[BF4]: Silver-free and acid-free catalysts for water-inclusive gold-mediated organic transformations

Article abstract of DOI:10.1021/om301249r

The synthesis of a series of digold hydroxide complexes is reported. These diaurated species, of the formula [{Au(NHC)}₂(μ-OH)][BF ₄] (where NHC = IPr^Cl, IPr, IPent), were easily prepared via the cationic species [Au(NHC)(NCCH₃)][BF₄] in aqueous media. The catalytic activity of these novel complexes was tested and compared to that of the previously reported IPr and SIPr derivatives. These digold hydroxide species are highly active in water-inclusive organic transformations, such as the alkyne and nitrile hydration reactions, and the Meyer-Schuster rearrangement. One salient feature of these systems is the lack of any additive to induce catalytic activity.

Full text of DOI:10.1021/om301249r

Article
pubs.acs.org/Organometallics
[
{Au(NHC)} (μ-OH)][BF ]: Silver-Free and Acid-Free Catalysts
2 4
for Water-Inclusive Gold-Mediated Organic Transformations
́ ́ ́
Adrian Gomez-Suarez, Yoshihiro Oonishi, Sebastien Meiries, and Steven P. Nolan*
EaStCHEM School of Chemistry, University of St Andrews, St Andrews KY16 9ST, U.K.
*
S Supporting Information
ABSTRACT: The synthesis of a series of digold hydroxide
complexes is reported. These diaurated species, of the formula
Cl
[
{Au(NHC)} (μ-OH)][BF ] (where NHC = IPr , IPr*, IPent),
2
4
were easily prepared via the cationic species [Au(NHC)-
NCCH )][BF ] in aqueous media. The catalytic activity of
(
3
4
these novel complexes was tested and compared to that of the
previously reported IPr and SIPr derivatives. These digold
hydroxide species are highly active in water-inclusive organic
transformations, such as the alkyne and nitrile hydration
reactions, and the Meyer−Schuster rearrangement. One salient
feature of these systems is the lack of any additive to induce
catalytic activity.
INTRODUCTION
Scheme 1. Reaction Sequence Leading to the Formation of
the Diaurated Species 2a
■
Homogeneous gold catalysis has emerged as one of the most
practical and important tools for organic chemists during the
1
last few decades. The success of gold catalysis can be explained
by the ability of the gold center to activate C−C multiple
2
bonds, specially alkynes, toward nucleophilic attack. Generally,
organogold(I) species are linear, two-coordinate complexes of
the formula [Au(L)Cl], where L is a phosphine or N-heterocyclic
1
carbene (NHC) ligand. The use of a halide abstractor, usually a
silver salt, is necessary in order to generate the active catalyst from
1
Au(I) halide complexes. This procedure has several drawbacks,
such as the high price of the silver salt activator, the light
sensitivity of these silver salts, and the fact that silver can itself be
a catalyst, oftentimes exhibiting a different reactivity profile that
To the best of our knowledge, only a handful of digold
hydroxide complexes of the formula [{Au(L)} (μ-OH)][X]
2
3
have been reported to date (Figure 1). We have reported the
can modify the otherwise gold-only catalyzed reaction. For these
synthesis and characterization of 2a and [{Au(SIPr)} (μ-OH)]-
2
reasons the development of new silver-free protocols has become
an important issue in gold catalysis. Our group has recently
contributed to this field with the synthesis of the gold hydroxide
species [Au(IPr)(OH)] (1a), which can be easily activated by
an acid, e.g. HBF or HSbF , to generate the active species
[
BF ] (2b), while Maier et al. have most recently disclosed the
4
synthesis of two diaurated complexes bearing Buchwald-type
8
phosphine ligands and [{Au(IMes)} (μ-OH)][BF ]. Up until
2
4
now, only the catalytic activity of the IPr derivative 2a has been
4a,b,9
4
6
studied.
This diaurated complex has proven to be highly
+
4
[
Au(IPr)] . In the course of these studies a diaurated species of
active in a number of water-inclusive gold-catalyzed trans-
formations, such as alkyne hydration, nitrile hydration, and the
Meyer−Schuster rearrangement, all being conducted without
the formula [{Au(IPr)} (μ-OH)][BF ] (2a) was discovered
2
4
4a
(Scheme 1).
4
a,b,9
Dinuclear organogold species, such as gem-diaurated
compounds or σ,π-diaurated acetylide complexes, have recently
any additives to induce catalyst activation.
With these early
results in hand, we now expand the library of diaurated
hydroxide complexes and test their catalytic activity in order to
illustrate the feasibility of silver-free, acid-free gold-catalyzed
attracted increased attention as key intermediates in gold-
5
catalyzed reactions. A number of research groups have targeted
6
the study and isolation of such species. We have recently
methodologies. Herein we report the synthesis of three new
Cl
[
{Au(NHC)} (μ-OH)][BF ] complexes bearing IPr (2c),
reported that 2a can be used to gain access to both types of
complexes, gem-diaurated and σ,π-acetylides, in a straightfor-
ward manner from aryl- and vinylboronic acids and terminal
2
4
Received: December 22, 2012
Published: February 6, 2013
7
alkynes, respectively.
©
2013 American Chemical Society
1106
dx.doi.org/10.1021/om301249r | Organometallics 2013, 32, 1106−1111

Organometallics
Article
Figure 1. [{Au(L)} (μ-OH)][X] (L = NHC, PR ) complexes reported to date.
2
3
Scheme 2. Synthesis of Digold Complexes 2c−e
1
0
13,14
IPr* (2d), and IPent (2e) ligands and a study of their
respective catalytic activity in several gold-catalyzed trans-
formations which permits a comparison to that of the
previously reported IPr (2a) and SIPr (2b) derivatives.
significant impact of the carbonyl motif in organic synthesis.
