Arylgold(I) complexes from base-assisted transmetalation: Structures, NMR properties, and density-functional theory calculations

Article abstract of DOI:10.1021/ic3009464

The synthesis of gold(I) complexes of the type LAuR (L = PCy₃, IPr; R = aryl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) starting from LAuX (X = Br, OAc) and boronic acids in the presence of Cs ₂CO₃ has been investigated. The reactions proceed smoothly in good to excellent yields over the course of 24-48 h in isopropyl alcohol at 50-55 °C. The aryl groups include a variety of functionalities and steric bulk, and in two cases, are heterocyclic. All of the products have been characterized by multinuclear NMR spectroscopy and elemental analysis and most by X-ray crystallography. This work affirms that, almost without exception, base-assisted auration is a useful and reliable way to form gold-carbon bonds.

Full text of DOI:10.1021/ic3009464

Article
pubs.acs.org/IC
Arylgold(I) Complexes from Base-Assisted Transmetalation:
Structures, NMR Properties, and Density-Functional Theory
Calculations
David V. Partyka,† Matthias Zeller,‡ Allen D. Hunter,‡ and Thomas G. Gray*,†
†Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, United States
‡Department of Chemistry, Youngstown State University, 1 University Plaza, Youngstown, Ohio 44555, United States
S
* Supporting Information
ABSTRACT: The synthesis of gold(I) complexes of the type LAuR (L = PCy3, IPr; R =
aryl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) starting from LAuX (X =
Br, OAc) and boronic acids in the presence of Cs2CO3 has been investigated. The
reactions proceed smoothly in good to excellent yields over the course of 24−48 h in
isopropyl alcohol at 50−55 °C. The aryl groups include a variety of functionalities and
steric bulk, and in two cases, are heterocyclic. All of the products have been characterized
by multinuclear NMR spectroscopy and elemental analysis and most by X-ray
crystallography. This work affirms that, almost without exception, base-assisted auration
is a useful and reliable way to form gold−carbon bonds.
groups.39−43 There remains the possibility of transmetalation
INTRODUCTION
■
from organomercurials, with all their attendant hazards.44
The organometallic chemistry of gold draws increasing
attention. A growing body of work suggests that stable
Reports from this laboratory disclose that gold(I) displaces
boron in reactions of (organophosphine)- or (N-heterocyclic
molecules and transient intermediates having gold−carbon
bonds possess useful photophysical1−15 and catalytic16−23
properties. In continuing efforts to determine how attaching
gold to aromatic hydrocarbons alters their photophysical
properties,24 we have demonstrated that N-heterocyclic
carbene- and tricyclohexylphosphine-ligated pyrenylgold(I)
complexes show phosphorescence that extends past 800
nm.25 Naphthalene, when σ-bonded to (phosphine)gold(I)
fragments, shows dual singlet- and triplet-state emission at
room temperature. Emission is sensitive to the site of auration
on the naphthalene core.26 Numerous reports show that
gold(I) efficiently catalyzes a variety of organic transformations
and have implicated organogold(I) intermediates.27−33 Huisgen
[3 + 2] dipolar cycloaddition chemistry proceeds in high yield
from the reaction of gold(I) azides with terminal alkynes to
yield C-bound gold(I) triazolate complexes.34,35 Recently,
Hashmi and collaborators have reported [3 + 2] cycloaddition
reactions of gold(I) isonitriles and azomethine ylides to yield
abnormal N-heterocyclic carbene complexes of gold(I).36 In the
presence of copper(I), gold(I) alkynyls cycloadd to alkyl and
benzyl azides with 1,4-regiochemistry.37 Potential applications
to human medicine have been demonstrated by the synthesis of
(phosphine)gold(I) indolyl derivatives, where the indole
nitrogen bears electron-withdrawing or -releasing groups.
Two such compounds are promiscuous inhibitors of human
kinase enzymes. They act synergistically with 137Cs γ-radiation
to elicit cell death in irradiated cultures.38 Earlier syntheses of
arylated gold(I) complexes have often relied on organolithium
or Grignard reagents, which preclude sensitive functional
carbene)gold(I) halides.45−49 Sensitive functional groups are
tolerated, and a range of phosphines and N-heterocyclic
carbenes may be used as capping ligands on gold. In an effort
to expand the scope of base-assisted transmetalation, we report
the synthesis of new gold(I) organometallics relying on this
protocol. Several are crystallographically characterized. Com-
plications from rearrangement of an allenylboronate and
protodeboronation of an unprotected indole are discussed
alongside density-functional theory computations. We find that
base-assisted transmetalation, although robust, can be compli-
cated for Brønsted acidic or rearrangeable substrates.
RESULTS AND DISCUSSION
■
Synthesis. Gold(I) bromides were treated with a variety of
boronic acids as shown in Scheme 1. Compound 6 is
representative. A base appears to be necessary in these
reactions, although we have not tested this for every substrate.
