Synthesis of propargyl-functionalized NHC gold complexes

Article abstract of DOI:10.1021/acs.organomet.7b00012

A series of propargyl functionalized N-heterocyclic carbene gold(I) complexes have been synthesized from the corresponding imidazolium salts with tetrabutylammonium acetylacetonate in the presence of a gold(I) precursor in a onepot reaction. Several complexes of different stoichiometries are described: [AuBr(NHC)], [Au(NHC)₂]Br and [Au(C₆F₅) (NHC)], and many of these have been characterized by Xray diffraction studies. Aurophilic interactions are present in the compounds bearing less sterically hindered carbenes, and secondary interactions such as hydrogen bonds, π-π stacking, or weak contacts of the gold center with the carbon of the propargyl unit have also been found. These complexes possess a high degree of water solubility, which makes them potentially useful for the synthesis of biologically active compounds or as gold catalysts in water. Activation of the propargyl unit in [AuBr(NHC)] complexes leads to the formation of interesting trimers with bridging bidentate C^C alkynyl-carbene ligands.

Full text of DOI:10.1021/acs.organomet.7b00012

Article
pubs.acs.org/Organometallics
Synthesis of Propargyl-Functionalized NHC Gold Complexes
Alice Johnson and M. Concepcion Gimeno*
́
́ ́ ́
Departamento de Química Inorganica, Instituto de Síntesis Química y Catalisis Homogenea (ISQCH), CSIC-Universidad de
Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
S
* Supporting Information
ABSTRACT: A series of propargyl functionalized N-hetero-
cyclic carbene gold(I) complexes have been synthesized from
the corresponding imidazolium salts with tetrabutylammonium
acetylacetonate in the presence of a gold(I) precursor in a one-
pot reaction. Several complexes of different stoichiometries are
described: [AuBr(NHC)], [Au(NHC)2]Br and [Au(C6F5)
(NHC)], and many of these have been characterized by X-
ray diffraction studies. Aurophilic interactions are present in
the compounds bearing less sterically hindered carbenes, and
secondary interactions such as hydrogen bonds, π−π stacking,
or weak contacts of the gold center with the carbon of the propargyl unit have also been found. These complexes possess a high
degree of water solubility, which makes them potentially useful for the synthesis of biologically active compounds or as gold
catalysts in water. Activation of the propargyl unit in [AuBr(NHC)] complexes leads to the formation of interesting trimers with
bridging bidentate C∧C alkynyl-carbene ligands.
allows the isolation of otherwise highly unstable intermediates,
e.g. vinyl gold derivatives,11 gold(I) hydrides,12 and gold(I) or
gold(III) intermediates in gold-only photoredox catalysis,13
thus providing chemists with a better understanding of key
steps in reaction mechanisms.
NHC gold complexes are also of biological importance. The
strong gold−carbene bonds in NHC-Au(I) complexes cause
them to be inert toward biologically important thiol groups and
hence have potential medical applications. In 2004 the first
report of the antimicrobial activity of NHC gold complexes was
INTRODUCTION
■
N-heterocyclic carbenes (NHCs) are of ever-increasing interest
due to the multiple and diverse applications of their
corresponding transition metal complexes.1 Their strong σ-
donor capacity makes them excellent ligands, and generally they
form very stable complexes. A huge variety of different
substituents can be introduced at the nitrogen atoms, allowing
both steric and electronic requirements to be fine-tuned for
specific applications and giving them an incredibly versatile
coordination chemistry.2−5 They are currently among some of
the most important ligands and are ubiquitous within
organometallic chemistry.
published by Çetinkaya, in which a series of gold bis-carbene
complexes were found to be effective with a variety of both
Gram-positive and Gram-negative bacteria.14 Following this,
significant contributions were made by Berners-Price and co-
workers with studies of the mitochondrial permeability of
NHC-Au(I) complexes.15 The complexes were found to induce
mitochondrial membrane permeabilization, a unique property
which gives them the potential to be excellent anticancer
agents, since when a cell undergoes apoptosis it will not harm
the surrounding cells.
NHC gold complexes were first isolated in 1989 by Bonati;6
however the potential of these compounds was not realized
until many years later. They now have numerous applications in
catalysis,7 medicine,8 and luminescence.9 NHC-Au(I) com-
plexes are commonly used in homogeneous gold catalysis and
are considered powerful synthetic tools in organic synthesis.
They have unique catalytic activity because the strong σ-donor
ability of the NHC ligand results in these complexes being
more electron rich than other homogeneous gold catalysts.
Since their first reported use by Herrmann and co-workers in
2003 for the gold-catalyzed hydration of 3-hexyne,10 they have
been successfully employed in a wide variety of organic
transformations, including enyne cycloisomerizations, alkyne
hydration, propargylic ester activation, alkene activation, alkane
C−H bond activation, and cross-coupling reactions. However,
the importance of NHC gold complexes in catalysis comes
from not only their use as highly selective catalysts in directed
organic synthetic strategies but also their ability to stabilize
intermediates in catalytic reactions. Recent reports have
described how the stabilization imparted by the NHC ligand
Another important property of NHC gold complexes is their
luminescence. This was first reported in 1999 by Lin and co-
workers, in which a series of NHC-Au(I) complexes bearing a
benzimidazol-2-ylidene ligand were found to exhibit long-lived
luminescence at room temperature, both in the solid state and
in acetonitrile solutions.16 More recently some NHC gold
complexes have been found to have low-energy excitation and
emission bands at suitable wavelengths for use in cellular
distribution studies using fluorescence confocal microscopy.17
Received: January 6, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
NHC ligands have also been found to stabilize three-coordinate
gold complexes incorporating a nido-carborane diphosphine.18
These brightly luminescent complexes were found to have
incredibly high quantum yields, giving them the potential for
future practical applications such as in OLEDs. Simple changes
in the structure of the NHC ligand result in changes in the
emission of the NHC gold complexes, and hence ligand design
can allow the luminescent properties to be fine-tuned for
specific applications.
Scheme 1. Formation of Imidazolium Bromide Salts
Propargyl-functionalized NHC gold complexes are of
particular interest because of the amazing potential and
versatility imparted by the propargyl unit. Propargyl-function-
alized NHC complexes of silver are known to show biological
activity,19 and the propargyl unit also gives the complexes a
degree of water solubility. Alkyne groups can be used in “click”
reactions, and recently Cai and co-workers were able to create
polymer-supported NHC silver complexes through the “click”
reaction of propargyl-functionalized imidazolium salts.20 Such
supported NHC metal complexes are advantageous in catalysis
due to their recyclability. For optical applications, the formation
of polynuclear complexes is desirable and the propargyl unit
can provide an additional coordination site with the potential
for the formation of allenyl complexes. Recently, we found that
allenyl gold complexes derived from propargyl-functionalized
phosphonium salts exhibit an unusual regioselectivity depend-
ent on the oxidation state of the gold,21 where allenyl ligands
substituted at the α or γ carbon were obtained for gold(I) or
gold(III), respectively, and hence further studies on the
reactions of propargyl-functionalized ligands with gold are of
interest.