Alkyne hydration can be catalyzed either by Brønsted acids or
15
by a variety of transition-metal complexes. Among the latter,
organogold species stand out as some of the most efficient and
4f,16
milder catalysts.
gold(I)-catalyzed alkyne hydration using [Au(PPh
0.1−1.0 mol %) and 50% sulfuric acid in methanol as the
In 2002, Tanaka et al. reported the first
RESULTS AND DISCUSSION
3
)(Me)]
■
(
(
There are two main routes for the synthesis of [{Au(NHC)} -
2
16a
catalytic system. Despite the efficiency of this groundbreaking
methodology, the use of such large quantities of a strong acid
was bothersome. In 2008, we reported the hydration of alkynes
at very low catalyst loadings (10−1000 ppm) using [Au(IPr)Cl]/
AgSbF in a mixture of 1,4-dioxane and H O as the catalytic
μ-OH)][BF ] complexes: (a) reaction of [Au(NHC)(OH)]
4
4a,9
with 0.5 equiv. of a strong acid, such as HBF4,
and (b)
chloride abstraction from [Au(NHC)Cl] by a silver salt, e.g.
AgBF , in acetonitrile, forming the corresponding [Au(NHC)-
4
6
2
(
NCCH )][BF ] complex in situ, and subsequent addition of
3 4
11
16c
system. This novel procedure replaced the use of concentrated
solutions of strong acids for a stoichiometric amount (relative to
the catalyst) of a silver salt to activate the gold complex. In 2009,
Corma et al. reported the first acid-free, silver-free gold(I)-
water. For synthetic purposes the route used in the present
study was the latter methodology. According to this procedure
the following complexes were obtained in good yields:
{Au(IPr )} (μ-OH)][BF ] (2c; 81%), [{Au(IPr*)} (μ-OH)]-
BF ] (2d; 72%), and [{Au(IPent)} (μ-OH)][BF ] (2e; 80%)
Scheme 2). The diaurated nature of complexes 2c−e was
confirmed by H and C NMR spectroscopy as well as by
elemental analysis. Compounds 2c,e present the characteristic
Cl
[
[
(
2
4
2
17
catalyzed alkyne hydration using Gagosz-type complexes
4
2
4
t
[
Au(L)(NTf )] (where L = SPhos, PPh , P Bu ) at room
Despite the milder reaction conditions, this
new methodology required the use of higher catalyst loadings
0.5−5 mol %) and longer reaction times. With the aim of
developing new silver-free protocols, we have recently reported
the use of gold hydroxide 1a activated by an excess of acid
3 equiv. with respect to gold) at low catalyst loadings (100−
2
3
3
1
6d
1
13
temperature.
16d
1
(
OH resonance between 0 and 1 ppm in H NMR spectrum,
while for the IPr* derivative 2d a significant shift toward higher
fields can be observed (−0.74 ppm). This shift may be due to
the high steric hindrance provided by the IPr* ligand.
(
1
4f
000 ppm).
As [{Au(NHC)} (μ-OH)][BF ] complexes have been
2
4
Digold hydroxide complexes have also been shown to be
postulated as possible catalytic intermediates for gold-catalyzed
water-inclusive transformations, their activity was tested in
alkyne and nitrile hydration, as well as in the Meyer−Schuster
4a
suitable catalysts for silver-free and acid-free alkyne hydration.
In order to test the catalytic activities of the new complexes
and compare them with the previously reported catalytic
results, we next performed the hydration of alkynes in a mixture
rearrangement. In order to confirm their utility as a source of
+
[
Au(IPr)] when activated by an acid, their catalytic activity
was also investigated in the rearrangement of allylic acetates.
Alkyne Hydration. The hydration of alkynes to obtain
carbonyl derivatives represents one of the most environmentally
friendly and atom-economical procedures for the formation of
CO bonds. The importance of this reaction is related to the
of 1,4-dioxane and H O (2/1) at 80 °C for 3 h. Dipheny-
2
lacetylene (3) was chosen as the test substrate, as it is one of
the most challenging substrates for this transformation. To
challenge our catalysts, relatively low catalyst loadings (0.5 mol %)
were employed. As shown in Table 1, IPr* complex 2d performed
1
2
1
107
dx.doi.org/10.1021/om301249r | Organometallics 2013, 32, 1106−1111

Organometallics
Article
a
Table 1. Gold-Catalyzed Alkyne Hydration
was possible to obtain excellent conversions (75−100%) and sub-
21
stantial improvements for two particularly troublesome substrates.
Encouraged by these results, the activity of the new catalysts was
tested in this transformation. p-Methoxybenzonitrile (6) was the
substrate of choice for this transformation, as a 20% improve-
ment was observed when 2a was used as catalyst instead of the
monomeric 5a. The experiments were carried out under the
conditions mentioned above, but using lower catalyst loadings
b
entry
cat. [amt, mol %]
conversion, %
9
1
2
3
4
5
[{Au(IPr)} (μ-OH)][BF ] (2a) [0.5]
92
83
2
4
[{Au(SIPr)} (μ-OH)][BF ] (2b) [0.5]
2
4
(
0.5 mol %) (Table 2). As in the case of the alkyne hydration,
Cl
[{Au(IPr )} (μ-OH)][BF ] (2c) [0.5]
91
2
4
[{Au(IPr*)} (μ-OH)][BF ] (2d) [0.5]
55
a
2
4
Table 2. Gold-Catalyzed Nitrile Hydration
[{Au(IPent)} (μ-OH)][BF ] (2e) [0.5]
74
2
4
c
6
[{Au(IPr)} (μ-OH)][BF ] (2a) [0.1]
57
2
4
c
Cl
7
[{Au(IPr )} (μ-OH)][BF ] (2c) [0.1]
95
2
4
d
Cl
8
[{Au(IPr )} (μ-OH)][BF ] (2c) [0.05]
95 (90)
2
4
a
Reaction conditions unless stated otherwise: [Au] (2.5 μmol), 3
0.5 mmol) in a mixture of 1,4-dioxane and H O (2/1, 2 mL), 80 °C,
(
3
b
2
b
entry
cat. [amt, mol %]
conversion, %
h. Conversions determined by GC. Average of at least two runs.