The reaction solvent (2-propanol) dissolved both base and
boronic acid at 50 °C. Products precipitate readily; most have
Scheme 1
Received: May 8, 2012
Published: July 19, 2012
© 2012 American Chemical Society
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Table 1. Gold(I) Products, Yields, and Designation of Compounds
little or no solubility in 2-propanol. In all cases, the workup
followed a simple protocol that was performed in air. The
solvent was removed by rotary evaporation, followed by
extraction into toluene or benzene, filtration through Celite
and collection of the filtrate, removal of solvent, and trituration
(or crystallization) with pentane. In some cases, trace boronic
acid remained, so an additional wash with ice-cold methanol
was necessary.
Potentially sensitive functional groups on the boronic acids
(or boropinacolate ester) include amide, ketone, aldehyde,
allenyl, and amine. However, in our hands, isolated yields are
high. Results appear in Table 1.
Most reactions were executed using a gold(I) bromide as
starting material, but in one case (Entry 8), the product was
formed in higher yield when a gold(I) acetate was used as the
starting reagent (39% isolated yield). An analogous reaction
with Cy3PAuBr as starting material gave the same product in
9% yield. The choice of gold(I) bromides as reactants was
circumstantial; the corresponding gold(I) chlorides often
transmetallate with comparable efficiency.47,49 Product 11
indicates that steric bulk does not inhibit transmetalation, as
found earlier.50 Table 1 shows that most reactions proceed in
moderate to excellent yield, except 4 and 9.
Crystallography. Eight compounds were characterized by
single crystal X-ray diffraction. While most reactions yielded the
expected products, the combination of crystallographic and
NMR analysis proves that, as solids and in solution, two (7 and
9) did not. Typical phosphine-ligated arylgold(I) complexes are
the isomeric tolyls 1 and 2, Figures S1 and S2, Supporting
Information. Isomers 1 and 2 differ in solubility. Whereas the
para-isomer 2 is insoluble in hexanes and pentane and
crystallized readily, the meta-isomer 1 has some solubility in
pentane and does not easily crystallize. The density as
calculated from the unit cell contents suggests that the more
symmetric isomer 2 packs more efficiently than 1 (1.645 vs
1.628 kg m−3, respectively). Both compounds crystallize in the
same space group. Thus, packing may account for some of the
difference in solubility. Bond angles and lengths at gold are
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a
Table 2. Crystallographic Data for 1−3, 5, 7−9, and 11 at 100 K
1
2
3
5
7
8
9
11
formula
fw
C25H40AuP
568.51
C25H40AuP
568.51
C26H40AuOP
596.52
C23H37AuNP
555.47
C21H36AuP
516.43
C20H36AuO2P · 1/2 C6H6
575.48
C26H39AuNP
593.52
C36H47AuN2
704.72
crystal system
space group
a, Å
triclinic
triclinic
monoclinic
P21/c
triclinic
monoclinic
P21/c
triclinic
orthorhombic
P21P21P21
8.2372(7)
17.1313(2)
17.2431(2)
monoclinic
C2/c
P1
̅
P1
P1
̅
P1
̅
̅
9.170(2)
10.837(3)
12.505(3)
80.933(4)
71.423(4)
82.979(4)
1159.9(5)
2
8.9329(5)
10.5661(6)
12.5173(7)
96.753(1)
101.367(1)
92.489(1)
1147.5(1)
2
11.3384(8)
16.1535(1)
13.7362(1)
9.4903(7)
11.3240(9)
11.6943(9)
76.596(1)
67.719(1)
81.084(1)
1128.1(2)
2
17.478(3)
7.5496(1)
17.326(3)
9.074(2)
10.612(2)
12.973(3)
107.093(4)
100.704(4)
96.207(4)
1155.5(4)
2
20.220(2)
16.0965(2)
23.180(4)
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
104.374(1)
118.546(2)
114.506(2)
2437.1(3)
4
2008.3(6)
4
2433.2(4)
4
6864.7(2)
8
Z
D
calcd, mg m−3
1.628
1.645
1.626
1.635
1.708
1.654
1.620
1.364
T, K
μ, mm−1
100(2)
100(2)
100(2)
6.117
100(2)
100(2)
7.404
100(2)
100(2)
6.124
100(2)
4.310
6.418
6.487
6.598
6.450
θmin, θmax, deg
2.46, 30.39
1.058
1.67, 28.28
1.056
2.24, 30.53
1.052
2.40, 30.53
1.087
2.65, 31.53
1.191
3.04, 30.48
1.128
2.36, 31.89
1.020
1.68, 28.28
1.006
b
GOF on F2
c
final R indices
[I > 2σ(I)] R1
0.0169
0.0215
0.0297
0.0205
0.0402
0.0424
0.0200
0.0241
wR2
0.0418
0.0534
0.0797
0.0532
0.1342
0.1179
0.0426
0.0491
a
b
c
Mo Kα radiation, λ = 0.71073 Å. GOF = [Σw(Fo2 − Fc2)2/(n − p)]1/2; n = number of reflections, p = number of parameters refined. R1 = Σ(∥Fo|
− |Fc∥)/Σ|Fo|; wR2 = [Σw(Fo − Fc2)2/ΣwFo ]1/2
.
2
4
unremarkable. Table 2 summarizes crystallographic data for the
new structures.
