Expedient Syntheses of Neutral and Cationic Au(I)-NHC Complexes

Article abstract of DOI:10.1021/acs.organomet.7b00622

The synthesis and isolation of gold(I) precatalysts often requires the generation of several isolable intermediates as well as numerous purification steps. New protocols for the expedient synthesis of neutral [Au(OH)(NHC)] and [Au(CH₂COCH₃)(NHC)] species from [AuCl(NHC)] or [AuCl(DMS)] precursors bearing a variety of N-heterocyclic carbene (NHC) ligands are presented. These methods can be employed in a telescoping manner for the synthesis of catalytically relevant [Au(NTf₂)(NHC)] and [Au(NHC)(NCCH₃)][BF₄] complexes. These attractive methods are straightforward and practical leading to various complexes in high isolated yields and purity.

Full text of DOI:10.1021/acs.organomet.7b00622

Article
pubs.acs.org/Organometallics
Expedient Syntheses of Neutral and Cationic Au(I)−NHC Complexes
Richard M. P. Veenboer,† Danila Gasperini,† Fady Nahra,‡ David B. Cordes,† Alexandra M. Z. Slawin,†
Catherine S. J. Cazin,*,‡ and Steven P. Nolan*,‡,§
†School of Chemistry, University of St Andrews, North Haugh, St Andrews KY16 9ST, United Kingdom
‡Department of Inorganic and Physical Chemistry, Ghent University, Building S3, Krijgslaan 281, 9000 Gent, Belgium
§Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
S
* Supporting Information
ABSTRACT: The synthesis and isolation of gold(I) precatalysts often
requires the generation of several isolable intermediates as well as
numerous purification steps. New protocols for the expedient synthesis
of neutral [Au(OH)(NHC)] and [Au(CH2COCH3)(NHC)] species
from [AuCl(NHC)] or [AuCl(DMS)] precursors bearing a variety of
N-heterocyclic carbene (NHC) ligands are presented. These methods
can be employed in a telescoping manner for the synthesis of
catalytically relevant [Au(NTf2)(NHC)] and [Au(NHC)(NCCH3)]-
[BF4] complexes. These attractive methods are straightforward and
practical leading to various complexes in high isolated yields and purity.
INTRODUCTION
■
The field of gold chemistry and catalysis continues to flourish
after a decade of important advances.1 The exploration of
gold(I)−NHC chemistry in particular has gained increased
attention mainly due to the ever-growing development of NHC
(NHC = N-heterocyclic carbene) ligand design and tunability
(Figure 1).2 Our synthetic studies of Au−NHC complexes
Figure 2. General synthetic analysis for the formation of gold(I)−
NHC complexes: IA silver-based, IB silver-free, and IC acid−based
transformations.
Problematically, silver salts were shown to persist as
impurities and interfere with catalytic reactions through the
formation of silver-stabilized intermediates (e.g., gem-dimeta-
Figure 1. Selected NHCs used in this work.
lated complexes)6 or catalytically active acids.7 Furthermore,
avoiding the use of light- and moisture-sensitive silver salts is
highly desirable in an effort to decrease cost and to simplify
handling.8 In this context, gold hydroxide complexes, [Au-
(OH)(NHC)] (2), have been developed (Figure 2, route IB);9
these complexes can be activated by Brønsted acids (e.g.,
HOTf, HNTf2, HBF4·OEt2, H3OPF6, 2HF·SbF5, or NEt3·
3HF10) and mineral acids (HNO3, H2SO4, or H3PO4)11 instead
of silver salts to deliver the same catalytically active cationic
species (Figure 2, route IC). These formal acid−base reactions
initially targeted the isolation of [AuCl(NHC)] (1) via the
reaction of [AuCl(DMS)] (DMS = dimethylsulfide) with the
free NHC.2b This and following simpler synthetic protocols
have rendered gold(I) complexes such as 1 excellent precursors
for a variety of neutral and cationic gold(I) species (Figure 2).3
Active gold catalysts are generally prepared by anion metathesis
through the addition of a silver(I) salt AgX (X = OTf, NTf2,
BF4, PF6, or SbF6) to these gold(I) chloride precursors (Figure
2, route IA).3 Using this strategy, [Au(NHC)(NCCH3)][X] (X
= BF4, PF6)4 and [Au(NTf2)(NHC)]5 complexes have readily
been accessed.
Received: August 14, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00622
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are facilitated by the high Brønsted basicity of the hydroxide
precursors.12
demonstrated (Scheme 1, route IIG). Although route IIC is
one of the best procedures to form 2, it still requires long
reaction times (24 h). Examining these reports, we noticed that
the use of a toluene solution of the alkoxide base, to form
species 2 starting from 1 (Scheme 1, route IIE−IIF), avoids
problems associated with the use of hygroscopic hydroxide salts
(e.g., KOH, CsOH) while significantly accelerating reactions. In
the context, we aim herein to extend this procedure to other
NHC ligands (Scheme 2, route IIIA−IIIC). Another objective
Even though numerous catalytic methodologies have
successfully employed this mode of activation in situ,13 the
use of preformed catalysts is still desirable to avoid issues with
acid-sensitive reactions, substrates, and parasitic or undesired
silver-mediated reactions. Consequently, these silver-free
protocols have allowed the isolation of key precursors such as
[Au(NTf2)(IPr)] (4a)5 and [Au(IPr)(NCCH3)][BF4] (5a)14
starting from [Au(OH)(IPr)] (2a) (Figure 2, route IC).
Recently, the newly reported neutral gold(I)−acetonyl
complex, [Au(CH2COCH3)(IPr)] (3a), has displayed similar
interesting reactivity.15 Release of acetone upon reaction of
gold−acetonyl complexes with acids resulted in a range of gold
complexes, including 4a (Figure 2, route IC)15 and [Au(OTf)-
(IPr)].16
Scheme 2. Targeted Sequential Formation of Complexes 2−
5
An evaluation of the previously reported procedures for
syntheses of [AuCl(NHC)] (1) and [Au(OH)(NHC)] (2)
indicates that gold(I)−NHC species are compatible with
various bases (Scheme 1). The first synthesis of [AuCl(IPr)]
Scheme 1. Synthetic Access to [AuCl(IPr)] (1a) and
a
[Au(OH)(IPr)] (2a)
of the present study was to synthesize species 2 directly from
[AuCl(DMS)] and NHC·HCl (Scheme 2, route IIIB,IIIC).