The recently reported use of tetrabutylammonium acetyla-
cetonate for the preparation of NHC gold complexes was found
to be an economical and incredibly versatile method.22 This
method is particularly advantageous when sterically smaller
NHCs are used, as generally they are less stable and
decomposition is observed when standard synthetic methods
are employed. Since propargyl-functionalized NHCs are
sterically small, this method is the ideal choice for the synthesis
of their gold complexes. Furthermore, this method is suitable
for poorly soluble imidazolium salts, as in this case.
dichloromethane led to solutions of the [imidazolium]-
[AuBrCl] salts. Subsequent addition of NBu4(acac) gave the
[AuBr(NHC)] complexes with reaction times of just 1 h
(Scheme 2). The complexes 1 could be separated from the
NBu4Cl formed in the reaction by a simple filtration through
silica, giving the complexes in good yields (73−82%).
Molecular structures of complexes 1a−d were determined by
single-crystal X-ray diffraction. Suitable crystals were obtained
by the slow diffusion of pentane into solutions of the complexes
in dichloromethane. In all of the complexes the carbon−carbon
triple bond of the propargyl unit is maintained and no
interaction with the gold center is observed.
Complex 1a with the smallest substituent on the NHC, a
methyl group, shows a structure in which intermolecular
aurophilic interactions are present, with Au···Au distances of
3.324(1) Å (Figure 1). The propargyl substituent is orientated
perpendicular to the coplanar Br−Au−NHC unit. The Au−C
bond distance is 1.985(5) Å, which is the shortest described for
an NHC−Au−Br complex and indicates a strong bond, as
expected for strong σ-donor NHCs. The Au−Br distance of
2.4038(15) Å is longer than that reported by Meyer and co-
workers25 with an aryl-substituted carbene, 2.3904(4) Å. The
C−C distances within the propargyl unit are C(5)−C(6)
1.472(6) Å and C(6)−C(7) 1.183(7) Å, which correspond to
single and triple bonds, respectively. The gold center is in a
linear geometry with a C(1)−Au(1)−Br(1) angle of
174.35(12)°.
Herein we report the synthesis of several new propargyl-
functionalized NHC gold complexes using NBu4(acac) with
reactions carried out at room temperature, in air, and with very
short reaction times. Additionally, to demonstrate the reaction
possibilities of these complexes, the synthesis of double alkynyl-
carbene species is described.
RESULTS AND DISCUSSION
■
Synthesis and Structural Characterization. A series of
propargyl-functionalized imidazolium bromide salts were
prepared by reaction of the imidazoles with propargyl bromide
following a previously reported procedure for the methyl and
benzyl derivatives (Scheme 1).23
The structures of complexes 1b−d (Figure 2) show patterns
similar to those found in 1a, excluding the aurophilic
interactions. The increase in the steric demand of the
substituents on the nitrogen atom of the imidazole ring causes
the disappearance of this intermolecular contact. As expected
when changing to substituents with a weaker donor capacity,
the Au−Ccarbene bond distances are slightly longer in these
complexes, following the order Me < CH2CCH < CH2Ph ≈
py, although the values for py and CH2Ph are similar within the
errors and the differences may not be significant. Additionally a
concurrent decrease in the Au−Br distance is observed with
increasing Au−Ccarbene bond distance.
The 1,3-dipropargylimidazolium bromide salt was prepared
by another previously reported procedure,24 and the pyridyl
species is described for the first time. All, apart from the methyl
derivative, were off-white solids at room temperature and were
insoluble in all common organic solvents but soluble in water
and alcohols. The methyl derivative was a pale yellow ionic
liquid, immiscible with organic solvents but miscible with water
and alcohols.
When the reaction of the imidazolium bromide salts,
[AuCl(tht)], and NBu4(acac) was carried out in THF, rather
than dichloromethane, a white precipitate was observed in all
Addition of a stoichiometric amount of [AuCl(tht)] (tht =
tetrahydrothiophene) to the imidazolium bromide salts in
B
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 2. Formation of [AuBr(NHC)] Complexes
angle of 178.6(5)° (Figure 3). The Au−C bond lengths are
2.011(13) and 2.015(12) Å, which as expected are longer than
those in the [AuBr(NHC)] complexes. The molecules are
associated in dimers with some secondary π−π stacking
contacts, resulting in a long Au···Au interaction of 3.797 Å
between the gold centers. The distance between the centroids
of the imidazolyl rings is 3.848 Å, although there are shorter
contacts between the carbene carbon and the nitrogen atom of
the other molecule. Additionally, a weak Au−C interaction of
3.243 Å is observed with the alkyne carbon. The bromide atoms
form hydrogen bonds in an octahedral fashion with the protons
of the propargyl units, most of which are above the sum of the
van der Waals radii, the shortest value being 2.487 Å.
The structure of complex 2d is shown in Figure 4. The
molecule lies on a 2-fold axis, and therefore only half
corresponds to the asymmetric unit. The Au−C distance of
2.21(8) Å is slightly longer than that found in complex 2c, as
expected for a less donating carbene.
Figure 1. Molecular structure of complex 1a and association in dimers
through aurophilic interactions. Selected bond lengths (Å) and angles
(deg): Au(1)−C(1) 1.985(5), Au(1)−Br(1) 2.4038(15), N(1)−C(1)
1.353(6), N(2)−C(1) 1.342(6), C(5)−C(6) 1.472(6), C(6)−C(7)
1.183(7), C(1)−Au(1)−Br(1) 174.35(12).
The bromide makes weak hydrogen bonds of 2.522 and
2.594 Å with the alkyne protons, giving rise to a supramolecular
structure with formation of squares (Figure 5).
Pentafluorophenyl derivatives were also prepared. In this
case, reaction of the imidazolium bromide salts with [Au-
(C6F5)(tht)] gave the [imidazolium][AuBr(C6F5)] salts and
subsequent addition of NBu4(acac) gave rise to the formation
of the desired [Au(C6F5)(NHC)] 3 (Scheme 4i). Initial NMR
studies of the reaction showed the formation of small amounts
of NBu4[Au(C6F5)2], and washing the reaction mixture with
water led to an increase in the ratio of this product compared to
the desired [Au(C6F5)(NHC)]. This can be explained by the
equilibrium shown in Scheme 4ii. Since the bis-carbene
complexes 2 are soluble in water, washing the reaction mixture
with water would result in removal of this product, forcing the
equilibrium to produce more with concurrent formation of
NBu4[Au(C6F5)2].
Before washing with water the equilibrium lies far toward the
side of the desired product 3. Therefore, these complexes could
be obtained cleanly in high yields by using an alternative
purification method. Simply filtering the reaction mixture
through silica led to removal of NBu4Br and any of the
byproducts formed as a result of the equilibrium of the
products, thus leaving [Au(C6F5)(NHC)] 3 in good yields.
The molecular structure of 3c was obtained by single-crystal
X-ray diffraction (Figure 6). The gold center is linearly
coordinated with a C−Au−C angle of 175.79(19)°, to two
different carbon donor ligands. The Ccarbene−Au distance is
2.022(5) Å, while the Cpentafluorophenyl−Au distance is 2.048(5)
Å.
