Gold(I) and Gold(III) Complexes of Expanded-Ring N-Heterocyclic Carbenes: Structure, Reactivity, and Catalytic Applications

Article abstract of DOI:10.1021/acs.organomet.9b00718

The oxidative addition of bromine to homo- and heterobis(carbene) gold(I) complexes 1-6 containing expanded-ring N-heterocyclic carbene (erNHC) ligands was explored to prepare the first examples of gold(III) erNHC complexes. The use of stoichiometric amou

Full text of DOI:10.1021/acs.organomet.9b00718

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Gold(I) and Gold(III) Complexes of Expanded-Ring N‑Heterocyclic
Carbenes: Structure, Reactivity, and Catalytic Applications
Anuj Kumar, Chandan Singh, Hendrik Tinnermann, and Han Vinh Huynh*
Department of Chemistry, National University of Singapore, Science Drive 3, Singapore 117543
*
S Supporting Information
ABSTRACT: The oxidative addition of bromine to homo- and
heterobis(carbene) gold(I) complexes 1−6 containing expanded-ring N-
heterocyclic carbene (erNHC) ligands was explored to prepare the first
examples of gold(III) erNHC complexes. The use of stoichiometric
amounts of bromine consistently gave clean gold-centered oxidations
leading to the isolation of monocarbene and mixed carbene complexes of
i
the type [AuBr (erNHC)] (7−9) and trans-[AuBr ( Pr -bimy)(erNHC)]-
3
2
2
BF (13−15), respectively. The use of excess bromine additionally led to
ligand brominations in the monocarbene series affording [Au-
Br (erNHC )] complexes (10−12), while in the case of the heterobis-
carbene) series, tribromide complexes of the type trans-[AuBr ( Pr -
4
Br2
3
i
(
2
2
bimy)(erNHC)]Br (16−18) were obtained instead. Comparison of the
3
catalytic activities of all complexes in the hydroamination of alkynes
revealed the superior performance of mono-erNHC complexes in all cases.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
I
N-Heterocyclic carbenes (NHCs) are state-of-the-art ligands in
organometallic chemistry.
five-membered heterocycles, but expanded-ring NHCs
erNHCs) have also received an increasing amount of
attention in recent years.
donating and bulkier compared to classical five-membered
NHCs due to their larger N−C−N angles.
we have reported a detailed stereoelectronic profiling of
Gold(I) Complexes. The syntheses of Au NHC complexes
1, 2, 4, and 5 containing the six- and seven-membered erNHCs
1
−5
Most NHCs are derived from
6-Mes and 7-Mes, respectively, have been reported recently by
17
our group (Scheme 1). Similarly, the eight-membered NHC
complex [AuBr(8-Mes)] (3) has been prepared in a moderate
yield of 64% by the reaction of salt C with [AuCl(tht)] in the
presence of KHMDS starting at −78 °C with gradual warming
to ambient temperature. The successful complex formation was
evident from the absence of the NCHN resonance character-
(
6
−11
In general, erNHCs are more
12−16
In this respect,
saturated erNHCs with ring sizes ranging from six to eight
1
1
7
istic for ligand precursor C in the H NMR spectrum of 3,
atoms using gold(I) and palladium(II). Very recently,
Hashmi and co-workers managed to prepare the first gold(I)
complexes of nine- and ten-membered erNHCs as the largest
while a new gold-bound carbene resonance (Au NCN) is
1
3
observed at 202.8 ppm in the C NMR spectrum.
Single crystals of 3 suitable for X-ray diffraction studies were
grown by slow evaporation of its saturated solution in CH CN.
The molecular structure depicted in Figure 1 confirms the
proposed composition of species 3 as a neutral and linear
bromido-monocarbene gold(I) complex. Using this structure, a
18
members in this family. These and other studies demonstrate
that the coordination of erNHCs is well explored with gold(I)
3
1
9,20
centers.
The resulting linear complexes are usually air- and
moisture-stable and can be handled with ease, which should
allow for further reactivity studies. One common reaction of
electron-rich gold(I) NHC complexes is the oxidative addition
of halogens, which usually affords the respective square-planar
percentage of buried volume (%V ) of 46.5 was determined
bur
as an estimate for the steric bulk of the 8-Mes ligand. As
expected, 8-Mes is bulkier than 7-Mes (43.1), but smaller %
Vbur values were also determined for 9-Mes (43.6) and 10-Mes
(43.3) using their [AuCl(erNHC)] complexes. As for other
gold(I) erNHC complexes, ligand disproportionation
not observed for complex 3 upon prolonged standing in
solution.
1
7
2
1
gold(III) NHC complexes. Although erNHCs are known to
be stronger donors than classical NHCs, it is surprising that
gold(III) complexes of erNHCs are unknown so far. In a
search for such compounds, we explored reactions of mono-
and heterobis(carbene) gold(I) complexes containing erNHC
ligands with stoichiometric and excess amounts of bromine.
Herein, we report the preparation and characterization of the
first gold(III) erNHC complexes. In addition, the catalytic
activities of gold(I) and gold(III) erNHC complexes in the
hydroamination of alkynes are compared.
1
8
2
2,23
was
Complex 3 provides access to the respective heterobis-
i
(
NHC) complex [Au( Pr -bimy)(8-Mes)]BF (6) in excellent
2
4
Received: October 24, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00718
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Organometallics
Article
I
21
Scheme 1. Preparation of Expanded-Ring Au erNHC
Complexes
to afford the gold(III) NHC analogues. This reaction is
usually straightforward because NHCs are very good electron
donors. It is therefore surprising that Au complexes of
III
erNHCs are unknown thus far, although erNHCs are even
stronger donors compared to their classical five-membered
NHC counterparts. To explore such reactivity, the charge-
I
neutral bromido-erNHC Au complexes 1−3 were treated with
bromine in an initial trial (Scheme 2). Indeed, gold-centered
Scheme 2. Synthetic Route to erNHC AuIII Complexes
oxidative additions occurred readily, and gold(III) mono-
carbene complexes of the formula [AuBr (erNHC)] (7−9)
3
were obtained in good yields of 88−93% when 1 equiv of
bromine was used. The notable upfield shifts of the carbene
resonances to 169.0 ppm (7), 176.6 ppm (8), and 174.6 ppm
Figure 1. Molecular structures of complexes 3 showing 50%
probability ellipsoids. Hydrogen atoms have been omitted for the
sake of clarity. Selected bond lengths (angstroms) and angles
1
3
(
9) observed in the C NMR spectra agree well with the
21
III
formation of Au species. The presence of dominant peaks
for the [M − Br] ions in positive mode ESI mass spectra
+
(
degrees) for 3: Au1−C1, 2.026(3); Au1−Br1, 2.417(1); C1−
Au1−Br1, 179.62(8); N1−C1−N2, 123.4(3); C16−N2−C1,
16.2(2); C7−N1−C1, 116.3(2); Au1−C1−N2, 118.2(1); Au1−
C1−N1, 118.4(2).
provides additional support. Finally, their identities as
tribromido-erNHC gold(III) complexes were corroborated
by X-ray diffraction of single crystals obtained by slow
evaporation of their concentrated solutions in acetonitrile.
The solid-state molecular structures of 7−9 depicted in
1
i
yields of 96% upon treatment with Pr -bimy·HBF and Ag O
2
4
2
III
at ambient temperature in dichloromethane. Support for the
Figure 2 reveal Au centers that are coordinated by three
formation of complex 6 was obtained by positive mode ESI
bromido ligands and one erNHC in a square-planar geometry.
i
III
MS, which shows a base peak for the respective [Au( Pr -
Au −C bond distances of 2.058(8) Å (7), 2.057(4) Å (8),
2
+
1
bimy)(8-Mes)] cation. H NMR spectroscopy reveals the
isopropyl methine signal of the Pr -bimy ligand in complex 6
and 2.072(4) Å (9) were found to be slightly longer than the
respective distances of 2.003(3) Å (1), 2.004(3) Å (2), and
i
2
I
17
at 3.72 ppm, which is notably more upfield than those in the
six- and seven-membered analogues 4 and 5, respectively (i.e.,
2.026(3) Å (3), respectively, in their Au precursors.
Supposedly, this bond elongation is due to enhanced crowding
with the increase in the coordination number from two to four.
On the other hand, N−C−N angles of 121.8(7)° (7),
122.9(3)° (8), and 124.6(3)° (9) differ only marginally from
1
7
3
.93 and 3.82 ppm, respectively). This upfield shift is in line
24
with the increased anisotropic effect of mesityl rings due to
the larger NCN angle of the eight-membered 8-Mes ligand in
complex 6. As anticipated, two distinct carbene signals are
found in the C NMR spectrum of this complex. The carbene
atom of 8-Mes resonates at 209.6 ppm, while that for the Pr -
I
those of the parent Au complexes, i.e., 118.9(3)° (1),
1
3
119.8(2)° (2), and 123.4(3)° (3), respectively. Nevertheless,
complex 9 exhibits the largest N−C−N angle among all
reported Au−erNHC complexes, including those of nine- and
i
2
bimy is found at 186.5 ppm. A significant downfield shift of the
former was noted compared to that in precursor complex 3
18
ten-membered erNHCs.
