Cationic NHC-gold(I) complexes: Synthesis, isolation, and catalytic activity

Article abstract of DOI:10.1016/j.jorganchem.2008.10.047

The reaction of [(NHC)AuCl] complexes (NHC = N-heterocyclic carbene) with a chloride abstractor of the type AgX, where X is a non-coordinating anion, led, in the presence of a neutral coordinating solvent S, to a series of cationic gold(I) complexes of formulae [(NHC)Au(S)]X. Hence, different cationic NHC-gold(I) species bound to acetonitrile, pyridine, 2-Br-pyridine, 3-Br-pyridine, norbornadiene, and THF could be synthesized and characterized by ¹H and ¹³C NMR spectroscopies. Among these, the results of X-ray diffraction studies for [(IPr)Au(NCMe)]SbF₆, [(IAd)Au(NCMe)]PF₆, [(IPr)Au(pyr)]PF₆, [(IPr)Au(2-Br-pyr)]PF₆, [(IPr)Au(3-Br-pyr)]PF₆ are discussed. As special feature, the structure of [(IPr)Au(2-Br-pyr)]PF₆ presented a secondary interaction between the gold and bromine atoms. Additionally, while attempting to obtain crystals of [(IPr)Au(nbd)]PF₆, we crystallized a decomposition product featuring a very rare PF₄^- anion as bridging ligand with formulae [(μ-PF₄)((IPr)Au)₂]PF₄. The observation of a possible P-F bond activation has important implications for cationic Au-based homogeneous catalysis. Finally, we compared the catalytic activities of the different cationic [(NHC)Au(S)]X complexes in the allylic acetate rearrangement reaction and notably observed the inertness of pyridine-based catalysts.

Full text of DOI:10.1016/j.jorganchem.2008.10.047

Journal of Organometallic Chemistry 694 (2009) 551–560
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cationic NHC–gold(I) complexes: Synthesis, isolation, and catalytic activity
a
b
a,b,*
Pierre de Frémont , Nicolas Marion , Steven P. Nolan
a
Chemistry Department, University of New Orleans, New Orleans, LA 70148, USA
Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 July 2008
Received in revised form 13 September
The reaction of [(NHC)AuCl] complexes (NHC = N-heterocyclic carbene) with a chloride abstractor of the
type AgX, where X is a non-coordinating anion, led, in the presence of a neutral coordinating solvent S, to
a series of cationic gold(I) complexes of formulae [(NHC)Au(S)]X. Hence, different cationic NHC–gold(I)
species bound to acetonitrile, pyridine, 2-Br-pyridine, 3-Br-pyridine, norbornadiene, and THF could be
2
008
Accepted 29 October 2008
Available online 6 November 2008
1
13
synthesized and characterized by H and C NMR spectroscopies. Among these, the results of X-ray dif-
fraction studies for [(IPr)Au(NCMe)]SbF , [(IAd)Au(NCMe)]PF , [(IPr)Au(pyr)]PF , [(IPr)Au(2-Br-pyr)]PF
(IPr)Au(3-Br-pyr)]PF are discussed. As special feature, the structure of [(IPr)Au(2-Br-pyr)]PF presented
6
6
6
6
,
[
6
6
Keywords:
Allylic rearrangement
Cationic
a secondary interaction between the gold and bromine atoms. Additionally, while attempting to obtain
ꢀ
crystals of [(IPr)Au(nbd)]PF
6
, we crystallized a decomposition product featuring a very rare PF4 anion
as bridging ligand with formulae [(
4 2 4
l-PF )((IPr)Au) ]PF . The observation of a possible P–F bond activation
Gold
N-Heterocyclic carbene
Pyridine
has important implications for cationic Au-based homogeneous catalysis. Finally, we compared the cat-
alytic activities of the different cationic [(NHC)Au(S)]X complexes in the allylic acetate rearrangement
reaction and notably observed the inertness of pyridine-based catalysts.
Ó 2008 Elsevier B.V. All rights reserved.
1
. Introduction
As part of an ongoing program aimed at examining the role of
conception has now been shattered, as numerous examples of
phosphine– and NHC–gold mediated transformations have re-
cently appeared [8,9]; gold(I) halide complexes being especially
efficient at activating alkyne moieties toward nucleophilic addition
under mild reaction conditions. The use of silver salts, with an
accompanying non-coordinating anion, is usually required to gen-
erate the active catalyst. It is commonly accepted that silver assists
in halide abstraction from the gold center generating a highly elec-
trophilic monoligated cationic gold complex [10]. Nevertheless,
such complexes have proven difficult to isolate. Notably, attempts
N-heterocyclic carbenes (NHCs) in transition metal-mediated reac-
tions, we have recently studied the stabilizing effects of NHCs sur-
rounding unsaturated and ‘‘reactive” metal centers. Since the
isolation of the first stable ‘‘free” NHC, bearing two sterically
demanding adamantyl groups on the nitrogens of an imidazolyl
framework, by Arduengo [1], sterically encumbering NHCs have al-
lowed for the isolation of a great variety of unusual organometallic
species [2]. In view of their highly interesting steric and electronic
properties [3], NHCs have also been employed to prepare efficient
and robust catalysts for a wide array of organic transformations
to synthesize or isolate [(ItBu)Au]BF
tert-butylimidazol-2-ylidene) and [(Ph
4
by Baker [11] (ItBu = 1,3-di-
P)Au]X (X = BF , PF , SbF
3
4
6
6
)
by Gagosz [12] have so far failed due to rapid decomposition of
these complexes to colloidal gold(0). To prevent such decomposi-
tion, we thought of using a coordinating solvent, and consequently
reported the acetonitrile adduct of a cationic gold(I) complex
[(IPr)Au(NCMe)]PF (1) (Fig. 1, IPr = 1,3-bis(diisopropylphenyl)imi-
6
dazol-2-ylidene) [13], bearing a bulky NHC ligand, that proved to
be active in the enyne cycloisomerization reaction [14]. Similarly,
[
4].
We recently reported the synthesis and isolation of a series of
well-defined NHC–gold(I) complexes [5]. The first NHC–gold(I)
complexes were reported in 1989 [6] and these usually bore two
strongly bound ligands arranged in a linear fashion around a gold
cation. They can be neutral or cationic and present the [(NHC)AuX]
or [(NHC)
gold chemistry appeared to have been somewhat forgotten. The
‘noble” character of the metal was possibly at the origin of the
misconception that it would perform poorly in catalysis. This mis-
2
Au]X composition [7]. Until recently, catalytic organo-
3 6
Echavarren reported the isolation of [(Ph P)Au(NCMe)]PF [15],
highlighting the importance of the non-coordinating anion as well
as the neutral coordinating molecule in the stabilization of such
species. In the same report, acetonitrile and arene adducts of
monoligated cationic gold(I) complexes such as 2 and 3 (Fig. 1),
bearing very bulky ortho-diphenylphosphine ligands, could also
be isolated. Recently, the use of CAAC ligand (CAAC = cyclic alkyl
amino carbene) by Bertrand, led to further advances in gold(I)
‘
*
Corresponding author. Address: Institute of Chemical Research of Catalonia
(
ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain.
E-mail address: snolan@iciq.es (S.P. Nolan).
0
022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.10.047

5
52
P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
and a weakly coordinating solvent such as acetonitrile or THF lead-
ing to relatively stable yet reactive cationic gold(I) complexes.
i-Pr
i-Pr
N
N
N
Ar
2. Results and discussion
PF6
B(C F )
Au NCMe
i-Pr
6
5 4
Au
2.1. Acetonitrile-containing cationic NHC–gold(I) complexes
NH3
i-Pr
The previously reported [(IPr)AuCl] [5], [(IMes)AuCl] [5]
4
(IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), [(ItBu)
AuCl] [11] and [(IAd)AuCl] [5] (IAd = 1,3-diadamantylimidazol-2-
1
6 6 4
ylidene) were dissolved in acetonitrile and AgPF , AgSbF , AgBF ,
or AgB(C was added in slight excess, leading to the rapid for-
6 5 4
F )
mation of a precipitate (AgCl). After stirring the solutions for one
minute, the suspensions were filtered through a plug of Celite
affording acetonitrile solutions of [(NHC)Au(NCMe)]X complexes
t-Bu
t-Bu
t-Bu
t-Bu
P
Au NCMe
P
Au
SbF6
SbF6
5
–10 (Scheme 1).
Attempts to obtain solid materials for all complexes by simply
removing the solvent under vacuum led to a white powder turning
grey with the appearance of colloidal silver(0). To remove the ex-
cess of silver, complexes were dissolved in cold DCM and filtered
over a plug of silicagel. All complexes are stable in air and can be
stored as a white powder indefinitely in a freezer. They are stable
in acetonitrile and chlorinated solvents at room temperature for
2
3
Fig. 1. Structures of selected cationic gold(I) complexes.
coordination chemistry, with the isolation of both arene- [16] and
ammonia-adducts [17] of cationic gold(I) complexes, such as 4.