Figure 2. Molecular structures of complexes 1b−d. Selected bond
lengths (Å) and angles (deg): 1b, Au(1)−C(1) 2.004(5), Au(1)−
Br(1) 2.3927(7), N(1)−C(1) 1.341(6), N(2)−C(1) 1.327(6), C(4)−
C(5) 1.453(7), C(5)−C(6) 1.179(7), C(1)−Au(1)−Br(1)
177.78(12); 1c, Au(1)−C(1) 1.994(4), Au(1)−Br(1) 2.4057(4),
N(1)−C(1) 1.337(5), N(2)−C(1) 1.346(5), C(5)−C(6) 1.176(7),
C(8)−C(9) 1.172(6), C(1)−Au(1)−Br(1) 177.23(12); 1d, Au(1)−
C(1) 1.988(10), Au(1)−Br(1) 2.3967(10), N(1)−C(1) 1.347(12),
N(2)−C(1) 1.354(11), C(4)−C(5) 1.478(13), C(5)−C(6)
1.191(15), C(8)−C(9) 1.172(6), C(1)−Au(1)−Br(1) 174.6(2).
cases except for that with the benzyl derivative b (Scheme 3).
This was identified as the bis-carbene species [Au(NHC)2]Br
(2), and its formation is likely favored in this case because of its
insolubility in THF. Complexes 2 could be formed in excellent
yields (82−95%) by reaction of 2 equiv of the imidazolium salt
with 1 equiv of [AuCl(tht)] and 2 equiv of NBu4(acac) in THF
with precipitation of the product (Scheme 3ii). Due to its
solubility in THF, bis-carbene species 2b was prepared by
reaction in dichloromethane followed by washing with water to
remove NBu4Cl; however, 2b also exhibits some water
solubility and hence was only isolated in moderate yield (63%).
The molecular structures of bis-carbene complexes 2c,d were
obtained by single-crystal X-ray diffraction. Complex 2c
presents an almost ideal linear geometry with a C−Au−C
C
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 3. Formation of [Au(NHC)2]Br Compounds
Figure 3. Molecular structure of complex 2c and associated dimers
through different secondary interactions. Selected bond lengths (Å)
and angles (deg): Au(1)−C(10) 2.011(13), Au(1)−C(1) 2.015(12),
N(1)−C(1) 1.342(15), N(2)−C(1) 1.353(15), N(3)−C(10)
1.368(16), N(4)−C(10) 1.351(17), C(4)−C(5) 1.469(18), C(5)−
C(6) 1.185(19), C(7)−C(8) 1.457(17), C(8)−C(9) 1.182(19),
C(13)−C(14) 1.489(18), C(14)−C(15) 1.18(2), C(16)−C(17)
1.466(19), C(17)−C(18) 1.19(2), C(10)−Au(1)−C(1) 178.6(5).
Figure 4. Molecular structure of complex 2d. Selected bond lengths
(Å) and angles (deg): Au(1)−C(1) 2.021(8), C(5)−C(6) 1.176(14),
C(5)−C(4) 1.463(15), C(1)#1−Au(1)−C(1) 179.997(1). Symmetry
transformations used to generate equivalent atoms: (#1) −x + 1/2, −y
+ 1/2, −z.
The molecules of 3c are associated in dimers with a weak
intermolecular Au···Au interaction of 3.3506(8) Å, together
with some slipped π−π stacking interactions between the
imidazolyl and the pentafluorophenyl rings; the shortest
contacts are 3.386 and 3.420 Å.
To illustrate the reactivity of these propargyl-functionalized
NHC gold complexes, we aimed to deprotonate the alkyne
moiety and coordinate to an additional gold center. The
reaction of complexes [AuBr(NHC)] (1) with HNiPr2 in the
presence of CuI as a catalyst led to the elimination of both the
alkyne proton and the bromide ligand bound to gold to afford
the sparingly soluble trinuclear complexes 4 (Scheme 5).
The elimination of the alkyne proton has been confirmed by
NMR spectroscopy and the formation of trimers by HRMS-
(ESI-QTOF), with spectra showing the presence of the
molecular peaks [M + Na]+ as the most intense peaks. The
IR spectra of these new complexes 4 lack the CC−H
vibration present in the starting products 1 at around 3260
Figure 5. Formation of a supramolecular structure by Br···H
interactions in complex 2d.
cm−1, while the −CC− vibration mode at around 2160 cm−1
is maintained.
D
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 4. Formation of [Au(C6F5)(NHC)] Species and Their Equilibrium in Water
Figure 6. Molecular structure of complex 3c and formation of dimers through secondary bonds. Selected bond lengths (Å) and angles (deg):
Au(1)−C(1) 2.022(5), Au(1)−C(10) 2.048(5), Au(1)−Au(1)#1 3.3506(8), N(1)−C(1) 1.353(7), C(4)−C(5) 1.462(7), C(5)−C(6) 1.181(8),
C(7)−C(8) 1.455(8), C(8)−C(9) 1.184(8), C(1)−Au(1)−C(10) 175.79(19).
derivatives show interesting structural features because of the
presence of different secondary bonds, including aurophilic
interactions for the sterically small NHC complexes, hydrogen
bonds between the bromide and the alkyne protons, slipped
π−π interactions between the imidazole rings or between the
imidazole and pentafluorophenyl rings, and some close Au−C
contacts with the propargyl unit.
Scheme 5. Formation of Trimers 4
These new propargyl-functionalized gold NHC complexes
have great potential due to the versatility of the propargyl unit,
which may be used as an additional coordination site for the
formation of polynuclear complexes, or may be functionalized
itself. This is exemplified by the synthesis of interesting
trinuclear derivatives with the propargyl-carbene ligand acting
as bidentate C∧C ligands. Many of the complexes are soluble in
water, which could be of significance in the development of
biologically active gold complexes or in the development of
water-soluble gold catalysts.
EXPERIMENTAL SECTION
CONCLUSIONS
■
■
1
Instrumentation. H and 13C{1H} NMR, including 2D experi-
Several new propargyl-functionalized NHC gold complexes
have been prepared. The recently reported procedure for the
synthesis of gold NHC complexes from their corresponding
imidazolium salts and NBu4(acac) has been used with reactions
carried out at room temperature in air and using standard
reagent grade solvents. All reaction times are under 1 h, and
only very basic purification is needed to obtain the pure
products in good to excellent yields. These propargyl
ments, were recorded at room temperature on a Bruker AVANCE 400
spectrometer (1H, 400 MHz; 13C, 100.6 MHz) or on a Bruker
AVANCE II 300 spectrometer (1H, 300 MHz; 13C, 75.5 MHz), with
chemical shifts (δ, ppm) reported relative to the solvent peaks of the
deuterated solvent.26
Starting Materials. The starting materials [AuCl(tht)]27 and
[Au(C6F5)(tht)],27 1-pyridylimidazole,28 and the imidazolium salts23
were prepared according to published procedures. All other reagents
E
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
were commercially available. Solvents were used as received without
purification or drying.
