New heterogenized gold(I)-heterocyclic carbene complexes as reusable catalysts in hydrogenation and cross-coupling reactions

Article abstract of DOI:10.1002/adsc.200606163

Mononuclear unsymmetrical N-heterocyclic carbene-gold complexes and the corresponding solid catalysts in which a gold-carbene complex has been immobilized on silica gel, ordered mesoporous silica (MCM-41), and delaminated zeolite (ITQ-2) have been prepared. These new catalysts have been tested in the hydrogenation of alkenes and the Suzuki cross-coupling reaction to afford selectively non-symmetrical biaryls. These reactions were studied with the soluble as well as with the heterogenized counterpart catalysts. The high accessibility introduced by the structure of the supports allows the preparation of highly efficient immobilized catalysts with TOFs up to 400 h^-1. Moreover, the heterogenized complexes were reused and no deactivation of the catalysts can be observed.

Full text of DOI:10.1002/adsc.200606163

FULL PAPERS
DOI: 10.1002/adsc.200606163
New Heterogenized Gold(I)-Heterocyclic Carbene Complexes as
Reusable Catalysts in Hydrogenation and Cross-Coupling Reac-
tions
A. Corma,a,* E. Gutiérrez-Puebla,b M. Iglesias,b,* A. Monge,b S. Pérez-Ferreras,b,c
and F. Sánchezc,*
a
Instituto de Tecnología Química, UPV-CSIC, Avda. de los Naranjos, s/n, 46022 Valencia, Spain
Fax: (+49)-6221-487-672; e-mail: acorma@itq.upv.es
Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain
b
Fax: (+34)-91-372-0623; e-mail: marta.iglesias@icmm.csic.es
Instituto de Química Orgánica General, CSIC, C/Juan de la Cierva, 3, 28006 Madrid, Spain
c
Fax: (+34)-91-564-4872; e-mail: felix-iqo@iqog.csic.es
Received: April 5, 2006; Accepted: July 11, 2006
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: Mononuclear unsymmetrical N-heterocy- counterpart catalysts. The high accessibility intro-
clic carbene-gold complexes and the corresponding duced by the structure of the supports allows the
solid catalysts in which a gold-carbene complex has preparation of highly efficient immobilized catalysts
been immobilized on silica gel, ordered mesoporous with TOFs up to 400 hꢀ1. Moreover, the heterogen-
silica (MCM-41), and delaminated zeolite (ITQ-2) ized complexes were reused and no deactivation of
have been prepared. These new catalysts have been the catalysts can be observed.
tested in the hydrogenation of alkenes and the
Suzuki cross-coupling reaction to afford selectively
non-symmetrical biaryls. These reactions were stud- Keywords: cross-coupling; gold; heterogenized; hy-
ied with the soluble as well as with the heterogenized drogenation; NHC ligands
Introduction
ments in the field of metal-mediated catalysis over
recent years and valuable contributions have been
Recently there has been a resurgence of interest in made to a diversity of reactions.[7] Commonly, NHCs
the chemistry of gold compounds in general and that have been described as alternatives to tertiary phos-
of gold(I) compounds in particular. A major driving phines in terms of bonding and reactivity,[8] but metal-
force for this interest has been the utility of soluble carbene complexes are often more stable than similar
gold compounds, and the observation that gold nano- metal-phosphine complexes,[9] and NHCs have been
particles and supported gold nanoparticles can stabi- used as alternatives to phosphines as ligands in a
lize cationic gold and this is active, for instance, for broad range of transition metal catalysts owing to
[2]
CO oxidation,[1] C C bond formation, and selective their special donor properties.[8] As a result, a large
ꢀ
oxidation of alcohols.[3] Moreover, the use of Au com- variety of metal-NHC complexes are known, many of
plexes in homogeneous catalysis has undergone a ren- which have been successfully used in catalytic applica-
aissance as of late and spectacular achievements have tions.[10] Interestingly, most studies focussing on cata-
recently been reported.[4] Among Au(I) compounds, lysts incorporating NHC ligands have revolved
there has been considerable success in the preparation around the platinum metal groups. In numerous in-
of alkynylgold complexes.[5] These are among the stances simple substitution reaction routes involving
most stable organogold complexes.[5] One interesting replacement of phosphines by NHC ligands lead to
aspect of these complexes has been the ability to ex- higher catalytic activity as well as improved thermal
hibit rich photophysical and photochemical behav- stability of the resulting organometallic complex. The
iour.[6]
common knowledge that NHC ligands should be con-
The application of N-heterocyclic carbene (NHC) sidered as simple s donors is being replaced by the
ligands represents one of the most important develop- idea that NHCs are electronically much more flexible.
