[{Au(IPr)}2(μ-OH)]X complexes: Synthetic, structural and catalytic studies

Article abstract of DOI:10.1002/chem.201002607

The synthesis of a series of dinuclear gold hydroxide complexes has been achieved. These complexes of type [{Au(IPr)}₂(Iμ-OH)]X (X=BF ₄, NTf₂, OTf, FABA, SbF₆; IPr=2,6- bis(disopropylphenyl)imidazol-2-ylidene; NTf₂= bis(trifluoromethanesulfonyl)imidate; OTf=trifluoromethanesulfonate; FABA=tetrakis(pentafluorophenyl)borate) are easily formed in the presence of water and prove highly efficient in the catalytic hydration of nitriles. Their facile formation in aqueous media suggests they are of relevance in gold-catalyzed reactions involving water. Additionally, a series of [Au(IPr)(NCR)][BF₄] (R=alkyl, aryl) complexes was synthesized as they possibly occur as intermediates in the catalytic reaction mechanism. ¹H and ¹³C NMR data as well as key bond lengths obtained by X-ray diffraction studies are compared and reveal an interesting structure-activity relationship. The collected data indicate a negligible effect of the nature of the nitrile on the reactivity of [Au(L)(NCR)][X] complexes in catalysis.

Full text of DOI:10.1002/chem.201002607

DOI: 10.1002/chem.201002607
[{AuACHTUNGTRENNUNG(IPr)}2ACHTUNGTRENNUNG(m-OH)]X Complexes: Synthetic, Structural and Catalytic Studies
Rubꢀn S. Ramꢁn,[a] Sylvain Gaillard,[a] Albert Poater,[b, c] Luigi Cavallo,[b]
Alexandra M. Z. Slawin,[a] and Steven P. Nolan*[a]
Abstract: The synthesis of a series of
dinuclear gold hydroxide complexes
has been achieved. These complexes of
ficient in the catalytic hydration of ni-
triles. Their facile formation in aqueous
media suggests they are of relevance in
complexes was synthesized as they pos-
sibly occur as intermediates in the cata-
lytic reaction mechanism. 1H and
13C NMR data as well as key bond
lengths obtained by X-ray diffraction
studies are compared and reveal an
interesting structure–activity relation-
ship. The collected data indicate a neg-
ligible effect of the nature of the nitrile
type [{Au
NTf2, OTf, FABA, SbF6; IPr=2,6-bis-
(disopropylphenyl)imidazol-2-ylidene;
NTf2 =bis(trifluoromethanesulfonyl)-
ACHTUNGTRENNUNGimidate; OTf=trifluoromethanesulfo-
A
N
gold-catalyzed
water. Additionally, a series of [Au-
(IPr)(NCR)][BF4] (R=alkyl, aryl)
reactions
involving
E
A
R
ACHTUNGTRENNUNG
Keywords: gold
·
homogeneous
nate; FABA=tetrakis(pentafluorophe-
nyl)borate) are easily formed in the
presence of water and prove highly ef-
catalysis · hydration · N-heterocy-
clic carbenes · nitriles
on the reactivity of [Au(L)
complexes in catalysis.
ACHTUNGTRENN(UNG NCR)][X]
Introduction
Recently, research into mechanistic aspects of gold cataly-
sis has permitted useful synthetic insights. Isolating reactive
intermediates involved in gold-based catalytic cycles is
highly relevant to the development and evaluation of accu-
rate mechanistic hypotheses.[6] In the course of investiga-
tions on gold-mediated transformations, some of which in-
volved water, computational results suggested the viability
The last decade has witnessed enormous activity in the area
of homogenous gold catalysis allowing for significant devel-
opments in organic synthesis.[1] Earliest catalysts were
simple gold salts such as AuCl3, NaAuCl4, and AuCl. More
sophisticated organogold complexes bearing either phos-
phane or N-heterocyclic carbene (NHC)[2] ligands have
gained popularity in recent years, but still require the use of
a silver activator to enable catalysis.[3,4] The resulting active
species is postulated to be a cationic AuI complex.[4b] The
first such species was isolated and characterized because of
the stabilising effect imparted by the supporting NHC
ligand.[5]
of a [Au
ACHTUNGTREN(NGNU IPr)(OH)] (1; IPr=2,6 bis(disopropylphenyl)imid-
AHCTUNGTRENNUNG
transformations such as the Meyer–Schuster rearrangement
of propargylic alcohols to conjugated enones[7a] and the hy-
dration of nitriles to amides[8] made clear the next synthetic
approach: the synthesis and isolation of 1. This task was un-
dertaken to hopefully permit these transformations in a
more efficient way and with a catalytically more relevant
entity, circumventing the need for silver co-catalysts. It
would also address experimentally the hypothesis of the in-
volvement of 1 as an intermediate in aqueous gold catalysis.
The synthesis and complete characterization of [Au-
[a] R. S. Ramꢀn, Dr. S. Gaillard, Prof. Dr. A. M. Z. Slawin,
Prof. Dr. S. P. Nolan
EaStCHEM School of Chemistry
University of St Andrews, North Haugh
St Andrews, KY16 9ST (UK)
Fax : (+44)01334463808
AHCTUNGTRENNUNG
(IPr)(OH)] (1) was achieved recently.[9] Complex 1 proved
E-mail: snolan@st-andrews.ac.uk
to be an excellent precursor to a plethora of new gold spe-
cies, but exhibited only moderate catalytic efficacy in nitrile
hydration and Meyer–Schuster rearrangement. In the course
of recent NMR studies and upon acid activation of 1, the
[b] Dr. A. Poater, Prof. L. Cavallo
Dipartimento di Chimica, Universitꢁ di Salerno
Via ponte don Melillo, 84084, Fisciano (SA) (Italy)
[c] Dr. A. Poater
Catalan Institute for Water Research (ICRA), H2O Building
Scientific and Technological Park of the University of Girona
Emili Grahit 101, 17003 Girona (Spain)
gold complex [{AuCAHTUGNTREN(NNUG IPr)}2ACHTUNRGTEG(NNUN m-OH)]ACHTNUGRTNEN[UGN BF4] (2) was isolated and
its formation as a function of acid was investigated.[10] En-
couraged by the reactivity of 2 in various gold-catalyzed
transformations in terms of reactivity and stability, a series
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002607.
1238
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Chem. Eur. J. 2011, 17, 1238 – 1246

FULL PAPER
of [{Au
SbF6; NTf2 =bis(trifluoromethanesulfonyl)imidate; OTf=
trifluoromethanesulfonate; FABA=tetrakis(pentafluoro-
ACHTUNGTRENNUNG(IPr)}2ACHTUNGTRENNUNG(m-OH)][X] (X=BF4, NTf2, OTf, FABA, and
phenyl)borate) complexes was synthesized and applied to
the hydration of nitriles in order to evaluate possible
counterACHTUNGTRENNUNGanion effects. The formation of [{AuACHTNUTRGEG(NNUN IPr)}2ACHTNUGTRNE(NUGN m-OH)]
[X] and their stability/reactivity have been further investi-
gated by DFT calculations and deactivation patterns in the
nitrile hydration have been identified.
