Simple Synthetic Routes to N-Heterocyclic Carbene Gold(I)–Aryl Complexes: Expanded Scope and Reactivity

Article abstract of DOI:10.1002/chem.202000876

The discovery of sustainable and scalable synthetic protocols leading to gold–aryl compounds bearing N-heterocyclic carbene (NHC) ligands sparked an investigation of their reactivity and potential utility as organometallic synthons. The use of a mild base and green solvents provide access to these compounds, starting from widely available boronic acids and various [Au(NHC)Cl] complexes, with reactions taking place under air, at room temperature and leading to high yields with unprecedented ease. One compound, (N,N′-bis[2,6-(di-isopropyl)phenyl]imidazol-2-ylidene)(4-methoxyphenyl)gold, ([Au(IPr)(4-MeOC₆H₄)]), was synthesized on a multigram scale and used to gauge the reactivity of this class of compounds towards C?H/N?H bonds and with various acids, revealing simple pathways to gold–based species that possess attractive properties as materials, reagents and/or catalysts.

Full text of DOI:10.1002/chem.202000876

A Journal of
Accepted Article
Title: Simple Synthetic Routes to N-Heterocyclic Carbene Gold(I)-Aryl
Complexes : Expanded Scope and Reactivity
Authors: Steven Patrick Nolan, Nikolaos Tzouras, Marina Saab, Wim
Janssens, Thibault Cauwenbergh, Kristof Van Hecke, and
Fady Nahra
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To be cited as: Chem. Eur. J. 10.1002/chem.202000876
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Simple Synthetic Routes to N-Heterocyclic Carbene Gold(I)-Aryl
Complexes: Expanded Scope and Reactivity
Nikolaos V. Tzouras,[a] Marina Saab,[a] Wim Janssens†,[a] Thibault Cauwenbergh†,[a] Kristof Van
Hecke,[a] Fady Nahra[a,b] and Steven P. Nolan*[a]
[a]
[b]
N. V. Tzouras, M. Saab, W. Janssens, T. Cauwenbergh, Prof. Dr. K. Van Hecke, Dr. F. Nahra and Prof. Dr. S. P. Nolan
Department of Chemistry and Centre for Sustainable Chemistry
Ghent University
Krijgslaan 281,S-3, 9000 Ghent, Belgium
E-mail: steven.nolan@ugent.be
Dr F. Nahra
Separation and Conversion Technology Unit,
VITO (Flemish Institute for Technological Research),
Boeretang 200, B-2400 Mol, Belgium
† These authors contributed equally
Supporting information for this article is given via a link at the end of the document.
Abstract: The discovery of sustainable and scalable synthetic
protocols leading to gold-aryl compounds bearing N-heterocyclic
carbene (NHC) ligands sparked an investigation of their reactivity
and potential utility as organometallic synthons. The use of a mild
base and green solvents provide access to these compounds,
starting from widely available boronic acids and various [Au(NHC)Cl]
complexes, with reactions taking place under air, at room
temperature and leading to high yields with unprecedented ease.
synthetic approaches making use of Cs2CO3 and boronic acids
to obtain phosphine- as well as N-heterocyclic carbene (NHC)-
stabilized Au(I)-aryl complexes.[12,13] We have also contributed to
this area, by making use of our “golden synthon”, [Au(IPr)OH]
(IPr
= N,N’-bis[2,6-(di-isopropyl)phenyl]imidazol-2-ylidene), in
the transmetallation of organosilanes and organoboranes to
gold,[14] and also, along with Larrosa, by using a decarboxylative
approach to [Au(NHC)(Ar)] complexes.[15] However, all of these
approaches involve the use of either harsh reaction conditions,
reagents that require special handling, toxic solvents or at least
two synthetic steps, and to the best of our knowledge, none of
these have been evaluated on large scale, most likely because
of a simple lack of practicality (Scheme 1). Herein, we disclose
sustainable, operationally simple and scalable synthetic
methods for the preparation of these multipurpose organogold
complexes. Importantly, we showcase for the first time, that N-
alkyl substituted NHCs can participate in these processes as we
begin to uncover the synthetic potential of [Au(NHC)Ar] (Ar =
aryl) complexes.
One
compound,
(N,N’-bis[2,6-(di-isopropyl)phenyl]imidazol-2-
([Au(IPr)(4-MeOC6H4)]), was
ylidene)(4-methoxyphenyl)gold,
synthesized on a multigram scale and used to gauge the reactivity of
this class of compounds towards C-H/N-H bonds and with various
acids, revealing simple pathways to gold-based species that
possess attractive properties as materials, reagents and/or catalysts.
Introduction
Metal-carbon bond-bearing complexes are the foundation of
organometallic chemistry and the importance of such species is
paramount, as their ubiquitous involvement in catalysis attests.[1]
We have had a longstanding interest in gold catalysis and the
unique stabilizing role N-heterocyclic carbenes (NHCs) as
supporting ligands.[2] In this context, we have considered the
gold-carbon bond (whether involved in bonding as part of the
NHC or as part of an additional hydrocarbyl moiety) central to
the reactivity of gold complexes.[3,4] More specifically, gold-aryl
complexes are frequently invoked as intermediates in gold-
mediated reactions.[4] Certain members of this family of
organometallic complexes also exhibit interesting photophysical
and biological properties, and therefore are extremely valuable
materials.[5,6] These compounds have also been used as
substrates in cross-coupling reactions,[7] and have recently been
shown as efficient pre-catalysts in the acid- and silver-free
hydrophenoxylation of alkynes.[8] Despite recent advances,[3-8,9]
their reactivity remains largely unexplored, presumably because
of the methods used for their preparation, which can be viewed
as operationally complex.
Early synthetic approaches proved lacking in efficiency and
involved the use of aryl-magnesium and aryl-lithium reagents
with all associated drawbacks, such as a limited functional group
tolerance and the need for inert conditions and low
temperatures,[7d,10] however they are still used to this day.[11]
Groundbreaking advances have been achieved by Gray and
later by Stockland, Gray and co-workers, who developed
Scheme 1. State-of-the-art methods for the synthesis of gold(I)-aryl
complexes.
Results and Discussion
Our initial approach questioned whether the transmetallation
reaction between [Au(IPr)Cl] (1) and an equimolar amount of
1
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hours. [b] Phenylboronic acid (1.0 equiv.). [c] Incomplete conversion. [d]
Room temperature (RT) under operating condition can range from 25 to 35oC.
[e] [Au(DMS)Cl] (0.10 mmol), IPr•HCl (1 equiv.), Phenylboronic acid (1.1
equiv,), K2CO3 (5.0 equiv.). [f] Phenylboronic acid pinacol ester (1.1 equiv.).
phenylboronic acid was feasible in technical grade acetone in
the presence of K2CO3 (entry 1, Table 1). This initial hypothesis
is based on our recent work using a weak inorganic base to form
M-C bonds.[16] Even though the desired aryl-gold complex 2a
was obtained, traces of 1 were still present in the reaction crude,
thus suggesting that a small excess of the boron reagent was
required to reach full conversion. A reaction carried out in
isopropanol at lower temperatures led to a 94% yield of 2a,
highlighting that very high temperatures were unnecessary as
were anhydrous solvents and anaerobic conditions (entry 2,
Table 1).[12,13] This prompted us to examine ethanol as a more
sustainable and lower boiling solvent. [17] The reaction at room
temperature led to a 96% yield of 2a (entry 3, Table 1). An
attempt was made to synthesize 2a in a telescoping fashion,
starting directly from the precursors of 1 and phenylboronic acid,
and led to a 64% yield yet produced significant decomposition
(entry 4, Table 1). The two-step approach appears optimum.
Interestingly, the synthesis of 2a can be carried out in an ethyl
acetate/water mixture leading to a high yield of the product
without the need for a filtration step (vide infra), and allows for
visual monitoring, since the initial biphasic suspension turns into
a biphasic clear solution after complete conversion of 1 (entries
5 and 6, Table 1). The use of K3PO4, another mild and
sustainable base, led to an 85% yield of 2a, this time in an
ethanol/water mixture. When the reaction was carried out in
water, full conversion was not observed even after 2 days
(entries 7-10, Table 1). Of note, using phenylboronic acid
pinacol ester as the boron reagent led to a similar reaction
outcome (entry 11, Table 1).