The high reactivity of [Au(OtAm)(IPr)] (as apparent from its
rapid hydrolysis in air) prompted us to further investigate the
feasibility of quenching this Au−OR moiety with various acidic
partners, such as acetone, trifluoromethanesulfonimide acid, or
tetrafluoroboric acid to form complexes 3−5, respectively, in a
sequential manner (Scheme 2, routes IIID−IIIF). In addition,
we herein expand the utility of [Au(CH2COCH3)(NHC)] (3)
as silver-free synthons for the formation of a range of new
[Au(NHC)(NCCH3)][BF4] (5) via reactions with tetrafluor-
oboric acid−diethyl ether complex (Scheme 2, route IIIG).
a
Procedures: IIA: (1) KOtBu (1.1 equiv), THF, argon, rt; (2)
[AuCl(DMS)], THF, argon, rt;2d IIB: [AuCl(DMS)], K2CO3 (1
equiv), acetone, in air, 60 °C;19 IIC: (1) NaOH (6 equiv), AmOH
t
(0.2 equiv), THF, in air, rt; (2) H2O, in air, rt;20 IID: acetone, rt;15
IIE: KOtAm (1.3 equiv), C6H6, argon, rt;20 IIF: H2O, in air, rt;20 IIG:
(1) [AuCl(DMS)], KOtBu (1.5 equiv), THF; (2) KOtBu (3 equiv),
toluene; (3) filtration, H2O, in air, rt.20
RESULTS AND DISCUSSION
(1a) consisted of generating the free carbene by reacting IPr·
HCl17 with KOtBu18 followed by the addition of [AuCl(DMS)]
(Scheme 1, route IIA).2b This has now been improved upon,
using a straightforward one-pot system with potassium
carbonate as base; the reaction proceeds via the in situ
formation of “ate” complexes, [NHC·H][AuCl2] (Scheme 1,
routes IIB and IIC).19 Crucially, use of an excess of base and
prolonged reaction time in the latter procedure leads to
[Au(CH2COCH3)(IPr)] (3a) instead of 1a.15 Alternatively,
this gold(I)−acetonyl complex can be formed from [Au(OH)-
(IPr)] (2a) in the absence of an external base by simply stirring
it in acetone (Scheme 1, route IID).15
The formation of [Au(OH)(IPr)] (2a) from [AuCl(IPr)]
(1a) was initially performed using alkali earth hydroxide bases
at slightly elevated temperatures;9a,c,21 however, an improved
procedure using a mixture of NaOH and tert-amyl alcohol was
later reported (Scheme 1, route IIC).20 This latter route was
demonstrated to proceed through formation of [Au(OtAm)-
(IPr)], and the overall transformation could be carried out
sequentially by first reacting 1a with a toluene solution of
potassium tert-amylate followed by the addition of water
(Scheme 1, route IIE, IIF). Furthermore, the viability of a one-
pot sequential approach starting from IPr·HCl was also
■
Synthesis of [Au(OH)(NHC)]. We began by adapting the
previously described syntheses of [Au(OH)(IPr)] (2a) from
[AuCl(IPr)] (1a) (Scheme 1, route IIE−IIF) to a procedure
that could be performed in air using technical-grade toluene
and a toluene solution of potassium tert-amylate (commercially
available) as base (Table 1, route IVC).22 Reactions reached
completion within 1 h, and 2a−d could be isolated in similar or
improved yields as compared to the previously reported
procedure that involved overnight reactions (Table 1, entries
1−4, routes IVA versus IVC). Due to its low solubility in
toluene, the reaction of the complex bearing the IPr* ligand did
not reach completion in 1 h initially, but complete conversion
was obtained by using a mixture of toluene and THF (1:1). As
expected from the precedent study,20 the gold hydroxide
complexes bearing IMes, ICy, or IAd could not be cleanly
isolated (in air) (Table 1, entries 5−7, routes IVA and IVC).
A change of solvent to a 1:1 toluene/THF mixture allowed
the sequential formation of [Au(OH)(NHC)] (2) directly
from [AuCl(DMS)] and NHC·HCl, but not selectively and in
reduced yields (Table 1, route IVD). Products bearing ligands
IPr, SIPr, and IPrCl consistently contained a small amount of
the corresponding [Au(NHC)2][Cl] side-product. These bis-
B
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a
a
Table 1. Synthesis of [Au(OH)(NHC)] (2)
Table 2. Synthesis of [Au(CH2COCH3)(NHC)] (3)
entry
complex (NHC)
IVA20
IVB21
IVC
IVD
b
1
2
3
4
5
6
7
2a (IPr)
2b (SIPr)
2c (IPrCl)
2d (IPr*)
2e (IMes)
2f (ICy)
87
72
76
75
0
-
-
92
71
79
(79)
(51)
c
d
-
(31)
entry
complex (NHC)
VA
VB
VC
VD
e
b
8015
9715
9215
8115
7115
-
46
8215
51
54
-
86
77
-
1
2
3
4
5
6
7
3a (IPr)
3b (SIPr)
3c (IPrCl)
3d (IPr*)
3e (IMes)
3f (ICy)
c
98
93
80
0
0
0
41
-
-
-
-
-
-
0
-
56
d
56
2g (IAd)
0
-
71
74
a
e
Isolated yields (%) of syntheses on a 0.3 mmol scale are given.
0
0
(>99)
0
t
Procedures: IVA NaOH (6 equiv), AmOH (0.2 equiv), THF, in air,
rt; IVB CsOH (10 equiv), C6H6, argon, rt;21 IVC (1) KOtAm (1.5
equiv), toluene; (2) H2O, in air, rt; IVD (1) KOtAm (1.5 equiv),
e
3g (IAd)
6515
(>99)
71
a
Isolated yields (%) of syntheses on a 0.3 mmol scale are given.
b
toluene/THF (1:1); (2) H2O, in air, rt. Mixture with [Au(IPr)2][Cl]
Procedures: VA K2CO3 (6 equiv), acetone, in air, 60 °C;15 VB KOtAm
c
d
(5%). Mixture with [Au(SIPr)2][Cl] (16%). Mixture with [Au-
(3 equiv), acetone, in air, rt; VC acetone, rt;15 VD KOtAm (3 equiv),
e
(IPrCl)2][Cl] (35%). Toluene/THF (1:1).