Results and Discussion
The synthesis of 2 can be achieved using a number of ap-
proaches (Scheme 1) that were revealed upon workup of the
water-insoluble [AuACHTUNGTRENNUNG(IPr)ACHUTNRTEGG(NNUN CH3CN)]ACTHGUNTREN[UNGN BF4] (3). In the initial
synthetic route, stirring 3 in water at 608C for three days, in
air, led to the formation of 2 in high yield.[11] Attempted ex-
traction of 2 from the aqueous mother liquor with CH2Cl2
proved critical, as it re-converted 2 into 3 (see Supporting
Information). However, washing the organic phase with
water led to the isolation of pure 2. A more economical
(and practical) synthetic route[12] is to take advantage of the
versatile synthon [AuACTHNUTRGNE(NUG IPr)(OH)] (1) and its straightforward
reaction with 0.5 equivalents HBF4·OEt2 in benzene at room
temperature for 4 h to produce 3 in 90% isolated yield.[13]
Interestingly, 1 can also function as a precursor to [Au-
ACHTUNGTRENNUNG(IPr)ACHTUNGTRENNUNG(CH3CN)]ACHTUNGTRENNUNG[BF4] (3) under anhydrous conditions and
without the use of costly light- and moisture-sensitive silver
salts. Complex 1 reacts with one equivalent HBF4·OEt2 in
the presence of one equivalent of acetonitrile to afford com-
plete conversion into 3 (Scheme 1).[14] NMR studies on the
acid activation of 1 are consistent with the sensitive equilib-
rium between these gold complexes determined by acid,
water concentration, and the solvent used.[10]
To investigate the effect of the counteranion, a series of
analogue complexes in which X=NTf2 (4), OTf (5), FABA
(6), and SbF6 (7) was synthesized (for the solid state struc-
tures of 5–7, see Figure 1). Of note, 4 has been recently re-
ported and successfully applied in the Meyer–Schuster rear-
rangement.[15] Satisfyingly, all catalysts were obtained in
good to excellent yields by using the synthetic protocol de-
scribed to synthesize 2. However, attempts to synthesize the
PF6 or succinimide analogues gave a mixture of products
Figure 1. X-ray structures of (from left to right) [{Au
ACHUTGTNRNE(NUG IPr)}2HCATUNGTREN(NGUN m-OH)][X]
(X=OTf (5), FABA (6), SbF6 (7)). Selected bond lengths [ꢃ] and angles
ꢀ
ꢀ
ꢀ
ꢀ
[8] for 5: Au1 O1 2.052(3), O1 Au31 2.042(4), Au1 C1 1.972(5), Au31
ꢀ
ꢀ
C31 1.961(5), Au31-O1-Au1 124.18(17), O1 H1O 0.95(2); for 6: Au1 O1
ꢀ
ꢀ
ꢀ
2.040(4), O1 Au31 2.049(4), Au1 C1 1.961(6), Au31 C31 1.951(5),
ꢀ
ꢀ
ꢀ
Au31-O1-Au1 118.5(2), O1 H1O 0.96(2); for 7: Au1 O1 2.026(8), O1
ꢀ
ꢀ
Au31 2.055(8), Au1 C1 1.943(11), Au31 C31 1.957(11), Au31-O1-Au1
ꢀ
127.6(4), O1 H1O 0.9800.
(X=PF6) or a monogold complex (X=succinimide), respec-
tively.
Additionally, DFT calculations were used to shed light on
the energetics of these transformations. Firstly, the binding
Scheme 1. Synthetic routes to [Au
ACHTNUGTERNN(UGN IPr)ACHTUGTNRENNUG(CH3CN)]ACHTUNGERT[GNNUN BF4] 3 and [{AuACHTNUGERTN(NUGN IPr)}2-
G
ACHTUNGTRENNUNG
Chem. Eur. J. 2011, 17, 1238 – 1246
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1239

S. P. Nolan et al.
of nitriles and water to [Au
(IPr)]+ is highly competitive (the
11.5 kcalmolꢀ1 in benzene. Key to the stability of 2 is the
bond dissociation energies (BDE) of MeCN, PhCN, and
H2O in CH2Cl2 are 31.0, 30.8 and 31.0 kcalmolꢀ1, respective-
ly). This suggests that in aqueous solution, the large excess
of water present should completely displace the nitrile in 3.
Secondly, the 1!3 transformation in Scheme 1 is favored by
14.7 kcalmolꢀ1 in benzene. Thirdly, the 1!2 transformation
in Scheme 1 is favored by 16.7 kcalmolꢀ1 in benzene.
DFT calculations were also carried out on the structure
and nature of 2. The optimized computationally obtained
structure of 2[16] is in good agreement with its X-ray struc-
ture.[10] Focusing on a comparison between the DFT struc-
weak coordinating ability of [BF4]ꢀ in benzene, the BDE of
ꢀ
BF4 to [Au
(IPr)]+ is 81.5 kcalmolꢀ1 lower than that of
OHꢀ. Furthermore, the stability of 2 towards water was ex-
amined. Aqueous dissociation of a Au fragment in 2 to 1+
[Au
contrast, proton transfer from 2 to a water molecule to give
(OH2)]+ +[BF4]ꢀ is favored by 1.0 kcalmolꢀ1. In
ACHUTGTNRENNUG(IPr)ACHTUTGNRENNUGN
(m-O)]+H3O+, is energetically disfavored by
[{AuACTHNUTRGENN(UG IPr)}2ACHTUNGTRENNUGN
47.0 kcalmolꢀ1, indicating that the weak links in 2 are the
ꢀ
Au O bonds.
The ease with which these transformations can be accom-
plished, and the calculated DFT energetic are suggestive of
ꢀ
tures of 1 and 2, the Au O bond is slightly shorter in 1 (by
an equilibrium between [Au
ACHTUNGTREN(UGNN IPr)ACHTUNRTGEN(GNUN CH3CN)]ACHTUNGTERN[NUGN BF4] and [{Au-
ꢀ
0.08 ꢃ), whereas the O H bond does not significantly vary
A
N
ACHTUNGTRENNUNG
(0.002 ꢃ longer in 1). These essentially unaltered distances
suggest a similar bonding scheme is present in 1 and 2. How-
ever, Mayer bond order (MBO)[17] within natural population
analysis (NPA)[18] indicates remarkable changes. The MBO
of the Au O bonds in 2 (0.60) is almost half that found in 1
(1.16). In contrast, the MBO of the O H bond is slightly re-
duced, from 0.92 in 1 to 0.86 in 2. This indicates that dimer
formation principally affects the Au O bond rather than the
O H bond. Furthermore, a non-negligible MBO (0.14) is
present between the Au centers, indicative of an interaction
implicates the direct involvement of a species such as 2 in
catalysis involving water and cationic gold entities.[19]
With the series of catalysts in hand, their activity was
tested in the hydration of nitriles. Recent investigations
(NTf2)][4a] (8) to be the most effec-
have determined [AuACTHNGUTRENNU(G IPr)ACTHUNGTRENNNUG
ꢀ
ꢀ
tive Au catalyst under optimized conditions (microwave
heating).[8a,20] To adequately follow the reaction, the catalyst
loading was lowered to 1 mol% gold and conversions were
monitored by GC. Results of other relevant gold catalysts as
well as in situ activated catalysts have been added to com-
plete the screening (Table 1). No significant difference be-
ꢀ
ꢀ
between the two [Au
ACHTUNGTRENNUNG
dicates that donation occurs from each [Au
N
tween the [{AuACTHUNGTERNNU(G IPr)}2ACHTUGNTREN(NUGN m-OH)][X] catalysts was observed.
into an empty acceptor pz MO on the other Au center (one
of the interactions is illustrated in Figure 2). An estimate of
With the exception of 8, which showed slightly poorer cata-
lytic performance, and 1, which afforded poor overall
yields,[21] all catalysts showed comparable catalytic activity.[22]
Using 10% HBF4·OEt2 in the absence of gold led to no con-
version, even after 3 h. It is of interest that [AuACHTUNGTRENNUNG(IPr)-
ACHUTNGRENU(NG CH3CN)]ACHUTGNTREN[NUGN BF4] (3) displays higher activity than 8, as this is
in contrast to the current results in nitrile hydration.[23] It
was reasoned that under the reaction conditions (THF/H2O
1:1), [{Au
to outperform 8. The better coordinating NTf2 ligand pre-
vents the conversion of 8 to the corresponding [{Au(IPr)}2-
(m-OH)][NTf2] (4) at ambient temperature.
ACHTUGNTERN(UNGN IPr)}2ACHTUNREGTG(NNUN m-OH)]ACHTNUGTNER[NUNG BF4] (2) easily forms in situ from 3
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
Figure 2. Schematic representation of the (IPr)Au··Au interactions and of
the molecular orbitals involved.
Table 1. Conversions [%] of various gold systems in the hydration of nitrile.
this donor–acceptor interaction
energy, in the framework of
second-order
perturbation
theory, E(2), amounts to
8.7 kcalmolꢀ1. This bimetallic
cooperativity, together with the
short Au···Au distance derived
from the X-ray structure, indi-
cates an intriguing deviation
from the classical isolobal anal-
ogy between Au+ and H3O+.