Figures S3 and S4, Supporting Information, show thermal
ellipsoid representations of 3 and 5, respectively. Metrics at
gold are typical. The lack of disorder at the acetyl functionality
of 3 is surprising considering that there should be a negligible
energy difference between this conformer and the 180° rotated
(about the C4−C7 bond) conformer. Examination of the
packing diagram does not suggest any kind of intermolecular
interactions that might lead to exclusivity of conformation. In
the case of 5, the pyridyl nitrogen atom is not hydrogen bonded
nor does it form any close contact with the gold atom of an
adjacent molecule.
Compound 7 is a rearranged product. Its structure appears as
Figure 1. Whereas the starting reagent is an allenylboronic acid,
7 is a gold(I) propynyl. The propynyl ligand is nearly linear
(∠C19−C20−C21 = 178.6(9)°), whereas the angle at the
metalated carbon atom deviates slightly from linearity (∠Au1−
C19−C20 = 173.4(8)°). This angle is marginally more acute
than observed for other crystallographically characterized
phosphine-ligated alkynylgold(I) complexes.51−55 Metrics
involving gold are normal.
Density-functional theory (DFT) calculations were per-
formed on allenyl and alkynyl model complexes having
trimethylphosphine ligands instead of tricyclohexylphosphine.
This substitution is made for computational tractability.
Geometries were optimized without imposed symmetry or
other restraints. Harmonic frequency calculations confirm that
the converged structures are potential energy minima. Full
computational details appear in the Experimental Section. We
find that the propynyl complex is more stable than the allenyl
isomer. This conclusion is based on sums of electronic and
thermal free energies at 298 K. The gold(I) alkynyl is calculated
to be 5.34 kcal mol−1 stabler than the allenyl, eq 1. If the allenyl
does form, its isomerization to the alkynyl is predicted to be
spontaneous.
Figure 1. Thermal ellipsoid representation of 7 showing 50%
probability ellipsoids and partial atom-labeling. Hydrogen atoms are
omitted for clarity; unlabeled atoms are carbon. Selected bond lengths
(Å) and angles (°): Au1−C19 2.007(8), Au1−P1 2.286(2), C19−C20
1.195(1), C20−C21 1.474(1), Au1−C19−C20 173.4(8), C19−C20−
C21 178.6(9), and C19−Au1−P1 175.5(2).
Figure 2 depicts the crystal structures of 8 and 9. The
synthesis of 9 (from 8) proceeded in lower yield than those of
1
the other gold(I) species here. Both the 31P and H NMR
spectra suggested the product was not carbon-bound. This
hypothesis was supported by X-ray crystallography (Figure 2b),
which shows that the product contains a nitrogen-bound
indolyl ligand that has undergone protodeboronation.44
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the N-indolyl ligand of 9. As the structure of 9 shows, the
indolyl ligand has undergone protodeboronation with loss of
the B(OH)2 group, and NMR suggests this protodeboronation
reaction has no indolyl byproducts after workup.
(N-Heterocyclic carbene)gold(I) precursors also undergo
base-assisted transmetalation.25 Accordingly, a typical (NHC)-
gold(I) bromide was reacted with two arylboronic acids.
Although spectroscopic and microanalytical data support the
formation of the phenyl complex 10, repeated attempts at
crystallographic characterization proved unsuccessful. However,
in the case of the bulkier analogue 11, a suitable crystal was
found. The structure of 11 appears as Figure 3. The potency of
Figure 3. Thermal ellipsoid representation of 11 showing 50%
probability ellipsoids and partial atom-labeling. Hydrogen atoms are
omitted for clarity, and unlabeled atoms are carbon. Selected bond
lengths (Å) and angles (°): Au1−C1 2.026(3), Au1−C28 2.038(2),
C1−Au1−C28 178.0(1), N2−C1−N1 104.1(2), N2−C1−Au1
128.34(2), and N1−C1−Au1 127.53(2).
Figure 2. Thermal ellipsoid depictions of (a) 8 and (b) the coupling
product 9 showing 50% probability ellipsoids and partial atom-
labeling. Hydrogen atoms are omitted for clarity; unlabeled atoms are
carbon. Selected bond lengths (Å) and angles (°): (8) Au1−O1
2.052(4), Au1−P1 2.2245(2), and O1−Au1−P1 173.88(1). (9) Au1−
N1 2.028(3), Au1−P1 2.2465(9), and N1−Au1−P1 177.16(8).
the trans influence of the mesityl ligand is clear when compared
to (IPr)AuBr (Au−C = 1.975(5) Å).60 Steric clash between the
mesityl and IPr ligands is minimized in three ways. First, ∠C1−
Au1−C28 is nearer 180° than in any other complex in this
investigation. Second, the torsion angle between the mean
mesityl plane (C6 ring) and the mean imidazolium plane
(67.5°) is such that the mesityl ligand resides in the cleft
formed by the 2,6-diisopropylphenyl substituents. Third, one
2,6-diisopropylphenyl group rotates such that one of its
isopropyl groups cants away from the proximal methyl group
(of the mesityl ligand). Overall, these features confer C1
symmetry on 11.
