Gold phenolate complexes: Synthesis, structure, and reactivity

Article abstract of DOI:10.1021/om400060s

Seven different NHC gold(I) phenolate complexes were synthesized. Structural data, including X-ray crystal structure analyses, could be obtained for each of them. An investigation by computational chemistry, including NBO analysis, indicates three-center-four-electron hyperbonds among the carbene carbon, the gold atom, and the oxygen atom of the phenolate with an approximate 60:40 distribution of the bonding interaction in favor of the carbene-gold bond. The new class of complexes shows only moderate catalytic activity.

Full text of DOI:10.1021/om400060s

Article
pubs.acs.org/Organometallics
Gold Phenolate Complexes: Synthesis, Structure, and Reactivity
Nada Ibrahim,† Mie Højer Vilhelmsen,‡ Markus Pernpointner,§ Frank Rominger,‡,∥
and A. Stephen K. Hashmi*,†,‡
†CaRLa-Catalysis Research Laboratory, Im Neuenheimer Feld 584, 69120 Heidelberg, Germany
‡Organisch-Chemisches Institut, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 270, 69221 Heidelberg, Germany
̈
§Physikalisch-Chemisches Institut, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: Seven different NHC gold(I) phenolate complexes were synthesized. Struc-
tural data, including X-ray crystal structure analyses, could be obtained for each of them. An
investigation by computational chemistry, including NBO analysis, indicates three-center−
four-electron hyperbonds among the carbene carbon, the gold atom, and the oxygen atom
of the phenolate with an approximate 60:40 distribution of the bonding interaction in favor
of the carbene−gold bond. The new class of complexes shows only moderate catalytic
activity.
A range of gold(I) phenolate complexes were synthesized
from these potassium aryloxide salts by reaction with the known
gold chloride complexes IMesAuCl, SIPrAuCl, and IPrAuCl (see
Figure 1).10
The preliminary experiments showed that by using phosphine
ligands the desired gold phenolate product was not obtained.
However, due to the stronger electron donating ability of the
NHC ligands and the normally higher thermal stability of the
corresponding complexes in comparison to the phosphine complexes,
we assumed that the NHC would lead to stable compounds
which could be isolated.11−13
INTRODUCTION
■
Gold alkoxide complexes were first recognized as catalysts by
Komiya et al. in condensation reactions of benzaldehyde and
later by the same group as stoichiometric reagents in hydride
abstraction from transition metals.1,2 Recently, Nolan et al. have
demonstrated the potential of gold hydroxide complexes as
catalysts in organic synthesis: for example, in reactions with
CO2.3,4 In general, only a few examples of complexes containing
gold−oxygen bonds are known; the other typical examples are
the gold acetate complexes5 and gold oxonium species.6 A
few aryloxide complexes of gold have been mentioned in the
literature, but they have not been structurally characterized.2,7
The studies have suggested that the mononuclear gold(I)
aryloxide form is unstable. This explanation was given on the
basis of observed aurophilic interactions in monovalent gold(I)
aryloxide species.8 However, taking the publication by Nolan
on gold(I) hydroxides into account, gold(I) complexes with the
less basic and weaker coordinating phenolate anion should be
structurally interesting species with possible use in homogeneous
catalysis.9
No reaction between IMesAuCl and potassium 3,5-
dimethoxyphenolate in different solvents in THF or dichloro-
1
methane at room temperature was detectable by H NMR
(Scheme 2). This is probably due to the low solubility of the
phenolate salt in these solvents at room temperature. Interestingly,
a homogeneous solution was obtained in acetonitrile, and the
formation of the phenolate complex could be monitored in 13C
NMR spectroscopy by the downfield shift of the carbene carbon
to 171.9 ppm in CD3CN. Unfortunately, due to the inherent
instability of this complex during the isolation process, the initial
yield of complex 1 could not be determined. However, it was
possible to unambiguously assign the structure by an X-ray crystal
structure analysis (Figure 2).14 After several recrystallizations a 6%
yield of pure compound was obtained.
By this facile methodology, we obtained the six gold(I)
phenolate complexes 2−6 in good yields (Figure 3) from
IPrAuCl and SIPrAuCl. The products were obtained by simple
precipitation of the inorganic salt in dichloromethane followed
by filtration and removal of the solvent in vacuo. In spite of
being sensitive and unfortunately quickly decomposing (which
did not allow efficient purification and full characterization by
Herein, we report the synthesis and experimental and theoretical
characterization as well as the reactivity of a series of NHC−gold(I)
aryloxide complexes.
RESULTS AND DISCUSSION
■
Synthesis and Structure. Our attempts to synthesize the
gold(I) phenolate complexes from IPrAuCl and phenol by use
of a range of different bases, such as diisopropyethylamine,
triethylamine, and cesium carbonate, failed to deliver the de-
sired product. An alternative synthetic procedure, namely a salt
metathesis reaction from aryloxide salts as described in the
literature, was successful.1,2,4,5
Thus, the straightforward synthesis of the potassium phenolates
from phenols and potassium hydride in refluxing THF delivered
the five phenolates shown in Scheme 1 in good to excellent yields.
Received: January 23, 2013
© XXXX American Chemical Society
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Scheme 1. Synthesis of Potassium Phenolates
Figure 1. NHC−gold chloride complexes used in the synthesis of complexes of the phenolate derivatives.
Scheme 2. Synthesis of the NHC−Gold(I) Phenolate Complex 1
Figure 3. NHC−gold(I) phenolate complexes 2−7 obtained. Yields
are given in parentheses.
Figure 2. Solid-state molecular structure of 1.
