Dual catalysis with an IrIII-AuI heterodimetallic complex: Reduction of nitroarenes by transfer hydrogenation using primary alcohols

Article abstract of DOI:10.1002/chem.201103657

A triazolyl-di-ylidene ligand has been used for the preparation of a homodimetallic complex of gold, and a heterodimetallic compound of gold and iridium. Both complexes have been fully characterized and their molecular structures have been determined by means of X-ray diffraction. The catalytic properties of these two complexes have been evaluated in the reduction of nitroarenes by transfer hydrogenation using primary alcohols. The two complexes afford different reaction products; whereas the Au^I-Au^I catalyst yields a hydroxylamine, the Ir^III-Au^I complex facilitates the formation of an imine. Copyright

Full text of DOI:10.1002/chem.201103657

DOI: 10.1002/chem.201103657
Dual Catalysis with an IrIII–AuI Heterodimetallic Complex: Reduction of
Nitroarenes by Transfer Hydrogenation using Primary Alcohols
Sara Sabater, Jose A. Mata,* and Eduardo Peris[a]
In memory of Purificaciꢀn Escribano
Abstract: A triazolyl-di-ylidene ligand
has been used for the preparation of
a homodimetallic complex of gold, and
a heterodimetallic compound of gold
and iridium. Both complexes have
been fully characterized and their mo-
lecular structures have been deter-
mined by means of X-ray diffraction.
The catalytic properties of these two
complexes have been evaluated in the
reduction of nitroarenes by transfer hy-
drogenation using primary alcohols.
The two complexes afford different re-
action products; whereas the AuI–AuI
catalyst yields a hydroxylamine, the
IrIII–AuI complex facilitates the forma-
tion of an imine.
Keywords: gold
·
heterometallic
complexes · hydrogenation · iridi-
um · oxidation · reduction
Introduction
esting approach, the use of gold nanoparticles led to high ac-
tivities and chemoselectivities in the reduction of nitroar-
enes, in which a cooperative effect between the metal and
the support played a key role.[10]
Synthesis and catalytic applications of complexes with
NHCs have become well-established in the last decade.[11]
Based on our previous experience in the field, in the last
few years we have focused our interest on the use of two
transition metals for the design of tandem catalytic process-
es. Our initial idea was to combine two mechanistically dis-
tinct catalytic cycles, each one facilitated by one of the
metals present in the catalytic system. Following this idea,
we developed well-defined
The use of two transition metals to simultaneously catalyze
a reaction can afford an interesting opportunity to achieve
new reactivity and selectivity patterns when compared with
the use of a single-metal catalytic system. In this regard,
gold is an attractive metal for dual-catalyzed reactions due
to the unique rearrangement products accessible through
gold-only catalysis.[1] Several homogenously catalyzed reac-
tions have been published in which the unique reactive
properties of organogold complexes are combined with the
catalytic properties of palladium,[2] iron,[3] nickel,[4] or rhodi-
um.[5] Furthermore, synthetic sequences combining organo-
catalysis or enzyme catalysis and gold have been de-
scribed.[6] Dual-catalyzed reactions have provided new or
improved catalytic outcomes, or complementary reactivity
to approaches that are already available through known
functionalization methods.
homo- and heterodimetallic cat-
alysts (Figure 1)[12] that were
used in a series of tandem cata-
lytic processes.[13] In particular,
the iridium–palladium complex
The reduction of nitroarenes is a useful method for the
preparation of amines or derivatives such us azo, hydrazo,
or hydroxy compounds.[7] The development of catalytic
methodologies that afford high chemo- and regioselectivity
under mild reaction conditions is an intriguing area of re-
search.[8] Recently, Beller et al. have developed novel iron-
based catalytic systems that selectively reduce nitroarenes
under transfer-hydrogenation conditions.[9] In another inter-
3 was found to be an efficient
catalyst for a series of tandem
reactions based on transfer hy-
À
drogenation and carbon carbon
coupling.[14] The same catalyst is
active in a tandem process that
has been used in the synthesis
of imines from an oxidative
Figure 1. Previously developed
dimetallic catalysts.
coupling of nitroarenes with
benzylalcohols by a “borrow-
ing-hydrogen” procedure.[15] In
[a] S. Sabater, J. A. Mata, E. Peris
Departamento de Quꢀmica Inorgꢁnica y Orgꢁnica
Universitat Jaume I. Av. Sos Baynat s/n
Castellꢂn, 12071 (Spain)
an extension of our work, and
encouraged by the unique properties of organogold com-
plexes, we now describe the preparation of dimetallic com-
plexes of gold and iridium–gold. These complexes have
been fully characterized, and their catalytic properties have
been studied in the reduction of nitroarenes using alcohols.
