Synthesis and characterization of gold complexes with pyridine-based SNS ligands and as homogeneous catalysts for reduction of 4-nitrophenol

Article abstract of DOI:10.1039/c5ra01749a

Three gold complexes with pyridine-based SNS type ligands, 2,6-bis(1-methylimidazole-2-thione)pyridine (Bmtp), 2,6-bis(1-ethylimidazole-2-thione)pyridine (Betp) and 2,6-bis(1-isopropylimidazole-2-thione)pyridine (Bptp) have been synthesized and characteri

Full text of DOI:10.1039/c5ra01749a

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Synthesis and characterization of gold complexes
with pyridine-based SNS ligands and as
homogeneous catalysts for reduction of
Cite this: RSC Adv., 2015, 5, 29491
4-nitrophenol†
Wei-Guo Jia,* Yuan-Chen Dai, Hai-Ning Zhang, Xiaojing Lu and En-Hong Sheng
Three gold complexes with pyridine-based SNS type ligands, 2,6-bis(1-methylimidazole-2-thione)pyridine
(
Bmtp), 2,6-bis(1-ethylimidazole-2-thione)pyridine (Betp) and 2,6-bis(1-isopropylimidazole-2-thione)-
pyridine (Bptp) have been synthesized and characterized. Reactions of HAuCl $H O with three pyridine-
based SNS ligands result in the formation of the complexes [(L)AuCl
]Cl (L ¼ Bmtp (1); L ¼ Betp (2) and
4
2
2
L ¼ Bptp (3)). All compounds are investigated by elemental analysis, NMR, MS and UV-Vis as well as IR
spectral analysis. The molecular structure of 3 has been confirmed by X-ray crystallography. Moreover,
all gold complexes are efficient homogeneous catalysts and catalyze the reduction of 4-nitrophenol
Received 29th January 2015
Accepted 20th March 2015
DOI: 10.1039/c5ra01749a
4
(4-NP) to 4-nitroaniline (4-AP) in the presence of NaBH reducing agent in water. And complex
ꢀ1
www.rsc.org/advances
3 exhibits an exceptionally high turn over frequency (TOF) of 1.20 min for the reduction of 4-NP.
In previous studies, we synthesized Ir and Rh complexes
based on organochalcogen ligands (SS, SeSe and SNS) and
Introduction
Gold-based compounds including complexes and nano- studied their catalytic activities in norbornene polymeriza-
9,10
materials (particles, boxes, cages and tubes) have exhibited tion. Organochalcogen chemistry revolving transition metal
extraordinarily rich catalytic activity for a variety of reactions complexes is one of research focuses of our groups, and we seek
involving oxidation and reduction due to their unique physi- to discover new transition metal complexes and study their
1,2
cochemical properties over the past few decades. The interest potential catalytic applications. Herein, the gold complexes
of exploring gold-based catalysts has been substantially boom- with three pyridine-based SNS ligands [(L)AuCl
]Cl (L ¼ Bmtp
2
ing. For heterogeneous gold-based catalytic systems, a high (1); L ¼ Betp (2) and L ¼ Bptp (3)) have been synthesized and
dispersion of gold nanoparticles is necessary to exhibit high characterized. Moreover, the molecular structure of 3 has been
catalytic activity. Subsequently, many solid supporting gold determined by X-ray crystallography. The various organo-
3
4
5
catalysts including polymer, hydrogel, silica particles, metal chalcogen ligands were selected in order to investigate the
6
7
2
oxides and magnetic materials have been developed. In inuence of alkyl substituents on imidazole ring with different
contrast to the heterogeneous catalytic system, homogeneous electronic properties on catalytic properties of the resulting
gold catalysts have been found to be very effective for complexes. The results show that all gold complexes are effi-
8
construction of C–C and C–N bonds through C–H activation.
ciently catalyze 4-NP reduction to 4-AP in the presence of NaBH
4
The mechanisms of the heterogeneous reactions are not yet well reducing agent under homogeneous conditions. Furthermore,
understood, whereas the mechanisms have been well explored the steric and electronic effects of the alkyl group in the orga-
in the case of the homogeneous reactions. Therefore, the design nochalcogen ligands have a strong inuence on the 4-NP
and synthesis of homogeneous gold catalysts with stable and reduction (i-Pr > Et > Me).
high catalytic efficiency has received increasing attention
recently.