Adv. Synth. Catal. 2006, 348, 1899 – 1907
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A. Corma et al.
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Both filled and empty p, p* orbitals on the NHC ring
can be deeply involved in the bonding to the metal.
They can contribute to stabilize electron-rich metals
through a d!p* back-donation scheme, but they are
so flexible that they can also stabilize electron-defi-
cient metals through a p!d donation scheme.[11]
Au(I)-carbene complexes have been known since
more than a quarter of a century,[12] but chemical re-
actions have been less studied than those of Au(I)-
phosphine complexes. Most publishing works dealing
with Au(I)-carbenes concerns oxidative addition reac-
Scheme 1. Synthesis of imidazolium salts 2 and 3.
Wang and Lin[18] reported that simple imidazolium
(carbene)
tions.[13] The first example in literature for the use of salts react with Ag2O to yield Ag(I)-bis
ACHTREUNG
a gold(I)-carbene complex in homogeneous catalysis complexes which can then be used as possible transfer
was reported for the addition of water to 3-hexyne in agents to synthesize Au(I)-carbene complexes. There-
the presence of a Lewis acid as co-catalyst.[14] Recent- fore the silver(I)-carbene complexes 1–3Ag were syn-
ly Nolan et al. reported the synthesis and structural thesized by stirring imidazolium salts 1–3 in CH2Cl2
characterization of a series of symmetric N-heterocy- with Ag2O for 4 h. Subsequent work-up of the filtered
clic carbene-gold(I) complexes and their application solution afforded the complexes 1–3Ag ([Ag-
for carbene transfer reactions from ethyl diazoace-
U
G
cross-coupling and hydrogenation reactions.
chloride 1–3Au in nearly quantitative yield (80–92%).
In a typical reaction the silver complex was stirred
with the gold precursor in CH2Cl2 solution for 3 h. af-
terwards the reaction mixture was filtered to remove
the precipitated AgI. Complexes 1–3Au(I) are readily
Results and Discussion
The symmetrical 1,3-bis-(2,4,6-trimehylphenyl)imida- soluble in most common polar organic solvents (di-
zolium salt 1 was obtained as reported in the litera- chloromethane, THF), but insoluble in hexane or di-
ture[16] and the unsymmetrical salts 2 and 3 were syn- ethyl ether. The Au-carbene compounds are thermally
thesized by reacting propyl iodide with 1-(2,4,6-trime- stable up to >2508C.
thylphenyl)-1H-imidazole in acetonitrile (for 2) or di-
The complexes were characterized by 1H and
glyme (for 3) according to Scheme 1. Alternatively, 13C NMR spectroscopy, elemental analysis and mass
we have found that microwave activation without sol- spectrometry. The 13C NMR resonances of the car-
vent affords the imidazolium salts cleanly and quanti- bene atoms in complexes 2–3Au occur at d=170.78
tatively in 15 seconds at 350 W.[17]
and 171.50, respectively. This signal is shifted down-
Scheme 2. Synthesis of gold-carbene complexes.
1900
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Heterogenized Gold(I)-Heterocyclic Carbene Complexes
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field compared to the corresponding imidazolium 2- 1.99(1) Å in both molecules and suggest a single-bond
carbon resonance (141.04 for 2, 140.34 for 3). For character, in good accordance with their strong s-
both Au(I)-carbene complexes the most prominent donor characteristics, comparable to those reported
ꢀ
peak in the mass spectra is the [(NHC)Au]+ fragment for other Au(I)(carbene) complexes.[19] The Au Cl
A
indicating
a
molecular structure of the type distances lie in the range 2.298–2.323(3) Å. The dispo-
(NHC)AuX instead of a ionic one of the type sition of the propyl group is directed toward the gold
[(NHC)2Au]+[AuX2]ꢀ for these compounds. The com- atom. The distance Au···Au (>6.7 Å) indicates that
ACHTREUNG
plexes are colourless with fairly featureless absorption are no aurophilic interactions between the Au atoms.
bands deep in the UV. In dichloromethane, the car-
bene precursor has two absorption bands at 279,
352 nm (2) or 299, 366 nm (3). The electronic absorp- Preparation of Immobilized Complexes
tion spectra for the Au(I)-carbene complexes show
the bands at 302, 368 nm and 315 (2Au), 413 nm In the last years we have developed a modular system
(3Au).