c
1
2
3
4
5
[{Au(IPr)} (μ-OH)][BF ] (2a) [0.5]
86
92 (90)
91
The isolated yield is given in parentheses. Reaction conditions: [Au]
2
4
(
(
3
1.25 μmol), 3 (1.25 mmol) in a mixture of 1,4-dioxane and H O
2/1, 5 mL), 120 °C, 24 h. Reaction conditions: [Au] (1.25 μmol),
[{Au(SIPr)}
2
(μ-OH)][BF
4
] (2b) [0.5]
] (2c) [0.5]
2
d
Cl
[{Au(IPr )}
(μ-OH)][BF
2
4
(2.50 mmol) in a mixture of 1,4-dioxane and H O (2/1, 10 mL),
[{Au(IPr*)} (μ-OH)][BF ] (2d) [0.5]
53
2
2
4
1
20 °C, 24 h.
[{Au(IPent)} (μ-OH)][BF ] (2e) [0.5]
90
2
4
c
6
[{Au(SIPr)} (μ-OH)][BF ] (2b) [0.25]
70
2
4
c
Cl
poorly in this transformation, with only 55% conversion to the
desired ketone (4) after 3 h (Table 1, entry 4). The SIPr- and
IPent-bearing complexes, 2b,e, furnished similar activities with
better conversions (74−83%; Table 1, entries 2 and 5). The IPr
derivative 2a and the newly synthesized IPrCl complex 2c were
the best catalysts for the hydration of diphenylacetylene, with 92%
and 91% conversions, respectively (Table 1, entries 1 and 3). To
determine which of the two complexes, 2a or 2c, was the most
active, experiments at lower catalyst loadings were performed
7
c
[{Au(IPr )} (μ-OH)][BF ] (2c) [0.25]
59
2
4
8
[{Au(IPent)} (μ-OH)][BF ] (2e) [0.25]
57
2
4
a
Reaction conditions unless stated otherwise: [Au] (2.5 μmol), 6
(0.5 mmol) in a mixture of THF and H O (1/1, 1 mL), 140 °C, 2 h.
Conversions determined by H NMR. Average of at least two runs.
The isolated yield is given in parentheses. Reaction conditions: [Au]
1.25 μmol), 6 (0.5 mmol) in a mixture of THF and H O (1/1, 1 mL),
40 °C, 2 h.
2
b
1
c
(
1
2
(
Table 1, entries 6−8). To the best of our knowledge, in the
the complex bearing IPr*, 2d, performed poorly in this reac-
tion with only 53% conversion after 2 h (Table 2, entry 4). On
the other hand, the reactions using 2a−c,e gave excellent
conversions, between 86 and 92% (Table 2, entries 1−3 and 5).
In order to determine which was the most active complex,
experiments at lower catalyst loadings were performed. Gratify-
ingly, a difference in reactivity could be observed at 0.25 mol %.
literature the optimum results for the hydration of diphenylace-
tylene at low catalyst loadings were obtained using 0.1 mol % of
either [Au(IPr)Cl]/AgSbF or [Au(IPr)OH]/HBF at 120 °C for
6
4
4
f,16c
2
4 h, with conversions between 70 and 77%.
Gratifyingly,
9
5% conversion (90% isolated yield) to the desired product could
be obtained under the same conditions using 0.05 mol % of 2c
Table 1, entry 8). This result highlights that the digold species
Cl
(
While the IPr (2c) and IPent derivatives (2e) provided
Cl
[{Au(IPr )} (μ-OH)][BF ] (2c) is the best catalyst reported to
moderate conversions, ca. 58% (Table 2, entries 7 and 8), the
SIPr derivative (2b) was the most active catalyst with 70%
conversion (Table 2, entry 6). 2b is therefore the catalyst of
choice for gold-catalyzed nitrile hydration reactions.
2
4
date for the hydration of challenging alkynes at low catalyst
loadings. Our findings are in direct contrast with the recent
contribution by Shi et al. regarding the “silver effect” in gold
catalysis, where Shi claims that the gold-catalyzed alkyne hydration
cannot be catalyzed only by [Au] and that the presence of silver
is required for the reaction to proceed. As is the case for the
Meyer−Schuster Rearrangement. An alternative trans-
formation to the classical route for the synthesis of α,β-
unsaturated ketones is the rearrangement of propargylic alcohols,
+
18
16d
22
Corma system (2009)4 and our previous contribution on silver-
known as the Meyer−Schuster rearrangement. This reaction
a
22,23
free protocols (2010), here no additive (acid, silver) is required
can be catalyzed by acid or by several metal complexes.
The
4b,24
to perform the catalytic reaction.
case of gold has been widely studied by several groups.
In
Nitrile Hydration. The hydration of nitriles represents the
2009, we reported that α,β-unsaturated ketone 8 could be
obtained in good yield and good E/Z selectivity by heating
propargylic alcohol 9 at 60 °C for 16 h in a 10/1 mixture of
MeOH and H O in the presence of [Au(IPr)Cl]/AgSbF
most atom-economical synthetic pathway toward the formation
1
9
of amides. This procedure has been described as catalyzed by
1
9
all the transition metals of groups 8−11, including gold.