25
due to the coordination of a second strong NHC donor.
We found that stoichiometry control is very important in the
formation of complexes 7−9. The use of excess bromine
additionally led to the bromination of the mesityl wing tips of
Gold(III) Monocarbene Complexes. Gold(I) NHC
complexes can easily undergo oxidative addition with halogens
B
DOI: 10.1021/acs.organomet.9b00718
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Article
Figure 2. Molecular structures of complexes 7·0.5H O, 8, and 9 showing 50% probability ellipsoids. Only one independent molecule is shown for
2
7
. Hydrogen atoms and solvent molecules have been omitted for the sake of clarity. Selected bond lengths (angstroms) and angles (degrees) for 7:
Au1−C1, 2.058(8); Au1−Br1, 2.415(1); Au1−Br2, 2.437(9); Au1−Br3, 2.421(1); C1−Au1−Br2, 175.4(2); Br1−Au1−Br3, 177.5(4); N2−C1−
N1, 121.8(7). Selected bond lengths (angstroms) and angles (degrees) for 8: Au1−C1, 2.057(4); Au1−Br1, 2.412(5); Au1−Br2, 2.456(4); Au1−
Br3, 2.413(5); C1−Au1−Br2, 173.4(1); Br1−Au1−Br3, 176.2(2); N2−C1−N1, 122.9(3). Selected bond lengths (angstroms) and angles
(
1
degrees) for 9: Au1−C1, 2.072(4); Au1−Br1, 2.423(5); Au1−Br2, 2.450(4); Au1−Br3, 2.422(4); C1−Au1−Br2, 176.8(1); Br1−Au1−Br3,
76.4(1); N2−C1−N1, 124.6(3).
the erNHC ligands by electrophilic substitution. Interestingly,
the introduction of one bromo substituent deactivates each
aryl ring for a second bromination, giving rise to gold(III)
complexes of dibrominated erNHCs as the final products
(Scheme 2). Because the reactions did not reach completion
with 3 or 4 equiv of bromine, a 10-fold excess of bromine was
used at ambient temperature instead. Under these conditions,
Br2
the [AuBr (erNHC )]-type complexes (10−12) were
3
isolated in good yields of 73−93%. Notably, the bromination
of the erNHC ligands leads to a reduced solubility of the
respective complexes, and complexes 10−12 show very poor
solubility in common organic solvents such as dichloro-
methane, chloroform, acetonitrile, and dimethyl sulfoxide.
Figure 3. Molecular structures of complexes 11·H O showing 50%
+
2
Positive mode ESI MS shows strong [M − Br] peaks for all
probability ellipsoids. Disordered atoms of lower occupancy, the
solvent molecule, and hydrogen atoms have been omitted for the sake
of clarity. Selected bond lengths (angstroms) and angles (degrees) for
11: Au1−C1, 2.071(2); Au1−Br1, 2.449(2); Au1−Br2, 2.411(2);
Au1−Br3, 2.418(2); C1−Au1−Br2, 178.0(5); Br2−Au1−Br3,
179.3(1); N2−C1−N1, 123.7(1).
three complexes due to loss of one bromido ligand. Upon
bromination of the mesityl substituent, all methyl groups
become inequivalent, and accordingly, three different methyl
1
signals are observed in the H NMR spectra of complexes 10−
1
3
1
2. The
C
NMR signals detected at 169.6 ppm (10),
carbene
1
76.7 ppm (11), and 175.1 ppm (12) are in the same range as
those of their nonbrominated analogues 7−9, indicating that
the remote brominations have little effect on the carbene
donor. On the other hand, all aromatic carbon atoms of each
mesityl ring become distinct, and an increase in the resonances
in the aromatic region is expected. Moreover, the various
degrees of backbone twisting of the erNHC ligands result in
different orientations of the brominated wing tips relative to
i
the cationic heterobis(carbene) complexes [Au( Pr -bimy)-
2
(
erNHC)]BF (4−6) were also subjected to different amounts
of bromine in dichloromethane at ambient temperature
Scheme 3). The addition of 1 equiv of bromine resulted in
a clean oxidative addition at the gold(I) center giving the
cationic gold(III) complexes [AuBr ( Pr -bimy)(6-Mes)]BF
4
(
i
2
2
4
each other, which complicate the 1 C NMR spectra of the
3
i
i
(
13), [AuBr ( Pr -bimy)(7-Mes)]BF (14) and [AuBr ( Pr -
2 2 4 2 2
Br2
complexes further. Single crystals of [AuBr (7-Mes )] (11)
3
bimy)(8-Mes)]BF (15) in high yields of >95%.
4
obtained from a concentrated solution in dichloromethane
In all three cases, base peaks are observed at m/z 879 (13),
m/z 893 (14), and m/z 907 (15) for the respective
[AuBr ( Pr -bimy)(erNHC)] molecular cations in their
were found to be suitable for X-ray diffraction studies. Due to
Br2
i
+
the many possible orientations of the highly flexible 7-Mes
2 2
ligand, only highly disordered structures could be obtained
despite several attempts. A best representative depiction of the
molecular structure is shown in Figure 3, which in combination
with other spectroscopic and spectrometric analytical methods
can confirm the monobromination of each mesityl ring.
Gold(III) Heterobis(carbene) Complexes. To explore
the structural diversity of gold(III) erNHC complexes further,
positive mode ESI mass spectra. The erNHC carbene signals
are found at 178.3 ppm (13), 187.7 ppm (14), and 184.1 ppm
(15), while those for the benzimidazolin-2-ylidenes resonate at
155.6 ppm (13), 155.8 ppm (14), and 154.8 ppm (15). All of
these carbene signals are significantly upfield-shifted relative to
those in the gold(I) precursors 4−6, clearly indicating an
oxidation of the gold center from I to III.
C
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Scheme 3. Synthetic Route to Hetero-Bis(carbene) AuIII
Complexes
observed this phenomenon in isoelectronic and isostructural
palladium(II) complexes as well as in the gold(I) heterobis-
(
carbene) complexes 4 and 5 and ascribed it to the increasing
anisotropic effects of the mesityl substituents in the erNHC
17
ligands. Single-crystal X-ray diffraction studies confirm the
identities of all three gold(III) heterobis(carbene) complexes
(
see the Supporting Information).
The reactions of cationic Au heterobis(carbene) complexes
I
4
−6 with 10 equiv of bromine show a very different outcome
compared to those of the charge-neutral monocarbene
complexes 1−3. In these cases, no wing-tip brominations
took place at all after the gold-centered oxidations. Instead, the
excess of bromine led to the formation of tribromides, which
replaced the tetrafluoroborate counteranions, and the new
i
gold(III) complexes [AuBr ( Pr -bimy)(6-Mes)]Br (16),
[
2
2
3
i
i
AuBr ( Pr -bimy)(7-Mes)]Br (17), and [AuBr ( Pr -bimy)-
2 2 3 2 2
(
8-Mes)]Br (18) were obtained in good yields of >85%.
3
Supposedly, electrophilic substitution of the mesityl groups is
prevented by the positive charge of complexes 4−6.
Complexes 13−15 and 16−18 show very similar analytical
characteristics, because they differ in only the counteranion.
However, complete replacement of the tetrafluoroborate
anions is supported by the lack of any fluorine signals in the
1
9
F NMR spectra of complexes 16−18.
The molecular structures of all heterobis(carbene) gold(III)
complexes (13−18) were also established by single-crystal X-
ray diffraction, and those of 16−18 are depicted in Figure 4.
III
Another interesting observation is that the signals for the
isopropyl methine protons shift stepwise upfield from 3.51
ppm (13) to 3.47 ppm (14) and finally to 3.39 ppm (15) with
increasing ring sizes of the erNHC ligands. We have previously
All complexes are square planar, in which the Au centers are
coordinated by two different NHCs and two bromido ligands
III
in an exclusively trans arrangement. The Au −erNHC bond
distances in the range of 2.072−2.105 Å are notably longer
Figure 4. Molecular structures of complexes 16·CHCl , 17·CHCl , and 18 showing 50% probability ellipsoids. Hydrogen atoms and the solvent
3
3
molecule have been omitted for the sake of clarity. Selected bond lengths (angstroms) and angles (degrees) for 16: Au1−C1, 2.033(4); Au1−C14,
2
.076(4); Au1−Br1, 2.426(1); Au1−Br2, 2.420(1); C14−Au1−C1, 176.3(2); Br1−Au1−Br2, 170.8(2); N4−C14−N3, 120.6(3). Selected bond
lengths (angstroms) and angles (degrees) for 17: Au1−C1, 2.041(3); Au1−C14, 2.085(3); Au1−Br1, 2.416(1); Au1−Br2, 2.420(1); C14−Au1−
C1, 176.7(1); Br1−Au1−Br2, 173.7(1); N4−C14−N3, 121.6(3). Selected bond lengths (angstroms) and angles (degrees) for 18: Au1−C1,
2.043(2); Au1−C14, 2.105(2); Au1−Br1, 2.422(3); Au1−Br2, 2.422(3); C14−Au1−C1, 178.2(1); Br1−Au1−Br2, 170.5(1); N4−C14−N3,
124.9(2).