b
acetone/toluene, in air, rt. Mixture with [Au(CH2COC(H)C-
c
(CH3)2)(IPr)] (3a′, 28%). Mixture with [Au(CH2COC(H)C-
d
ligated complexes are known to form upon reaction of the
imidazolium salt with the in situ formed [AuCl(IPr)] (1)
(assisted by base)23 or with [Au(OH)(NHC)] (2).24 The
absence of this side-product in the reaction involving the IPr*
ligand was attributed to its increased steric bulk.25 Interestingly,
when the reaction of [AuCl(DMS)] and IPr*·HCl was
performed under these conditions but using THF as sole
solvent, [AuCl(IPr*)] (1c) rather than [Au(OH)(IPr*)] (2c)
was obtained exclusively in 73% yield, providing an alternative
synthesis to the previously reported method.19
(CH3)2)(SIPr)] (3b′, 16%). Acetone/THF (1:1), mixture with 2d
e
1
(18%). Conversion of 1 to 3, determined by H NMR.
Scheme 4. Hypothetical Formation of Au(I)−NHC−Ketonyl
Products 3 and 3′
The practical value of a new methodology is best evaluated
by testing its scalability. The most recent procedure for the
formation of [Au(OH)(NHC)] (2) from the corresponding
[AuCl(NHC)] (1) (Table 1, route IVA) was demonstrated to
be scalable up to multigram quantities.20,26 We obtained a very
good yield of 90% when we conducted a large scale synthesis of
[Au(OH)(SIPr)] (2b) (Scheme 3). It should be noted that,
We found 3′ to be equally susceptible to protonolysis as the
corresponding [Au(CH2COCH3)(NHC)] (3), and the mix-
tures could be used in subsequent transformations toward
[Au(NTf2)(NHC)] (4) and [Au(NHC)(NCCH3)][BF4] (5)
without affecting the overall outcome of the reactions (see
Table 4). Unexpectedly, when we tested the formation of
[Au(CH2COCH3)(IPr*)] (3d) from [AuCl(IPr*)] (1d), we
obtained a mixture of the desired product and [Au(OH)-
(IPr*)] (2d). This result can be explained either by the slower
reaction of 2d with acetone to form 3d because of the sheer
bulk of the IPr* ligand25 or the operation of two different
mechanisms. This mixture could be used in subsequent
synthetic steps (toward 4d and 5d) without affecting the
overall outcome. Alternatively, adding THF to the reaction
mixture restored full conversion to 3d in 1 h (Table 2, route
VB, entry 4). Similar to the previous synthesis of [Au(OH)-
(NHC)] (2), decomposition occurred for complexes bearing
IMes or ICy ligands (Table 2, route VB, entries 5,6). In
contrast, the reaction of [AuCl(IAd)] (1g) gave complete
conversion to [Au(CH2COCH3)(IAd)] (3g); however, several
purification attempts were insufficient to remove unidentified
minor impurities (Table 2, route VB, entry 7).
Scheme 3. Large-Scale Synthesis of [Au(OH)(SIPr)] (2b)
although the yield is similar to the one obtained with the
previously reported procedure,20 the reaction time can be
dramatically shortened (2 h compared to 24 h).
Synthesis of [Au(CH2COCH3)(NHC)]. We continued our
exploration by evaluating the direct synthesis of [Au-
(CH2COCH3)(NHC)] (3) from [AuCl(NHC)] (1) or
[AuCl(DMS)] and NHC·HCl using KOtAm in toluene as
base (Table 2, routes VB and VD). These transformations
could be performed using acetone and a mixture of acetone and
toluene (1:1) as solvents, respectively. The synthesis from
[AuCl(NHC)] (1) gave lower yields than the previously
reported procedure for complexes bearing IPr, SIPr, or IPrCl
(Table 2, entries 1−3, route VB versus route VA). Moreover,
significant amounts of side-product were formed in reactions
with the IPr or SIPr ligands. These were assigned to the
corresponding carbon-bound complexes of the self-condensa-
tion product of acetone, [Au(CH2COC(H)C(CH3)2)(NHC)]
(3′) (Scheme 4).
The sequential synthesis of [Au(CH2COCH3)(NHC)] (3)
directly from [AuCl(DMS)] and NHC·HCl were performed
using a mixture of acetone and toluene (1:1) using 3 equiv of
KOtAm in toluene (Table 2, route VD).27 This amount of base
was selected on the basis of various sequential routes available
(Scheme 5). [AuCl(NHC)] (1) would form first from reaction
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entries 2,3) compared to that of 3a (Table 2, route VB and VD,
entry 1) suggested that part of the latter intermediate was lost
during the purification procedure and that a sequential
transformation is preferred.
Scheme 5. Routes to [Au(CH2COCH3)(NHC)] (3)
Syntheses of [Au(NTf2)(NHC)] and [Au(NHC)(NCCH3)]-
[BF4]. The efficacy of various protocols for the synthesis of
cationic [Au(NTf2)(NHC)] (4) and [Au(NHC)(NCCH3)]-
[BF4] (5) bearing a variety of NHC ligands was assessed next
(Table 4). Reported yields of silver-based single-step (Table 4,
Table 4. Syntheses of [Au(NTf2)(NHC)] (4) and
a
[Au(NHC)(NCCH3)][BF4] (5)
of the starting materials with the first equivalent of base.19 The
second equivalent of base would then form [Au(OtAm)(IPr)]
that would react with acetone to produce 3. Alternatively, the
base was hypothesized to activate acetone to its potassium
enolate form, directly substituting the chloride of 1 with the
acetonyl fragment.
entry
complex (NHC)
VIIA
VIIB
VIIC
VIID
VIIE
This method proved successful for all ligands tested, except
for IMes and ICy (Table 2, route VD, entries 1−7); 3e was
obtained with impurities, and in the case of 3f, decomposition
occurred (Table 2, route VD, entries 6−7). The disadvantage of
reduced yields compared to the previously reported procedure
(Table 2, route VA) might be outweighed by the significantly
reduced reaction times from multiple days to as short as 1 h in
some cases.