DFT calculations were conducted on model (indolyl)gold(I)
complexes, again with PMe3 in place of PCy3. The free-energy
gain on isomerizing from C-bound to N-bound product is
substantial, eq 2. This result, alongside the isolation of 9, is
NMR Spectroscopy. The most diagnostic spectroscopic
signatures are the 31P or 13C (carbene) resonances of each
product. All spectra were measured in C6D6. In general, 31P
signals for arylgold(I) complexes appeared between 57 and 58
ppm, with electron-withdrawing substituted aryl ligands leading
to slightly lower-field signals. This observation corresponds
with earlier work.45 The 31P signal of other products (7−9) had
lower-field resonances than the arylgold(I) complexes, and this
was particularly useful in the determination of 9 as an N-bound
product. Furthermore, there is a rough correlation between
Au−P bond le ngt h a nd 3 1 P chemical shift .
(Tricyclohexylphosphine)gold(I) complexes show Au−P
bond lengths that fall in a narrow range, 2.224(2) Å (8) to
2.3058(6) Å (2). Corresponding 31P chemical shifts (in C6D6)
notable in that indole is a privileged structure in biology.56
Recent work38 shows that gold(I) complexes of N-protected
indoles are broadly cytotoxic to malignant cell lines. At least
some such compounds potentiate the cell-killing action of
ionizing radiation. For bioactive indoles where gold binds to
carbon, protection of the indole nitrogen appears prudent.
An advantage of acetate complex 8 as a carrier of gold is its
solubility in alcohols. Its structure, Figure 2a, is similar to that
of other gold(I) acetates.57,58 As is common for d10 group 11
centers, acetate binds in a κ1-fashion,59 and the metal adopts a
linear geometry. Comparison of the phosphorus−gold bond
lengths shows that acetate is a weaker trans-influencer than any
C-bonded aryl considered here. The same observation holds for
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fall in an approximately 2 ppm window (centered at ∼57.5
ppm). The observed chemical shift of 9 (50.1 ppm)
immediately suggested that 9 was not C-bound, and X-ray
crystallography confirms this conclusion for solid 9. The bond
length-chemical shift correlation has been observed before with
13C nuclei (a gold(I)-carbene series)58 and other metals with
various nuclei.61−64 If the correlation in ref 58 holds, then the
gold(I)-carbene carbon bond distance in 11 is longer than in
10. That is, mesityl exerts a stronger trans influence than
phenyl, as 13C carbene-carbon chemical shifts are 200.88 and
198.39 ppm, respectively. This supposition is intuitively
appealing. Provided steric effects do not materially alter
binding; a mesityl ligand should have more electron density
at the bound carbon because of its three methyl substituents.
1H NMR was also useful for determining solution
conformation and corroborating identities of certain products
(4, 7, and 9) in particular. All products except 1 have
spectroscopic signatures that indicate local mirror symmetry of
the aryl ligand. For 4, mass spectrometry and 1H NMR
suggested that the desired para-aurated benzamide was the
isolated product. For 7, the lack of multiple allenyl resonances
suggested that the allenyl group was no longer present. In fact,
the observed doublet was that of a propynyl methyl group that
was coupled to phosphorus. Under the experimental con-
ditions, the allenyl group had rearranged. Lowering the
temperature (room temperature with longer stirring) led to
the same result. As discussed above, 9 was found to be N-
bound by X-ray crystallography, and this was corroborated by
1H and 31P NMR. Furthermore, the observation of six signals
by 1H NMR suggested protodeboronation, as proved to be the
case. Although we have not observed this in gold trans-
metalation chemistry up to this point, this phenomenon has
been observed in the literature.65−67 Protodeboronation
reactions have been shown to be catalyzed separately by the
presence of base68 and metal ions;69 therefore, it is not
surprising the conditions here (involving both a base and a
metal ion) lead to clean protodeboronation. Note that this
selectivity for nitrogen is opposite that observed in the reaction
of (PPh3)AuN3 with terminal alkynes, in which the [3 + 2]
cycloaddition product is exclusively C-bound.34,35
EXPERIMENTAL SECTION
■
All solvents and reagents were used as received. Microanalyses (C, H,
and N) were performed by Quantitative Technologies Inc. NMR
spectra (1H, 13C{1H}, and 31P{1H}) were recorded on a Varian AS-
400 spectrometer operating at 399.7, 100.5, and 161.8 MHz,
respectively.
Cy3PAu(3-tolyl) (1). In 5 mL of 2-propanol were suspended
Cs2CO3 (101 mg, 0.31 mmol) and 3-tolylboronic acid (41 mg, 0.30
mmol). Cy3PAuBr (93 mg, 0.17 mmol) was added to the reaction
mixture, and the mixture was stirred for 24 h at 50 °C, cooled, and
taken to dryness in vacuo. The dry solid was extracted with ∼15 mL of
benzene, filtered, and washed thoroughly with ethylene glycol (2 × 5
mL) and water (5 mL) in a separatory funnel. The benzene layer was
collected and dried with MgSO4, filtered, and taken to a residue in
vacuo. The residue was triturated with pentane to liberate a white free-
flowing solid. Yield: 54 mg (57%). 1H NMR (C6D6): δ 7.91−7.97 (m,
2H, C6H4(CH3)), 7.47 (td, 1H, C6H4(CH3), J = 1.6, 7.2 Hz), 7.08 (d,
1H, C6H4(CH3), J = 7.2 Hz), 2.35 (s, 3H, C6H4(CH3)), 0.92−1.90
(m, 33H, C6H11) ppm. 31P{1H} NMR (C6D6): δ 57.5 (s) ppm. Anal.