D
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Article
III
i
a
than the Au − Pr -bimy bond lengths ranging from 2.034 to
Table 1. Catalyst Screening
2
2
.053 Å, possibly indicating the increased strengths of the
latter. Specifically, the Au −erNHC distances of 2.084(5) Å in
4 and 2.085(3) Å in 17 were found to be larger than the
III
1
distance of 2.035(4) Å for the respective bond found in their
I
common parent Au complex 5, which can be ascribed to an
b
conversion /
c
increase in the coordination number (vide supra).
To the best our knowledge, complexes 7−18 are the first
examples of Au complexes bearing erNHC ligands.
Hydroamination of Alkynes with Primary Amines.
The gold-catalyzed hydroamination reaction of alkynes and
amines represents a good example for a simple one-step
conversion of inexpensive and readily available substrates,
entry
Au NHC
[AuBr(6-Mes)] (1)
[AuBr(7-Mes)] (2)
[AuBr(8-Mes)] (3)
Ag salt
yield
1
2
3
4
5
6
7
8
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
−
91
96
98/94
86
88
90
80
74
80
0
0
0
13
0
0
III
[AuBr (6-Mes)] (7)
3
[AuBr (7-Mes)] (8)
3
[AuBr (8-Mes)] (9)
3
26−33
Br
which is 100% atom efficient.
Thus, we were interested in
[AuBr (6-Mes )] (10)
3
Br
examining and comparing the catalytic efficiencies of all of our
synthesized Au erNHC complexes in this important reaction.
In a preliminary study, all Au erNHC complexes 1−18 have
been tested as precatalysts for the hydroamination of alkynes
and primary amines as a standard test reaction. Initially, the
simplest precatalyst [AuBr(6-Mes)] (1) was chosen for the
exploration of reaction conditions. The complex was found to
catalyze the hydroamination of phenylacetylene and mesityl-
amine at 50 °C using AgBF as a bromide scavenger and gave
2% conversion (by GC/GC-MS) after 24 h with respect to
the mesitylamine, which was chosen as the limiting substrate in
this reaction (Table S1, entry 1). The use of AgSbF gave
better product conversion [73% (Table S1, entry 2)] under the
same reaction condition. The performance was further
improved at 90 °C, which allowed for shorter reaction times
Table S1, entries 3 and 5). Among the different halide
scavengers (AgPF , AgOAc, NaBF , and KBF ), AgSbF was
[AuBr (7-Mes )] (11)
3
Br
9
[AuBr (8-Mes )] (12)
3
i
10
11
12
13
14
15
16
[Au( Pr -bimy)(6-Mes)]BF (4)
[Au( Pr -bimy)(7-Mes)]BF (5)
2
4
i
−
−
2
2
2
4
4
4
i
[Au( Pr
-bimy)(8-Mes)]BF
-bimy)(6-Mes)]BF
-bimy)(6-Mes)]BF
-bimy)(7-Mes)]BF
-bimy)(8-Mes)]BF
(6)
(4)
i
[Au( Pr
AgSbF
(13) AgSbF
(14) AgSbF
(15) AgSbF
6
6
6
6
i
[AuBr
[AuBr
[AuBr
( Pr
2
2
2
2
2
2
4
4
4
i
( Pr
i
( Pr
0
0
0
0
4
i
1
1
1
7
8
9
[AuBr ( Pr -bimy)(6-Mes)]Br (16)
[AuBr ( Pr -bimy)(7-Mes)]Br (17)
[AuBr ( Pr -bimy)(8-Mes)]Br (18)
AgSbF6
AgSbF6
AgSbF6
5
2
2
3
i
2
2
3
i
2
2
3
6
a
Reaction conditions: phenylacetylene (0.3 mmol, 1.5 equiv),
mesitylamine (0.2 mmol, 1 equiv), AgSbF (0.004 mmol, 2 mol %),
Au NHC (0.004 mmol, 2 mol %) in CH CN (∼1 mL) heated at 90
C in a screw cap tube under air. GC/GC-MS conversion to
6
3
b
°
(
c
product. Isolated yield.
6
4
4
6
found to be the most suitable for the present reaction
With [AuBr(8-mes)] (3) having been identified as the most
active precatalyst, a small substrate scope study was conducted
with different alkynes and amines. Notably, various substituted
anilines and phenylacetylenes were found to undergo hydro-
aminations, giving the desired products in excellent yields
condition in acetonitrile (Table S1, entries 3−8). Solvents
other than CH CN were found to be less suitable for the
3
reaction (Table S1, entries 9−13). Exceptionally, comparable
conversion was observed in 1,4-dioxane. However, acetonitrile
gave cleaner reactions. Finally, poor hydroamination activity
was noted in the absence of any gold complex. The very low
yield in this case is attributed to a low background catalytic
(
2
Table 2). In particular, sterically demanding mesitylamine and
,6-diisopropylaniline showed very good reactivity (>99%) and
gave addition products to phenylacetylene in excellent yields
Table 2, entries 1 and 3). The parent aniline also reacted very
activity of AgSbF (Table S1, entry 14).
6
(
With optimized reaction conditions in hand, the remaining
complexes 2−18 were benchmarked against complex 1 to
evaluate their catalytic efficiency in the hydroamination of
phenyl acetylene with mesitylamine.
The seven-membered erNHC complex 2 was found to be
more active than its six-membered analogue 1 and yielded 96%
conversion (Table 1, entry 2). Within the same series, the
well (Table 2, entry 2). 4-Methoxyphenylamine and 1-
naphthylamine gave excellent reaction product conversion
(
Table 2, entries 4 and 5). Phenylacetylenes with electron-
donating substituents, e.g., 4-methoxyphenylacetylene, 4-
methylphenylacetylene, and 4-(dimethylamino)-
phenylacetylene, or with electron-withdrawing substituents,
e.g., 4-fluorophenylacetylene, gave excellent reaction outcomes
under standard reaction condition (Table 2, entries 6−9).
However, the aliphatic butylamine was found to be unreactive.
Likewise, the aliphatic 1-hexyne also gave poor conversion
when reacted with mesitylamine under this reaction condition
eight-membered erNHC complex 3 gave the best results with
III
9
8% conversion (Table 1, entry 3). Au complexes 7−12 with
I
a single erNHC ligand are all active but are inferior to their Au
counterparts 1−3 (Table 1, entries 4−9). Moreover, a decrease
in conversion was observed with complexes 10−12 containing
the electron-poorer, bromo-substituted erNHCs ligands.
Notably, all cationic heterobis(carbene) complexes were
inactive regardless of the gold oxidation state, the nature of
the counteranion, and the presence of the halide scavenger
(
Table 2, entries 10 and 11).
In general, the catalytic efficiency of our most active
I
precatalyst 3 compares well with those of other reported Au
NHC complexes for the intermolecular hydroamination of
terminal alkynes and primary amines. However, a fair
comparison is often not possible due to the application of
different reaction conditions and times, varying additives, and
varying catalyst loadings. Nevertheless, precatalyst 3 gave
(
Table 1, entries 10−19). The inactivity of these complexes
could be rationalized by the lack of binding sites for incoming
substrates due to the presence of two strong Au−NHCs bonds
I
I
and the increased steric bulk. Overall, charge-neutral Au
better results than 1,2,4-triazole- and imidazole-derived Au
complexes under similar reaction conditions. Similarly,
2
6
complexes with larger and supposedly stronger donating
erNHCs ligands gave rise to better precatalysts in this reaction.
precatalyst 3 shows far better reactivity than pyrazole-
E
DOI: 10.1021/acs.organomet.9b00718
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Table 2. Substrate Scope Study
a
Reaction conditions: alkyne (0.75 mmol, 1.5 equiv), amine (0.5 mmol, 1 equiv), AgSbF (0.01 mmol, 2 mol %), Au NHC (0.01 mmol, 2 mol %)
6
b
c
d
in CH CN (∼1 mL) heated at 90 °C in a screw cap tube under air. GC/GC-MS conversion to product. Isolated yield. Decomposition of the
product during column chromatography.
