Pincer-type pyridine-based N-heterocyclic carbene amine Ru(II) complexes as efficient catalysts for hydrogen transfer reactions

Article abstract of DOI:10.1021/om101179a

Stable well-defined pincer-type N-heterocyclic carbene-ruthenium complexes were developed as an alternative to phosphine complexes. These highly stable phosphine-free complexes were found to be efficient catalysts for transfer hydrogen reactions: the conversion of primary alcohols to esters and the reduction of carbonyl compounds. We also describe one approach toward immobilization through covalent bonding to silica via a pendant alkoxysilane group.

Full text of DOI:10.1021/om101179a

ARTICLE
pubs.acs.org/Organometallics
Pincer-type Pyridine-Based N-Heterocyclic Carbene Amine Ru(II)
Complexes as Efficient Catalysts for Hydrogen Transfer Reactions
Carolina del Pozo,†,‡ Marta Iglesias,*,† and Fꢀelix Sꢀanchez*,‡
†Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, C/Sor Juana Inꢀes de la Cruz 3,
Cantoblanco 28049 Madrid, Spain
‡Instituto de Química Orgꢀanica General, Consejo Superior de Investigaciones Científicas, C/Juan de la Cierva 3, 28006 Madrid, Spain
S Supporting Information
b
ABSTRACT: Stable well-defined pincer-type N-heterocyclic carbeneꢀ
ruthenium complexes were developed as an alternative to phosphine com-
plexes. These highly stable phosphine-free complexes were found to be
efficient catalysts for transfer hydrogen reactions: the conversion of primary
alcohols to esters and the reduction of carbonyl compounds. We also describe
one approach toward immobilization through covalent bonding to silica via a
pendant alkoxysilane group.
’ INTRODUCTION
compounds, homogeneous and heterogenized on MCM-41, are
selective catalysts for some organic reactions.12We know that
ruthenium complexes play a major role in catalytic transforma-
tions in organic chemistry.13,14 With these results on hand,
we now reported the synthesis of new (NHC)NNꢀRu(II)
pincer-type complexes, referable to recent reported PNN-
deprotonatedRu(II)-pincer complexes [PNN = 2-(di-tert-
butylphosphinomethyl)-6-(diethylaminomethyl)pyridine],15
useful as catalysts in dehydrogenation of secondary alcohols to
ketones, dehydrogenative coupling of alcohols into esters, hydro-
genation of esters to alcohols, reaction of alcohols with amines to
form amides with liberation of H2, selective synthesis of primary
amines directly from alcohols and ammonia, and direct conversions
of alcohols to acetals.
Catalytic dehydrogenation of alcohols to carbonyl compounds
and molecular hydrogen, without the need for a hydrogen
acceptor, is attractive economically and environmentally.16 How-
ever, relevant reports are limited to a few nonselective hetero-
geneous reactions17 or homogeneous systems that utilize
sacrificial hydrogen acceptors. In general, homogeneous systems
capable of thermally catalyzing acceptorless dehydrogenation of
alcohols are relatively rare.18 In addition, transfer hydrogenation
N-Heterocyclic carbenes (NHCs) are one of the most pro-
mising new classes of ligands in the design of highly efficient
transition metal homogeneous catalysts.1 NHCs are more elec-
tron-donating and tend to be sterically more demanding than
phosphine ligands with the same substituents and are generally
more stable toward molecular oxygen.2 The use of NHC ligands
in catalysis continues to develop through the introduction of new
NHC ligand architectures and the involvement of additional
donor groups on NHC ligands to generate chelating ligands.1l,3
Among these, chelating bis(N-heterocyclic carbenes) have been
introduced as promising ligands. On the other hand, functiona-
lized NHCs4 having an additional donor group are important in
organometallic catalysis, and several reports have appeared
on NHCs functionalized with phosphine,5 pyridine,6 and
oxazoline,7 amide,8 or ether9 donor functions. These ligands
allow for potential hemilability, and several such cases have been
reported.10 Few examples of such ruthenium complexes and their
applications in catalysis have been reported.11
Recently, we have reported the synthesis of electron-rich
(NHC)NN pincer-type ligands with N-heterocyclic carbene
and pyrrolidine moieties {2-[(3-aryl-2,3-dihydro-1H-imidazol-
1-yl)methyl]-6-(pyrrolidin-1-ylmethyl)pyridine, where aryl =
mesityl, 2,6-diisopropylphenyl) and their corresponding
rhodium(I), palladium(II), and gold(III) complexes; these
Received: December 17, 2010
Published: March 23, 2011
r
2011 American Chemical Society
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Organometallics
ARTICLE
Scheme 1. Synthesis of Ru Complexes
of CdO is a reaction for which NHC metal complexes19 have
demonstrated particularly good activity.
The imidazolium salts used as precursors for the chelating
NHC-pyridine-amine ligands of type 3 and 4 were synthesized
by direct monoalkylation of 1-substituted imidazoles. Thus, the
reaction of 2,6-bis(bromomethyl)pyridine with substoichio-
metric amounts of 1-aryl-1H-imidazole in refluxing acetone
give the corresponding imidazolium salts [2a]Br and [2b]Br
(Scheme 1). The salts were isolated in good yields and were
characterized by elemental analysis and 1H and 13C{1H} NMR
spectroscopy. The monoalkylated salts [2a]Br and [2b]Br
react in acetone or acetonitrile with pyrrolidine or N-methyl-
3-(triethoxysilyl)propan-1-amine in the presence of a base
(NaHCO3 or Na2CO3) to quantitatively yield [3a]Br or
[4b]Br. The 1H NMR spectra of [3a]Br and [4b]Br in CDCl3
showed a very low field resonance in the range δ 10.11 ppm and
10.22 ppm, characteristic of the NCHN imidazolium proton.
The bridging methylene (NimCH2C) moiety appeared as a
singlet at 5.99 ppm ([3a]Br) and 6.18 ppm ([4b]Br), and
CCH2Nam at 3.73 ppm ([3a]Br) and 3.58 ppm ([4b]Br). The
13C NMR spectrum of [3a]Br presents signals at 60.97
(CCH2Npyrr), 52.92 (NimCH2CPy) ppm. The 13C NMR
spectrum of [4b]Br presents characteristic signals at 63.81
(CCH2N), 53.94 (NimCH2CPy), and 9.51 (CH2Si) ppm. In the
electrospray mass spectrum, the imidazolium cation appeared as
molecular peaks at m/z 361 ([3a]þ) or 609 ([4b]þ) respectively,
in 100% abundance.
Synthesis of NHC Ruthenium Complexes. Several methods
have been used for the formation of NHCꢀmetal complexes.