Calcd. for C25H40AuP: C, 52.82; H, 7.09. Found: C, 52.66; H, 7.27.
Cy3PAu(4-tolyl) (2). In 5 mL of 2-propanol were suspended
Cs2CO3 (94 mg, 0.29 mmol) and 4-tolylboronic acid (39 mg, 0.29
mmol). Cy3PAuBr (84 mg, 0.15 mmol) was added, and this mixture
was heated at ∼50 °C for 24 h. After cooling, the suspension was taken
to dryness in vacuo, extracted into benzene, filtered through Celite,
and taken to dryness in vacuo. The residue was washed with pentane,
dried, re-extracted into a minimum of benzene, and filtered, and
pentane vapor was diffused to cause separation of colorless crystals.
The crystals were washed with a small amount of cold methanol and
pentane and dried. Yield: 63 mg (73%). 1H NMR (C6D6): δ 8.05 (dd,
2H, C6H4(CH3), J = 4.8, 8.0 Hz), 7.35 (d, 2H, C6H4(CH3), J = 8.0
Hz), 2.31 (s, 3H, C6H4(CH3)), 0.91−1.88 (m, 33H, C6H11) ppm.
31P{1H} NMR (C6D6): δ 57.6 (s) ppm. Anal. Calcd. for C25H40AuP:
C, 52.82; H, 7.09. Found: C, 53.01; H, 7.16.
Cy3PAu(4-acetylphenyl) (3). In 5 mL of 2-propanol were
suspended Cs2CO3 (104 mg, 0.32 mmol) and 4-acetylphenylboronic
acid (53 mg, 0.32 mmol). To this suspension was added Cy3PAuBr
(89 mg, 0.16 mmol), and the mixture was stirred at 50 °C for 30 h.
After cooling, the mixture was stripped of solvent in vacuo, extracted
into benzene, filtered through Celite, and taken to dryness in vacuo.
The white solid was washed thoroughly with pentane, dried, extracted
into benzene, filtered through Celite, and concentrated to saturation.
Pentane vapor was diffused to cause separation of colorless crystals,
which were washed with cold methanol and pentane, dried, and
collected. Yield: 81 mg (85%). 1H NMR (C6D6): δ 8.06−8.16 (m, 4H,
C6H4(COCH3)), 2.21 (s, 3H, C6H4(COCH3)), 0.92−1.86 (m, 33H,
C6H11). 31P{1H} NMR (C6D6): δ 57.3 (s) ppm. Anal. Calcd. for
C26H40AuOP: C, 52.35; H, 6.76. Found: C, 52.57; H, 6.80.
CONCLUSIONS
■
The base-mediated transmetalation of aryl groups from boron
to gold has been elaborated. The reaction generally proceeds in
high yield and circumvents functional group incompatibilities of
organolithium and Grignard chemistry. Bulky phosphines and
N-heterocyclic carbenes are suitable ancillary ligands on
gold(I), and acetate has been found to be a suitable leaving
group on gold(I), conferring solubility in alcohol onto the gold
substrate. As anticipated, a phosphine-ligated, pyridine-
containing product shows no evidence for any equilibrium
between the N-bound and P-bound isomers. Furthermore, in
the case of 11 (an IPr-ligated mesitylgold(I) complex),
considerable steric hindrance does not prevent formation of
the organogold complex in high yield. The transmetalation
reactions generally proceeded as expected, but in two cases, an
unexpected rearrangement and isomerization product were
cleanly formed. DFT investigations corroborate the spontaneity
of these rearrangements; future investigations may address if
these rearrangements can be exploited to yield new organo-
metallic products.
Cy3PAu(4-benzamide) (4). In 5 mL of 2-propanol were
suspended Cs2CO3 (97 mg, 0.30 mmol) and 4-carbamoylphenylbor-
onic acid (51 mg, 0.31 mmol). To this suspension was added
Cy3PAuBr (83 mg, 0.15 mmol), and the mixture was stirred at 50 °C
for 30 h. After cooling, the mixture was stripped of solvent in vacuo,
extracted into benzene, filtered through Celite, and taken to dryness in
vacuo. The white solid was washed thoroughly with pentane, dried,
extracted into benzene, filtered through Celite, and concentrated to
saturation. Pentane vapor was diffused to cause separation of colorless
1
crystals. Yield: 17 mg (19%). H NMR (C6D6): δ 8.02−8.06 (m, 2H,
C6H4(CONH2)), 7.90 (dd, 2H, C6H4(CONH2), J = 1.6, 8.0 Hz),
0.90−1.89 (m, 33H, C6H11). 31P{1H} NMR (C6D6): δ 57.3 (s) ppm.