2
6
24d
However, only two catalytic systems based on gold have been
(2 mol %). Further investigations of this reaction allowed us
9
,20
reported.
We described the first gold-catalyzed nitrile
hydration in 2009. Moderate to excellent yields (34−99%)
were obtained using the well-defined Gagosz-type complex
to report, 1 year later, the use of the Meyer−Schuster rearrange-
20
4b
ment for the synthesis of prostaglandins. Using 2 mol %
of gold hydroxide 1a (acid activated) or digold complex 2a, in a
17b
[
Au(IPr)(NTf )] (5a) in reactions conducted in a mixture
10/1 mixture of MeOH and H O, ketone 8 was obtained in
2
2
4b
of THF and H O (10/1) at 140 °C for 2 h under microwave
excellent yields (93−97%) within 1 h at room temperature.
2
2
0
irradiation. After this initial study, and once the digold species
a had been synthesized, it was postulated as a potential key
The catalyst screening was commenced using these conditions.
Initial results using 1 and 0.5 mol % of digold complex 2a
allowed us to obtain 99% and 69% conversions, respectively, in
2
9
intermediate in this process. Using 1 mol % of 2a as catalyst, it
1
108
dx.doi.org/10.1021/om301249r | Organometallics 2013, 32, 1106−1111

Organometallics
h at room temperature. In order to use the lowest amount of
Article
a
3
Table 4. Gold-Catalyzed Allylic Acetate Rearrangement
catalyst combined with the shortest reaction times possible,
experiments were conducted using 0.5 mol % of our diaurated
complexes at 60 °C for 2 h (Table 3). Unfortunately, under these
a
Table 3. Gold-Catalyzed Meyer−Schuster Rearrangement
b
entry
cat. [amt, mol %]
conversion, %
1
2
3
4
5
[{Au(IPr)} (μ-OH)][BF ] (2a) [0.25]
63
99
2
4
[{Au(SIPr)} (μ-OH)][BF ] (2b) [0.25]
2
4
Cl
[{Au(IPr )} (μ-OH)][BF ] (2c) [0.25]
94
2
4
[{Au(IPr*)} (μ-OH)][BF ] (2d) [0.25]
59
2
4
b
entry
cat. [amt, mol %]
conversion, %
[{Au(IPent)} (μ-OH)][BF ] (2e) [0.25]
67
2
4
c
1
2
3
4
5
[{Au(IPr)} (μ-OH)][BF ] (2a) [0.5]
98 (95)
6
[{Au(SIPr)}
2
(μ-OH)][BF
4
] (2b) [0.1]
99 (90)
52
2
4
c
Cl
[{Au(SIPr)} (μ-OH)][BF ] (2b) [0.5]
85
18
3
7
[{Au(IPr )}
(μ-OH)][BF
2
] (2c) [0.1]
4
2
4
Cl
a
[{Au(IPr )} (μ-OH)][BF ] (2c) [0.5]
Reaction conditions unless stated otherwise: [Au] (0.75 μmol),
2
4
[{Au(IPr*)} (μ-OH)][BF ] (2d) [0.5]
HBF ·OEt (0.75 μmol), 10 (0.3 mmol), in DCE (3 mL), 80 °C,
4 2
b
2
4
[{Au(IPent)} (μ-OH)][BF ] (2e) [0.5]
27
74
12 min. Conversions determined by GC. Average of at least two runs.
2
4
c
c
6
[{Au(IPr)} (μ-OH)][BF ] (2a) [0.1]
The isolated yield is given in parentheses. Reaction conditions: [Au]
2
4
a
(0.3 μmol), HBF
4 2
·OEt (0.3 μmol), 8 (0.3 mmol), in DCE (3 mL),
Reaction conditions unless stated otherwise: [Au] (1 μmol), 9
0.2 mmol) in a mixture of methanol and H O (10/1, 1 mL), 60 °C,
8
0 °C, 12 min.
(
2
2
b
h. Conversions determined by GC. Average of at least two runs.
c
The isolated yield is given in parentheses. Reaction conditions: [Au]
1 μmol), 7 (1.0 mmol) in a mixture of methanol and H O (10/1,
diaurated complexes 2a,d,e provided moderate conversions
59−67%; Table 4, entries 1, 4, and 5). On the other hand, the
(
1
2
(
mL), 60 °C, 24 h.
Cl
use of the SIPr and IPr derivatives 2b,c, gave excellent
conversions (94−99%; Table 4, entries 2 and 3). In order to
determine the best catalyst, a reaction was performed under the
same conditions but at lower catalyst loading (0.1 mol %). We
were very pleased to observe that, even at these low loadings,
catalyst 2b provided very high yields (90%).
conditions complexes 2c−e showed poor reactivity for this
transformation, yielding conversions between 3 and 27%
(
Table 3, entries 3−5). In the case of 2d, this may be due to
its poor solubility in the reaction mixture. On the other hand, the
complexes bearing SIPr (2b) and IPr ligands (2a) showed good
reactivity with excellent conversions (85 and 98%, respectively;
Table 3, entries 1 and 2). In order to test the limit of the system,
a reaction was performed with 0.1 mol % of 2a over 24 h.
Gratifyingly, good conversion (74%) was obtained (Table 3,
entry 6). These results place the digold catalyst 2a among the
best for the gold-catalyzed Meyer−Schuster rearrangement.