A further comparison with the gold chloride compounds
shows that the Au−CNHC bond lengths are also influenced
by the change from the chloride to the phenolate ligand. The
Au−CNHC bond lengths in IMesAuCl, IPrAuCl, and SIPrAuCl
are 1.998(5), 1.942(3), and 1.979(3) Å, respectively.10 The cor-
responding bond lengths are 1.961(3), 1.957(4), and 1.960(4) Å
in compounds 1, 2, and 6, respectively.
spectroscopy), the gold phenolate complex 7 could also be
characterized by X-ray crystallography (Figure 4).14
The other synthesized gold phenolates 2−6 could also be
characterized by crystal structure analyses, and the ORTEP
representations of the complexes 2−7 are shown in Figure 4.14
For complexes 1, 2, 4, 5, and 7, a single molecule is found
in the asymmetrical cell. Complexes 2 and 4 each crystallized
with one molecule of chloroform. For complexes 3 and 6, two
independent molecules are found in the asymmetrical cell.
In all the complexes, gold is two-coordinated and exhibits a
nearly linear geometry with CNHC−Au−O bond angles ranging
from 174.9 to 179.1° (Table 1). The Au−O bond distances
range from 2.000(18) to 2.030(3) Å. As expected, the Au−O
bonds are all shorter than the Au−Cl bonds observed in the cor-
responding gold chloride compounds (2.2756(12)−2.306(3) Å).10
The bond rotation was studied in compounds 1 and 4. It was
observed at elevated temperatures by 1H NMR spectroscopy in
1
CDCl3 (22−60 °C) for compound 4 by H NMR in Figure 5.
At room temperature a splitting of the peaks (6.45−6.98 ppm)
was observed in the aromatic region. This was attributed
to a hindered rotation of the 3,5-dimethoxyphenolate or the
3,5-dibromophenolate group. When the temperature was raised
to 50 °C, the peaks at 6.45, 6.75, 6.81, and 6.98 ppm started to
broaden and at 60 °C they started to coalesce. However,
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Figure 4. Solid-state molecular structures of 2−7.
Table 1. Selected Structural Data from the X-ray Crystal Structure Analyses of Complexes 1−7 along with the Geometrical Data
Obtained by Calculation
experimental data
bond length (Å)
computational data
bond length (Å)
O−Au
2.010
compd
O−Cipso
O−Au
Au−CNHC O−Au−C angle (deg)
O−Cipso
1.335
Au−CNHC
1.984
O−Au−C angle (deg)
1
2
3
4
5
6
7
1.329(4)
1.331(4)
1.324(6)
1.331(7)
1.353(6)
1.337(5)
1.34(2)
2.013(2)
2.014(3)
2.030(3)
2.002(4)
2.023(3)
2.017(3)
2.000(18)
2.078(6)
2.2698(11)
1.961(3)
1.957(4)
1.964(5)
1.956(6)
1.959(4)
1.960(4)
1.962(5)
1.935(6)
1.942(3)
174.86(11)
178.59(12)
179.1(2)
174.8
a
1.334 0.06
1.323
2.014 0.66
2.036
1.987 0.33
1.987
175.5 0.11
179.7
178.78(19)
177.31(16)
176.80(13)
179.1(9)
1.324
2.028
1.987
176.6
1.335
2.018
1.988
176.1
1.337
2.010
1.985
174.4
1.338
2.022
1.988
177.3
IPrAuOH15
IPrAuCl10
177.1(3)
1.985
1.987
176.6
b
c
a
c
177.0(4)
2.307
2.004
180.0
a
b
c
Error calculated on the basis of a B3LYP/cc-pVTZ optimization of complex 2. Cl−Au bond length (Å). Cl−Au−C bonding angle (deg).
1
Figure 5. Variable-temperature H NMR (CDCl3, 200 MHz) of compound 4.
a complete coalescence was not observed in this experiment, as
a temperature above 60 °C resulted in decomposition of the
compound. Most probably, rotation around the aryl−O and/or
O−Au bond is involved.
Compounds 1, 5, and 7 were observed to decompose to a
black precipitate when kept in solution for prolonged periods,
even at room temperature. The stability of compound 2 in THF
solution was examined at elevated temperatures. No decomposition
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Table 2. Selected Data from the NBO Analyses Performed on Complexes 1−7
NBO charge
strongest interactions (kcal/mol)
a
compd
CNHC−Au−O hyperbond (%)
Au
CNHC
O
Au→CNNHC
O→Au−CNHC
1
2
3
4
5
6
7
60.7/39.3
60.5/39.5
62.3/37.7
62.3/37.7
60.4/39.6
60.6/39.4
60.9/39.1
54.9/45.1
53.8/46.1
0.439
0.441
0.442
0.443
0.440
0.450
0.442
0.406
0.383
0.177
0.177
0.180
0.180
0.178
0.255
0.178
0.171
0.167
−0.806
−0.811
−0.791
−0.796
−0.811
−0.809
−0.819
−1.035
−0.615
15.70
15.26
14.45
14.66
15.18
115.86
114.08
105.28
109.12
113.41
114.93
111.89
155.92
b
24.26
15.08
16.61
14.08
IPrAuOH
IPrAuCl
c
d
208.87
a
The given value is summed over the energy gain of the interactions between the up to three lone pairs of the oxygen and the antibonding orbital of
b
c
d
the Au−CNHC bond. Interaction from lone pair on gold to the carbene carbon and not the C−N bond. NBO charge of the Cl atom. The energy
gain for the Cl→Au−CNHC interaction: sum of all lone pairs of the Cl atom and the antibonding orbital of the Au−CNHC bond.