Herein, we present the continuation of our work on NHC-based
cationic gold(I) species, including the isolation and characteriza-
tion of such complexes by using a NHC ligand of sufficient bulk
several days, with the exception of [(IMes)Au(NCMe)]PF
and [(ItBu)Au(NCMe)]PF (9), which both rearrange into [(NHC)
Au(PF )] and [Au(NCMe) ]PF . Interestingly, in these cases no for-
6
(10)
6
2
6
4
6
mation of gold(0) was observed.
R
N
R
N
MeCN
AgCl
X
Au Cl
AgX
Au NCMe
-
N
N
R
R
5-10
F
F
F
F
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
N
N
N
N
N
N
B
F
SbF6
BF4
Au NCMe
i-Pr
Au NCMe
Au NCMe
i-Pr
i-Pr
4
i-Pr
5, [(IPr)Au(NCMe)]SbF6
6, [(IPr)Au(NCMe)]BF4
7, [(IPr)Au(NCMe)][B(C F ) ]
6
5 4
N
N
N
N
PF6
Au NCMe
Au NCMe
Au NCMe
PF6
PF6
N
N
9, [(ItBu)Au(NCMe)]PF6
8
, [(IAd)Au(NCMe)]PF6
10, [(IMes)Au(NCMe)]PF6
Scheme 1. Synthesis of cationic [(NHC)Au(NCMe)]X complexes 5–10.

P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
553
Table 1
1
3C NMR data for [(NHC)AuCl] and [(NHC)Au(NCMe)]X complexes.
[
(NHC)AuCl] Solvent dc Au–C [(NHC)Au(NCMe)]X
Solvent dc Au–C
(ppm)
(ppm)
[
(IPr)AuCl]
CDCl
3
175.1
[(IPr)Au(NCMe)]PF
6
(1)
(5)
(6)
CDCl
CDCl
CDCl
3
3
3
3
3
166.1
166.0
165.9
166.1
157.7
[
[
[
(IPr)Au(NCMe)]SbF
(IPr)Au(NCMe)]BF
(IPr)Au(NCMe)]B(C
6
4
6
F
5
)
4
(7) CDCl
CDCl
[
[
[
(IAd)AuCl]
(ItBu)AuCl] CDCl
(IMes)AuCl] CDCl
CDCl
3
3
3
166.3
168.2
173.4
[(IAd)Au(NCMe)]PF
[(ItBu)Au(NCMe)]PF
[(IMes)Au(NCMe)]PF (10)
6
6
(8)
(9)
6
CD
CD
3
CN 159.7
CN 165.3
3
1H and 13C NMR spectra of the neutral precursors and the novel
1
cationic complexes were recorded. While the pattern of the
H
NMR spectra remained the same with no trace of decomposition
products between neutral and cationic gold(I) complexes, we ob-
served a slight downfield shift for the backbone protons of the
imidazole fragment. We attribute this change to a loss of electronic
density in the heterocyclic system, due a delocalization of the
p-
electrons toward the more acidic gold center. The 13C NMR spectra
present signals for the carbenic carbons that are significantly
shifted upfield for all complexes (Table 1).
Once again, this observation confirmed a more acidic gold cen-
1
13
ter. Both H and C NMR studies support the presence of an elec-
tron deficient gold center, confirming the very likely presence of
monoligated gold(I) complexes.
To unambiguously establish the solid state structure of these
complexes, suitable X-ray quality crystals for single crystal diffrac-
tion studies were grown from saturated acetonitrile solutions of
Fig. 3. Crystal structure of [(IAd)Au(NCMe)]PF
probability level; hydrogen atoms are omitted for clarity). Selected bond lengths
(Å): Au(1)–C(1) 1.990(2); Au(1)–N(3) 2.008(2); C(1)–N(1) 1.359(3); C(1)–N(2)
6
(8) (thermal ellipsoids at 50%
1.358(3); N(3)–C(4) 1.139(3); P(1)–F(1) 1.605(2). Selected angles (°): C(1)–Au(1)–
N(3) 178.75(10); Au(1)–N(3)–C(4) 176.2(2); N(1)–C(1)–Au(1) 127.02(16); N(1)–
C(1)–N(2) 106.1(2). Selected torsion angles (°): N(1)–C(2)–C(3)–N(2) 0.4(3).
[
6 6
(IPr)Au(NCMe)]SbF (5) and [(IAd)Au(NCMe)]PF (8). For 6, 7, 9
and 10, no suitable crystals could be obtained for X-ray diffraction.
Results from the diffraction studies confirmed the structure deter-
mined by NMR and, notably, the coordination of one acetonitrile
molecule to the gold center (Figs. 2 and 3).
arrangement with a C–Au–N angle close to 180°. The C–Au bond
lengths range between 1.952(2) and 1.990(2) Å; they are similar
to those found for the neutral corresponding [(NHC)AuCl]. The
N–Au bond lengths range between 2.008(2) Å and 2.022(2) Å,
which is in the range of reported gold complexes with nitrogen do-
nor ligands [18], but slightly longer than known gold(I) complexes
6
Both structures, as the one of [(IPr)Au(NCMe)]PF that we re-
ported earlier [13], revealed a nearly linear (NHC)–Au–(NCMe)
2
with coordinated acetonitrile such as [Au(NCMe) ]X [19] with a
Au–N length bond equal to 1.96 Å.
2.2. Cationic [(NHC)Au(L)]X complexes (X = THF, nbd, pyr, 2-Br-pyr, 3-
Br-pyr)
We were interested in further testing the stability of such com-
plexes. Attempts to synthesize a cationic gold(I) complex in dry
dichloromethane or dry chloroform with silver salts led to the ra-
1
pid appearance of large amounts of colloidal gold(0). The H NMR
spectra of these products indicated the existence of two different
NHC environments attributed to at least two NHC–gold species
in solution. Nevertheless, these species decomposed rapidly and
we were not able to obtain further characterization. It should be
noted that in most cases we observed very broad NMR signals in
1
the H spectrum, indicating the possibility of a polymeric structure,
which also decomposed rapidly before full characterization. We
confirmed in this manner the necessity of a coordinating solvent
to stabilize the cationic gold center.
Tetrahydrofuran (THF) was then employed as an alternative to
6
acetonitrile to generate [(IPr)Au(S)]PF (S = coordinating solvent).
In THF, no decomposition was observed, as long as an excess of
THF was maintained (i.e. at least a three fold excess to the gold
complex), even after subjecting the THF solution to air for 24 h.
Surprisingly, a gel was obtained, attributed to the ring-opening
polymerization of THF [20]. On the other hand, any attempt to
Fig. 2. Crystal structure of [(IPr)Au(NCMe)]SbF
probability level; hydrogen atoms are omitted for clarity). Selected bond lengths
Å): Au(1)–C(1) 1.974(2); Au(1)–N(3) 2.013(3); C(1)–N(1) 1.344(3); C(1)–N(2)
.353(3); N(3)–C(4) 1.137(4); Sb(1)–F(1) 1.865(3). Selected angles (°): C(1)–Au(1)–
6
(5) (thermal ellipsoids at 50%
(
1
N(3) 175.57(10); Au(1)–N(3)–C(4) 173.5(3); N(1)–C(1)–Au(1) 130.94(17); N(1)–
C(1)–N(2) 105.4(2). Selected torsion angles (°): N(1)–C(2)–C(3)–N(2) 0.9(3).
6
dry the sample led to decomposition of [(IPr)Au(THF)]PF (11).

5
54
P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
The 13C NMR spectrum indicated a gold species in THF that is even
more acidic than in acetonitrile with a carbenic carbon appearing
at a more upfield resonance (d = 159.7 ppm versus 167.6 ppm in
similar H and 13C NMR signals pattern. The carbenic carbons res-
onate between 166.0 and 167.1 ppm. The bromide group does not
appear to noticeably influence the electronic properties of the pyr-
idine ligands.
1
8
THF-d ). The complex in THF also displayed a second, more down-
field, signal with a low intensity (after few hours) for the deuter-
ated THF that confirmed the formation of poly-THF [21]. It is
noteworthy that the cationic polymerization of THF by ring-open-
X-ray quality crystals suitable for single crystal diffraction stud-
ies were grown from saturated DCM solutions of [(IPr)Au(pyr)]PF
(12), [(IPr)Au(2-Br-pyr)]PF (13), and [(IPr)Au(3-Br-pyr)]PF (14)
6
6
6
ing, in the presence of a Lewis acids such as FeCl
3
or the trityl cat-
(Figs. 4–6). The structures present a classical linear arrangement
around the gold(I) center with only slight variation of the Au–(pyr-
idine) and Au–(NHC) bond lengths. As special feature, we observed
in complex 13 a secondary interaction between the bromine of the
ion is well known [21]. In the present case, this polymerization
behavior confirms the presence of a cationic gold centered complex
capable of acting as a Lewis acid for polymerization reactions; an
interesting reaction profile that we have recently examined [22].