While Shi et al. found that this transformation can only be
CONCLUSION
■
In conclusion, three novel digold complexes have been
synthesized and their catalytic activity has been tested in
important organic transformations. Gratifyingly, over 90%
isolated yields were obtained at low catalyst loadings (0.05−
0.5 mol %) in the reactions examined. In addition, these digold
catalysts do not require any additive (e.g., acid, silver salts) to
promote the reactions. Particularly interesting are the results for
the hydration of diphenylacetylene and the Meyer−Schuster
rearrangement, as they are in contradiction with some recent
literature reports. These results are part of our ongoing investiga-
tions to clarify the role of gold in organic transformations and to
develop new silver-free, acid-free gold-catalyzed processes.
25
poorly performed by [Au(IPr)][SbF ] (26% conversion), and
that the addition of silver salts greatly enhanced the reactivity
6
(
94% conversion), our results, in accordance with those
24g,i 24h
published by Sheppard
and Shi himself,
highlight that
gold alone can catalyze the Meyer−Schuster rearrangement in
high yields. Interestingly, Sheppard also noticed that the presence
of silver impurities in his gold catalyst afforded the substitution of
the alcohol with methoxide, derived from the MeOH employed
during the reaction.
revealed that AgNTf could catalyze this process. Further work
to explore the role of silver is ongoing in our laboratories.
Rearrangement of Allylic Acetates. Finally, the rearrange-
ment of allylic acetates was tested in order to study the
potential of the new complexes as acid-activated precatalysts.
This classical skeletal rearrangement has been catalyzed by
several transition metals, including gold. We reported in 2007
the complete conversion of allylic acetate 10 into 11 after
EXPERIMENTAL SECTION
General Considerations. Unless otherwise stated, all solvents and
reagents were used as purchased and all reactions were performed
under air. Deuterated solvents (CD Cl , CDCl ) were filtered through
■
2
4i,26
An exhaustive study of the reaction
24i
2
2
2
3
basic alumina in order to remove traces of HCl. NMR spectra were
recorded on 400 and 300 MHz spectrometers at room temperature
in CD Cl or CDCl . Chemical shifts are given in parts per million
2
2
3
(
ppm) with respect to TMS. Elemental analyses were performed by
the analytical services of London Metropolitan University. [{Au(IPr)}2-
μ-OH)][BF ] (2a) and [{Au(SIPr)} (μ-OH)][BF ] (2b) were
27
(
4
2
4
9
,11
synthesized according to our previous reports.
General Procedure for the Synthesis of [{Au(NHC)} (μ-OH)]-
1
2 min at 80 °C in 1,2-dichloroethane using microwave
2
[
BF ] (2c−e). To a solution of the corresponding [Au(NHC)Cl]
irradiation and a combination of [Au(IPr)Cl] (3 mol %) and
AgBF (2 mol %). More recently, we described the use of
1
4
27b
(1 equiv.) in dry acetonitrile (5 mL), under an argon atmosphere, was
4
added AgBF (1.1 equiv.). The reaction mixture was stirred at room
4
mol % of [{Au(IPr)} (μ-OH)][BF ]/HBF under the
2 4 4
temperature, in the absence of light, for 5 h. The reaction mixture was
then filtered through a pad of Celite, the solvent removed in vacuo,
and the crude reaction product dissolved in ca. 10 mL of CH Cl . The
organic solution was washed three times with ca. 30 mL of water, dried
over anhydrous MgSO , and concentrated under vacuum. To purify
conditions previously mentioned over 30 min to obtain full
4a
conversion of 10 into 11. To determine the lowest amount of
catalyst combined with shorter reaction times, reactions were
carried out using 0.25 mol % of digold hydroxides, at 80 °C in a
microwave reactor (Table 4). Under these reaction conditions,
2
2
28
4
the final product, the resulting solid was dissolved in the minimum
1
109
dx.doi.org/10.1021/om301249r | Organometallics 2013, 32, 1106−1111

Organometallics
Article
amount of CH Cl (ca. 2 mL), and the product was precipitated by
addition of pentane (ca. 8 mL). If after evaporation of the solvent an
2
2
REFERENCES
■
(
2
1) (a) Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem., Int. Ed.
oil is obtained, the final product can be triturated by addition of Et O
2
006, 45, 7896−7936. (b) Hashmi, A. S. K. Chem. Rev. 2007, 107,
(
ca. 4 mL). The precipitate was collected by filtration, affording the
3
180−3211. (c) Hashmi, A. S. K.; Rudolph, M. Chem. Soc. Rev. 2008,
desired complexes as white solids.
Cl
37, 1766−1775. (d) Li, Z.; Brouwer, C.; He, C. Chem. Rev. 2008, 108,
[
{Au(IPr )} (μ-OH)][BF ] (2c). Following the general procedure
2 4
Cl
3239−3265. (e) Hashmi, A. S. K.; Hubbert, C. Angew. Chem., Int. Ed.
3
00 mg (0.434 mmol) of [Au(IPr )Cl] and 93 mg (0.478 mmol) of
2
010, 49, 1010−1012. (f) Nolan, S. P. Acc. Chem. Res. 2011, 44, 91−
AgBF were used. The desired complex was obtained as a white solid
4
1
100. (g) Rudolph, M.; Hashmi, A. S. K. Chem. Commun. 2011, 47,
in 81% isolated yield (497 mg). H NMR (CD Cl ; 400 MHz): δ 7.59
2
2
6
4
536−6544. (h) Rudolph, M.; Hashmi, A. S. K. Chem. Soc. Rev. 2012,
(
(
t, J = 7.8 Hz, 4H, CHp‑Ar), 7.32 (d, J = 7.8 Hz, 8H, CHm‑Ar), 2.29
sept, J = 6.9 Hz, 8H, CH ), 1.23 (d, J = 6.9 Hz, 24H, CH ), 1.13 (d,
1, 2448−2462.
iPr
3
13
(2) (a) Hashmi, A. S. K. Gold Bull. 2003, 36, 3−9. (b) Hashmi, A. S.