1
was observed by H NMR after 24 h at 70 °C. However,
GC-MS measurements revealed liberation of 3,5-dimethoxyphenol
when the sample was heated to 100 °C for 24 h. Similarly,
heating compound 4 to 60 °C resulted in partial decomposition,
as seen by the development of peaks at 2.22 and 9.82 ppm in the
1H NMR. However, the decomposition products could not be
identified.
charges of these atoms, and the stabilization energy21 associated
with the donor−acceptor interactions in which gold is parti-
cipating. The results of these calculations are summarized in
Table 2.
The comparison of the three-center−four-electron hyper-
bonds detected among the carbene carbon, the gold atom, and
the oxygen of the phenolate shows an approximately 60:40
distribution of the bonding interaction in favor of the carbene−
gold bond. However, for the bis(trifluoromethyl)- and dibro-
mophenolate complexes a slight diversion is seen. The in-
creased weight of the carbene−gold bond is most likely due to
the electron-withdrawing properties of the two substituents.
Thus, the natural charge on the oxygen of these two complexes
is slightly less negative than for the remaining phenolate
complexes. Likewise, the interactions between the lone pairs of
the phenolate oxygen and the antibonding orbital of the Au−CNHC
bond are the lowest with an energy gain of only 105.28 and
109.12 kcal/mol for complexes 3 and 4, respectively. The
calculated bond lengths further reflect this decreased
interaction from the oxygen toward the gold−carbene bond
by yielding elongated O−Au bonds. In contrast, the calculated
O−Cipso bond lengths were found to be slightly shortened,
which again is in agreement with an enhanced interaction
between the phenolate oxygen and the electron-withdrawing
groups. However, from the experimental data, the effect is
primarily seen for the bis(trifluoromethane)phenolate complex,
with strongly electron withdrawing substituents, which exhibits
the longest Au−O bond (2.030(3) Å) and the shortest O−Cipso
bond (1.324(6) Å). In contrast. the hyperbonding displayed in
the more classic gold−hydroxy and gold−chloride complexes
shows an increased favor for the Au−X bond (X = O, Cl),
testifying to the increased electron-donating abilities of the
simple anions in comparison to the phenolates. This enhanced
donation is validated by the great increase in energy gained by
the interaction of the heteroatom lone pairs with the anti-
bonding orbital of the Au−CNHC bond.
Computational Chemistry. Each of the phenolate
complexes characterized by crystallography, i.e. compounds
1−7, was subsequently examined by DFT and natural bond
order (NBO) calculations to study the geometric and electronic
properties, respectively, of the compounds as well as to com-
pare the experimental and computational data. The geometry
optimizations were carried out with the Gaussian program package16
using the B3LYP hybrid functional along with the correlation-
consistent double-ζ basis (cc-pVDZ) for all atoms.17 A single
complex was optimized with the higher order correlation-consistent
triple-ζ basis (cc-pVTZ)18 to estimate the error in the cal-
culated geometries. Additionally for gold, a relativistic effective
core potential was used.19 The NBO calculations were performed
with the NBO 5.0 program package.20
The relevant results of the DFT geometry optimizations are
given in Table 1. Overall, the bond lengths obtained by the
calculations correspond well with the experimental values.
However, some deviations should be noted. First, for all
compounds the calculated lengths of the Au−CNHC bond are
approximately 2 pm longer than the corresponding exper-
imental value. Second and likewise, the calculated Au−O bonds
of complexes 4 and 7 were longer by 2.6 and 2.1 pm,
respectively. Finally, the calculated length of the Cipso−O bond
of complex 5 is 1.9 pm shorter than the value determined by
X-ray crystallography. The calculated bonding angles of the
O−Au−CNHC bonds differ somewhat from the corresponding
experimentally determined angles, but this is to be expected as a
result of crystal packing, which will affect the geometries ob-
tained by crystallography. However, both sets of geometrical
data show the near-linearity of the bonding around the gold
atom. Included in Table 1 are also the experimental and cal-
culated geometric data for the two simpler compounds IPrAuOH
and IPrAuCl. For these two phenolate complexes the calculated
Au−CNHC bond lengths are slightly longer than the experimentally
determined lengths. The calculated values for the Au−heteroatom
bond lengths fit well with the experimentally determined values.
Apart from the geometry optimizations, the seven complexes
were subjected to NBO analyses to determine the bonding
character of the bonds surrounding the gold atom, the natural
In general, it should be noted that as the substituents, with
the exception of the propene substituent of complex 7, are all
in meta positions with respect to the phenolate oxygen, the
primary electronic effect will be inductive. Thus, both the
calculated and the experimentally observed lengths for the
O−Cipso bond do not differ markedly from one another. The
exceptions are complexes 5 and 7, which lack any electron-
withdrawing groups, giving rise to slightly longer O−Cipso
bonds, and as noted above complex 3, with its strongly
electron withdrawing CF3 groups. This is in agreement with
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earlier calculated results on the effect of substituents on phenols
by Klein et al. They found the C−O bond lengths of m-methoxy,
unsubstituted, m-bromo, and m-trifluoromethyl phenols to be
1.3708, 1.3704, 1.3668, and 1.3658 Å, respectively.22
that of the standard gold chloride catalysts, which in standard
protocols usually are preactivated with a silver salt of a non-
coordinating anion. This result emphasizes the potential of the
NHC−gold phenolate complexes in silver-free transformations,
especially if weakly basic counterions are needed.
