Asymmetric carbon-carbon bond forming reactions catalysed by metal(II) bis(oxazoline) complexes immobilized using supported ionic liquids

Article abstract of DOI:10.1002/adsc.201000953

A series of bis(oxazoline) metal(II) complexes has been supported on silica and carbon supports by non-covalent immobilisation using an ionic liquid. The catalytic performance of these solids was compared for the enantioselective Diels-Alder reaction between N-acryloyloxazolidinone and cyclopentadiene and the Mukaiyama-aldol reaction between methyl pyruvate and 1-methoxy-1- trimethylsilyloxypropene. In both reactions the enantioselectivity was strongly influenced by the choice of support displaying enantioselectivies (ee values) up to 40% higher than those conducted under homogeneous reaction conditions.

Full text of DOI:10.1002/adsc.201000953

FULL PAPERS
DOI: 10.1002/adsc.201000953
Asymmetric Carbon-Carbon Bond Forming Reactions Catalysed
by Metal(II) Bis(oxazoline) Complexes Immobilized using
Supported Ionic Liquids
a
a,
a
b
a
P. Goodrich, C. Hardacre, * C. Paun, A. Ribeiro, S. Kennedy,
b
a
b
c
M. J. V. LourenÅo, H. Manyar, C. A. Nieto de Castro, M. Besnea,
and V. I. Pꢀrvulescu
School of Chemistry and Chemical Engineering/QUILL, Queenꢁs University, Stranmillis Road, Belfast, Northern Ireland
BT9 5AG, U.K.
c
a
Fax : (+44)-28-9097-4687; e-mail: c.hardacre@qub.ac.uk
Departmento de Quꢂmica e Bioquꢂmica e Centro de CiÞncias Moleculares e Materiais Faculdade de CiÞncias,
Universidade de Lisboa, 1749-016 Lisboa, Portugal
b
c
University of Bucharest, Department of Chemical Technology and Catalysis, B-dul Regina Elisabeta 4-12, Bucharest
030016, Romania
Received: December 16, 2010; Published online: April 13, 2011
Abstract: A series of bis(oxazoline) metal(II) com- strongly influenced by the choice of support display-
plexes has been supported on silica and carbon sup- ing enantioselectivies (ee values) up to 40% higher
ports by non-covalent immobilisation using an ionic than those conducted under homogeneous reaction
liquid. The catalytic performance of these solids was conditions.
compared for the enantioselective Diels–Alder reac-
tion between N-acryloyloxazolidinone and cyclopen-
tadiene and the Mukaiyama-aldol reaction between Keywords: asymmetric catalysis; Diels–Alder reac-
methyl pyruvate and 1-methoxy-1-trimethylsilyloxy- tion; ionic liquids; Mukaiyama-aldol reaction; sup-
propene. In both reactions the enantioselectivity was ported catalysts
Introduction
the homogeneous catalyst immobilised on a high sur-
face area support material (Table 1). The resulting
The development of heterogeneous catalysts able to catalyst behaves similarly to those found under homo-
promote enantioselective organic reactions is a field geneous reaction conditions due to the solvation of
of growing interest. A major advantage of the use of the metal complex by the ionic liquid with the reac-
a heterogeneous catalyst for reactions is the ease with
which it can be recovered and subsequently reused.
Some of the most widely used methods to immobilize
expensive catalysts, such as those based on metal bis-
Table 1. Surface area and pore volume for the silica and
carbon supports.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(oxazoline) complexes include covalent grafting of Support/Ionic Liquid
Surface Average
Pore
[
1,2,3]
area pore diame- volume
the ligand
or electrostatic immobilisation of the
2
À1
3
À1
[4]
[m g ] ter [nm]
[cm g ]
metal anion. Although covalent grafting has been
the more successful technique, this methodology often
results in lower activity and selectivity compared with
SI1032
MCM-41
273
1011
995
206
14.2
2.5
3.4
0.97
1.07
1.29
0.51
[
5]
the analogous homogeneous reactions.
These SBA-15
changes may be due to modifications in the structure Carbon Nano Tubes
of the catalyst and the conformational preference of (CNT)
the chiral ligand; however, the nature of the support
effect is not well understood.
In order to alleviate these problems, immobilisation
without covalent bonding has been developed. This
method utilises a thin film of ionic liquid containing
9.3
Graphite
Activated Carbon (AC) 767
11
5.4
2.7
0.02
0.59
Theoretical surface area 540
of a monolayer of
[
C mim] ACHTUNTGNERNUG[ NTf ]
2 2
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995

P. Goodrich et al.
FULL PAPERS
Scheme 1. The Diels–Alder reaction between N-acrolyloxazolidinone and cyclopentadiene using 10 mol% M(II) bis(oxzao-
line) catalysts.
tion taking place in the thin liquid film. Supported Results
ionic liquid phase (SILP) catalysis has been the sub-
[
6]
ject of a number of reviews and has been reported Diels–Alder Reaction
to effectively immobilise homogeneous catalysts for
[
7]
[8]
use in hydroformylations, carbonylations, hydroge- Table 2 summarises the results of a comparative study
[
9]
[10]
nations,
hydroaminations,
Heck and Suzuki– of the Diels–Alder reaction (Scheme 1) catalysed by a
series of copper(II), magnesium(II) and zinc(II) tri-
[
11]
Miyaura reactions.