E-mail: jmata@qio.uji.es
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201103657.
6380
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FULL PAPER
Results and Discussion
Synthesis and characterization: The new dimetallic com-
plexes 7 and 8 were obtained as described in Scheme 1. The
Figure 2. Molecular diagram of complex 7. Ellipsoids shown at 50%
probability level. Hydrogen atoms are omitted for clarity. Selected bond
lengths [ꢄ] and angles [8]: Au(1)–C(5) 1.953(11), Au(2)–C(1) 1.982(10),
Au(1)–Cl(1) 2.270(3), Au(2)–Cl(2) 2.258(3), C(5)–Au(1)–Cl(1) 178.1(3),
C(1)–Au(2)–Cl(2) 176.9(3).
Scheme 1. Synthesis of 7 and 8.
for Au(1) and 176.98 for Au(2). The intramolecular distance
À
digold complex 7 was obtained in high yield (ca. 80%) by
a transmetallation procedure from the silver carbene deriva-
tives described by Bertrand and co-workers.[16] This protocol
between the gold atoms is 6.02 ꢄ and the average Au C dis-
tance is 1.97 ꢄ.[18] The molecule is essentially planar except
for the methyl of the ethyl group. Interestingly, the crystal
I
I
À
involves the reaction of [AuCl
N
packing of complex 7 shows an intermolecular Au Au in-
teraction contact distance of 3.26 ꢄ.[19] This aurophilic inter-
action results in the formation of polymeric zig-zag chains in
the crystal packing (Figure 3). The ethyl group points out-
fide) with 4-ethyl-1,2-dimethyltriazolium bistetrafluorobo-
rate (5), in the presence of two equivalents of silver acetate,
at room temperature in acetonitrile. The reaction affords
the digold complex 7 as a white solid in high yield (80%).
Attempts to obtain the same complex but using the “ditz”
ligand (derived from the 1,2,4-trimethyltriazolium salt),[17]
were unsuccessful due to solubility problems and very low
yields. The IrIII–AuI heterodimetallic complex 8 was ob-
tained by reaction of [AuClACTHNUTRGNE(UNG SMe2)] with triazoliumylidene-
iridium (6)[14] and silver oxide in acetonitrile at room tem-
perature. Complex 8 was isolated as a pale-yellow solid in
high yield (70%). Complexes 7 and 8 are stable in the solid
state and can be handled in air.
Figure 3. Crystal packing of complex 7 showing the zig-zag polymeric
chain.
The coordination of two gold units to 4-ethyl-1,2-dime-
thyltriazol-di-ylidene was confirmed by NMR spectroscopic
analysis. The first indication that the coordination of the
ligand had occurred was the disappearance of the signal at
d=10.03 ppm of the bisazolium salt 5. Complex 7 exhibited
a characteristic 13C NMR shift at d=174.5 ppm for the car-
bene carbon, also confirming the coordination of the NHC
to the metal center. For the heterodimetallic complex 8, the
most representative 13C NMR signals appeared at d=177.0
and 162.5 ppm, and were attributed to the metalated car-
bene carbon atoms bound to Au and Ir, respectively. The di-
metallic nature of these two complexes was also confirmed
by high-resolution mass spectroscopy, in which the main
peaks were found at m/z 595.0235 [MÀCl+CH3CN]+ and
706.0634 [MÀCl]+ for 7 and 8, respectively.
side the polymeric chain, preventing strong chain-to-chain
À
aurophilic interactions, although the Au Au distance be-
tween adjacent chains is 3.50 ꢄ, which can still be consid-
ered a weak aurophilic interaction.[20] We believe that these
interactions may be responsible of the low solubility found
for the analogous complex using the 1,2,4-trimethyltriazoli-
um salt.