Results and discussion
Synthesis of ligands and gold complexes
College of Chemistry and Materials Science, Center for Nano Science and Technology,
The Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Three pyridine-based SNS ligands, 2,6-bis(1-methylimidazole-2-
Laboratory of Molecular-Based Materials, Anhui Normal University, Wuhu, 241000,
thione)pyridine (Bmtp), 2,6-bis(1-ethylimidazole-2-thione)-
pyridine (Betp) and 2,6-bis(1-isopropylimidazole-2-thione)-
pyridine (Bptp) were prepared in one-pot via the reactions of
China. E-mail: wgjiasy@mail.ahnu.edu.cn
†
Electronic supplementary information (ESI) available: Crystallographic
information les (CIFs) for complex 3 are available. CCDC 1044349. For ESI and
pyridine bridged imidazolium dibromide derivatives with sulfur
crystallographic data in CIF or other electronic format see DOI:
1
0.1039/c5ra01749a
2 3
powder in the presence of K CO according to the previous
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ꢁ
Table 2 Selected bond lengths ( A˚ ) and bond angles ( ) for gold
complex 3
Au1–S1
2.340(5)
Au1–S2
2.332(4)
Au1–Cl1
2.320(4)
Au1–Cl2
2.315(5)
S1–Au1–S2
S1–Au1–Cl2
S2–Au1–Cl2
88.86(15)
178.51(17)
89.80(16)
S1–Au1–Cl1
S2–Au1–Cl1
Cl1–Au1–Cl2
90.10(17)
178.08(19)
91.22(18)
Scheme 1 Synthesis of pyridine-based SNS ligands.
When HAuCl4 was treated with three pyridine-based SNS
ligands: Bmtp, Betp and Bptp in MeOH at room temperature,
the orange crystals of gold complexes (1–3) were isolated in
moderate yields as air and moisture-stable, respectively
(Scheme 2). Complexes 1–3 were fully characterized by IR, NMR
spectroscopy, elemental analysis as well as MS. All these gold
complexes have similar characteristic peaks on NMR spectra, so
1
it is feasible to take 1 for an example. The H NMR spectrum of 1
show signals at d 4.13, 7.75, 7.85, 7.94 and 8.47 ppm, which can
be assigned to the methyl, imidazole, and pyridyl groups,
Scheme 2 Synthesis of gold complexes (1–3) with pyridine-based SNS
ligands.
respectively. Likewise, upeld shis of up to 15.4 ppm for the
13
thione carbons in their
C NMR were measured upon
complexation to gold metal, which also prove the formation of
the gold complex.
10,11
literature method (Scheme 1).
All these compounds were
Crystals of 3 suitable for X-ray crystallographic diffraction
were obtained by slow diffusion of diethyl ether into a
concentrated solution of the complex in methanol solution.
Crystallographic data and details of data collection and
renement for complex 3 are summarized in Table 1, the
important bond lengths and angles are given in Table 2. The
molecular structure of 3 is shown in Fig. 1.
stable towards air and moisture in the solid state, and exhibit
good solubility in common organic solvents. All compounds
were characterized by NMR, IR spectroscopy as well as elemental
1
analysis. The H NMR spectrum of Betp show signals at d 1.42,
4
.18, 6.82, 7.49, 8.02 and 8.88 ppm, which can be assigned to the
1
3
alkyl, imidazole, and pyridyl groups, respectively. And the
C
NMR spectra show singlet at about d 161.8 ppm for C]S group
in Betp, which is also consistent with Bmtp and Bptp.
The molecular structure of 3 is solved in the triclinic crystal
ꢀ
system and P1 space group. As can be seen, the coordination
geometry of the central gold center can be best described as a
Table 1 Crystallographic data and structure refinement parameters nearly square-planar geometry with two Cl atoms and two N
for gold complex 3
ꢁ
ꢁ
atoms (S1–Au1–S2 88.86(15) , S1–Au1–Cl1 90.10(17) ,
ꢁ
ꢁ
S1–Au1–Cl2 178.51(17) , S2–Au1–Cl1 178.08(19) , S2–Au1–Cl2
3
ꢁ
ꢁ
8
9.80(16) and Cl1–Au1–Cl2 91.22(18) ). Both sulfur atoms and
two chlorine atoms of Bptp ligand in a cis disposition. Bond
Empirical formula
Formula weight
C
18 3 5 2 2
H21AuCl N O S
706.830
Triclinic, P1ꢀ
7.981 (4)
distances around the gold ion are as expected (Au–Clav ¼ 2.318
Crystal syst., space group
A˚ and Au–Sav ¼ 2.336 A˚ ) and are comparable to the distances
˚
a (A)
˚
observed in the [AuCl
2
(S
2
CNBn
2
)] (Au–Cl ¼ 2.3116(15) A,
˚
b (A)
11.981 (6)
15.652 (8)
106.507 (6)
104.098 (6)
97.096 (6)
1361.5 (12), 2
1.724
5.873
˚
12
Au–S ¼ 2.3005(14) A).