3
I
III
13
functionalized imidazole-derived Au and Au NHC com-
adduct, which leads to an expected upfield shift of the C
carbene
3
1
plexes. Dinuclear Au NHC complexes and [AuCl(IPr)]
showed results comparable to those for complex 3 under neat
conditions. Finally, some hexaazatriphenylene-bridged,
benzoferrocenyl-fused, and polyaromatic-annulated NHC
complexes outperformed precatalyst 3 and were more active at
comparatively lower catalyst loadings. However, these
precatalysts contain much more complicated ligand systems.
To gain insight into the catalytically active species generated
resonance (see Figure S82B). Addition of 2 equiv of aniline
and phenylacetylene yielded the hydroamination product
almost immediately, and three carbene resonances for three
3
0
34
35
36
I
distinct Au erNHC adducts {e.g., [Au(erNHC)L]SbF , where
6
1
3
L = PhNH , PhCCH, or CD CN} were observed in the
NMR spectrum (Figure S82C). Further heating of the reaction
mixture indicated the presence of only Au erNHC species,
while no signals for Au erNHC species could be observed.
The study was repeated with Au precatalyst 9, which,
however, showed poor solubility in CD CN, and the initial C
NMR spectrum was not very conclusive (Figure S83A).
C
2
3
I
III
I
III
13
III
by the Au and Au precatalysts, detailed C NMR studies
have been performed. Thus, the most active precatalyst 3 and
its direct Au analogue 9 were chosen for catalytic NMR
1
3
3
III
monitoring experiments at 50 mol % loading in CD CN to
However, addition of an equimolar amount of AgSbF led to
3
6
ensure decent resolution of the NMR spectra. Precatalyst 3 was
the formation of two new species by the presence of two new
methylene carbon signals (Figure S83B). The introduction of
substrates resulted in product formation; new Au −erNHC
first heated with an equimolar amount of AgSbF at 90 °C.
6
I
Halide abstraction should lead to formation of a CD CN
3
F
DOI: 10.1021/acs.organomet.9b00718
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
adducts were also observed in the 13C NMR spectra, while
CDCl
) δ 202.8 (C8‑Mes), 147.2, 138.3, 134.4, 130.7 (Ar−C), 53.6,
3
III
2
9.1, 22.8 (CH ), 21.7, 19.5 (CH ); MS (ESI) m/z calcd for
48 64
Au species were absent (Figure S83C). In conclusion, this
2
3
+
III
C H BrN Au [2 M − Br] 1171, found 1171. Anal. Calcd for
C H BrN Au: C, 46.09; H, 5.16; N, 4.48. Found: C, 46.40; H, 5.18;
study supports the notion that the Au precatalyst 9 is
4
2
I
24 22 2
reduced to an Au erNHC adduct as the likely active species
N, 4.88.
(
Figure S84). Supposedly, this can occur via reductive
i
[
Au( Pr -bimy)(8-Mes)]BF (6). A mixture of [AuBr(8-Mes)] (3)
2 4
i
elimination of Br2.
(
0.160 g, 0.255 mmol), Pr -bimy·HBF (0.074 g, 0.255 mmol), and
2 4
Ag O (0.059 g, 0.255 mmol) was allowed to stir in CH Cl (40 mL)
2
2
2
CONCLUSIONS
We have reported the preparation and full characterization of
the first gold(III) complexes bearing expanded-ring NHCs
■
at ambient temperature for 1 h. Then, the reaction mixture was
filtered through Celite, and the solvent of the filtrate was removed
under vacuum to give the crude product as a white solid, which was
purified by washing with hexane (∼3 × 5 mL) to give a white solid
(
erNHCs) by simple oxidative addition of bromine to the
1
3
(
0.204 g, 96%): H NMR (500 MHz, CDCl ) δ 7.48 [dd, J(H,H) =
Hz, 2 H, Ar−H], 7.25 [dd, J(H,H) = 6 Hz, 2 H, Ar−H], 6.98 (s, 4
3
respective gold(I) erNHC precursors. Using this approach,
charge-neutral [AuBr (erNHC)] or cationic [AuBr ( Pr -
3
6
i
3
2
2
3
H, Ar−H), 4.19 (br, 4 H, CH ), 3.72 [sept, J(H,H) = 7 Hz, 2 H,
+
2
bimy)(erNHC)] complexes derived from six- to eight-
membered heterocycles were obtained in generally high yields.
Stoichiometry control was found to be important, because an
excess of bromine led to different side reactions depending on
the precursor complex used. In the case of the neutral
monocarbene complexes, ligand brominations were observed,
while the formation of tribromide counteranions was noted for
cationic bis(carbene) complexes. Finally, the catalytic perform-
ance of 18 gold erNHC complexes in the hydroamination of
alkynes was compared, which revealed that monocarbene
complexes consistently performed better than their bis-
CH(CH ) ], 2.40 (s, 12 H, CH ), 2.32 (s, 6 H, CH ), 2.08 (br, 6 H,
3
2
3
3
3
13
1
CH ), 1.27 [d, J(H,H) = 7 Hz, 12 H, CH(CH ) ]; C{ H} NMR
2
3 2
(125 MHz, CDCl ) δ 209.6 (C8‑Mes), 186.5 (Cprobe), 146.6, 138.3,
135.2, 132.8, 130.7, 124.6, 114.2 (Ar−C), 54.8 (CH ), 54.4
[CH(CH ) ], 29.1, 22.3 (CH ), 21.8, 21.8, 19.4 (CH ); F{ H}
3
2
1
9
1
3 2 2 3
1
0
11
NMR (376 MHz, CDCl ) δ −154.21 (s, BF ), −154.26 (s, BF );
3
4
4
+
MS (ESI) m/z calcd for C H N Au [M − BF ] 747, found 747.
3
7
50
4
4
Anal. Calcd for C H BF N Au: C, 53.25; H, 6.04; N, 6.71. Found:
3
7
50
4
4
C, 52.67; H, 6.53; N, 5.70. The elemental analysis remains
unsatisfactory despite repeated purification and analysis, possibly
because of solvation.
[
AuBr (6-Mes)] (7). Bromine (∼10 μL, 0.201 mmol) was added
3
(
carbene) counterparts. The [AuBr(8-Mes)] complex 3
dropwise to a stirred solution of [AuBr(6-Mes)] (1) (0.120 g, 0.201
mmol) in CH Cl (∼5 mL) at ambient temperature, and the reaction
mixture was allowed to stir for a further 30 min. Then, volatiles were
removed under vacuum, and the residue was washed with diethyl
ether. Finally, the residue was dried under vacuum to give the product
bearing the bulkiest erNHC was identified as the best
precatalyst, which was used for a small substrate scope study
generally revealing good performance. Overall, this study
diversifies the applications of erNHC ligands in organometallic
chemistry. The isolation of the first gold(III) erNHC
complexes could pave the way for new potential applications
of this class of nonclassical N-heterocyclic carbenes.
2
2
as an orange solid (0.141 g, 93%). Single crystals of 7 were grown
from evaporation of a concentrated solution in CH CN: H NMR
1
3
3
(
500 MHz, CDCl ) δ 6.92 (s, 4 H, Ar−H), 3.74 [t, J(H,H) = 6 Hz, 4
3
H, CH ], 2.50 (s, 12 H, CH ), 2.47−2.44 (m, 2 H, CH ), 2.27 (s, 6
H, CH ); C{ H} NMR (125 MHz, CDCl ) δ 169.0 (C ), 140.4,
2
3
2
1
3
1
3
3
6‑Mes
EXPERIMENTAL SECTION
■
139.4, 136.1, 130.9 (Ar−C), 50.9, 21.7 (CH
2
), 21.3, 20.9 (CH
3
); MS
Au [M − Br] 677, found 677. Anal.
Au: C, 34.90; H, 3.73; N, 3.70. Found: C,
34.98; H, 3.73; N, 4.52.
+
General Procedures. All manipulations were carried out using
(ESI) m/z calcd for C22
Calcd for C22H28Br N
3 2
H28Br N
2 2
i
standard Schlenk techniques. Pr -bimy·HBF was prepared according
2
4
3
7
to a literature procedure. The ligand precursors A−C were
38,39
1
synthesized according to modified literature procedures.