In an attempt to gather information about the events that
transpire prior to transmetallation, general procedure A was
followed in the absence of the boronic acid (See Experimental
Section). An aliquot was taken from the reaction mixture via
pipette and was dried under high vacuum for 30 minutes. To that
was added deuterated chloroform, which had been neutralized
by filtration through (dried) basic alumina and the sample was
transferred to an NMR tube. Comparison of the obtained spectra
with those of [Au(IPr)Cl] and [Au(IPr)OH] (prepared the same
way) revealed that [Au(IPr)Cl] was no longer present in the
reaction mixture, as it had been converted to a mixture of
[Au(IPr)OH] as determined by the presence of a singlet at 7.11
ppm and [Au(IPr)OEt], as determined by the presence of a
broad singlet at 7.13 ppm (NHC backbone: NCH, Figure 1). It
should be noted that [Au(IPr)OH] could be generated in the
reaction mixture because of the existence of water in the
reaction.[14c] It is also possible however, that its presence in the
obtained spectra is attributed to the reaction of [Au(IPr)OEt] with
water present in the NMR solvent. Repeating this experiment
several times led to varying ratios of the two complexes,
suggesting that the water content variations affect this
measurement. This however, does not invalidate the possibility
that [Au(IPr)OH] is actually an intermediate in this transformation,
as [Au(IPr)OEt] is not a stable complex and would react with
moisture as well as with the boronic acid.[14a,14c,18,19] Importantly,
following general procedures B and C in the absence of the
boronic acid lead to 0% conversion of [Au(IPr)Cl]. This suggests
that the solvent effect is paramount for the observation of this
phenomenon and also raises a question as to whether these
reactions involve the same intermediates or follow different
pathways. Furthermore, signals attributed to the presence of
ethanol in the obtained NMR spectra, suggest that ethanol might
have a stabilizing interaction with the generated [Au(IPr)OEt]
(Figure 1). Repeated attempts to isolate both intermediates from
the reaction mixture were not successful. However, this
phenomenon is observed for the first time in such systems and
sheds light on possible intermediates, the involvement of which
has only been postulated thus far.[14c] Interestingly, no other
solvent/base combination described here lead to such
observable intermediates.
Table 1. Optimization of the synthetic protocol.
Entry[a]
Solvent
Base
Temp (oC)
Isolated
yield (%)
1[b]
2
Me2CO
iPrOH
EtOH
EtOH
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
60
81[c]
94
50
3
RT[d]
RT
RT
96
4
64[e]
92
5
40%
EtOH/H2O
6
50%
K2CO3
RT
94
EtOAc/H2O
[c]
7
8
EtOH
K3PO4
K3PO4
RT
RT
-
[c]
50%
-
EtOAc/H2O
9
40%
K3PO4
RT
85
EtOH/H2O
[c]
10
11
H2O
K2CO3
K2CO3
RT
RT
-
EtOH
95[f]
[a] Conditions unless otherwise noted: [Au(IPr)Cl] (50 mg, 0.08 mmol),
Phenylboronic acid (1.1 equiv.), Base (3.0 equiv.), 0.5 mL of solvent, 16
2
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Figure 1. Stacked 1H-NMR spectra of [Au(IPr)Cl] (1), [Au(IPr)OH] (2) and an aliquot (3, taken from the reaction and dried under high vacuum) in CDCl3 .
equiv.), EtOH (0.8 mL), 16 hours. [b]. From the corresponding boronic acid
pinacol ester. [c] 2-furanylboronic acid (1.4 equiv.).
The reaction conditions shown in entry 3 (Table 1) were chosen
in order to explore the scope of boronic acids (Scheme 2). An
electron-donating 4-methoxy group led to 2b in excellent yield. A
more sterically demanding boronic acid also led to high yield of
the corresponding gold complex under these conditions (2c).
In order to assess the scalability of this approach the synthesis
of 2b was successfully carried out on a gram scale, leading to a
Compound 2d, which was shown to possess interesting physical
nearly quantitative yield of the product (Scheme 3). A greater
properties, was obtained in an excellent yield.[12e] Boronic acids
than 6-gram-scale synthesis of 2b was successfully performed,
using the convenient biphasic system which obviates reaction
monitoring and allowed the separation/removal of by-products
by decantation of the aqueous phase in a simple separatory
bearing electron-withdrawing groups at various positions also
led to the desired gold-aryl complexes in high yields (2e, 2f and
2g). A boronic acid pinacol ester bearing an alkyne group was
successfully aurated (2h), demonstrating the high functional
funnel.
group tolerance of this method and its potential as a tool for gold
installation on complex organic scaffolds. A heteroaryl-boronic
acid was also compatible to these reaction conditions, leading to
compound 2i in quantitative yield. Of note, the synthesis of 2i
was the only case described here where a considerable excess
of the boron reagent had to be used (1.4 equiv.) to reach full
conversion to the aurated-heteroaryl product.
Scheme 3. Synthesis of 2b on larger scale. Conditions A: [Au(IPr)Cl] (1.00 g,
1.61 mmol), 4-methoxy-phenylboronic acid (0.257 g, 1.69 mmol, 1.05 equiv.),
EtOH (8 mL), 4 hours. Conditions B: [Au(IPr)Cl] (6.00 g, 9.66 mmol), 4-
methoxy-phenylboronic acid (1.50 g, 9.85 mmol,1.02 equiv.), EtOAc (30
mL)/H2O (30 mL), 16 hours.
Next, we turned our attention to the nature of the ligands that
could be compatible with the synthetic route (Scheme 4). In this
regard, 3 bearing a carbene ligand with a saturated backbone
was obtained in 74% (a slightly higher yields than that obtained
with the more elaborate state-of-the-art method).[8] Complex 4,
Scheme 2. Scope of boron reagents. [a] Conditions unless otherwise noted:
[Au(IPr)Cl] (100 mg, 0.161 mmol), boron reagent (1.1 equiv.), K2CO3 (3.0
3
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possessing electron-withdrawing chloride substituents on the
NHC backbone, was efficiently synthesized. Importantly, gold-
aryl complexes 5 and 6, stabilized by electron-rich, N-alkyl
substituted NHCs, were obtained in high yields. Such
compounds are unprecedented in the literature, and the fact that
the corresponding [Au(NHC)OH] complexes present a non-trivial
synthetic challenge, renders the current approach particularly
expedient in these cases.[20] Finally, the methodology was used
Intrigued by the fact that 2b can be produced sustainably on a
multigram scale, we probed its reactivity. When 2b was
dissolved in acetonitrile and HBF4•Et2O was added, the cationic
gold 8 was rapidly formed (Scheme 5).[21] This catalytically active
complex is also a valuable precursor to the [{Au(IPr)}2(µ-
OH)][BF4] catalyst.[22] When 2b was treated with p-
toluenesulfonic acid in benzene at room temperature, complex 9
was observed along with another species that was identified as
a gem-diaurated arene.[23] Heating the mixture with an excess of
the sulfonic acid led to 9 after workup. Interestingly, treatment of
2b with methylsulfonic acid led to 10 directly. A similar result
was obtained when (+)-camphorsulfonic acid was employed,
forming 11, which is a novel gold complex bearing a chiral
counterion. Mesitylsulfonic acid led to a similar outcome as p-
toluenesulfonic, as heating was required for the gem-diaurated
species to be eliminated from the mixture (12). When 2b and
phenylacetylene were reacted in benzene, 13 was efficiently
obtained, a rapid reaction involving the C-H bond is attributed to
the methoxy group electronic effect, as recent literature
suggests that this reaction does not take place under such mild
conditions with 2a.[10b] Finally, when 2b and carbazole were
reacted in benzene, the gold-amido complex 14 was obtained in
high yield, easily activating the N-H bond and significantly
improving upon the state-of-the-art method for access to such
complexes.[24]
to synthesize
a phosphine ligated gold-aryl complex (7),
illustrating the versatility of this approach.
Scheme 4. Scope of ligands. Conditions: [Au(L)Cl] (1.0 equiv.), boronic acid
(1.1 equiv.), K2CO3 (3.0 equiv.), EtOH (0.5-0.8 mL), 16 hours.
