Noteworthy is
an important difference between values for 2f and 2c [SIMes f
(34.7%) and SIPr b (38.8%)], which is probably due to the
difference in torsion angle of the N(1)-C-C-N(2), 10.5°
Noteworthy, IPr a, SIPr b, IPrMe c, and IPrCl d in gold(I)
chloride complexes exhibited a buried volume increased by
around 10 units compared to their analogous gold(III)
complexes 2a, 2b, 2c, and 2d. To understand this particular-
ity of the 2,6-diisopropylphenyl substituent in the NHC
compared to mesityl framework, the distances between the
four carbon atoms in ortho position on the aromatic group to
the gold center (d) were measured for 1a, 1e, 2a, and 2e
(Figure 7).
For gold(III) chlorides 2a and 2e, all distances d measured
˚
were similar in IPr a and IMes e (between 3.993 and 4.637 A),
as well as in the gold(I) chloride series (between 3.984 and
˚
4.212 A). This observation is in agreement with the similar
buried volumes between IPr a and IMes e in the gold(III)
chloride series. Then, distances between the four closest
methyl groups of the isopropyl group to the gold center
(d0) were measured for 1a and 2a (Figure 7). In the case of 1a,
0
˚
d were found to measure 3.886 to 4.235 A, whereas they are
˚
significantly longer, at 4.228 to 5.123 A, in [AuCl3(IPr)], 2a.
This difference parallels the %VBur values and may very well
result from the electronic repulsion of the methyl groups by
the chlorine atoms in [AuCl3(IPr)], 2a. The shorter Au-
(37) Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.;
Scarano, V.; Cavallo, L. Eur. J. Inorg. Chem. 2009, 1759–1766.
(38) For the values obtained for the real bond length for Au-C of
each complex see Supporting Information.
˚
Ccarbene bond length in linear gold(I) (1.974 A on average)
˚
compared to gold(III) (1.999 A on average) could also be
another factor influencing this interaction.

400 Organometallics, Vol. 29, No. 2, 2010
Gaillard et al.
Figure 5. Ball-and-stick representations of complexes [AuCl3(SIPr)], 2b; [AuCl3(IPrMe)], 2c; [AuCl3(IPrCl)], 2d; [AuCl3(IMes)], 2e;
[AuCl3(SIMes)], 2f; [AuCl3(ItBu)], 2g; [AuCl3(IAd)], 2h; and [AuCl3(ICy)], 2i. Most hydrogen atoms are omitted for clarity. Selected
˚
bond distances (A) and angles (deg) are summarized in Tables 3 and 4.
Figure 7. Representation of distances d and d0 in complexes 2a
and 2e.
Figure 6. Graphical Representation of the Sphere Used for the
%VBur Calculations.
the reaction stoichiometry. Moreover, reactions were per-
formed at room temperature instead of at low temperature
when chlorine gas was used. All new complexes were fully
characterized by NMR and X-ray analysis. The X-ray data
permitted the examination of the steric effects of the most
common NHCs by calculation of the buried volume (%VBur)
Table 5. Steric Parameter (%VBur) Calculated for NHCs a-i in
[AuCl3(NHC)] 2a-i, [AuBr3(NHC)], and [AuCl(NHC)]
Complexes 1a-i
%VBur for
[AuBr3(NHC)]a
values. This new computational steric model proves efficient
in rapidly affording measurable descriptors for this highly
important ligand parameter. We have also extended this
study to IPrMe and IPrCl in order to evaluate the influence
of substitution on the NHC backbone. Studies aimed at
exploring the effects of this substitution on metal-catalyzed
reactions are ongoing in our laboratories.
entry
ligand
%VBur for 2a
%VBur for 1a
1
2
3
4
5
6
7
8
9
IPr a
34.9
38.8
35.7
35.5
34.2
34.7
36.0
36.5
27.7
33.3
37.6
45.6
47.4
44.5
43.8
36.5
37.1
n.a.