They are based on (i) in situ deprotonation of the azolium salts,
(ii) complexation of the free NHC carbene or its protected form,
(iii) thermal cleavage of electron-rich alkenes (NHC)2 resulting
from the dimerization of nonsterically hindered NHC and formal
insertion of the metal in a CdC bond, (iv) transmetalation from
a silverꢀNHC complex, or (v) direct oxidative addition to the
metal center.21 The Ru(II) complexes were prepared by in situ
transmetalation from the silver carbene complexes of com-
pounds [1a]Br, [1b]Br, [3a]Br, and [4b]Br (Scheme 1). Treat-
ment with Ag2O or soluble AgOC(CF3)3, which act as both base
and halide scavenger, under light-free conditions in CH2Cl2 at
In many cases, NHC-containing complexes have the potential
to promote any reaction catalyzed by traditional tertiary phos-
phine- and phosphite-based catalysts.2a,20 We now report that
the novel chelating (NHC)NNꢀRu complexes are catalytically
active for two useful reactions involving hydrogen transfer: the
dehydrogenation of alcohols and the reduction of aldehydes
and ketones. We also report the heterogenization of these Ru
complexes on a mesoporous support as MCM-41; the resulting
materials have been applied in the dehydrogenation of alcohols
and the recycling of the catalytic materials has been studied.
’ RESULTS AND DISCUSSION
The new neutral N-heterocyclic carbene pincer-type ligands
were designed with the objective to stabilize metal complexes
with enhanced catalytic properties. The present ligand design
was adopted in the hope that the potentially labile pyrrolidine
would provide hemilability so that the free pyrrolidine group
might then act as an internal base, perhaps obviating the need for
added base in catalysis. As discussed below, we found evidence
of hemilability in one reaction. We have now incorporated a
triethoxysilyl group on the amine substituent into the CNN-
pincer backbone. The purpose of incorporating this functionality
is to obtain CNN pincer-type ligands that can be attached to silica
carrier by covalent bonds.
Synthesis of Precursors for Chelating NHC Pyridine
Pyrrolidine Ligands. In this work we have employed the
unsymmetrical CNN pincer-type ligands 2-[(3-mesityl-2,3-
dihydro-1H-imidazol-1-yl)methyl]-6-(pyrrolidin-1-ylmethyl)-
pyridine (3a), 2-[[3-(2,6-diisopropylphenyl)-2,3-dihydro-
1H-imidazol-1-yl]methyl]-6-[[N-methyl-3-(triethoxysilyl)-
propan-1-amino]methyl]pyridine (4b) and the symmetrical
NHC-bis(carbenes) 2,6-bis[(3-mesityl-2,3-dihydro-1H-imidazol-1-
yl)methyl]pyridine (1a) and 2,6-bis[[3-(2,6-diisopropylphenyl)-
2,3-dihydro-1H-imidazol-1-yl]methyl]pyridine (1b), as ligands for
ruthenium complexes (Scheme 1).
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Organometallics
ARTICLE
room temperature formed the silver carbene.22 The mixture was
filtered through Celite to remove unreacted silver oxide and
insoluble residues. The absence of the downfield-shifted H
in ∼90% yield. The IR spectrum shows ν(Ru-CO) at 1985 cmꢀ1
(1aRu-H) and 1946 cmꢀ1 (3aRu-H).
1
It is also possible to obtain the desired ruthenium complex
by direct reaction between the imidazolium salt [3a]Br and
[RuHCl(CO)(PPh3)3] (Scheme 2). The 1H NMR spectra
showed the presence of an imidazolium (NCHN) resonance at
∼10.00 ppm owing to the acidic imidazolium proton; this
intermediate, in the presence of a base as [(CH3)3Si]2NK, yields
the formation of 3aRu complex.
Immobilization of Ru Pincer-type Complexes on MCM-41.
The ruthenium complex with a triethoxysilyl group, [4b]Ru,
was heterogenized on the MCM-41 mesoporous silica sup-
port. MCM-41 is a short-range amorphous material that
contains a large number of silanol groups available for graft-
ing; however, it presents a long-range ordering of hexagonal
symmetry with regular, monodirectional channels of 3.5 nm
diameter.
The solid was functionalized according to the procedure
shown in Scheme 3. Supported complexes were obtained by
refluxing a mixture of the precursor [4b]Ru and the support,
in toluene, for 16 h. The catalyst prepared in this way
presented metal loading of 0.06 mmol of metal/g of support
as determined by atomic absorption analysis. Heterogeniza-
tion process yielded materials with the expected ratios of
metal to nitrogen loadings.
NMR signal of the imidazolium ring (NCHN) along with the
appearance of a diagnostic silver-bound carbene (NCNꢀAg)
peak at ∼174 ppm in the 13C NMR spectra of 1aAg, 1bAg, 3aAg,
and 4bAg are the characteristic features of the resulting silver
complexes. Silver NHC complexes then easily underwent ex-
change reactions with binuclear halide-bridged metal complexes
of rhodium and ruthenium.23 In this work the filtrate was treated
with RuHCl(CO)(PPh3)3 to give [RuHCl(CO)L] complexes
1aRu, where L = 2,6-bis[(3-mesityl-2,3-dihydro-1H-imidazol-1-
yl)methyl]pyridine; 1bRu, where L = 2,6-bis[[3-(2,6-diisopro-
pylphenyl)-2,3-dihydro-1H-imidazol-1-yl]methyl]pyridine; 3aRu,
where L = 2-[(3-mesityl-2,3-dihydro-1H-imidazol-1-yl]methyl]-
6-(pyrrolidin-1-ylmethyl)pyridine; and 4bRu, where L = 2-[[3-(2,
6-isopropylphenyl)-2,3-dihydro-1H-imidazol-1-yl]methyl-6-[[N-me-
thyl-3-(triethoxysilyl)propan-1-amino]methyl]pyridine (Scheme 1).
Ru complexes were isolated upon precipitation with diethyl ether
as brown powders in >90% yield.24 The IR spectra show two absorp-
tions due to the hydride ν(RuꢀH) at ∼2050 cmꢀ1 and the ν(CO)
appears at ∼1937 cmꢀ1. 13C NMR chemical shifts, which provide a
useful diagnostic tool for metal carbene complexes, display the
expected resonances with a single Ru carbene 13C resonance at
δ 175.0 ppm and the CO signal at δ 191.18 ppm (3aRu) and
δ 186.54 ppm and the CO signal at δ 206.16 ppm (4bRu). The ESI
mass spectra show peaks of two ions obtained from Ru complexes via
loss of one chloride ligand; the signals display the characteristic Ru
isotopic pattern.