Scheme 5. Exploration of the reactivity of 2b.
All new complexes were fully characterized and their molecular
structures were unambiguously determined by single crystal X-
ray diffraction analysis, as shown in Figure 2.[25] Based on key
structural features outlined in the legend of Scheme 2, no
4
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conclusions can be drawn with regards to the effect of the
electron-donating character of the NHC on the length of the Au-
CAr bond in the solid state, as only slight differences are
observed. With regards to the sulfonate counterion-bearing
complexes, the length of the Au-O bond is slightly higher in the
case of 11. Interestingly, in the solid state, the distance between
the hydrogen atoms of the methyl groups of the camsylate anion
and those of the IPr ligand is around 3 Å in some cases,
however no related crosspeaks were detected in 2D-NOESY
NMR. This suggests that in solution these distances are
significantly larger. However, as judged by the 1H-NMR
spectrum of 11, the two N-Aryl groups of IPr give distinct signals,
suggesting that this anion is in close proximity to gold in solution
and has a relatively fixed orientation with respect to IPr.
Figure 2. X-ray molecular structures of new complexes are presented, showing thermal displacement ellipsoids at the 50% probability level and hydrogen atoms
omitted for clarity. In the case of complex 6, three distinct structures exist in the unit cell, one of which was arbitrarily chosen for this figure.[25] Selected bond
lengths (Å) and angles (o) for each complex: 2h (CNHC-Au = 2.027(9), Au-CAr = 2.033(9), CNHC-Au-CAr = 175.7(3)), 4 (CNHC-Au = 2.015(2), Au-CAr = 2.028(2), CNHC
-
Au-CAr = 177.6(1)), 5 (CNHC-Au = 2.047(2), Au-CAr = 2.033(2), CNHC-Au-CAr = 178.7(1)), 6 (CNHC-Au = 2.057(5), Au-CAr = 2.033(5), CNHC-Au-CAr = 175.8(2)), 11
(CNHC-Au = 1.952(6), Au-O = 2.044(5), CNHC-Au-O = 176.4(2)), 12 (CNHC-Au = 1.957(3), Au-O = 2.048(2), CNHC-Au-O = 176.6(1)).
Conclusion
Experimental Section
In conclusion, we have developed efficient, sustainable and
operationally simple synthetic routes to a wide range of gold(I)-
aryl complexes. The scalability and simplicity of our protocols
are remarkable features that will permit further exploration into
gold chemistry and catalysis. Notably, this was demonstrated by
the promising synthetic uses of 2b,[26] which we have begun to
evaluate as alternatives to more traditional practices in gold
chemistry. Further investigations focusing on the uses of these
gold-aryl complexes in organometallic chemistry and catalysis
are ongoing in our laboratory.
General information
All reactions were carried out in air. Solvents and all other reagents were
purchased and used as received without further purification unless
otherwise stated. [AuCl(DMS)] was prepared from HAuCl4∙nH2O, which
was supplied by Umicore. All [Au(NHC)Cl] complexes were synthesized
according to known procedures.[16a,20,27] [Au(PPh3)Cl] was purchased
from Strem Chemicals, Inc. and was used as received. [Au(IPr)OH] was
synthesized using known protocols.[14a,18] Purification of compounds by
filtration was performed using basic alumina or celite purchased from
Sigma Aldrich. Unless otherwise noted, absolute ethanol, deionized
water and freshly crushed potassium carbonate were used. 1H, 13C-{1H}
and 19F Nuclear Magnetic Resonance (NMR) spectra were recorded on a
Bruker Avance 400 Ultrashield, Bruker Avance 300 Ultrashield or a
Bruker Avance 500 spectrometer at 298 K using the residual solvent
peak as reference (CDCl3: δH = 7.26 ppm, δC = 77.16 ppm; CD2Cl2: δH
=
5.32 ppm, δC = 54.00 ppm, C6D6: δH = 7.16 ppm, δC = 128.4 ppm). Peaks
are assigned as: s (singlet), d (doublet), t (triplet), h (heptuplet) and m
5
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(multiplet). The specific rotation of 11 was determined using a Perkin
Elmer 241 Polarimeter. All chlorinated solvents were neutralized prior to
use by filtration through dried basic alumina. Elemental analyses were
either performed at London Metropolitan University 166-220, Holloway
Road, London, N7 8DB.
acetate (0.25 mL) and water (0.25 mL). Evaporation of the solvent after
purification afforded the desired product as a white powder in 94% yield
(50.1 mg, 0.076 mmol).
Procedure C:Synthesized following the general procedure with
[Au(IPr)Cl] (50 mg, 0.08 mmol), phenylboronic acid (10.8 mg, 0.089
mmol,1.1 equiv.), K2CO3 (33.4 mg, 0.242 mmol, 3 equiv.) and 0.5 mL of a
40% v/v aqueous solution of ethanol. Evaporation of the solvent after
purification afforded the desired product as a white powder in 92% yield
(48.5 mg, 0.076 mmol). 1H NMR (400 MHz, C6D6): δ (ppm) = 7.52 (dd, J
= 7.8, 1.4 Hz, 2H), 7.22 (m, 4H, overlapping peaks), 7.08 (d, J = 7.8 Hz,
4H), 6.99 (tt, J = 7.7, 1.5 Hz, 1H), 6.32 (s, 2H), 2.67 (hept, J = 6.8 Hz,
4H), 1.49 (d, J = 6.9 Hz, 12H), 1.10 (d, J = 6.9 Hz, 12H). 13C {1H} NMR
(101 MHz, C6D6): δ (ppm) = 198.5, 169.9, 145.9, 141.3, 135.1, 130.5,
127.1, 124.7, 124.2, 122.5, 29.1, 24.8, 23.9. Analytical data obtained are
in agreement with reported values.[14a,7a]
General synthetic procedures
Procedure A: A 4-mL screwcap vial equipped with a septum cap and a
stirring bar was charged with [Au(L)Cl] (50 or 100 mg, 1 equiv.), the
boron reagent (1.1 equiv.), K2CO3 (3 equiv.) and ethanol (0.5 or 0.8 mL).
The resulting suspension was stirred at 35 °C for 16 h on a metal heating
plate. Upon full conversion of [Au(L)Cl] (as judged by NMR analysis of an
aliquot), the solvent was removed under vacuum and either
dichloromethane, benzene or ethyl acetate was added to the residue.
The resulting mixture was filtered through either celite or basic alumina
and the filtrate was concentrated to dryness, affording the desired
[Au(L)Ar] complex as a microcrystalline solid. Residual solvents or minor
impurities present in the obtained solid can be removed by trituration of a
saturated dichloromethane solution with pentane or washing with
pentane (or diethyl ether) and drying under high vacuum.
Synthesis of [N,N-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene](4-
methoxyphenyl)gold(I) [Au(IPr)C7H7O] (2b):
Procedure A (small scale):Synthesized following the general procedure
with [Au(IPr)Cl] (50 mg, 0.08 mmol), 4-methoxy-phenylboronic acid (13.5
mg, 0.089 mmol,1.1 equiv.), K2CO3 (33.4 mg, 0.242 mmol, 3 equiv.) and
ethanol (0.5 mL). Purification of the product was carried out by filtration
through celite with dichloromethane (4 mL). Evaporation of the solvent,
washing with pentane (3x3 mL) and drying under high vacuum afforded
the product as a white powder in 97% yield (54.0 mg, 0.078 mmol).