40.0
27.6
SIPr b
IPrMe c
IPrCl d
IMes e
SIMes f
ItBu g
IAd h
ICy i
34.1
34.0
35.8
35.8
26.8
Experimental Section
aCalculation were achieved using a crystallographically determined
General Considerations. All reactions were carried out using
standard Schlenk techniques under an atmosphere of dry argon.
Anhydrous solvents were either distilled from appropriate dry-
ing agents or purchased from Aldrich and degassed prior to use
by purging with dry argon and kept over molecular sieves.
Solvents for NMR spectroscopy were degassed with argon
and dried over molecular sieves. NMR spectra were recorded
on a 400 MHz Varian Gemini spectrometer. Elemental analyses
were performed by St Andrews analytical services. AuCl and
SMe2 were purchased from Strem and Acros, respectively, and
[Au(SMe2)Cl] was prepared according to the reported proce-
dure.20
bond length for the Au-Ccarbene bond and the radius of sphere was fixed
at R = 3.5 A.
38
˚
Conclusion
In summary, we have described the syntheses of a series of
[AuCl3(NHC)] 2 complexes in excellent yields by oxidative
addition of chlorine onto AuCl(NHC) 1 with chlorine gas or
PhICl2. PhICl2 was revealed to be more selective than
chlorine gas especially in the case of IPrMe and precluded
decomposition in the case of ICy and SIMes. This reagent
presents several advantages compared to chlorine gas. In-
deed, PhICl2 is easily handled, resulting in a good control of
Synthesis of [AuCl(IPrCl)] (1d). In a Schlenk tube, IPr HBF4
3
(953 mg, 2 mmol) was added to a suspension of NaH (96 mg,
4 mmol) in THF (10 mL). A spatula of KOtBu was added, and

Article
Organometallics, Vol. 29, No. 2, 2010 401
the reaction mixture was stirred at room temperature overnight.
The solution was filtered and CCl4 (386 μL, 4 mmol) was added
to the filtrate. The reaction mixture was stirred an additional 3 h,
and AuCl(SMe2) (589.1 mg, 2 mmol) was added. The reaction
mixture was stirred in darkness at room temperature during
14 h. The reaction mixture was filtered on a pad of silica, and
solvent was removed under vacuum. The crude mixture was
dissolved in dichloromethane, and charcoal was added. The
resulting mixture was stirred at room temperature overnight.
The solution was filtered on a pad of silica. Solvent was reduced
to 2 mL under vacuum, and hexane (10 mL) was added. The
resulting pale yellow precipitate was filtered, washed with
hexane (3 ꢀ 5 mL), and dried under vacuum. Yield: 771 mg
(56%). 1H NMR (400 MHz, CDCl3): δ 7.56 (t, J=7.8 Hz, 2H,
CH aromatic), 7.32 (d, J=7.8 Hz, 4H, CH aromatic), 2.45 (sept,
J = 6.8 Hz, 4H, CH(CH3)2), 1.35 (d, J = 6.8 Hz, 12H, CH-
(CH3)2), 1.26 (d, J = 6.8 Hz, 12H, CH(CH3)2) ppm. 13C NMR
(100 MHz, CDCl3): δ 175.1 (s, C carbene), 146.0 (s, C aromatic),
131.6 (s, CH aromatic), 130.0 (s, C aromatic), 124.6 (s, CH
aromatic), 118.9 (s, CCl imidazole), 29.1 (s, CH(CH3)2), 24.6 (s,
CH(CH3)2), 23.4 (s, CH(CH3)2) ppm. Anal. Calcd for
C29H40N2AuCl (689.90): C, 47.01; H, 4.97; N, 4.06. Found: C,
47.05; H, 4.72; N, 3.90.