2-bromopyridine and the gold center (d(Au–Br) = 3.34 Å versus
P
We also noticed that adding [(IPr)Au(NCMe)]PF
6
(1), synthesized
rvdw = 3.54 Å). Interestingly, this secondary interaction forces
from acetonitrile, into THF led to THF polymerization. Since the
acetonitrile needs to be displaced from the gold center by THF to
initiate the polymerization, this result shows that in solution the
molecules of solvent are weakly bound, labile and can be easily dis-
placed from gold.
To broaden the range of available cationic NHC–gold(I)
complexes, different pyridines, and norbornadiene were employed
to generate respectively the following new complexes [(IPr)Au
the pyridine plane to be coplanar with the imidazole plane,
whereas they are almost perpendicular in complexes 12 and 14
(see Figs. 4–6).
6
[(IPr)Au(nbd)]PF (15) is stable in air, on the contrary to other
olefin–gold(I) complexes previously described [23]. It can be kept
as a white powder in the freezer but slowly decomposes in THF
1
or DCM. After a few days in solution, the H NMR spectrum of 15
presents the same aspect while the characteristic septuplet of
ꢀ
31
(
pyr)]PF
6
(12), [(IPr)Au(2-Br-pyr)]PF
(15). These new cationic gold(I) com-
(1)
(11) by substitution of acetonitrile or THF
6
(13), [(IPr)Au(3-Br-pyr)]PF
6
PF at ꢀ141.3 ppm on the P NMP spectrum disappears to be re-
6
(14) and [(IPr)Au(nbd)]PF
6
placed by a broad triplet at ꢀ11.5 ppm. From both spectra, it can be
pounds were obtained in high yields from [(IPr)Au(NCMe)]PF
and [(IPr)Au(THF)]PF
6
assumed that 15 is degraded by decoordination of norbornadiene
+
6
from the [(IPr)Au] fragment, which would further interact with
ꢀ
1
13
bound to gold. In the case of 15 a large excess of norbornadiene
and a longer reaction time were required (Scheme 2).
Complexes 12–14 are stable in air and can be stored as a white
powder indefinitely in a freezer. They are also stable in acetonitrile,
THF, and chlorinated solvents, at room temperature. They display
PF . H and C NMR spectra of 15 exhibit a norbornadiene ligand
6
with two non-equivalent olefin sides characterized by two differ-
ent sets of broad signals. One set exhibits the chemical shift of free
norbornadiene while the second one is slightly upfield. Such NMR
spectra are characteristic of a gold(I) center possessing a norborna-
R
N
R
N
DCM or THF
PF6
PF6
L
Au L
Au
S
-
S
N
R
(excess)
N
R
1
or 11
12-15
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
Br
i-Pr
Br
i-Pr
Au
i-Pr
i-Pr
Au
N
N
N
N
N
N
PF6
PF6
PF6
N
Au N
N
i-Pr
i-Pr
1
2, [(IPr)Au(pyr)]PF6
13, [(IPr)Au(2-Br-pyr)]PF6
14, [(IPr)Au(3-Br-pyr)]PF6
i-Pr
i-Pr
Au
N
N
PF6
i-Pr
i-Pr
1
5, [(IPr)Au(nbd)]PF6
6
Scheme 2. Synthesis of cationic [(NHC)Au(L)]PF complexes.

P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
555
Fig. 4. Crystal structure of [(IPr)Au(pyr)]PF
6
(12) (thermal ellipsoids at 50%
probability level; hydrogen atoms are omitted for clarity). Selected bond lengths
Å): Au(1)–C(1) 1.961(7); Au(1)–N(3) 2.049(6); C(1)–N(1) 1.344(8); C(1)–N(2)
.369(8); P(1)–F(1) 1.597(5). Selected angles (°): C(1)–Au(1)–N(3) 177.1(3); N(1)–
C(1)–Au(1) 128.4(5); N(1)–C(1)–N(2) 103.9(5). Selected torsion angles (°): N(2)–
C(1)–N(3)–C(4) 94.54(9); N(1)–C(2)–C(3)–N(2) 0.1(8).
Fig. 6. Crystal structure of [(IPr)Au(3-Br-pyr)]PF
6
(14) (thermal ellipsoids at 50%
(
1
probability level; hydrogen atoms are omitted for clarity). Selected bond lengths
Å): Au(1)–C(1) 1.974(3); Au(1)–N(3) 2.055(3); C(1)–N(1) 1.355(3); C(1)–N(2)
.349(5); C(5)–Br(1) 1.879(3); P(1)–F(1) 1.604(2). Selected angles (°): C(1)–Au(1)–
(
1
N(3) 175.54(10); Au(1)–N(3)–C(4) 120.3(2); N(1)–C(1)–Au(1) 129.2(2); N(1)–C(1)–
N(2) 104.9(2). Selected torsion angles (°): N(1)–C(2)–C(3)–N(2) 0.3(4); N(1)–C(1)–
N(3)–C(4) 76.65(4).
diene bound by only one double bond. The slight upfield shift ob-
served for the olefin signals indicates that the olefin is acting al-
most as a pure electron donor with negligible back-bonding from
the gold(I) center [24].
Repeated attempts to crystallize 15 in a saturated solution of
dried THF/octane, gave white crystals suitable for X-ray diffraction
study. Nevertheless, the structure of 15 was not confirmed and the
Fig. 7). Such complex can be seen as an intermediate in the decom-
position pathway of 15. It is worthy to note that structures featur-
ꢀ
ing a PF4 anion are extremely scarce [25] and unknown in gold
chemistry [26]. The formation of this decomposition product from
an unsaturated cationic gold(I) species probably occurred via P–F
bond activation with pre-coordination of the PF
4 2 4
complex [(l-PF )((IPr)Au) ]PF (16) was observed instead (see
6
anion to the gold
center of the type Auꢁ ꢁ ꢁF–PF
5
. Even though the mechanistic details
for the formation of 16 remain elusive, this observation is of impor-
tance in the context of cationic gold(I) catalysis since the most uti-
lized weakly coordinating counteranions are all perfluoro anions
(
4 6 6
i.e. BF , PF , SbF ). Finally, it is noteworthy that decomposition
of the cationic gold complexes never occurred through the cleav-
age of the Au–(NHC) bond.
2.3. Comparative study of [(NHC)Au(L)]X complexes in the
rearrangement of allylic acetates
Having in hands the cationic NHC–gold(I) complexes described
above, we were interested in testing their catalytic activity, notably
in order to obtain further information on the nature of the bonding
between gold and the different neutral coordinating molecules
used [27]. We decided to carry out preliminary investigations on
the rearrangement of allylic acetates [28], a reaction that we re-
cently reported using an in situ protocol for the formation of the ac-
tive cationic gold(I) catalyst [29]. Results are reported in Table 2.
Several conclusions can be drawn from these preliminary re-
sults. The principal one is that pyridine-containing complexes
Fig. 5. Crystal structure of [(IPr)Au(2-Br-pyr)]PF
probability level; hydrogen atoms are omitted for clarity). Selected bond lengths
Å): Au(1)–C(1) 1.976(5); Au(1)–N(3) 2.069(5); Au(1)–Br(1) 3.344; C(1)–N(1)
6
(13) (thermal ellipsoids at 50%
1
2–14 did not catalyze the conversion of allylic acetate 17 into
(
its isomer 18 (Entries 10–12). We believe that this is mainly due
to the strong affinity of pyridine derivatives for the cationic gold(I)
center, as demonstrated by the stability of numerous isolated
pyridine–gold(I) adducts [30–31]. Remarkably, even the presence
1.352(7); C(1)–N(2) 1.339(6); N(3)–C(4) 1.338(9); C(4)–Br(1) 1.853(8); P(1)–F(1)
1.488(14). Selected angles (°): C(1)–Au(1)–N(3) 178.5(2); Au(1)–N(3)–C(4)
124.2(5); N(1)–C(1)–Au(1) 126.0(4); N(1)–C(1)–N(2) 105.2(4). Selected torsion
angles (°): N(1)–C(1)–N(3)–C(4) 0.05(7); N(1)–C(2)–C(3)–N(2) 0.0(0).

5
56
P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
Fig. 7. Crystal structure of [(
C(1) 1.956(5); Au(1)–F(1) 2.055(4); C(1)–N(1) 1.351(6); C(1)–N(2) 1.345(6); P(1)–F(1) 1.482(4); P(1)–F(2) 1.489(4); P(1)–F(3) 1.527(6); P(1)–F(4) 1.553(5); Au(2)–F(2)
.042(4); Au(2)–C(4) 1.962(5); C(4)–N(3) 1.349(7); C(4)–N(4) 1.352(6); P(2)–F(5) 1.353(8). Selected angles (°): F(1)–P(1)–F(2) 115.5(3); F(3)–P(1)–F(4) 105.0(4); C(1)–Au(1)–
4 2 4
l-PF )((IPr)Au) ]PF (16) (thermal ellipsoids at 50% probability level; hydrogen atoms are omitted for clarity). Selected bond lengths (Å): Au(1)–
2
F(1) 179.04(18); Au(1)–F(1)–P(1) 128.3(3); C(4)–Au(2)–F(2) 177.40(18); Au(2)–F(2)–P(1) 132.3(3); N(1)–C(1)–N(2) 105.2(4); N(3)–C(4)–N(4) 105.7(4). Selected torsion
angles (°): N(1)–C(2)–C(3)–N(2) 0.3(6); N(3)–C(5)–C(6)–N(4) 0.5(7).
of a bulky bromine atom in ortho-position did not lead to a more
facile decoordination from the cationic center (Entry 11).