J = 6.8 Hz, 24H, CH ), 0.77 (s, 1H, OH). C NMR (CD Cl ; 101
3
2
2
K. Angew. Chem., Int. Ed. 2010, 49, 5232−5241.
MHz): δ 163.0 (Ccarb), 146.4 (Co‑Ar), 132.2 (CHp‑Ar), 131.1 (CN−Ar),
(
3) Schmidbaur, H.; Schier, A. Z. Naturforsch. 2011, 66b, 329−350.
(4) (a) Gaillard, S.; Bosson, J.; Ramon, R. S.; Nun, P.; Slawin, A. M.
, R.
1
25.1 (CHm‑Ar), 120.1 (C ), 29.4 (CH ), 24.8 (CH ), 23.5 (CH ).
Cl
iPr
3
3
1
9
́
F NMR (CD Cl ; 376 MHz): δ −153.89, −153.94. Anal. Calcd for
2
2
Z.; Nolan, S. P. Chem. Eur. J. 2010, 16, 13729−13740. (b) Ramon
́
C H Au BCl F N O (1412.70): C, 45.91; H, 4.92; N, 3.97. Found:
54
69
2
4
4
4
S.; Gaillard, S.; Slawin, A. M. Z.; Porta, A.; D’Alfonso, A.; Zanoni, G.;
Nolan, S. P. Organometallics 2010, 29, 3665−3668. (c) Nun, P.;
Gaillard, S.; Slawin, A. M. Z.; Nolan, S. P. Chem. Commun. 2010, 46,
C, 45.86; H4.83; N, 3.87.
{Au(IPr*)} (μ-OH)][BF ] (2d). Following the general procedure
[
2
4
3
00 mg (0.262 mmol) of [Au(IPr*)Cl] and 56 mg (0.288 mmol) of
9
113−9115. (d) Nun, P.; Dupuy, S.; Gaillard, S.; Poater, A.; Cavallo,
AgBF were used. The desired complex was obtained as a white solid
4
1
L.; Nolan, S. P. Catal. Sci. Technol. 2011, 1, 58−61. (e) Nun, P.;
in 72% isolated yield (438 mg). H NMR (300 MHz; CD Cl ): δ
2
2
Gaillard, S.; Poater, A.; Cavallo, L.; Nolan, S. P. Org. Biomol. Chem.
7
.28−7.24 (m, 24H, CH ), 7.06 (s, 8H, CH ), 7.00−6.87 (m, 56H,
Ar
m‑Ar
2
́
011, 9, 101−104. (f) Nun, P.; Ramon, R. S.; Gaillard, S.; Nolan, S. P.
CH ), 5.98 (s, 4H, CH
), 5.24 (s, 8H, CHPh ), 2.36 (s, 12H,
Ar
imidazole
2
1
3
J. Organomet. Chem. 2011, 696, 7−11. (g) Nun, P.; Egbert, J. D.; Oliva-
CH ), −0.76 (s, 1H, OH). C NMR (75 MHz; CD Cl ): δ 164.2
3
2
2
Madrid, M.-J.; Nolan, S. P. Chem. Eur. J. 2011, 18, 1064−1067.
(
(
1
C
), 142.85 (C ), 142.68 (C ), 141.3 (Co‑Ar), 140.9 (CN−Ar), 134.0
carb Ar Ar
(
8
5) Gom
156−8159.
(6) (a) Cheong, P. H.-Y.; Morganelli, P.; Luzung, M. R.; Houk, K. N.;
Toste, F. D. J. Am. Chem. Soc. 2008, 130, 4517−4526. (b) Weber, D.;
Tarselli, M. A.; Gagne, M. R. Angew. Chem., Int. Ed. 2009, 48, 5733−
736. (c) Seidel, G.; Lehmann, C. W.; Furstner, A. Angew. Chem., Int.
́ ́
ez-Suarez, A.; Nolan, S. P. Angew. Chem., Int. Ed. 2012, 51,
Cp‑Ar), 131.0 (CHm‑Ar), 130.0 (CH ), 129.6 (CH ), 129.1 (CH ),
28.8 (CH ), 127.6 (CH ), 127.1 (CH ), 124.4 (CHimidazole), 51.9
Ar
Ar
Ar
Ar
Ar
Ar
19
(
−
4
CHPh ), 22.1 (CH ). F NMR (282 MHz; CD Cl ): δ −153.96,
2
3
2
2
154.02. Anal. Calcd for C138H Au BF N O (2324.14): C, 71.32; H,
113 2 4 4
́
.90; N, 2.41. Found: C, 71.17; H, 4.77; N, 2.33.
{Au(IPent)} (μ-OH)][BF ] (2e). Following the general procedure
5
̈
[
2
4
Cl
Ed. 2010, 49, 8466−8470. (d) Hooper, T. N.; Green, M.; Russell, C.