The stability of 2 towards
various dissociation pathways
was examined next. Possible
Catalyst
Conv
(0.25 h)
Conv
(0.5 h)
Conv
(0.75 h)
Conv
(1 h)
Conv
(2 h)
Conv
(3 h)
N
G
E
G
G
ACHTUNGTRENNUNG
[{(Au
[{(Au
[{(Au
[{(Au
[{(Au
N
2A
2A(m -OH)]
2A(m -OH)]
2A(m -OH)]
2A(m -OH)]
(IPr)] 1 + 0.5 HBF4
(IPr)] 1 + 1.5 HBF4
(CH3CN)][BF4] 3
(NTf2)(IPr)] 8
(IPr)] 1
G
37
37
37
39
38
31
36
39
19
9
44
48
51
52
53
43
50
51
28
10
0
54
57
62
61
60
52
59
62
44
12
0
61
62
70
71
68
59
66
71
58
12
0
79
80
87
85
83
75
84
83
74
12
0
89
88
93
94
90
84
91
91
87
17
0
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
R
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
[Au(OH)
[Au(OH)AHCUTNGTRENNUNG
ACHTUNGTRENNUNG
[Au
[Au
N
E
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
[Au(OH)
HBF4
ACHTUNGTRENNUNG
0
dissociation of
(IPr)]
2 to 1+[Au-
A
R
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Chem. Eur. J. 2011, 17, 1238 – 1246

Gold Catalysis
FULL PAPER
To support this hypothesis, the proposed equilibrium be-
tween complexes 3 and 2 in aqueous reaction media was ex-
amined.
When 3 is dissolved in CH2Cl2 and the resulting solution
simply washed with water (3 times), 2 is formed in 96%
yield. Since this reaction appears facile, the formation of 2
from [AuCl
ACHTUNGTRENNUNG
with AgBF4 generates the putative [Au
N
CHTUNGTRENNUNG
and after removal of AgCl by filtration through Celite the
organic phase was washed three times with water, in a simi-
lar manner as above. Recrystallization from CH2Cl2/pentane
afforded 2 in 81% yield. The rapid and straightforward for-
mation of 2 in aqueous media and similar conversion rates
in nitrile hydration strongly support the conclusion that 2 is
an important gold species in reactions containing water. To
further support this hypothesis, [AuClACTHNUTRGNEUNG(IPr)] was dissolved in
CD2Cl2 and activated with AgBF4. After separating the pre-
cipitated AgCl, D2O (50 mL) was added to the solution and
1
a H NMR sprectrum of the resulting solution was recorded.
[{Au
dition of D2O. The remaining 25% appeared to be “bare”
[Au(IPr)]
+A[BF4]ꢀ. Additionally, we simulated reaction con-
ACHTUNGTRENNUNG(IPr)}2ACHTUNGTRENNUNG(m-OD)]ACHTUNGTRENNUNG[BF4] was formed in 75% yield upon ad-
A
CHTUNGTRENNUNG
1
ditions in a H NMR experiment using [D8]THF/D2O, con-
firming the formation of significant amounts of complex 2.
1
Interestingly, repeating the H NMR experiment in coordi-
nating [D6]DMSO yielded the [D6]DMSO complex quanti-
tatively. The structure of the analogue [AuACHTUGNRTNEN(NUG IPr)AHCTUNRTGE(GNNUN dmso)]ACTHNUGTRENN[GUN BF4]
(9) was confirmed by X-ray diffraction (see Figure 3). While
these observations are not direct evidence for the active in-
volvement of 2 in the catalytic cycle, it strongly suggests that
2 might be a relevant catalytic resting state in aqueous
media. Furthermore, the excellent reactivity of [{Au
ACHTUNGTNER(NUNG IPr)}2-
A
ACHTUNGTRENNUNG
mediate, rather stating that this species might have a catalyt-
ically more active role appears more appropriate.
With the formation of 2 excluded as a deactivation route,
possible alternatives were considered. Referring to the dra-
matically decreased reaction rate with increasing product
formation, amido complexes have been considered as cul-
prites. In a first approach, a 1:1 reaction of 4 and acetonitrile
was conducted at 1008C for 5 h in order to recover the cata-
1
lyst at the end of the reaction. The corresponding H NMR
showed the formation of acetic acid and signals for two dif-
ferent and unknown [Au
ACHTUNGTRENNUNG
vealed the formation of [{Au
N
N
ACHTUNGTRENNUNG
For metal-catalyzed nitrile hydration, the unusual formation
of carboxylic acid is rationalized by the stoichiometric
amount of catalyst used. However, the formation of 10
strongly suggested to us the need to synthesize the amido
Figure 3. X-ray structures of ( from left to right) [Au
G
E
ACHTUNGTRENNUNG[BF4]
(9), [Au(NHCOPh)(IPr)] (11), and [{Au(IPr)}2A(PhCONH)]
A
R
G
U
ACHTUNGTRENNUNG
ꢀ
ꢀ
lected bond lengths [ꢃ] and angles [8] for 9: Au1 C1 1.951(4), Au1 O31
complexes [AuACHTUNGTRENNUNG(IPr)ACHTUNTREG(NGNUN NHCOPh)] (11) and [{AuACHTNGURTEN(UNNG IPr)}2-
ꢀ
2.057(3), O31 S31 1.536(3), C1-Au1-O31 174.66(15), S31-O31-Au1
A
ACHTUNGTRENNUNG
ꢀ
ꢀ
ꢀ
122.56(17); for 11: Au1 C1 1.973(11), Au1 N30 2.015(10), N30 H30N
0.97(2), C1-Au1-N30 174.4(4), C31-N30-Au1 132.8(9), C31-N30-H30N
metric amounts yielded 11 in 70% yield, as a 3:1 mixture of
isomers. Under standard reaction conditions, 11 displayed
very poor conversions in nitrile hydration, thus explaining
the low reactivity of 1. The most evident synthetic approach
ꢀ
130(6), Au1-N30-H30N 97(6), O31-C31-N30 125.1(12); for 12: Au1 C1
ꢀ
ꢀ
1.983(7), Au1 N31 2.030(6), N31 H31N 0.97(2), Au41 C41 1.965(7),
ꢀ
O31 Au41 2.023(5), C1-Au1-N31 176.7(2), C31-N31-Au1 130.7(5), C31-
N31-H31N 91(6), Au1-N31-H31N 138(7), O31-C31-N31 125.0(6), C41-
Au41-O31 176.1(2), C31-O31-Au41 125.0(4).
to 12, namely the reaction of [{Au
ACHTUNGRTEN(NUNG IPr)}2ACHTUNRTGEN(GNUN m-OH)]ACTHUNGTREN[NUGN BF4] with
benzamide, led to the desired complex 12 in 81% yield.
Chem. Eur. J. 2011, 17, 1238 – 1246
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1241

S. P. Nolan et al.
Table 2. Scope of nitrile hydration using [{(Au
and [Au(NTf2)
(IPr)] (8).[8a]
ACHTUNGRTEN(NUNG IPr)}2ACHTUNRTGEN(GNUN m-OH)]ACHTUNGTRENNUNG[BF4] (2)
Interestingly, X-ray crystallographic studies on 11 and 12
revealed that the spatial location of the amido proton is sig-
nificantly influenced by the gold centers (Figure 3). In 11,
the C31-N30-H30N angle is 1308 and Au1-N30-H30N is 978,
whereas in 12 a strong orientation of the proton towards the
oxo-coordinating gold center is observed (C31-N31-H31N,
918, Au1-N31-H31N, 1388). Application of 12 in nitrile hy-
dration as well as the addition of one equivalent of p-chloro-
benzamide to a standard reaction using catalyst 2 resulted in
very poor conversions. It appears plausible that the amide
product poisons the reaction by trapping the active catalyst,
resulting in a decreased reaction rate with progressing con-
version. This fact appears to limit catalyst loadings to
amounts above 1 mol% Au. Moreover, neither structure 11
or 12 can possibly act as an intermediate in the catalytic
cycle. If so, a drop of reactivity should be noted after the
very first cycle, but this is not the observed. In addition to
acting in a deactivation manner, the formation of 12 from 2
presents another interesting aspect. While catalytic results
does not correspond well with typical mechanistic ap-
proaches involving a metal hydroxide acting as a nucleo-
phile,[24] it represents a rare example of a catalyst with dual
G
ACHTUNGTRENNUNG
Substrate
Product
Conv [%]
Conv [%]
with 8
with 2
1
2
98
97
99
82
3
4
94
76
100
100
5
6
90[a]
75[c]
30[b]
31[d]
reactivity. On the one hand, there is the [Au
moiety acting as a base and deprotonating the amide, while
the [Au(IPr)][BF4] moiety coordinates through the oxygen
ACHTUNGTRENUN(NG IPr)(OH)]
A
ACHTUNGTRENNUNG
atom. This is in fairly good agreement with a proposal by
Toste et al. that deals with an equilibrium of tris[phosphine-
gold(I)]oxonium in the presence of allenynes in cycloisom-
[a] 2.5 mol% 2 [b] 5 mol% 8 [c] 2.5 mol% 2, 6 h [d] 5 mol% 8, 6 h.