While the whole series of acetonitrile-containing [(NHC)Au(NC-
Me)]X complexes allowed for good yields in the formation of 18
NHC–gold(I) catalyst, the cationic metal center can be considered
as ‘‘bare” since the reaction is performed in a non-coordinating sol-
vent (DCE), leading to enhance catalytic activity. The catalytic
activity of the norbornadiene gold complex 15 can be considered
intermediate between that of the acetonitrile and pyridine ad-
ducts. Indeed, only moderate conversion was observed after pro-
longed reaction time (Entry 13).
Finally, to further demonstrate the importance of an available
coordination site on the gold center, and the role of subtrate/sol-
vent binding equilibrium, we carried out two reactions using the
in situ procedure in coordinating solvents, as depicted in Eqs. (1)
and (2). Hence, the formation of 18 was greatly slowed down in
acetonitrile (Eq. (1)) and required several days in order to reach a
similar conversion as the one previously observed in DCE. As ex-
pected, the use of pyridine proved detrimental to the rearrange-
ment of 17 into 18, and even after several days, no formation of
internal alkene was observed (Eq. (2)). It should be noted that, in
both cases, no precipitation of colloidal gold was observed, high-
lighting the stability of both the acetonitrile and the pyridine ad-
ducts of NHC–gold(I) complexes.
(
(
Entries 5–9), it should be noted that prolonged reaction times
48 h) were required when compared to the in situ prepared cat-
ionic gold(I) catalyst (Entry 4). This can be explained by the neces-
sity for the olefin substrate to displace a coordinating molecule of
acetonitrile from the gold center. In the case of the in situ generated
Table 2
[
(NHC)Au(L)]X-Catalyzed rearrangement of allylic acetate.
OAc
OAc
Catalyst (2 mol %)
DCE (4 mL), rt
17
18
Entry
Catalyst (2 mol%)
Time
18 (GC conversion) (%)a
1
2
3
4
5
6
7
8
9
None
10 d
10 d
6 h
NR
NR
70
69
69
67
73
68
67
NR
NR
NR
50
AgBF
[PdCl
[(IPr)AuCl]/AgBF
[(IPr)Au(NCMe)]PF
[(IPr)Au(NCMe)]SbF
[(IPr)Au(NCMe)]BF
[(IPr)Au(NCMe)]B(C
[(ItBu)Au(NCMe)]PF
[(IPr)Au(pyr)]PF (12)
4
2
2
(PhCN) ]
4
10 h
48 h
48 h
48 h
48 h
48 h
10 d
10 d
10 d
5 d
6
(1)
(5)
(6)
6
OAc
OAc
[
4
(IPr)AuCl]/AgBF (2 mol %)
4
6
F
5
)
4
(7)
MeCN (4 mL), rt
10 days
(9)
17
18, 67%
6
10
11
12
13
6
ð1Þ
[(IPr)Au(2-Br-pyr)]PF
[(IPr)Au(3-Br-pyr)]PF
[(IPr)Au(nbd)]PF (15)
6
6
(13)
(14)
OAc
OAc
6
[
4
(IPr)AuCl]/AgBF (2 mol %)
pyridine (4 mL), rt
15 days
a
17
18
GC conversions are the average of at least 2 runs. NR = no reaction; pyr = pyr-
idine; nbd = norbornadiene.
ð2Þ

P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
557
3
. Conclusion
ene (246 mg, 1.05 equiv., 0.25 mmol) was added. The solution
was stirred for 1 min. Acetonitrile was removed under vacuum
and DCM (2 mL) added. Filtration over a plug of silicagel gave a
clear greenish solution. After removal of the DCM under vacuum,
We have isolated and characterized by NMR spectroscopy and
X-ray diffraction study several well-defined cationic [(NHC)Au(L)]X
complexes, which are postulated as the active catalysts in numer-
ous gold mediated organic transformations. A comparative study
of their catalytic activity showed that acetonitrile-based complexes
are best suited for potential applications in catalysis while pyri-
dine-based compounds proved to be inactive in the rearrangement
of allylic acetates. Studies aimed at exploring this relative stability/
activity issue are presently ongoing in our laboratories.
the desired complex was obtained as a white powder. Yield:
1
307 mg (98%). H NMR (CDCl
3
): d (ppm) = 7.56 (t, J = 8.0 Hz, 2H,
Ar
Ar
imidazole
CH ), 7.36 (d, J = 8.0 Hz, 4H, CH ), 7.32 (s, 2H, CH
(septuplet, J = 7.0 Hz, 4H, CH(CH ), 2.22 (s, 3H, N„C–CH
J = 7.0 Hz, 12H, CH(CH ), 1.25 (d, J = 7.0 Hz, 12H, CH(CH
NMR (CDCl ): d (ppm) = 166.1 (C, C
), 2.47
)
3 2
3
), 1.29 (d,
13
)
3 2
3 2
) ).
C
carbene
3
), 148.3 (d, J = 246 Hz, C,
Ar
Ar
Ar
C –F), 145.7 (C, C ), 139.5 (broad s, C, C –B), 137.6 (broad s, C,
Ar
Ar
Ar
Ar
C –F), 137.0 (broad s, C, C –F), 133.0 (C, C ), 131.5 (CH, CH ),
Ar
imidazole
1
24.7 (CH, CH ), 124.7 (CH, CH
), 119.6 (C, N„C), 29.0 (CH,
4
. Experimental
CH(CH ) ), 24.6 (CH , CH(CH ) ), 23.9 (CH , CH(CH ) ), 2.4 (CH ,
3
2
3
3 2
3
3 2
3
19
1
1
ꢀ
N„C–CH
3
). B NMR (CDCl
3
): d (ppm) = ꢀ16.7 (s, BðC
6
F
5
Þ ).
F
4
Ar
3 19 19
4.1. General information
NMR (CDCl ): d (ppm) = ꢀ132.7 (s, o-C –F), ꢀ163.3 (t, J ( F– F) =
3
Ar
3 19 19
Ar
2
1.0 Hz, p-C –F), ꢀ167.0 (broad t, J ( F– F) = 21.0 Hz, m-C –F).
All reactions were carried out open to air unless indicated
otherwise. All NHCs were synthesized according to literature pro-
4.2.4. [(IAd)Au(NCMe)]PF (8)
In a scintillation vial, [(IAd)AuCl] (100 mg, 1 equiv., 0.18 mmol)
was partially dissolved in dry acetonitrile (2 mL) and AgPF (47 mg,
6
1
cedures.[32] Anhydrous pentane was used as purchased. H and
1
3
C nuclear magnetic resonance (NMR) spectra were recorded on
a Varian-400, Bruker-400 or Bruker-500 MHz spectrometer at
ambient temperature in CDCl , THF-d and CD CN containing tetra-
methylsilane (Cambridge Isotope Laboratories, Inc).
6
1.05 equiv., 0.18 mmol) was added. The solution was stirred for
3
8
3
one minute. Acetonitrile was removed under vacuum and DCM
(2 mL) was added. Filtration over a plug of silicagel gave a clear
greenish solution. After removal of the DCM under vacuum, the de-
sired complex was obtained as a white powder. Yield: 113 mg
4
4
.2. Synthesis of cationic gold(I) complexes
1
imidazole
(
88%). H NMR (CDCl
3
): d (ppm) = 7.35 (s, 2H, CH
), 2.47
.2.1. [(IPr)Au(NCMe)]SbF
In a scintillation vial, [(IPr)AuCl] (250 mg, 1 equiv., 0.40 mmol)
was dissolved in dried acetonitrile (2 mL) and AgSbF (152 mg,
.05 equiv., 0.43 mmol) was added. The solution was stirred for
min. Acetonitrile was removed under vacuum and DCM (2 mL)
6
(5)
(m, 14H, CH ), 2.25 (s, 6H, CH ), 2.18 (s, 3H, N„C–CH ), 1.77 (m,
2
2
3
1
3
carbene
10H, CH2). C NMR (CDCl ): d (ppm) = 157.7 (C, C
3
), 120.4
), 45.3
imidazole
adamantyl
6
(C, N„C), 118.6 (CH, CH
), 60.5 (CH, N–CH
31
1
1
(CH ), 36.4 (CH ), 31.0 (CH ), 2.8 (CH , N„C–CH ). P NMR
2
2
2
3
31
3
1
19
ꢀ
(CDCl ): d (ppm) = ꢀ141.3 (septuplet, J ( P– F) = 712.0 Hz, PF ).
3
6
1
9
1 19 31
ꢀ
was added. Filtration over a plug of silicagel gave a clear greenish
solution. After removal of the DCM under vacuum, the desired
complex was obtained as a white powder. Yield: 310 mg (90%).