The molecular structure of complex 8 (Figure 4) contains
a “IrCp*Cl2” fragment connected to a “AuCl” unit by the
triazolyl-di-ylidene bridge. The iridium bond lengths and
angles about the iridium sphere lie in the expected range,
A complete determination of the molecular structures of
7 and 8 was achieved by means of X-ray diffraction studies.
The crystal data and experimental details are given in the
Supporting Information. Figure 2 and Figure 4 show the mo-
lecular diagrams of 7 and 8 with selected bond lengths and
angles.
Figure 4. Molecular diagram of complex 8. Ellipsoids shown at 50%
probability level. Hydrogen atoms omitted for clarity. Selected bond
lengths [ꢄ] and angles [8]: Ir(1)–C(1) 2.027(14), Ir(1)–Cl(1) 2.407(3),
The molecular structure of 7 (Figure 2) consists of two fa-
À
cially opposed Au Cl fragments connected by the 4-ethyl-1,
2-dimethyltriazol-3,5-diylidene ligand. The coordination
Ir(1)–Cl(2) 2.413(3), Ir(1)–C
1.807, Au(2)–C(2) 1.962(13), Au(2)–
centr
about the two metal centers is linear, with angles of 178.18
Cl(3) 2.273(4), Cl(1)–Ir(1)–C(1) 89.4(3), C(2)–Au(2)–Cl(3) 177.3(4).
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J. A. Mata et al.
when compared to similar complexes reported by us for the
same metal fragment containing the triazolyl-di-ylidene li-
gand.[12b] The coordination about the gold center is linear,
poses two possible reaction pathways. One is the direct re-
duction of nitroarene, which involves a sequential hydroge-
nation/dehydration process via nitroso and hydroxy inter-
mediates. The second route involves a condensation reaction
between the nitroso and hydroxy products leading to the
azoxy compound, which is then hydrogenated/dehydrated to
afford the azo compound. The latter compound is subse-
quently hydrogenated to the hydrazo, which finally gener-
ates the amine. For the hydrogenation of nitroarenes, the
traditional process typically involves the use of molecular
hydrogen and Pd/C. This catalytic system is very active in
the hydrogenation of many functional groups, although the
main drawback is the lack of chemoselectivity.
À
with an angle of 177.3(4)8, and an Au C distance of
1.962(13) ꢄ. The crystal packing of complex 8 shows the for-
mation of dimers. Two molecules in an anti disposition show
hydrogen-bonding interactions between one chloride and
one methyl group of the ligand (Figure 5). In general, these
We recently studied the reduction of nitrobenzene deriva-
tives using benzyl alcohol as hydrogen donor.[15] The use of
this primary alcohol leads to the formation of benzaldehyde,
which, in turn, condenses with the amine produced, generat-
ing an imine. Under similar reaction conditions, we have
now tested catalysts 7 and 8 (Table 1). The results show a dif-
ferent catalytic outcome depending on the catalyst used.
As can be seen in Table 1, both iridium-containing com-
plexes (1 and 8) provided good to excellent yields of the
imine. On the other hand, the gold catalyst 7, afforded mod-
erate to good yields of the hydroxy and azo compounds
(Table 1, entries 1 and 4). Because the overall reaction in-
volves the concomitant formation of water, the reaction
yields were improved by adding molecular sieves to the re-
action media (compare Table 1, entries 4–6 with 1–3).
The Ir–Au heterodimetallic complex 8 provided the best
catalytic outcomes in this reaction (Table 1, entries 2, 5, 8,
and 11). The differences in activity are very significant in
the case of 4-substituted nitrobenzenes. In the reduction of
p-methylnitrobenzene (Table 1, entries 7–9), the gold com-
plex 7 is completely inactive, whereas the iridium-containing
complexes 1 and 8 show moderate to excellent catalytic out-
comes. Interestingly, the heterodimetallic complex 8 is more
effective than the only-iridium
Figure 5. Crystal packing of complex 8 showing the dimers that form in
the solid state.
types of chloride–hydrogen interactions are not very strong,
À
but in this case the distance Cl Cmethyl of 3.52 ꢄ is signifi-
cantly shorter.[21] We did not find any AuI–AuI interaction
contact as observed for compound 7.