A comparison of compounds 1, 2, and 6 should show the
differences induced in the system by changes in the NHC
moiety. The change of the nitrogen substituents from mesityl
groups to 2,6-diisopropylphenyl groups, i.e. complex 1 versus 2,
does not seem to influence the geometry or bonding properties
around the gold atom greatly. On a shift to a saturated NHC
ligand, the SIPr of complex 6, an enhancement of the natural
charge of the carbene carbon and an increased interaction from
the gold toward the NHC ligand are observed. The latter
interaction is generally directed from a d orbital on gold toward
the π* orbital of the CN of the NHC. However, for complex
6 it should be noted that, unlike the case for the remaining
complexes, this interaction is not directed toward the π* bond
but to the empty pz* orbital on the carbene carbon itself.
The NBO calculations show a partially occupied lone pair (0.73
electron in the pz orbital)23 on the carbene carbon of the SIPr
ligand with which the gold lone pair interacts. The degree of
overlap between the dyz and the pz orbitals of complex 6 is
CONCLUSION
■
The results might impact related areas of organogold chemistry
and gold catalysis in the future. Especially, these new struc-
tural and electronic insights create the basis for a better funda-
mental understanding of the properties of the gold−oxygen
bond and the electronic communication of the two ligands on
gold(I). In addition, an understanding of this type of system
could potentially lead to the discovery of new catalytic C−O
bond formations as well as to the development of new gold
systems for materials science and medical applications.
EXPERIMENTAL SECTION
■
Commercially available reagents and solvents were used without
further purification. Acetonitrile was distilled over CaH2. Mass spectra
were recorded on a Vacuum Generators ZAB-2F, Finnigan MAT TSQ
700, or JEOL JMS-700 spectrometer. IR spectra were recorded on a
Bruker Vector 22 FT-IR instrument. Crystal structure analysis was
accomplished on a Bruker Smart CCD or Bruker APEX diffractometer.
NMR spectra were recorded on a Bruker Avance 500 or Bruker
2
much higher than the corresponding dz /π* overlap between
gold and the CN bond of the unsaturated NHCs. Despite
this shift in the electronic structure of complex 6, the geometry
is not influenced in any distinguishable way, as can be seen
from both the calculated and the experimental data.
Avance 300 spectrometer. Chemical shifts of H NMR and 13C NMR
1
are reported in ppm (δ units), and residual nondeuterated solvent was
Catalysis. Finally, the catalytic activities of complexes 2 and 3
were tested in the hydration of phenylacetylene to acetophenone
(Table 3). This reaction type of hydration of an alkyne has
used as internal reference.
The following abbreviations were used to designate the multi-
plicities: s = singlet, d = doublet, t = triplet, q = quartet, bs = broad
signal, m = multiplet.
General Procedure for the Preparation of Potassium
Phenolate (GP A). A solution of potassium hydride KH (3 equiv)
in anhydrous THF and phenol was stirred overnight under argon at
70 °C. Then the reaction mixture was cooled to room temperature,
filtered under argon, and dried under high vacuum. Due to their
hygroscopic character, the phenoxide salts were kept in a glovebox.
Potassium Phenolate.
Table 3. Hydration of Phenylacetylene Catalyzed by Gold
Complexes
catalytic loading
(mol %)
TFA
(mol %)
time
(days)
yield
a
entry catalyst
(%)
1
2
3
4
5
2
2
2
2
3
1
2
10
10
10
3
1
35
60
GP A: KH (1.20 g, 30.0 mmol), THF (100 mL), and phenol (1.00 g,
10.0 mmol). The product was obtained as a white solid in 100% yield.
1H NMR (200 MHz, DMSO-d6): δ 6.66 (t, J = 8 Hz, 2 H), 6.00 (d, J =
8 Hz, 2H), 5.82−5.75 (m, 1H). 13C NMR (50 MHz, DMSO-d6): δ
172.31 (1C), 128.57 (2C), 118.93 (2C), 105.75 (1C). Anal. Calcd for
1
2
10
1
40
n-Tetradecane was used as the internal standard for GC.25
1
a
C6H5KO + /2 H2O: C, 51.03; H, 4.28. Found: C, 51.99; H, 4.34.
Potassium 3,5-Dimethoxyphenolate.
become a kind of benchmark in many investigations of gold
catalysts.24 The catalysts fully dissolve; a clear yellow solution
was observed during the catalysis reaction (as in our previous
study on NAC complexes of gold(I), n-tetradecane was used as
internal standard for GC).25 Clean but incomplete conversion
(probably due to the intrinsic instability of the catalysts; because of
the reducing properties of the phenolate counterions, the catalyst
lifetime is limited) and a moderate yield were obtained within 24 h
at room temperature with catalyst 2 when a catalytic loading of
2 mol % was employed along with an additive of 10 mol %
trifluoroacetic acid (TFA) (entry 2).26 When the same reaction
was performed with compound 3, the catalyst provided a 40%
yield (entry 5). Two test reactions were performed to ensure
the necessity of both the gold catalyst and the TFA additive
(entries 3 and 4). The catalytic activity of the gold phenolates,
despite the strong gold−oxygen interaction, is in contrast to
GP A: KH (1.50 g, 37.5 mmol), THF (100 mL), and 3,5-
dimethoxyphenol (1.90 g, 12.3 mmol). After general workup the
product was obtained as a beige solid in 97% yield. H NMR (200
1
MHz, DMSO-d6): δ 5.27−5.26 (d, J = 2 Hz, 2 H), 5.09 (t, J = 2 Hz,
1H). 13C NMR (50 MHz, DMSO-d6): δ 173.80 (1C), 161.01 (2C),
1
96.64 (2C), 81.70 (1C). Anal. Calcd for C8H9KO3 + /3 H2O: C,
48.46; H, 4.91. Found: C, 48.32; H, 5.04.
Potassium 3,5-Bis(trifluoromethyl)phenolate.