Procedure B: A 4-mL screwcap vial equipped with a septum cap and a
stirring bar was charged with [Au(L)Cl] (1 equiv.), the boron reagent (1.1
equiv.), K2CO3 (3 equiv.), and ethyl acetate/water (1:1). The resulting
biphasic suspension was stirred at 35 °C for 16 h on a metal heating
plate. Upon full conversion of [Au(L)Cl] (as judged by NMR analysis of an
aliquot, or by the formation of a clear organic phase), the reaction mixture
was transferred to a separating funnel with ethyl acetate (5 mL) and
water (5 mL). The aqueous phase was discarded and the organic phase
was washed with water (5 mL), dried over anhydrous magnesium sulfate,
filtered and concentrated to dryness, affording the desired [Au(L)Ar]
complex as a microcrystalline solid. Residual solvents present in the
Procedure A (large scale):Synthesized following the general procedure
in a 40 mL scintillation vial equipped with with a septum cap and a stirring
bar using [Au(IPr)Cl] (1.00 g, 1.61 mmol,), 4-methoxy-phenylboronic acid
(0.257 g, 1.69 mmol,1.05 equiv.), K2CO3 (0.668 mg, 4.83 mmol, 3 equiv.)
and ethanol (8 mL). Full conversion had been achieved in 4 hours, as
judged by NMR analysis of an aliquot. After concentrating the reaction
mixture to dryness, purification of the product was carried out by filtration
through celite with dichloromethane (60 mL). Evaporation of the solvent,
washing with pentane (3x30 mL) and drying under high vacuum afforded
the product as a white powder in 98% yield (1.09 g, 1.58 mmol).
obtained
solid
can
be
removed
by
trituration
with
dichloromethane/pentane or washing with pentane (or diethyl ether) and
drying under high vacuum.
Procedure C: A 4-mL screwcap vial equipped with a septum cap and a
stirring bar was charged with [Au(L)Cl] (1 equiv.), the boron reagent (1.1
equiv.), K2CO3 (3 equiv.), and a 40% v/v aqueous solution of ethanol.
The resulting suspension was stirred at 35 °C for 16 h on a metal heating
plate. Upon full conversion of [Au(L)Cl] (as judged by NMR analysis of an
aliquot),the solvents were evaporated under vacuum and the residue was
dissolved and transferred to a separating funnel with ethyl acetate (5 mL)
and water (5 mL). The aqueous phase was discarded and the organic
phase was washed with water (5 mL), dried over anhydrous magnesium
sulfate, filtered and concentrated to dryness, affording the desired
[Au(L)Ar] complex as a microcrystalline solid. Residual solvents present
in the obtained solid can be removed by trituration with
dichloromethane/pentane or washing with pentane (or diethyl ether) and
drying under high vacuum.
Procedure B (large scale): Synthesized following the general procedure
in a 100 mL round bottom flask equipped with with a septum and a
stirring bar using [Au(IPr)Cl] (6.00 g, 9.66 mmol,), 4-methoxy-
phenylboronic acid (1.5 g, 9.85 mmol,1.02 equiv.), K2CO3 (4.01 g, 29.0
mmol, 3 equiv.) and ethyl acetate (30 mL) and water (30 mL). Full
conversion had been achieved after 16 hours, as judged by the evolution
of a completely clear, biphasic solution. The reaction mixture was
transferred to a 1.0 L separation funnel using 220 mL of ethyl acetate
and 220 mL of water. After vigorous mixing of the two phases, the
aqueous phase was separated and extracted with 50 mL of ethyl acetate
which was subsequently added to the organic phase. The organic phase
was washed with 50 mL of water, dried over anhydrous magnesium
sulfate, filtered and concentrated under vacuum. The product was
precipitated by the addition of pentane (200 mL) to the obtained
saturated solution, filtered on a sintered glass crucible, washed with
pentane (2x100 mL) and dried under high vacuum. The product was
Scope of boron reagents
Synthesis
of
[N,N-Bis(2,6-diisopropylphenyl)imidazol-2-
ylidene](phenyl)gold(I) [Au(IPr)C6H5] (2a):
1
isolated as a white solid in 95% yield (6.37 g, 9.19 mmol). H NMR (400
MHz, CDCl3): δ (ppm) = 7.45 (t, J = 7.8 Hz, 2H), 7.27 (d, J = 7.1 Hz, 4H),
7.13 (s, 2H), 7.00 (d, J = 8.4 Hz, 2H), 6.63 (d, J = 8.4 Hz, 2H), 3.65 (s,
3H), 2.67 (hept, J = 6.9 Hz, 4H), 1.40 (d, J = 6.9 Hz, 12H), 1.23 (d, J =
6.9 Hz, 12H). 13C {1H} NMR (101 MHz, CDCl3): δ (ppm) = 197.3, 156.9,
145.9, 140.8, 134.8, 130.2, 124.0, 122.9, 122.8, 112.8, 55.1, 28.9, 24.7,
24.1. Elemental analysis calcd (%) for C34H43AuN2O: C 58.95, H 6.26, N
4.04; found: C 58.97, H 6.38, N 3.91. Analytical data obtained are in
agreement with reported values.[14c]
Procedure A:Synthesized following the general procedure with
[Au(IPr)Cl] (50 mg, 0.08 mmol), phenylboronic acid (10.8 mg, 0.089
mmol,1.1 equiv.), K2CO3 (33.4 mg, 0.242 mmol, 3 equiv.) and ethanol
(0.5 mL). Purification of the product was carried out by filtration through
celite with dichloromethane (4 mL). Evaporation of the solvent, washing
with pentane (3x3 mL) and drying under high vacuum afforded the
product as a white powder in 96% yield (51.2 mg, 0.077 mmol).
Procedure B:Synthesized following the general procedure with
[Au(IPr)Cl] (50 mg, 0.08 mmol), phenylboronic acid (10.8 mg, 0.089
mmol,1.1 equiv.), K2CO3 (33.4 mg, 0.242 mmol, 3 equiv.) and ethyl
Synthesis
of
[N,N-Bis(2,6-diisopropylphenyl)imidazol-2-
ylidene](2,4,6-trimethylphenyl)gold(I) [Au(IPr)C9H13] (2c):
6
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10.1002/chem.202000876
Chemistry - A European Journal
FULL PAPER
Procedure A:Synthesized following the general procedure with
[Au(IPr)Cl] (100 mg, 0.161 mmol), 2,4,6-trimethylphenylboronic acid
(29.1 mg, 0.177 mmol,1.1 equiv.), K2CO3 (66.8 mg, 0.484 mmol, 3
equiv.) and ethanol (0.8 mL). Purification of the product was carried out
by filtration through celite with dichloromethane (6 mL). Evaporation of
the solvent, washing with pentane (3x3 mL) and drying under high
vacuum afforded the product as a white powder in 83% yield (94.0 mg,
0.134 mmol). 1H NMR (400 MHz, C6D6): δ (ppm) = 7.27 (t, J = 7.8 Hz,
2H), 7.10 (d, J = 7.8 Hz, 4H), 6.98 (s, 2H), 6.36 (s, 2H), 2.66 (hept, J =
6.8 Hz, 4H), 2.28 (s, 3H), 2.24 (s, 6H), 1.44 (d, J = 6.9 Hz, 12H), 1.10 (d,
J = 6.9 Hz, 12H). 13C {1H} NMR (101 MHz, C6D6): δ (ppm) = 201.0, 167.1,
146.6, 146.2, 135.3, 133.1, 130.4, 128.3, 128.1, 127.8, 126.1, 124.1,
122.31, 29.1, 26.4, 24.7, 24.1, 21.5. Analytical data obtained are in
agreement with reported values.[7a]
19F NMR (471 MHz, CDCl3) δ (ppm) = -119.06 (m). Analytical data
obtained are in agreement with reported values.[14c,28]
Synthesis of [N,N-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene](4-
nitrophenyl)gold(I) [Au(IPr)C6H4NO2] (2g):
Procedure A:Synthesized following the general procedure with
[Au(IPr)Cl] (100 mg, 0.161 mmol), 4-nitrophenylboronic acid (29.6 mg,
0.177 mmol,1.1 equiv.), K2CO3 (66.8 mg, 0.484 mmol, 3 equiv.) and
ethanol (0.8 mL). Purification of the product was carried out by filtration
through celite with dichloromethane (6 mL). Evaporation of the solvent,
washing with pentane (3x3 mL) and drying under high vacuum afforded
the product as a bright yellow powder in 88% yield (100 mg, 0.141 mmol).