combining functionalized ligands with different sup-
ports and linkers in order to have a systematic access
to a variety of immobilized chiral catalysts.[20] We
have applied this methodology here (Scheme 3) to im-
mobilize unsymmetrical carbene ligands on silica gel
Crystal Structure Studies of Complex 2Au
The structure of 2Au was confirmed by X-ray diffrac- (Merck silica, average pore diameter 40 Å), a meso-
tion studies (Figure 1). The gold(I) atom is two-coor- porous silica support such as MCM-41, [BET surface
area (m2·gꢀ1)=1030, micropore surface (t-plot
m2·gꢀ1)=0, external (or mesoporous) surface area
(m2·gꢀ1)=1030],[21] and delaminated zeolite ITQ-2,
[BET surface area (m2·gꢀ1)=830, micropore surface
(t-plot m2·gꢀ1)=130, external (or mesoporous) surface
area (m2·gꢀ1)=700].[22] Silica and MCM-41 are short-
range amorphous materials containing a large number
of silanol groups available for grafting. In the case of
MCM-41, however, the material presents a long-range
ordering with hexagonal symmetry and regular mono-
directional channels of 3.5 nm diameter. On the other
hand, ITQ-2 delaminated zeolite presents both short-
and long-range order, together with a very large, well
structured external surface on which the silanol
groups act as grafting centers.
The solid was functionalized according to the pro-
Figure 1. ORTEP representation for 2Au.
cedure shown in Scheme 3. Supported complexes,
3Au(support), were obtained by refluxing a mixture
G
of the precursor 3Au and the support, in toluene, for
16 h. These materials were characterized by micro-
ꢀ
dinate in an essentially linear environment with C
Au Cl bond angles close to 1808 (178.8, 174.6). There analysis, FT-IR, DFTR and 13C NMR. The catalysts
are two crystallographically independent molecules in prepared in this way presented metal loadings of
the asymmetric unit, which are bonded to each other 0.20–30 mmol-metal/g support as determined by
by a non-classic hydrogen bond [C(15)-H(15)···Cl(2)] atomic absorption analysis. The solid was character-
ꢀ
ꢀ
forming dimers. The Au C
(NHC) distances are ized by FT-IR, DFTR and 13C NMR spectroscopy.
A
Scheme 3. Heterogenization of 3Au complex on silica, MCM-41 and ITQ-2.
Adv. Synth. Catal. 2006, 348, 1899 – 1907
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A. Corma et al.
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Infrared and Electronic Spectra
conditions (EtOH as the solvent, 4 atm hydrogen
pressure, 408C). In these hydrogenation reactions we
Peaks due to the support dominate the spectra. These have paid special attention to the influence of the
ꢀ
include the O H vibration in the range 3700– nature of the support, and the comparison of the ac-
3300 cmꢀ1. Some of the bands characteristic of the tivity and stability of the supported catalysts with re-
complexes could, however, be distinguished. Major spect to their homogeneous counterparts and the pos-
zeolite framework bands appeared around 1140, 1040, sibilities of recycling the supported catalysts. Table 1
960, 785 and 740 cmꢀ1. FT-IR spectra are characteris-
tic for the binding of imine nitrogen. The 1600 cmꢀ1
frequencies may be assigned to C=C shifted to lower
wavenumbers (relative to the free ligands) due to co-
ordination. New bands in the cmꢀ1 region at ca.
ꢀ
Table 1. Turnover rates[a] for the catalytic hydrogenation of
diethyl citraconate and diethyl benzylidensuccinate with Au-
carbene catalysts.[b]
330 cmꢀ1 are ascribed to n
(Au Cl).
A
The Au-carbene complexes immobilized on sup-
ports have been characterized by diffuse reflectance
UV spectroscopy. The DFTR spectra for all com-
plexes were obtained in the 200–800 nm range. The
complexes show several band maxima in the UV
region agreeing with the assignment of the bands as
intraligand transitions in the aromatic ring, imidazoli-
um group and charge-transfer transition. The diffuse
Catalyst
Conv.(%)
[h]
TOF[a] Conv.(%)
[h]
TOF[a]
A
100 [3]c
97 [3]
97 [3]
100 [1]
100 [3]
25
50
225
250
300
50 [6]
55 [7]
75 [7]
90 [6]
95 [7]
6
20
75
100
170
1Au
2Au
3Au-(Sil)
3Au-(MCM-
41)
reflectance spectra of Au(carbene) complexes are
A
almost identical before and after heterogenization
process, indicating that the complexes maintain their
geometry and their electronic surroundings even after
heterogenization without significant distortion.
3Au-(ITQ-2)
100 [2]
425
90 [6]
300
[a]
TOF: mmol subs./mmol cat. h.
Conditions: 4 atm, 408C. S/C ratio 500:1.