A
after 6 h, while using 5 mol% 8 only led to a low 31% con-
version.
ACHTUNGTRENNUNGactions of digold complexes with amides would explain the
observed formation of complex 12 (Scheme 2, I–III).
The nature of the substituents on a nitrile substrate, next
to the nature of the metal center, influences the reactivity of
the nitrile in hydrolysis.[26] Electron-acceptor groups improve
the hydration on metal-bound nitriles.[27] This trend was also
recognized for the gold catalysts.[8a] The synthesis of gold
catalysts bearing nitrile ligands is well-known.[4c,5a,c] As these
complexes can be considered intermediates in the hydration
of nitrile mechanistic cycle, a series of ten representative
The excellent catalytic activity of 2 having been con-
firmed, a narrow reaction scope was examined with repre-
sentative nitrile substrates. As shown in Table 2, good to ex-
cellent conversions were obtained for all substrates tested.
Substrates that gave good conversions with 8 resulted in
nearly quantitative conversion with 3 (Table 2, entries 1-4).
Furthermore, substrates that proved problematic in re-
A
[AuACTHNGUTRENNU(G IPr)ACHTUGNTREN(NNUG NCR)][X] complexes was synthesized in order to
cacy of 3. Using 3-phenylpropanenitrile, the corresponding
amide (Table 2, entry 5) was obtained in excellent conver-
sion (90%) compared to the previously obtained 30% when
8 was used. Moreover, with 2.5 mol% 2, isonicotinonitrile
(Table 2, entry 6) afforded 75% yield of the desired amide
possibly correlate the reactivity of the nitrile with relevant
1H and 13C NMR shifts and bond length data obtained by X-
ray diffraction (Table 3).
Of note, several attempts to synthesize benzonitrile com-
plexes bearing strong electron-withdrawing substituents,
such as NO2, with the devloped procedures remained unsuc-
cessful. As shown in Table 3, benzonitrile ligands bearing
electron-donating substituents tend to lead to a slight down-
field shift of the carbenic carbon resonance. The proton shift
on the imidazolylidene backbone appears too minor for an
adequate interpretation. By analogy, a comparison of the
ꢀ
ꢁ
Au N and N C bond lengths confirmed the lack of signifi-
cant effects of the nitrile substituents. In the case of 21 and
22, X-ray diffraction revealed, as expected, a preferred coor-
dination of the gold center to the pyridine moiety[28] involv-
ing a decreased reactivity of those heterocycles in nitrile hy-
Scheme 2. Analogy for a proposal of Toste et al. for an equilibrium of
ꢀ
dration. Interestingly, the Au N distance is higher than in
the complexes coordinating through a nitrile. The decrease
tris
ACHTUNGTRENNUNG[phosphinegold(I)]oxonium in the presence of allenynes in cycloiso-
merization with complexes 2, 4–7 with amides.
1242
www.chemeurj.org
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 1238 – 1246

Gold Catalysis
FULL PAPER
Table 3. Characteristic shifts and bond distances of complexes 13–22.
the use of gold halide com-
plexes requiring a silver-based
halide abstractor.
ꢀ
ꢁ
[Au
(IPr)(R)]
E
d (Ccarbene
G
)
d (Hbackbone
[ppm]
)
Au N
[ꢃ]
N
[ꢃ]
U
1
2
3
4
5
6
7
8
9
R=NCPh
R=NCC6H4CH3
R=NCC6H4N(CH3)2
R=NCC6H4OCH3
R=NCC6H3A(CH3)2
R=NCPhBr
R=NCC6H4A(COCH3)
R=NCC(CH3)3
13
14
15
16
17
18
19
20
21
22
165.5
165.6
166.4
166.1
165.4
165.6
165.3
165.3
166.0
166.2
7.48
7.51
7.49
7.48
7.57[b]
7.46
7.46
7.47
7.43
7.42
2.018(7)[a]
2.011(4)[a]
2.04(2)
2.013(5)
2.014(10)
2.015(3)
n.d.[c]
2.023(7)
2.064(3)[d]
2.056(5)[d]
1.141(10)[a]
1.136(5)[a]
1.15(3)
1.146(7)
1.147(14)
1.143(4)
n.d.[c]
1.136(10)
1.136(5)[d]
1.142(8)[d]
ACHTUNGTRENNUNG
Experimental Section
CHTUNGTRENNUNG
If not otherwise stated, manipulations
were performed under air. Solvents
were of puriss grade and used as re-
ceived. NMR spectra were collected
on 400 MHz and 300 MHz spectrome-
ters at ambient temperature in CDCl3.
Chemical shifts are given in parts per
million (ppm) with respect to TMS.
Chemical shifts of 19F spectra are
given in parts per million (ppm) with
respect to CFCl3.
CHTUNGTRENNUNG
G
R=2-cyanopyridine
R=4-cyanopyridine
10
[a] Bond length determined from one out two independent molecules. [b] Shift determined out of a multiplet.
[c] Attempts to grow crystals remained unsuccessful. [d] 2- and 4-cyanopyridine are coordinated to the gold
center through the pyridine moiety.
Synthesis of [{AuACTHUNGTRNE(NNUG IPr)}2ACHTUNRTGE(NGNUN m-OH)]CAHTNUGTNER[NUGN BF4] (3)
in reactivity is smaller for 2-cyanopyridine as the nitrile
moiety is in direct proximity to the coordinated gold center,
while in the case of 4-cyanopyridine the gold center is
simply too remotely located. From a catalytic point of view,
the choice of the nitrile ligand does not significantly influ-
ence catalytic reaction yields.[29] Therefore, other aspects,
such as nitrile economic costs, toxicity, ease of preparation,
and complex stability, should be key considerations in the
Route A: Complex 2 (2.0 g, 2.80 mmol) was suspended in water (3 mL,
167 mmol) and stirred at 608C for 72 h in air. The reaction mixture was
extracted with CH2Cl2 and the organic phase was washed four times with
a large excess of water (20 mL) and dried over MgSO4. The mixture was
filtered and the volatiles were evaporated under reduced pressure. The
resulting white crude product was recrystallized from CH2Cl2/pentane to
give 1.71 g (96%) of a white microcrystalline solid.
Route B: Complex 1 (97 mg, 0.160 mmol) was dissolved in benzene
(2 mL) and tetrafluoroboric acid/diethyl ether complex (11.0 mL,
0.080 mmol) was added by syringe. The reaction mixture was stirred 4 h
at room temperature. Pentane was added to the reaction to precipitate
the product as a white solid. The crude white product was recrystallized
from CH2Cl2/pentane to give 92 mg (90%) of a white microcrystalline
solid. 1H NMR (400 MHz, CDCl3): d=7.50 (t, J=7.8 Hz, 4H), 7.26 (s,
4H), 7.24 (d, J=7.8 Hz, 8H), 2.39 (sept, J=6.9 Hz, 8H), 1.19 (d, J=
6.9 Hz, 24H), 1.11 ppm (d, J=6.9 Hz, 24H).13C NMR (75 MHz, CDCl3):
d=162.6, 145.4, 133.6, 130.7, 124.2, 124.1, 28.6, 24.4, 23.8 ppm; 19F NMR
(185 MHz, CDCl3): d=ꢀ154.90, ꢀ154.85 ppm; elemental analysis calcd
(%): C 50.87, H 5.77, N 4.39; found: C 51.06, H 5.27, N 4.36.
preparation of [Au(L)ACTHNUTRGNEUGN(NCR)][X] complexes.