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GP A: KH (700 mg, 4.34 mmol), THF (70.0 mL), and 3,5-bis-
(trifluoromethyl)phenol (387 mg, 1.44 mmol). The product was
isolated as a beige solid in 86% yield. 1H NMR (200 MHz, DMSO-d6):
δ 6.50 (m, 2H), 6.29 (s, 1H). 13C NMR (50 MHz, DMSO-d6): δ
171.97, 130 (q, J = 30 Hz), 124 (q, J = 271 Hz), 118.09 (br s), 96.40
(br s). Anal. Calcd for C8H3F6KO: C, 35.83; H, 1.13. Found: C, 35.36;
H, 1.52.
spectrometry FD/LIFDI (toluene): 654.3 [M+]. IR (film): ν (cm−1)
2919, 2852, 1599, 1488, 1457, 1378, 1201, 1192, 1146.
(1,3-Bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-imidazol-2-yl)-
(3,5-dimethoxyphenoxy)gold(I) (2).
Potassium 3,5-Dibromophenolate.
GP A: KH (240 mg, 6.00 mmol), THF (50.0 mL), and 3,5-
dibromophenol (500 mg, 1.99 mmol). The product was obtained as a
IPrAuCl (50.0 mg, 0.08 mmol) in MeCN (9.00 mL) and potassium
3,5-dimethoxyphenolate (30.0 mg, 0.116 mmol) were stirred overnight at
room temperature. After general workup the product was obtained as a
white solid in 96% yield. Crystallization was performed by slow diffusion of
petroleum ether into a saturated solution of the compound in chloroform.
1H NMR (500 MHz, CDCl3): δ 7.50 (m, 2 H, CH aromatic of carbene
1
beige solid in 80% yield. H NMR (CD3CN, 200 MHz): δ 6.42−6.41
(d, J = 2 Hz, 2 H), 6.32 (t, J = 3 Hz). 13C NMR (CD3CN, 50 MHz): δ
172.39, 121.25, 119.54, 111.21. Anal. Calcd for C16H16Br4K2O4
(compound + 1/2 THF): C, 28.68; H, 2.41. Found: C, 28.37; H, 2.64.
Potassium 2-Allylphenolate.
ligand), 7.30 (d, 4 H, J = 10 Hz, aryl H of the carbene ligand), 7.18 (s, 2H,
H of the imidazole), 5.69 (s, 3H, aryl H of the phenolate), 3.52 (s, 6H,
CH3O), 2.62−2.58 (m, 4H, CH(CH3)2), 1.37−1.36 (d, J = 5 Hz, 12H,
CH(CH3)2), 1.23−1.22 (d, J = 5 Hz, 12H, CH(CH3)2). 13C NMR (125
MHz, CDCl3): δ 169.69 (1C, C carbene), 169.04 (1C, Cipso phenolate),
160.93 (2C, Cm phenolate), 145.66 (4C, aryl C of the carbene ligand),
134.19 (2C, aryl C of the carbene ligand), 130.72 (2C, aryl CH of the
carbene ligand), 124.28 (4C, aryl CH of the carbene ligand), 123.18 (2C,
imidazole CH), 96.53 (2C, phenolate CH), 89.50 (1C, phenolate CH),
55.03 (2C, CH3O), 28.89 (4C, CH(CH3)2), 24.51 (4C, CH(CH3)2), 24.08
(4C, CH(CH3)2). Mass spectrometry FD/LIFDI (DCM): 738.0101 [M+].
IR (film): ν (cm−1) 2263, 1594, 1471, 1458, 1202, 1160, 1145, 759.
(1,3-Bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-imidazol-2-yl)-
(3,5-bis(trifluoromethyl)phenoxy)gold(I) (3).
GP A: KH (100 mg, 2.50 mmol), THF (30.0 mL), and 2-allylphenol
(200 mg, 1.49 mmol). The salt was obtained as a beige solid in 63%
yield. H NMR (200 MHz, DMSO-d6): δ 6.70−6.65 (m, 2 H, H
aromatic), 6.08−5.78 (m, 3 H), 4.99−4.84 (m, 2H), 3.14 (d, J = 6 Hz,
2H). Anal. Calcd for C27H29K3O4: C, 60.64; H, 5.47. Found: C, 60.02;
H, 5.58.
General Procedure for the Preparation of Gold Phenolate
Complexes (GP B). The reagents were weighed in a glovebox; the
reactions and workup were performed outside the glovebox.
In a dry flask 1 equiv of the gold chloride complex was dissolved in
distilled acetonitrile. Then 2 equiv of phenolate salt was added. The
reaction mixture was stirred overnight at room temperature. Then (unless
mentioned otherwise), the solvent was removed, cold dichloromethane
was added, and the mixture was filtered. The solvent was reduced, and
pentane was added again; the product precipitated and then was isolated
by filtration.
1
The crystallization was performed in a mixture of DCM (unless
otherwise stated) and pentane or hexane either in the freezer or at
room temperature by slow vapor diffusion of hexane into a saturated
solution of the complexes in DCM.
(1,3-Dimesityl-2,3-dihydro-1H-imidazol-2-yl)(3,5-dimethoxyphenoxy)-
gold(I) (1).