[b]
NMR Spectra
Diamagnetic gold complexes have been characterized and Figure 1 summarize the catalytic results obtained
by 13C NMR spectroscopy. In all cases, the spectra for homogeneous catalysts compared with those of
show the simultaneous occurrence of two sets of sig- corresponding carbene complexes immobilized on
nals which are attributable on the one hand to the MCM-41. The results show that the homogeneous sys-
imidazolium entity and on the other hand to the ali- tems lead to quantitative conversion of olefins under
phatic and aromatic part of the ligand. The 13C NMR the hydrogenation conditions. While it is common to
spectra show the signals assigned to the carbene characterize the steric demand of PR3 ligands using
carbon at d ~175 downfield shifted.
the Tolman cone angle, in the case of NHC ligands Ja-
cobsen et al. reported[11] that the use of the %VBur
molecular descriptor (amount of volume of a sphere
centered on the metal, buried by overlap with atoms
of the various NHC ligands) is a convenient method.
Catalytic Activity
In order to evaluate the catalytic performances of The %VBur for PPh3 is 27 or 22 and 1 presents a simi-
these new soluble and the corresponding heterogen- lar value (26, 20). The better reactivity found for car-
ized counterparts gold(I)-carbene complexes we have bene-gold complexes compared with phosphine-gold
tested them in the hydrogenation of alkenes and the chloride could be explained by electronic effects
Suzuki cross-coupling reaction between halobenzene being more important than steric factors in this case.
and arylboronic acids.
As Table 1 shows, the heterogenized catalysts had,
in general, higher activities than the homogeneous
ones (see also Figure 2). These results indicate that
either the support or the metal complexes have a con-
siderable effect on the catalytic process, because of
Catalytic Hydrogenation of Olefins
The Au(I)-carbene complexes enable us to explore the stability of the active metallic species formed. The
the possibilities of these complexes in hydrogenation fact that the heterogenized catalysts have higher reac-
reactions. Thus, the hydrogenation of diethyl citraco- tion rate is one of the expected advantages of using
nate and diethyl benzylidenesuccinate with (carbe- heterogenized catalysts and is in good agreement with
ne)Au complexes were carried out under the usual our former results.[23] In different systems we have ob-
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Heterogenized Gold(I)-Heterocyclic Carbene Complexes
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age of hydrogen by Au complexes have been rein-
forced from our experiments using more polar and
protonic acid media which produces a significant in-
crease of reaction rate, probably favouring charge
separation in the step of formation of intermediate.
Recycling of Heterogenized Catalysts
The major advantage of the use of heterogenized
metal complexes as catalysts, is the ease with which
they can be recovered as stable species from the reac-
tion mixture by simple filtration and reused. We have
carried out the heterogeneous hydrogenation of ole-
fins until completion, filtered and washed the hetero-
genized catalyst, then added fresh substrate, and sol-
vent without further addition of catalyst, for several
consecutive experiments and have found that both
yield and activity are retained (Figure 3). After each
experiment a portion of the supported catalyst was
Figure 2. Comparison of the catalytic activities (homogene-
ous and heterogenized complexes) on the hydrogenation re-
action of diethyl citraconate.
served higher reaction rates on heterogenized sam- analyzed to determine the concentration of metal still
ples. The explanation could be that in the homogene- present in the support. The filtrate has been used in a
ous condition the reaction rate is decreased by the new reaction and was found not to catalyze hydroge-
poor solubility of these complexes in most organic nation.
solvents and by self-degradation. If we eliminate
these factors by heterogenizing the complex we can
expect a higher reaction rate. The site isolation effect
which works on the heterogenized condition may also
be an explanation for the higher rate, since the com-
plex is in a molecularly dispersed form and because
of this, is not subject to self-degradation. After pro-
longed storage at room temperature our heterogen-
ized catalysts showed the same features as the freshly
prepared catalysts in the standard hydrogenation re-
action.
From the above work it appeared to us that meso-
structured solids could be suitable supports for immo-
bilizing homogeneous hydrogenation catalysts, since
they could avoid the mass transfer limitations of the
previously reported support. Moreover, the fact that
we could control, up to a certain point, the polarity
(acidity) of the catalyst surface, could introduce an
Figure 3. Recycling of 3Au-(MCM-41) in the hydrogenation
of diethyl citraconate
additional benefit from the point of view of increasing
reactant concentration at the surface, and/or stabiliz-
ing reaction transition states. Therefore, we should
not see the support only as a tool to immobilize and
disperse the metal complexes, but, if properly de-
signed, it can contribute in a collaborative way to the Catalytic Suzuki Coupling
final activity and selectivity observed.[24]
The accumulated evidence concerning the mecha- The carbene Au(I) complexes were also studied for
nisms of homogeneously catalyzed hydrogenation in- the Suzuki cross-coupling of Br-Ph and I-Ph with a
dicates that three principal modes of hydrogen activa- series of arylboronic acids. The standard reaction con-
tion are suitable: oxidative addition, and homolytic or ditions were applied to a series of catalysts and the
heterolytic hydrogen cleavage. In the case of these Au conversions are tabulated in Table 2. In our experi-
complexes, heterolytic cleavage is preferred to give a ments, we have chosen K3PO4 as mild base because
hydride intermediate which involve charge separation with K2CO3 longer reaction times were necessary to
without any oxidation of the metal. Heterolytic cleav- obtain reasonable conversions.