Catalytic studies: To test the catalytic properties of 7 and 8,
we evaluated the catalytic reduction of nitroarenes. We de-
cided to study this important transformation instead of de-
signing a tandem process by the combination of reactions
typically catalyzed by IrIII and AuI because we wanted to
assess the catalytic outcomes of using 7 and 8 and, especial-
ly, to test whether there is any influence of using two metals
with distinct reactivity patterns in 8 on the distribution of re-
action products of this interesting reaction. Many intermedi-
ates have been proposed to be involved in the mechanism of
the reduction of nitrobenzene leading to aniline
(Scheme 2).[22] The most widely accepted mechanism pro-
complex 1 both in terms of yield
and selectivity, thus providing
a neat example of a dual catalyt-
ic system. We also performed
some reactions using nitroben-
zene substrates with electron-ac-
cepting groups (F and p-CF3),
but the catalytic outcomes were
negligible. Additionally, we stud-
ied the catalytic activity of a mix-
ture of
1
and
7
(Table 1,
entry 13), and observed that the
activity of the mixture of the
two homodimetallic complexes
afforded less activity than that
shown by the heterodimetallic
complex 8 (Table 1, entry 5). In
this regard, we recently ob-
served that a series of triazolyl-
Scheme 2. Catalyzed tandem reaction between nitrobenzene and benzyl alcohol as solvent and reagent: a) two
pathways in the reduction of nitroarene; b) alcohol oxidation, and c) amine/aldehyde condensation products. di-ylidene-based heterodimetal-
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Chem. Eur. J. 2012, 18, 6380 – 6385

Reduction of Nitroarenes
FULL PAPER
Table 1. Catalyst screening for the reaction of nitrobenzene and benzyl
alcohol.[a]
Scheme 3. Mechanistic investigation using azoxybenzene.
Entry
Cat
R
t
Hydroxy
[%][a]
Azo
Imine
[%][a]
Amine
[%][b]
[h]
[%][a]
tion of the imine when using the iridium-containing com-
plexes 1 and 8 goes through the direct condensation route.
1
2
3
7
8
1
7
8
1
7
8
1
7
8
1
H
H
H
H
H
H
Me
Me
Me
OMe
OMe
OMe
H
22
22
22
15
15
15
15
15
15
15
15
15
15
55
–
–
81
–
–
–
–
–
–
17
–
–
9
–
–
–
–
–
–
–
–
–
4
96
60
–
99
86
–
93
48
–
41
7
–
2
–
–
–
12
–
–
–
–
4[c]
5[c]
6[c]
7
Conclusion
8
9
10
11
12
13[c]
We have prepared two new Au-based complexes with a tria-
zolyl-di-ylidene ligand, thus illustrating the chemical versa-
tility of this ligand. The catalytic properties of both com-
plexes (Au–Au and Au–Ir) have been studied in the cou-
pling of nitrobenzene with benzyl alcohol to form N-benzyli-
deneaniline. The results show different activities and prod-
uct formation depending of the catalyst employed. Under
the same reaction conditions, the activity of the heterodime-
tallic IrIII–AuI complex is higher than the sum of the homo-
dimetallic catalysts IrIII–IrIII and AuI–AuI, and studies on the
mechanism of the reaction indicate that the iridium-contain-
ing catalyst operates through a direct condensation route.
–
–
–
–
–
9
7+1
81
[a] Reagents and conditions: nitrobenzene (0.3 mmol), benzyl alcohol (as
solvent and reagent; 10 mmol), Cs2CO3 (0.3 mmol), anisole (as internal
reference; 0.3 mmol), 1008C, aerobic conditions. [b] Yield determined by
GC chromatographic analysis. [c] Using 4 ꢄ molecular sieves.
lic complexes afforded better catalytic outcomes than the re-
lated mixture of homodimetallic species.[12b,13b,14,15] Although
we performed some experiments to determine the origin of
this dimetallic cooperativity, none of our results were con-
clusive. For example, cyclic voltammetric studies performed
on 1 and 7, and other ditz-based heterodimetallic studies af-
forded irreversible waves that provided very little informa-
tion. UV/Vis analyses of the same compounds did not pro-
vide any indication of charge-transfer bands, which are an
indication of a clear electronic communication between the
metals. At this point, we do not have any experimental evi-
dence to prove that there is any electronic communication
between the metals connected by the ditz ligands. To shed
some light on this important point, theoretical investigations
are underway.