˚
c (A)
ꢁ
a ( )
ꢁ
b ( )
ꢁ
g ( )
3
˚
Volume (A ), Z
D (mg m )
c
ꢀ3
ꢀ1
m (Mo-Ka) (mm
F(000)
q Range ( )
)
684
1.81–27.62
ꢁ
Limiting indices
Reections/unique [R(int)]
Completeness to q ( )
Data/restraints/parameters
Goodness-of-t on F
Final R indices [I > 2s(I)]
R Indices (all data)
ꢀ10, 10; ꢀ15, 14; ꢀ20, 20
6033/2740 [0.0988]
27.62 (95.2%)
6033/0/243
ꢁ
2
0.956
a
R
R
1
¼ 0.0797, wR
¼ 0.1977, wR
P
2
¼ 0.1770
¼ 0.2250
1
2
P
P
P
+
a
2
o
2
c
2
2 2 1/2
R
1
¼
o
||F | ꢀ |F
c
||/ |F
o
|; wR
2
¼ [ w(|F
| ꢀ |F
|) / w|F
o
| ]
.
Fig. 1 Crystal structure of [(Bptp)AuCl
2
]
anion, hydrogen atoms are
omitted for clarity.
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Fig. 2 View of 1D intertwined supramolecular polymeric chains in 3.
As shown in the Fig. 2, in complex 3, there are two kinds of reactions were monitored by UV-Vis spectroscopy, by recording
weak intermolecular C–H/Cl hydrogen bonds between chlo- the UV spectra of aliquots withdrawn from the reaction
rine anion and carbon of ligand. One is C–H/Cl hydrogen medium at 1 min intervals. In Fig. 3 are presented the time-
˚
ꢁ
bond (C(4)–C1(3) ¼ 3.49(2) A, C(4)–H(4)/Cl(3) ¼ 169 ) and the dependent UV-Vis spectra of the 4-NP reduction catalyzed by
˚
other is C–H/Cl hydrogen bond (C(13)–C1(3) ¼ 3.484(14) A, gold complexes catalysts. As shown in Fig. 3, upon the increase
ꢁ
C(13)–H(13)/Cl(3)
¼
174 ). These weak intramolecular of the reaction time, the intensity of the absorption band at
hydrogen bonds play a crucial role in the construction of 1D l ¼ 400 nm from 4-nitrophenolate ion becomes weaker, and at
polymeric chain structure in the solid states. And the similar the same time, an absorption band around l ¼ 300 nm appears
weak interactions have been found among the transition metal due to the formation of 4-AP, which increases in intensity
13
coordination complexes.
during the course of the reaction.
Fig. 3(A–C) provides the time-dependent UV-Vis adsorption
spectra of the reaction mixture catalyzed by gold complexes. All
gold catalysts are highly active in the 4-NP reduction, with the
Catalytic degradation of 4-NP
Catalytic reduction of 4-NP is possibly the most oen used reaction catalyzed by complex 1 reaching the maximum
reaction to test the catalytic activity of gold-based catalysts in substrate conversion of 93.2% within 13 minutes, whereas for
14
aqueous solution. 4-NP is one of the most common organic the reaction catalyzed by complex 2 and 3 the maximum
pollutants found in dye industrial and agricultural wastewa- conversion of 97.5% and 96.5% were achieved aer 11 and
ters. The reduction of 4-NP by gold-based catalysts in the 8 minutes of reaction time, respectively. Since the concentration
presence of NaBH
-AP, which is an useful compound for a wide range of appli- ESI†), the rate of reduction of 4-AP is independent of the NaBH4
cations include pharmaceuticals, corrosion treatments, and so concentration which allows this reaction to be evaluated by
4
4
reducing agent leads to the formation of of NaBH is much higher than that of 4-NP (100-fold times, see
4
15
on. The catalytic performance of the gold complexes were pseudo-rst-order kinetics. The kinetic proles of the 4-NP
evaluated in the reduction of 4-NP in the presence of NaBH4 reduction using all gold catalysts are presented in Fig. 3(D),
under homogeneous conditions in water. The catalytic
Fig. 3 UV-Vis adsorption spectra of the reduction of 4-NP by NaBH
(D) plot of ln(C /C ) of 4-NP against time for the catalysts.