The impact of immobilization of [4b]Ru on the structure of
complexes was studied by Fourier transform infrared (FTIR)
spectroscopy, electronic spectra cross-polarization magic-angle
1
spinning (CP MAS) NMR spectroscopy (13C, H), and ele-
mental analysis. Peaks due to the support dominate the spectra
(around 1240, 1060, and 806 cmꢀ1). Some of the bands
characteristic of the complexes could be, however, distinguished.
A weak band at 1942 cmꢀ1 corresponds to ν(CO) stretching.
The 1640ꢀ1600 cmꢀ1 frequencies may be assigned to CdN and
CdC. A strong ν(OꢀH) stretch appeared in heterogenized
compounds from 3200 to 3700 cmꢀ1, confirming the presence of
surface silanol groups and the inability to react all silanols with
bulky complexꢀMCM-41. The complexes immobilized on sup-
ports have been characterized by diffuse reflectance UV spec-
troscopy. The diffuse reflectance spectrum of Ru complex is
almost identical before and after the heterogenization process,
indicating that the complexes maintain their geometry and their
electronic surroundings even after heterogenization without
significant distortion.
1aRu and 3aRu were treated with 1 equiv of KOtBu at ꢀ32 °C,
resulting in the brown-red Ru(II) complexes 1aRu-H and 3aRu-H
Scheme 2. Synthesis of Ru Complexes by Metalation with
NHC in the Presence of Base
Scheme 3. Heterogenization of Ru Complex
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Organometallics
ARTICLE
The solid-state 13C CP MAS NMR spectrum of supported
complex is dominated by the resonances of the aliphatic and aromatic
groups. These signals appear at 9.2 (SiCH2) and 26.1 (CH2CH2-
CH2) ppm, and the last one shifts to ca. 54 ppm (NꢀCH2). The
aromatic region is δ = 156ꢀ117 ppm, and δ = 175 ppm (RuꢀC).
The majority peaks corresponding to the 13C NMR spectrum of
homogeneous complex were present in the 13C spectrum of their
heterogenized counterpart.
Catalytic Dehydrogenation of Alcohols. Given the recent
interest in alcohol dehydrogenation25,20 and the results obtained
with the complex PNNꢀRu, complex A, in the presence of 1
equiv of base, should be an excellent catalyst for the dehydro-
genation of primary alcohols to esters and molecular hydrogen.
The catalyst is the dearomatized complex, formed by deprotona-
tion of A (Scheme 4). With complex B as catalyst, dehydrogena-
tion of alcohols to esters was accomplished under neutral
conditions.18a Given these results, we tested the catalytic activity
of described NHC-pincerꢀRu complexes in the dehydrogena-
tion of primary alcohols to esters.
Bis(NHC) complexes 1aRu and 1bRu catalyze this reaction in
moderate yields (Table 1) but require the presence of base.
When 1-hexanol and 1-butanol were refluxed in toluene with
1 mol % 1aRu and KOH, over 30% of the corresponding esters
were formed after 72 h (Table 1, entry 1). No reaction took place
in the absence of a base (entry 2). 1bRu yields only ∼15% ester
after 72 h; this illustrates the importance of steric hindrance of
the aromatic ring substituent. When the reaction takes place with
the bis(carbene) 1aRu-H26 as catalyst (analogous to dipho-
sphine RuPNP complex, PNPꢀbis[2,6-(di-tert-butyl)phosphi-
nomethyl]pyridine), in the absence of base, the catalytic activity
significantly improves and 100% yields of ester after 4 h were
obtained (entry 4).
Aiming at improving the catalytic activity, we have prepared
the complex 3aRu, which has a potentially hemilabile amine
substituent (similar to complex A of Scheme 4). Complex 3aRu
in the presence of 1 equiv of base is an efficient dehydrogenative
esterification catalyst, exhibiting superior activity relative to that
of 1aRu. Thus, upon heating a 1 mol % solution of complex 3aRu
with KOH (1 equiv relative to Ru) and 1-butanol in refluxing
toluene under argon for 24 h, 91.5% butyl butyrate was formed
(entry 6). Also, no reaction took place in the absence of base.
Other alcohols react similarly. To further improve the reaction,
we also proceed at totally eliminating the need for a base. A
possible role of the base is deprotonation of 3aRu to 3aRu-H
complex (the real catalyst), which must correspond to an
induction period in the reaction, and that does happen when
previously formed and isolated 3aRu-H is used. Deprotona-
tion of the benzylic phosphine “arm” took place, similarly to
the Milstein PNPꢀRu complex resulting in the stable brown
Ru(II) complex. Complex 3aRu-H is the best catalyst of the
complexes reported here for acceptorless dehydrogenative
esterification of alcohols; ester yields of over 100% (TOF
35 hꢀ1) were obtained from butanol in relatively short reac-
tion times (3 h); starting from hexanol or benzyl alcohol,
conversions of 90% or 20% were achieved. This reaction
provides a convenient method for the synthesis of esters
because of its high efficiency, simplicity, and facile isolation of
the desired products.
Heterogeneous Experiments. The reactions catalyzed by
4bRu-MCM-41 (entry 12, Table 1) show similar activity to that
achieved with the soluble complex. To evaluate the catalyst
lifetime and stability, two experiments were carried out:
(a) When the reaction is complete, new reagents were added
and the same activity was observed after 24 h; this process could
be repeated three times without loss of activity, after the fourth
cycle, the catalyst activity decreases dramatically. (b) The solid
was separated by centrifugation. The supernatant liquid was
allowed to react with new fresh reagents and no conversion was
observed; no appreciable leaching of catalyst was detected. The
residue containing the catalyst was washed twice with ethanol
and diethyl ether (3 mL) and each time, after centrifugation, the
organic phase was removed. The recovered solid was reused in a
new reaction with new fresh reagents and any conversion was
observed.
Scheme 4
Table 1. Dehydrogenation of Primary Alcohols to Esters and H2 Catalyzed by Ru Complexes.a
entry
catalyst
substrate
KOH (equiv)
T (h)
yieldb (%)
TOFc (hꢀ1
)
1
1aRu
butanol
1
0
1
0
0
1
1
1
0
0
0
1
72
72
72
4
25
1.38
2
1aRu
butanol
0
15
3
1bRu
butanol
0.30
25
4
1aRu-H
1bRu-H
3aRu
butanol
100 (95)
25
5
butanol
72
72
24
72
3
0.35
0.92
4
6
butanol
40
7
3aRu
hexanol
90 (84)
10
8
3aRu
benzylalcohol
butanol
9
3aRu-H
3aRu-H
3aRu-H
4bRu-MCM-41
100 (92)
90
35
19
1
10
11
12
hexanol
8
benzylalcohol
24
20
hexanol
24
88
5
a Conditions: 0.01 mmol KOH, 0.01 mmol of catalyst, 1 mmol of alcohol, toluene (2 mL) at 110 °C. b Determined by GC; in some experiments we have
isolated the reaction products and found that the performance is very close to what we determined by GC. c Millimoles of substrate per millimoles of
catalyst per hour.