F NMR (CDCl ): d (ppm) = ꢀ74.0 (d, J ( F– P) = 712.0 Hz, PF ).
3
6
4.2.5. [(ItBu)Au(NCMe)]PF (9)
6
1
Ar
H NMR (CDCl
3
): d (ppm) = 7.57 (t, J = 8.0 Hz, 2H, CH ), 7.36 (s,
In a scintillation vial, [(ItBu)AuCl] (50 mg, 1 equiv., 0.12 mmol)
was dissolved in acetonitrile (2 mL) and AgPF6 (31 mg, 1 equiv.,
0.12 mmol) was added. The solution was stirred one minute and
filtered over Celite to give a colorless solution. After removal of
imidazole
Ar
2
H, CH
J = 7.0 Hz, 4H, CH(CH
J = 7.0 Hz, 12H, CH(CH
NMR (CDCl ): d (ppm) = 166.0 (C
), 7.34 (d, J = 8.0 Hz, 4H, CH ), 2.45 (septuplet,
3
)
2
), 2.31 (s, 3H, N„C–CH
3
), 1.28 (d,
), 1.23 (d, J = 7.0 Hz, 12H, CH(CH
). 13
C
3
)
2
3
)
2
carbene
Ar
Ar
1
3
Ar
), 145.7 (C ), 133.1 (C ),
acetonitrile under vacuum, a white powder was isolated. H NMR
Ar
imidazole
imidazole
1
(
(
31.5 (CH ), 125.0 (CH ), 124.6 (CH
CH, CH(CH ), 24.8 (CH , CH(CH ), 24.1 (CH
CH , N„C–CH ). F NMR (CDCl ): No signals visible, due to the
), 120.5 (N„C), 28.9
(CD CN) d (ppm) = 7.38 (s, 2H, CH
), 1.83 (s, 18H, C(CH3)3).
3
1
3
carbene
)
3 2
3
3
)
2
3
, CH(CH ), 2.6
3
)
2
C NMR (CD CN) d (ppm) = 159.7 (C, C
), 60.6 (C, C(CH3)3),
3
1
9
3
3
3
3 3 3
32.7 (CH , C(CH ) .
antimony nucleus (I = 7/2).
4.2.6. [(IMes)Au(NCMe)]PF
6
(10)
4
.2.2. [(IPr)Au(NCMe)]BF
In a scintillation vial, [(IPr)AuCl] (300 mg, 1 equiv., 0.48 mmol)
was dissolved in dry acetonitrile (2 mL) and AgBF (94 mg, 1 equiv.,
.48 mmol) was added in the dark. The solution was stirred for
min. Acetonitrile was removed under vacuum and DCM (2 mL)
4
(6)
In a scintillation vial, [(IMes)AuCl] (50 mg, 1 equiv., 0.09 mmol)
was dissolved in acetonitrile (2 mL) and AgPF6 (24 mg, 1 equiv.,
0.09 mmol) was added. The solution was stirred one minute and
filtered over Celite to give a colorless solution. After removal of
acetonitrile in vacuum, a white powder is isolated which decom-
4
0
1
1
was added. Filtration over a plug of silicagel gave a colorless
solution. After removal of the DCM under vacuum, the desired
complex was obtained as a white powder. Yield: 328 mg (96%).
poses in air, turning purple after few hours. H NMR (CD CN) d
3
imidazole
Ar
(ppm) = 7.50 (s, 2H, CH
), 7.15 (s, 4H, CH ), 2.38 (s, 6H,
CH ), 1.31 (s, 12H, CH ). C NMR (CD CN) d (ppm) = 165.3 (C, C
141.9 (C, C ), 136.4 (C, C ), 135.6 (C, C ), 130.0 (CH, CH ), 125.6
), 21.5 (CH ), 18.2 (CH ). NB: It should be noted that
3 3
after one day in acetonitrile, 10 showed extra signals in the
2
6
NMR spectrum that were attributed to [(IMes) Au ][PF ].
13
carbene
3
3
3
),
1
Ar
Ar
Ar
Ar
Ar
H NMR (CDCl
3
): d (ppm) = 7.56 (t, J = 8.0 Hz, 2H, CH ), 7.41 (s,
imidazole
Ar
imidazole
2
7
1
H, CH
.0 Hz, 4H, CH(CH
2H, CH(CH
): d (ppm) = 165.9 (C, C
), 7.32 (d, J = 8.0 Hz, 4H, CH ), 2.43 (septuplet, J =
(CH, CH
13
3
)
2
), 2.37 (s, 3H, N„C–CH
3
), 1.27 (d, J = 7.0 Hz,
C
1
3
+
ꢀ
3
)
2
), 1.23 (d, J = 7.0 Hz, 12H, CH(CH
3
)
2
).
C NMR
carbene
Ar
Ar
Ar
(
CDCl
3
), 145.6 (C, C ), 133.2 (C, C ),
Ar
imidazole
1
31.4 (CH, CH ), 125.1 (CH, CH ), 124.6 (CH, CH
), 121.0
), 24.1 (CH
6
4.2.7. [(IPr)Au(THF)]PF (11)
(
C, N„C), 28.9 (CH, CH(CH
3
)
2
), 24.8 (CH
3
, CH(CH
3
)
2
3
,
In a scintillation vial, [(IPr)AuCl] (200 mg, 1 equiv., 0.32 mmol)
was dissolved in THF (2 mL) and AgPF6 (81 mg, 1 equiv.,
0.32 mmol) was added. The solution was stirred one minute and
filtered over Celite to give a colorless solution. Overnight, the
THF becomes a gel and two extra signals appear for the residual
protons of the deuterated THF at 2.7 and 1.0 ppm downfield from
the two normal THF signals. Appearance of colloidal gold(0) was
11
CH(CH
3
)
2
19
), 2.6 (CH
3
, N„C–CH
3
). B NMR (CDCl
3
): d (ppm) = ꢀ1.1
ꢀ
ꢀ
(
s, BF ). F NMR (CDCl
3
): d (ppm) = ꢀ153.7 (s, BF ).
4
4
4
.2.3. [(IPr)Au(NCMe)][B(C
In a scintillation vial, [(IPr)AuCl] (150 mg, 1 equiv., 0.24 mmol)
was dissolved in dry acetonitrile (2 mL) and AgB(C
ꢁ 0.5 tolu-
6 5 4
F ) ] (7)
6 5 4
F )

5
58
P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
carbene
), 150.9 (C ), 149.5 (broad s, Cpyr),
pyr
observed after 3 days. After removal of THF under vacuum, a white
powder was isolated and decomposed after a few hours, turning
(ppm) = d 166.0 (C, C
Ar
pyr
Ar
145.6 (C, C ), 144.6 (broad s, C ), 133.3 (C, C ), 128.9 (broad s,
1
imidazole
Ar
pyr
Ar
imidazole
Ar
grey. H NMR (THF-d
J = 8.0 Hz, 2H, CH ), 7.42 (d, J = 8.0 Hz, 2H, CH ), 2.57 (sept,
8
) d (ppm) = 7.82 (s, 2H, CH
), 7.59 (t,
C
), 131.4 (CH, CH ), 125.2 (CH, CH
), 124.6 (CH, CH ),
), 24.8 (CH , CH(CH ),
): d (ppm) = ꢀ141.3 (septu-
plet, J ( P– F) = 711.0 Hz, PF ). F NMR (CDCl
): d (ppm) = ꢀ73.5
Ar
pyr
122.9 (broad s, C ), 28.9 (CH, CH(CH
3
)
2
3
3 2
)
3
1
J = 6.8 Hz, 4H, CH(CH
3
)
2
), 1.33 (d, J = 6.8 Hz, 12H, CH(CH
3
)
2
), 1.26
3 3 2 3
24.0 (CH , CH(CH ) ). P NMR (CDCl
13
1 31
19
ꢀ
19
(
(
(
d, J = 6.8 Hz, 12H, CH(CH
3
)
2
). C NMR (THF-d8) d (ppm) = 159.7
3
6
carbene
Ar
Ar
Ar
Ar
1 19 31
ꢀ
C, C
), 146.7 (C, C ), 134.8 (C, C ), 131.7 (CH, CH ), 126.3
(d, J ( F– P) = 711.0 Hz, PF ).
6
imidazole
CH, CH ), 125.1 (CH, CH
3 2 3
), 29.7 (CH, CH(CH ) ), 25.8 (CH ,
3
CH(CH )
2
), 24.7 (CH
3
, CH (CH
3
)
2
).
4.2.11. [(IPr)Au(nbd)]PF
6
(15)
In a scintillation vial, [(IPr)Au(NCMe)]PF
6
(1) (500 mg, 1 equiv.,
4
.2.8. [(IPr)Au(pyr)]PF
In a scintillation vial, [(IPr)Au(NCMe)]PF
.13 mmol) was partially dissolved in dry DCM (2 mL) and pyridine
l, 1.1 equiv., 1.44 mmol) was added. The solution was stirred
6
(12)
0.66 mmol) was partially dissolved in dry DCM (5 mL) and norbor-
nadiene (nbd) (612 mg, 0.68 mL, 10 equiv., 6.6 mmol) was added.