4
in the presence of gold complexes (A) complex 1 (B) complex 2 (C) complex
RSC Adv., 2015, 5, 29491–29496 | 29493
3
t
0
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Table 3 Comparison of catalytic activity by gold based catalysts for
the reduction of 4-NP
The UV-Vis absorbance of gold complexes
The absorption spectra of all gold complexes and ligands
measured at room temperature in MeOH solvents were given in
Fig. 4. All ligands and gold complexes show intense absorptions
at 208 nm which can be assigned to p–p* of pyridine-based SNS
ligand. The peaks at 225 and 321 nm were found to become
weak in gold complexes, which may be attributed to the charge
transfer between pyridine-based SNS ligand and Au(III) metal
centre.
TOF
(min
Catalysts
(mol%)
ꢀ1
Catalysts
)
References
Complex 1
Complex 2
Complex 3
Au(0)@TpPa-1
0.71
0.88
1.20
0.17
0.11
1.53
0.73
1.6
10
10
10
45
46
7
This work
This work
This work
16
16
17
18
19
20
21
22
4 2
HAuCl $3H O
Au–PMMA
Fe
Fe
3
O
O
4
4
@SiO
2
–Au@mSiO
2
9
3
@P(EGDMA-co-MAA)/Au
2.5
28
57
7
Au NPs/SNTs
PDEAEMA–AuNP
0.77
0.47
0.45
Conclusion
Au@SiO
2
In conclusion, we have reported three gold complexes with
pyridine-based ligands. A combination of spectroscopic studies
and X-ray crystallographic conrmed the molecular structures
of gold complexes. And all gold complexes are highly catalyze
through the representation of ln(C
reaction time, where C and C are the concentration of 4-NP at
the beginning and at a certain reaction time respectively.
Fig. 3(D) shows the ln(C /C ) versus time for all gold catalysts
systems and good linear relationships are observed, indicating
that the reduction of 4-NP to 4-AP follows the pseudo-rst-order
kinetics. The kinetic reaction rate constants (k) were deter-
t 0
/C ) as a function of the
4
-NP reduction to 4-AP in the presence of NaBH reducing agent
4
t
0
under homogeneous conditions in water. And the complex 3
ꢀ
1
exhibits an exceptionally high TOF of 1.20 min for reduction
of 4-NP.
t
0
ꢀ
3
Sꢀ1 Experimental section
mined from the slope of the straight line which is 2.6 ꢂ 10
ꢀ
3
ꢀ1
ꢀ3 ꢀ1
for complex 1, 2.7 ꢂ 10
S
for complex 2 and 5.1 ꢂ 10
S
General
for complex 3, respectively. This result means that complex 3
possess the faster reduction rate and thus higher catalytic
activity for the reduction of 4-NP, which should be attributed to
the size and electronic effect of alkyl substituent on imidazole
ring in gold complexes (i-Pr > Et > Me).
All manipulations were carried out under nitrogen using stan-
dard schlenk and vacuum-line techniques. All solvents were
puried and degassed by standard procedures. The starting
materials, Bmtp and Bptp were synthesized according to the
10,11
procedures described in the literature.
Other chemicals were
In order to evaluate the catalytic results, we use the turnover
frequency (TOF) to determine the efficiency of our gold
complexes catalysts for 4-NP reduction and compare with
previously reported gold based catalysts. The TOF of complex 3
1
13
analytical grade and used as received. H and C NMR were
recorded on a 300 MHz or 500 MHz NMR spectrometer at room
temperature. Chemical shis (d) are given in ppm relative to
1
internal TMS and are internally referenced to residual H and
ꢀ
1
catalyst is 1.20 min , calculated by the moles of 4-NP reduced 13
per mole of gold complex per consumed time under the present
reaction conditions. As shown in Table 3, in comparison with
other gold-based catalysts, our gold complexes catalysts showed
a higher catalytic efficiency than most of other gold-based
catalysts for the reduction of 4-NP. The above results showed
C solvent resonances. IR spectra were recorded on a Nicolet
AVATAR-360IR spectrometer. Element analyses were performed
on an Elementar III vario EI Analyzer. Mass spectrometry was
performed on Bruker BIFLEX III MALDI-TOF-MS instrument.
that gold complexes with pyridine-based SNS ligands possessed Synthesis of Betp
superior high catalytic activity, which should be attributed to
the homogeneous catalytic system.