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ARTICLE
Catalytic Transfer Hydrogenation of Aldehydes and Ke-
tones. Ruthenium complexes have been used as active catalysts
for transfer hydrogenation reactions.27 However, only a very
limited number of RuꢀNHC complexes have been reported
as catalysts for this transformation.28 Thus 3aRu-H was
tested as catalyst for transfer hydrogenation of carbonyl
compounds with 2-propanol as the hydrogen donor in the
presence of base at 82 °C. Complex 3aRu-H was found to be
an efficient catalyst in transfer hydrogenation of aliphatic
aldehydes (heptanal, 100% conversion after 1 h; Table 2) but
not aromatic aldehydes (benzaldehyde, <10% conversion at
24 h). We further explored its catalytic potential in the
reduction of ketones with identical reaction conditions to
those used in the transfer hydrogenation of aliphatic alde-
hydes It was found that 3aRu-H is efficient in transfer hydro-
genation of isobutyl methyl ketone or 2-hexanone (100%
conversion after 1 h) and moderately active for acetophenone
(36% after 4 h) but shows poor activity in the reduction of
acetylacetone (20% after 24 h).
Proposed Mechanism. A proposed mechanism for these
reactions is depicted in Scheme 5. The mechanism of this
reaction is very likely as reported for active complex RuꢀPNN
(B in Scheme 4), which can donate or accept a proton via a facile
dearomatizationꢀaromatization process in cooperation with the
metal center.18a,29 Detailed density functional theory (DFT)
calculations to investigate the energetics and mechanism of
thermal H2 production from water splitting mediated by this
Ru(II)ꢀPNN complex have been also reported.30 In this work,
the authentic catalyst is the dearomatized complex 3aRu-H
formed by deprotonation of 3aRu. Upon reaction of 3aRu-H
with the alcohol, an aromatic, coordinatively saturated ruthenium
alkoxyde hydride species complex may be generated. Amine
ligand opening would enable the subsequent β-hydrogen elim-
ination process, followed by carbonyl elimination to generate the
trans-Ru(II) dihydride species 3aRu-H2. Dihydrogen elimina-
tion from 3aRu-H2 regenerates 3aRu-H, as described above. The
generation of RuꢀH2 with the help of a base have been suggested
in catalytic alcohol dehydrogenation,15d N-alkylation of amines
with alcohols,31 and esterification of alcohols.32
Table 2. Transfer Hydrogenation of Aldehydes and Ketones
with 3aRu-H.a
entry
aldehyde
T (h)
yieldb (%)
S:Cc
1
2
3
4
5
6
benzaldehyde
24
1
traces
100
100
98
1:100
1:100
1:100
1:100
1:100
5:100
heptanal
isobutyl methyl ketone
2-hexanone
1
0.75
4
acetophenone
36
acetylacetone
24
20
a Reaction conditions: 1 mmol of ketone or aldehyde, KOH (1 mol %), 1
mol % catalyst in 2.0 mL of PrOH at 82 °C. b Determined by GC.
i
c Substrate:catalyst ratio
Scheme 5
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On the other hand, for transfer hydrogenation of aldehydes or
ketones, complex 3aRu-H in the presence of H2 yields 3aRu-H2,
which reacts with the carbonyl compound (aldehyde or ketone)
and a coordinatively saturated alkoxy hydride complex may be
generated. The last step releases the alcohol and regenerates the
catalyst 3aRu-H.
silica gel eluted with acetone/ethanol (10:1) to yield a white solid (2.14
g, 26%). IR (KBr, cmꢀ1): ν = 3047 (CHCdC), 1594, 1574, 1546 (CdC,
CdN), 1458 (CꢀC). 1H NMR (CDCl3, ppm): δ = 10.75 (2H,
NCHN), 8.67 (2H, Himi), 7.84, 7.82 (2H, d, Hpy), 7.62 (2H, t, Harom),
7.26ꢀ7.22 (4H, m, Harom,), 7.05 (1H, t, Hpy,), 7.16 (2H, Himi), 6.13
(4H, s, NimCH2C), 2.28ꢀ2.21 (4H, m, CHiPr), 1.20 (24H, t, CH3). 13
C
NMR (CDCl3, ppm): δ = 153.30 (Cpy), 153.31 (NCHN), 131.85 (Carom),
124.63 (Carom), 124.03 (Cpy), 123.0 (CHimi), 53.45 (NimCH2C), 28.63
(CHiPr), 23.87, 23.78 (CH3).
’ CONCLUSION
In conclusion, we have described the preparation and catalytic
activities of well-defined Ru(II) hydride complexes based on
pincer-type pyridine-functionalized N-heterocyclic carbene li-
gands. Via the Ag carbene transmetalation route, these new
complexes were readily accessible and are effective catalyst
precursors for the dehydrogenation of primary alcohols to esters
and for the transfer hydrogenation of carbonyl compounds.
Heterogenization on a mesoporous support leads to a catalyst
with an activity similar to that of the homogeneous system for
three successive cycles. Although phosphine complexes are more
active than NHCꢀRu complexes reported in this paper, these
new complexes represent a promising alternative to them.
Preparation of Precursors 1-Mesityl-3-{[6-(amine-1-ylmethyl)-
pyridin-2-yl]methyl}-2,3-dihydro-1H-imidazol-3-ium Bromide ([3a]Br)
and 3-{[6-(Bromomethyl)pyridin-2-yl]methyl}-1-mesityl-1H-imida-
zol-3-ium ([2a]Br). A mixture of 2,6-bis(bromomethyl)pyridine
(6 mmol, 1.59 g) and 1-mesityl-1H-imidazole (4 mmol, 750 mg) in
acetone was refluxed for 16 h. The crude product was purified by
chromatography on silica gel eluted with acetone/ethanol (6:1) to
yield a white solid (1.082 g, 40%), mp = 207.5ꢀ209 °C. Anal. Calcd
for C19H21N3Br2 (451): C, 50.4; H, 4.9; N, 9.3. Found: C, 50.3; H,
4.8; N, 9.4. IR (KBr, cmꢀ1): ν = 3158, 3086 (CHCdC), 1591, 1565,
1
1549 (CdC, CdN), 1458 (CꢀC). H NMR (CDCl3, ppm): δ =
10.20 (1H, d, J = 1.7 Hz, NCHN), 8.06 (1H, d, J = 1.7, Himi), 7.83 and
7.37 (2H, Hpy, d, J = 7.57, 7.82, 0.74 Hz), 7.71 (1H, t, Hpy), 7.10 (1H,
d, J = 1.7 Hz, Himi), 6.99 (2H, s, Hmes), 6.18 (2H, s, NimCH2C), 4.41
(2H, s, CH2Br), 2.30 (3H, s, p-CH3), 2.08 (6H, s, o-CH3). 13C NMR
(CDCl3, ppm): δ = 156.69 (Cpy), 152.48 (Cpy), 141.19 (Cpy), 138.96
(NCHN), 137.99 (Cmes), 134.22 (Cmes), 130.57 (Cmes), 129.69
(Cmes), 123.96 (CHimi), 123.35 (Cpy), 123.11 (CHimi), 122.44
(Cpy), 53.42 (NimiCH2C), 33.27 (CH2Br), 20.97 (p-CH3), 17.55
(o-CH3). EM (m/z): 370 (Mþ, 100).