From the data shown in Table 1, it seems clear that the di-
metallic complex of gold (complex 7), tends to follow the
condensation route (Scheme 2), and stops at the formation
of azobenzene. On the other hand, the iridium-containing
complexes 1 and 8, afford the final imine, without any of the
possible reaction intermediates shown in Scheme 2 being de-
tected. To shed some light on the reaction mechanism fol-
lowed by catalysts 1 and 8, we performed the reaction start-
ing from azoxybenzene in the presence of benzyl alcohol
and a base (Scheme 3).[23] The results show that, in all cases,
the reaction stops at the formation of azobenzene, which is
the final product when the reaction starts from azoxyben-
zene. In a parallel experiment, when the same reaction was
performed using azobenzene as starting material, after ten
hours reaction at 1008C, the only product observed was the
same starting material. These results suggest that the forma-
Experimental Section
General Procedures: All manipulations were carried out under nitrogen
using standard Schlenk techniques and high vacuum. [IrCp*Cl2]2,[24]
[ClAuSMe2],[25] 5,[26] and 6[12b] were prepared according to literature pro-
cedures. Anhydrous solvents were either distilled from appropriate
drying agents or purchased from Aldrich and degassed prior to use by
purging with dry nitrogen and kept over molecular sieves. All other re-
agents were used as received from commercial suppliers. NMR spectra
were recorded with Varian spectrometers operating at 300 or 500 MHz
(1H NMR) and 75 and 125 MHz (13C NMR), respectively, and referenced
to SiMe4 (d in ppm and J in hertz). NMR spectra were recorded at RT
with CDCl3, CD3CN, or [D6]DMSO unless otherwise stated. A QTOF I
(quadrupole-hexapole-TOF) mass spectrometer with an orthogonal Z-
spray-electrospray interface (Micromass, Manchester, UK) was used. The
drying gas as well as the nebulizing gas was nitrogen at a flow of
400 LhÀ1 and 80 LhÀ1, respectively. The temperature of the source block
was set to 1208C and the desolvation temperature to 1508C. A capillary
voltage of 3.5 KV was used in the positive scan mode and the cone volt-
age was set to 30 V. Mass calibration was performed using a solution of
sodium iodide in isopropanol/water (50:50) from m/z 150 to 1000 a.m.u.
Sample solutions (ca. 1ꢅ10À4 m) were infused by using a syringe pump di-
rectly connected to the interface at a flow of 10 mLminÀ1. A 1 mgmLÀ1 so-
lution of 3,5-diiodo-l-tyrosine was used as lock mass.
X-ray data collection was performed at RT with a Siemens Smart CCD
diffractometer using graphite monochromated MoKa radiation (l=
0.71073 ꢄ) with a nominal crystal-to-detector distance of 4.0 cm. Single
crystals were mounted on a glass fiber in a random orientation. A hemi-
sphere of data was collected based on three w-scan runs (starting w=
À288) at values f=0, 90, and 180 with the detector at 2q= 288. During
each of these runs, frames (606, 435, and 230, respectively) were collected
at 0.38 intervals. The crystal data and experimental details are given in
the Supporting Information.[27]
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J. A. Mata et al.
General procedure for catalytic reactions: Nitroarene (0.3 mmol), benzyl
alcohol (used as reagent and solvent; 10 mmol), catalyst (1% metal),
Cs2CO3 (0.3 mmol), and anisole (as the internal reference; 0.3 mmol)
were placed in a capped vessel containing a stirrer bar. The resulting mix-
ture was vigorously stirred at 1008C under aerobic conditions for the
given reaction time. The products were identified with a GC–MS-QP2010
(Shimadzu) gas chromatograph/mass spectrometer equipped with a Te-
knokroma (TRB-5MS, 30 m, 0.25 ꢅ0.25 mm) column, and the spectra ob-
tained were compared to standard spectra. The yields, conversion, and
product selectivity were determined with a GC-2010 (Shimadzu) gas
chromatograph equipped with a FID and a Teknokroma (TRB-5MS,
30 m, 0.25 ꢅ0.25 mm) column.