were mixed in CH2Cl2 (10 mL) until a colorless solution formed (5
min). NBu4(acac) (0.0683 g, 0.2 mmol) was added and the mixture
stirred for 1 h. The solution was filtered through a plug of silica and
the colorless filtrate evaporated to minimum volume. Pentane was
added to precipitate a white solid, which was collected and vacuum-
dried to give the product (0.0718 g, 78%). 1H NMR (300 MHz,
DMSO): δ 8.63 (m, 1H, Py), 8.20 (dd, 3JHH = 7.1, 4JHH = 1.0 Hz, 1H,
Py), 8.17−8.09 (m, 1H, Py), 8.03 (d, 3JHH = 2.1 Hz, 1H, CH), 7.82 (d,
3JHH = 2.1 Hz, 1H, CH), 7.61 (m, 1H, Py), 5.17 (d, 4JHH = 2.5 Hz, 2H,
1,3-Bis(2-propyn-1-yl)-1H-imidazol-3-ium Bromide (c). To a
solution of imidazole (0.2723 g, 4.0 mmol) in acetonitrile (30 mL) was
added propargyl bromide (0.86 mL, 8.0 mmol, 80 wt % solution in
toluene) and the mixture heated to reflux for 24 h. After the mixture
was cooled to room temperature, solvent was removed in vacuo to
leave an oily solid, which was recrystallized in acetonitrile/Et2O,
washed with further Et2O, and vacuum-dried to give the product as a
beige solid (0.2851 g, 32%).
4
CH2), 3.69 (t, JHH = 2.5 Hz, 1H, CCH). 13C APT (75 MHz,
Spectral data are in agreement with those previously reported in the
literature.
DMSO): δ 171.96 (s, N−C−N), 150.28 (s, ipso-Py), 149.17 (s, CH
(Py)), 139.61 (s, CH (Py)), 124.75 (s, CH (Py)), 122.43 (s, CH),
121.50 (s, CH), 118.07 (s, CH (Py)), 77.87 (s, CCH), 77.80 (s,
CCH), 40.91 (s, CH2−CCH).
1-Pyridyl-3-(2-propyn-1-yl)-1H-imidazol-3-ium Bromide (d).
To a solution of 1-pyridylimidazole (0.7259 g, 5.0 mmol) in
acetonitrile (50 mL) was added propargyl bromide (1.1 mL, 10.0
mmol, 80 wt % solution in toluene) and the mixture heated to reflux
for 24 h. A pale yellow precipitate formed, which was collected by
vacuum filtration, washed with Et2O, and vacuum-dried to give the
product (0.9504 g, 72%).
Synthesis of [Au(NHC)2]Br (2). Complex 2a. 1-Methyl-3-(2-
propyn-1-yl)-1H-imidazol-3-ium bromide (0.0804 g, 0.4 mmol) and
[AuCl(tht)] (0.0641 g, 0.2 mmol) were mixed in THF (10 mL) until a
colorless solution formed (5 min). NBu4(acac) (0.1366 g, 0.4 mmol)
was added and the mixture stirred. After approximately 30 min a white
precipitate formed. The mixture was stirred for 12 h and then the
precipitate collected by vacuum filtration and dried to give the product
(0.0848 g, 82%). 1H NMR (300 MHz, DMSO): δ 7.60 (d, 3JHH = 1.8
1H NMR (300 MHz, DMSO): δ 10.20 (s, 1H, N−CH−N,
imidazole), 8.65 (dd, 3JHH = 4.8, 4JHH = 1.0 Hz, 1H, Py), 8.60 (m, 1H,
CH), 8.27−8.18 (m, 1H, Py), 8.16−8.05 (m, 2H, Py and CH), 7.72−
7.60 (m, 1H, Py), 5.35 (d, 4JHH = 2.6 Hz, 2H, CH2), 3.92 (t, 4JHH = 2.6
Hz, 1H, CCH). 13C APT (75 MHz, DMSO): δ 149.25 (s, CH
(Py)), 146.29 (s, ipso-Py), 140.63 (s, CH (Py)), 135.13 (s, N−C−N),
125.39 (s, CH (Py)), 123.38 (s, CH), 119.74 (s, CH), 114.49 (s, CH
(Py)), 79.30 (s, CCH), 75.85 (s, CCH), 39.24 (s, CH2−C
CH).
3
Hz, 1H, CH imidazole), 7.55 (d, JHH = 1.8 Hz, 1H, CH imidazole),
5.13 (d, 4JHH = 2.5 Hz, 2H, CH2), 3.90 (s, 3H, Me), 3.65 (t, 4JHH = 2.5
Hz, 1H, CCH). 13C APT (75 MHz, DMSO): δ 183.28 (s, N−C−
N), 123.51 (s, CH), 122.05 (s, CH), 78.60 (s, CCH), 77.45 (s, C
CH), 39.69 (s, CH2−CCH), 37.75 (s, CH3). HRMS (ESI/QTOF)
m/z: [M]+ calcd for C14H16AuN4 437.1035; found 437.1049.
Synthesis of [AuBr(NHC)] (1). Complex 1a. 1-Methyl-3-(2-
propyn-1-yl)-1H-imidazol-3-ium bromide (0.0402 g, 0.2 mmol) and
[AuCl(tht)] (0.0641 g, 0.2 mmol) were mixed in CH2Cl2 (10 mL)
until a colorless solution formed (5 min). NBu4(acac) (0.0683 g, 0.2
mmol) was added and the mixture stirred for 1 h. The solution was
filtered through a plug of silica and the colorless filtrate evaporated to
minimum volume. Pentane was added to precipitate a white solid,
which was collected and vacuum-dried to give the product (0.0646 g,
Complex 2b. 1-Benzyl-3-(2-propyn-1-yl)-1H-imidazol-3-ium bro-
mide (0.1109 g, 0.4 mmol) and [AuCl(tht)] (0.0641 g, 0.2 mmol)
were mixed in CH2Cl2 (10 mL) until a colorless solution formed (5
min). NBu4(acac) (0.1366 g, 0.4 mmol) was added and the mixture
stirred for 1 h. The solution was washed with H2O (3 × 25 mL) and
dried over Na2SO4. The solution was evaporated to minimum volume
under reduced pressure and pentane added to precipitate a white solid,
which was collected and vacuum-dried to give the product (0.0803 g,
63%). 1H NMR (300 MHz, DMSO): δ 7.70 (s, 1H, CH), 7.66 (s, 1H,
CH), 7.34 (m, 5H, Ph), 5.44 (s, 2H, CH2-Ph), 5.13 (d, 4JHH = 1.9 Hz,
2H, CH2-CCH), 3.64 (s, 1H, CCH). 13C APT (75 MHz,
DMSO): δ 182.89 (s, N−C−N), 136.68 (s, ipso-Ph), 128.79 (s, m-Ph),
128.15 (s, p-Ph), 127.63 (s, o-Ph), 122.75 (s, CH), 122.49 (s, CH),
78.36 (s, CCH), 77.54 (s, CCH), 53.82 (s, CH2−Ph), 39.96 (s,
CH2−CCH). HRMS (ESI/QTOF) m/z: [M]+ calcd for
C26H24AuN4 589.1661; found 589.1634.