1H NMR (400 MHz, CDCl3): δ (ppm) = 7.79 (d, J = 8.5 Hz, 2H), 7.50 (t, J
= 7.8 Hz, 2H), 7.30 (d, J = 7.8 Hz, 4H), 7.18 (s, 2H), 7.16 (d, J = 8.5 Hz,
2H), 2.64 (hept, J = 6.8 Hz, 2H), 1.38 (d, J = 6.9 Hz, 12H), 1.25 (d, J =
6.9 Hz, 12H). 13C {1H} NMR (101 MHz, CDCl3): δ (ppm) = 195.2, 182.2,
145.9, 145.3, 140.3, 134.5, 130.5, 124.2, 123.2, 120.5, 28.9, 24.7, 24.1.
Analytical data obtained are in agreement with reported values.[14c]
Synthesis
of
[N,N-Bis(2,6-diisopropylphenyl)imidazol-2-
ylidene)](1,1’-napthalenyl)gold(I) [Au(IPr)C10H7] (2d):
Procedure A:Synthesized following the general procedure with
[Au(IPr)Cl] (100 mg, 0.161 mmol), naphthalene-1-boronic acid (30.4 mg,
0.177 mmol,1.1 equiv.), K2CO3 (66.8 mg, 0.484 mmol, 3 equiv.) and
ethanol (0.8 mL). Purification of the product was carried out by filtration
through celite with dichloromethane (6 mL). Evaporation of the solvent,
washing with pentane (3x3 mL) and drying under high vacuum afforded
the product as a white powder in 96% yield (94.0 mg, 0.154 mmol). 1H
NMR (400 MHz, CDCl3): δ (ppm) = 7.59 (d, J = 8.4 Hz, 1H), 7.57 – 7.51
(m, 3H), 7.38 (t, J = 4.7 Hz, 1H), 7.34 (d, J = 7.8 Hz, 4H), 7.21 (s, 2H),
7.19 (t, J = 1.4 Hz, 1H), 7.16 (m, 2H), 7.01 (ddd, J = 8.2, 6.7, 1.4 Hz, 1H),
2.83 – 2.65 (m, 4H), 1.39 (d, J = 6.9 Hz, 12H), 1.26 (d, J = 6.9 Hz, 12H).
13C {1H} NMR (101 MHz, CDCl3): δ (ppm) = 197.9, 173.1, 146.1, 143.8,
136.7, 134.8, 134.8, 133.9, 130.3, 127.7, 125.1, 124.1, 123.9, 123.71,
122.9, 122.7, 29.0, 24.6, 24.2. Analytical data obtained are in agreement
with reported values.[14c]
Synthesis of [N,N-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene](4-
(phenylethynyl)phenyl)gold(I) [Au(IPr)C6H4CCC6H4] (2h):
Procedure A:Synthesized following the general procedure with
[Au(IPr)Cl] (100 mg, 0.161 mmol), 4-(phenylethynyl)phenylboronic acid
pinacol ester (53.8 mg, 0.177 mmol,1.1 equiv.), K2CO3 (66.8 mg, 0.484
mmol, 3 equiv.) and ethanol (0.8 mL). Purification of the product was
carried out by filtration through basic alumina with benzene (6 mL).
Evaporation of the solvent, washing with pentane (3x3 mL) and drying
under high vacuum afforded the product as a light yellow solid in 73%
yield (100 mg, 0.118 mmol). 1H NMR (400 MHz, C6D6): δ (ppm) = 7.56 (d,
J = 8.0 Hz, 2H, HAr), 7.49 (d, J = 8.0 Hz, 2H, HAr), 7.38 (dd, J = 7.8, 1.6
Hz, 2H, HAr), 7.23 (t, J = 7.8 Hz, 2H, HAr(IPr)), 7.07 (d, J = 7.8 Hz, 4H,
HAr(IPr)), 6.97 – 6.87 (m, 3H, HAr), 6.32 (s, 2H, HImid), 2.65 (hept, J = 6.8
Hz, 4H, CH(CH3)2(IPr)), 1.46 (d, J = 6.9 Hz, 12H, CH(CH3)2(IPr)), 1.10 (d, J
= 6.9 Hz, 12H, CH(CH3)2(IPr)). 13C {1H} NMR (101 MHz, C6D6): δ (ppm) =
197.6 (NCN), 172.4 (CAr-Au), 145.9 (CAr(IPr)), 141.0 (CHAr-CAr-Au), 134.9
(NCAr(IPr)), 131.9 (CHAr), 130.6 (CHAr(IPr)), 130.0 (Au-C=CH-CHAr), 128.3
(CHAr, seen in HSQC), 127.4 (CHAr), 125.2 (CAr), 124.2 (CHAr(IPr)), 122.6
(CHImid), 119.2 ((Au-C=CH-CHAr-CHAr-CAr-CC), 92.6 (CC, close to Au),
88.3 (CC), 29.1 (CH(CH3)2(IPr)), 24.8 (CH(CH3)2(IPr)), 23.9 (CH(CH3)2(IPr)).
Elemental analysis calcd (%) for C41H45AuN2: C 64.56, H 5.95, N 3.67;
found: C 64.61, H 5.87, N 3.61.
Synthesis
of
[N,N-Bis(2,6-diisopropylphenyl)imidazol-2-
ylidene)](3,4-dichlorophenyl)gold(I) [Au(IPr)C6H3Cl2] (2e):
Procedure A:Synthesized following the general procedure with
[Au(IPr)Cl] (100 mg, 0.161 mmol), 3,4-dichlorophenylboronic acid (33.8
mg, 0.177 mmol,1.1 equiv.), K2CO3 (66.8 mg, 0.484 mmol, 3 equiv.) and
ethanol (0.8 mL). Purification of the product was carried out by filtration
through celite with dichloromethane (6 mL). Evaporation of the solvent,
washing with pentane (3x3 mL) and drying under high vacuum afforded
the product as a white powder in 94% yield (110 mg, 0.150 mmol). 1H
NMR (400 MHz, CDCl3): δ (ppm) = 7.49 (t, J = 7.8 Hz, 2H), 7.29 (d, J =
7.8 Hz, 4H), 7.15 (s, 2H), 7.10 (d, J = 1.0 Hz, 1H), 7.05 (d, J = 7.7 Hz,
1H), 6.83 (dd, J = 7.7, 1.0 Hz, 1H), 2.63 (hept, J = 6.9 Hz, 4H), 1.37 (d, J
= 6.9 Hz, 12H), 1.24 (d, J = 6.9 Hz, 12H). 13C {1H} NMR (101 MHz,
CDCl3): δ (ppm) = 195.4, 170.0, 145.9, 141.2, 139.3, 134.5, 130.9, 130.5,
128.2, 127.5, 124.1, 123.0, 28.9, 24.7, 24.1. Analytical data obtained are
in agreement with reported values.[14c]
Synthesis
of
[N,N-Bis(2,6-diisopropylphenyl)imidazol-2-
ylidene](furan-2-yl)gold(I) [Au(IPr)C4H3O] (2i):
Procedure A: Synthesized following the general procedure with
[Au(IPr)Cl] (100 mg, 0.161 mmol), 2-furanylboronic acid (19.8 mg, 0.225
mmol,1.4 equiv.), K2CO3 (66.8 mg, 0.484 mmol, 3 equiv.) and ethanol
(0.8 mL). Purification of the product was carried out by filtration through
celite with dichloromethane (6 mL). Evaporation of the solvent, washing
with pentane (3x3 mL) and drying under high vacuum afforded the
Synthesis of [N,N-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene)](4-
fluorophenyl)gold(I) [Au(IPr)C6H4F] (2f):
1
product as a white powder in >99% yield (105 mg, 0.161 mmol). H NMR
(400 MHz, CDCl3): δ (ppm) = 7.49 (d, J = 1.3 Hz, 1H), 7.47 (t, J = 7.8 Hz,
2H), 7.27 (d, J = 7.8 Hz, 4H), 7.14 (s, 2H), 6.24 (dd, J = 2.9, 1.7 Hz, 1H),
5.80 (d, J = 2.9 Hz, 1H), 2.64 (hept, J = 6.8 Hz, 4H), 1.38 (d, J = 6.9 Hz,
12H), 1.23 (d, J = 6.9 Hz, 12H). 13C {1H} NMR (101 MHz, CDCl3): δ
(ppm) = 194.6, 192.3, 145.8, 143.9, 134.6, 130.4, 124.2, 123.1, 117.9,
107.7, 28.9, 24.7, 24.1. Analytical data obtained are in agreement with
reported values.[15a]
Procedure A:Synthesized following the general procedure with
[Au(IPr)Cl] (100 mg, 0.161 mmol), 4-fluorophenylboronic acid (24.8 mg,
0.177 mmol,1.1 equiv.), K2CO3 (66.8 mg, 0.484 mmol, 3 equiv.) and
ethanol (0.8 mL). Purification of the product was carried out by filtration
through celite with dichloromethane (6 mL). Evaporation of the solvent,
washing with pentane (3x3 mL) and drying under high vacuum afforded
the product as a white powder in 91% yield (100 mg, 0.147 mmol). 1H
NMR (400 MHz, CDCl3): δ (ppm) = 7.47 (t, J = 7.8 Hz, 2H), 7.28 (d, J =
7.8 Hz, 4H), 7.14 (s, 2H), 7.04 – 6.96 (m, 2H), 6.76 – 6.69 (m, 2H), 2.66
(hept, J = 6.8 Hz, 4H), 1.39 (d, J = 6.9 Hz, 12H), 1.24 (d, J = 6.9 Hz, 12H).