48, 8243; c) L. A. Jones, S. Sanz, M. Laguna, Catal. Today 2007, 122,
403; d) B. Panda, T. K. Sarkar, Chem. Commun. 2010, 46, 3131; e) Y.
Shi, S. D. Ramgren, S. A. Blum, Organometallics 2009, 28, 1275;
f) Y. L. Shi, S. M. Peterson, W. W. Haberaecker, S. A. Blum, J. Am.
Chem. Soc. 2008, 130, 2168; g) Y. L. Shi, K. E. Roth, S. D. Ramgren,
S. A. Blum, J. Am. Chem. Soc. 2009, 131, 18022; h) A. L. Casado, P.
Espinet, J. Am. Chem. Soc. 1998, 120, 8978.
[3] A. S. K. Hashmi, L. Molinari, Organometallics 2011, 30, 3457.
[4] J. J. Hirner, S. A. Blum, Organometallics 2011, 30, 1299.
[5] a) Y. L. Shi, S. A. Blum, Organometallics 2011, 30, 1776; b) P. J.
Zhao, C. D. Incarvito, J. F. Hartwig, J. Am. Chem. Soc. 2007, 129,
1876; c) A. S. K. Hashmi, P. Haufe, C. Schmid, A. R. Nass, W. Frey,
Chem. Eur. J. 2006, 12, 5376.
[6] a) A. S. K. Hashmi, C. Hubbert, Angew. Chem. 2010, 122, 5360;
Angew. Chem. Int. Ed. 2010, 49, 1010; b) A. S. K. Hashmi, F. Ata, P.
Haufe, F. Rominger, Tetrahedron 2009, 65, 1919; c) M. Asikainen, N.
Krause, Adv. Synth. Catal. 2009, 351, 2305.
Synthesis of 7: The reactions were shielded from light. Tetrafluoroborate
2-ethyl 1,4-dimethyl triazolium salt 5 (93 mg, 0.31 mmol) and silver ace-
tate (104 mg, 0.62 mmol, 2 equiv.) were heated to reflux under nitrogen
in anhydrous THF (10 mL). The mixture was cooled to RT and anhy-
drous acetonitrile (20 mL), [ClAuSMe2] (183 mg, 0.62 mmol) and KCl
(70 mg, 0.93 mmol) were added. The mixture was stirred at RT overnight,
then the suspension was filtered through Celite and the solvents were
concentrated under reduced pressure. Crystallization from acetonitrile/di-
ethyl ether gave 7 as a white crystalline solid (147 mg, 80%). 1H NMR
[7] H. U. Blaser, Science 2006, 313, 312.
[8] H. U. Blaser, H. Steiner, M. Studer, ChemCatChem 2009, 1, 210.
[9] a) G. Wienhçfer, I. Sorribes, A. Boddien, F. Westerhaus, K. Junge,
H. Junge, R. Llusar, M. Beller, J. Am. Chem. Soc. 2011, 133, 12875;
b) R. V. Jagadeesh, G. Wienhçfer, F. A. Westerhaus, A. E. Surkus,
M. M. Pohl, H. Junge, K. Junge, M. Beller, Chem. Commun. 2011,
47, 10972.
[10] a) A. Grirrane, A. Corma, H. Garcia, Science 2008, 322, 1661; b) M.
Boronat, P. Concepcion, A. Corma, S. Gonzalez, F. Illas, P. Serna, J.
Am. Chem. Soc. 2007, 129, 16230; c) K. Junge, B. Wendt, N. Shaikh,
M. Beller, Chem. Commun. 2010, 46, 1769; d) R. G. de Noronha,
C. C. Romao, A. C. Fernandes, J. Org. Chem. 2009, 74, 6960; e) Y.
Sunada, H. Kawakami, T. Imaoka, Y. Motoyama, H. Nagashima,
Angew. Chem. 2009, 121, 9675; Angew. Chem. Int. Ed. 2009, 48,
9511; f) L. He, L. C. Wang, H. Sun, J. Ni, Y. Cao, H. Y. He, K. N.
Ean, Angew. Chem. 2009, 121, 9702; Angew. Chem. Int. Ed. 2009,
48, 9538.