Adv. Synth. Catal. 2006, 348, 1899 – 1907
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A. Corma et al.
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Table 2. Influence of ligands on Au(I) reactivity for Suzuki
hydrogenation reactions were higher than with the
homogeneous counterpart catalysts.
cross-coupling reactions.[a]
.
Experimental Section
Catalyst
4-BrPh
Conv.%
[h]
4-MeOPh
Conv.%
[h]
Sel.[b,c]
[%]
Sel.[b,c]
[%]
General Remarks
1Au
2Au
30 [6]/51
[22]
65 [6]/79
[24]
100
100
100
25 [6]/62
[22]
53 [6]/72
[24]
55 [6]/62
[22]
100
100
100
All preparations of metal complexes were carried out under
dinitrogen by conventional Schlenk-tube techniques. Sol-
vents were carefully degassed before use. The (tht)gold(I)
chloride was prepared by known methods.[27] 1,3-(2,4,6-Tri-
methylphenyl)-1H-imidazol-3-ium chloride (1) and the re-
spective Au((I)-carbene complex (1Au) were prepared ac-
cording with published methods.[16,19] Metal contents were
analyzed by atomic absorption using a Perkin–Elmer AAna-
lyst 300 atomic absorption apparatus and plasma ICP
Perkin–Elmer 40. IR spectra were recorded on a Bruker IFS
66v/S spectrophotometer (range 4000–200 cmꢀ1) in KBr pel-
A
[22]
[a]
Ratio catalyst:IPh=1:30, IPh (1 mmol), arylboronic
(1.5 mmol), K3PO4 (2 mmol).
Cross-coupling/conversion.
Reaction with K2CO3 as base gives 20% cross-coupling
with selectivity 100%.
[b]
[c]
1
lets. H NMR and 13C NMR, spectra were taken on Varian
XR300 and Bruker 200 spectrometers. Chemical shifts being
referred to tetramethylsilane (internal standard). High reso-
lution 13C MAS or CP/MAS NMR spectra of powdered
samples, in some cases also with a Toss sequence in order to
eliminate the spinning side bands, were recorded at
100.63 MHz, 6 ms 908 pulse width, 2 ms contact time and 5–
10 recycle delay, using a Bruker MSL 400 spectrometer
equipped with an FT unit. The spinning frequency at the
magic angle (54844’) was 4 kHz. Gas chromatography analy-
sis were performed in a Hewlett–Packard 5890 II with a
flame ionization detector or/and in a Hewlett–Packard
G1800 A with a quadrupole mass detector using a cross-
linked methylsilicone column.[28] The inorganic supports for
anchoring were silica gel [Merck silica, average pore diame-
ter 40 Å], purely siliceous MCM-41,[21] and delaminated zeo-
lites ITQ-2.[22]
The general utility of the reaction conditions with a
variety of arylboronic acid substrates (aryl=Ph, 3-
and 4-BrC6H4, 4-MeOC6H4) and aryl halides (BrPh,
IPh) was studied. Au(I) complexes are ineffective
with phenyl bromide. On the other hand, the gold(I)
complex with ligand 1 gives lower activity towards the
Suzuki reaction (Table 2). The effect of electron-do-
nating and electron-withdrawing substituents in the
boronic acid on reactivity can be seen in Table 2. In
general, moderate yields (calculated with respect to
PhI) and 100% selectivity towards the cross-coupling
product were found with Au(I)-carbene complexes
(homogeneous and heterogenized) (only traces of
boronic homocoupling were detected).