1
3
82%). H NMR (400 MHz, DMSO): δ 7.53 (d, JHH = 1.9 Hz, 1H,
3
4
CH), 7.48 (d, JHH = 1.9 Hz, 1H, CH), 5.00 (d, JHH = 2.5 Hz, 2H,
CH2), 3.76 (s, 3H, CH3), 3.59 (t, JHH = 2.5 Hz, 1H, CCH). 13C
4
APT (75 MHz, DMSO): δ 172.52 (s, N−C−N), 123.16 (s, CH),
121.35 (s, CH), 78.21 (s, CCH), 77.30 (s, CCH), 39.88 (s, CH2)
37.79 (s, CH3).
Complex 1b. 1-Benzyl-3-(2-propyn-1-yl)-1H-imidazol-3-ium bro-
mide (0.0554 g, 0.2 mmol) and [AuCl(tht)] (0.0641 g, 0.2 mmol)
were mixed in CH2Cl2 (10 mL) until a colorless solution formed (5
min). NBu4(acac) (0.0683 g, 0.2 mmol) was added and the mixture
stirred for 1 h. The solution was filtered through a plug of silica and
the colorless filtrate evaporated to minimum volume. Pentane was
added to precipitate a white solid, which was collected and vacuum-
dried to give the product (0.0696 g, 74%). 1H NMR (300 MHz,
Complex 2c. 1,3-Bis(2-propyn-1-yl)-1H-imidazol-3-ium bromide
(0.0900 g, 0.4 mmol) and [AuCl(tht)] (0.0641 g, 0.2 mmol) were
mixed in THF (10 mL) until a colorless solution formed (5 min).
NBu4(acac) (0.1366 g, 0.4 mmol) was added and the mixture stirred.
After approximately 30 min a white precipitate formed. The mixture
was stirred for 12 h and then the precipitate collected by vacuum
3
3
1
DMSO): δ 7.60 (d, JHH = 2.0 Hz, 1H, CH), 7.57 (d, JHH = 2.0 Hz,
1H, CH), 7.42−7.27 (m, 5H, Ph), 5.36 (s, 2H, CH2−Ph), 5.03 (d,
filtration and dried to give the product (0.1074 g, 95%). H NMR
(300 MHz, DMSO): δ 7.68 (s, 1H, CH), 5.20 (d, 4JHH = 2.5 Hz, 2H,
4JHH = 2.5 Hz, 2H, CH2-CCH), 3.60 (t, JHH = 2.5 Hz, 1H, C
4
4
CH2), 3.66 (t, JHH = 2.5 Hz, 1H, CCH). 13C APT (75 MHz,
CH). 13C APT (75 MHz, DMSO): δ 172.55 (s, N−C−N), 136.44 (s,
ipso-Ph), 128.78 (s, m-Ph), 128.18 (s, p-Ph), 127.65 (s, o-Ph), 122.10
(s, CH), 121.87 (s, CH), 78.02 (s, CCH), 77.39 (s, CCH), 53.85
(s, CH2−Ph), 40.03 (s, CH2−CCH).
DMSO): δ 183.12 (s, N−C−N), 122.32 (s, CH), 78.27 (s, CCH),
77.64 (s, CCH), 40.13 (s, CH2−CCH). HRMS (ESI/QTOF) m/
z: [M]+ calcd for C18H16AuN4 485.1035; found 485.1044.
Complex 2d. 1-Pyridyl-3-(2-propyn-1-yl)-1H-imidazol-3-ium bro-
mide (0.1056 g, 0.4 mmol) and [AuCl(tht)] (0.0641 g, 0.2 mmol)
were mixed in THF (10 mL) until a colorless solution formed (5 min).
NBu4(acac) (0.1366 g, 0.4 mmol) was added and the mixture stirred.
After approximately 30 min a white precipitate formed. The mixture
was stirred for 12 h and then the precipitate collected by vacuum
Complex 1c. 1,3-Bis(2-propyn-1-yl)-1H-imidazol-3-ium bromide
(0.0450 g, 0.2 mmol) and [AuCl(tht)] (0.0641 g, 0.2 mmol) were
mixed in CH2Cl2 (10 mL) until a colorless solution formed (5 min).
NBu4(acac) (0.0683 g, 0.2 mmol) was added and the mixture stirred
for 1 h. The solution was filtered through a plug of silica and the
colorless filtrate evaporated to minimum volume. Pentane was added
to precipitate a white solid, which was collected and vacuum-dried to
1
filtration and dried to give the product (0.1159 g, 90%). H NMR
3
(300 MHz, DMSO): δ 8.54 (m, 1H, Py), 8.15 (d, JHH = 2.0 Hz, 1H,
1
give the product (0.0616 g, 73%). H NMR (300 MHz, CD2Cl2): δ
CH), 8.13 (d, 3JHH = 5.3 Hz, 1H, Py), 8.01 (m, 1H, Py), 7.91 (d, 3JHH
7.29 (s, 2H, CH), 5.04 (d, 4JHH = 2.6 Hz, 4H, CH2), 2.63 (t, 4JHH = 2.6
Hz, 1H, CCH). 13C APT (75 MHz, CD2Cl2): δ 175.44 (s, N−C−
N), 121.09 (s, CH), 76.22 (s, CCH), 41.48 (s, CH2−CCH).
Complex 1d. 1-Pyridyl-3-(2-propyn-1-yl)-1H-imidazol-3-ium bro-
mide (0.0528 g, 0.2 mmol) and [AuCl(tht)] (0.0641 g, 0.2 mmol)
= 2.0 Hz, 1H, CH), 7.59 (m, 1H, Py), 5.27 (d, JHH = 2.4 Hz, 2H,
4
4
CH2), 3.69 (t, JHH = 2.4 Hz, 1H, CCH). 13C APT (75 MHz,
DMSO): δ 181.34 (s, N−C−N), 150.01 (s, ipso-Py), 148.95 (s, CH
(Py)), 139.67 (s, CH (Py)), 124.65 (s, CH (Py)), 123.10 (s, CH),
121.71 (s, CH), 117.53 (s, CH (Py)), 77.96 (s, CCH), 77.83 (s,
F
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CCH), 40.87 (s, CH2−CCH). HRMS (ESI/QTOF) m/z: [M]+
was collected by vacuum filtration, washed with distilled water (20
calcd for C22H18AuN6 563.1253; found 563.1247.
mL) and acetone (20 mL), and vacuum-dried to give the product
1
Synthesis of [Au(C6F5)(NHC)] (3). Complex 3a. 1-Methyl-3-(2-
propyn-1-yl)-1H-imidazol-3-ium bromide (0.0804 g, 0.4 mmol) and
[Au(C6F5)(tht)] (0.1809 g, 0.4 mmol) were mixed in CH2Cl2 (10
mL) until a colorless solution formed (5 min). NBu4(acac) (0.1366 g,
0.4 mmol) was added and the mixture stirred for 1 h. The solution was
filtered through a plug of silica and the colorless filtrate evaporated to
minimum volume. Pentane was added to precipitate a white solid,
which was collected and vacuum-dried to give the product (0.1466 g,
(0.0242 g, 77%). H NMR (400 MHz, DMSO): δ 7.52 (s, 1H, CH),
7.45 (s, 1H, CH), 5.14 (s, 2H, CH2), 3.85 (s, 3H, CH3). 13C APT (75
MHz, DMSO): δ 182.74 (s, N−C−N), 122.45 (s, CH), 122.18 (s,
CH), 102.90(s, CCH), 43.29 (s, CH2), 38.01 (s, CH3). HRMS (ESI-
QTOF) m/z: [M + 3MeOH + Na]+ calcd for C24H33Au3N6O3Na
1067.1503; found 1067.1523.