Asymmetric metal-catalysed SILP-mediated reac- flate-based chiral Lewis acids (10 mol%) in homoge-
[
12]
tions have been limited to hydrogenations,
oxida- neous conditions at room temperature in dichlorome-
[13]
[14]
[15]
tions, cyclopropanations and Mukaiyama-aldol
thane, diethyl ether and [C mim] ACHTUNGTNERNU[G NTf ]. A compari-
2 2
reactions. In all cases, immobilisation of the chiral son with the competing racemic reaction conducted in
complexes onto silica using an ionic liquid resulted in the absence of catalyst was also undertaken. Interest-
similar ee values and conversions compared with the ingly in the molecular solvents, the non-metal-cata-
same reactions conducted under homogeneous condi- lysed reaction showed significant conversions which,
tions. In contrast, moderate to poor ee values were in some cases, were comparable with those of the
observed for the bis(oxazoline)-Cu(II)-catalysed metal-catalysed reactions. However, in the ionic
Diels–Alder reaction between N-acryloyloxazolidi- liquid, the non-metal-catalysed reaction showed poor
none (1) and cyclopentadiene (Scheme 1) when im- conversion probably due to the high rates of diene
mobilised onto silica using SILP technology despite polymerisation. In [C mim] ACHTUNGTERNNN[UG NTf ], all the metal-cata-
2
2
high ee values being obtained under homogeneous lysed reactions showed complete conversion within
[
16]
conditions in the ionic liquid. This paper reports on 1 min at room temperature; with ee values higher
the general applicability of SILP metal-bis(oxazoline) than the analogous reactions conducted in dichloro-
catalysts for asymmetric Diels–Alder and Mukaiya- methane. Overall, the ee values found in diethyl ether
ma-aldol reactions.
were poor (ꢀ22%) when compared with reactions
performed in either dichloromethane or
[C mim][NTf ]. The increased enantioselection found
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
2
2
in the ionic liquid is partly due to the fact that the
Table 2. Comparison of homogeneous Diels–Alder reaction conducted in dichloromethane, diethyl ether and
[a]
ACHTUNGTRENNUNG[ C mim] ACHTUNGTRENNUNG[ NTf ] using a series of 10 mol% Cu(II), Mg(II) and Zn(II) bis(oxazoline) catalysts. Enantioselectivities deter-
2 2
mined on the endo isomer.
[b]
2
[b]
[c]
Catalyst
CH Cl
Et O
2
ACTHUNGTNERNUN[G C mim] ACHTUNGTERNNNU[G NTf ]
2 2
2
%
conv.
% endo
% ee
% conv.
% endo
% ee
% conv.
% endo
% ee
–
1
2
3
4
56
78
44
87
88
82
80
83
–
40
32
38
49
44
88
87
80
80
80
–
12
86
89
88
92
85
–
70 (S)
16 (S)
50 (S)
4 (S)
14 (S)
15 (R)
22 (S)
7 (R)
100
100
100
100
90 (S)
19 (R)
80 (R)
20 (R)
61 [
c]
100
[
[
[
a]
b]
c]
3
3
Reactions conducted at 258C in 5 cm of molecular solvent and 2 cm of [C mim]
Conversions recorded after 15 min.
Conversion recorded after 1 min.
A
H
U
G
E
N
N
[NTf ].
2
2
996
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ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 995 – 1004

Asymmetric Carbon-Carbon Bond Forming Reactions Catalysed by Metal(II) Bis(oxazoline) Complexes
Table 3. Comparison of the Lewis acid-catalysed Diels–Alder reaction under SILP reaction conditions in diethyl ether.
Entry
Support
Catalyst 1
Catalyst 2
Catalyst 3
Catalyst 4
[a,b]
[a,b]
[c]
[a,b]
[c]
[a,b]
[c]
[c]
%
conv.
% ee
% conv.
% ee
% conv.
% ee
% conv.