CH(CH3)2) ppm. 13C NMR (100 MHz, CD2Cl2): δ 147.2 (s,
C aromatic), 141.4 (s, C carbene), 132.0 (s, C aromatic), 131.3 (s,
C imidazole), 131.0 (s, C aromatic), 125.7 (s, CH aromatic), 29.1
(s, CH(CH3)2), 25.5 (s, CH(CH3)2), 24.7 (s, CH(CH3)2), 11.3 (s,
CH3 imidazole) ppm. Anal. Calcd for C29H40N2AuCl3 (718.19):
C, 48.38; H, 5.60; N, 3.89. Found: C, 48.28; H, 5.50; N, 3.79.
Synthesis of [AuCl3(IPrCl)] (2d). Method A afforded 2d as a
pale yellow solid. Yield: 131.7 mg (80%). Method B gave 2d as a
pale yellow solid. Yield: 84 mg (92%).1H NMR (400 MHz,
CDCl3): δ 7.61 (t, J = 7.8 Hz, 2H, CH aromatic), 7.40 (d, J =
7.8 Hz, 4H, CH aromatic), 2.79 (sept, J=6.6 Hz, 4H, CH(CH3)2),
1.41 (d, J = 6.5 Hz, 12H, CH(CH3)2), 1.20 (d, J = 6.8 Hz, 12H,
CH(CH3)2) ppm. 13C NMR (100 MHz, CDCl3): δ 148.4 (s,
C carbene), 147.0 (s, C aromatic), 132.7 (s, CH aromatic), 129.6
(s, C aromatic), 125.6 (CH, aromatic), 123.0 (s, CCl imidazole),
29.2 (s, CH(CH3)2), 25.5 (s, CH(CH3)2), 24.3 (s, CH(CH3)2) ppm.
Anal. Calcd for C27H34N2AuCl5 (758.08): C, 42.62; H, 4.50; N,
3.68. Found: C, 42.44; H, 4.50; N, 3.67.
Synthesis of [AuCl3(IMes)] (2e). Method A: Excess chlorine
was bubbled into a solution of 1e (100 mg, 0.186 mmol) in
dichloromethane (2 mL) at -78 °C, and the reaction mixture
was stirred at -78 °C during 7 h. The solvent volume was
reduced by half under vacuum, and hexane (5 mL) was added.
The resulting precipitate was collected and washed with hexane
(3 ꢀ 5 mL). The solid was dried under vacuum to afford 2e as a
pale yellow powder. Yield: 89.7 mg (79%).
Method B afforded 2e as a pale yellow solid. Yield: 105.7 mg
(94%). 1H NMR (400 MHz, CDCl3): δ 7.30 (s, 2H, CH
imidazole), 7.03 (s, 4H, CH aromatic), 2.36 (s, 6H, CH3 mesityl),
2.25 (s, 12H, CH3 mesityl) ppm. 13C NMR (100 MHz, CDCl3): δ
144.6 (s, C carbene), 141.0 (s, C aromatic), 135.3 (s, C aromatic),
132.3 (s, C aromatic), 129.9 (s, CH aromatic), 125.6 (s, CH
imidazole), 21.2 (s, CH3 mesityl), 18.5 (s, CH3 mesityl) ppm.
Anal. Calcd for C27H36N2AuCl3 with 10% of dichloromethane
(606.06): C, 41.08; H, 3.96; N, 4.54. Found: C, 41.08; H, 3.56; N,
4.35.
Synthesis of [AuCl3(SIMes)] (2f). Method B: A preparation
method similar to that used for compound 2a gave 2f as a pale
yellow solid. Yield: 108 mg (95%). 1H NMR (400 MHz,
CD2Cl2): δ 7.03 (s, 4H, CH aromatic), 4.24 (s, 4H, CH imi-
dazole), 2.48 (s, 12H, CH3 mesityl), 2.34 (s, 6H, CH3 mesityl)
ppm. 13C NMR (100 MHz, CD2Cl2): δ 171.5 (s, C carbene),
140.7 (s, C aromatic), 136.6 (s, C aromatic), 132.2 (s, C aro-
matic), 130.3 (s, CH aromatic), 52.7 (s, CH2 imidazole), 21.2
(s, CH3 mesityl), 19.0 (s, CH3 mesityl) ppm. Anal. Calcd for
C21H26N2AuCl3 (608.08): C, 41.36; H, 4.30; N, 4.59. Found: C,
41.71; H, 4.12; N, 4.23.