For comparison purposes (PPh3)AuCl has also
been prepared and tested under the same reaction
conditions (Table 2). The results show that activity
and selectivity of 2Au(I) and (PPh3)AuCl complexes
are similar, though the (PPh3)AuCl is systematically
more active. These results are in accordance with pre-
vious obtained in our group with Au(I)-Shiff base
Synthesis of Ligands: 1-(2,4,6-Trimehylphenyl)-3-
propyl-1H-imidazol-3-ium Iodide (2)
Method A: To a solution of 3 g (0.016 mol) of 1-(2,4,6-trime-
hylphenyl)-1H-imidazole in acetonitrile (100 mL) was added
dropwise 1.61 mL (1,016 mol) of propyl iodide. The reaction
mixture was refluxed for 12 h, the solvent removed under
reduced pressure and the resulting solid washed with Et2O
and dried under vacuum; yield: 80–95%
complexes,[25] the respective Au
(III) complexes only
G
give boronic homocoupling.[26]
Method B (Microwave heating):[17] In a 15-mL round-bot-
tomed flask 7 mL (0.072 mol) of propyl iodide and 2.0 g
(0.011 mol) of 1-mesityl-1H-imidazole were added. The
flask was closed and three cycles of 350 Watt were done for
5 seconds each. Two phases appeared and the product was
precipitated by addition of AcOEt; yield: 95%; mp 1288C.
Anal. calcd. for C15H21N2I (356): C 50.6, H 5.9, N 7.9; found:
Conclusions
We were able to successfully employ [(carbene)AuCl]
as catalysts for the hydrogenation of diethyl succi-
nates and the Suzuki coupling between PhI and aryl-
boronic acids (Ar=4-Br, 4-OMe). We have shown
that it is possible to boost the activity of a transition
metal complex catalyst by using an adequate support.
We have seen that by using mesostructured silicates
as carriers, with very high surface areas and accessibil-
ity to reactants, together with high adsorption capaci-
1
C 50.2, H 5.8, N: 7.9%; H NMR (CDCl3): d=9.80 (dd, 1H,
H3, J31 =1.7 Hz, J32 =1.6 Hz), 8.00 (dd, 1H, H1, J12 =1.7 Hz,
J13 =1.7 Hz), 7.21 (dd, 1H, H2, J21 =1.7 Hz, J23 =1.6 Hz), 6.89
(s, 2Harom), 4.54 (t, 2H, -CH2-N-; J=7.08 Hz), 2.23 (s, 3H,
CH3 para), 1.96 (s, 6H, CH3 ortho), 1.94 (m, 2H, -CH2-),
0.89 (t, 3H, CH3-CH2); 13C NMR (CDCl3): d=141.04
(Ccarbene), 136.68 (Carom-CH3 para), 133.92 (Carom-CH3 ortho),
129.61 (CHarom), 130.29 (Carom-N), 123.57 (CHimin-Naliph),
ty, the activities of the grafted Au complexes in the 123.30 (CHimin-Narom), 51.45 (-CH2-N), 23.72 (-CH2-), 20.85
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Heterogenized Gold(I)-Heterocyclic Carbene Complexes
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(CH3 para), 17.54 (CH3 ortho), 10.24 (-CH2-CH3); IR (KBr):
n=3116, 3080 (C=H), 3000–2800 (C-H), 1606 (C=H);
1559, 1544 (C=N), 1483, 1452 (C=N), 1203, 1160, 1067 cm-1
(C-N); UV-vis: l=279, 352 nm; MS (IE): m/z (%)=255
(M+ꢀI, 7); 229 (75); 227 (M+ꢀIꢀ2H; 100), 200 (42), 185
(53), 158 (30).
[1-(2,4,6-Trimehylphenyl)-3-(3-triethoxysilyl)propyl-
2,3-dihydro-1H-imidazol-2-yl]gold(I) Chloride (3Au)
Yield: 80%; anal. calcd. for C21H35AuClN2O3Si (624): C
1
40.4, H 5.6, N 4.5; found: C 40.6, H 5.5, N 4.3%; H NMR
(CDCl3): d=6.92–6.85 (m, 2Him, 2Harom), 4.30 (br, -CH2-N-),
3.68 (q, 6H, -OCH2CH3, J=6.84 Hz), 2.29 (s, 3H, CH3
para), 1.99 (s, 2H, -CH2-), 1.98 (s, 6H, 2CH3 ortho), 1.20 (t,
9H, -OCH2CH3, J=6.84 Hz), 0.86–0.82 (m, 2H, -CH2-Si-);
13C NMR (CDCl3): d=171.50 (C-Au), 139.34 (Carom-N),
134.67 (Carom-CH3 ortho), 129.83 (Carom-CH3 para), 129.23
(CHarom), 122.49 (CHimin-Naliph), 121.99 (CHimin-Narom), 58.22
(-OCH2CH3), 53.41 (-CH2-N-), 29.59 (-CH2-), 21.01 (CH3
ortho), 18.32 (-OCH2CH3), 17.81 (CH3 para), 17.26 (CH2-Si-
); IR (KBr), n=1608 (C=C), 1076 (Si-O), 782 (Si-C), 334
cm-1 (Au-Cl); UV-vis: l=154, 315, 413 nm; MS (EI): m/z
(%)=405 (M+ꢀ3EtOꢀCl), 219, 187, 119.