’ EXPERIMENTAL SECTION
General Remarks. Unless otherwise noted, all reactions were
carried out by standard Schlenk techniques. Solvents were carefully
degassed before use. C, H, and N analysis were carried out by the
analytical department of the Instituto de Química Orgꢀanica (CSIC) with
a Lecco apparatus. Metal contents were analyzed by plasma ICP Perkin-
Elmer Optima 2100 DV. IR spectra were recorded on a Bruker IFS
66v/S spectrophotometer (range 4000ꢀ200 cmꢀ1) in KBr pellets. 1H
and 13C NMR spectra were taken on Varian XR300 and Bruker 200
spectrometers. Chemical shifts were referred to tetramethylsilane
(internal standard). High-resolution 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 μs
90° pulse width, 2 ms contact time and 5ꢀ10 recycle delay, on a Bruker
MSL 400 spectrometer equipped with an FT unit. The spinning
frequency at the magic angle (54° 440) was 4 kHz. Gas chromatography
analysis was performed with a Hewlett-Packard 5890 II. MCM-41
employed for grafting has BrunauerꢀEmmettꢀTeller (BET) surface
1-Mesityl-3-{[6-(pyrrolidin-1-ylmethyl)pyridin-2-yl]methyl}-2,3-di-
hydro-1H-imidazol-3-ium Bromide ([3a]Br). A mixture of [2a]Br (5
mmol, 2.25 g), sodium carbonate (75 mmol, 7.9 g), and pyrrolidine (6
mmol, 0.5 mL) in acetone was stirred at room temperature for 12 h. The
crude product was washed with diethyl ether to afford the product as a
beige solid (1.65 g, 75%), mp = 148.0ꢀ151.0 °C. Anal. Calcd for
C23H29N4Br (441): C, 62.6; H, 6.6; N, 12.7. Found: C, 62.4; H, 6.5; N,
12.5. IR (KBr, cmꢀ1): ν = 3050 (CHarom), 1700, 1663 (CdC, CdN).
1H NMR (CDCl3, ppm): δ = 10.11 (1H, br s, NCHN), 8.10 (1H, d,
J = 1.7 Hz, Himi), 7.73 and 7.62 (2H, d, Hpy, J = 7.66, 7.42 Hz,), 7.31 (1H,
t, Hpy), 7.10 (1H, d, J = 1.7 Hz, Himi), 6.92 (2H, s, Hmes), 5.99 (2H, s,
NimCH2C), 3.73 (2H, s, CCH2Npyrr), 2.55 (2H, s, CH2pyrr), 2.25 (3H, s,
p-CH3), 2.06 (6H, s, o-CH3), 1.80 (2H, s, CH2pyrr). 13C NMR (CDCl3,
ppm): δ = 157.13 (Cpy), 149.98 (Cpy), 138.43 (NCHN), 137.20 (Cpy),
136.11 (Cmes), 132.34 (Cmes), 132.11 (Cmes), 127.94 (Cmes), 122.12
(Cimi), 121.43 (Cpy), 120.64 (Cimi), 120.52 (Cpy), 59.77 (CCH2Npyrr),
52.02 (CH2pyrr), 51.44 (NimiCH2C), 21.65 (CH2pyrr), 19.18 (p-CH3),
15.71 (o-CH3). EM (m/z): 361 (Mþ, 100).
1-(2,6-Diisopropylphenyl)-3-{[6-(aminomethyl)pyridin-2-yl]methyl}-
2,3-dihydro-1H-imidazol-3-ium Bromide ([3b]Br) and 3-{[6-
(Bromomethyl)pyridin-2-yl]methyl}-1-(2,6-diisopropylphenyl)-1H-
imidazol-3-ium Bromide ([2b]Br). A mixture of 2,6-bis(bromomethyl)-
pyridine (11.32 mmol, 3 g) and 1-(2,6-diisopropylphenyl)-1H-imidazole
(7.59 mmol, 1.73 g) in acetone was refluxed for 18 h. The crude product
was purified by chromatography on silica gel eluted with acetone/ethanol
(10:1) to yield a white solid (2.14 g, 40%), mp = 200.5ꢀ202.0 °C. Anal.
Calcd for C22H27N3Br2 (493): C, 53.5; H, 5.7; N, 8.5. Found: C, 53.1; H,
5.2; N, 8.1. IR (KBr, cmꢀ1): ν = 3047 (CHCdC), 1594, 1574, 1546
(CdC, CdN), 1458 (CꢀC). 1H NMR (CDCl3, ppm): δ = 10.08 (1H,
NCHN), 8.16 (1H, Himi), 7.84 (1H, Hpy, d, J = 7.7 Hz), 7.71 (1H, t, Hpy,
J = 7.60, 7.7 Hz), 7.48 (1H, Harom, t, J = 7.8, 7.7 Hz), 7.35 (1H, d, Hpy,
J = 7.5 Hz), 7.26ꢀ7.22 (2H, m, Harom,), 7.10 (1H, Himi), 6.21 (2H, s,
NimCH2C), 4.39 (2H, s, CH2Br), 2.34ꢀ2.21 (2H, m, CHiPr), 1.16 (6H, d,
J = 6.8 Hz, CH3), 1.08(6H, d, J = 6.8Hz, CH3). 13CNMR (CDCl3, ppm):
δ = 156.30 (Cpy), 152.10 (Cpy), 138.27 (Cpy), 138.15 (NCHN), 137.71
area 1030 m2 ꢀ1, micropore surface (t-plot) 0 m2 ꢀ1, and external
g g
3
3
(or mesoporous) surface area 1030 m2 gꢀ1
.
3
Preparation of Precursors. Imidazolium salts [1a]Br and [1b]Br
were obtained as subproducts in the synthesis of [2a]Br and [2b]Br.