IPrAuCl (100 mg, 0.116 mmol) in MeCN (18.0 mL) and potassium
3,5-bis(trifluoromethyl)phenolate (86.0 mg, 0.322 mmol) were stirred
overnight at room temperature. After general workup the compound
was obtained as a yellowish solid in 90% yield. Crystallization of the
1
complex was done in a mixture of chlroform and pentane (1/10). H
NMR (500 MHz, CDCl3): δ 7.52 (m, 2H, aryl H of the carbene
ligand), 7.31−7.30 (d, 4H, J = 5 Hz, aryl H of the carbene ligand), 7.22
(s, 1H, imidazole H), 6.92 (s, 1H, aryl H of the phenolate), 6.76 (s,
2H, aryl H of the phenolate), 2.56 (septet, J = 5 Hz, 4H, CH(CH3)2),
1.34−1.33 (d, J = 5 Hz, 12 H, CH(CH3)2), 1.24−1.23 (d, J = 5 Hz, 12
H, CH(CH3)2). 13C NMR (125 MHz, CDCl3): δ 168.04 (1C, C of the
phenolate), 167.63 (1C, carbene C), 145.53 (4C, aryl C of the
carbene), 133.8 (2C, aryl C of the carbene), 131.42 (q, 2C, J = 31 Hz,
C of the phenolate), 131.04 (2C, aryl CH of the carbene), 124.07 (4C,
aryl CH of the carbene), 123.8 (q, 2C, J = 271 Hz, CF3), 123.35 (2C,
imidazole CH), 118.18 (2C, CH of the phenolate), 108.27 (1C, CH of
the phenolate), 28.90 (4C, CH(CH3)2), 24.35 (4C, CH(CH3)2), 24.09
(4C, CH(CH3)2). Mass spectrometry FD/LIFDI (toluene): 814.05 [M+].
IR (film): ν (cm−1) 2965, 1569, 1463, 1381, 1257, 1168, 1128, 804, 759.
IMesAuCl (60.0 mg, 0.119 mmol) in MeCN (9.00 mL) and potassium
3,5-dimethoxyphenolate (45.6 mg, 0.238 mmol) were stirred overnight
at room temperature. After general workup, a brown oil and a solid
were obtained. A small portion of pure white compound could be
obtained in 6% yield (crystallized from a mixture of chloroform and
hexane (1/4) at −30 °C). 1H NMR (500 MHz, CDCl3): δ 7.71 (s, 2H,
imidazole), 7.00 (s, 4H, H aromatic), 5.77−5.76 (d, J = 5 Hz, H
phenolate), 5.72 (m, 1H, H phenolate), 3.58 (s, 6H, CH3O), 2.34 (s,
CH3), 2.13 (s, CH3). 13C NMR (50 MHz, CDCl3): δ 169.51 (1C, C
phenolate), 167.18 (1C, C carbene), 160.91 (2C, Cipso phenolate),
139.85 (2C, C aromatic of carbene), 134.8 (4C, C aromatic of
carbene), 129.47 (4C, CH aromatic of carbene), 122.15 (2C, CH
imidazole), 96.70 (2C, CH phenolate), 89.32 (1C, CH phenolate),
54.87 (2C, CH3O), 21.12 (2C, CH3), 17.77 (4C, CH3). Mass
F
dx.doi.org/10.1021/om400060s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(1,3-Bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-imidazol-2-yl)-
(3,5-dibromophenoxy)gold(I) (4).
SIPrAuCl (50.0 mg, 0.08 mmol) in MeCN (9.00 mL) and potassium
3,5-dimethoxyphenolate (30.0 mg, 0.16 mmol) were stirred overnight.
The solvent was removed; the crude mixture was diluted in DCM/
CCl4, filtered, and evaporated. The solid was dissolved again with CCl4
and the solution filtered and evaporated. The compound was obtained
as a white solid in 40% yield. Crystallization was achieved from a
1
solution of chloroform and hexane (1/4) at −30 °C. H NMR (500
MHz, CDCl3): δ 7.43−7.40 (m, 2 H, aryl H of the carbene ligand),
7.24−7.23 (m, 4H, aryl H of the carbene ligand), 5.66 (m, 1H,
phenolate H), 5.58 (d br, 2H, phenolate H), 4.06 (s, 4H, imidazole
H), 3.49 (s, 6H, CH3O), 3.09−3.04 (m, 4H, CH(CH3)2), 1.44−1.41
(m, 12 H, CH(CH3)2), 1.35−1.34 (m, 12 H, CH(CH3)2). 13C NMR
(125 MHz, CDCl3): δ 190.76 (C carbene), 169.62, 160.87, 160.87,
146.61, 134.26, 130.05, 124.66, 96.44, 89.53, 55.04, 53.46, 29.05,
25.22, 24.17. Mass spectrometry LIFDI (toluene): 740.3 [M+].
(2-Allylphenoxy)(1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-
imidazol-2-yl)gold(I) (7).
IPrAuCl (50.0 mg, 0.08 mmol) in MeCN (9.00 mL) and potassium
3,5-dibromophenolate (23.0 mg, 0.08 mmol) were stirred overnight at
room temperature. After workup the product was obtained as a
brownish solid in 95% yield. The crystallization was performed by
evaporation of a solution of the complex in chloroform. In the NMR
1
spectra two rotamers were found (ratio 3/1). H NMR (500 MHz,
CDCl3): δ 7.55 (m, 2H, aryl H), 7.33 (d, J = 5 Hz, 4 H, aryl H), 7.22
(2H, imidazole H), 7.02 and 6.74 (both broad singlets, 1H, phenolate H),
6.81 and 6.45 (broad singlets, 2 H, phenolate H), 2.55 (m, 4H,
CH(CH3)2), 1.35 (d, J = 5 Hz, 12 H, CH(CH3)2), 1.23 (d, J = 10 Hz,
12 H, CH(CH3)2). The peaks at 1.21 and 4.03 ppm in Figure 5 originate
from the slow decomposition of the complex in the NMR tube upon
heating. 13C NMR (125 MHz, CDCl3): δ 169.01 (1C, carbene C), 167.91
(1C, phenolate C), 145.52 (4C, aryl C of the carbene), 133.85 (2C, aryl C
of the carbene), 131.11 (2C, aryl CH of the carbene), 124.42 (4C, aryl
CH of the carbene), 123.25 (2C, imidazole CH), 122.72, 121.97, 120.77,
120.31, 118.34, 28.90 (4C, CH(CH3)2), 24.36 (4C, CH(CH3)2), 24.15
(4C, CH(CH3)2). Mass spectrometry LIFDI (toluene): 836.4 [M+]. IR
(film): ν (cm−1) 2963, 1635, 1458, 1436, 907, 804, 758, 740.