% ee
1
2
3
4
5
6
SI1302
MCM-41
SBA-15
AC
CNT
Graphite
100
100
100
94
100
100
87 (S)
95 (S)
96 (S)
0
92 (S)
85 (S)
100
100
100
29
100
100
8 (R)
16 (R)
17 (R)
0
3 (R)
2 (R)
100
100
100
66
100
100
66 (R)
70 (R)
72 (R)
51 (R)
65 (R)
25 (R)
100
100
100
100
100
100
22 (R)
53 (R)
32 (R)
0
37 (R)
56 (R)
[
[
[
a]
b]
c]
Conversion at 208C recorded after 3 min.
Determined by HPLC.
endo ee determined by HPLC.
contribution from the uncatalysed racemic reaction is SILPs to these systems. Small increases in ee of up to
minimised. However, the exception to this is Zn(II) 6% were observed for catalyst 1 in the case of MCM-
bis(oxazoline) catalyst 4 which also shows complete 41, SBA-15 and CNT supported materials. In contrast,
conversion after 1 min in both dichloromethane and with the exception of AC supported SILP catalysts,
ionic liquid. Therefore, the differences in ee observed Zn(II) bis(oxazoline) catalyst 4 showed significant in-
with respect to the choice of solvent are not solely creases in ee from 2–36% on immobilisation com-
due to the competing background racemic reaction pared with the homogeneous ionic liquid reaction. Al-
but could also be due to changes in the catalyst geom- though the non-covalent immobilisation of bis(oxazo-
etry. In ionic liquids, the high concentration of ions line) complexes, for example, by using supported
could encourage chelation of the anions to the metal ionic liquid phase methodologies, is believed to
centre which are known to dissociate to some degree reduce conformational differences between the homo-
[
4e,17]
in molecular solvents.
This non-dissociation in geneous and heterogeneous systems the results from
ionic liquids would result in the reaction proceeding Table 3 show that this is not always the case. Immobi-
via an octahedral rather than a tetrahedral complex. lisation can have beneficial effects on selectivity, for
Interestingly, for all the catalysts 2–4, a reversal of example, as well as providing a method to separate
configuration was found in dichloromethane com- the catalyst and the reaction mixture easily. There-
pared with ionic liquid which would be consistent fore, the influence of the support on the reaction was
with a change in catalyst geometry. A similar concept further analysed by varying the support to ionic liquid
was proposed by Carbone et al. to account for the mass ratio.
switch in configuration for Diels–Alder reactions con-
ducted in the presence of coordinating solvents.
The results for the MCM-41 and graphite supported
systems for catalysts 1–4 are shown in Table 4 and
[
18]
Immobilisation of catalysts 1–4 using the ionic Table 5, respectively, for the Diels–Alder reaction as
liquid onto a range of silica and carbon supports was a function of the IL:support ratio used. Herein, the
performed by wet impregnation. For the supported standard SILP preparation procedure was employed
catalysts, the performance for the Diels–Alder reac- with 10 mol% catalyst with respect to the dieneophile
tion was studied using diethyl ether as the solvent due loaded onto 0.05 g, 0.10 g and 0.20 g of each support
to its low rate of reaction for all the homogeneous using 0.15 g of ionic liquid, that is, 25 wt%, 40 wt%
catalysts. In addition, [C mim] ACHTUNGRETNN[UNG NTf ] has a low solu- and 57 wt% support being used. For comparison,
2
2
bility in diethyl ether compared with dichloromethane Table 4 and Table 5 also include the results from the
3
and thus reducing the possibility of ionic liquid/cata- biphasic IL-Et O (0.15 g/5 cm ) reaction (0 wt%), i.e.,
2
lyst leaching. Table 3 summarises the results for the where no support was present, and the catalyst was
SILP-catalysed Diels–Alder reaction. In all cases the immobilised onto the support (0.1 g) in the absence of
configurations were identical to those obtained under ionic liquid (denoted 100 wt%). With the exception of
homogeneous ionic liquid conditions. With the excep- catalyst 2 which performed poorly throughout, the
tion of activated carbon (AC), all SILP catalysts presence of an ionic liquid thin film was found to be
showed complete conversion after 3 min under the crucial in obtaining high enantioselectivities and activ-
present conditions. SILP catalysts supported on AC ity. In the absence of ionic liquid significant drops in
showed lower activity and/or enantioselectivities for ee were observed. Interestingly, the MCM-41 SILP
all catalysts examined. For most supports, the SILP based catalysts 1–3 showed comparable or little
catalysts 2 and 3 showed comparable or slightly lower change in ee as a function of the ionic liquid loading
ee values to those found under homogeneous ionic between 0–57 wt%. For MCM-41 SILP catalyst 4, all
liquid conditions demonstrating the applicability of supported systems showed significantly higher ee
Adv. Synth. Catal. 2011, 353, 995 – 1004
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P. Goodrich et al.
FULL PAPERS
Table 4. Ionic liquid/MCM-41 support effects on catalysed Diels–Alder reaction under heterogeneous reaction conditions in
diethyl ether.