[11] a) W. A. Herrmann, M. Elison, J. Fischer, C. Kocher, G. R. J. Artus,
Chem. Eur. J. 1996, 2, 772; b) W. A. Herrmann, M. Elison, J. Fischer,
C. Kocher, G. R. J. Artus, Angew. Chem. 1995, 107, 2602; Angew.
Chem. Int. Ed. Engl. 1995, 34, 2371; c) M. Poyatos, J. A. Mata, E.
Peris, Chem. Rev. 2009, 109, 3677; d) S. Dꢀez-Gonzꢁlez, N. Marion,
S. P. Nolan, Chem. Rev. 2009, 109, 3612; e) S. P. Nolan, Acc. Chem.
Res. 2011, 44, 91; f) J. A. Mata, M. Poyatos, Curr. Org. Chem. 2011,
15, 3309; g) F. E. Hahn, Angew. Chem. 2006, 118, 1374; Angew.
Chem. Int. Ed. 2006, 45, 1348; h) F. E. Hahn, M. C. Jahnke, Angew.
Chem. 2008, 120, 3166; Angew. Chem. Int. Ed. 2008, 47, 3122.
[12] a) E. Mas-Marzꢁ, J. A. Mata, E. Peris, Angew. Chem. 2007, 119,
3803; Angew. Chem. Int. Ed. 2007, 46, 3729; b) A. Zanardi, R. Cor-
beran, J. A. Mata, E. Peris, Organometallics 2008, 27, 3570; c) A.
Zanardi, J. A. Mata, E. Peris, Organometallics 2009, 28, 1480.
[13] a) A. Zanardi, J. A. Mata, E. Peris, Organometallics 2009, 28, 4335;
b) A. Zanardi, J. A. Mata, E. Peris, Chem. Eur. J. 2010, 16, 13109.
[14] A. Zanardi, J. A. Mata, E. Peris, J. Am. Chem. Soc. 2009, 131,
14531.
(300 MHz, [D6]DMSO): d=4.32 (c, 3J
4.10 (s, 6H; NCH3), 1.50 ppm (t, 3J
(H,H)=7.2 Hz, 3H; NCH2CH3);
ACHTUGNTRENN(NUG H,H)=7.5 Hz, 2H; NCH2CH3),
AHCTUNGTRENNUNG
13C{1H} NMR (75 MHz, [D6]DMSO): d=174.9 (C-Au carbene), 48.7
(NCH2 CH3), 38.7 (NCH3), 16.9 ppm (NCH2CH3); MS (ESI, Cone 20 V):
m/z: 595 [MÀCl+CH3CN]+; HRMS (ESI-TOF-MS, +ve): m/z: monoiso-
topic peak calcd for C8H14N4Au2Cl: 595.0238 [MÀCl+CH3CN]+; found:
595.0235 (er 0.5 ppm); elemental analysis calcd (%) for
C6H11N3Au2Cl2·2H2O (626.04): C 11.51, H 2.42, N 6.71; found: C 11.25, H
2.78, N 6.62.
Synthesis of 8: The reactions were shielded from light. Compound 6
(100 mg, 0.17 mmol) and Ag2O (20 mg, 0.085 mmol) were stirred under
nitrogen in anhydrous THF (10 mL) at RT for 8 h. Anhydrous acetoni-
trile (20 mL), [ClAuSMe2] (50 mg, 0.17 mmol), and KCl (18 mg,
0.24 mmol) were then added and the mixture was stirred at RT overnight.
The final suspension was filtered through Celite and the solvents were
concentrated under reduced pressure. Crystallization from acetonitrile/di-
ethyl ether gave 8 as a yellow crystalline solid (88 mg, 70%). 1H NMR
(500 MHz, CD3CN): d=4.23 (s, 3H; NCH3), 4.14 (s, 3H; NCH3), 4.09 (s,
3H; NCH3), 1.61 ppm (s, 15H;
CD3CN): d=175.0 (Ccarbene-Au), 164.9 (Ccarbene-Ir), 94.1 (C
(NCH3) 39.2 (NCH3), 38.8 (NCH3), 9.2 ppm (C5A(CH3)5); MS (ESI, Cone
C5ACHTUNTGRENNUNG
(CH3)5); 13C{1H} NMR (125 MHz,
5A(CH3)5), 41.1
CTHUNGTRENNUNG
CTHUNGTRENNUNG
15 V): m/z: 706 [MÀCl]+; HRMS (ESI-TOF-MS, +ve): m/z: monoiso-
topic peak calcd for C15H24N3IrAuCl2: 706.0628 [MÀCl]+; found:
706.0634 (er 0.8 ppm); elemental analysis calcd (%) for
C15H24N3AuIrCl3·H2O·CH3CN (800.98): C 25.49, H 3.65, N 6.99; found: C
25.95, H 3.88, N 6.97.