H,
[AuBr (7-Mes)] (8). Complex 8 was prepared in analogy to
compound 7 using bromine (∼10 μL, 0.201 mmol) and [AuBr(7-
Mes)] (2) (0.120 g, 0.197 mmol) and isolated as an orange solid
3
13
1
19
1
C{ H}, and F{ H} NMR spectra were recorded on Bruker 400
1
MHz or Bruker 500 MHz NMR spectrometers. H NMR peaks are
labeled as singlet (s), doublet (d), triplet (t), broad (br), doublet of
doublets (dd), multiplet (m), and septet (sept). ESI mass spectra
were measured using a Finnigan MAT LCQ spectrometer. Elemental
analyses were performed on an Elementar Vario Micro Cube
elemental analyzer at the Department of Chemistry, National
University of Singapore. X-ray data for 3, 7−9, 11, and 13−18
were collected with a Bruker AXS SMART APEX diffractometer,
(0.135 g, 88%). Single crystals of 8 were grown from evaporation of a
1
concentrated solution in CH
CN: H NMR (500 MHz, CDCl
) δ
), 2.35
); C{ H} NMR (125 MHz,
) δ 176.6 (C7‑Mes), 141.0, 140.3, 135.9, 131.2 (Ar−C), 58.7,
24.7 (CH ), 21.8, 21.7 (CH ); MS (ESI) m/z calcd for
Au [M − Br] 691, found 691. Anal. Calcd for
Au: C, 35.82; H, 3.92; N, 3.63. Found: C, 35.86; H,
3
3
6.93 (s, 4 H, Ar−H), 4.10 (br, 4 H, CH ), 2.58 (s, 12 H, CH
2
3
1
3
1
(br, 4 H, CH
CDCl
), 2.27 (s, 12 H, CH
3
2
3
2
3
+
C
C
H
H
30Br
30Br
N
2 2
23
23
40
using Mo Kα radiation with the SMART suite of programs, and
refinement parameters are summarized in Tables S2−S4.
N
3 2
3.84; N, 3.81.
[AuBr (8-Mes)] (9). Complex 9 was prepared in analogy to
compound 7 using bromine (∼11 μL, 0.224 mmol) and [AuBr(8-
Mes)] (3) (0.140 g, 0.224 mmol) and isolated as an orange solid
(0.165 g, 92%). Single crystals of 9 were grown from evaporation of a
concentrated solution in CH
[AuBr(8-Mes)] (3). A mixture of 8-Mes·HBr (C) (0.431 g, 1.00
3
mmol) and [AuCl(tht)] (0.320 g, 1.00 mmol) was dried under
vacuum for 30 min in a Schlenk tube. Then, dry THF (∼30 mL) was
added to the mixture under an argon atmosphere, and the solution
was cooled to −78 °C. KHMDS (0.91 M in THF, 1.10 mL, 1.2
mmol) was added via a syringe, and the reaction mixture was stirred at
1
CN: H NMR (500 MHz, CDCl
) δ
3
3
6.94 (s, 4 H, Ar−H), 4.12−4.10 (m, 4 H, CH
2.27 (s, 10 H, CH and CH ), 1.96−1.92 (m, 2 H, CH
NMR (125 MHz, CDCl ) δ 174.6 (C8‑Mes), 141.7, 140.3, 135.9, 131.4
(Ar−C), 59.5, 26.6, 25.1 (CH ), 22.6, 21.6 (CH ); MS (ESI) m/z
calcd for C H Br N Au [M − Br] 705, found 705. Anal. Calcd for
), 2.58 (s, 12 H, CH ),
2
3
1
3
1
−78 °C for a further 30 min. The cooling bath was removed, and the
3
2
); C{ H}
2
reaction mixture was allowed to stir at ambient temperature for 3 h.
The reaction mixture was filtered through Celite, and drying under
vacuum gave the crude product as a brown solid. The latter was
redissolved in CH Cl and filtered through Celite. The solvent of the
3
2
3
+
2
4
32
2
2
C H Br N Au: C, 36.71; H, 4.11; N, 3.57. Found: C, 36.58; H, 4.00;
24 32
2
2
3
2
filtrate was removed, and the residue was washed with hexane (3 × 3
N, 3.70.
Br2
mL). Drying under vacuum gave the product an air-stable, white solid
[AuBr (6-Mes )] (10). Bromine (∼40 μL, 0.840 mmol) was
3
(
0.409 g, 65%). Single crystals of 3 were grown from evaporation of a
added dropwise to a stirred solution of [AuBr(6-Mes)] (1) (0.050 g,
0.084 mmol) in CH Cl (∼5 mL) at ambient temperature, and the
1
concentrated solution in CH CN: H NMR (500 MHz, CDCl ) δ
3
3
2
2
6
.90 (s, 4 H, Ar−H), 4.08 (br, 4 H, CH ), 2.33 (s, 12 H, CH ), 2.26
reaction mixture was allowed to stir for a further 2 h. Then, the
volatiles were removed under vacuum, and the residue was washed
2
3
1
3
1
(
s, 6 H, CH ). 2.06 (br, 6 H, CH ); C{ H} NMR (125 MHz,
3 2
G
DOI: 10.1021/acs.organomet.9b00718
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
i
with diethyl ether followed by drying under vacuum to give the
product as an orange solid (0.69 g, 89%): H NMR (500 MHz,
[AuBr ( Pr -bimy)(8-Mes)]BF (15). Complex 15 was prepared in
2 2 4
1
analogy to compound 13 using bromine (∼4 μL, 0.091 mmol) and
[Au( Pr -bimy)(8-Mes)]BF (6) (0.076 g, 0.091 mmol) and isolated
as a yellow solid (0.089 g, 97%). Single crystals of 15 were grown
from evaporation of a concentrated solution in CHCl : H NMR (500
i
CD Cl ) δ 7.13 (s, 4 H, Ar−H), 3.73 (br, 4 H, CH ), 2.57 (s, 6 H,
2
2
2
2
4
1
3
1
CH ), 2.50 (s, 8 H, CH and CH ), 2.43 (s, 6 H, CH ); C{ H}
3
3
2
3
Br2
6‑Mes
1
NMR (125 MHz, CD Cl ) δ 169.6 (C
), 141.1, 140.2, 136.8,
2
2
3
3
1
35.3, 135.2, 136.6, 126.6 (Ar−C), 51.3 (CH ), 24.3, 23.8 (CH ),
MHz, CDCl ) δ 7.57 [dd, J(H,H) = 8 Hz, 2 H, Ar−H], 7.33 [dd,
2
3
3
3
2
1.0 (CH ), 20.8 (CH ); MS (ESI) m/z calcd for C H Br N Au [M
J(H,H) = 8 Hz, 2 H, Ar−H], 7.02 (s, 4 H, Ar−H), 4.29 (br, 4 H,
2
3
22 26
4
2
+
3
−
Br] 835, found 834. Anal. Calcd for C H Br N Au: C, 28.88; H,
22 26 5 2
CH ), 3.39 [sept, J(H,H) = 7 Hz, 2 H, CH(CH ) ], 2.59 (s, 12 H,
2
3 2
2
.86; N, 3.06. Found: C, 28.42; H, 2.76; N, 3.60.
CH ), 2.38 (s, 6 H, CH ), 2.24 (br, 4 H, CH ), 2.06 (br, 2 H, CH ),
1.33 [d, J(H,H) = 7 Hz, 12 H, CH(CH ) ]; C{ H} NMR (125
MHz, CDCl ) δ 184.1 (C8‑Mes), 154.8 (Cprobe), 143.3, 139.5, 137.2,
33.4, 131.1, 125.2, 114.8 (Ar−C), 58.6 (CH ), 54.4 [CH(CH ) ],
8.3, 23.4 (CH ), 22.3, 21.9, 20.8 (CH ); F{ H} NMR (376 MHz,
3
3
2
2
Br2
[
AuBr (7-Mes )] (11). Complex 11 was prepared in analogy to
3
13
1
3
3 2
compound 10 using bromine (∼40 μL, 0.840 mmol) and [AuBr(7-
Mes)] (2) (0.050 g, 0.082 mmol) and isolated as an orange solid
3
1
2
2
3 2
(
0.071 g, 93%). Single crystals of 11 were grown from evaporation of
19 1
2
3
1
a concentrated solution in CD Cl : H NMR (500 MHz, CD Cl ) δ
10
11
2
2
2
2
CDCl ) δ −153.93 (s, BF ), −153.99 (s, BF ); MS (ESI) m/z
3
4
4
7
.12 (s, 4 H, Ar−H), 4.10 (br, 4 H, CH ), 2.65 (s, 6 H, CH ), 2.56 (s,
+
2
3
calcd for C H Br N Au [M − BF ] 907, found 907. Anal. Calcd for
3
7
50
2
4
4
1
3
1
6
H, CH ), 2.42 (s, 6 H, CH ), 2.37 (br, 4 H, CH ); C{ H} NMR
3
3
2
C H Br BF N Au·0.5CHCl : C, 42.73; H, 4.83; N, 5.32. Found: C,
37 50 2 4 4 3
Br2
(
125 MHz, CD Cl ) δ 176.7 (C
), 142.0, 140.8, 136.5, 136.5,
2
2
7‑Mes
43.11; H, 4.92; N, 5.56.