Conclusion
The high-yield synthesis of a dinuclear gold complex 2 has
been achieved and this species has demonstrated high cata-
lyst efficiency in the hydration of nitriles and also permitted
an expansion of the reaction scope. Advantageously, this
simple synthetic protocol makes use of the readily available
synthon 1. Using the air- and moisture stable 1, a highly
active catalytic species can be generated in situ and this
methodology has proven exceedingly effective in the hydra-
tion of nitriles. The facile formation of 2 and 3 from 1 sug-
gests a broader potential role of 1 and 2 as “pre-catalytic”
species in gold-mediated transformations. Formation of 2
Synthesis of [(AuACHTNUGRTNE(NNUG IPr)ACHTUNREGT(NGNUN CH3CN)]ACHTGUNTREN[NGUN BF4] (2) from 1: Complex 1 (100 mg,
0.166 mmol) was dissolved in toluene (2 mL) and tetrafluoroboric acid/di-
ethyl ether complex (0.023 mL, 0.166 mmol) was added by syringe. Then,
acetonitrile (8.67 mL, 0.166 mmol) was added and the heterogeneous re-
action mixture was stirred 2 h at room temperature. Pentane was added
to precipitate 114 mg (96%) of a white microcrystalline solid the NMR
data of which confirms the synthesis of 2. 1H NMR (400 MHz, CDCl3):
d=7.58 (t, J=7.8 Hz, 2H), 7.38 (s, 2H), 7.34 (d, J=7.8 Hz, 4H), 2.44
(sept, J=6.9 Hz, 4H), 2.39 (s, 3H), 1.29 (d, J=6.9 Hz, 12H), 1.24 ppm
(d, J=6.9 Hz, 12H); 13C NMR (100 MHz, CDCl3): d=166.3, 145.5, 133.0,
131.5, 124.8, 124.6, 121.0, 28.9, 24.7, 24.0, 2.7 ppm; 19F NMR (185 MHz,
CDCl3): d=ꢀ154.98, ꢀ153.92 ppm.
from 3 and [AuClACHTUNGTRENNUNG(IPr)]/ACHUTNGTREN[NUGN AgBF4] by simple addition of water
strongly suggests 2 to be a reactive intermediate or relevant
resting state in water-inclusive reactions. Mono- and di-gold
complexes of benzamide have been isolated and proved in-
Synthesis of [{AuCAHTUNGRTNE(NNUG IPr)}2ACHTUNTRGEGN(NNU m-OH)]ACHTNGUERTN[NUGN NTf2] (4): Trifluoromethanesulfonimide
(73 mg, 0.260 mmol) was dissolved under N2 in anhydrous toluene (2 mL)
and complex 1 (313 mg, 0.519 mmol) was added. The reaction mixture
was stirred overnight at room temperature. Pentane (10 mL) was added
to the reaction to ensure complete precipitation of the product. The
white solid was collected by filtration, washed with pentane (2ꢄ5 mL)
and dried under vacuum to give 381 mg (100%) of a white microcrystal-
line solid. 1H NMR (300 MHz, CDCl3): d=7.49 (t, J=7.8 Hz, 4H), 7.26–
7.20 (m, 12H), 2.37 (sept, J=6.8 Hz, 8H), 1.17 (d, J=6.8 Hz, 24H),
1.11 ppm (d, J=6.8 Hz, 24H); 13C NMR (100 MHz, CDCl3): d=162.9,
145.6, 133.7, 130.9, 124.3, 124.2, 120.1 (q, J=321.7 Hz), 28.8, 24.6,
23.9 ppm; 19F NMR (282 MHz, CDCl3): d=ꢀ79.2 ppm; elemental analy-
sis calcd (%): C 45.81, H 5.01, N 4.77; found: C 45.78, H 4.92, N 4.57.
effective in nitrile hydration. Finally, a series of [Au
ACHTUNGTRNE(NUNG IPr)-
A
ACHTUNGTRENNUNG
ine mechanistic arguments presented in the literature in the
context of diverse reactivities involving nitrile substrates.
data, as well as comparison of bond lengths obtained from
X-ray diffraction studies do not clearly indicate any trend as
to the optimum ligand to use; all appear equally competent.
Reactivity involving heterocyclic nitriles such as cyanopyri-
dines is clearly influenced by the coordination of the aro-
matic heteroatom to the gold center.
Synthesis of [{AuACHTUNGERTN(NNUG IPr)}2ACHTUNRTGEGUNN(N m-OH)]ACTHNUGTREN[NGUN OTf] (5): Triflic acid (5.5 mL,
0.06 mmol) was added to anhydrous toluene (2 mL) and complex 1
(75 mg, 125 mmol) was added. The reaction mixture was stirred overnight
The simple use of a gold complex in conjunction with a
protic acidic activator represents an attractive alternative to
Chem. Eur. J. 2011, 17, 1238 – 1246
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1243

S. P. Nolan et al.
at room temperature. Pentane (2 mL) was added to the reaction to
ensure complete precipitation of the product. The white solid was collect-
ed by filtration, washed with pentane (2ꢄ5 mL) and dried under vacuum
Synthesis of [AuACHTUNTGERG(NUNN IPr)ACHTUNRTGEGN(NNU NCPh)]CAHTNUGTRENUN[NG BF4] (13): 48 wt% aqueous BF4 (22 mL,
0.17 mmol) was added to a dispersion of complex 1 (100 mg, 0.17 mmol)
and benzonitrile (24 mL, 0.18 mmol) in toluene (2 mL). The reaction mix-
ture was stirred overnight at room temperature. Pentane (2 mL) was
added to the reaction to ensure complete precipitation of the product.
The white solid was collected by filtration, washed with pentane (2ꢄ
5 mL), and dried under vacuum to give 123 mg (96%) of a white micro-
crystalline solid. 1H NMR (400 MHz, CDCl3): d=7.86–7.74 (m, 3H),
7.66–7.55 (m, 4H), 7.48 (s, 2H), 7.37 (d, J=7.7 Hz, 4H), 2.50 (sept, J=
6.9 Hz, 4H), 1.33 (d, J=6.9 Hz, 12H), 1.27 ppm (d, J=6.9 Hz, 12H);
13C NMR (101 MHz, CDCl3): d=165.5, 145.8, 136.8, 133.8, 133.2, 131.4,
130.2, 125.4, 124.7, 119.8, 106.4, 29.0, 24.9, 24.1 ppm; 19F NMR (376 MHz,
to give 71 mg (85%) of
a
white microcrystalline solid. 1H NMR
(400 MHz, CDCl3): d=7.50 (t, J=7.9 Hz, 4H), 7.25 (s, 4H), 7.24 (d, J=
7.9 Hz, 8H), 2.39 (sept, J=6.9 Hz, 8H), 1.19 (d, J=6.9 Hz, 24H),
1.12 ppm (d, J=6.9 Hz, 24H); 13C NMR (101 MHz, CDCl3): d=162.8,
145.4, 133.6, 130.7, 124.2, 124.1, 28.7, 24.5, 23.9 ppm; 19F NMR (376 MHz,
CDCl3): d=ꢀ78.6 ppm; elemental analysis calcd (%): C 49.40, H 5.50, N
4.19; found: C 49.95, H 5.88, N 3.91.