Entry
Support [wt%]
Catalyst 1
Catalyst 2
Catalyst 3
Catalyst 4
[a,b]
[
a,b]
[c]
[a,b]
[c]
[a,b]
[c]
[c]
%
conv.
% ee
% conv.
% ee
% conv.
% ee
% conv.
% ee
1
2
3
4
5
0
100
100
100
100
83
90 (S)
92 (S)
95 (S)
90 (S)
66 (S)
100
100
100
100
100
19 (R)
16 (R)
17 (R)
16 (R)
21 (R)
100
100
100
100
100
80 (R)
77 (R)
70 (R)
68 (R)
37 (R)
100
100
100
100
22
46 (R)
42 (R)
53 (R)
48 (R)
2 (S)
25
40
57
100
[
[
[
[
a]
b]
c]
d]
Conversion at 208C after 3 min.
Determined by HPLC.
endo ee and configuration determined by HPLC.
.100 g of support used (??where??).
0
Table 5. Ionic liquid/graphite support effects on catalysed Diels–Alder reaction under heterogeneous reaction conditions in
diethyl ether.
Entry
Support [wt%]
Catalyst 1
Catalyst 2
Catalyst 3
Catalyst 4
[a,b]
[
a,b]
[c]
[a,b]
[c]
[a,b]
[c]
[c]
%
conv.
% ee
% conv.
% ee
% conv.
% ee
% conv.
% ee
1
2
3
4
5
0
100
100
100
100
100
90 (S)
88 (S)
85 (S)
80 (S)
42 (S)
100
100
100
100
100
19 (R)
12 (R)
17 (R)
18 (R)
21 (R)
100
55
100
82
80 (R)
30 (S)
25 (S)
17 (S)
37 (S)
100
100
100
100
22
46 (R)
43 (R)
56 (R)
12 (R)
2 (S)
25
40
57 [
d]
100
100
[
[
[
[
a]
b]
c]
d]
Conversion at 208C after 3 min.
Determined by HPLC.
endo ee and configuration determined by HPLC.
.100 g of support used.
0
values compared with the biphasic ionic liquid-diethyl
ether reaction. In contrast, graphite SILP based cata-
lysts 3 and 4 showed large variations in ee with the
IL:support ratio. For the MCM-41 support, the ab-
sence of IL will result in an increase in exposure of
surface silanol groups increasing the rate of the silica-
catalysed racemic reaction and a drop in ee. In the
case of graphite the poor ee in the absence of IL
maybe associated with other surface heteroatoms fa-
cilitating the non-metal-catalysed reaction.
The support to IL mass ratio has been shown to
have a significant effect for other SILP catalysed reac-
tions. Riisager et al. observed that the performance of
the Rh-catalysed hydroformylation using propene was
strongly linked to ionic liquid loading on the silica
[8a]
support. In addition, following optimisation of the
acidic chloroaluminate SILP catalyst for a slurry
phase Friedel–Crafts alkylation of cumene, a critical
ionic liquid loading value was found to be necessary
to overcome the neutralisation of the chloroaluminate
with the surface silanol groups on the silica.
The effect of temperature was also studied for cata-
lyst 4 immobilised on MCM-41 and graphite SILP cat-
Figure 1. Variation in endo % ee as a function of tempera-
ture on the for the Zn(II) bis(oxazoline)-catalysed homoge-
nous Diels–Alder reaction in dichloromethane (*) and the
[
19]
biphasic mixture [C mim] ACHTUNGTERNNUN[G NTf ]+diethyl ether (ꢄ) and the
2
2
alysts and compared with homogenous reactions con- heterogeneous SILP catalysed Diels–Alder reaction sup-
ducted in IL and dichloromethane (Figure 1). Com- ported on graphite (+) and supported on MCM-41 (&).
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Asymmetric Carbon-Carbon Bond Forming Reactions Catalysed by Metal(II) Bis(oxazoline) Complexes
plete conversions were noted for all reactions run the ethereal layer of fresh MCM-41 and CNT SILP
below room temperature after 3 min. Unsurprisingly, catalyst 1 led to little change in the conversion but a
decreasing the temperature resulted in an increase in marked decrease in ee from 95% to 8% for MCM-41
ee for both the SILP catalysts and the homogeneous and from 85% to 3% ee for graphite supported SILP
reaction conducted in dichloromethane. At À408C, catalyst 1.