A. Chem. Commun. 2010, 46, 2313−2315. (e) Himmelspach, A.; Finze,
M.; Raub, S. Angew. Chem., Int. Ed. 2011, 50, 2628−2631. (f) Brown,
T. J.; Widenhoefer, R. A. Organometallics 2011, 30, 6003−6009.
3
00 mg (0.409 mmol) of [Au(IPr )Cl] and 87.6 mg (0.450 mmol) of
AgBF were used. The desired complex was obtained as a white solid
4
1
in 80% isolated yield (491 mg). H NMR (CD Cl ; 300 MHz): δ 7.53
2
2
(
t, J = 7.8 Hz, 4H, CHp‑Ar), 7.20 (d, J = 7.8 Hz, 8H, CHm‑Ar), 7.07 (s,
́
g) Grirrane, A.; Garcia, H.; Corma, A.; Alvarez, E. ACS Catal. 2011, 1,
(
1
4
H, CHimidazole), 1.97 (quintet, J = 7.1 Hz, 8H, CH), 1.66−1.37 (m,
647−1653. (h) Simonneau, A.; Jaroschik, F.; Lesage, D.; Karanik, M.;
Guillot, R.; Malacria, M.; Tabet, J.-C.; Goddard, J.-P.; Fensterbank, L.;
Gandon, V.; Gimbert, Y. Chem. Sci. 2011, 2, 2417−2422. (i) Brown, T.
J.; Weber, D.; Gagne,
32H, CH ), 0.72 (dt, J = 12.9, 7.3 Hz, 48H, CH ), 0.20 (s, 1H, OH).
2
3
1
3
C NMR (CD Cl ; 75 MHz): δ 163.4 (Ccarb), 143.7 (Co‑Ar), 136.8
2
2
(
(
(
CN−Ar), 130.8 (CHp‑Ar), 125.1 (CHm‑Ar), 124.8 (CH
), 43.2
imidazole
́
M. R.; Widenhoefer, R. A. J. Am. Chem. Soc.
1
9
CH), 29.5 (CH ), 28.6 (CH ), 13.2 (CH ), 12.6 (CH ). F NMR
2
2
3
3
2
3
012, 134, 9134−9137. (j) Weber, D.; Gagne, M. Chem. Sci. 2013, 4,
CD Cl ; 282 MHz): δ −153.94, −154.00. Anal. Calcd for
2
2
35−338. (k) Weber, D.; Jones, T. D.; Adduci, L. L.; Gagne, M. R.
́
C H Au BF N O (1499.35): C, 56.07; H, 7.06; N, 3.74. Found:
70
105
2
4
4
Angew. Chem., Int. Ed. 2012, 51, 2452−2456. (l) Hashmi, A. S. K.;
C, 55.89; H 7.12; N, 3.84.
Braun, I.; Nosel, P.; Schadlich, J.; Wieteck, M.; Rudolph, M.;
̈
̈
Rominger, F. Angew. Chem., Int. Ed. 2012, 51, 4456−4460.
(m) Hashmi, A. S. K.; Braun, I.; Rudolph, M.; Rominger, F.
Organometallics 2012, 31, 644−661. (n) Hashmi, A. S. K.; Wieteck,
ASSOCIATED CONTENT
■
*
S
Supporting Information
̈
M.; Braun, I.; Nosel, P.; Jongbloed, L.; Rudolph, M.; Rominger, F. Adv.
Text giving additional experimental details and figures giving
NMR spectra. This material is available free of charge via the
Internet at http://pubs.acs.org.
Synth. Catal. 2012, 354, 555−562. (o) Hashmi, A. S. K.; Wieteck, M.;
Braun, I.; Rudolph, M.; Rominger, F. Angew. Chem., Int. Ed. 2012, 51,
1
4
0633−10637. (p) Schmidbaur, H.; Schier, A. Chem. Soc. Rev. 2012,
1, 370−412. (q) Ye, L.; Wang, Y.; Aue, D. H.; Zhang, L. J. Am. Chem.
̌
́ ́ ̌ ́ ́ ̌
J.; Jankova, S.; Jasíkova, L.; Vana,
Soc. 2012, 134, 31−34. (r) Roithova,
J.; Hybelbauerova,
s) Heckler, J. E.; Zeller, M.; Hunter, A. D.; Gray, T. G. Angew. Chem.,
Int. Ed. 2012, 51, 5924−5928. (t) Hashmi, A. S. K.; Lauterbach, T.;
Nosel, P.; Vilhelmsen, M. H.; Rudolph, M.; Rominger, F. Chem. Eur. J.
2013, 19, 1058−1065.
7) Gomez-Suarez, A.; Dupuy, S.; Slawin, A. M. Z.; Nolan, S. P.
Angew. Chem., Int. Ed. 2013, DOI: 10.1002/anie.201208234.
8) Zhdanko, A.; Strobele, M.; Maier, M. E. Chem. Eur. J. 2012, 18,
4732−14744.
9) Ramon, R. S.; Gaillard, S.; Poater, A.; Cavallo, L.; Slawin, A. M.
Z.; Nolan, S. P. Chem. Eur. J. 2011, 17, 1238−1246.
AUTHOR INFORMATION
■
́
S. Angew. Chem., Int. Ed. 2012, 51, 8378−8382.
(
Corresponding Author
*E-mail: sn17@st-andrews.ac.uk.
̈
Notes
(
́
́
The authors declare no competing financial interest.
(
1
(
̈
ACKNOWLEDGMENTS
■
́
The ERC (Advanced Investigator Award-FUNCAT) and the
EPSRC are gratefully acknowledged for support of this work.
Umicore AG is acknowledged for their generous gift of auric
acid. We thank Dr. Ruben S. Ramon and Dr. David J. Nelson
for helpful discussions. S.P.N. is a Royal Society Wolfson
Research Merit Award holder. Y.O. is supported by the Uehara
Memorial Foundation Research Fellowship.
Cl
(
10) Abbreviations: IPr , 4,5-dichloro-1,3-bis(2,6-diisopropylphenyl)
imidazol-2-ylidene;, IPent , 1,3-bis(2,6-bis(1-ethylpropyl)phenyl)-1,3-
dihydro-2H-imidazol-2-ylidene; IPr*, 1,3-bis(2,6-bis(diphenylmethyl)-
4
-methylphenyl)imidazol-2-ylidene.