Synthesis of 3,30-[Pyridine-2,6-diylbis(methylene)]bis(1-mesityl-1H-
imidazol-3-ium) Bromide ([1a]Br). A mixture of 2,6-bis(bromome-
thyl)pyridine (6 mmol, 1.59 g) and 1-mesityl-1H-imidazole (4 mmol,
750 mg) in acetone was refluxed for 16 h. The crude product was
purified by chromatography on silica gel eluted with acetone/ethanol
(6:1) to yield a white solid (764 mg, 20%). IR (KBr, cmꢀ1): ν = 3047
1
(CHCdC), 1594, 1574, 1546 (CdC, CdN), 1458 (CꢀC). H NMR
(CDCl3, ppm): δ = 10.85 (2H, d, NCHN), 8.68 (2H, d, Himi), 7.83, 7.37
(2H, d, Hpy), 7.25 (4H, t, Hmes), 7.11 (1H, s, HPy), 6,99 (2H, Himi), 6.18
(4H, s, NimCH2C), 2.30 (6H, s, p-CH3), 2.00 (12H, s, o-CH3). 13C
NMR (CDCl3, ppm): δ = 153.30 (Cpy), 145.62 (Carom), 139.31 (NCHN),
131.85 (Carom), 130.64 (Cpy), 124.63 (Carom), 124.03 (Cpy), 123.0 (CHimi),
53.45 (NimCH2C), 23.87 (p-CH3), 23.78 (o-CH3). EM (m/z): 588 (Mþ ꢀ
Br, 100).
Synthesis of 3,30-[Pyridine-2,6-diylbis(methylene)]bis[1-(2,6-
diisopropylphenyl)-1H-imidazol-3-ium] Bromide ([1b]Br). A mixture
of 2,6-bis(bromomethyl)pyridine (11.32 mmol, 3 g) and 1-(2,6-
diisopropylphenyl)-1H-imidazole (23 mmol, 16.56 g) in acetone was
refluxed for 18 h. The crude product was purified by chromatography on
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Organometallics
ARTICLE
(Carom), 131.45 (Carom), 129.63 (Carom), 124.20 (Carom), 123.64
2.55ꢀ2.31 (4H, m, CHiPr), 1.20 (24H, d, CH3). 13C NMR (CDCl3,
ppm) (partial): δ = 144.39 (Cpy), 134.18 (Cpy), 133.18 (Cpy), 131.14
(Carom), 130.95 (2Carom), 130.79 (CPy), 128.70 (Carom), 127.56
(Carom), 127.40 (Carom), 126.82 (CHimi), 124.00 (Cpy), 123.62
(CHimi), 31.17 (NimCH2C), 28.67 (CHiPr), 23.71, 23.30 (CH3). EM
(m/z): 729 (Mþ).
[RuHCl(CO)(3a)] (3aRu). C24H29ClN4ORu (528.05). IR (KBr,
cmꢀ1): ν = 3050 (CHarom), 2052 (RuꢀH), 1939 (RuꢀCO), 1610,
1630 (CdC, CdN). UVꢀvis: λ (nm) = 258, 276, 334, 425. 1H NMR
(CDCl3, ppm): 7.85ꢀ7.67 (m, 2H, HPy), 7.64ꢀ7.50 (m, 1Himi),
7.48ꢀ7.35 (m, 2H, Harom), 7.34ꢀ7.28 (m, 1Himi), 7.22 (m, 1HPy),
6.12ꢀ5.99 (m, 2H, NimiCH2Cpy), 3.62ꢀ6.55 (m, 2H, CPyCH2Npyrr),
2.97ꢀ2.68 (m, 2H, CH2Npyrr), 2.50ꢀ2.45 (m, 2H, CH2Npyrr), 2.33
(3H, s, p-CH3), 2.00 (6H, s, o-CH3), 1.98 ꢀ1.77 (m, 4H, CH2-
CH2), ꢀ2.97 (s, 1H, HꢀRu). 13C NMR (CDCl3, ppm): δ = 191.18
(CO), 175.21 (CꢀRu), 158.70, 141.70, 134.67 (Cpy), 132.65 (Carom),
132.5 (Carom), 132.42 (Cpy), 130.28 (Carom), 128.97 (Carom), 128.82
(2Carom), 128.58 (CHimi), 123.98 (CHimi), 128.34 (Cpy), 65.60
(CpyCH2Npyrr), 60.23 [Npyrr(CH)2], 54.9 (NimiCH2CPy), 23.52
(CH2CH2Npyrr), 21.07 (p-CH3), 17.70 (o-CH3). EM (m/z): 493
([3aRu] ꢀ Cl).
(CHimi), 123.03 (Cpy), 122.91 (CHimi), 53.07 (NimiCH2C), 32.87
(CH2Br), 28.13 (CHiPr), 23.84, 23.78 (CH3). EM (m/z): 413 (Mþ
Br, 100).
ꢀ
1-(2,6-Diisopropylphenyl)-3-[(6-{[N-methyl-3-(triethoxysilyl)pro-
pan-1-amino]methyl}pyridin-2-yl)methyl]-1H-imidazol-3-ium Bro-
mide ([4b]Br). C35H56BrN4O3Si (687.33). IR (KBr, cmꢀ1): ν = 2963
(CHarom), 1591, 1574 (CdC, CdN). UVꢀvis (λ, nm): 288, 373. 1H
NMR (CDCl3, ppm): δ = 10.22 (1H, NCHN), 8.22 (1H, Himi), 7.82
(1H, Hpy), 7.71 (1H, m, Hpy), 7.53 (1H, Harom), 7.44 (1H, HPy), 7.30
(2H, m, Harom), 7.13 (1H, Himi), 6.18 (2H, s, NimiCH2Cpy), 4.19ꢀ4.00
[3H, m, OCH(CH3)2], 3.58ꢀ3.51 (2H, m, CPyCH2Npro), 2.36ꢀ
2.33 (2H, m, CH2CH2N), 2.31ꢀ2.25 (2H, m, CHiPr), 2.19ꢀ2.15
(3H, m, CH3N), 1.60ꢀ1.58 (2H, m, CH2CH2CH2), 1.19 (12H,
d, CH3), 1.16 (18H, d, CH3), 0.50 (2H, m, CH2Si). 13C NMR
(CDCl3, ppm): δ = 160.14 (Cpy), 151.81 (Cpy), 145.42 (Carom),
138.25 (NCHN), 132.00 (Carom), 138.23 (Cpy), 130.35 (Carom),
124.77 (2Carom), 123.94 (CHimi), 123.52 (CHimi), 123.29 (Cpy),
122,45 (Cpy), 64.98 (CHCH3), 63.81 (CpyCH2N), 60.91 (CH2N),
53.94 (NimiCH2Cpy), 42.24 (NCH3), 28.59 [CH(CH3)2], 25.50
[CH(CH3)2], 24.40 (CH3CH), 20.86 (CH2CH2CH2), 9.51 (CH2Si).