X-ray crystal data: CCDC-854420 (7) and CCDC-854421 (8) contain the
supplementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
[15] A. Zanardi, J. A. Mata, E. Peris, Chem. Eur. J. 2010, 16, 10502.
[16] O. Guerret, S. Sole, H. Gornitzka, G. Trinquier, G. Bertrand, J. Or-
ganomet. Chem. 2000, 600, 112.
Acknowledgements
[17] O. Guerret, S. Sole, H. Gornitzka, M. Teichert, G. Trinquier, G. Ber-
trand, J. Am. Chem. Soc. 1997, 119, 6668.
We thank the MCINN of Spain (CTQ2008–04460) and Bancaixa
(P1.1B2010–02 and P1.1B2008–16) for financial support. We would also
like to thank the ꢆBancaixaꢇ for a fellowship (S.S.). The authors are grate-
ful to the Serveis Centrals dꢇInstrumentaciꢂ Cientꢀfica (SCIC) of the Uni-
versitat Jaume I for providing us with spectroscopic facilities.
[18] a) A. Laguna, T. Lasanta, J. M. Lopez-de-Luzuriaga, M. Monge, P.
Naumov, M. Elena Olmos, J. Am. Chem. Soc. 2010, 132, 456;
b) J. M. Lꢂpez-de-Luzuriaga, M. Monge, M. E. Olmos, M. Rodri-
guez-Castillo, A. Laguna, F. Mendizabal, Theor. Chem. Acc. 2011,
129, 593.
[19] a) R. L. White-Morris, M. M. Olmstead, F. L. Jiang, D. S. Tinti, A. L.
Balch, J. Am. Chem. Soc. 2002, 124, 2327; b) H. Schmidbaur, A.
Schier, Chem. Soc. Rev. 2008, 37, 1931.
[20] L. Ray, M. M. Shaikh, P. Ghosh, Inorg. Chem. 2008, 47, 230.
[21] A. Singh, A. Ramanan, D. Bandyopadhyay, Cryst. Growth Des.
2011, 11, 2743.
[1] J. J. Hirner, Y. L. Shi, S. A. Blum, Acc. Chem. Res. 2011, 44, 603.
[2] a) A. S. K. Hashmi, R. Dopp, C. Lothschꢈtz, M. Rudolph, D. Riedel,
F. Rominger, Adv. Synth. Catal. 2010, 352, 1307; b) A. S. K. Hashmi,
C. Lothschꢈtz, R. Dopp, M. Rudolph, T. D. Ramamurthi, F. Ro-
minger, Angew. Chem. 2009, 121, 8392; Angew. Chem. Int. Ed. 2009,
[22] F. Haber, Z. Elektrochem. 1898, 22, 506.
6384
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 6380 – 6385

Reduction of Nitroarenes
FULL PAPER
[23] H. U. Blaser, C. Malan, B. Pugin, F. Spindler, H. Steiner, M. Studer,
Adv. Synth. Catal. 2003, 345, 103.
[24] R. G. Ball, W. A. G. Graham, D. M. Heinekey, J. K. Hoyano, A. D.
McMaster, B. M. Mattson, S. T. Michel, Inorg. Chem. 1990, 29, 2023.
[25] R. Uson, A. Laguna, M. Laguna, D. A. Briggs, H. H. Murray, J. P.
Fackler, Inorg. Synth. 1989, 26, 85.
[27] a) G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112; b) O. V.
Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Pusch-
mann, J. Appl. Crystallogr. 2009, 42, 339.
Received: November 21, 2011
[26] T. J. Curphey, K. S. Prasad, J. Org. Chem. 1972, 37, 2259.
Published online: March 27, 2012
Chem. Eur. J. 2012, 18, 6380 – 6385
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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