IPrAuCl (50.0 mg, 0.08 mmol) in MeCN (9.00 mL) and potassium
2-allylphenolate (27.0 mg, 0.16 mmol) were stirred overnight. The
product crystallized at −30 °C from a mixture of chloroform and
hexane (1/4). The product is not stable in solution; it rapidly
decomposes. Thus, NMR data are not available. IR (film): ν (cm−1)
2963, 1593, 1471, 1459, 1193, 1160, 1145, 1061.
(1,3-Bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-imidazol-2-yl)-
(phenoxy)gold(I) (5).
Catalytic Hydration of Phenylacetylene. In a 4 mL vial
phenylacetylene (50.0 mg, 0.48 mmol), catalyst (1 or 2 mol %), TFA
(10 mol %), and methanol/water (3/1) were stirred. The conversion
and yield of acetophenone were determined by gas chromatography.
The product, acetophenone, was purified by column chromatography
1
on silica gel using DCM as eluent. H NMR (CDCl3, 200 MHz): δ
7.96 (m, 2 H), 4.49 (m, 3 H), 2.61 (s, 3H).
ASSOCIATED CONTENT
■
IPrAuCl (50.0 mg, 0.08 mmol) in MeCN (9.00 mL) and potassium
phenolate (21.0 mg, 0.16 mmol) were stirred overnight at room
temperature. The solvent was removed, and then DCM/pentane
(8/2) was added; the mixture was filtered, dried, and evaporated under
high vacuum. The product was obtained as a white solid in 94% yield.
1H NMR (500 MHz, CDCl3): δ 7.53 (t, J = 10 Hz, 2H, aryl H of the
carbene ligand), 7.31 (d, J = 5 Hz, 4 H, aryl H of the carbene ligand),
7.21 (s, 2H, imidazole H), 6.85 (m, 2 H, phenolate H), 6.44 (m, 1H,
phenolate H), 6.34 (d, J = 10 Hz, 2 H), 2.59 (m, 4 H, CH(CH3)2),
1.34 (d, J = 10 Hz, 12 H, CH(CH3)2), 1.22−1.23 (d, J = 5 H, 12 H,
CH(CH3)2). 13C NMR (125 MHz, CDCl3): δ 169.92 (1C, carbene C),
167.57 (1C, phenolate C), 145.77 (4C, aryl C), 134.24 (2C, aryl C),
130.62 (2C, aryl CH), 128.40 (2C, phenolate CH), 124.25 (4C, aryl
CH), 123.04 (2C, imidazole CH), 118.39 (2C, phenolate CH),
114.82 (1C, phenolate CH), 28.9 (4C, CH(CH3)2), 24.33 (4C,
CH(CH3)2), 24.19 (4C, CH(CH3)2). Mass spectrometry LIFDI
(toluene): 678.1 [M+].
S
* Supporting Information
Text and figures giving additional experimental details and
characterization data, tables giving Cartesian coordinates for the
calculated structures, and a CIF file giving crystal data for
compounds 1−6. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*A.S.K.H.: tel, +49(0)6221-548413; fax, +49(0)6221-544205;
e-mail, hashmi@hashmi.de.
Author Contributions
∥Crystallographic investigation.
Notes
(1,3-Bis(2,6-diisopropylphenyl)imidazolidin-2-yl)(3,5-dimethoxy-
phenoxy)gold(I) (6).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Dedicated to Professor Antonio Laguna on the occasion of his
65th birthday. N.I. worked at CaRLa of Heidelberg University,
being cofinanced by University of Heidelberg, the State of
Baden-Wurttemberg, and BASF SE. Support of these
̈
institutions is greatly acknowledged. M.H.V. is grateful to the
Danish Council for Independent Research, Natural Sciences,
for a fellowship.
G
dx.doi.org/10.1021/om400060s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(18) Kendall, R. A.; Dunning, T. H., Jr.; Harrison, R. J. J. Chem. Phys.
1992, 96, 6796−6806.
REFERENCES
■
(1) (a) Komiya, S.; Sone, T.; Usui, Y.; Hirano, M.; Fukuoka, A. Gold
Bull. 1996, 29, 131−136. (b) Usui, Y.; Hirano, M.; Fukuoka, A.;
Komiya, S. Chem. Lett. 1997, 26, 981−982.
(2) (a) Usui, Y.; Noma, J.; Hirano, M.; Komiya, S. Inorg. Chim. Acta
2000, 309, 151−154. (b) Komiya, S.; Iwata, M.; Sone, T.; Fukuoka, A.
J. Chem. Soc., Chem. Commun. 1992, 1109−1110.
(3) (a) Gaillard, S.; Slawin, A. M. Z.; Nolan, S. P. Chem. Commun.
2010, 46, 2742−2744. (b) Ramon, R. S.; Gaillard, S.; Poater, A.;
Cavallo, L.; Slawin, A. M. Z.; Nolan, S. P. Chem. Eur. J. 2011, 17,
1238−1246.
(4) Boogerts, I. I.; Nolan, P. S. J. Am. Chem. Soc. 2010, 132, 8858−
8859.