1
2
35.0, 135.0, 131.8, 131.7, 126.8, 126.7 (Ar−C), 59.3, 59.2 (CH ),
i
2
[AuBr ( Pr -bimy)(6-Mes)]Br (16). Bromine (∼96 μL, 1.86
2
2
3
4.5, 24.2 (CH ), 24.2, 24.2 (CH ), 21.5, 21.5 (CH ); MS (ESI) m/z
i
3
2
3
mmol) was added dropwise to a stirred solution of [Au( Pr -
2
+
calcd for C H Br N Au [M − Br] 849, found 848. Anal. Calcd for
C H Br N Au: C, 29.74; H, 3.04; N, 3.02. Found: C, 30.17; H, 3.05;
23
28
4
2
bimy)(6-Mes)]BF (4) (0.150 g, 0.186 mmol) in CH Cl (∼5 mL) at
ambient temperature, and the reaction mixture was allowed to stir for
h. The volatiles were removed under vacuum, and the residue was
washed with diethyl ether followed by drying under vacuum to give
the product as a yellow solid (0.178 g, 85%). Single crystals of 16
were grown from evaporation of a concentrated solution in CHCl :
4
2
2
23
28
5
2
N, 3.26.
2
[
AuBr (8-MesBr2)] (12). Complex 12 was prepared in analogy to
3
compound 10 using bromine (∼99 μL, 1.91 mmol) and [AuBr(8-
Mes)] (3) (0.120 g, 0.191 mmol) and isolated as an orange solid
1
3
(
4
0.132 g, 73%): H NMR (500 MHz, CD Cl ) δ 7.12 (s, 4 H, Ar−H),
1
3
2
2
H NMR (500 MHz, CDCl ) δ 7.56 [dd, J(H,H) = 6 Hz, 2 H, Ar−
3
.12 (br, 4 H, CH ), 2.62 (s, 6 H, CH ), 2.53 (s, 6 H, CH ), 2.42 (s, 6
H, CH ), 2.25 (br, 4 H, CH ), 1.95 (br, 4 H, CH ); C{ H} NMR
3
2
3
3
1
3
1
H], 7.34 [dd, J(H,H) = 6 Hz, 2 H, Ar−H], 7.02 (s, 4 H, Ar−H), 3.88
3
2
2
3
3
Br2
8‑Mes
[t, J(H,H) = 5 Hz, 4 H, CH
], 3.51 [sept, J(H,H) = 7 Hz, 2 H,
2
(
125 MHz, CD Cl ) δ 175.1 (C
), 142.8, 140.8, 136.6, 136.6,
2
2
CH(CH ) ], 2.62 (br, 2 H, CH ), 2.55 (s, 12 H, CH ), 1.33 [d,
3
2
2
3
1
2
35.1, 135.1, 132.0, 132.0, 127.0 (Ar−C), 60.2, 26.2 (CH ), 25.1,
2
3
13
1
J(H,H) = 7 Hz, 12 H, CH(CH ) ]; C{ H} NMR (125 MHz,
CDCl ) δ 178.3 (C6‑Mes), 155.8 (Cprobe), 139.9, 139.7, 137.6, 133.5,
3
2
5.0 (CH ), 24.6 (CH ), 24.3, 22.3, 22.3 (CH ); MS (ESI) m/z calcd
3
2
3
+
3
for C H Br N Au [M − Br] 863, found 862. Anal. Calcd for
C H Br N Au: C, 30.57; H, 3.21; N, 2.97. Found: C, 30.69; H, 3.19;
24
30
4
2
1
(
30.6, 125.3, 114.8 (Ar−C), 54.7 (CH ), 50.2 [CH(CH ) ], 22.0
2
3 2
24
30
5
2
CH ), 21.3, 21.1, 20.9 (CH ); MS (ESI) m/z calcd for
N, 3.20.
2
3
+
i
C H Br N Au [M − Br ] 879, found 879. Anal. Calcd for
[AuBr ( Pr -bimy)(6-Mes)]BF (13). Bromine (∼13 μL, 0.248
35 46
2
4
3
2
2
4
i
C H Br N Au·CHCl : C, 34.91; H, 3.82; N, 4.52. Found: C, 34.65;
mmol) was added dropwise to a stirred solution of [Au( Pr -bimy)(6-
35 46 5 4 3
2
H, 3.77; N, 4.62.
Mes)]BF (4) (0.200 g, 0.248 mmol) in CH Cl (∼5 mL) at ambient
4
2
2
i
[
AuBr ( Pr -bimy)(7-Mes)]Br (17). Complex 17 was prepared in
temperature, and the reaction mixture was allowed to stir for 30 min.
The volatiles were removed under vacuum, and the residue was
washed with diethyl ether. Finally, the residue was dried under
vacuum to give the product as a yellow solid (0.201 g, 95%). Single
crystals of 13 were grown from evaporation of a concentrated solution
2 2 3
analogy to compound 16 using bromine (∼44 μL, 0.851 mmol) and
i
[
Au( Pr -bimy)(7-Mes)]BF (5) (0.070 g, 0.085 mmol) and isolated
2
4
as a yellow solid (0.088 g, 92%). Single crystals of 17 were grown
from evaporation of a concentrated solution in CHCl : H NMR (500
1
3
3
1
3
MHz, CDCl ) δ 7.57 [dd, J(H,H) = 6 Hz, 2 H, Ar−H], 7.34 [dd,
in CHCl : H NMR (500 MHz, CDCl ) δ 7.57 [dd, J(H,H) = 6 Hz,
3
3
3
3
3
J(H,H) = 8 Hz, 2 H, Ar−H], 7.03 (s, 4 H, Ar−H), 4.24 (br, 4 H,
2
H, Ar−H], 7.35 [dd, J(H,H) = 6 Hz, 2 H, Ar−H], 7.02 (s, 4 H,
3
3
3
Ar−H), 3.85 [t, J(H,H) = 5 Hz, 4 H, CH ], 3.51 [sept, J(H,H) = 7
CH
CH
2
), 3.48 [sept, J(H,H) = 7 Hz, 2 H, CH(CH
3
)
2
], 2.62 (s, 12 H,
2
3
Hz, 2 H, CH(CH ) ], 2.61 (br, 2 H, CH ), 2.60 (s, 12 H, CH ), 2.38
3
), 2.49 (br, 4 H, CH
2
), 2.38 (s, 6 H, CH
3
), 1.34 [d, J(H,H) = 7
]; C{ H} NMR (125 MHz, CDCl ) δ 185.8
(C7‑Mes), 155.8 (Cprobe), 141.4, 139.8, 137.3, 133.5, 130.9, 125.3,
114.8 (Ar−C), 58.0 (CH ), 54.6 [CH(CH ], 25.2 (CH ), 22.0,
21.7, 20.8 (CH ); MS (ESI) m/z calcd for C36 Au [M −
] 893, found 893. Anal. Calcd for C36 Au: C, 38.15; H,
4.27; N, 4.94. Found: C, 38.03; H, 4.20; N, 5.03.
3
2
2
3
3
13
1
13
1
(
s, 6 H, CH ), 1.34 [d, J(H,H) = 7 Hz, 12 H, CH(CH ) ]; C{ H}
Hz, 12 H, CH(CH
3
)
2
3
3
3 2
NMR (125 MHz, CDCl ) δ 178.3 (C6‑Mes), 155.6 (Cprobe), 139.8,
3
1
39.6, 137.6, 133.5, 130.6, 125.3, 114.7 (Ar−C), 54.7 (CH ), 50.1
2
)
3
2
2
2
1
9
1
[
(
(
CH(CH ) ], 22.0 (CH ), 21.0, 20.8, 20.6 (CH ); F{ H} NMR
3
H48Br N
2 4
3
2
2
3
1
0
11
+
376 MHz, CDCl ) δ −154.09 (s, BF ), −154.15 (s, BF ); MS
Br
3
H48Br N
5 4
3
4
4
+
ESI) m/z calcd for C H Br N Au [M − Br ] 879, found 879.