Synthesis of [AuCl3(IPr)] (2a). Method A: Excess chlorine was
bubbled into a solution of 1a (200 mg, 0.32 mmol) in dichloro-
methane (4 mL) at -78 °C, and the reaction mixture was slowly
warmed to room temperature over 5 h with stirring. The solvent
volume was reduced by half under vacuum, and hexane (10 mL)
was added. The resulting precipitate was collected and washed
with hexane (3 ꢀ 5 mL). The solid was dried under vacuum to
afford 2a as a pale yellow powder. Yield: 209.7 mg (95%).
Method B: In a vial, 1a (1 equiv) and PhICl2 (1.1 equiv) were
dissolved in dichloromethane and stirred at room temperature
overnight. Solvent volume was reduced by half under vacuum,
and hexane was added. The resulting precipitate was collected
and washed with hexane. The solid was dried under vacuum to
1
afford 2a as a pale yellow powder. Yield: 209.7 mg (95%). H
NMR (400 MHz, CDCl3): δ 7.56 (t, J = 7.8 Hz, 2H, CH
aromatic), 7.36 (d, J = 7.8 Hz, 4H, CH aromatic), 7.34 (s, 2H,
CH imidazole); 2.85 (sept, J=6.7 Hz, 4H, CH(CH3)2), 1.40 (d,
J = 6.7 Hz, 12H, CH(CH3)2), 1.13 (d, J = 6.7 Hz, 12H, CH-
(CH3)2) ppm. 13C NMR (100 MHz, CDCl3): δ 146.0 (s, C
aromatic), 145.7 (s, C carbene), 132.2 (s, C aromatic), 131.8 (s,
CH imidazole), 126.4 (s, CH aromatic), 124.7 (s, CH aromatic),
29.0 (s, CH(CH3)2), 26.5 (s, CH(CH3)2), 22.7 (s, CH(CH3)2)
ppm. Anal. Calcd for C27H36N2AuCl3 (691.91): C, 46.87; H,
5.24; N, 4.05. Found: C, 46.96; H, 4.82; N, 3.94.
Synthesis of [AuCl3(ItBu)] (2g). Method A gave 2g as a pale
yellow solid. Yield: 226 mg (96%). Method B provided 2g as a
pale yellow solid. Yield: 111.9 mg (96%). 1H NMR (400 MHz,
CDCl3): δ 7.45 (s, CH imidazole), 1.96 (s, 18H, C(CH3)3) ppm.
13C NMR (100 MHz, CDCl3): δ 135.7 (s, C carbene), 122.1
(s, CH imidazole), 62.5 (s, C(CH3)3), 31.9 (s, C(CH3)3) ppm.
Anal. Calcd for C11H20N2AuCl3 (483.62): C, 27.32; H, 4.17; N,
5.79. Found: C, 27.43; H, 3.97; N, 5.66.
Synthesis of [AuCl3(IAd)] (2h). Method A afforded 2h as a pale
yellow solid. Yield: 204.2 mg (91%). Method B gave 2h as a pale
yellow solid. Yield: 102.4 mg (92%). 1H NMR (300 MHz,
CDCl3): δ 7.51 (s, CH imidazole), 2.58 (d, J = 2.8 Hz, 12H,
adamantyl), 2.34 (s, 4H, adamantyl), 1.77 (t, J = 2.8 Hz, 12H,
adamantyl) ppm. 13C NMR (100 MHz, CDCl3): δ 134.2 (s,
C carbene), 121.0 (s, CH imidazole), 63.8 (s, N-C adamantyl),
43.9 (s, CH2 adamantyl), 35.3 (s, CH2 adamantyl), 30.0 (s, CH
adamantyl) ppm. Anal. Calcd for C23H32N2AuCl3 (639.83): C,
43.17; H, 5.04; N, 4.38. Found: C, 43.46; H, 5.02; N, 4.07.