13C {1H} NMR (101 MHz, CDCl3): δ (ppm) = 196.6 (s), 164.3 (s), 161.0 (d,
JCF = 240.9 Hz), 145.9 (s), 140.9 (d, JCF = 5.0 Hz), 134.7 (s), 130.3 (s),
124.1 (s), 122.9 (s), 113.4 (d, JCF = 17.2 Hz), 28.9 (s), 24.7 (s), 24.1 (s).
Scope of ligands
Synthesis of [N,N-Bis(2,6-diisopropylphenyl)imidazolin-2-ylidene](4-
methoxyphenyl)gold(I) [Au(SIPr)C7H7O] (3):
7
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10.1002/chem.202000876
Chemistry - A European Journal
FULL PAPER
Procedure A: Synthesized following the general procedure with
[Au(SIPr)Cl] (50.15 mg, 0.08 mmol), 4-methoxyphenylboronic acid (13.5
mg, 0.089 mmol,1.1 equiv.), K2CO3 (33.44 mg, 0.242 mmol, 3 equiv.) and
ethanol (0.5 mL). Purification of the product was carried out by filtration
through celite with dichloromethane (6 mL). Evaporation of the solvent,
washing with pentane (3x3 mL) and drying under high vacuum afforded
the product as a white powder in 74% yield (41.4 mg, 0.060 mmol). 1H
NMR (400 MHz, CDCl3): δ (ppm) = 7.37 (t, J = 7.8 Hz 2H), 7.22 (d, J =
7.8 Hz, 4H), 6.92 (d, J = 8.4 Hz, 2H), 6.61 (d, J = 8.4Hz, 2H), 4.00 (s, 4H),
3.64 (s, 3H), 3.15 (hept, J = 6.9 Hz, 4H), 1.47 (d, J = 6.8 Hz, 3H), 1.35 (d,
J = 6.8 Hz, 12H). 13C {1H} NMR (101 MHz, CDCl3): δ (ppm) = 216.8,
161.0, 156.9, 146.9, 140.8, 134.9, 129.5, 124.4, 112.7, 55.1, 53.9, 29.1,
25.2, 24.2. Analytical data obtained are in agreement with reported
values.[8]
the product as a white, microcrystalline solid in 77% yield (90 mg, 0.186
mmol). 1H NMR (400 MHz, CDCl3): δ (ppm) = 7.51 (d, J = 8.4 Hz, 2H,
HAr), 7.04 (s, 2H, NCH), 6.86 (d, J = 8.4 Hz, 2H, HAr), 3.78 (s, 3H, OCH3),
1.94 (s, 18H, NC(CH3)3). 13C {1H} NMR (101 MHz, CDCl3): δ (ppm) =
193.3 (NCN), 157.7 (CAr-Au), 157.3 (CAr-OMe), 141.5 (CHAr), 116.0
(NCH=CHN), 113.3 (CHAr), 58.6 (NCAlk), 55.2 (OCH3), 32.0 (CCH3).
Elemental analysis calcd (%) for C18H27AuN2O: C 44.63, H 5.62, N 5.78;
found: C 44.82, H 5.70, N 5.65.
Synthesis of [Triphenylphosphine](phenyl)gold(I) [Au(PPh3)C6H5]
(7):
Procedure A: Synthesized following the general procedure with
[Au(PPh3)Cl] (50.0 mg, 0.101 mmol), phenylboronic acid (13.6 mg, 0.111
mmol,1.1 equiv.), K2CO3 (42.0 mg, 0.304 mmol, 3 equiv.) and ethanol
(0.5 mL). Purification of the product was carried out by filtration through
basic alumina with dichloromethane (4 mL). Evaporation of the solvent,
washing with pentane (3x3 mL) and drying under high vacuum afforded
the product as a white, microcrystalline solid in 82% yield (44.0 mg,
0.082 mmol). 1H NMR (400 MHz, C6D6): δ (ppm) = 8.13 (m, 2H), 7.52 (td,
J = 7.7, 1.6 Hz, 2H), 7.46 – 7.38 (m, 6H), 7.27 (tt, J = 7.4, 1.3 Hz, 1H),
7.00 – 6.89 (m, 9H). 13C {1H} NMR (101 MHz, C6D6): δ (ppm) = 173.7 (d,
JCP = 117.7 Hz), 140.4 (s), 134.6 (d, JCP = 13.7 Hz), 131.7 (d, J = 48.2
Hz), 131.0 (d, J = 2.2 Hz), 129.2 (d, J = 10.6 Hz), 126.3 (s). 31P NMR
(162 MHz, C6D6): δ (ppm) = 56.85. 1H NMR (400 MHz, CDCl3): δ (ppm)
= 7.65 – 7.54 (m, 8H), 7.52 – 7.42 (m, 9H), 7.31 – 7.26 (m, 2H), 7.11 –
7.06 (m, 1H). 13C {1H} NMR (101 MHz, CDCl3): δ (ppm) = 172.1 (d, J =
116.9 Hz), 139.7 (s), 134.5 (d, J = 13.7 Hz), 131.3 (d, J = 2.2 Hz), 131.3
(d, J = 2.2 Hz), 129.2 (d, J = 10.7 Hz), 127.7 (d, J = 6.0 Hz), 126.0 (s).
31P NMR (162 MHz, CDCl3): δ (ppm) = 43.53. Analytical data obtained
are in agreement with reported values.[9a]
Synthesis of [4,5-dichloro-N,N-Bis(2,6-diisopropylphenyl)imidazol-2-
ylidene](4-methoxyphenyl)gold(I) [Au(IPrCl)C7H7O] (4):
Procedure A: Synthesized following the general procedure with
[Au(IPrCl)Cl] (100 mg, 0.145 mmol), 4-methoxyphenylboronic acid (24.22
mg, 0.159 mmol,1.1 equiv.), K2CO3 (60.1 mg, 0.435 mmol, 3 equiv.) and
ethanol (0.8 mL). Purification of the product was carried out by filtration
through basic alumina with benzene (6 mL, ethyl acetate can also be
used). Evaporation of the solvent, washing with pentane (3x3 mL) and
drying under high vacuum afforded the product as a white powder in 91%
1
yield (100 mg, 0.131 mmol). H NMR (400 MHz, CDCl3): δ (ppm) = 7.51
(t, J = 7.8 Hz, 2H, HAr(IPrCl)), 7.30 (d, J = 7.8 Hz, 4H, HAr(IPrCl)), 6.95 (d, J =
8.4 Hz, 2H, HAr), 6.63 (d, J = 8.4 Hz, 2H, HAr), 3.65 (s, 3H,OCH3), 2.56
(hept, J = 6.9 Hz, 4H, CH(CH3)2(IPrCl)), 1.40 (d, J = 6.9 Hz, 12H,
CH(CH3)2(IPrCl)), 1.27 (d, J = 6.9 Hz, 12H, CH(CH3)2(IPrCl)). 13C {1H} NMR
(101 MHz, CDCl3): δ (ppm) = 197.3 (NCN), 158.9 (CAr-Au), 157.1 (CAr-
OMe), 146.4 (CAr(IPrCl)), 140.8 (CHAr), 131.7 (NCAr(IPrCl)), 131.2 (CHAr(IPrCl)),
124.3 (CHAr(IPrCl)), 118.8 (CImid-Cl), 112.8 (CHAr), 55.1 (OCH3), 29.3
(CH(CH3)2(IPrCl)), 24.7 (CH(CH3)2(IPrCl)), 23.6 (CH(CH3)2(IPrCl)). Elemental
analysis calcd (%) for C34H41AuCl2N2O: C 53.62, H 5.43, N 3.68; found:
C 53.55, H 5.44, N 3.61.