3
5
46
2
4
3
i
Anal. Calcd for C H Br BF N Au·CHCl : C, 43.50; H, 4.80; N,
[AuBr ( Pr -bimy)(8-Mes)]Br (18). Complex 18 was prepared in
35
46
2
4
4
3
2 2 3
5
.80. Found: C, 43.57; H, 4.79; N, 6.20.
analogy to compound 16 using bromine (∼123 μL, 2.39 mmol) and
[Au( Pr -bimy)(8-Mes)]BF (6) (0.200 g, 0.239 mmol) and isolated
i
i
[
AuBr ( Pr -bimy)(7-Mes)]BF (14). Complex 14 was prepared in
2
2
4
2
4
analogy to compound 13 using bromine (∼3 μL, 0.062 mmol) and
as a yellow solid (0.265 g, 93%). Single crystals of 17 were grown
i
1
[
Au( Pr -bimy)(7-Mes)]BF (5) (0.053 g, 0.062 mmol) and isolated
from evaporation of a concentrated solution in CHCl : H NMR (400
2
4
3
3
as a yellow solid (0.061 g, 99%). Single crystals of 14 were grown
MHz, CDCl ) δ 7.56 [dd, J(H,H) = 6 Hz, 2 H, Ar−H], 7.33 [dd,
3
1
3
from evaporation of a concentrated solution in CHCl : H NMR (500
J(H,H) = 6 Hz, 2 H, Ar−H], 7.03 (s, 4 H, Ar−H), 4.36 (br, 4 H,
3
3
3
MHz, CDCl ) δ 7.57 [dd, J(H,H) = 8 Hz, 2 H, Ar−H], 7.33 [dd,
3
CH ), 3.41 [sept, J(H,H) = 7 Hz, 2 H, CH(CH ) ], 2.61 (s, 12 H,
2
3 2
3
J(H,H) = 8 Hz, 2 H, Ar−H], 7.01 (s, 4 H, Ar−H), 4.19 (br, 4 H,
CH ), 3.47 [sept, J(H,H) = 7 Hz, 2 H, CH(CH ) ], 2.60 (s, 12 H,
CH ), 2.45 (br, 4 H, CH ), 2.37 (s, 6 H, CH ), 1.33 [d, J(H,H) = 7
Hz, 12 H, CH(CH ) ]; C{ H} NMR (125 MHz, CDCl ) δ 187.7
CH ), 2.39 (s, 6 H, CH ), 2.27 (br, 4 H, CH ), 2.10 (br, 2 H, CH ),
3
3
2
2
3
3
13
1
2
3
2
1.34 [d, J(H,H) = 7 Hz, 12 H, CH(CH ) ]; C{ H} NMR (125
3 2
3
3
2
3
MHz, CDCl ) δ 184.0 (C8‑Mes), 155.1 (Cprobe), 143.4, 137.3, 133.5,
3
1
3
1
3
2
3
131.2, 125.2, 114.8 (Ar−C), 59.0 (CH ), 54.3 [CH(CH ) ], 28.4,
2
3 2
(
1
C7‑Mes), 155.8 (Cprobe), 141.4, 139.7, 137.3, 133.4, 130.8, 125.2,
23.5 (CH ), 22.6, 22.0, 20.9 (CH ); MS (ESI) m/z calcd for
2
3
+
14.8 (Ar−C), 57.7 (CH ), 54.6 [CH(CH ) ], 25.1 (CH ), 21.9,
C H Br N Au [M − Br ] 907, found 907. Anal. Calcd for
37 50 5 4
2
3
2
2
37 50
2
4
3
1
9
1
2
1.4, 20.8 (CH ); F{ H} NMR (376 MHz, CDCl ) δ −154.16 (s,
BF ), −154.21 (s, BF ); MS (ESI) m/z calcd for C H Br N Au
3
3
C H Br N Au: C, 38.73; H, 4.39; N, 4.88. Found: C, 38.50; H, 4.26;
10
11
4
4
36 48
2
4
N, 5.25.
+
[
4
M − BF ] 893, found 893. Anal. Calcd for C H Br BF N Au: C,
General Procedure for the Optimization of Hydroamination
Reactions and Catalyst Screening. A mixture of phenylacetylene
4
36 48
2
4
4
4.10; H, 4.94; N, 5.71. Found: C, 43.32; H, 4.82; N, 5.92.
H
DOI: 10.1021/acs.organomet.9b00718
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
0.3 mmol, 1.5 equiv), mesitylamine (0.2 mmol, 1 equiv), Ag, K, or
Na salt (0.004 mmol, 2 mol %), and the respective Au NHC complex
0.004 mmol, 2 mol %) was heated in acetonitrile (∼1 mL) in a screw
(5) Vivancos, A.; Segarra, C.; Albrecht, M. Mesoionic and Related
Less Heteroatom-Stabilized N-Heterocyclic Carbene Complexes:
Synthesis, Catalysis, and Other Applications. Chem. Rev. 2018, 118,
9493−9586.
(6) Sebest, F.; Dunsford, J. J.; Adams, M.; Pivot, J.; Newman, P. D.;
Diez-Gonzalez, S. Ring-Expanded N-Heterocyclic Carbenes for
Copper-Mediated Azide-Alkyne Click Cycloaddition Reactions.
ChemCatChem 2018, 10, 2041−2045.
(7) Hall, J. W.; Unson, D. M. L.; Brunel, P.; Collins, L. R.; Cybulski,
M. K.; Mahon, M. F.; Whittlesey, M. K. Copper-NHC-Mediated
Semihydrogenation and Hydroboration of Alkynes: Enhanced
Catalytic Activity Using Ring-Expanded Carbenes. Organometallics
(
cap tube under air. The reaction temperatures and times are
summarized in Table 1 and Table S1. The reaction mixture was
cooled to ambient temperature, and an aliquot was diluted with ethyl
acetate and analyzed by GC/GC-MS.
General Procedure for the Substrate Scope Study. A mixture
of alkyne (0.75 mmol, 1.5 equiv), amine (0.5 mmol, 1 equiv), AgSbF6
(
0.010 mmol, 2 mol %), and [AuBr(8-Mes)] (3) (0.010 mmol, 2 mol
) was heated in acetonitrile (∼1 mL) at 90 °C in a screw cap tube
%
under air for 14 h. The volatiles were removed under vacuum to give
the crude product. Conversion to products was determined by GC/
GC-MS, and isolated yields were obtained by column chromatog-
raphy using a mixture of petroleum ether and EtOAc as the eluent.
2
(
018, 37, 3102−3110.
8) Morozov, O. S.; Gribanov, P. S.; Asachenko, A. F.;
Dorovatovskii, P. V.; Khrustalev, V. N.; Rybakov, V. B.; Nechaev,
M. S. Hydrohydrazination of Arylalkynes Catalyzed by an Expanded
Ring N-Heterocyclic Carbene (er-NHC) Gold Complex Under
Solvent-Free Conditions. Adv. Synth. Catal. 2016, 358, 1463−1468.
(9) Yang, B. M.; Xiang, K.; Tu, Y. Q.; Zhang, S. H.; Yang, D. T.;
Wang, S. H.; Zhang, F. M. Spiro-fused six-membered N-heterocyclic
carbene: a new scaffold toward unique properties and activities. Chem.
Commun. 2014, 50, 7163−5.
ASSOCIATED CONTENT
■
*
S
Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.9b00718.
Characterization data for catalysis products, optimiza-
tion of catalytic conditions, molecular structures of 13−
(10) Kumar, A.; Katari, M.; Ghosh, P. Understanding the lability of a
15, selected crystallographic data, NMR spectra, and ESI
trans bound pyridine ligand in a saturated six-membered N-
mass spectra (PDF)
Accession Codes
CCDC 1951134−1951139, 1951141−1951143, 1951847, and
952089 contain the supplementary crystallographic data for
heterocyclic carbene based (NHC)PdCl (pyridine) type complex: A
2
case study. Polyhedron 2013, 52, 524−529.
(11) Teng, Q.; Wu, W.; Duong, H. A.; Huynh, H. V. Ring-expanded
N-heterocyclic carbenes as ligands in iron-catalysed cross-coupling
reactions of arylmagnesium reagents and aryl chlorides. Chem.
Commun. 2018, 54, 6044−6047.
1
this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing 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.
(12) Huynh, H. V. Electronic Properties of N-Heterocyclic Carbenes
and Their Experimental Determination. Chem. Rev. 2018, 118, 9457−
492.
13) Davies, C. J.; Page, M. J.; Ellul, C. E.; Mahon, M. F.; Whittlesey,
9
(
M. K. Ni(I) and Ni(II) ring-expanded N-heterocyclic carbene
complexes: C-H activation, indole elimination and catalytic hydro-
dehalogenation. Chem. Commun. 2010, 46, 5151−3.
(14) Hauwert, P.; Dunsford, J. J.; Tromp, D. S.; Weigand, J. J.; Lutz,
M.; Cavell, K. J.; Elsevier, C. J. Zerovalent [Pd(NHC)(Alkene)1,2]
Complexes Bearing Expanded-Ring N-Heterocyclic Carbene Ligands
in Transfer Hydrogenation of Alkynes. Organometallics 2013, 32,
AUTHOR INFORMATION
Corresponding Author
E-mail: chmhhv@nus.edu.sg. Phone: (65) 65162670. Fax:
65) 67791691.
■
*
(
ORCID
Han Vinh Huynh: 0000-0003-4460-6066
Funding
Supported by the Singapore Ministry of Education (WBS R-
43-000-669-112).
1
31−140.