In a 100 mL round-bottomed ask tted with reux condenser
were placed 2,6-bis(1-ethylimidazolium)pyridine dibromide
3.31 g, 10 mmol), S (0.64 g, 20 mmol), K CO (2.8 g, 20 mmol)
(
2
3
and 50 mL methanol as solvent. The mixture was allowed to
reux for 8 h aer which the methanol was removed with a rotary
evaporator. The remaining solid was shaken with 2 ꢂ 30 mL
2 2
CH Cl which was then ltered and rotary evaporated. The
product was recrystallized from CH
solid. Yield: (1.92 g, 58%) Anal. Calcd for C15
2
Cl
2
/MeOH to give colorless
(331.09): C,
17 5 2
H N S
1
54.37; H, 5.17; N, 21.15. Found: C, 54.30; H, 5.25; N, 21.30. H
NMR (500 MHz CDCl
3
): 8.88 (d, J ¼ 8 Hz, pyridine, 2H), 8.02
(
t, pyridine, 1H), 7.49 (d, J ¼ 3 Hz, imidazole, 2H), 6.82 (d, J ¼ 3
Hz, imidazole, 2H), 4.18 (m, 2CH 4H), 1.42 (t, 2CH , 6H) ppm.
2
3
1
3
Fig. 4 The UV-Vis absorption of gold complexes (1 ꢂ 10ꢀ4 mol L ) in
ꢀ1
3
C NMR (500 MHz, CDCl ): d 161.8, 148.4, 139.7, 117.0, 116.3,
ꢀ
1
MeOH.
116.8, d 42.7, 13.9 ppm. IR (KBr cm ): 1143 (m) (C]S).
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Synthesis of complex 1
development of a new electronic band at l ¼ 300 nm corre-
sponding to the formation of 4-AP. A stock solution of 4-NP
In a 100 mL round-bottomed ask were placed Bmtp (152 mg,
ꢀ
4
ꢀ1
(
3 ꢂ 10 mol L ) was prepared. For the study of reduction
4
0.5 mmol), HAuCl (206 mg, 0.5 mmol), 30 mL methanol as
kinetics, 1 mL of 4-NP stock solution were transferred to the UV-
Vis cell and 1.13 mg of NaBH
solvent. The mixture was stirred at room temperature overnight
and then the solvent was removed with a rotary evaporator; the
resulting solid was washed with methanol, and then dried in
vacuo. The product was recrystallized from MeOH/hexane to
give orange powder. Yield: (137 mg, 45%). Anal. Calcd for C -
ꢀ
5
4
(1 mL, 3 ꢂ 10 mol) were added.
Upon addition of the reducing agent, the band at l ¼ 400 nm
remained unaltered until addition of the gold catalyst (1 mL,
ꢀ
8
3
ꢂ 10 mol). In this case, the electronic spectra of the reaction
1
3
mixtures were acquired at each 1 min by withdrawing 3 mL
aliquots from the reaction medium.
H Cl N S Au (606.73): C, 25.79; H, 2.17; N, 11.57. Found: C,
1
3
3 5 2
1
25.90; H, 2.28; N, 11.66. H NMR (300 MHz, CD CN) d 8.47
3
(
t, pyridine, 1H), 7.94 (d, J ¼ 2.1 Hz, imidazole, 2H), 7.85–7.87
(
d, pyridine, 2H), 7.75 (d, J ¼ 2.1 Hz, imidazole, 2H), 4.13 (s, 6H). X-ray structure determination
1
3
C NMR (500 MHz, CD
3
CN) d 147.54, 144.90, 125.90, 123.95,
Diffraction data of 3 was collected on a Bruker AXS SMART APEX
diffractometer, equipped with a CCD area detector using Mo Ka
3
+
1
5
3
(
(
21.80, 30.29. MS (MALDI-TOF): calcd for C13H N S Au
00.0278 (M ), found 500.1567 (M ). IR (KBr cm ): 3451 (m),
136 (w), 3114 (w), 3077 (w), 1595 (m), 1551 (w), 1477 (s), 1400
13 5 2
3
+
3+
ꢀ1
˚
radiation (l ¼ 0.71073 A). All the data were collected at 298 K
and the structures were solved by direct methods and subse-
w), 1317 (w), 1239 (m), 1165 (w), 1087 (w), 999 (w), 819 (m), 767
w), 748 (m), 718 (w), 680 (w), 615 (w), 543 (w).