reactions using graphite and MCM-41 SILP systems
Supported homogeneous catalysts have been re-
resulted in ee values of 71% and 69%, respectively, ported previously for similar enantioselective Diels–
[
21,22]
which are significantly higher than that obtained Alder reactions. Rechavi and Lemaire
used a co-
when using dichloromethane (31% ee at À408C). Sur- valently-supported ligand based on IndaBOX for the
prisingly, lowering the temperature in the biphasic IL/ same Diels–Alder reaction. Using this silica grafted
Et O reaction showed no increase in ee. A homogene- ligand with Cu
ous comparison of catalyst 1 in ionic liquid at low reached although the ee dropped to 81% at room
temperature was impossible due to the high viscosity temperature. OꢁLeary et al. immobilised catalyst 2
of the reaction media; however, an ee of 25% was ob- onto chromatographic silica through electrostatic in-
served in the analogous homogeneous reaction con- teractions and the same Diels–Alder reaction con-
A
H
U
G
R
N
N
(ClO ) , an ee of 92% at À788C was
2
4 2
[
23]
ducted at 08C.
ducted at À508C resulted in an ee of 57% at 43%
Recycle experiments were also performed using conversion. In contrast, Xiao and Li also studied elec-
catalysts 1 and 4 supported on MCM-41, SBA-15, trostatic immobilisation of 2 onto silica where up to
CNT and graphite and monitored after 3 min conver- 93% ee at 83% conversion over 8 h was observed for
sion (Table 6). The use of MCM-41 maintained excel- a similar Diels–Alder reaction between cyclopenta-
[
24]
lent conversion with a slight decrease in ee upon recy- diene and N-crotonoyloxazolidinone.
Recently, ee
cle. Although the carbon supported catalysts also values greater than 95% were recorded with moder-
showed excellent conversion upon recycle, a more ate conversion (30–60%) under homogeneous condi-
marked decrease in ee was observed. Analysis of the tions for the same Diels–Alder reaction (Scheme 1)
supernatant and product following recycle showed using a palladium-based BINAP catalyst and a range
[
25]
that, for all the supports studied, the metal leaching of ionic liquids. While there has been extensive use
was below 0.01 mol% by ICP per reaction and HPLC of oxides as supports in enantioselective catalysis,
analysis showed that ligand leaching was below the with the exception of asymmetric keto ester hydroge-
[
26]
detection limit. The decrease in enantioselectivity on nations involving a surface chiral modifier, the use
recycle was, therefore, attributed to the build up of of carbon-based supports has been limited. Baleiz
[
20]
cyclopentadiene dimer
on the support surface as et al. anchored a chiral vanadium salen complex to
has been previously observed in other SILP catalysed various supports in order to develop a recyclable cata-
[
16]
Diels–Alder reactions. This proposal was supported lyst for the enantioselective cyanosilylation of benzal-
[
27]
by the fact that the addition of cyclopentadiene dimer dehyde. Therein, an 85% ee was obtained when the
(
1.5 molar equivalents with respect to substrate) to catalyst was immobilised onto silica, which compared
favourably with the analogous homogeneous reactions
89% ee. In contrast, grafting the vanadium complex
onto single walled nanotubes (SWNTs) resulted in a
modest 66% ee. Even lower ee values (48%) were
achieved when the complex was anchored onto acti-
vated carbon. These poor ee values were attributed to
the significant amount of heteroatoms on the surface
and, in the case of AC, ill-defined structure of the
support. To the best of our knowledge the present
MCM-41 or SBA-15 SILP system using catalyst 1 has
the highest reported ee with complete conversion
using a supported catalyst system for this particular
Diels–Alder reaction and is able to achieve these re-
sults at room temperature. Moreover, for the Zn-
based catalyst system, the increase in ee on immobili-
sation is the largest reported to date compared with
that found in the homogeneous IL reaction. Further-
more, the use of a supported ionic liquid provides rea-
sonable ee of up to 56% for Zn(II)-based catalysts of
this type for the first time.
Table 6. Recycle of the Diels–Alder reaction catalysed by
catalysts 1 and 4 conducted in diethyl ether under SILP re-
action conditions at room temperature.
[a,b]
[c]
Catalyst
Support (0.1 g)
MCM-41
Cycle
% conv.
% ee
1
1
2
3
1
2
3
1
2
3
1
2
3
100
100
95
100
100
97
100
100
100
100
100
97
95
93
91
85
77
74
53
51
50
56
55
49
Graphite
MCM-41
Graphite
4
[
[
[
a]
b]
c]
Conversion recorded after 3 min at 208C.
Determined by HPLC.
endo ee determined by HPLC.
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P. Goodrich et al.
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Table 7. Comparison of Lewis acid catalysed Mukaiyama-aldol reaction under homogeneous and heterogeneous reaction
conditions in different solvents.
Entry
Support
Solvent
Time [min]
Catalyst 1
Catalyst 2
Catalyst 4
[a,b]
[a,b]
[c]
[a,b]
[c]
[c]
%
conv.
% ee
% conv.
% ee
% conv.