Synthesis of [{AuACHTUNGTRENNUNG(IPr)}2ACHTUNGTRENNUNG(m-OH)]ACHTNUGERTN[NUGN FABA] (6): N,N -dimethylanilinium tet-
rakis(pentafluorophenyl)borate (DAN FABA) (33 mg, 0.04 mmol) was
dissolved in anhydrous toluene (2 mL) and complex 1 (50 mg, 0.08 mmol)
was added. The reaction mixture was stirred overnight at room tempera-
ture. Pentane (2 mL) was added to the reaction to ensure complete pre-
cipitation of the product. The white solid was collected by filtration,
washed with pentane (2ꢄ5 mL) and dried under vacuum to give 73 mg
CDCl3): d=ꢀ154.64, ꢀ154.69 ppm; elemental analysis calcd (%):
C
52.66, H 5.33, N 5.42; found: 51.77, H 5.22, N 5.32.
Synthesis of [AuACHTNUGTRENN(GU IPr)(NCC6H4CH3)]AHCUTNGTRNE[NUGN BF4] (14): AgBF4 (31 mg,
0.16 mmol) was placed under argon in a Schlenk tube wrapped with alu-
mina foil. CH2Cl2 (4 mL) was added followed by 4-toluonitrile (19 mg,
1
0.16 mmol). Then, [AuClACTHNUTRGNE(NUG IPr)] (100 mg, 0.16 mmol) was added and the
(94%) of a white microcrystalline solid. H NMR (300 MHz, CDCl3): d=
reaction mixture was stirred 30 min at RT. CH2Cl2 (5 mL) was added and
the reaction mixture was filtered over a plug of silica. Volatile com-
pounds were removed under reduced pressure to yield a colorless oil. Re-
crystallization with CH2Cl2/pentane and addition of some ether yielded a
colorless solid (62 mg, 49%). 1H NMR (400 MHz, CDCl3): d=7.67 (d,
J=8.2 Hz, 2H), 7.60 (t, J=7.9 Hz, 2H), 7.51 (s, 2H), 7.43–7.33 (m, 6H),
2.51 (sept, J=6.9 Hz, 4H), 2.45 (s, 3H), 1.33 (d, J=6.8 Hz, 12H),
1.27 ppm (d, J=6.8 Hz, 12H); 13C NMR (101 MHz, CDCl3): d=165.6,
148.7, 145.7, 133.7, 133.3, 131.4, 130.9, 125.5, 124.6, 120.4, 103.0, 28.9,
24.9, 24.1, 22.4 ppm; 19F NMR (376 MHz, CDCl3): d=ꢀ154.66.
ꢀ154.73 ppm; elemental analysis calcd (%): C 52.19, H 5.38, N 5.22;
found: C 52.63, H 5.08, N 6.12.
7.49 (t, J=7.8 Hz, 4H), 7.24 (d, J=7.8 Hz, 8H), 7.14 (s, 4H), 2.37 (sept,
J=6.8 Hz, 8H), 1.17 ppm (d, J=6.9 Hz, 24H), 1.11 (d, J=6.9 Hz, 24H);
13C NMR (101 MHz, CDCl3): d=163.3, 145.4, 133.5, 130.9, 124.3, 123.8,
28.7, 24.4, 23.8 ppm; 19F NMR (282 MHz, CDCl3): d=ꢀ133.06, ꢀ163.95,
ꢀ167.54 ppm; elemental analysis calcd (%): C 50.17, H 3.94, N 3.00;
found: C 50.25, H 4.10, N 3.01.
Synthesis of [{AuACHTUNGTRENNUNG(IPr)}2ACHTUNRTGENN(GUN m-OH)]CAHTNUGTERNN[UNG SbF6] (7): 65 wt% aqueous HSbF6
(31 mg, 85 mmol) was added to toluene (2 mL) and complex 1 (103 mg,
170 mmol) was added. The reaction mixture was stirred overnight at
room temperature. Pentane (2 mL) was added to the reaction to ensure
complete precipitation of the product. The white solid was collected by
filtration, washed with pentane (2ꢄ5 mL) and dried under vacuum to
Synthesis of [AuCATHUGNRETNU(NNG IPr)ACHTUNGTRNENG{U NCC6H4NACHNUTGRETNN(GNU CH3)2}]CAHTNUGTREN[NUGN BF4] (15): AgBF4 (125 mg,
0.64 mmol) was placed under argon in a Schlenk tube wrapped with alu-
mina foil. CH2Cl2 (14 mL) was added followed by 4-dimethylaminoben-
1
give 101 mg (83%) of a white microcrystalline solid. H NMR (300 MHz,
CDCl3): d=7.50 (t, J=7.8 Hz, 4H), 7.24 (d, J=7.8 Hz, 8H), 7.22 (s, 4H),
2.39 (sept, J=6.8 Hz, 8H), 1.19 (d, J=6.8 Hz, 24H), 1.11 ppm (d, J=
6.8 Hz, 24H); 13C NMR (101 MHz, CDCl3): d=162.6, 145.5, 133.6, 130.7,
124.2, 124.1, 28.6, 24.4, 23.8 ppm; elemental analysis calcd (%): C 45.55,
H 5.17, N 3.40; found: C 45.49, H 5.18, N 3.40.
zonitrile (94 mg, 0.64 mmol). Then, [AuClACTHNUTRGNEU(GN IPr)] (400 mg, 0.64 mmol) was
added and the reaction mixture was stirred 30 min at RT. CH2Cl2
(10 mL) was added and the reaction mixture was filtered over a plug of
silica. Volatile compounds were removed under reduced pressure to yield
a colorless oil. Recrystallization with CH2Cl2/pentane and addition of
some ether yielded a colorless solid (179 mg, 34%). 1H NMR (400 MHz,
CDCl3): d=7.57 (t, J=7.9 Hz, 2H), 7.49 (s, 2H), 7.44 (d, J=9.2 Hz, 2H),
7.34 (d, J=7.9 Hz, 4H), 6.64 (d, J=9.2 Hz, 2H), 3.06 (s, 6H), 2.49 (sept,
J=6.8 Hz, 4H), 1.30 (d, J=6.8 Hz, 12H), 1.25 ppm (d, J=6.8 Hz, 12H);
13C NMR (101 MHz, CDCl3): d=166.4, 154.5, 145.7, 134.9, 133.4, 131.3,
125.3, 124.6, 123.9, 111.9, 88.2, 40.0, 28.9, 24.8, 24.0 ppm; 19F NMR
(376 MHz, CDCl3): d=ꢀ154.67, 154.73 ppm; elemental analysis calcd
(%): C 52.88, H 5.66, N 6.84; found: C 53.65, H 5.89, N 6.28.
Synthesis of [AuACHTUNGTRENNUNG(IPr)ACHTUNGTRENNUNG(dmso)]AHCUNTGTREGN[NNU BF4] (9): In a NMR tube complex 2
(20 mg, 0.028 mmol) was diluted in DMSO (500 mL). NMR spectroscopy
showed immediate full conversion. Volatile compounds were separated
under low pressure to obtain colorless microcrystalline solid in quantita-
tive yield (21 mg, 99%). 1H NMR (400 MHz, [D6]DMSO): d=7.95 (s,
2H), 7.58 (t, J=7.9 Hz, 2H), 7.41 (d, J=7.9 Hz, 4H), 2.39 (sept, J=
6.8 Hz, 4H), 1.22 (d, J=6.8 Hz, 12H), 1.17 ppm (d, J=6.8 Hz, 12H);
13C NMR (101 MHz, [D6]DMSO): d=160.9, 145.3, 133.5, 130.9, 125.4,
124.3, 28.4, 24.0, 23.6 ppm; 19F NMR (376 MHz, [D6]DMSO): d=
ꢀ148.63, ꢀ148.68 ppm; elemental analysis calcd (%): C 46.04, H 5.64, N
3.70; found: C 45.71, H 5.50, N 3.53.
Synthesis of [AuACHTNUGTRENN(GU IPr)(NCC6H4OCH3)]CAHTUNGTRNEN[UGN BF4] (16): AgBF4 (25 mg,
0.13 mmol) was placed under argon in a Schlenk tube wrapped with alu-
mina foil. CH2Cl2 (4 mL) was added followed by anisonitrile (17 mg,
Synthesis of [AuACHTUNGTRENNUNG(IPr)ACHTUNGTRENNUNG(NHCOPh)] (11): Complex 1 (50 mg, 0,083 mmol)
was dispersed in toluene (2 mL) and benzamide (10 mg, 0,083 mmol) was
added. The reaction mixture was stirred overnight at RT. Then, pentane
(2 mL) was added and precipitate was collected by filtration, washed
with pentane (3ꢄ5 mL), and dried under reduced pressure to obtain a
colorless solid (51%, 87 mg).