Complex 4b. To a solution of 1b (0.0473 g, 0.1 mmol) in CH2Cl2
(5 mL) were added diisopropylamine (0.0350 mL, 0.25 mmol) and
CuI (2 mg), and the mixture was stirred for 2 h. A white precipitate
formed, which was collected by vacuum filtration, washed with distilled
water (20 mL) and acetone (20 mL), and vacuum-dried to give the
product (0.0255 g, 65%). 1H NMR (400 MHz, DMSO): δ 7.54−7.28
(m, 7H, 2CH + Ph), 5.30 (s, 2H, CH2), 5.17 (s, 2H, CH2). The
compound was too insoluble to obtain a 13C NMR spectrum. HRMS
(ESI-QTOF) m/z: [M + Na]+ calcd for C39H33Au3N6Na 1199.1655;
found 1199.1721.
Complex 4d. To a solution of 1d (0.0460 g, 0.1 mmol) in CH2Cl2
(5 mL) were added diisopropylamine (0.0350 mL, 0.25 mmol) and
CuI (2 mg), and the mixture was stirred for 2 h. A white precipitate
formed, which was collected by vacuum filtration, washed with distilled
water (20 mL) and acetone (20 mL), and vacuum-dried to give the
product (0.0311 g, 82%). The compound was too insoluble to obtain
NMR spectra. HRMS (ESI-QTOF) m/z: [M + Na]+ calcd for
C33H24Au3N9Na 1160.1043; found 1160.1031.
Crystallography. Crystals were mounted in inert oil on glass fibers
and transferred to the cold gas stream of a Xcalibur Oxford Diffraction
diffractometer equipped with a low-temperature attachment. Data
were collected using monochromated Mo Kα radiation (λ = 0.71073
Å). Scan type ω. An absorption correction based on multiple scans was
applied using spherical harmonics implemented in the SCALE3
ABSPACK29 scaling algorithm. The structures were solved by direct
methods and refined on F2 using the program SHELXL-97.30 All non-
hydrogen atoms were refined anisotropically. The hydrogen atoms
were included in some cases in calculated positions and refined using a
riding model but in other cases were localized in the Fourier map.
Refinements were carried out by full-matrix least squares on F2 for all
data. Further details of the data collection and refinement are given in
Tables S1−S7 in the Supporting Information.
1
3
76%). H NMR (300 MHz, CD2Cl2): δ 7.23 (d, JHH = 1.9 Hz, 1H,
3
4
CH), 7.02 (d, JHH = 1.9 Hz, 1H, CH), 5.09 (d, JHH = 2.6 Hz, 2H,
CH2), 3.90 (s, 3H, CH3), 2.61 (t, JHH = 2.6 Hz, 1H, CCH). 19F
4
NMR (377 MHz, CD2Cl2): δ −116.54 to −116.86 (m, 2F, o-C6F5),
3
−160.80 (t, JFF = 19.8 Hz, 1F, p-C6F5), −163.61 to −163.89 (m, 2F,
m-C6F5). 13C APT (75 MHz, CD2Cl2): δ 188.06 (s, N−C−N), 122.90
(s, CH), 120.73 (s, CH), 76.90 (s, CCH), 75.73 (s, CCH), 40.90
(s, CH2−CCH), 38.51 (s, CH3).
Complex 3b. 1-Benzyl-3-(2-propyn-1-yl)-1H-imidazol-3-ium bro-
mide (0.1109 g, 0.4 mmol) and [Au(C6F5)(tht)] (0.1809 g, 0.4 mmol)
were mixed in CH2Cl2 (10 mL) until a colorless solution formed (5
min). NBu4(acac) (0.1366 g, 0.4 mmol) was added and the mixture
stirred for 1 h. The solution was filtered through a plug of silica and
the colorless filtrate evaporated to minimum volume. Pentane was
added to precipitate a white solid, which was collected and vacuum-
dried to give the product (0.1758 g, 78%). 1H NMR (300 MHz,
CD2Cl2): δ 7.49−7.32 (m, 5H, Ph), 7.25 (d, 3JHH = 1.9 Hz, 1H, CH),
7.03 (d, 3JHH = 1.9 Hz, 1H, CH), 5.43 (s, 2H, CH2-Ph), 5.11 (d, 4JHH
=
2.6 Hz, 1H, CH2-CCH), 2.61 (t, JHH = 2.6 Hz, 1H, CCH). 19F
3
NMR (282 MHz, CD2Cl2): δ −115.78 to −117.58 (m, 2F, o-C6F5),
3
−160.81 (t, JFF = 19.8 Hz, 1F, p-C6F5), −163.16 to −165.55 (m, 2F,
m-C6F5). 13C APT (75 MHz, CD2Cl2): δ 187.70 (s, N−C−N), 136.19
(s, ipso-Ph), 129.56 (s, m-Ph), 129.21 (s, p-Ph), 128.75 (s, o-Ph),
121.64 (s, CH), 121.16 (s, CH), 76.76 (s, CCH), 75.89 (s, C
CH), 55.63 (s, CH2−Ph), 41.09 (s, CH2−CCH).
Complex 3c. 1,3-Bis(2-propyn-1-yl)-1H-imidazol-3-ium bromide
(0.0900 g, 0.4 mmol) and [Au(C6F5)(tht)] (0.1809 g, 0.4 mmol) were
mixed in CH2Cl2 (10 mL) until a colorless solution formed (5 min).
NBu4(acac) (0.1366 g, 0.4 mmol) was added and the mixture stirred
for 1 h. The solution was filtered through a plug of silica and the
colorless filtrate evaporated to minimum volume. Pentane was added
to precipitate a white solid, which was collected and vacuum-dried to
ASSOCIATED CONTENT
* Supporting Information
■
1
give the product (0.1768 g, 87%). H NMR (300 MHz, CD2Cl2): δ
S
7.29 (s, 2H, CH), 5.10 (d,4JHH = 2.6 Hz, 2H, CH2), 2.63 (t, 4JHH = 2.6
Hz, 1H, CCH). 19F NMR (377 MHz, CD2Cl2): δ −116.09 to
The Supporting Information is available free of charge on the
ACS Publications Web site. The Supporting Information is
available free of charge on the ACS Publications website at
DOI: 10.1021/acs.organomet.7b00012.
3
−116.87 (m, 2F, o-C6F5), −160.34 (t, JFF = 19.8 Hz, 1F, p-C6F5),
−163.26 to −163.61 (m, 2F, m-C6F5). 13C APT (75 MHz, CD2Cl2): δ
187.87 (s, N−C−N), 121.18 (s, CH), 76.55 (s, CCH), 76.03 (s,
CCH), 41.19 (s, CH2−CCH).