% ee
e
1
2
3
4
5
6
7
8
9
–
–
–
CH Cl
15
15
1
5
5
5
5
5
5
43
32
82 (S)
80 (S)
90 (S)
86 (S)
88 (S)
89 (S)
53 (S)
86 (S)
87(S)
67
8
47 (S)
61 (S)
60 (S)
73 (S)
71 (S)
73 (S)
70 (S)
68 (S)
76 (S)
100
44
4 (S)
7 (R)
20 (R)
21 (R)
24 (R)
23 (R)
2
2
Et O
2
IL
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0
[
d]
SI1302
MCM-41
SBA-15
AC
CNT
Graphite
IL/Et O
2
[
d]
IL/Et O
2
[d]
IL/Et O
2
[
d]
IL/Et O
2
[
d]
IL/Et O
100
100
25 (S)
3 (S)
2
[d]
IL/Et O
2
[
[
[
[
[
a]
b]
c]
d]
e]
Conversion at 208C.
Determined by HPLC.
ee determined by HPLC.
Time taken for maximum conversion.
1% selectivity to the desired product.
9
Although catalyst 1 in ionic liquids produced the
1
highest ee, a by-product, identified by H NMR spec-
troscopy as 3-hydroxy-1,3-diphenylbutan-1-one, was
consistently formed in ~9% yield. Interestingly, this
by-product was only generated during reactions con-
ducted in ionic liquid with catalyst 1 and there was no
evidence for its formation with any other catalyst/sol-
vent system. This by-product results from a Mukaiya-
ma-aldol reaction between 1-phenyl-1-trimethylsiloxy-
AHCTUNGTRENNUNG
Scheme 2. The Mukaiyama-aldol condensation reaction be-
tween methyl pyruvate and 1-phenyl-1-trimethylsiloxy-
ethene using 10 mol% M(II) bis(oxazoline) catalysts.
using the ionic liquid on silica and carbon supports
were also performed. All silica supports showed com-
plete conversion and 100% selectivity to the Mu-
kaiyama-aldol product under SILP conditions for all
catalysts. In contrast with the Diels–Alder reaction re-
ported herein, a minimal change in ee was observed
Mukaiyama-Aldol Reaction
Table 7 summarises the results of a comparative study for the three catalysts. The conversions and ee values
of the Mukaiyama-aldol reaction (Scheme 2) cata- were more varied for the reaction catalysed by SILP
lyzed by a series of copper(II) and zinc(II) triflate catalysts supported on carbon. For example, with cat-
based chiral Lewis acids (10 mol%) in homogeneous alyst 1 only 53% ee was observed compared with 86%
conditions at room temperature in various solvents and 87% ee obtained with CNT and graphite. For the
(
entries 1–3). For Cu catalysts 1 and 2, and Zn cata- SILP based Zn catalyst on AC no conversion was
lyst 4, increasing conversions followed the trend noted and a poor ee was observed with graphite.
Et O<CH Cl !IL. It should be noted at this point
2
2
2
that there was no reaction was observed for the anal-
ogous Mg(II) catalyst 3.
Discussion
Typically, complete conversions were achieved
within 1 min at room temperature with catalysts 1, 2 The large variation in ee upon change of oxide sup-
and 4 in the ionic liquid, whereas in dichloromethane port or support to IL mass ratio may indicate that the
and diethyl ether moderate to good conversions were confinement of the catalyst and/or reactants within
[
28]
only achieved after 15 min. Interestingly, all the cata- the support is important. Caplan et al. showed that
lysts gave a markedly higher ee in ionic liquid com- surface confinement could be observed in the carbon-
pared with dichloromethane and, in most cases, dieth- yl-ene reaction between methylenecyclopentene and
[
29]
yl ether. Exceptionally, no improvement in ee was ob- ethyl glyoxylate.
Therein, impregnation of
(BOX-Ph)] in a zeolite Y utilising the ꢅship in a
bottleꢁ methodology showed a 93% ee compared with
a
2+
tained on comparing the ionic liquid and diethyl ether [Cu
for catalyst 2.
ACHTUNGTRENNUNG
1000
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Adv. Synth. Catal. 2011, 353, 995 – 1004

Asymmetric Carbon-Carbon Bond Forming Reactions Catalysed by Metal(II) Bis(oxazoline) Complexes
5
7% ee obtained in the analogous homogeneous reac- Conclusions
tion. A similar enhancement in ee was also observed
in the epoxidation of a-methylstyrene. Encapsulation For the majority of reaction systems studied, SILP
of an Mn
ACHTUNGTRENNUNG( salen) complex in MCM-22 resulted in an catalysis was found to show significantly higher activi-
increased ee of 91% in comparison with 51% ee ob- ties and ee values compared with the corresponding
[
30]
tained for the homogeneous reaction.