Sequential Synthesis of [Au(NTf2)(IPr)]. Having estab-
lished that [Au(OH)(IPr)] (2a) and [Au(CH2COCH3)(IPr)]
(3a) are accessible from [AuCl(IPr)] (1a) or [AuCl(DMS)]
and IPr·HCl (Tables 1 and 2, entry 1), we began evaluating the
different sequential two-step and three-step transformations to
access [Au(NTf2)(IPr)] (4a) (Table 3).
b
4 (X = NTf2)
d
1
2
3
4
5
6
4a (IPr)
4b (SIPr)
4c (IPrCl)
4d (IPr*)
4e (IMes)
4g (IAd)
695
735
8421
93
92
97
97
91
95
79
-
-
-
-
7121
6221
7321
-
93
90
86
-
8730
9325
865
e
n.d.
755
-
-
80
c
5 (X = BF4)
f
7
8
5a (IPr)
5b (SIPr)
5c (IPrCl)
5d (IPr*)
5g (IAd)
-
-
-
-
-
96
-
99
94
99
78
-
91
97
97
91
84
-
-
-
-
9
-
10
11
-
e
-
n.d.
a
Isolated yields (%) are given. Procedures (those for 5 are indicated
a
with a prime in the experimental section): VIIA AgX, CH2Cl2, in air,
rt; VIIB (1) KOH, THF, 30 °C; (2) HX, C6H6, rt, in air; VIIC (1)
KOtAm (1.5 equiv), toluene; (2) HX, solvent, in air, rt; VIID HX,
solvent, in air, rt; VIIE (1) KOtAm (3.0 equiv), acetone/toluene; (2)
HX, solvent, in air, rt. Solvent = CH2Cl2 in procedures VIIC and
VIID. Solvent = CH2Cl2 in procedure VIIA (with stoichiometric
Table 3. Sequential Synthesis of [Au(NTf2)(IPr)] (4a)
b
c
CH3CN) and CH3CN in procedures VIIC and VIID; HBF4·OEt was
d
e
used. Identical to Table 3, entry 1. n.d. = not determined: product
could not be isolated from mixture with unidentified side-products.
f
Yield from 2a is given.14
entry
route
solvent
yield 4a (%)
1
2
3
VIA
VIB
VIC
toluene
acetone
93
87
93
route VIIA) and silver-free two-step (Table 4, route VIIB)
transformations starting from [AuCl(NHC)] (1) were
compared to the single-step transformations using [Au-
(CH2COCH3)(NHC)] (3) (Table 4, route VIIC) and to the
two-step transformations starting either from [AuCl(NHC)]
(1) (Table 4, route VIID) or from [AuCl(DMS)] and NHC·
HCl (Table 4, route VIIE).28
acetone/toluene
a
R = OtAm, H. Reaction conditions: (1) VIA KOtAm (1.5 equiv), rt;
VIB KOtAm (1.5 equiv), rt; VIC NHC·HCl (1.0 equiv), KOtAm (3.0
equiv), rt; (2) HNTf2, CH2Cl2, in air, rt.
Solvent was removed from the filtrate after the first reaction
step, and the crude material was subsequently used without
further purification. Starting from 1a, 4a was obtained in high
yields irrespective of the choice of solvent and the resulting
nonisolated intermediate formed in the first reaction step
(Table 3, entries 1,2). Beneficially, the second reaction step
could be performed in dichloromethane instead of the
previously used benzene.15,21 To avoid the previously observed
[Au(IPr)2][Cl] side-product in the reaction of [AuCl(DMS)]
and IPr·HCl with KOtAm (Table 1, route IVD, entry 1), the
sequential reaction was performed with acetone in the first
reaction step to ensure the formation of 3a as intermediate. In
this manner, 4a was obtained as the sole product (Table 3,
entry 3). The significantly higher isolated yields of 4a (Table 3,
[Au(NTf2)(NHC)] (4a−e,g) could be directly synthesized
from [Au(CH2COCH3)(NHC)] (3a−e,g) in similar or higher
yields compared to previous procedures (Table 4, routes VIIA,
VIIB vs VIID, entries 1−6). The sequential procedure
permitted synthesis of [Au(NTf2)(NHC)] (4a−d) from
[AuCl(NHC)] (1a−d) in generally slightly reduced yields
(Table 4, route VIIC, entries 1−4). For complexes bearing
IMes and IAd ligands, a pathway proceeding via [Au-
(CH2COCH3)(IMes)] (3e) and [Au(CH2COCH3)(IAd)]
t
(3g) instead of [Au(NHC)(OR)] (R = H, Am) was preferred
due to the sensitivity of the [Au(OH)(IMes)] (2e) and
[Au(OH)(IAd)] (2g) intermediates that are formed in the
sequential reactions according to route VIIC. In this context, a
D
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a
Table 5. Chemical Shifts in [Au(NHC)(NCCH3)][BF4] (5)
entry
complex (NHC)
C2 δ(13C) (ppm)
CN δ(13C) (ppm)
CH3 δ(13C) (ppm)
CH3 δ(1H) (ppm)
1
2
3
4
5
5a (IPr)
5b (SIPr)
5c (IPrCl)
5d (IPr*)
5g (IAd)
166.3
188.3
166.4
166.7
156.9
121.0
121.1
121.8
120.8
121.9
2.7
2.7
2.9
2.9
3.2
2.39
2.33
2.27
2.62
2.31
a
Value from measurements in CDCl3 are given.
different sequential transformation was tested starting from
[AuCl(DMS)] and NHC·HCl (Table 4, route VIIE). [Au-
(NTf2)(IMes)] (4e) was obtained as the main product,
although we were unable to isolate it from a small amount of
unidentified side-product (Table 4, route VIIE, entry 5). Also,
[Au(NTf2)(IAd)] (4g) was isolated in good yield and purity
(Table 4, route VIIE, entry 6).