Reactivity of 2b
Synthesis of [Au(IPr)(MeCN)][BF4] (8):
A 4-mL screwcap vial equipped with a septum cap and a stirring bar was
charged with 2b (50 mg, 0.072 mmol, 1 equiv.) and acetonitrile (0.5 mL).
To the resulting solution was added HBF4•Et2O (13 mg, 0.079 mmol, 1.1
equiv.) via a micropipette. After stirring at room temperature for 5 minutes,
the solvent was removed under vacuum and diethyl ether was added to
the residue. The resulting mixture was filtered, and the solid product was
washed with diethyl ether and dried under vacuum. The product was
obtained as a white, microcrystalline solid in 94% yield (48.4 mg, 0.068
mmol). 1H NMR (400 MHz, CDCl3): δ (ppm) = 7.57 (t, J = 7.8 Hz, 2H),
7.40 (s, 2H), 7.34 (d, J = 7.8 Hz, 4H), 2.44 (hept, J = 6.9 Hz, 4H), 2.39 (s,
3H), 1.29 (d, J = 6.9 Hz, 12H), 1.24 (d, J = 6.9 Hz, 12H). 13C {1H} NMR
(101 MHz, CDCl3): δ (ppm) = 166.4, 145.6, 133.1, 131.6, 125.0, 124.7,
121.2, 29.0, 24.8, 24.1, 2.8. 19F NMR (471 MHz, CDCl3): δ (ppm) = -
153.59, -153.64. Analytical data obtained are in agreement with reported
values.[22]
Synthesis of [N,N-Bis(adamantyl)imidazol-2-ylidene](phenyl)gold(I)
[Au(IAd)C6H5] (5):
Procedure A: Synthesized following the general procedure with
[Au(IAd)Cl] (45.8 mg, 0.08 mmol), phenylboronic acid (10.8 mg, 0.089
mmol,1.1 equiv.), K2CO3 (33.4 mg, 0.242 mmol, 3 equiv.) and ethanol
(0.5 mL). Purification of the product was carried out by filtration through
celite with dichloromethane (4 mL). Evaporation of the solvent, washing
with pentane (3x3 mL) and drying under high vacuum afforded the
product as a white, microcrystalline solid in 81% yield (39.8 mg, 0.065
1
mmol). H NMR (400 MHz, CDCl3): δ (ppm) = 7.60 (dd, J = 7.8, 1.5 Hz,
2H, HAr), 7.23 (t, J = 7.5 Hz, 2H, HAr), 7.05 (s, 2H, NCH), 7.04 – 6.99 (m,
1H, HAr), 2.68 (m, 12H, NCCH2), 2.29 (s, 6H, CHAlk), 1.82 (m, 12H, CH2).
13C {1H} NMR (101 MHz, CDCl3): δ (ppm) = 191.9 (NCN), 166.8 (CAr-Au),
141.6 (CHAr), 127.3 (CHAr), 124.6 (CHAr), 115.0 (NCH=CHN), 58.8
(NCAlk), 44.5 (NCCH2), 36.23 (CH2), 30.2(CHAlk). Elemental analysis
calcd (%) for C29H37AuN2: C 57.05, H 6.11, N 4.59; found: C 57.18, H
6.23, N 4.45.
Synthesis of [Au(IPr)(OTs)] (9):
A 4 mL screwcap vial equipped with a septum cap and a stirring bar was
charged with 2b (20 mg, 0.029 mmol, 1 equiv.), p-toluenesulfonic acid
monohydrate (8.2 mg, 0.043 mmol, 1.5 equiv.) and benzene (0.6 mL).
This solution was stirred overnight at 50 °C. Afterwards, dichloromethane
was added and the mixture was pushed through a microfilter, in order for
a clear solution to be obtained. The solvent was evaporated, and the
white residue was washed with diethyl ether (2x3 mL) and pentane. The
product was obtained as a white solid in 64% yield (14 mg, 0.019 mmol).
1H NMR (400 MHz, CDCl3): δ (ppm) = 7.55 (t, J = 7.8 Hz, 2H), 7.41 (d, J
= 7.6 Hz, 2H), 7.31 (d, J = 7.8 Hz, 4H), 7.21 (s, 2H), 6.99 (d, J = 7.9 Hz,
2H), 2.55 – 2.42 (hept, J = 6.8 Hz, 4H), 2.32 (s, 3H), 1.29 (d, J = 6.9 Hz,
12H), 1.21 (d, J = 6.9 Hz, 12H). 13C {1H} NMR (75 MHz, CDCl3): δ (ppm)
= 164.6, 145.7, 133.8, 131.0, 128.8, 126.4, 124.5, 123.6, 29.0, 24.4, 24.3,
21.5. Analytical data obtained are in agreement with reported values.[29]
Synthesis
of
[N,N-Bis(tert-butyl)imidazol-2-ylidene](4-
methoxyphenyl)gold(I) [Au(ItBu)C7H7O] (6):
Procedure A: Synthesized following the general procedure with
[Au(ItBu)Cl] (100 mg, 0.242 mmol), 4-methoxyphenylboronic acid (32.5
mg, 0.266 mmol,1.1 equiv.), K2CO3 (50.2 mg, 0.363 mmol, 3 equiv.) and
ethanol (0.7 mL). Purification of the product was carried out by filtration
through basic alumina with dichloromethane (6 mL). That solution was
filtered again though celite and the filter cake was washed with
dichloromethane (4 mL) The filtrate was concentrated and pentane (4
mL) was added, leading to precipitation of a white solid. Filtration,
washing with pentane (3x3 mL) and drying under high vacuum afforded
8
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Synthesis of [Au(IPr)(OMs)] (10):
Synthesis of [Au(IPr)CCPh] (13):
A 4 mL screwcap vial equipped with a septum cap and a stirring bar was
charged with 2b (100 mg, 0.144 mmol, 1 equiv.), chloroform (3.0 mL) and
methanesulfonic acid (10.0 µL, 0.159 mmol, 1.1 equiv.). This solution
was stirred overnight at room temperature. Afterwards, dichloromethane
was added and the mixture was filtered through a microfilter, in order for
a clear solution to be obtained. The solvent was evaporated, and the
white residue was washed with diethyl ether (2x5 mL) and dried under
vacuum. The product was obtained as a white solid in 88% yield (84 mg,
0.123 mmol). 1H NMR (400 MHz, CD2Cl2): δ (ppm) = 7.57 (t, J = 7.8 Hz,
2H), 7.36 (d, J = 7.8 Hz, 4H), 7.29 (s, 2H), 2.52 (hept, J = 6.9 Hz, 4H),
2.36 (s, 3H), 1.35 (d, J = 6.9 Hz, 12H), 1.23 (d, J = 6.9 Hz, 12H). 13C {1H}
NMR (75 MHz, CD2Cl2): δ (ppm) = 164.5, 146.4, 134.3, 131.4, 124.9,
124.4, 39.6, 29.4, 24.7, 24.4. Analytical data obtained are in agreement
with reported values.[30]
A 4 mL screwcap vial equipped with a septum cap and a stirring bar was
charged with 2b (20.0 mg, 0.029 mmol, 1 equiv.), benzene (0.6 mL) and
phenylacetylene (3.6 μL, 0.032 mmol, 1.1 equiv.). This solution was
stirred for 16 hours at 80 °C. The solvent was evaporated under vacuum
and the white residue was washed with diethyl ether (2x2 mL) and dried
The product was obtained as a white solid in 92% yield (18 mg, 0.027
mmol). 1H NMR (400 MHz, CDCl3): δ (ppm) = 7.49 (t, J = 7.8 Hz, 2H),
7.32 – 7.28 (m, 6H), 7.12 (s, 2H), 7.11 – 7.01 (m, 3H), 2.70 – 2.51 (hept,
J = 6.9 Hz, 4H), 1.38 (d, J = 6.9 Hz, 12H), 1.21 (d, J = 6.9 Hz, 12H). 13C
{1H} NMR (101 MHz, CDCl3): δ (ppm) = 191.2, 145.8, 134.5, 132.4,
130.6, 129.3, 127.6, 126.1, 125.9, 124.3, 123.3, 103.9, 28.9, 24.8, 24.2.