The solution was stirred overnight. All the DCM and the excess nor-
bonadiene was removed under vacuum and DCM (10 mL) was
added. Filtration over a plug of silicagel gave a clear greenish
solution. After removal of the DCM under vacuum, the desired
complex was obtained as a white powder. Yield: 457 mg (84%).
6
(1) (100 mg, 1 equiv.,
0
(
12
l
for six hours. DCM and the excess pyridine were removed under
vacuum. The desired complex was obtained as a white powder.
Yield: 91 mg (91%). H NMR (CDCl
m, 3H, CH ), 7.58–7.52 (broad m, 2H, CH ), 7.55 (t, J = 8.0 Hz,
2
2
1
3
): d (ppm) = 8.05–7.80 (broad
pyr
pyr
1
Ar
3
H NMR (CDCl ) d (ppm) = 7.53 (t, J = 8.0 Hz, 2H, CH ), 7.50 (s,
Ar
imidazole
Ar
imidazole
Ar
nbd
H, CH ), 7.46 (s, 2H, CH
), 7.33 (d, J = 8.0 Hz, 4H, CH ),
), 1.30 (d, J = 7.0 Hz, 12H,
2H, CH
), 7.30 (d, J = 8.0 Hz, 4H, CH ), 6.85 (s, 2H, CH ),
nbd
nbd
nbd
.53 (septuplet, J = 7.0 Hz, 4H, CH(CH )
3 2
6.52 (s, 2H, CH ), 3.62 (s, 2H, CH ), 2.40 (septuplet, J = 7.0 Hz,
13
CH(CH
3
)
2
), 1.24 (d, J = 7.0 Hz, 12H, CH(CH
3
)
2
). C NMR (CDCl
3
): d
4H, CH(CH
CH(CH ), 1.23 (d, J = 7.0 Hz, 12H, CH(CH
(ppm) = 182.0 (C, C
134.4 (very broad s [only seen by HMQC sequence], CH, CH ),
3
)
2
), 1.40 (s, 2H, CH
2
), 1.25 (d, J = 7.0 Hz, 12H,
) ). C NMR (CDCl ): d
3 2 3
), 145.7 (C, C ), 143.2 (broad s, CH, CH ),
carbene
Ar
pyr
Ar
13
(
(
ppm) = 167.1 (C, C
C, C ), 131.3 (CH, CH ), 127.7 (broad s, CH, CH ), 126.8 (CH,
), 150.6 (CH, CH ), 145.8 (C, C ), 133.2
3
)
2
Ar
pyr
carbene
Ar
nbd
pyr
Ar
imidazole
nbd
CH ), 125.0 (CH, CH ), 124.7 (CH, CH
CH(CH ), 24.5 (CH , CH(CH ), 23.8 (CH , CH(CH
), 29.0 (CH,
31
Ar
Ar
Ar
3
)
2
3
3
)
2
3
3
)
2
). P NMR
133.1 (C, C ), 131.5 (CH, CH ), 125.1 (CH, CH ), 124.9 (CH,
1
31
19
ꢀ
imidazole
nbd
nbd
(
CDCl
3
): d (ppm) = ꢀ141.4 (septuplet, J ( P– F) = 711.0 Hz, PF ).
CH
CH(CH
), 52.2 (CH, CH ), 30.3 (CH
), 25.0 (CH , CH(CH ), 24.0 (CH
2
, CH
, CH(CH
2
), 28.9 (CH,
6
1
9
1 19 31
ꢀ
31
F NMR (CDCl
3
): d (ppm) = ꢀ74.2 (d, J ( F– P) = 711.0 Hz, PF ).
3
)
2
3
3
)
2
3
3
)
2
). P NMR
6
1
31
19
ꢀ
(
CDCl
3
): d (ppm) = ꢀ141.4 (septuplet, J ( P– F) = 713.0 Hz, PF ).
6
1
9
1 19 31
ꢀ
4
.2.9. [(IPr)Au(2-Br-pyr)]PF
In a scintillation vial, [(IPr)Au(NCMe)]PF
.26 mmol) was partially dissolved in dry DCM (2 mL) and 2-bro-
l, 1.05 equiv., 0.27 mmol) was added. The solu-
tion was stirred for 6 h and the DCM was removed under
6
(13)
F NMR (CDCl
3
): d (ppm) = ꢀ73.7 (d, J ( F– P) = 713.0 Hz, PF ).
6
6
1 (200 mg, 1 equiv.,
0
4.3. Cationic gold(I)-catalyzed rearrangement of allylic acetates
mopyridine (26
l
4.3.1. Synthesis of allylic acetate (17)
O
OH
OAc
BrMg
Ac
2
O/DMAP/Et
3
N
H
THF, 0°C
DCM, reflux
1
7-0
17, 78% over 2 steps
vacuum. The remaining solid was washed with pentane. The de-
sired complex was obtained as a white powder. Yield: 192 mg
4.3.1.1. Dec-1-en-3-ol 17-0. In an oven-dried round-bottom flask, a
solution of the 1-octanal (4.70 mL, 30 mmol, 1 equiv.) in THF
(70 mL) was stirred for 10 min under nitrogen at 0 °C. To the reac-
tion mixture, allyl magnesiumbromide 1.6 M (22.5 mL, 36 mmol,
1.2 equiv.) was added and the reaction was stirred for 20 min.
The reaction was then allowed to warm up to room temperature,
1
pyr
(
82%). H NMR (CDCl
3
): d (ppm) = 7.95 (broad m, 1H, CH ), 7.71
pyr
pyr
(
broad m, 2H, CH ), 7.65 (broad m, 1H, CH ), 7.57 (t, J = 8.0 Hz,
Ar
imidazole
Ar
2
2
H, CH ), 7.45 (s, 2H, CH
.53 (septuplet, J = 7.0 Hz, 4H, CH(CH
), 1.26 (d, J = 7.0 Hz, 12H, CH(CH
), 7.35 (d, J = 8.0 Hz, 4H, CH ),
3 2
)
), 1.31 (d, J = 7.0 Hz, 12H,
13
CH(CH
(
1
(
3
)
2
3
)
2
). C NMR (CDCl
3
): d
4
quenched with a saturated aqueous NH Cl solution and extracted
carbene
pyr
Ar
pyr
ppm) = 166.9 (C, C
43.1 (C ), 133.7 (C, C ), 131.7 (C ), 131.3 (CH, CH ), 126.0
), 152.7 (C ), 145.3 (C, C ), 143.2 (C ),
with diethyl ether. The combined organic layers were washed with
brine, dried over magnesium sulfate, filtered and evaporated to
give the crude allylic alcohol 17-0 that was engaged in the next
step without further purification.
pyr
Ar
pyr
Ar
pyr
imidazole
Ar
C
), 125.6 (CH, CH
), 124.9 (CH, CH ), 29.0 (CH, CH(CH
3
)
2
),
31
2
4.7 (CH , CH(CH ) ), 24.2 (CH , CH(CH ) ). P NMR (CDCl
3
3 2 3 3 2 3
): d
1
31
19
ꢀ
19
1
(
(
ppm) = ꢀ141.3 (septuplet, J ( P– F) = 711.0 Hz, PF ). F NMR
H NMR (400 MHz, CDCl3): d (ppm) = 5.86–5.77 (m, 1H,
6
1
19 31
ꢀ
CDCl
3
): d (ppm) = ꢀ74.2 (d, J ( F– P) = 711.0 Hz, PF ).
CH@CH
H, CH@CH
1.46 (m, 2H, CH
J = 6.8 Hz, 3H, CH
CH@CH ), 114.3 (CH
31.8 (CH ), 29.5 (CH
(CH ).