relative to noncoordinated acetonitrile: CN-δ(13C) = 116.9,35
CH3-δ(13C) = 1.9, and CH3-δ(1H) = 2.10.36
Changes to the electronic configuration of the acetonitrile
fragment in 5 were next probed by comparing the CN
stretching frequencies from infrared spectra to those in
noncoordinated acetonitrile. The σ-donor lone pair on the N
atom of acetonitrile is weakly antibonding, and upon
complexation, electron donation from the lone pair to the
gold center would be expected to remove weakly antibonding
Considering [Au(NHC)(NCCH3)][BF4] (5), only the
synthesis of the congener bearing an IPr ligand (5a)14 has
been previously reported. Complexes bearing SIPr (5b)29 or
IPrCl (5c)29 ligands have been used as catalysts, but their
syntheses have not been disclosed, and complexes bearing IPr*
(5d) and IAd (5g) ligands are yet to be reported. [Au(IPr)-
(NCCH3)][BF4] (5a) has been described to decompose to
[Au(NCCH3)4][BF4] when synthesized from [AuCl(IPr)]
(1a) and AgBF4 (Table 4, route VIIA, entry 7).4 The successful
silver-free synthesis starting from [Au(OH)(IPr)] (2a) (Table
4, route VIIB, entry 7) encouraged us to test the applicability of
our new methods. We were able to prepare 5 in an analogous
fashion to [Au(NTf2)(NHC)] (4) starting from [Au-
(CH2COCH3)(NHC)] (3), simply by switching from bis-
(trifluoromethanesulfonyl)amine to tetrafluoroboric acid and
from dichloromethane to acetonitrile (to provide the auxiliary
ligand). With these modifications, [Au(NHC)(NCCH3)][BF4]
(5a−d,g) could be isolated in good to excellent yields (Table 4,
route VIID, entries 7−11).
electrons from the CN bond, thereby strengthening it and
37
increasing νCN
.
Indeed, blue-shifted values of νCN were
measured for 5a−d (Table 6) relative to noncoordinated
Table 6. IR Features of [Au(NHC)(NCCH3)][BF4] (5)
a
entry
complex (NHC)
νCN (cm−1
)
1
2
3
4
5a (IPr)
5b (SIPr)
5c (IPrCl)
5d (IPr*)
2359−2310
2359−2303
2359−2309
2357−2308
a
Values of neat complexes measured by FTIR-ATR are given.
acetonitrile (νCN = 2254, 2293 cm−1, doublet).38 The poor
resolution and small range of νCN prohibits meaningful
comparison to known metrics of π-accepting potential of
ligands.39
X-ray Structure Determination of [Au(NHC)(NCCH3)]-
[BF4]. To unambiguously establish the solid state structure of
the new [Au(NHC)(NCCH3)][BF4], crystals suitable for X-ray
diffraction analyses were grown from slow diffusion of pentane
into solutions of [Au(SIPr)(NCCH3)][BF4] (5b) and [Au-
(IPrCl)(NCCH3)][BF4] (5c) in ethyl acetate and into a
solution of [Au(IPr*)(NCCH3)][BF4] (5d) in acetone (Figure
3). The results of diffraction studies performed on the obtained
single crystals agreed with the structures determined by NMR,
and the coordination of acetonitrile to the gold center was
confirmed. Bond angles C−Au−N indicated near-linear
structures and bond lengths C−Au and Au−N showed little
variation (Table 7). As previously observed for the PF6-based
analogous compound [Au(IPr)(NCCH3)][PF6],4 the NC
bonds in the coordinated acetonitrile molecules were slightly
shorter than in noncoordinated acetonitrile (1.141 Å),40
consistent with the measured increases in stretching frequencies
(Table 6).
The two step sequential route from [AuCl(NHC)] (2) via
[Au(OH)(NHC)] (3) was then applied to the synthesis of
[Au(NHC)(NCCH3)][BF4] (5). Complexes 5a−d were
obtained in good to excellent yields (Table 4, route VIIC,
entries 7−10). Again, a sequential route starting from
[AuCl(DMS)] and IAd·HCl that would proceed through
[Au(CH2COCH3)(IAd)] (3g) was preferred for the synthesis
of [Au(IAd)(NCCH3)][BF4] (5g). While the expected product
formed predominantly in this reaction, a small amount of an
unidentified product also formed. Attempts to purify this
mixture resulted in decomposition (Table 4, route VIIE, entry
11).
Spectroscopic Data of [Au(NHC)(NCCH3)][BF4]. Having
in hand a series of [Au(NHC)(NCCH3)][BF4], (5), the
influence of the different NHC ligands on the [Au(NCCH3)]+
fragment was investigated (Table 5). 13C chemical shifts of the
C2 carbene in NHCs (C2-δ(13C)), are indicative of the
environment around [Au(NHC)] fragments and are thus
used to gauge the Lewis acidity of gold complexes.31,32
A
CONCLUSIONS
■
downfield shift C2-δ(13C) of 166.3 ppm in [Au(IPr)-
(NCCH3)][BF4] (5a) relative to 159.0 ppm in [Au(IPr)]-
[BF4]33 is indicative of a less electron-deficient gold center in
the former, as expected from coordination of the second ligand
(NCCH3).14,34 Net electron transfer from the coordinated
acetonitrile to the gold center was also apparent from downfield
shifts (caused by lower shielding) of the 1H and 13C resonances
We have shown that the use of a solution of potassium tert-
amylate in toluene leads to the rapid synthesis of [Au(OH)-
(NHC)] (2) from [AuCl(NHC)] (1) and from [AuCl(DMS)]
and NHC·HCl salts. Expansion of this methodology has
permitted the synthesis of [Au(NHC)(CH2COCH3] (3) from
the same starting materials by simply exchanging the solvent.
These gold−acetonyl complexes have been shown as excellent
E
DOI: 10.1021/acs.organomet.7b00622
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Organometallics
Article
Figure 3. Thermal ellipsoid representations of [Au(NHC)(NCCH3)][BF4] (5b−d) at 50% probability. Most hydrogen atoms and a molecule of
ethyl acetate have been omitted from 5c for clarity. Selected bond lengths C1−Au1, Au1−N30, C30−N30, C72−N71 (Å) and angles C1−Au1−
N30 and C1−Au1−N71 (deg) are given in Table 7.
Table 7. Bond Angles and Lengths in 5b−d
complex
(NHC)
C−Au−N
C−Au
Au−N
NC
entry
1
(deg)
(Å)
(Å)
(Å)
5b (SIPr)
5c (IPrCl)
5d (IPr*)
178.54(13)
176.1(4)−179.0(4)
176.6(2)
1.981(3)
1.957(8)−1.965(8)
1.963(4)
2.005(3)
1.986(8)−2.000(8)
2.016(5)
1.132(5)
1.099(12)−1.114(14)
1.080(11)
a
2
3
a
Two molecules were found in the crystal lattice of this complex: the range of distances and angles obtained is given.
filtered through Celite with additional toluene (about twice the
reaction volume). Water (excess) was added to the filtrate,
concentrated (to about 2 mol L−1), and the product was precipitated
by addition of pentane (about the initial reaction volume). It was
collected by filtration, washed with additional pentane (about twice the
initial reaction volume), and dried under high vacuum.
replacements for gold hydroxides and can be used as precursors
for the synthesis of [Au(NTf2)(NHC)] (4) and [Au(NHC)-
(NCCH3)][BF4] (5). Combination of these steps has
permitted the sequential syntheses of a range of cationic
complexes directly from the various chloride precursors. The
possibility to tune the solvent used in the first reaction step of
these procedures to ensure the formation of a stable
intermediate (i.e., an acetonyl complex instead of a hydroxide
complex) holds significant potential. By employing these
strategies, known [Au(NTf2)(IMes)] (4e) and [Au(NTf2)-
(IAd)] (4g) are now available in a silver-free fashion, and the
range of [Au(NHC)(NCCH3)][BF4] (5) has been expanded
to those bearing SIPr, IPrCl, IPr*, and IAd ligands. Further
investigations on the properties and applications of these
complexes are currently ongoing in our laboratory.