EM (m/z): 609 (Mþ ꢀ Br, 100).
[RuH(CO)(3a)] (3aRu-H). General procedure: To a suspension of
complex 3aRu (50 mg, 0.1 mmol) in THF (5 mL) was added KOtBu
(11.2 mg, 0.1 mmol) at ꢀ32 °C and the mixture was stirred at ꢀ32 °C
for 4 h and then filtered. The dark-red filtrate was concentrated under
vacuum to 0.5 ml, and 5 mL of pentane was added to precipitate a brown-
red solid, which was filtered and washed with pentane (3 ꢁ 2 mL) and
then dried under vacuum (40 mg, 89%). IR (KBr, cmꢀ1): ν = 3050
(CHarom), 1946 (CO, RuH), 1610, 1630 (CdC, CdN). UVꢀvis: λ
(nm) = 258, 276, 334, 425. 1H NMR (CDCl3, ppm): 7.85ꢀ7.55 (m, 3H,
HPy), 7.64ꢀ7.50 (m, 1Himi), 7.42ꢀ7.10 (m, 2H, Harom), 6.12ꢀ5.99 (m,
1Himi), 3.62ꢀ6.55 (m, 2H, CPyCH2Cpyrr), 2.53ꢀ2.45(m, 4H,
CH2Npyrr), 2.33 (3H, s, p-CH3), 2.00 (6H, s, o-CH3), 1.98ꢀ1.77 (m,
4H, CH2CH2), ꢀ2.50 (s, 1H, HꢀRu). 13C NMR (CDCl3, ppm):
143.21, 134.10, 133.67 (Cpy), 132.65 (Carom), 132.5 (Carom), 132.42
(Cpy), 130.28 (Carom), 128.97 (Carom), 128.82 (Carom), 128.42 (Carom),
126.03 (CHimi), 123.13 (CHimi), 122.5 (CPy), 60.43 (CH2Npyrr), 55.76
(CpyCH2Npyrr), 22.40 (CH2CH2Npyrr), 21.52 (p-CH3), 16.70 (o-CH3).
[Ru(H)2(CO)(3a)] (3aRu-H2). A suspension of complex 3aRu (50
mg, 0.1 mmol) in CDCl3 (5 mL) was stirred for 12 h under 5 atm of H2.
The solvent was evaporated and the solid was dried under vacuum. IR
(KBr, cmꢀ1): ν = 3050 (CHarom), 2050, 2006 (RuꢀH), 1936 (CO),
1610, 1630, (CdC, CdN). UVꢀvis: λ (nm) = 258, 276, 334, 425. 1H
NMR (CDCl3, ppm): 7.80ꢀ7.62 (m, 3H, HPy), 7.64ꢀ7.50 (m, 1Himi),
7.55ꢀ7.32 (m, 2H, Harom), 7.01ꢀ6.99 (m, 1Himi), 6.99ꢀ6.85 (m, 2H,
NimiCH2Cpy), 3.70ꢀ6.62 (m, 2H, CPyCH2Npyrr), 2.50ꢀ2.30 (m, 2H,
CH2CH2Npyrr), 2.33 (3H, s, p-CH3), 2.03 (6H, s, o-CH3), 1.81ꢀ1.77
(m, 4H, CH2CH2), ꢀ2.46 (s, 2H, HꢀRu). 13C NMR (CDCl3, ppm):
δ = 158.70, 141.70, 134.67 (Cpy), 132.65 (Carom), 132.5 (Carom), 132.42
(Cpy), 130.28 (Carom), 128.97 (Carom), 128.82 (Carom), 128.58 (CHimi),
127.45 (CHimi), 123.98 (CHimi), 123.34 (Cpy), 65.60 (NpyrrCH2), 60.23
(CpyCH2Npyrr), 54.9 (NimiCH2CPy), 23.51 (CH2CH2CH2), 21.11
(p-CH3), 17.70 (o-CH3).
Synthesis of Ruthenium Complexes. (a) A solution of [3a]Br
(1 mmol, 442 mg) or [3b]Br (1 mmol, 504 mg) and [RuHCl(CO)-
(PPh3)3]33 (0.1 mmol, 100 mg) in 2 mL of tetrahydrofuran (THF) was
stirred at reflux temperature under N2 atmosphere. After being stirred
overnight, the solution was filtered, the solvents were removed in vacuo,
and the residue was washed several times with diethyl ether. A solution
of KHMDS in toluene (0.5 M, 19.6 μL, 1.02 mmol) was added to Ru
complex in dry THF (5 mL). The resulting suspension was stirred for
2 h. The mixture was filtered and evaporated. Since the desired complex
was dissolved in CH2Cl2, ethyl ether was used to precipitate. The
complex was filtered off as a brown powder in 75% yield.
(b) The milder conditions of the transmetalation pathway make it an
attractive choice also for the synthesis of ruthenium complexes. The
imidazolium salt [3a]Br (2 mmol, 884 mg) or [3b]Br (2 mmol, 1.08 g)
was dissolved in 25 mL of dichloromethane and transferred into a
Schlenk vessel. Silver(I) oxide (1 mmol, 231 mg) was added, and the
mixture was stirred for 24 h at room temperature under an Ar atmo-
sphere. The unreacted Ag2O was filtered through a plug of Celite, and in
most cases the solution was directly applied for further synthetic steps.
The product can be isolated by removing the solvent in vacuo to give a
solid stable to oxygen and water. [RuHCl(CO)(PPh3)3] (1 mmol) was
taken up in 5 mL of dichloromethane and added to a solution of Ag
complex in 10 mL of CH2Cl2. A white precipitate (AgCl) formed, and
the mixture was stirred overnight at room temperature. After filtration in
air, the solvent was removed in vacuum to give a brown waxy substance.
The waxy substance was triturated with diethyl ether. The final
compound is stable in air.
[RuHCl(CO)(1a)] (1aRu). C32H34ClN5ORu (641.2). IR (KBr,
cmꢀ1): ν = 3050 (CHarom), 2051 (RuꢀH), 1937 (CO), 1610, 1630
1
(CdC, CdN). UVꢀvis: λ (nm) = 298. H NMR (CDCl3, ppm): δ
=7.89ꢀ6.99 (11H, m, Hpy, Harom, Himi), 6.13ꢀ6.02 (4H, m, NimCH2C),
2.27 (6H, s, p-CH3), 2 0.00 (12 H, s, o-CH3). 13C NMR (CDCl3, ppm)
(partial): δ = 144.25 (CPy), 134.39 (Cpy), 133.23 (Cpy), 133.18 (Carom),
132.15 (Carom), 131.93 (Carom), 131.85 (CPy), 128.56 (Carom), 128.40
(Carom), 128.11 (Carom), 125.00 (CHimi), 124.00 (Cpy), 123.62 (CHimi),
32.18 (NimCH2C), 26.38, 29.69 (p-CH3), 23.41, 21.15 (o-CH3).