Synthesis of [AuCl3(ICy)] (2i). Method B: A preparation
method similar to that used for compound 2a gave 2i as a pale
yellow solid. Yield: 104.6 mg (91%). 1H NMR (400 MHz, CDCl3):
δ 7.21 (s, 2H, CH imidazole), 4.57-4.68 (m, 2H, CH cyclohexyl),
2.22-2.29 (m, 4H, CH2 cyclohexyl), 1.88-1.95 (m, 4H, CH2
Synthesis of [AuCl3(SIPr)] (2b). Method A afforded 2b as a
pale yellow solid. Yield: 300 mg (90%). Method B provided 2b
as a pale yellow solid. Yield: 102.5 mg (92%). H NMR (400
1
MHz, CDCl3): δ 7.46 (t, J=7.8 Hz, 2H, CH aromatic), 7.29 (d,
J=7.8 Hz, 4H, CH aromatic), 4.28 (s, 4H, CH2 imidazole), 3.33
(sept, J = 6.7 Hz, 4H, CH(CH3)2), 1.46 (d, J = 6.7 Hz, 12H,
CH(CH3)2), 1.27 (d, J = 6.7 Hz, 12H, CH(CH3)2) ppm. 13C
NMR (100 MHz, CDCl3): δ 172.8 (s, C carbene), 146.9 (s,
C aromatic), 132.0 (s, C aromatic), 131.1 (s, CH aromatic), 125.2
(s, CH aromatic), 54.7 (s, CH2 imidazole), 29.0 (s, CH(CH3)2),
27.1 (s, CH(CH3)2), 23.6 (s, CH(CH3)2) ppm. Anal. Calcd for
C27H38N2AuCl3 (693.93): C, 46.73; H, 5.52; N, 3.64. Found: C,
46.49; H, 5.16; N, 3.64.
Synthesis of [AuCl3(IPrMe)] (2c). Method A: A preparation
method similar to that used for compound 2a gave an insepar-
able mixture of 2c and 3 in a ratio 1.5:1 in favor of 2c as a pale
yellow solid. Yield: 67 mg (88%).
Method B: A preparation method similar to that used for
compound 2a gave 2c as a pale yellow solid. Yield: 99.7 mg
(90%). 1H NMR (400 MHz, CD2Cl2): δ 7.61 (t, J=7.8 Hz, 2H,
CH aromatic), 7.42 (d, J=7.8 Hz, 4H, CH aromatic), 2.82 (sept,
J = 6.7 Hz, 4H, CH(CH3)2), 2.08 (s, 6H, CH3 imidazole), 1.39
(d, J = 6.6 Hz, 12H, CH(CH3)2), 1.12 (d, J = 6.8 Hz, 12H,

402 Organometallics, Vol. 29, No. 2, 2010
Gaillard et al.
cyclohexyl), 1.76-1.84 (m, 2H, CH2 cyclohexyl), 1.45-1.63 (m,
8H, CH2 cyclohexyl), 1.15-1.31 (m, 2H, CH2 cyclohexyl) ppm.
13C NMR (100 MHz, CDCl3): δ 138.7 (s, C carbene), 120.2 (s, CH
imidazole), 61.1 (s, CH cyclohexyl), 33.4 (s, CH2 cyclohexyl), 25.1
(s, CH2 cyclohexyl), 24.8 (s, CH2 cyclohexyl) ppm. Anal. Calcd for
C15H24N2AuCl3 (534.07): C, 33.63; H, 4.52; N, 5.23. Found: C,
33.88; H, 4.51; N, 5.05.