Procedure VB for Synthesis of [Au(CH2COCH3)(NHC)] (3). A
solution of KOtAm in toluene (1.7 mol L−1, 3.0 equiv) was added to a
stirred solution of [AuCl(NHC)] (1) (1 equiv) in acetone (0.1 mol
L−1). It was stirred at rt for 1 h and then filtered through Celite with
additional toluene (about twice the reaction volume). Solvent was
removed from the filtrate under vacuum, and the solid was dissolved in
dichloromethane (about 0.5 mol L−1) and filtered through silica with
additional dichloromethane (about the initial reaction volume). The
solution was concentrated (to about 2 mol L−1), and the product was
precipitated by addition of pentane (about the initial reaction volume).
It was collected by filtration, washed with additional pentane (about
twice the initial reaction volume), and dried under high vacuum.
Procedure VD for Synthesis of [Au(CH2COCH3)(NHC)] (3). A
solution of KOtAm in toluene (1.7 mol L−1, 3.0 equiv) was added to a
stirred solution of [AuCl(DMS)] (1 equiv) and NHC·HCl (1 equiv)
in toluene/acetone (1:1, 0.1 mol L−1). It was stirred at rt for 1 h and
then filtered through Celite with additional toluene (about twice the
reaction volume). Solvent was removed from the filtrate under
vacuum, and the solid was dissolved in dichloromethane (about 0.5
mol L−1) and filtered through silica with additional dichloromethane
(about the initial reaction volume). The solution was concentrated (to
about 2 mol L−1), and the product was precipitated by addition of
pentane (about the initial reaction volume). It was collected by
filtration, washed with additional pentane (about twice the initial
reaction volume), and dried under high vacuum.
EXPERIMENTAL SECTION
■
General Information on reagents and characterization data for known
compounds can be found in the Supporting Information (SI). Yields
for syntheses according to the various procedures are listed in Tables
1−4.
Procedure IVC for Synthesis of [Au(OH)(NHC)] (2). A solution
of KOtAm in toluene (1.7 mol L−1, 1.5 equiv) was added to a stirred
solution of [AuCl(NHC)] (1) (1 equiv) in toluene (0.1 mol L−1). The
reaction was stirred at rt for 1 h and then filtered through Celite with
additional toluene (about twice the reaction volume). Water (excess,
about the same value as base used) was added to the filtrate, and it was
concentrated. The product was precipitated by addition of pentane
(about the initial reaction volume), collected by filtration, washed with
additional pentane (about twice the initial reaction volume), and dried
under high vacuum.
Procedure IVD for Synthesis of [Au(OH)(NHC)] (2). A solution
of KOtAm in toluene (1.7 mol L−1, 1.5 equiv) was added to a stirred
solution of [AuCl(DMS)] (1) (1 equiv) and NHC·HCl (1 equiv) in
THF/toluene (1:1, 0.1 mol L−1). It was stirred at rt for 1 h and then
Procedure VIID for Synthesis of [Au(NTf2)(NHC)] (4). Bis-
(trifluoromethanesulfonyl)amine (1.1 equiv) was added to a stirred
solution of [Au(CH2COCH3)(NHC)] (3) (1 equiv) in dichloro-
methane (0.1 mol L−1). After 10 min at rt, the solution was filtered
through Celite with additional dichloromethane (about the initial
reaction volume). The solution was concentrated (to about 2 mol
F
DOI: 10.1021/acs.organomet.7b00622
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
L−1), and the product was precipitated by addition of pentane (about
the initial reaction volume). It was collected by filtration, washed with
additional pentane (about twice the initial reaction volume), and dried
under high vacuum.
Hz, 4H; CH), 2.33 (s, 3H; CH3), 1.34 (d, 3JH,H = 6.7 Hz, 12H; CH3),
3
1.33 (d, JH,H = 6.5 Hz, 12H; CH3). 13C{1H}-NMR (126 MHz,
CDCl3): δ = 188.3 (Ccarb), 146.7 (o-PhC), 133.2 (i-PhC), 130.7 (p-
PhC), 124.9 (m-PhC), 121.1 (CN), 54.2 (CH2), 29.0 (CH), 25.5
(CH3), 24.1 (CH3), 2.7 (CH3). 19F{1H}-NMR (377 MHz, CDCl3): δ
= −153.6. FTIR (ATR): ν = 2359−2303 cm−1 (CN).
Procedure VIIC for Synthesis of [Au(NTf2)(NHC)] (4). A
solution of KOtAm in toluene (1.7 mol L−1, 1.5 equiv) was added
to a stirred solution of [AuCl(NHC)] (1) (1 equiv) in toluene (0.1
mol L−1). It was stirred at room temperature for 1 h and then filtered
through Celite with additional toluene (about twice the reaction
volume). Solvent was removed under vacuum, the solid was dissolved
in dichloromethane (0.1 mol L−1), and bis(trifluoromethanesulfonyl)-
amine (1.1 equiv) was added to this stirred solution. After 10 min at rt,
the solution was filtered through Celite with additional dichloro-
methane (about the initial reaction volume). The solution was
concentrated (to about 2 mol L−1), and the product was precipitated
by addition of pentane (about the initial reaction volume). It was
collected by filtration, washed with additional pentane (about twice the
initial reaction volume), and dried under high vacuum.