MS (ESI+): m/z = 620.2326 (M + Na)+. Anal. Calcd. for
C25H39AuNOP: C, 50.25; H, 6.58; N, 2.34. Found: C, 50.36; H,
6.68; N, 2.31.
Cy3PAu(4-pyridyl) (5). In 5 mL of 2-propanol were suspended
Cs2CO3 (95 mg, 0.29 mmol) and 4-pyridylboronic acid (36 mg, 0.29
mmol). To this suspension was added Cy3PAuBr (81 mg, 0.15 mmol),
and the mixture was stirred at 50 °C for 24 h. After cooling, the
mixture was stripped of solvent in vacuo, extracted into benzene,
filtered through Celite, and taken to dryness by rotary evaporation.
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Inorganic Chemistry
Article
The solid was triturated with pentane, and the pentane was decanted.
The solid was extracted into benzene, filtered through Celite, and
concentrated past the point of saturation. Pentane vapor was diffused
to complete separation of light brown crystals, which were washed
with cold methanol and pentane, dried, and collected. Yield: 70 mg
amount of purple material). The crystals were collected and dried.
Yield: 29 mg (39%). This product was spectroscopically identical to 9.
IPrAu(phenyl) (10). A flask was loaded with IPrAuBr60 (81 mg,
0.12 mmol), phenylboronic acid (31 mg, 0.25 mmol), and Cs2CO3 (83
mg, 0.26 mmol). To this flask was added 2-propanol (5 mL), and the
suspension was stirred at ∼55 °C for 24 h. After cooling, the
suspension was rotovapped to dryness, extracted into benzene, filtered,
and taken to dryness. It was extracted again into benzene, filtered, and
evaporated to saturation, and finally, pentane vapor was diffused into
the saturated solution. The crystalline solid that separated was
collected and dried. Yield: 71 mg (88%). 1H NMR (C6D6): δ 7.52 (dd,
2H, C6H5, J = 1.6, 8.0 Hz), 7.18−7.24 (m, 4H, IPr (para-H) + C6H5),
7.07 (d, 4H, IPr (meta-H), J = 8.0 Hz), 6.99 (tt, 1H, para-C6H5, J =
1.6, 8.0 Hz), 6.30 (s, 2H, imidazole CH), 2.66 (sep, 4H, CH(CH3)2, J
= 6.8 Hz), 1.48 (d, 12H, CH(CH3)2, J = 6.8 Hz), 1.09 (d, 12H,
CH(CH3)2, J = 7.2 Hz). 13C{1H} NMR (C6D6): δ 198.39 (s, C
carbene), 169.89 (s, CH aromatic), 145.89 (s, CH aromatic), 141.19
(s, CH aromatic), 134.99 (s, CH aromatic), 130.48 (s, CH aromatic),
127.08 (s, CH aromatic), 124.69 (s, CH aromatic), 124.12 (s, CH
aromatic), 122.45 (s, CH imidazole), 29.00 (s, CH(CH3)2), 24.77 (s,
CH(CH3)2), 23.86 (s, CH(CH3)2) ppm. Anal. Calcd. for C33H41AuN2:
C, 59.81; H, 6.24; N, 4.23. Found: C, 59.96; H, 6.19; N, 4.16.
IPrAu(mesityl) (11). A flask was loaded with IPrAuBr (63 mg,
0.095 mmol), mesitylboronic acid (57 mg, 0.35 mmol), and Cs2CO3
(108 mg, 0.35 mmol). To this flask was added 2-propanol (4 mL), and
the suspension was stirred at ∼55 °C for 48 h. After cooling, the
suspension was evaporated to dryness, extracted into toluene, filtered,
and taken to dryness. The solid was triturated with pentane and
collected, washed with cold methanol, and dried. Yield: 58 mg (87%).
1H NMR (C6D6): δ 7.26 (t, 2H, para-C6H3, J = 8.0 Hz), 7.10 (d, 4H,
meta-C6H3, J = 8.0 Hz), 6.97 (s, 2H, mesityl CH), 6.34 (s, 2H,
imidazole CH), 2.65 (sep, 4H, CH(CH3)2, J = 6.8 Hz), 2.27 (s, 3H,
para-mesityl singlet), 2.23 (s, 6H, ortho-mesityl singlet), 1.43 (d, 12H,
CH(CH3)2, J = 6.8 Hz), 1.09 (d, 12H, CH(CH3)2, J = 6.8 Hz) ppm.
13C{1H} NMR (C6D6): δ 200.88 (s, C carbene), 167.11 (s, ipso mesityl
C), 146.59 (s, CH aromatic), 146.07 (s, CH aromatic), 135.25 (s, CH
aromatic), 133.02 (s, CH aromatic), 130.33 (s, CH aromatic), 126.02
(s, CH aromatic), 124.03 (s, CH aromatic), 122.26 (s, CH imidazole),
29.02 (s, CH(CH3)2), 26.33 (s, ortho-mesityl CH3), 24.63 (s,
CH(CH3)2), 23.99 (s, CH(CH3)2), 21.41 (s, para-mesityl CH3)
ppm. Anal. Calcd. for C36H47AuN2: C, 61.18; H, 6.99; N, 3.96. Found:
C, 61.08; H, 6.85; N, 3.90.