2
), 5.16 (d, J = 17.2 Hz, 1H, CH@CH
), 4.03 (m, 1H, CH–OH), 2.65 (broad s, 1H, OH), 1.51–
–CH–OH), 1.32–1.18 (m, 10H, CH ), 0.85 (t,
): d 141.4 (CH,
), 73.1 (CH, CH–OH), 37.0 (CH ),
), 29.2 (CH ), 25.3 (CH ), 22.6 (CH ), 14.0
2
), 5.04 (d, J = 10.4 Hz,
6
1
2
4
.2.10. [(IPr)Au(3-Br-pyr)]PF
In a scintillation vial, [(IPr)Au(NCMe)]PF
.26 mmol) was partially dissolved in dry DCM (2 mL) and 3-bro-
l, 1.05 equiv., 0.27 mmol) was added. The solu-
6
(14)
2
2
1
3
6
1 (200 mg, 1 equiv.,
3
). C NMR (100 MHz, CDCl
, CH@CH
3
0
2
2
2
2
mopyridine (26
l
2
2
2
2
2
tion was stirred for 6 h and the DCM was removed under
vacuum. The remaining solid was washed with pentane. The de-
sired complex was obtained as a white powder. Yield: 188 mg
3
4.3.1.2. Dec-1-en-3-yl acetate (17). Allylic alcohol 17-0 (10 mmol,
1 equiv.), dichloromethane (30 mL), 4-dimethylaminopyridine
1
pyr
(
(
2
2
80%). H NMR (CDCl
3
) d (ppm) = 8.14 (broad m, 1H, CH ), 7.91
pyr
pyr
broad m, 2H, CH ), 7.70 (broad m, 1H, CH ), 7.59 (t, J = 8.0 Hz,
3
(DMAP) (0.360 g, 3.0 mmol, 0.3 equiv.), Et N (5.6 mL, 40 mmol,
Ar
imidazole
Ar
H, CH ), 7.45 (s, 2H, CH
.53 (septuplet, J = 7.0 Hz, 4H, CH(CH
3 2 3
), 1.27 (d, J = 7.0 Hz, 12H, CH(CH ) ). C NMR (CDCl ): d
), 7.36 (d, J = 8.0 Hz, 4H, CH ),
4 equiv.), and Ac O (1.8 mL, 20 mmol, 2 equiv.) were added in turn
2
3
)
2
), 1.32 (d, J = 7.0 Hz, 12H,
in a round-bottom flask equipped with a condenser. The reaction
mixture was heated overnight at reflux. The reaction was then
13
CH(CH
3
)
2

P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
559
4
quenched with a saturated aqueous NH Cl solution and extracted
[3] For reviews, see: (a) S. Díez-González, S.P. Nolan, Coord. Chem. Rev. 251
(
(
(
2007) 874;
with diethyl ether. The combined organic layers were washed with
brine, dried over magnesium sulfate, filtered and evaporated to
give a crude product that was purified by flash chromatography
b) L. Cavallo, A. Correa, C. Costabile, H. Jacobsen, J. Organomet. Chem. 690
2005) 5407;
(c) T. Strassner, Top. Organomet. Chem. 13 (2004) 1.
[
4] For recent reviews on NHCs in organometallic catalysis, see: (a) F. Boeda, S.P.
Nolan, Annu. Rep. Prog. Chem. Sect. B: Org. Chem. 104 (2008) 184;
2
on silica gel (pentane/Et O 95/5), and yielded 1.55 g (78% over 2
steps) of dec-1-en-3-yl acetate (17).
(
b) N. Marion, S.P. Nolan, Acc. Chem. Res. 41 (2008) 1440;
(c) E.A.B. Kantchev, C.J. O’Brien, M.G. Organ, Angew. Chem., Int. Ed. 46 (2007)
768;
1
H NMR (400 MHz, CDCl3): d (ppm) = 5.78-5.70 (m, 1H,
2
CH@CH
OAc), 2.02 (s, 3H, OAc), 1.62-1.51 (m, 2H, CH
.17 (m, 10H, CH ), 0.84 (t, J = 7.0 Hz, 3H, CH
): d 170.1 (C, C@O), 136.6 (CH, CH@CH
2 2
), 5.22-5.16 (m, 2H, CH@CH ), 5.13-5.10 (m, 1H, CH–
(
(
d) R.E. Douthwaite, Coord. Chem. Rev. 251 (2007) 702;
e) S. Díez-González, S.P. Nolan, Synlett (2007) 2158;
2
–CH–OH), 1.34-
1
3
1
2
3
).
C NMR
), 116.4
(f) L.H. Gade, S. Bellemin-Laponnaz, Coord. Chem. Rev. 251 (2007) 718;
(
(
(
g) V. Dragutan, I. Dragutan, L. Delaude, A. Demonceau, Coord. Chem. Rev. 251
2007) 765;
h) W.J. Sommer, M. Weck, Coord. Chem. Rev. 251 (2007) 860.
(
(
(
(
75 MHz, CDCl
3
2
CH
CH
CH
2
2
3
, CH@CH
), 29.1 (CH
). HMRS: Calc. for C12
2
), 74.7 (CH, CH–OH), 34.1 (CH
2
), 31.7 (CH
, OAc), 14.0
22 2
H O Na (M+Na): 198.1620. Found:
2
), 29.3
2
), 25.0 (CH
2
), 22.6 (CH
2
), 21.1 (CH
3
[5] P. de Frémont, N.M. Scott, E.D. Stevens, S.P. Nolan, Organometallics 24 (2005)
411.
6] F. Bonati, A. Burini, B.R. Pietroni, B.J. Bovio, J. Organomet. Chem. 375 (1989)
47.
2
[
[
1
98.1624.
1
7] For selected examples, see: (a) H.M.K. Wang, I.J.B. Lin, Organometallics 17
(1998) 972;
4.3.2. General procedure for the [(NHC)Au(L)]X-catalyzed
(
b) P.J. Barnard, M.V. Baker, S.J. Berners-Price, B.W. Skelton, A.H. White, Dalton
rearrangement of allylic acetates
To a DCE solution (3 mL) of [(NHC)Au(L)]X (2 mol %) in a 5 mL
vial, was added a DCE solution (1 mL) of allylic acetate 17
Trans. (2004) 1038.
[
8] (a) R. Skouta, C.-J. Li, Tetrahedron 64 (2008) 4917;
(b) B. Crone, S.F. Kirsch, Chem.-Eur. J. 14 (2008) 3514;
(
(
(
c) N. Bongers, N. Krause, Angew. Chem., Int. Ed. 47 (2008) 2178;
d) H.C. Shen, Tetrahedron 64 (2008) 3885;
e) A.S.K. Hashmi, Chem. Rev. 107 (2007) 3180;
(
0.25 mmol, 50 mg). The reaction mixture was stirred for the indi-
cated time, while the conversion was being controlled by GC, and
the resulting mixture was dissolved in pentane, filtered through
Celite and evaporated. The crude product was purified by flash
chromatography on silica gel.
(f) A. Fürstner, P.W. Davies, Angew. Chem., Int. Ed. 46 (2007) 3410;
(
(
(
(
(
(
g) N. Marion, S.P. Nolan, Angew. Chem., Int. Ed. 46 (2007) 2750;
h) A.S.K. Hashmi, Catal. Today 122 (2007) 211;
i) D.J. Gorin, F.D. Toste, Nature 446 (2007) 395;
j) N.T. Patil, Y. Yamamoto, ARKIVOC (2007) 6;
k) E. Jiménez-Núñez, A.M. Echavarren, Chem. Commun. (2007) 333;
l) A.S.K. Hashmi, G.J. Hutchings, Angew. Chem., Int. Ed. 45 (2006) 7896.
4.3.2.1. (E)-Dec-2-enyl acetate (18)
OAc
[9] For a review focused on catalytic applications of NHC–Au complexes, see: N.
Marion, S.P. Nolan, Chem. Soc. Rev. 37 (2008) 1776.
[
[
10] For seminal studies, see: (a) G.C. Bond, Gold Bull. 5 (1972) 11;
1
8
(
(
(
(
b) G.J. Hutchings, J. Catal. 96 (1985) 292;
c) Y. Ito, M. Sawamura, T. Hayashi, J. Am. Chem. Soc. 108 (1986) 6405;
d) M. Haruta, T. Kobayashi, H. Sano, N. Yamada, Chem. Lett. (1987) 405;
e) J.H. Teles, S. Brode, M. Chabanas, Angew. Chem., Int. Ed. 37 (1998) 1415.
1H NMR (400 MHz, CDCl
5
3
0
): d (ppm) = 5.79–5.70 (m, 1H, CH@), 5.63–
–OAc), 2.06 (s,
–CH@), 1.32–1.20 (m, 10H, CH ),
3
11] M.V. Baker, P.J. Barnard, S.K. Brayshaw, J.L. Hickey, B.W. Skelton, A.H. White,
Dalton Trans. (2005) 37.
12] N. Mézailles, L. Ricard, F. Gagosz, Org. Lett. 7 (2005) 4133.
13] P. de Frémont, E.D. Stevens, M.R. Fructos, M.M. Díaz-Requejo, P.J. Pérez, S.P.
Nolan, Chem. Commun. (2006) 2045.
.54 (m, 1H, CH@), 4.53 (dd, J = 6.8, 1.6 Hz, 2H, CH
H, OAc), 2.00–1.93 (m, 2H, CH
.83 (t, J = 6.9 Hz, 3H, CH ).
2
[
[
2
2
3
[
[
14] N. Marion, P. de Frémont, G. Lemière, E.D. Stevens, L. Fensterbank, M. Malacria,
S.P. Nolan, Chem. Commun. (2006) 2048.
15] E. Herrero-Gómez, C. Nieto-Oberhuber, S. López, J. Benet-Buchholz, A.M.
Echavarren, Angew. Chem., Int. Ed. 45 (2006) 5455.
Supplementary material
CCDC 692734, 692733, 692735, 692736, 692737 and 692738
contain the supplementary crystallographic data for ([(IPr)Au(NC-
[16] For a NHC–gold(I) toluene adduct, see: (a) V. Lavallo, G.D. Frey, S. Kousar, B.