Synthesis of [AgCl(IPrCl)] (6). In a flask, Ag2O (91.5 mg, 0.39
mmol) was added to a solution of IPrCl HCl, 5 (300 mg, 0.60
3
mmol), in dichloromethane (3 mL). The reaction mixture was
stirred in the dark at room temperature during 3 h and was then
filtered on a pad of Celite. Solvent was removed under vacuum,
and hexane was added (10 mL). The resulting precipitate was
collected by filtration, washed with hexane (3 ꢀ 5 mL), and dried
under vacuum to afford 6 as a white powder. Yield: 112.9 mg
(31%). 1H NMR (400 MHz, CDCl3): δ 7.56 (t, J=7.8 Hz, 2H,
CH aromatic), 7.33 (d, J=7.8 Hz, 4H, CH aromatic), 2.45 (sept,
J = 6.8 Hz, 4H, CH(CH3)2), 1.28 (d, J = 6.8 Hz, 12H, CH-
(CH3)2), 1.26 (d, J = 6.9 Hz, 12H, CH(CH3)2) ppm. 13C NMR
(100 MHz, CDCl3): δ 183.6 (dd, JC-109Ag=273.8 Hz, JC-107Ag=
236.9 Hz, C carbene), 145.9 (s, C aromatic), 131.6 (s, CH
aromatic), 131.6 (s, C aromatic), 124.6 (s, CH aromatic), 119.5
(d, JAg-C = 9.3 Hz, C imidazole), 29.0 (s, CH(CH3)2), 24.9 (s,
CH(CH3)2), 23.3 (s, CH(CH3)2) ppm. Anal. Calcd for
C27H34N2AgCl3 (600.80): C, 53.98; H, 5.70; N, 4.66. Found: C,
54.14; H, 5.64; N, 4.68.
Synthesis of IPrCl HCl (5). In a Schlenk under argon, a
3
spatula of KOtBu was added to a solution of IPr HBF4 (1.0 g,
3
2.1 mmol) and NaH (100.8 mg, 4.2 mmol) in THF (15 mL). The
reaction was stirred at room temperature overnight. The reac-
tion mixture was filtered under argon, and CCl4 (405 μL,
4.2 mmol) was added. The resulting solution was stirred an addi-
tional 3 h at room temperature. A solution of HCl in dioxane (4 M)
was added, and the resulting precipitate was collected to furnish 5
as a white powder. Yield: 873.4 mg (84%). (The H of the
1
imidazolium salt 5 was exchanged by D in CD3OD.) H NMR
of d1-5 (400 MHz, CD3OD): δ 7.75 (t, J = 7.8 Hz, 2H, CH
aromatic), 7.58 (d, J=7.8 Hz, 4H, CH aromatic), 2.46 (sept, J=
6.8 Hz, 4H, CH(CH3)2), 1.36 (d, J=6.8 Hz, 12H, CH(CH3)2), 1.25
(d, J = 6.8 Hz, 12H, CH(CH3)2). 13C NMR of d1-5 (100 MHz,
CD3OD): δ147.3 (s, Caromatic), 140.0 (t, CD imidazole), 134.6 (s,
CH aromatic), 128.2 (s, C aromatic), 126.6 (s, CH aromatic), 124.1
(s, C imidazole), 30.7 (s, CH(CH3)2), 25.1 (s, CH(CH3)2), 23.4 (s,
CH(CH3)2). Anal. Calcd for C27H35N2Cl3 (492.19): C, 65.65; H,
7.14; N, 5.67. Found: C, 65.79; H, 7.05; N, 5. 48.
Acknowledgment. Support of this work by the ERC
(Advanced Researcher Grant to S.P.N.) and the EPSRC
is gratefully acknowledged.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.