1-(2,4,6-Trimehylphenyl)-3-(3-(triethoxysilyl)propyl)-
1H-imidazol-3-ium Iodide (3)
To a solution of 1 g (5.38 mmol) of 1-(2,4,6-trimehylphenyl)-
1H-imidazole in diglyme (15 mL) was added 1.87 g
(6.58 mmol) of iodopropyltriethoxysilane. The reaction mix-
ture was stirred at 1608C for 24 h. After that the solvent
was removed under reduced pressure and the crude material
was purified using a mixture of AcOEt:MeOH (4:1); yield:
90%. Anal. calcd. for C21H35IN2O3Si (518.5): C 48.6, H 6.8,
1
N 5.4; found: C 48.2, H 6.5, N 5.6%; H NMR (CDCl3): d=
Heterogenization of 3Au [3 Au-(Support)]
9.51 (s, 1H, H3), 7.72 (t, 1H, H1, J12 =1.8 Hz), 7.16 (dd, 1H,
H2, J21 =1.8 Hz, 6.76 (s, 2Harom), 4.63 (t, 2H, -CH2-N-, J=
6.8 Hz), 3.76 (c, 6H, CH3-CH2-O-, J=7.0 Hz), 2.27 (s, 3H,
CH3 para), 2.02 (m, 8H, 2CH3 ortho, -CH2-), 1.14 (t, 9H,
CH3-CH2-O-, J=7.0 Hz), 0.58 (t, 2H, -CH2-Si-, J=7.9 Hz);
13C NMR (CDCl3): d=140.34 (Ccarbene), 135.96 (Carom-CH3
para), 133.35 (Carom-CH3 ortho), 128.95 (CHarom), 128.24
(Carom-N), 123.00 (CHimin-Naliph), 122.86 (CHimin-Narom), 57.73
(CH3CH2O-), 51.25 (-CH2-N), 23.64 (-CH2-), 20.23 (CH3
para), 17.46 (CH3CH2O-), 16.87 (CH3 ortho), 6.00 (-CH2-Si-);
IR (KBr): n=1608 (C=C), 1563, 1546 (C=N), 1075 (Si-O),
782 cm-1 (Si-C); UV-vis: l=299, 366 nm; MS (IE): m/z
(%)=391 (M+ꢀI; 100), 227 (4), 213 (11), 200 (21), 163 (28),
119 (13).
Heterogenized complexes were synthesized following the
general method: to a suspension of the support in toluene
(20 mL), at room temperature, was added a dichlorome-
thane solution of (1-(2,4,6-trimehylphenyl)-3-(3-triethoxysi-
lyl)propyl-2,3-dihydro-1H-imidazol-2-yl)gold(I)
chloride
complex (3Au) (20% in weight). The resulting mixture was
stirred under reflux for 12 h, cooled to room temperature
and filtered. The solid was washed several times with di-
chloromethane, dried and filtered to afford the respective
heterogenized complexes, complex-(support), in almost
quantitative yields. The loadings are based on the percent of
metal obtained from the elemental analysis data.
3Au-(MCM-41): anal. found: C 9.1, H 1.8, N, 0.6, Au
0.6% (0.21 mmol/g); 13C NMR (solid): d=174.3 (C-Au),
138.5 (Carom-N), 135.1 (Carom-CH3 ortho), 129.2 (Carom), 123.0
(CHimin-Naliph), 121.7 (CHimin-Narom), 65.8 (CH2O), 54.8
(CH2N), 31.0 (-CH2-), 25.5 (CH3 ortho), 15.5 (-OCH2CH3),
13.6 (CH3 para), 8.2 (CH2Si); IR (KBr): n=1631 (C=N),
1089 (Si-O), 325 (Au-Cl); UV-vis: l=216, 249, 262, 324,
414, 514 nm.
3Au-(Sil): anal. found: C 5.3, H 1.5, N 0.6, Au: 0.7%
(0.20 mmol/g); 13C NMR (solid): d=174.1 (C-Au). 138.0
(Carom-N). 135.4 (Carom-CH3 ortho), 129.0 (Carom), 123.2
(CHimin-Naliph), 121.8 (CHimin-Narom), 65.6 (CH2O), 54.5
(CH2N), 31.2 (-CH2-), 25.3 (CH3 ortho), 15.2 (-OCH2CH3),
13.8 (CH3 para), 8.3 (CH2Si); IR (KBr): n=1631 (C=N),
1095 (Si-O), 313 cm-1 (Au-Cl); UV-vis: l=215, 247, 263,
323, 416, 516 nm.