1
(88%). H NMR (C6D6): δ 8.81−8.84 (m, 2H, C6H4N), 7.72−7.76
(m, 2H, C6H4N), 0.90−1.93 (m, 33H, C6H11). 31P{1H} NMR (C6D6):
δ 57.2 (s) ppm. Anal. Calcd. for C23H37AuNP: C, 49.73; H, 6.71; N,
2.52. Found: C, 50.02; H, 6.75; N, 2.47.
Cy3PAu(4-styryl) (6). A flask was loaded with Cs2CO3 (34 mg,
0.10 mmol), 4-styrylboronic acid (16 mg, 0.11 mmol), and Cy3PAuBr
(36 mg, 0.065 mmol); 2-propanol (3 mL) was added. The mixture was
stirred at 50 °C for 24 h. After cooling, the mixture was stripped of
solvent in vacuo, extracted into toluene, filtered through Celite, and
taken to dryness by rotary evaporation. The solid was triturated with
pentane, and the pentane was decanted. The solid was washed with
1
cold methanol, dried, and collected. Yield: 34 mg (91%). H NMR
(C6D6): δ 8.06−8.11 (m, 2H, C6H4(C2H3)), 7.58 (d, 2H,
C6H4(C2H3), J = 7.2 Hz), 6.79 (dd, 1H, C6H4(C2H3), J = 10.4, 17.6
Hz), 5.73 (dd, 1H, C6H4(C2H3), J = 1.2, 17.6 Hz), 5.07 (dd, 1H,
C6H4(C2H3), J = 1.2, 10.4 Hz) 0.86−1.85 (m, 33H, C6H11). 31P{1H}
NMR (C6D6): δ 57.3 (s) ppm. Anal. Calcd. for C26H40AuP: C, 53.79;
H, 6.94. Found: C, 53.87; H, 6.95.
Cy3PAu(propynyl) (7). A flask was loaded with Cs2CO3 (46 mg,
0.14 mmol) and Cy3PAuBr (43.5 mg, 0.078 mmol). To this flask was
added allenylboropinacolate ester (26 mg, 0.16 mmol) in 3 mL of
degassed 2-propanol. The mixture was stirred at 50−55 °C for 36 h.
After cooling, the mixture was stripped of solvent in vacuo, extracted
into toluene, filtered through Celite, and taken to dryness by rotary
evaporation. The solid was triturated with pentane, and the pentane
was decanted. The solid was collected and dried; it was analytically
pure. Yield: 30 mg (74%). 1H NMR (C6D6): δ 2.05 (d, 3H, CC−CH3,
J = 1.6 Hz), 0.81−1.75 (m, 33H, C6H11). 31P{1H} NMR (C6D6): δ
56.7 (s) ppm. Anal. Calcd. for C21H36AuP: C, 48.84; H, 7.03. Found:
C, 48.83; H, 7.10.
Cy3PAu(OAc) (8). In 5 mL of benzene was dissolved Cy3PAuCl
(81 mg, 0.16 mmol), and to this solution was added 1.08 equiv (28
mg, 0.17 mmol) of Ag(OAc). The resultant suspension was stirred for
2 h and filtered through Celite. The solution was concentrated to a
residue via rotary evaporation. The residue was triturated with pentane
until it became a free-flowing, colorless solid. The solid was collected
1
and dried. Yield: 76 mg (90%). H NMR (C6D6): δ 2.32 (s, 3H,
X-ray Structure Determination. Compounds 1−3, 5, and 8 were
crystallized by diffusion of pentane into saturated benzene solutions.
Compounds 7, 9, and 11 were crystallized by diffusion of pentane into
saturated toluene solutions. Single crystal X-ray data were collected on
a Bruker AXS SMART APEX CCD diffractometer using mono-
chromatic Mo Kα radiation with omega scan technique. The unit cells
were determined using SMART and SAINT+. All structures were
solved by direct methods and refined by full matrix least-squares
against F2 with all reflections using SHELXTL. Refinement of
extinction coefficients was found to be insignificant. All nonhydrogen
atoms were refined anisotropically. All other hydrogen atoms were
placed in standard calculated positions, and all hydrogen atoms were
refined with an isotropic displacement parameter 1.5 (CH3) or 1.2 (all
others) times that of the adjacent carbon or nitrogen atom.
Calculations. Density-functional theory calculations were per-
formed within the Gaussian 09 program suite.70 All calculations were
spin-restricted and employ the parameter-free PBE0 functional.71
Calculations, including geometry optimizations, include continuum
solvation in benzene using the integral equation formalism of the
polarizable continuum model of Tomasi and co-workers.72,73 The
Stuttgart-Dresden basis set and pseudopotential were used for gold;74
the TZVP basis set of Godbelt, Andzelm, and co-workers was applied
for nonmetal atoms.75 Geometry optimizations proceeded in
redundant internal coordinates without imposed symmetry or any
other constraints. Harmonic frequency calculations on optimized
structures returned all real vibrational frequencies. Sums of electronic
and thermal free energies were calculated from harmonic vibrational
frequencies without scaling.