X-ray crystallographic data for complexes 1a−d, 2c,d,
and 3c (CCDC reference numbers 1517836−1517842)
and NMR spectra for all of the compounds (PDF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Complex 3d. 1-Pyridyl-3-(2-propyn-1-yl)-1H-imidazol-3-ium bro-
mide (0.1056 g, 0.4 mmol) and [Au(C6F5)(tht)] (0.1809 g, 0.4 mmol)
were mixed in CH2Cl2 (10 mL) until a colorless solution formed (5
min). NBu4(acac) (0.1366 g, 0.4 mmol) was added and the mixture
stirred for 1 h. The solution was filtered through a plug of silica and
the colorless filtrate evaporated to minimum volume. Pentane was
added to precipitate a white solid, which was collected and vacuum-
dried to give the product (0.1911 g, 87%). 1H NMR (300 MHz,
3
CD2Cl2): δ 8.77 (d, JHH = 8.2 Hz, 1H, Py), 8.62−8.41 (m, 1H, Py),
8.01−7.85 (m, 2H, Py and CH), 7.51−7.19 (m, 2H, Py and CH), 5.28
(d, 4JHH = 2.6 Hz, 2H, CH2), 2.68 (t, 4JHH = 2.6 Hz, 1H, CCH). 19
F
NMR (377 MHz, CD2Cl2): δ −116.43 to −116.65 (m, 2F, o-C6F5),
3
−160.56 (t, JFF = 19.8 Hz, 1F, p-C6F5), −163.56 to −163.82 (m, 2F,
AUTHOR INFORMATION
Corresponding Author
*E-mail for M.C.G.: gimeno@unizar.es.
m-C6F5). 13C APT (75 MHz, CD2Cl2): δ 186.66 (s, N−C−N), 149.29
(s, CH (Py)), 139.37 (s, CH (Py)), 124.52 (s, CH (Py)), 121.22 (s,
CH), 121.08(s, CH), 120.13(s, ipso-Py), 117.69 (s, CH (Py)), 76.19 (s,
CCH), 75.23(CCH), 42.00 (s, CH2−CCH).
■
ORCID
Synthesis of [Au(RImCH2CC)]3 (4). Complex 4a. To a solution
of 1a (0.0397 g, 0.1 mmol) in CH2Cl2 (5 mL) were added
diisopropylamine (0.0350 mL, 0.25 mmol) and CuI (2 mg), and the
mixture was stirred for 2 h. A pale yellow precipitate formed, which
M. Concepcion Gimeno: 0000-0003-0553-0695
́
Notes
The authors declare no competing financial interest.
G
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
S. K. Isolable vinylgold intermediates  first access to phantoms of
homogeneous gold catalysis. Gold Bull. 2009, 42, 275−279.
ACKNOWLEDGMENTS
■
́
The authors thank the Ministerio de Economıa y Compet-
itividad (MINECO-FEDER CTQ2016-75816-C2-1-P) and
Gobierno de Aragon-Fondo Social Europeo (E77) for financial
́
support. A.J. thanks the MECD for a predoctoral FPU
fellowship.
(12) Tsui, E. Y.; Muller, P.; Sadighi, J. P. Reactions of a Stable
̈
Monomeric Gold(I) Hydride Complex. Angew. Chem., Int. Ed. 2008,
47, 8937−8940.
(13) Huang, L.; Rominger, F.; Rudolph, M.; Hashmi, A. S. K. A
general access to organogold(III) complexes by oxidative addition of
diazonium salts. Chem. Commun. 2016, 52, 6435−6438.
̈
́
̈
(14) Ozdemir, Y.; Denizci, A.; Ozturk, H. T.; Çetinkaya, B. Synthetic
̈
REFERENCES
■
and antimicrobial studies on new gold(I) complexes of imidazolidin-2-
ylidenes. Appl. Organomet. Chem. 2004, 18, 318−322.
(15) Barnard, P. J.; Berners-Price, S. J. Targeting the mitochondrial
cell death pathway with gold compounds. Coord. Chem. Rev. 2007,
251, 1889−1902.
(1) (a) Hahn, F. E.; Jahnke, M. C. Heterocyclic carbenes: synthesis
and coordination chemistry. Angew. Chem., Int. Ed. 2008, 47, 3122−
3172. (b) Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. An
overview of N-heterocyclic carbenes. Nature 2014, 510, 485−496.
(16) Wang, H. M. J.; Chen, C. Y. L.; Lin, I. J. B. Synthesis, Structure,
and Spectroscopic Properties of Gold(I)−Carbene Complexes.
Organometallics 1999, 18, 1216−1223.
(2) Kuhl, O. The chemistry of functionalised N-heterocyclic
̈
carbenes. Chem. Soc. Rev. 2007, 36, 592−607.
(3) Yuan, D.; Tang, H.; Xiao, L.; Huynh, H. V. CSC-pincer versus
pseudo-pincer complexes of palladium(II): a comparative study on
complexation and catalytic activities of NHC complexes. Dalton Trans.
2011, 40, 8788−8795.
(17) (a) Citta, A.; Schuh, E.; Mohr, F.; Folda, A.; Massimino, M. L.;
Bindoli, A.; Casini, A.; Rigobello, M. P. Fluorescent silver(I) and
gold(I)−N-heterocyclic carbene complexes with cytotoxic properties:
mechanistic insights. Metallomics 2013, 5, 1006−1015. (b) Visbal, R.;
(4) Gaillard, S.; Renaud, J.-L. When phosphorus and NHC (N-
heterocyclic carbene) meet each other. Dalton Trans. 2013, 42, 7255−
7270.
́
Fernandez-Moreira, V.; Marzo, I.; Laguna, A.; Gimeno, M. C.
Cytotoxicity and biodistribution studies of luminescent Au(I) and
Ag(I) N-heterocyclic carbenes. Searching for new biological targets.
Dalton Trans. 2016, 45, 15026−15033.
(5) John, A.; Ghosh, P. Fascinating frontiers of N/O-functionalized
N-heterocyclic carbene chemistry: from chemical catalysis to
biomedical applications. Dalton Trans. 2010, 39, 7183−7206.
(6) Bonati, F.; Burini, A.; Pietroni, B. R.; Bovio, B. Reactions of C-
imidazolyllithium derivatives with Group Ib compounds: Tris[μ-(1-
alkylimidazolato-N3,C2)]tri-gold(I) and -silver(I). Crystal structure of
bis(1-benzylimidazolin-2-yliden)gold(I) chloride. J. Organomet. Chem.
1989, 375, 147−160.
́
(18) Visbal, R.; Ospino, I.; Lopez-de-Luzuriaga, J. M.; Laguna, A.;
Gimeno, M. C. N-Heterocyclic Carbene Ligands as Modulators of
Luminescence in Three-Coordinate Gold(I) Complexes with Spec-
tacular Quantum Yields. J. Am. Chem. Soc. 2013, 135, 4712−4715.