Donnadieu, G. Bertrand, Proc. Natl. Acad. Sci. USA 104 (2007) 13569;
(
b) G.D. Frey, R.D. Dewhurst, S. Kousar, B. Donnadieu, G. Bertrand, J.
Me)]SbF
[(IPr)Au(2-Br-pyr)]PF
PF )((IPr)Au) ]PF 16). These data can be obtained free of charge
6
5), ([(IAd)Au(NCMe)]PF
6
8), ([(IPr)Au(pyr)]PF
6
12),
Organomet. Chem. 693 (2008) 1674.
(
6
13), ([(IPr)Au(3-Br-pyr)]PF
6
14), and ([(
l
-
[17] V. Lavallo, G.D. Frey, B. Donnadieu, M. Soleilhavoup, G. Bertrand, Angew.
Chem., Int. Ed. 47 (2008) 5224.
4
2
4
[
18] (a) W. Conzelmann, W. Hiller, J. Strähle, Z. Anorg. Allg. Chem. 485 (1982) 81;
b) P.W.R. Corfield, H.M.M. Shearer, Acta Crystallogr. 23 (1967) 156.
[19] (a) D.M.P. Mingos, J.J. Yau, J. Organomet. Chem. 479 (1994) C16;
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
(
(
(
b) S. Ahrland, K. Nilsson, I. Person, A. Yushi, J.E. Penner-Hahn, Inorg. Chem. 28
1989) 1833.
Acknowledgments
[
[
20] S. Kobayashi, K. Morikawa, T. Saegusa, Macromolecules 8 (1975) 954.
21] (a) I. Kuntz, J. Polym. Sci. Part B: Pol. Lett. 4 (1966) 427;
(
b) V.M. Siderko, V.P. Mardykin, USSR Vestn. Beloruss. Univ. 2 (1970) 35.
We acknowledge the Ministerio de Educación y Ciencia (Spain),
the ICIQ Foundation and ICREA for financial support. SPN is an
ICREA Research Professor. NM thanks the AGAUR for a pre-doctoral
fellowship (2007FI_A 01466). We thank Drs. Eduardo C. Escudero-
Adán and Jordi Benet-Buchholz (ICIQ) for performing the X-ray dif-
fraction studies. NM thanks Umicore for a Ph.D. award.
[
22] J. Urbano, A.J. Hormigo, P. de Frémont, S.P. Nolan, M.M. Díaz-Requejo, P.J.
Pérez, Chem. Commun. (2008) 759.
[23] For isolated Au -adducts of olefins, see: (a) D. Belli Dell’Amico, F. Calderazzo, R.
Dantona, J. Strähle, H. Weiss, Organometallics 6 (1987) 1207;
I
(
(
b) R.M. Dávila, R.J. Staples, J.P. Fackler Jr., Organometallics 13 (1994) 418;
c) M.A. Cinellu, G. Minghetti, F. Cocco, S. Stoccoro, A. Zucca, M. Manassero,
Angew. Chem., Int. Ed. 44 (2005) 6892;
d) M.A. Cinellu, G. Minghetti, F. Cocco, S. Stoccoro, A. Zucca, M. Manassero, M.
(
Arca, Dalton Trans. (2006) 5703;
(e) H.V.R. Dias, J. Wu, Angew. Chem., Int. Ed. 46 (2007) 7814;
References
(
f) H.V.R. Dias, M. Fianchini, T.R. Cundari, C.F. Campana, Angew. Chem., Int. Ed.
[
[
1] A.J. Arduengo III, R.L. Harlow, M. Kline, J. Am. Chem. Soc. 113 (1991) 361.
2] For reviews on coordination chemistry aspects of NHCs, see: (a) F.E. Hahn,
M.C. Jahnke, Angew. Chem., Int. Ed. 47 (2008) 3122;
47 (2008) 556;
(g) For a review, see: H.V.R. Dias, J. Wu, Eur. J. Inorg. Chem. (2008) 509.
[24] D.S. Mc Guinness, K.J. Cavell, B.W. Skelton, A.H. White, Organometallics 18
(1999) 1596.
[25] For scarce reports on the PF
20 (1981) 970;
(
(
(
(
(
b) P.L. Arnold, S. Pearson, Coord. Chem. Rev. 251 (2007) 596;
ꢀ
c) D. Pugh, A.A. Danopoulos, Coord. Chem. Rev. 251 (2007) 610;
d) E. Colacino, J. Martinez, F. Lamaty, Coord. Chem. Rev. 251 (2007) 726;
e) J.A. Mata, M. Poyatos, E. Peris, Coord. Chem. Rev. 251 (2007) 841;
f) P. de Frémont, N. Marion, S.P. Nolan, Coord. Chem. Rev. 252 (2008),
4
anion, see: (a) P. Wermer, B.S. Ault, Inorg. Chem.
(b) K.O. Christie, D.A. Dixon, H.P.A. Mercier, J.C.P. Sanders, G.J. Schrobilgen,
W.W. Wilson, J. Am. Chem. Soc. 116 (1994) 2850;
doi:10.1016/j.ccr.2008.05.018.

5
60
P. de Frémont et al. / Journal of Organometallic Chemistry 694 (2009) 551–560
(
c) K.O. Christie, D.A. Dixon, J.C.P. Sanders, G.J. Schrobilgen, W.W. Wilson,
For a DFT study on this reaction, see: (b) C. Gourlaouen, N. Marion, S.P. Nolan,
Inorg. Chem. 33 (1994) 4911.
26] Surprisingly, while the only structurally characterized PF4 anion showed a
F. Maseras, Org. Lett. 10 (2008), doi:10.1021/o1802430m.
[30] For pyridine–gold(I) adducts, see: (a) L.G. Vaughan, J. Am. Chem. Soc. 92 (1970)
730;
ꢀ
[
ꢀ
distorted trigonal bipyramidal geometry, in complex 16 the PF4 anions appear
with a strongly distorted tetrahedral geometry. This unexpected feature is
currently under scrutiny.
27] For our previous work on cationic [(NHC)Au(S)]X complexes formed in situ,
see: (a) N. Marion, S. Díez-González, P. de Frémont, A.R. Noble, S.P. Nolan,
Angew. Chem., Int. Ed. 45 (2006) 3647;
(b) H.-N. Adams, W. Hiller, J. Strähle, Z. Anorg. Allg. Chem. 485 (1982) 81;
(c) W. Conzelmann, W. Hiller, J. Strähle, G.M. Sheldrick, Z. Anorg. Allg. Chem.
512 (1984) 169;
(d) A. Hayashi, M.M. Olmstead, S. Attar, A.L. Balch, J. Am. Chem. Soc. 124
(2002) 5791.
[
(
b) N. Marion, P. Carlqvist, R. Gealageas, P. de Frémont, F. Maseras, S.P. Nolan,
Chem.-Eur. J. 13 (2007) 6437;
c) A. Correa, N. Marion, L. Fensterbank, M. Malacria, S.P. Nolan, L. Cavallo,
[31] For theoretical studies on pyridine–gold(I) adducts, see: (a) H.-C. Hsu, F.-W.
Lin, C.-C. Lai, P.-H. Su, C.-S. Yeh, New J. Chem. 26 (2002) 481;
(b) D.-Y. Wu, B. Ren, Y.-X. Jiang, X. Xu, Z.-Q. Tian, J. Phys. Chem. A 106 (2002) 9042;
(c) D.Y. Wu, M. Hayashi, C.H. Chang, K.K. Liang, S.H. Lin, J. Chem. Phys. 118 (2003)
4073;
(
Angew. Chem., Int. Ed. 47 (2008) 718.
[
[
28] For key references, see: (a) P.M. Henry, J. Chem. Soc. D (1971) 328;
(
(
(
(
(
b) P.M. Henry, J. Am. Chem. Soc. 94 (1972) 5200;
(d) D.-Y. Wu, M. Hayashi, Y.J. Shiu, K.K. Liang, C.H. Chang, Y.L. Yeh, S.H. Lin, J. Phys.
Chem. A 107 (2003) 9658;
(e) L.E.Sansores,R.Salcedo,A.Martinez,N.Mireles,J.Mol.Struct.(THEOCHEM)763
(2006) 7.
c) L.E. Overman, C.B. Campbell, J. Org. Chem. 41 (1976) 3338;
d) L.E. Overman, C.B. Campbell, F.M. Knoll, J. Am. Chem. Soc. 100 (1978) 4822;
e) L.E. Overman, F.M. Knoll, Tetrahedron Lett. 4 (1979) 321;
f) L.E. Overman, Angew. Chem., Int. Ed. Engl. 23 (1984) 579.
[32] For synthesis of NHCs, see: A.J. Arduengo III, J.C. Calabrese, F. Davidson, H.V.R.
Dias, J.R. Goerlich, R. Krafczyk, W.J. Marshall, M. Tamm, R. Schmutzler, Helv.
Chim. Acta 82 (1999) 2348 and references therein.
29] (a) N. Marion, R. Gealageas, S.P. Nolan, Org. Lett. 9 (2007) 2653. Additions and
Corrections, Org. Lett. 10 (2008) 1037;