(19) (a) Figgen, D.; Rauhut, G.; Dolg, M.; Stoll, H. Chem. Phys.
2005, 311, 227−244. (b) Peterson, K. A.; Puzzarini, C. Theor. Chem.
Acc. 2005, 114, 283.
(20) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J.
E.; Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5.0;
Theoretical Chemistry Institute, University of Wisconsin, Madison,
WI, 2001; http://www.chem.wisc.edu/∼nbo5.
(21) The values are the estimated strengths of the interactions on the
basis of the donor orbital occupancy, the orbital energies of the donor
and acceptor NBOs, and the off-diagonal NBO Fock matrix element.
See ref 18 for further details.
̌
(22) Klein, E.; Lukes, V. J. Mol. Struc. (THEOCHEM) 2006, 767, 43.
(5) (a) Laitar, D. S.; Muller, P.; Gray, G. T.; Sadighi, J. P.
̈
(23) For a discussion of “aromaticity” in the unsaturated NHC which
is consistent with C−N π bonds, see: (a) Lehmann, J. F.; Urquhart, S.
G.; Ennis, L. E.; Hitchcock, A. P.; Hatano, K.; Gupta, S.; Denk, M. K.
Organometallics 2005, 24, 4503−4505. (b) Kessler, F.; Szesni, N.;
Maaß, C.; Hohberger, C.; Weibert, B.; Fischer, H. J. Organomet. Chem.
2007, 692, 3005−3018.
(6) (a) Nesmcyanov, A. N.; Perevalova, E. O.; Struchkov, Yu. T.;
Antipin, M. Yu.; Grandberg, K. I.; Dyadchenko, V. P. J. Organomet.
Chem. 1980, 201, 343−349. (b) Kolb, A.; Bissinger, P.; Schmidbaur,
H. Inorg. Chem. 1993, 32, 5132−5135.
(7) Sone, T.; Iwata, M.; Kasuga, N.; Komiya, S. Chem. Lett. 1991,
1949−1952.
(8) Kolb, A.; Bissinger, P.; Schmidbaur, H. Inorg. Chem. 1993, 32,
5132−5135.
(9) (a) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2010, 49, 5232−5241.
For gold(I) complexes with a counterion of similar pKa, see work on
the Me3SiO− counterion: (b) Robilotto, T. J.; Bacsa, J.; Gray, T. G.;
Sadighi, J. P. Angew. Chem., Int. Ed. 2012, 51, 12077−12080.
(c) Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem., Int. Ed. 2006,
45, 7896−7936.
Organometallics 1999, 18, 1862−1872. (b) Díez-Gonzal
́
ez, S.; Nolan,
S. P. Coord. Chem. Rev. 2007, 251, 874−883.
(24) For early work, see: (a) Fukuda, Y.; Utimoto, K. J. Org. Chem.
1991, 56, 3729−3731. (b) Fukuda, Y.; Utimoto, K. Bull. Chem. Soc.
Jpn. 1991, 64, 2013−2015. For quite high turnover numbers, see:
́
(c) Marion, N.; Ramon, R. S.; Nolan, S. P. J. Am. Chem. Soc. 2009, 131,
448−449.
(25) Hashmi, A. S. K.; Hengst, T.; Lothschutz, C.; Rominger, F. Adv.
̈
Synth. Catal. 2010, 352, 1315−1337.
(26) If small gold particles were involved, much higher activities
should be observed, see: (a) Oliver-Meseguer, J.; Cabrero-Antonino, J.
́
R.; Domínguez, I.; Leyva-Perez, A.; Corma, A. Science 2012, 338,
1452−1455. (b) Hashmi, A. S. K. Science 2012, 338, 1434−1434.
(10) De Fremont, P.; Scott, N. M.; Stevens, E. D.; Nolan, S. P.
Organometallics 2005, 24, 2411−2418.
(11) Huang, J.; Stevens, E. D.; Nolan, S. P.; Peterson, J. L. J. Am.
Chem. Soc. 1999, 121, 2674−2678.
(12) (a) Samojlowics, C.; Bienkiek, M.; Grela, K. Chem. Rev. 2009,
109, 3708−3742. (b) Marion, M.; Mei, J.; Scott, N. M.; Nolan, S. P. J.
Am. Chem. Soc. 2006, 128, 4101−4111.
(13) (a) Hashmi, A. S. K.; Schuster, A.; Rominger, F. Angew. Chem.
2009, 121, 8396−8398; Angew. Chem., Int. Ed. 2009, 48, 8247−8249.
(b) Hashmi, A. S. K.; Ramamurthi, T. D.; Rominger, F. Adv. Synth.
Catal. 2010, 352, 971−975. (c) Hashmi, A. S. K.; Schuster, A. M.;
Gaillard, S.; Cavallo, L.; Poater, A.; Nolan, S. P. Organometallics 2011,
30, 6328−6337.
(14) CCDC 919901 (1), CCDC 919902 (2), CCDC 919903 (3),
CCDC 919904 (4), CCDC 919905 (5), CCDC 919906 (6), and
CCDC 919907 (7) contain supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(15) Gaillard, S.; Slawin, A. M. Z.; Nolan, S. P. Chem. Commun. 2010,
46, 2742−2744.
(16) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.;
Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, R. Cammi, A. J.; Pomelli, C.; Ochterski, J. W.;
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
Revision B.01’ Gaussian, Inc., Wallingford, CT, 2010.
(17) Dunning, T. H., Jr. J. Chem. Phys. 1989, 90, 1007−1023.
H
dx.doi.org/10.1021/om400060s | Organometallics XXXX, XXX, XXX−XXX