3Au-(ITQ-2): anal. found: C: 9.9, H 2.1, N 0.6, Au: 0.6%
(0.21 mmol/g); 13C NMR (solid): d=174.5 (C-Au), 138.1
(Carom-N), 135.0 (Carom-CH3 ortho), 129.0 (Carom), 123.3
(CHimin-Naliph), 122.0 (CHimin-Narom), 65.5 (CH2O), 55.0
(CH2N), 31.2 (-CH2-), 24.9 (CH3 ortho), 15.2 (-OCH2CH3),
13.3 (CH3 para), 8.0 (CH2Si); IR (KBr): n=1630 (C=N),
1094 (Si-O), 325 cm-1 (Au-Cl); UV-vis: l=213, 248, 262,
321, 422, 518 nm.
A
General Method:[19] A mixture of 100 mg of the imidazolium
salt (1–3) and 0.58 mmol of silver(I) oxide was taken up in
20 mL of dichloromethane and stirred for 4 h. The solution
was filtered and tetrahydrothiophene-gold(I) chloride
(1 mmol) was added to the filtrate. After 3 h, active carbon
was added and the reaction mixture was filtered through
celite. The solvent was removed under vacuum until ca.
5 mL remained, and hexane was added, causing a precipitate
to form.
[1-(2,4,6-Trimehylphenyl)-3-propyl-2,3-dihydro-1H-
imidazol-2-yl)gold(I) chloride (2 Au)
Yield=92%. C15H21AuClN2 (461.8): calcd. C: 39.0; H: 4.6;
1
N: 6.1; found C: 39.2; H: 4.6; N: 6.3%. H NMR (CDCl3) d-
A
4.28 (t, 2H, -CH2-N-; J=7.1 Hz); 2.31 (s, 3H, CH3pꢀ); 1.95
(s, 8H, CH3oꢀ, -CH2-); 0.98 (t, 3H, -CH2-CH3; J=7.1 Hz).
13C NMR (CDCl3) d
(ppm): 170.78 (C-Au); 138.60 (Carom-N);
R
133.88 (Carom-CH3o); 128.86 (CHarom-CH3p); 128.37 (CHarom);
121.29 (CHimin-Nalif); 119.43 (CHimin-Narom); 51.95 (-CH2-N);
23.34 (CH3o); 20.09 (CH3pꢀ); 16.74 (-CH2); 16.56 (-CH2-
CH3). IR (KBr, cmꢀ1): n=326 (Au-Cl). UV-vis (l, nm): 270,
302, 368. EM (ES) (m/z;%): 425 (M+ꢀCl); 418
(M+ꢀpropyl). Suitable crystals for crystallographic study
were grown by slow evaporation of a solution of dichloro-
methane-diethyl ether.
Catalytic Activity: Hydrogenation of Alkenes
The catalytic properties, in hydrogenation reactions, of the
complexes were examined under conventional conditions
for batch reactions in a reactor (Autoclave Engineers) of
100 mL capacity at 408C temperature, 4 atm dihydrogen
Adv. Synth. Catal. 2006, 348, 1899 – 1907
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
1905

A. Corma et al.
FULL PAPERS
pressure and 1/500, metal/substrate molar ratio. The evolu-
tion of the reaction of hydrogenated product was monitored
by gas-chromatography.
Acknowledgements
Financial support by the Dirección General de Investigación
Científica y Técnica of Spain (Project MAT2003–07945-C02–
01 and 02) and Ministerio de Educación y Ciencia (S.P.F.) is
gratefully acknowledged.
ꢀ
Suzuki C C Coupling
Typical procedure: The reaction was carried out in a 25 mL
vessel, at 1308C during a period of time ranging from 20 to
180 min. In
a typical run, a mixture of aryl halide
(10 mmol), boronic acid (15 mmol), aqueous potassium car-
bonate or phosphate (20 mmol) and catalyst (0.3 mmol) in
3 mL of o-xylene was stirred for the desired time. The solu-
tion was allowed to cool, and a 1:1 mixture of ether/water
(20 mL) was added. The organic layer was washed, separat-
ed, further washed with another 10 mL portion of diethyl
ether, dried with anhydrous MgSO4 and filtered. The solvent
and volatiles were completely removed under vacuum to
give the crude product which subjected to column chromato-
graphic separation which resulted in pure compounds. The
reaction was followed by GC-MS.
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Adv. Synth. Catal. 2006, 348, 1899 – 1907
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www.asc.wiley-vch.de
1907