Procedure VIIE for Synthesis of [Au(NTf2)(NHC)] (4). A
solution of KOtAm in toluene (1.7 mol L−1, 3.0 equiv) was added
to a stirred solution of [AuCl(DMS)] (1) (1 equiv) and NHC·HCl (1
equiv) in toluene/acetone (1:1, 0.1 mol L−1). It was stirred at rt for 1 h
and then filtered through Celite with additional toluene (about twice
the reaction volume). Solvent was removed under vacuum, the solid
was dissolved in dichloromethane (0.1 mol L−1), and bis-
(trifluoromethanesulfonyl)amine (1.1 equiv) was added to this stirred
solution. After 10 min at rt, the solution was filtered through Celite.
The solution was concentrated (to about 2 mol L−1), and the product
was precipitated by addition of pentane (about the initial reaction
volume). It was collected by filtration, washed with additional pentane
(about twice the initial reaction volume), and dried under high
vacuum.
1
[Au(IPrCl)(NCCH3)][BF4] (5c). H NMR (300 MHz, CDCl3): δ =
3
3
7.66 (t, JH,H = 7.8 Hz, 2H; p-PhH), 7.40 (d, JH,H = 7.8 Hz, 4H; m-
PhH), 2.44 (s, 3H; CH3), 2.32 (h, 3JH,H = 6.8 Hz, 4H; CH), 1.33−1.27
(m, 24H; CH3). 13C{1H}-NMR (126 MHz, CDCl3): δ = 166.4 (Ccarb),
146.0 (o-PhC), 132.7 (p-PhC), 130.3 (i-PhC), 125.2 (m-PhC), 121.8
(CN), 120.6 (C), 29.4 (CH), 25.0 (CH3), 23.6 (CH3), 2.9 (CH3).
Anal. Calcd for C29H37AuBCl2F4N3: C, 44.52; H, 4.77; N, 5.37.
Found: C, 44.51; H, 4.86; N, 5.31. 19F{1H}-NMR (282 MHz, CDCl3):
δ = −153.2. FTIR (ATR): ν = 2359−2309 cm−1 (CN).
1
[Au(IPr*)(NCCH3)][BF4] (5d). H NMR (500 MHz, CDCl3): δ =
7.28−7.18 (m, 32H; o-PhH + m-PhH), 6.88 (s, 4H; m-PhH) 6.85−
6.83 (m, 8H; p-PhH), 6.04 (s, 2H; CH), 5.07 (s, 4H; CH), 2.62 (s,
3H; CH3), 2.27 (s, 6H; CH3). 13C{1H}-NMR (126 MHz, CDCl3): δ =
166.7 (Ccarb), 142.8 (PhC), 141.6 (PhC), 141.1 (i-PhC), 140.6 (i-
PhC), 132.8 (p-PhC), 130.8 (p-PhH), 129.6 (m-PhC), 129.4 (m-PhC),
129.0 (o-PhC), 128.8 (o-PhC), 127.4 (m-PhC), 127.3 (m-PhC), 124.4
(C), 120.8 (CN), 51.5 (CH), 22.0 (CH3), 2.9 (CH3). 19F{1H}-NMR
(377 MHz, CDCl3): δ = −153.1. FTIR (ATR): ν = 2357−2308 cm−1
(CN).
[Au(IAd)(NCCH3)][BF4] (5g). 1H NMR (500 MHz, CDCl3): δ = 7.26
3
(s, 2H; CH), 2.63 (s, 3H; CH3), 2.45 (d, JH,H = 2.5 Hz, 12H; CH2),
2.31 (br m, 6H; CH), 1.77 (q, 3JH,H = 12.0 Hz, 12H; CH2). 13C{1H}-
NMR (126 MHz, CDCl3): δ = 156.9 (Ccarb), 121.9 (CN), 117.3 (CH),
59.8 (C), 44.9 (CH), 35.8 (CH2), 29.9 (CH2), 3.2 (CH3). 19F{1H}-
NMR (471 MHz, CDCl3): δ = −153.3. Anal. Calcd for
C25H35AuBF4N3: C, 45.40; H, 5.33; N, 6.35. Found: C, 45.23; H,
5.49; N, 6.17.
Procedure VIID′ for Synthesis of [Au(NHC)(NCCH3)][BF4] (5).
tetrafluoroboric acid−diethyl ether complex (1.1 equiv) was added to a
stirred solution of [Au(CH2COCH3)(NHC)] (3) (1 equiv) in
acetonitrile (0.1 mol L−1). After 10 min at rt, the solution was filtered
through magnesium sulfate. The solution was concentrated (to about
2 mol L−1), and the product was precipitated by addition of pentane
(about the initial reaction volume). It was collected by filtration,
washed with additional pentane (about twice the initial reaction
volume), and dried under high vacuum.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00622.
Procedure VIIC′ for Synthesis of [Au(NHC)(NCCH3)][BF4] (5).
A solution of KOtAm in toluene (1.7 mol L−1, 1.5 equiv) was added to
a stirred solution of [AuCl(NHC)] (1) (1 equiv) in toluene (0.1 mol
L−1). It was stirred at room temperature for 1 h and then filtered
through Celite with additional toluene (about twice the reaction
volume). Solvent was removed under vacuum, the solid was dissolved
in dichloromethane (0.1 mol L−1), and tetrafluoroboric acid−diethyl
ether complex (1.1 equiv) was added to this stirred solution. After 10
min at rt, the solution was filtered through Celite, concentrated, and
precipitated by addition of pentane (about the initial reaction volume).
It was collected by filtration, washed with additional pentane (about
twice the initial reaction volume), and dried under high vacuum.
Procedure VIIE′ for Synthesis of [Au(NHC)(NCCH3)][BF4] (5).
A solution of KOtAm in toluene (1.7 mol L−1, 3.0 equiv) was added to
a stirred solution of [AuCl(DMS)] (1 equiv) and NHC·HCl (1 equiv)
in toluene/acetone (1:1, 0.1 mol L−1). It was stirred at rt for 1 h and
then filtered through Celite with additional toluene (about twice the
reaction volume). Solvent was removed under vacuum, the solid was
dissolved in dichloromethane (0.1 mol L−1), and tetrafluoroboric
acid−diethyl ether complex (1.1 equiv) was added to this stirred
solution. After 10 min at rt, the solution was filtered through Celite.
The solution was concentrated (to about 2 mol L−1), and the product
was precipitated by addition of pentane (about the initial reaction
volume). It was collected by filtration, washed with additional pentane
(about twice the initial reaction volume), and dried under high
vacuum.