(15) Morozov, O. S.; Lunchev, A. V.; Bush, A. A.; Tukov, A. A.;
Asachenko, A. F.; Khrustalev, V. N.; Zalesskiy, S. S.; Ananikov, V. P.;
Nechaev, M. S. Expanded-ring N-heterocyclic carbenes efficiently
stabilize gold(I) cations, leading to high activity in pi-acid-catalyzed
cyclizations. Chem. - Eur. J. 2014, 20, 6162−70.
1
Notes
The authors declare no competing financial interest.
(
16) Iglesias, M.; Beetstra, D. J.; Stasch, A.; Horton, P. N.;
Hursthouse, M. B.; Coles, S. J.; Cavell, K. J.; Dervisi, A.; Fallis, I. A.
First Examples of Diazepanylidene Carbenes and Their Late-
Transition-Metal Complexes. Organometallics 2007, 26, 4800−4809.
ACKNOWLEDGMENTS
■
This work was supported by the National University of
Singapore. Technical support from staff at the Chemical,
Molecular and Materials Analysis Centre (CMMAC) of our
department is appreciated.
(
17) Kumar, A.; Yuan, D.; Huynh, H. V. Stereoelectronic Profiling of
Expanded-Ring N-Heterocyclic Carbenes. Inorg. Chem. 2019, 58,
7545−7553.
(18) Cervantes-Reyes, A.; Rominger, F.; Rudolph, M.; Hashmi, A. S.
REFERENCES
K. Gold(I) Complexes Stabilized by Nine- and Ten-Membered N-
■
(
Heterocyclic Carbene Ligands. Chem. - Eur. J. 2019, 25, 11745−
(
1) Huynh, H. V. The Organometallic Chemistry of N-heterocyclic
Carbenes; John Wiley & Sons, Ltd.: Chichester, U.K., 2017.
2) Danopoulos, A. A.; Simler, T.; Braunstein, P. N-Heterocyclic
Carbene Complexes of Copper, Nickel, and Cobalt. Chem. Rev. 2019,
19, 3730−3961.
3) Gan, M. M.; Liu, J. Q.; Zhang, L.; Wang, Y. Y.; Hahn, F. E.; Han,
1
(
1757.
19) Dunsford, J. J.; Cavell, K. J.; Kariuki, B. M. Gold(I) Complexes
Bearing Sterically Imposing, Saturated Six- and Seven-Membered
Expanded Ring N-Heterocyclic Carbene Ligands. Organometallics
2012, 31, 4118−4121.
1
(
Y. F. Preparation and Post-Assembly Modification of Metal-
losupramolecular Assemblies from Poly (N-Heterocyclic Carbene)
Ligands. Chem. Rev. 2018, 118, 9587−9641.
(20) Sampford, K. R.; Carden, J. L.; Kidner, E. B.; Berry, A.; Cavell,
K. J.; Murphy, D. M.; Kariuki, B. M.; Newman, P. D. Twisting the
arm: structural constraints in bicyclic expanded-ring N-heterocyclic
carbenes. Dalton trans. 2019, 48, 1850−1858.
(21) Huynh, H. V.; Guo, S.; Wu, W. Detailed Structural,
Spectroscopic, and Electrochemical Trends of Halido Mono- and
(
4) Nesterov, V.; Reiter, D.; Bag, P.; Frisch, P.; Holzner, R.; Porzelt,
A.; Inoue, S. NHCs in Main Group Chemistry. Chem. Rev. 2018, 118,
678−9842.
9
I
DOI: 10.1021/acs.organomet.9b00718
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Bis(NHC) Complexes of Au(I) and Au(III). Organometallics 2013,
Heterocyclic Carbenes: Salts, Free Carbenes, and Metal Complexes.
Organometallics 2011, 30, 5649−5655.
(40) APEX suite of crystallographic software, APEX 2, version 2008.4;
Bruker AXS Inc.: Madison, WI, 2008.
3
(
2, 4591−4600.
22) Guo, S.; Bernhammer, J. C.; Huynh, H. V. 1,2,4-Triazole-
derived carbene complexes of gold: characterization, solid-state
aggregation and ligand disproportionation. Dalton trans. 2015, 44,
1
(
5157−15165.
23) Sivaram, H.; Jothibasu, R.; Huynh, H. V. Gold Complexes of an
Alicyclic Indazole-Derived N-Heterocyclic Carbene: Syntheses,
Characterizations, and Ligand Disproportionation. Organometallics
2
(
012, 31, 1195−1203.
24) Huynh, H. V.; Wu, J. Rotamers of palladium complexes bearing
IR active N-heterocyclic carbene ligands: Synthesis, structural
characterization and catalytic activities. J. Organomet. Chem. 2009,
6
(
94, 323−331.
25) Teng, Q.; Huynh, H. V. A unified ligand electronic parameter
1
3
based on C NMR spectroscopy of N-heterocyclic carbene
complexes. Dalton trans. 2017, 46, 614−627.
(
26) Dash, C.; Shaikh, M. M.; Butcher, R. J.; Ghosh, P. Highly
convenient regioselective intermolecular hydroamination of alkynes
yielding ketimines catalyzed by gold(I) complexes of 1,2,4-triazole
based N-heterocyclic carbenes. Inorg. Chem. 2010, 49, 4972−4983.
(
27) Katari, M.; Rao, M. N.; Rajaraman, G.; Ghosh, P. Computa-
tional Insight into a Gold(I) N-Heterocyclic Carbene Mediated
Alkyne Hydroamination Reaction. Inorg. Chem. 2012, 51, 5593−5604.
(
28) Michon, C.; Gilbert, J.; Trivelli, X.; Nahra, F.; Cazin, C. S. J.;
Agbossou-Niedercorn, F.; Nolan, S. P. Gold(i) catalysed regio- and
stereoselective intermolecular hydroamination of internal alkynes:
towards functionalised azoles. Org. Biomol. Chem. 2019, 17, 3805−
3
(
811.
29) Cacchi, S.; Fabrizi, G.; Fochetti, A.; Ghirga, F.; Goggiamani, A.;
Iazzetti, A. Stereo- and regioselective gold(i)-catalyzed hydro-
amination of 2-(arylethynyl)pyridines with anilines. Org. Biomol.
Chem. 2019, 17, 527−532.
(
30) Baron, M.; Battistel, E.; Tubaro, C.; Biffis, A.; Armelao, L.;
Rancan, M.; Graiff, C. Single-Step Synthesis of Dinuclear Neutral
Gold(I) Complexes with Bridging Di(N-heterocyclic carbene)
Ligands and Their Catalytic Performance in Cross Coupling
Reactions and Alkyne Hydroamination. Organometallics 2018, 37,
4
(
213−4223.
31) Nair, A. G.; McBurney, R. T.; Gatus, M. R. D.; Binding, S. C.;
Messerle, B. A. Gold(III) NHC Complexes for Catalyzing
Dihydroalkoxylation and Hydroamination Reactions. Inorg. Chem.
2
017, 56, 12067−12075.
32) Hashmi, A. S. K. Gold-Catalyzed Organic Reactions. Chem. Rev.
007, 107, 3180−3211.
33) Mizushima, E.; Hayashi, T.; Tanaka, M. Au(I)-Catalyzed
Highly Efficient Intermolecular Hydroamination of Alkynes. Org. Lett.
003, 5, 3349−3352.
34) Ibanez, S.; Poyatos, M.; Peris, E. A D3h-symmetry
(
2
(
2
(
hexaazatriphenylene-tris-N-heterocyclic carbene ligand and its coor-
dination to iridium and gold: preliminary catalytic studies. Chem.
Commun. 2017, 53, 3733−3736.
(
35) Ibanez, S.; Poyatos, M.; Dawe, L. N.; Gusev, D.; Peris, E.
́
̃
Ferrocenyl-Imidazolylidene Ligand for Redox-Switchable Gold-Based
Catalysis. A Detailed Study on the Redox-Switching Abilities of the
Ligand. Organometallics 2016, 35, 2747−2758.
(
36) Ibanez, S.; Poyatos, M.; Peris, E. Gold Catalysts with
́
̃
Polyaromatic-NHC ligands. Enhancement of Activity by Addition of
Pyrene. Organometallics 2017, 36, 1447−1451.
(
37) Guo, S.; Sivaram, H.; Yuan, D.; Huynh, H. V. Gold and
Palladium Hetero-Bis-NHC Complexes: Characterizations, Correla-
tions, and Ligand Redistributions. Organometallics 2013, 32, 3685−
3
(
696.
38) Dunsford, J. J.; Cavell, K. J. Expanded ring N-heterocyclic
carbenes: a comparative study of ring size in palladium (0) catalysed
Mizoroki-Heck coupling. Dalton trans 2011, 40, 9131−5.
(
39) Lu, W. Y.; Cavell, K. J.; Wixey, J. S.; Kariuki, B. First Examples
of Structurally Imposing Eight-Membered-Ring (Diazocanylidene) N-
J
DOI: 10.1021/acs.organomet.9b00718
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