CO2CH3), 0.84−1.68 (m, 33H, C6H11) ppm. 31P{1H} NMR (C6D6): δ
47.9 (s) ppm. This compound was used without further purification.
Cy3PAu(N-indolyl) (9). Method A. In 3 mL of 2-propanol were
suspended Cs2CO3 (61 mg, 0.19 mmol), 5-indoleboronic acid (30 mg,
0.19 mmol), and Cy3PAuBr (52 mg, 0.093 mmol), and the mixture
was stirred at 50 °C for 24 h. After cooling, the mixture was stripped of
solvent in vacuo, extracted into toluene, filtered through Celite, and
taken to dryness by rotary evaporation. The residue was triturated with
pentane, and the pentane was decanted. The solid was extracted into
toluene and filtered through Celite, and pentane vapor was diffused to
complete separation of colorless crystals (sometimes coated with a
minute amount of purple material). The crystals were collected and
dried. Yield: 5 mg (9%). 1H NMR (C6D6): δ 8.25 (d, 1H, J = 8.0 Hz),
8.13 (d, 1H, J = 8.0 Hz), 7.78 (d, 1H, J = 2.4 Hz), 7.48 (t, 1H, J = 7.6
Hz), 7.36 (t, 1H, J = 7.6 Hz), 7.05 (m, 1H), 0.88−1.70 (m, 33H,
C6H11). 31P{1H} NMR (C6D6): δ 50.1 ppm. Anal. Calcd. for
C26H39AuNP: C, 52.61; H, 6.62; N, 2.36. Found: C, 52.69; H, 6.70;
N, 2.24.
Method B. In 3 mL of 2-propanol were suspended Cs2CO3 (80 mg,
0.25 mmol), 5-indoleboronic acid (40 mg, 0.25 mmol), and
Cy3PAu(OAc) (66 mg, 0.12 mmol), and the mixture was stirred at
50 °C for 24 h. After cooling, the mixture was stripped of solvent in
vacuo, extracted into toluene, filtered through Celite, and taken to
dryness by rotary evaporation. The solid was triturated with pentane,
and the pentane was decanted. The solid was extracted into toluene
and filtered through Celite, and pentane vapor was diffused to
complete separation of colorless crystals (coated with a minute
8399
dx.doi.org/10.1021/ic3009464 | Inorg. Chem. 2012, 51, 8394−8401

Inorganic Chemistry
Article
(23) Hashmi, A. S. K.; Braun, I.; Rudolph, M.; Rominger, F.
Organometallics 2012, 31, 644.
(24) Gray, T. G. Comments Inorg. Chem. 2007, 28, 181.
(25) Partyka, D. V.; Esswein, A. J.; Zeller, M.; Hunter, A. D.; Gray, T.
G. Organometallics 2007, 26, 3279.
(26) Gao, L.; Peay, M. A.; Partyka, D. V.; Updegraff, J. B., III; Teets,
T. S.; Esswein, A. J.; Zeller, M.; Hunter, A. D.; Gray, T. G.
Organometallics 2009, 28, 5669.
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystallographic data in .cif format and optimized Cartesian
coordinates of model complexes. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
(27) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2010, 49, 5232.
Corresponding Author
*E-mail: tgray@case.edu.
(28) Nieto-Oberhuber, C.; Lop
Soc. 2005, 127, 6178.
́
ez, S.; Echavarren, A. M. J. Am. Chem.
(29) Johansson, M. J.; Gorin, D. J.; Staben, S. T.; Toste, F. D. J. Am.
Chem. Soc. 2005, 127, 18002.
Notes
The authors declare no competing financial interests.
(30) Nieto-Oberhuber, C.; Munoz, M. P.; Lop
́
ez, S.; Jimen
́
ez-Nunez,
́
̃
̃
E.; Nevado, C.; Herrero-Gom
Chem.Eur. J. 2006, 12, 1677.
́
ez, E.; Raducan, M.; Echavarren, A. M.
ACKNOWLEDGMENTS
■
(31) Morita, N.; Krause, N. Angew. Chem., Int. Ed. 2006, 45, 1897.
(32) Ye, L.; Wang, Y.; Aue, D. H.; Zhang, L. J. Am. Chem. Soc. 2012,
134, 31.
The authors thank the U.S. National Science Foundation (grant
CHE-1057659 to T.G.G.) for support. T.G.G. was an Alfred P.
Sloan Foundation Fellow for 2009−2011. The diffractometer at
Youngstown State University was funded by NSF grant
0087210, by the Ohio Board of Regents grant CAP-491, and
by Youngstown State University.
(33) Tsui, E. Y.; Muller, P.; Sadighi, J. P. Angew. Chem., Int. Ed. 2008,
̈
47, 8937.
(34) Partyka, D. V.; Updegraff, J. B., III; Zeller, M.; Hunter, A. D.;
Gray, T. G. Organometallics 2007, 26, 183.
(35) Robilotto, T. J.; Alt, D. S.; von Recum, H. A.; Gray, T. G. Dalton
Trans. 2011, 40, 8083.
(36) Hashmi, A. S. K.; Riedel, D.; Rudolph, M.; Rominger, F.; Oeser,
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