Text, schemes, and tables giving general information on
optimization studies, references for known complexes,
and NMR spectra (PDF)
Accession Codes
CCDC 1510730−1510732 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
*S.P.N.: E-mail: Steven.Nolan@ugent.be; Tel: +32 (0) 9264
4458; Fax: +32 (0) 9264 4983
*C.S.J.C.: E-mail: Catherine.Cazin@ugent.be
ORCID
Richard M. P. Veenboer: 0000-0002-4878-580X
Fady Nahra: 0000-0002-1115-9725
Steven P. Nolan: 0000-0001-9024-2035
Characterization Data. [Au(SIPr)(NCCH3)][BF4] (5b). 1H NMR
(300 MHz, CDCl3): δ = 7.46 (t, 3JH,H = 7.8 Hz, 2H; p-PhH), 7.26 (d,
Notes
3
3JH,H = 7.8 Hz, 4H; m-PhH), 4.23 (s, 4H; CH2), 2.98 (h, JH,H = 6.8
The authors declare no competing financial interest.
G
DOI: 10.1021/acs.organomet.7b00622
Organometallics XXXX, XXX, XXX−XXX

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Article
Petersen, J. L.; Shi, X. J. Am. Chem. Soc. 2012, 134, 9012−9019.
(c) Barrio, P.; Kumar, M.; Lu, Z.; Han, J.; Xu, B.; Hammond, G. B.
Chem. - Eur. J. 2016, 22, 16410−16414. (d) Silver salts are also
present in the early synthesis of one [AuCl(NHC)] complex via
transmetallation using Ag−NHC: Schneider, S. K.; Herrmann, W. A.;
Herdtweck, E. Z. Anorg. Allg. Chem. 2003, 629, 2363−2370.
(8) Schmidbaur, H.; Schier, A. Z. Naturforsch., B: J. Chem. Sci. 2011,
66, 329−350.
ACKNOWLEDGMENTS
■
The European Research Council (ERC) and the Engineering
and Physical Sciences Research Council (EPSRC), UK are
gratefully acknowledged for their support. Umicore AG is
thanked for generous donations of auric acid. The EPSRC
National Mass Spectrometry Service Centre (NMSSC) is
gratefully acknowledged for HRMS analyses. S.P.N. thanks the
King Abdullah University of Science and Technology
(9) (a) Gaillard, S.; Slawin, A. M. Z.; Nolan, S. P. Chem. Commun.
2010, 46, 2742−2744. (b) Ramon
Porta, A.; D’Alfonso, A.; Zanoni, G.; Nolan, S. P. Organometallics
2010, 29, 3665−3668. (c) Gomez-Suarez, A.; Ramon, R. S.; Slawin, A.
́
, R. S.; Gaillard, S.; Slawin, A. M. Z.;
́
(KAUST) for support. Dr Alberto Gomez Herrera is thanked
for synthetic contributions.
́
́
́
M. Z.; Nolan, S. P. Dalton Trans. 2012, 41, 5461−5463.
(10) Nahra, F.; Patrick, S. R.; Bello, D.; Brill, M.; Obled, A.; Cordes,
D. B.; Slawin, A. M. Z.; O’Hagan, D.; Nolan, S. P. ChemCatChem
2015, 7, 240−244.
DEDICATION
■
Dedicated to the memory of Professor Istvan
́
E. Marko.
́
ABBREVIATIONS
́
(11) Brill, M.; Nahra, F.; Gomez-Herrera, A.; Zinser, C.; Cordes, D.
■
B.; Slawin, A. M. Z.; Nolan, S. P. ChemCatChem 2017, 9, 117−120.
(12) Boogaerts, I. I. F.; Nolan, S. P. J. Am. Chem. Soc. 2010, 132,
8858−8859.
DMS, dimethyl sulfide; IAd, 1,3-di(adamantyl)imidazol-2-
ylidene; ICy, 1,3-bis(cyclododecyl)imidazol-2-ylidene; IDD,
1,3-bis(cyclododecyl)imidazol-2-ylidene; IMes, 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-ylidene; IPr, 1,3-bis(2,6-di-
isopropylphenyl)imidazol-2-ylidene; IPrCl, 4,5-dichloro-1,3-bis-
(2,6-diisopropylphenyl)imidazol-2-ylidene; IPr*, 1,3-bis(2,6-
bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene;
IPr*Tol, 1,3-bis(2,6-bis(diptolylmethyl)-4-methylphenyl)-
imidazol-2- ylidene); ItBu, 1,3-bis(tertbutyl)imidazol-2-ylidene;
IPrMe, 4,5-dimethyl-bis(2,6-diisopropylphenyl)imidazol-2-yli-
dene; nd, not determined; NHC, N-heterocyclic carbene;
NMR, nuclear magnetic resonance; rt, room temperature;
SIMes, 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene;
SIPr, 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene
(13) Gaillard, S.; Bosson, J.; Ramon
Nolan, S. P. Chem. - Eur. J. 2010, 16, 13729−13740.
(14) Ramon, R. S.; Gaillard, S.; Poater, A.; Cavallo, L.; Slawin, A. M.
Z.; Nolan, S. P. Chem. - Eur. J. 2011, 17, 1238−1246.
(15) (a) Gasperini, D.; Collado, A.; Gomez-Suarez, A.; Cordes, D. B.;
́
, R. S.; Nun, P.; Slawin, A. M. Z.;
́
́
́
Slawin, A. M. Z.; Nolan, S. P. Chem. - Eur. J. 2015, 21, 5403−5412.
(b) A similar coumpound, phosphine-based [Au(CH2COCH3)
(PMes3)], recently showed some interesting activities, see: Hashmi,
A. S. K.; Schafer, S.; Wolfle, M.; Diez Gil, C.; Fischer, P.; Laguna, A.;
̈
̈
Blanco, M. C.; Gimeno, M. C. Angew. Chem., Int. Ed. 2007, 46, 6184−
6187.
(16) Gatto, M.; Belanzoni, P.; Belpassi, L.; Biasiolo, L.; Del Zotto, A.;
Tarantelli, F.; Zuccaccia, D. ACS Catal. 2016, 6, 7363−7376.
(17) Huang, J.; Nolan, S. P. J. Am. Chem. Soc. 1999, 121, 9889−9890.
(18) Jafarpour, L.; Stevens, E. D.; Nolan, S. P. J. Organomet. Chem.
2000, 606, 49−54.
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