0.13 mmol). Then, [AuClACTHNUTRGNEUGN(IPr)] (79 mg, 0.13 mmol) was added and the re-
action mixture was stirred 30 min at RT. CH2Cl2 (5 mL) was added and
the reaction mixture was filtered over a plug of silica. Volatile com-
pounds were removed under reduced pressure to yield a colorless oil. Re-
crystallization with CH2Cl2/pentane and addition of some ether yielded a
colorless solid (72 mg, 70%). 1H NMR (400 MHz, CDCl3): d=7.70 (d,
J=9.0 Hz, 2H), 7.60 (t, J=7.9 Hz, 2H), 7.48 (s, 2H), 7.37 (d, J=7.9 Hz,
4H), 7.08 (d, J=9.0 Hz, 2H), 3.90 (s, 3H), 2.50 (sept, J=6.8 Hz, 4H),
1.33 (d, J=6.8 Hz, 12H), 1.27 ppm (d, J=6.8 Hz, 12H); 13C NMR
(75 MHz, CDCl3): d=166.1, 166.0, 145.7, 136.1, 133.3, 131.4, 125.4, 124.7,
121.2, 116.2, 96.7, 56.3, 29.0, 24.9, 24.1 ppm; 19F NMR (376 MHz, CDCl3):
d=ꢀ154.57. ꢀ154.63 ppm; elemental analysis calcd (%): C 53.25, H 5.49,
N 5.32; found: C 53.35, H 5.23, N 6.13.
Synthesis of [{AuACHTUNGTRENNUNG(IPr)}2ACHTUNGERTNN(GUN PhCONH)]ACHTNRUGETNNUG[BF4] (12): Complex 3 (25 mg,
0.02 mmol) was dispersed in toluene (3 mL) and benzamide (2.4 mg,
0.02 mmol) added. The reaction mixture was stirred overnight at RT.
Then, pentane (2 mL) was added and the precipitate was collected via fil-
tration, washed with pentane (3ꢄ5 mL) and dried under reduced pres-
sure to obtain a colorless solid (81%, 22 mg). 1H NMR (400 MHz,
CDCl3): d=7.59 (t, J=7.9 Hz, 2H), 7.40 (s, 2H), 7.36 (t, J=7.9 Hz, 2H),
7.31 (d, J=7.9 Hz, 4H), 7.25 (s, 2H) 7.17 (d, J=7.9 Hz, 4H), 6.78 (t, J=
7.9 Hz, 2H), 5.13 (s, 1H), 2.45 (m, 8H), 1.27–1.18 (m, J=6.8 Hz, 24H),
1.17–1.11 ppm (m, J=7.5 Hz, 24H); 13C NMR (101 MHz, CDCl3): d=
180.2, 172.1, 163.9, 145.7, 135.9, 134.1, 133.8, 131.1, 131.0, 130.5, 128.1,
127.2, 124.6, 124.5, 124.3, 28.9, 24.7, 24.5, 24.1, 24.0 ppm; 19F NMR
(376 MHz, CDCl3): d=ꢀ154.92, ꢀ154.98 ppm; elemental analysis calcd
(%): C 53.17, H 5.71, N 5.08; found: C 52.71, H 5.60, N 4.81.
Synthesis of [AuCATHUGNRETNU(NNG IPr)ACHTUNGTRNENG{U NCC6H3AHCNUTGRETNN(GUN CH3)2}]CAHTNUGTREN[NUGN BF4] (17): AgBF4 (31 mg,
0.16 mmol) was placed under argon in a Schlenk tube wrapped with alu-
mina foil. CH2Cl2 (4 mL) was added followed by 2,6-dimethylbenzonitrile
(21 mg, 0.16 mmol). Then, [AuClACHTNUTRGNE(UNG IPr)] (100 mg, 0.16 mmol) was added
and the reaction mixture was stirred 30 min at RT. CH2Cl2 (5 mL) was
added and the reaction mixture was filtered over a plug of silica. Volatile
1244
www.chemeurj.org
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 1238 – 1246

Gold Catalysis
FULL PAPER
compounds were removed under reduced pressure to yield a colorless oil.
Recrystallization with CH2Cl2/pentane and addition of some ether yield-
ed a colorless solid (74 mg, 57%). H NMR (400 MHz, CDCl3): d=7.66–
ꢀ153.46 ppm; elemental analysis calcd (%): C 51.05, H 5.19, N 7.22;
found: C 49.12, H 5.08, N 6.67.
1
Synthesis of [AuACHTNUGTRENNUG(IPr)(4-cyanopyridine)]ACHTUNGTRENN[UNG BF4] (22): AgBF4 (75 mg,
7.48 (m, 5H), 7.36 (d, J=7.7 Hz, 4H), 7.20 (d, J=7.5 Hz, 2H), 2.52 (sept,
J=6.7 Hz, 4H), 2.36 (s, 6H), 1.31 (d, J=6.7 Hz, 12H), 1.28 ppm (d, J=
6.7 Hz, 12H); 13C NMR (101 MHz, CDCl3): d=165.4, 145.7, 144.6, 136.1,
133.3, 131.3, 128.5, 125.6, 124.6, 119.7, 107.6, 28.9, 24.8, 24.1, 20.6 ppm;
19F NMR (376 MHz, CDCl3): d=ꢀ154.58. ꢀ154.63 ppm; elemental anal-
ysis calcd (%): C 53.81, H 5.64, N 5.23; found: C 53.3, H 5.55, N 5.82.
0.39 mmol) was placed under argon in a Schlenk tube wrapped with alu-
mina foil. CH2Cl2 (10 mL) was added followed by 4-cyanopyridine
(40 mg, 0.39 mmol). Then, [AuClACHTNUTRGNE(UNG IPr)] (240 mg, 0.39 mmol) was added
and the reaction mixture was stirred 30 min at RT. CH2Cl2 (10 mL) was
added and the reaction mixture was filtered over a plug of silica. Volatile
compounds were removed under reduced pressure to yield a crude solid.
Recrystallization with CH2Cl2/pentane a colorless solid (213 mg, 71%).
1H NMR (300 MHz, CDCl3): d=8.26 (d, J=5.8 Hz, 2H), 7.92 (d, J=
5.8 Hz, 2H), 7.58 (t, J=7.8 Hz, 2H), 7.42 (s, 2H), 7.36 (d, J=7.8 Hz,
4H), 2.52 (sept, J=6.8 Hz, 4H), 1.34 (d, J=6.8 Hz, 12H), 1.27 ppm (d,
J=6.8 Hz, 12H); 13C NMR (101 MHz, CDCl3): d=166.2, 152.3, 145.6,
133.2, 131.5, 129.6, 125.0, 125.0, 124.7, 114.5, 28.9, 24.9, 24.0 ppm;
19F NMR (376 MHz, CDCl3): d=ꢀ154.55. ꢀ154.60 ppm; elemental anal-
ysis calcd (%): C 51.05, H 5.19, N 7.22; found: C 51.55, H 5.38, N 7.15.
Synthesis of [AuACHTUNGTRENNUNG(IPr)ACHTUNGTRENNUNG(NCPhBr)]ACTHNUGTRENN[UNG BF4] (18): 48 wt% aqueous BF4 (11 mL,
0.08 mmol) was added to a dispersion of complex 1 (50 mg, 0.08 mmol)
and benzonitrile (17 mL, 0.09 mmol) in toluene (2 mL). The reaction mix-
ture was stirred overnight at room temperature. Pentane (2 mL) was
added to the reaction to ensure complete precipitation of the product.