EM (m/z): 669 ([1aRu] ꢀ Cl þ CH3COOH), 653 ([1aRu] ꢀ Cl þ
EtOH).
[RuH(CO)Cl(4b)] (4bRu). C36H57ClN4O3RuSi (774.35). IR (KBr,
cmꢀ1): ν = 3053 (CHarom), 2041 (RuꢀH), 1937 (CO), 1657, 1594
(CdC, CdN), 1107.1 (vs, SiꢀO). UVꢀvis (λ, nm): 288, 333, 370. 1H
NMR (CDCl3, ppm): δ = 7.79 (1H, Himi), 7.67ꢀ7.28 (6H, Hpy, Harom),
6.97 (1H, Himi), 5.49 (2H, s, NimiCH2Cpy), 4.20ꢀ3.99 [3H, m, OCH-
(CH3)2], 3.67ꢀ3.62 (2H, m, CPyCH2N), 2.44ꢀ2.39 (2H, m,
CH2CH2N), 2.38ꢀ2.36 (2H, m, CHiPr), 2.32ꢀ2.29 (3H, m, CH3N),
1.63ꢀ1.58 (2H, m, CH2CH2CH2), 1.17 (12H, d, CH3), 1.0 (18H,
d, CH3), 0.54ꢀ0.56 (2H, m, CH2Si). 13C NMR (CDCl3, ppm):
δ = 206.16 (CO), 186.54 (CꢀRu), 159.72 (Cpy), 145.39 (Cpy),
140.42 (Carom), 134.78, (Carom), 134.67 (Cpy), 131.96 (Carom),
[RuHCl(CO)(1b)] (1bRu). C38H46ClN5ORu (725.24). IR (KBr,
cmꢀ1): ν = 3050 (CHarom), 2049 (RuꢀH), 1942 (CO), 1610, 1630,
(CdC, CdN). UVꢀvis: λ (nm) = 290. 1H NMR (CDCl3, ppm): δ =
7.98ꢀ7.0 (13H, m, Hpy, Harom, Himi), 6.13ꢀ6.02 (4H, m, NimiCH2C),
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Organometallics
ARTICLE
128.35 (2Carom), 124.62 (CHimi), 124.23 (CHimi), 123.16 (Cpy),
122.25 (Cpy), 64.87 (CHCH3), 63.91 (CpyCH2N), 61.14 (CH2N),
56.07 (NimiCH2Cpy), 42.13 (NCH3), 28.53 [CH(CH3)2], 25.54
[CH(CH3)2], 24.58 (CH3CH), 20.86 (CH2CH2CH2), 10.42 (CH2-
Si). EM (m/z): 609 (L), 688 (M ꢀ 2iPr), 715 (M ꢀ 4Me), 738 (M ꢀ
Cl ꢀ H).
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4bRu-MCM-41. Found: C, 5.10; H, 1.57; N, 0.65; Ru, 0.6, 0.06
mmol/g. IR (KBr, cmꢀ1): ν = 1942 (CO), 1649, 1625 (CdN, CdC),
1060 (SiꢀO). UVꢀvis: λ (nm) = 224, 264, 288, 324. 13C NMR (solid)
(ppm): δ = 175.0 (RuꢀC), 156.3ꢀ117.3 (CPy, CPh, Cimi), 73.8ꢀ54.0
(NCH2CPy, NimiCH2Cpy, CH2N,), 41.0 (CH3N), 28.7ꢀ15.9 (CH2CH2-
CH2, NCH3, CH3mes), 9.2 (CH2Si).
Typical Procedure for the Catalytic Transfer Hydrogenation of
Primary Alcohols. (a) The complex 3aRu (0.01 mmol), primary alcohol
(1 mmol), and KOH (0.01 mol) were dissolved in toluene (2 mL). The
solution was heated with stirring at the specified temperature, and the
yield was determined by GC. (b) The complex 3aRu-H (0.01 mmol)
and alcohol (1 mmol) were dissolved in toluene (2 mL). The solution
was heated with at the specified temperature, and the yield was
determined by GC. (c) The complex 4bRu-MCM-41 (0.1 mmol),
primary alcohol (1 mmol), and KOH (0.01 mol) were dissolved in
toluene (2 mL). The solution was heated with stirring at the specified
temperature, and the yield was determined by GC.
Typical Procedure for the Catalytic Transfer Hydrogenation of
Aldehyde and Ketones. The complex 3aRu-H (0.01 mmol) was
dissolved in 2-propanol (3 mL). The aldehyde or ketone (1.0 mmol)
and KOH (0.01 mmol) were added to the solution. The solution was
heated with stirring at the specified temperature and the yield was
determined by GC.
’ ASSOCIATED CONTENT
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Supporting Information. Details of the synthesis and
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b
characterization of new compounds, including images of 13C
NMR spectra and HPLC traces. This material is available free of
charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
€
(11) (a) Ozdemir, I.; Demir, S.; G€urb€uz, N.; C-etinkaya, B.; Toupet,
*(M.I.) telephone þ34 913349000, fax þ34 913720623, e-mail
marta.iglesias@icmm.csic.es; (F.S.) telephoneþ34 915622900,
fax þ34 915644853, e-mail felix-iqo@iqog.csic.es.
L.; Bruneau, Ch.; Dixneuf, P. H. Eur. J. Inorg. Chem. 2009, 1942–1949
and references therein. (b) Zhang, Y.; Chen, Ch.; Ghosh, S. C.; Li, Y.;
Hong, S. H. Organometallics 2010, 29, 1374–1378. (c) Ghosh, S. C.;
Muthaiah, S.; Zhang, Y.; Xu, X.; Hong, S. H. Adv. Synth. Catal. 2009,
351, 2643–2649.
(12) (a) Boronat, M.; Corma, A.; Gonzꢀalez-Arellano, C.; Iglesias,
M.; Sꢀanchez, F. Organometallics 2010, 29, 134–141. (b) del Pozo, C.;
Corma, A.; Iglesias, M.; Sꢀanchez, F. Organometallics 2010, 29,
4491–4498.
’ ACKNOWLEDGMENT
Financial support was provided by the Direcciꢀon General de
Investigaciꢀon Científica y Tꢀecnica of Spain (project MAT2006-
14274-CO2-02, Consolider-Ingenio 2010 (CSD-0050-MULTI-
CAT) for financial support. We thank J. A. Esteban for lab
assistance.
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