2
quently rened on F by using full-matrix least-squares tech-
23
24
niques (SHELXL), SADABS absorption corrections were
applied to the data, all non-hydrogen atoms were rened
anisotropically, and hydrogen atoms were located at calculated
positions. All calculations were performed using the Bruker
Smart program.
Synthesis of complex 2
A procedure similar to that used for the preparation of 1 was
employed. Yield: (159 mg, 50%). Anal. Calcd for C15H17Cl N -
3 5
S
2
1
2
Au (632.97): C, 28.44; H, 2.71; N, 11.06. Found: C, 28.56; H,
1
3
.88; N, 11.00. H NMR (500 MHz, CD OD) d 8.53 (t, pyridine,
Acknowledgements
H), 8.27 (d, J ¼ 2 Hz, imidazole, 2H), 8.10 (d, J ¼ 2 Hz, imid-
azole, 2H), 8.01 (d, pyridine, 2H), 4.56–4.74 (m, 2H, CH ), 1.60 (t, We acknowledges nancial support from the National Nature
2
1
3
6
1
C
H). C NMR (500 MHz, CD OD) d 147.71, 144.49, 143.74, Science Foundation of China (21102004), and the Natural
3
24.16, 123.89, 121.28, 46.32, 14.33. MS (MALDI-TOF): calcd for Science Foundation of the Anhui Higher Education Institutions
3
+
3+
3+
15
ꢀ
17 5 2
H N S
Au 528.0591 (M ), found 528.2131 (M ). IR (KBr of China (KJ2011A146), the Project-sponsored by SRF for ROCS
1
cm ): 3410 (m), 3127 (w), 3087 (w), 2978 (w), 2935 (w), 1597 (s), and Special and Excellent Research Fund of Anhui Normal
473 (s), 1455 (s), 1381 (w), 1347 (w), 1313 (w), 1270 (m), 1222 University, National Training Programs of Innovation and
m), 1167 (w), 1091 (w), 1050 (w), 815 (w), 775 (w), 753 (w), 733 Entrepreneurship for Undergraduates (201410370040).
1
(
(
w), 703 (w), 675 (w).
Training Programs of Innovation and Entrepreneurship of
Anhui Province for Undergraduates (AH201410370040).
Synthesis of complex 3
A procedure similar to that used for the preparation of 1 was Notes and references
3 5
employed. Yield: (199 mg, 60%). Anal. Calcd for C17H21Cl N -
1
(a) A. S. K. Hashmi and G. J. Hutchings, Angew. Chem., Int.
Ed., 2006, 45, 7896–7936; (b) A. S. K. Hashmi, Chem. Rev.,
S
3
1
2
Au (662.83): C, 30.86; H, 3.20; N, 10.59. Found: C, 30.75; H,
1
3
.18; N, 11.06. H NMR (500 MHz, CD OD) d 8.53 (t, pyridine,
2007, 107, 3180–3211; (c) J. Zeng, Q. Zhang, J. Chen and
H), 8.29 (d, J ¼ 2 Hz, imidazole, 2H), 8.18 (d, J ¼ 2 Hz, imid-
Y. Xia, Nano Lett., 2009, 10, 30–35; (d) J. Oliver-Meseguer,
J. R. Cabrero-Antonino, I. Dominguez, A. Leyva-Perez and
A. Corma, Science, 2012, 338, 1452–1455; (e) C. Della Pina,
E. Falletta, L. Prati and M. Rossi, Chem. Soc. Rev., 2008, 37,
3
azole, 2H), 8.01 (d, pyridine, 2H), 5.51 (m, CH, 2H), 1.74 (d, CH ,
1
3
6H), 1.51 (d, CH , 6H). C NMR (500 MHz, CD OD) d 147.65,
3 3
1
44.45, 142.90, 124.54, 121.38, 53.61, 22.70, 21.17. MS (MALDI-
3
+
3+
TOF): calcd for C H N S Au 556.0904 (M ), found 556.3727
1
7
ꢀ1
21
5 2
2077–2095; (f) Y.-F. Han, G.-X. Jin and F. E. Hahn, J. Am.
3
+
(
1
(
7
M ). IR (KBr cm ): 3408 (m), 3033 (w), 2976 (w), 1598 (m),
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