effect was also observed for a laponite exchanged thane. Although the presence of an ionic liquid thin
Cu(BOX-Ph)][OTf] catalyst in the Mukaiyama-aldol film was crucial in enabling high ee values to be ob-
A surface homogeneous reactions conducted in dichlorome-
[
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
2
reaction between 2-(trimethylsilyloxy)furan and tained, little reduction in activity was found compared
methyl 2-oxo-2-phenylacetate. The immobilisation re- with the homogeneous reactions conducted in ionic
sulted in a reversal of the anti/syn selectivity coupled liquid, thereby significantly reducing the amount of
with an increase in the ee from 16%, for the homoge- ionic liquid required. In some instances the non-cova-
neous reaction, to 90% ee, for the supported reac- lent immobilisation of bis(oxazoline) complexes using
[31]
tion. Structuring within the support may also play a SILP methodologies can reduce conformational dif-
role even in graphite-based catalysts which have large ferences between the homogeneous and heterogene-
layer spacing. These spaces could be filled by ionic ous systems. However, contrasting conversions and ee
liquid forming a highly ordered lamellar type struc- values were also observed demonstrating strong sup-
[
32]
ture.
have been used to functionalise CNTs,
ple, which produce soft functional materials with as- and highlights the complex nature of heterogeneous
In addition, imidazolium-based ionic liquids port effects. This support effect was found to be inde-
[33,34]
for exam- pendent of catalyst, reaction or support/IL loading
[
35]
sembled structures and are suitable for enantiose- catalysis even with SILP systems.
lective catalysis. Although a large change in ee was
observed little change in endo selectivity was found
on moving from molecular solvent to ionic liquid to
SILP systems. The fact that the confinement of the
catalyst within the pore has no significant effect on
Experimental Section
the endo/exo selectivity is surprising if the pore/ionic
Unless otherwise stated all reagents (ex Aldrich) were used
as received. Diethyl ether and dichloromethane were dried
and degassed prior to use. 1-Ethyl-3-methylimidazolium
liquid structure is influencing the structure of the cat-
alyst/reactant complex to the extent that the change
in ee indicates.
bis{(trifluoromethyl)sulfonyl}imide ([C mim] ACHTUGNTRNEUN[G NTf ]) was
2
[38]
2
As well as catalyst confinement, another possible
prepared in house using standard literature methods and,
explanation for the marked changes in ee, in particu- after drying for 24 h at 608C under a high vacuum whilst
lar the increased ee found for MCM-41, SBA-15 and stirring, was found to contain <0.13 wt% water, determined
CNT (Table 2, entries 7, 10, 12) compared with the by Karl-Fischer analysis, and <10 ppm halide, determined
by suppressed ion chromatography. Silica supports, MCM-41
homogeneous reaction (Table 2, entry 3), is the
and SBA-15, were synthesised using standard literature
change in thermal conductivity obtained when these
[39,40]
methods.
Silica supports, SI1302, SI10010 and SI10645,
supports are combined with ionic liquids. Cooling is
regularly used in enantioselective reactions to im-
prove the ee and stabilize the catalyst in the most se-
lective form. Therefore, for exothermic reactions,
local heating can cause lower ee values and by in-
were obtained from GRACE Davison. All silica supports
were calcined at 4008C prior to use. Carbon nanotubes were
obtained from Bayer Material Science. Activated carbon
and graphite were used as received from Aldrich. Table 1
summarises the BET surface areas and pore volumes for
creasing the thermal conductivity of the medium this each of the supports used and the theoretical surface area
effect may be reduced. Recent studies have shown for a monolayer of ionic liquid.
that when CNTs are combined with ionic liquids, the
The endo selectivity and conversions for the Diels–Alder
1
thermal conductivity can increase by up to 37% com- reaction were determined by H NMR and HPLC and the
pared with the pure ionic liquid and may contribute ee values based on the endo isomer were calculated from
[
36]
the HPLC profile using a Chiralcel OD-H column (hexane:-
to the increased ee observed. This effect has been
3
À1
propan-2-ol, 90:10, flow rate 1 cm min ). The retention
times of the endo enantiomers were major (S)-enantiomer,
t 25.5 min, and minor (R)-enantiomer, t 28.6 min. All data
observed in the gas-phase hydrogenation of 1,3-cyclo-
hexadiene catalysed by Rh
ACHTUNGTRENNUNG[ (nbd) ACHTUNGERTNNUNG( PPh )] ACHNUTGERTNNUN[G BF ]. There-
3 4
R
R
in, the use carbon nanofibres compared with a range
from the Diels–Alder reactions were averaged over three
runs.
[
37]
of oxides led to an improvement in selectivity. This
support effect was attributed to the support with the
highest thermal conductivity providing the most effec-
tive sink for the energy released.