(19) Haque, R. A.; Asekunowo, P. O.; Budagumpi, S. Binuclear
silver(I) complexes of p-xylyl/2,6-lutidinyl linked bis-N-heterocyclic
carbene ligands: Synthesis, crystal structures and biological evaluation.
Inorg. Chem. Commun. 2014, 47, 56−59.
(7) See for example: (a) Hashmi, A. S. K.; Hutchings, G. J. Gold
Catalysis. Angew. Chem., Int. Ed. 2006, 45, 7896−7936. (b) Hashmi, A.
S. K.; Rudolph, M. Gold catalysis in total synthesis. Chem. Soc. Rev.
(20) He, Y.; Lv, M.-F.; Cai, C. A simple procedure for polymer-
supported N-heterocyclic carbene silver complex via click chemistry:
an efficient and recyclable catalyst for the one-pot synthesis of
propargylamines. Dalton Trans. 2012, 41, 12428−12433.
(21) Johnson, A.; Laguna, A.; Gimeno, M. C. Axially Chiral Allenyl
Gold Complexes. J. Am. Chem. Soc. 2014, 136, 12812−12815.
(22) Johnson, A.; Gimeno, M. C. An efficient and sustainable
synthesis of NHC gold complexes. Chem. Commun. 2016, 52, 9664−
9667.
2008, 37, 1766−1775. (c) Pflasterer, D.; Hashmi, A. S. K. Gold
̈
catalysis in total synthesis − recent achievements. Chem. Soc. Rev.
2016, 45, 1331−1367. (d) Hashmi, A. S. K. Dual Gold Catalysis. Acc.
Chem. Res. 2014, 47, 864−876. (e) Friend, C. M.; Hashmi, A. S. K.
Gold Catalysis. Acc. Chem. Res. 2014, 47, 729−730. (f) Dorel, R.;
Echavarren, A. Gold(I)-Catalyzed Activation of Alkynes for the
Construction of Molecular Complexity. Chem. Rev. 2015, 115, 9028−
9072. (g) Marion, N.; Nolan, S. P. N-Heterocyclic carbenes in gold
catalysis. Chem. Soc. Rev. 2008, 37, 1776−1782. (h) de Haro, T.;
(23) Gonsior, N.; Ritter, H. Rheological Behavior of Polyelectrolytes
Based on Cellulose and Ionic Liquids Dissolved in 1-Ethyl-3-methyl
Imidazolium Acetate. Macromol. Chem. Phys. 2011, 212, 2633−2640.
(24) (a) Li, H.; Jin, L. Y.; Tao, R. J. 1,3-Diprop-2-ynyl-1H-imidazol-3-
ium bromide. Acta Crystallogr., Sect. E: Struct. Rep. Online 2008, 64,
o900. (b) Lukowiak, M. C.; Meise, M.; Haag, R. Synthesis and
Application of N-Heterocyclic Carbene−Palladium Ligands with
Glycerol Dendrons for the Suzuki−Miyaura Cross-Coupling in
Water. Synlett 2014, 25, 2161−2165. (c) Hollering, M.; Albrecht,
́
́
Gomez-Bengoa, E.; Cribiu, R.; Huang, X.; Nevado, C. Gold-Catalyzed
1,2-/1,2-Bis-acetoxy Migration of 1,4-Bis-propargyl Acetates: A
Mechanistic Study. Chem. - Eur. J. 2012, 18, 6811−6824.
(8) (a) Mercs, L.; Albrecht, M. Beyond catalysis: N-heterocyclic
carbene complexes as components for medicinal, luminescent, and
functional materials applications. Chem. Soc. Rev. 2010, 39, 1903−
1912. (b) Liu, W.; Gust, R. Metal N-heterocyclic carbene complexes as
potential antitumor metallodrugs. Chem. Soc. Rev. 2013, 42, 755−773.
(9) (a) Visbal, R.; Gimeno, M. C. N-heterocyclic carbene metal
complexes: photoluminescence and applications. Chem. Soc. Rev. 2014,
43, 3551−3574. (b) Bestgen, S.; Gamer, M. T.; Lebedkin, S.; Kappes,
M. M.; Roesky, P. W. Di- and Trinuclear Gold Complexes of
Diphenylphosphinoethyl-Functionalised Imidazolium Salts and their
N-Heterocyclic Carbenes: Synthesis and Photophysical Properties.
Chem. - Eur. J. 2015, 21, 601−614. (c) Yam, V. W.-W.; Cheng, E. C.-C.
Highlights on the recent advances in gold chemistry  a
photophysical perspective. Chem. Soc. Rev. 2008, 37, 1806−1813.
(10) Schneider, S. K.; Herrmann, W. A.; Herdtweck, E. Synthesis of
the First Gold(I) Carbene Complex with a Gold-Oxygen Bond 
First Catalytic Application of Gold(I) Complexes Bearing N-
Heterocyclic Carbenes. Z. Anorg. Allg. Chem. 2003, 629, 2363−2370.
(11) (a) Hashmi, A. S. K.; Schuster, A. M.; Rominger, F. Gold
Catalysis: Isolation of Vinylgold Complexes Derived from Alkynes.
Angew. Chem., Int. Ed. 2009, 48, 8247−8249. (b) Hashmi, A. S. K.;
Ramamurthi, T. D.; Rominger, F. On the Trapping of Vinylgold
Intermediates. Adv. Synth. Catal. 2010, 352, 971−975. (c) Hashmi, A.
M.; Kuhn, F. E. Bonding and Catalytic Application of Ruthenium N-
̈
Heterocyclic Carbene Complexes Featuring Triazole, Triazolylidene,
and Imidazolylidene Ligands. Organometallics 2016, 35, 2980−2986.
(25) Wimberg, J.; Meyer, S.; Dechert, S.; Meyer, F. Gold(I),
Gold(III), and Heterometallic Gold(I)−Silver(I) and Gold(I)−
Copper(I) Complexes of a Pyridazine-Bridged NHC/Pyrazole Hybrid
Ligand and Their Initial Application in Catalysis. Organometallics
2012, 31, 5025−5033.
(26) Fulmer, R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. NMR
Chemical Shifts of Trace Impurities: Common Laboratory Solvents,
Organics, and Gases in Deuterated Solvents Relevant to the
Organometallic Chemist. Organometallics 2010, 29, 2176−2179.
́
(27) Uson, R.; Laguna, A.; Laguna, M. (Tetrahydrothiophene)Gold-
(I) or Gold(III) Complexes. Inorg. Synth. 1989, 26, 85−91.
(28) Raba, A.; Anneser, M. R.; Jantke, D.; Cokoja, M.; Herrmann, W.
A.; Kuhn, F. E. Facile and scalable preparation of 2-imidazolylpyr-
̈
idines. Tetrahedron Lett. 2013, 54, 3384−3387.
H
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(29) CrysAlisPro, Version 1.171.35.11; Multiscan absorption correction
with SCALE3 ABSPACK scaling algorithm; Agilent Technologies.
(30) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 2008, 64, 112−122.
I
DOI: 10.1021/acs.organomet.7b00012
Organometallics XXXX, XXX, XXX−XXX