Analytical data obtained are in agreement with reported values.[14a,16c]
Synthesis of [Au(IPr)Cbz] (14):
Synthesis of [Au(IPr)(OCs)] (11):
A 4 mL screwcap vial equipped with a septum cap and a stirring bar was
charged with 2b (80.0 mg, 0.092 mmol, 1 equiv.), carbazole (19.2 mg,
0.092 mmol, 1.0 equiv.) and benzene (0.6 mL). This solution was stirred
for 16 hours at 80 °C. The solvent was evaporated under vacuum and
the white residue was washed with diethyl ether (3x3 mL) and dried The
product was obtained as a white solid in 91% yield (62.9 mg, 0.084
mmol). 1H NMR (400 MHz, CD2Cl2): δ (ppm) = 7.88 (ddd, J = 7.7, 1.2,
0.7 Hz, 2H), 7.65 (t, J = 7.8 Hz, 2H), 7.44 (d, J = 7.8 Hz, 4H), 7.35 (s, 1H),
7.03 (ddd, J = 8.2, 7.0, 1.3 Hz, 2H), 6.86 (ddd, J = 7.9, 7.1, 1.0 Hz, 2H),
6.73 (dt, J = 8.2, 0.8 Hz, 2H), 2.72 (hept, J = 6.9 Hz, 4H), 1.38 (d, J = 6.9
Hz, 12H), 1.29 (d, J = 6.9 Hz, 12H). 13C {1H} NMR (101 MHz, CD2Cl2): δ
(ppm) = 179.2, 149.9, 146.7, 134.9, 131.2, 124.8, 124.0, 123.9, 123.9,
119.6, 116.2, 114.0, 29.5, 24.7, 24.5. Analytical data obtained are in
agreement with reported values.[24]
A 4 mL screwcap vial equipped with a septum cap and a stirring bar was
charged with 2b (100 mg, 0.144 mmol, 1 equiv.), (+)-camphorsulfonic
acid (37 mg, 0.159 mmol, 1.1 equiv.) and chloroform (3 mL). This
solution was stirred overnight at room temperature. Afterwards,
dichloromethane was added and the mixture was pushed through a
microfilter, in order for a clear solution to be obtained. The solvent was
evaporated, and the white residue was washed with diethyl ether (2x5
mL) and dried under vacuum. The product was obtained as a white solid
in 82% yield (97 mg, 0.019 mmol). 1H NMR (400 MHz, CDCl3): δ (ppm) =
7.51 (t, J = 7.8 Hz, 2H, HAr(IPr)), 7.31 – 7.28 (m, 4H, HAr(IPr)), 7.22 (s, 2H,
HImid), 3.21 (d, J = 15.1 Hz, 1H, CHH(OCs)), 2.60 (d, J = 15.1 Hz, 1H,
CHH(OCs)), 2.56 – 2.38 (m, 5H, overlapping peaks CH(CH3)2(IPr), CH(OCs)),
2.28 – 2.25 (m, 1H, CHH(OCs)), 2.23 – 2.20 (m, 1H, CHH(OCs)) 1.91 (t, J =
4.3 Hz, 1H, CHH(OCs)), 1.85 – 1.71 (m, 3H, overlapping peaks CHH(OCs)),
1.34 (dd, J = 6.9, 1.2 Hz, 12H, CH(CH3)2(IPr)), 1.21 (d, J = 6.9 Hz, 12H,
CH(CH3)2(IPr)), 0.95 (s, 3H, CH3(OCs)), 0.70 (s, 3H, CH3(OCs)). 13C {1H}
NMR (101 MHz, CDCl3): δ (ppm) = 215.8 (C=O), 164.6 (NCN), 145.7
(CAr(IPr)), 133.8 (CAr(IPr)), 131.0 (CHAr(IPr)), 124.5 (CHAr(IPr)), 123.6 (NCH),
58.4 (C(OCs)), 47.5 (C(OCs)), 47.4 (CHH(OCs)), 43.0 (CHH(OCs)), 42.7
(CHH(OCs)), 29.0 (CH(CH3)2(IPr)), 27.1 (CHH(OCs)), 24.7 (CH(OCs)), 24.5
(CH(CH3)2(IPr)), 24.2 (CH(CH3)2(IPr)), 20.5 (CH3(OCs)), 19.9 (CH3(OCs)).
Elemental analysis calcd (%) for C37H51AuN2O4S: C 54.40, H 6.29, N
Acknowledgements
We gratefully acknowledge VLAIO (SBO project CO2PERATE),
the Special Research Fund (BOF) of Ghent University is also
acknowledged for Doctoral Scholarship (01D14919) to N.V.T.,
starting and project grants to S.P.N, and project grant
(01N03217) to KVH and MS. KVH thanks the Hercules
Foundation (project AUGE/11/029). Umicore AG is thankfully
acknowledged for generous gifts of materials.
20
3.43; found: C 54.29, H 6.43, N 3.62. [α]D = +14.7 (c = 1.0 in
chloroform).
Synthesis of [Au(IPr)(OMess)] (12):
Keywords: Synthetic methodology • Sustainability • Gold
synthon • Catalysts • N-Heterocyclic carbenes
A 4 mL screwcap vial equipped with a septum cap and a stirring bar was
charged with 2b (53.3 mg, 0.077 mmol, 1 equiv.), mesitylene sulfonic
acid dihydrate (20 mg, 0.085 mmol, 1.1 equiv.) and benzene (1.6 mL).
This solution was stirred overnight at 50 °C. After evaporation of the
solvent under vacuum, dichloromethane was added (3 mL) and the
mixture was pushed through celite, in order for a clear solution to be
obtained. The solvent was evaporated, and the white residue was
washed with diethyl ether (2x3 mL) and pentane. The product was
obtained as a white solid in 62% yield (37.2 mg, 0.047 mmol). 1H NMR
(400 MHz, CDCl3): δ (ppm) = 7.52 (t, J = 7.8 Hz, 2H, HAr(IPr)), 7.27 (d, J =
7.8 Hz, 4H, HAr(IPr)), 7.18 (s, 2H, HImid), 6.67 (s, 2H, HAr(OMess)), 2.51 – 2.40
(hept, J = 6.9 Hz, 4H, CH(CH3)2(IPr)), 2.33 (s, 6H, CH3(OMess)), 2.20 (s, 3H,
CH3(OMess))), 1.26 (d, J = 6.9 Hz, 12H, CH(CH3)2(IPr)), 1.19 (d, J = 6.9 Hz,
12H, CH(CH3)2(IPr)). 13C {1H} NMR (75 MHz, CDCl3): δ (ppm) = 164.9
(NCN), 145.6 (CAr(IPr)), 133.8 (CAr(IPr)), 131.1 (CHAr(IPr)), 131.0 (CHAr(OMess)),
124.4 (CHAr(IPr)), 123.5 (NCH), 29.0 (CH(CH3)2(IPr)), 24.4 (CH(CH3)2(IPr)),
24.2 (CH(CH3)2(IPr)), 23.0 (CH3(OMess)), 21.0 (CH3(OMess)). Certain signals
attributed to the anion could not be detected. This is consistent with the
literature.[10] Elemental analysis calcd (%) for C36H47AuN2O3S: C 55.09,
H 6.04, N 3.57; found: C 55.42, H 6.09, N 3.38.
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10
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Entry for the Table of Contents
Gilded arylation: New methods for the transmetallation of organoboranes to gold(I) centers allow for the synthesis of a plethora of
organogold complexes. The scalability of the synthetic methods, in combination with a diversity of reactivity, sets the stage for the
use of these complexes in catalytic and synthetic applications.
11
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