The white solid was collected by filtration, washed with pentane (2ꢄ
5 mL) and dried under vacuum to give 62 mg (87%) of a white micro-
1
crystalline solid. H NMR (400 MHz, CDCl3): d=7.81–7.66 (m, 4H), 7.60
General procedure for the nitrile hydration: In a typical reaction, [Au-
AHCTNURTGNEG(UN NTf2)ACHUTNGTNERNU(GN IPr)] (13 mg, 20 mmol, 2 mol%) or [{AuACHTUNRTGENN(GUN IPr)}2AHTCUNGRTEN(NUNG m-OH)]ACHTUNGTRENNUNG[BF4]
(t, J=7.9 Hz, 2H), 7.46 (s, 2H), 7.37 (d, J=7.9 Hz, 4H), 2.49 (sept, J=
6.8 Hz, 4H), 1.33 (d, J=6.8 Hz, 12H), 1.27 ppm (d, J=6.8 Hz, 12H);
13C NMR (101 MHz, CDCl3): d=165.6, 145.7, 135.1, 133.8, 133.2, 132.7,
131.5, 124.7, 119.3, 105.3, 29.0, 24.9, 24.1 ppm; 19F NMR (376 MHz,
(17 mg, 10 mmol, 1 mol%) was added to THF (0.5 mL) in a 2 mL micro-
wave vial in air. Benzonitrile (103 mg, 1 mmol) was added, followed by
distilled H2O (500 mL). The vial was sealed and heated in the microwave
for 2 h at 1408C (7 bar). The conversion was determined by gas chroma-
tography.
CDCl3): d=ꢀ154.20, ꢀ154.25 ppm; elemental analysis calcd (%):
C
47.80, H 4.72, N 4.92; found: C 48.06, H 4.68, N 4.64.
Synthesis of [AuACHTUNGTRENNUNG(IPr)ACHTUNGTRENNUNG(NCC6H4ACHTUNREGTGUN(NN COCH3))]CATHNUGTREN[NUGN BF4] (19): AgBF4 (48 mg,
0.25 mmol) was placed under argon in a Schlenk tube wrapped with alu-
mina foil. CH2Cl2 (6 mL) was added followed by 3-acetobenzonitrile
Computational details: The BP86[30] calculations were performed with
the Gaussian 03 package. The SVP basis set was used for main group
atoms,[31] while the relativistic SDD effective core potential in combina-
tion with a triple-z basis set was used for Au.[32] Solvent effects were in-
cluded through single-point calculations, on the gas-phase optimized ge-
(35 mg, 0.24 mmol). Then, [AuClACHTNUTRGNE(UNG IPr)] (150 mg, 0.24 mmol) was added
and the reaction mixture was stirred 30 min at RT. CH2Cl2 (5 mL) was
added and the reaction mixture was filtered over a plug of silica. Volatile
compounds were removed under reduced pressure to yield a colorless oil.
Recrystallization with CH2Cl2/pentane and addition of some ether yield-
ed a colorless solid (195 mg, 99%). 1H NMR (400 MHz, CDCl3): d=
8.43–8.30 (m, 2H), 8.11–7.99 (m, 1H), 7.89–7.77 (m, 1H), 7.66–7.55 (m,
2H), 7.46 (s, 2H), 7.38 (d, J=7.7 Hz, 4H), 2.64 (s, 3H), 2.50 (sept, J=
6.8 Hz, 4H), 1.35 (d, J=6.8 Hz, 12H), 1.27 ppm (d, J=6.8 Hz, 12H);
13C NMR (101 MHz, CDCl3): d=195.8, 165.3, 145.6, 137.8, 137.3, 136.1,
133.1, 131.4, 125.4, 124.6, 118.7, 107.3, 28.8, 26.7, 24.8, 24.0 ppm;
19F NMR (376 MHz, CDCl3): d=ꢀ154.08. ꢀ154.13 ppm; elemental anal-
ysis calcd (%): C 52.89, H 5.30, N 5.14; found: C 52.99, H 4.44, N 4.81.
AHCTUNGTRENNUNG
ometries, with the PCM approach.[33]
Acknowledgements
The ERC (Advanced Investigator Award-FUNCAT to S.P.N.) and the
EPSRC are gratefully acknowledged for support of this work. Syngenta
is thanked for a CASE studentship award. L.C. thanks the ENEA-
CRESCO for support and access to computational resources. We thank
Drs. Pierre de Frꢅmont and Nicolas Marion for helpful discussions and
preliminary synthetic contributions. S.P.N. is a Royal Society-Wolfson Re-
search Merit Award holder.
Synthesis of [AuACHTUNGTRENNUNG(IPr)ACHTUNGTRENNUNG(NCCACHTUNTREGGNN(NU CH3)3)]ACHTNUGERTN[UNNG BF4] (20): HBF4·OEt2 (11 mL,
0.08 mmol) was added to a dispersion of complex 1 (50 mg, 0.08 mmol)
and pivalonitrile (18 mL, 0.08 mmol) in toluene (2 mL). The reaction mix-
ture was stirred 3 h at room temperature. Pentane (2 mL) was added to
the reaction to ensure complete precipitation of the product. The white
solid was collected by filtration, washed with pentane (2ꢄ5 mL) and
dried under vacuum to give 52 mg (83%) of a white microcrystalline
solid. 1H NMR (400 MHz, CDCl3): d=7.60 (t, J=7.7 Hz, 2H), 7.47 (s,
2H), 7.36 (d, J=7.7 Hz, 4H), 2.47 (sept, J=6.8 Hz, 4H), 1.42 (s, 9H),
1.29 (d, J=6.8 Hz, 12H), 1.26 ppm (d, J=6.8 Hz, 12H); 13C NMR
(101 MHz, CDCl3): d=165.3, 145.7, 133.3, 131.3, 125.5, 124.7, 29.5, 28.9,
27.3, 24.8, 24.1 ppm; 19F NMR (376 MHz, CDCl3): d=ꢀ154.14,
ꢀ154.19 ppm; elemental analysis calcd (%): C 50.87, H 6.00, N 5.56;
found: C 49.58, H 5.79, N 4.93.
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0.16 mmol) was placed under argon in a Schlenk tube wrapped with alu-
mina foil. CH2Cl2 (5 mL) was added followed by 2-cyanopyridine (17 mg,
0.16 mmol). Then, [AuClACTHNUTRGNE(NUG IPr)] (100 mg, 0.16 mmol) was added and the
reaction mixture was stirred 30 min at RT. CH2Cl2 (5 mL) was added and
the reaction mixture was filtered over a plug of silica. Volatile com-
pounds were removed under reduced pressure to yield a colorless oil. Re-
crystallization with CH2Cl2/pentane a colorless solid (122 mg, 98%).
1H NMR (400 MHz, CDCl3): d=8.43–8.28 (m, 1H), 8.22–8.10 (m, 2H),
7.91 (d, J=7.3 Hz, 1H), 7.58 (t, J=7.9 Hz, 2H), 7.43 (s, 2H), 7.36 (d, J=
7.9 Hz, 4H), 2.54 (sept, J=6.8 Hz, 4H), 1.36 (d, J=6.8 Hz, 12H),
1.27 ppm (d, J=6.8 Hz, 12H); 13C NMR (101 MHz, CDCl3): d=166.0,
153.6, 145.6, 143.7, 133.3, 133.2, 132.2, 132.0, 131.6, 125.1, 124.7, 114.3,
29.1, 24.8, 24.2 ppm; 19F NMR (376 MHz, CDCl3): d=ꢀ153.40,
Chem. Eur. J. 2011, 17, 1238 – 1246
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1245

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best catalyst. In order to compare 3 to all other catalysts tested, we
subjected it to these same reaction conditions to seek the highest
conversion rate among all catalysts. Since the optimizations in refer-
ence [8] revealed the importance of the amount of water used, we
suggest that a lower conversion of [AuCl
ACHUTGTNRENG(UN IPr)]/AgBF4 and [AuACHTUNGTRENNUNG(IPr)-
AHCTUNGTRENNG(UN CH3CN)]BF4 into 3 occurs under these reaction conditions and
result in lower conversions than when using 4 under these “unopti-
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[Au(OH)(IPr)] in CH2Cl2 results in full conversion into catalyst 2.
AHCTUNGTRENNUNG
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AHCTUNGTRENNUNG
ꢀ
ꢀ
ꢀ
ꢀ
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Received: September 9, 2010
Published online: December 16, 2010
1246
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ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 1238 – 1246