(11) Gomez-Suarez, A.; Ramon, R. S.; Slawin, A. M. Z.; Nolan, S. P.
Dalton Trans. 2012, 41, 5461−5463.
́
́
́
1
110
dx.doi.org/10.1021/om301249r | Organometallics 2013, 32, 1106−1111

Organometallics
Article
(
(
12) Trost, B. M. Science 1991, 254, 1417−1477.
13) Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-VCH:
Weinheim, Germany, 2000.
(14) Brenzovich, W. E. Angew. Chem., Int. Ed. 2012, 51, 8933−8935.
(15) Hintermann, L.; Labonne, A. l. Synthesis 2007, 1121−1150.
(16) (a) Mizushima, E.; Sato, K.; Hayashi, T.; Tanaka, M. Angew.
Chem., Int. Ed. 2002, 41, 4563−4565. (b) Roembke, P.; Schmidbaur,
H.; Cronje, S.; Raubenheimer, H. J. Mol. Catal. A: Chem. 2004, 212,
3
2
2
́
5−42. (c) Marion, N.; Ramon, R. S.; Nolan, S. P. J. Am. Chem. Soc.
008, 131, 448−449. (d) Leyva, A.; Corma, A. J. Org. Chem. 2009, 74,
067−2074. (e) Krauter, C. M.; Hashmi, A. S. K.; Pernpointner, M.
ChemCatChem 2010, 2, 1226−1230. (f) Lein, M.; Rudolph, M.;
Hashmi, S. K.; Schwerdtfeger, P. Organometallics 2010, 29, 2206−
2210. (g) Pernpointner, M.; Hashmi, A. S. K. J. Chem. Theory Comput.
2
(
009, 5, 2717−2725.
́
17) (a) Mezailles, N.; Ricard, L.; Gagosz, F. Org. Lett. 2005, 7,
4
4
(
133−4136. (b) Ricard, L.; Gagosz, F. Organometallics 2007, 26,
704−4707.
18) Wang, D.; Cai, R.; Sharma, S.; Jirak, J.; Thummanapelli, S. K.;
Akhmedov, N. G.; Zhang, H.; Liu, X.; Petersen, J. L.; Shi, X. J. Am.
Chem. Soc. 2012, 134, 9012−9019.
(
19) (a) Kukushkin, V. Y.; Pombeiro, A. J. L. Inorg. Chim. Acta 2005,
358, 1−21. (b) Ahmed, T. J.; Knapp, S. M. M.; Tyler, D. R. Coord.
Chem. Rev. 2011, 255, 949−974. (c) The gold-catalyzed alcohol
addition to nitriles can form amides as well: Ibrahim, N.; Hashmi, A. S.
K.; Rominger, F. Adv. Synth. Catal. 2011, 353, 461−468.
(
8
(
20) Ramon
695−8697.
21) Hydrocinnamonitrile, from 30 to 90%, and 4-cyanopyridine,
from 31 to 75%.
22) Swaminathan, S.; Narayanan, K. V. Chem. Rev. 1971, 71, 429−
38.
23) (a) Engel, D. A.; Dudley, G. B. Org. Biomol. Chem. 2009, 7,
149−4158. (b) Cadierno, V.; Crochet, P.; Garcia-Garrido, S. E.;
Gimeno, J. Dalton Trans. 2010, 39, 4015−4031.
24) (a) Engel, D. A.; Dudley, G. B. Org. Lett. 2006, 8, 4027−4029.
b) Lee, S. I.; Baek, J. Y.; Sim, S. H.; Chung, Y. K. Synthesis 2007,
́
, R. S.; Marion, N.; Nolan, S. P. Chem. Eur. J. 2009, 15,
(
4
(
4
(
(
2
0
2
107−2114. (c) Lopez, S. S.; Engel, D. A.; Dudley, G. B. Synlett 2007,
949−0953. (d) Ramon, R. S.; Marion, N.; Nolan, S. P. Tetrahedron
́
009, 65, 1767−1773. (e) Rieder, C. J.; Winberg, K. J.; West, F. G. J.
Org. Chem. 2010, 76, 50−56. (f) Merlini, V.; Gaillard, S.; Porta, A.;
Zanoni, G.; Vidari, G.; Nolan, S. P. Tetrahedron Lett. 2011, 52, 1124−
1127. (g) Pennell, M. N.; Unthank, M. G.; Turner, P.; Sheppard, T. D.
J. Org. Chem. 2011, 76, 1479−1482. (h) Wang, D.; Zhang, Y.; Harris,
A.; Gautam, L. N. S.; Chen, Y.; Shi, X. Adv. Synth. Catal. 2011, 353,
2
584−2588. (i) Pennell, M. N.; Turner, P. G.; Sheppard, T. D. Chem.
Eur. J. 2012, 18, 4748−4758.
25) Reaction conditions: [Au(IPr)][SbF ] (2 mol%, filtered through
(
6
Celite), MeOH/H O (10/1), 60 °C, 4 h.
2
(
26)
(
27) (a) Buzas, A. K.; Istrate, F. M.; Gagosz, F. Org. Lett. 2007, 9,
9
85−988. (b) Marion, N.; Gealageas, R.; Nolan, S. P. Org. Lett. 2007,
9
, 2653−2656. (c) Gourlaouen, C.; Marion, N.; Nolan, S. P.; Maseras,
F. Org. Lett. 2008, 11, 81−84.
(
28) If the reaction was not complete at this stage, the crude product
was disolved in ca. 10 mL of CH Cl and washed twice more with ca.
2
2
3
0 mL of H O.
2
1
111
dx.doi.org/10.1021/om301249r | Organometallics 2013, 32, 1106−1111