The selectivity and conversions were for the Mukaiyama-
1
aldol reactions were determined by H NMR and HPLC
and the ee values were calculated from the HPLC profile
using a Chiralcel OD-H column (hexane:propan-2-ol, 96:4,
3
À1
flow rate 1 cm min ). The retention times of the endo
enantiomers were major (R)-enantiomer, tR 20.1 min, and
Adv. Synth. Catal. 2011, 353, 995 – 1004
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1001

P. Goodrich et al.
FULL PAPERS
minor (S)-enantiomer, tR 23.8 min. All data from the Mu- General Procedure for the Liquid-Liquid Biphasic
kaiyama-aldol reactions were averaged over three runs.
Lewis Acid-Catalyzed Diels–Alder Reactions in
[
C mim] ACHUTNGTNERN[GU NTf ]/Diethyl Ether
2 2
General Procedure for the Homogeneous Lewis
Acid-Catalyzed Diels–Alder or Mukaiyama-Aldol
Reactions in Molecular Solvents
A flame-dried Schlenk flask was charged with ligand
0.011 mmol) and metal(II) triflate (0.010 mmol, 10 mol%).
(
3
To this was added dichloromethane (5 cm ) and [C mim]-
ACHTUNGTNERNUN[G NTf ] (0.15 g, 0.23 cm ) and the resulting solution stirred at
2
3
A flame-dried Schlenk flask was charged with ligand
2
(
0.011 mmol), metal(II) triflate (0.010 mmol, 10 mol%) and
room temperature for 5 min. Dichloromethane was then re-
moved under high vacuum for one hour leaving the active
catalyst dissolved in the ionic liquid. Thereafter, diethyl
3
dichloromethane (5 cm ) and the resulting solution stirred at
room temperature for 3 h to afford a clear green solution.
Thereafter, N-acryloyloxazolidinone (0.0143 g, 0.1 mmol)
was added followed by freshly distilled cyclopentadiene
(
(
phenyl-1-trimethylsiloxyethene. The reaction mixture was
stirred at the desired temperature for the specified amount
of time and then diluted with 5 cm of 1:1 ethyl acetate:hex-
3
ether (5 cm ) was added followed by the Diels–Alder sub-
strates. The resulting mixture was stirred at the desired tem-
perature for the specified amount of time after which the di-
ethyl ether was removed and the remaining ionic liquid was
50 mL). For the Mukaiyama-aldol reaction, methyl pyruvate
0.0102 g, 0.1 mmol) followed by (0.0243 g, 0.12 mmol) of 1-
3
extracted with diethyl ether (2ꢄ5 cm ) in air. The Diels–
Alder products were worked up as previously described to
afford the unpurified products which were analysed directly.
3
ane.
Following concentration of the Diels–Alder reaction mix- General Procedure for the Heterogeneous Lewis
3
ture, the crude adduct was dissolved in 5 cm of diethyl
Acid-Catalyzed Reactions in Diethyl Ether
ether and filtered through a small plug of silica gel to afford
A flame-dried Schlenk flask was charged with ligand
unpurified product and analysed directly.
(
0.011 mmol), metal(II) triflate (0.010 mmol, 10 mol%) and
3
Following concentration of the Mukaiyama-aldol reaction
mixture, the residual oil was redissolved in THF (5 cm ) and
the corresponding silyl-adduct was hydrolysed by stirring for
h using 2M HCl (10 cm ). The THF was removed under
vacuum and the keto-alcohol was extracted from the aque-
ous by washing with Et O (3ꢄ5 cm ). The crude product
3
dichloromethane (5 cm ) and the resulting solution stirred at
room temperature for 3 h. To the resulting green solution
was added support (0.1 g) and for catalysts using a support-
3
1
3
ed ionic liquid film, 0.1 cm of ionic liquid was also added.
3
After stirring for 20 min, the dichloromethane was removed
under vacuum for one hour to afford a free flowing powder
after which the flask was charged with diethyl ether (5 cm )
followed by the addition of substrates. The reaction mixture
was stirred at room temperature for the specified amount of
2
was analysed directly.
3
For reactions conducted in diethyl ether, the catalyst was
activated in dichloromethane which was then removed
under vacuum followed by addition of diethyl ether (5 cm )
and stirred for 30 min after which the substrates were
added. Both the Diels–Alder and Mukaiyama-aldol reac-
tions were worked up as previously described to afford the
unpurified products which were analysed directly.
3
time after which the silica was extracted with diethyl ether
3
(
3ꢄ5 cm ) in air. Both the Diels–Alder and Mukaiyama-
aldol reactions were worked up as previously described to
afford the unpurified products which were analysed directly.
Procedure for Recycle of the Heterogeneously
Catalysed Reactions
General Procedure for the Homogeneous Lewis
Acid-Catalyzed Diels–Alder and Mukaiyama-Aldol
Reactions in 1-Ethyl-3-methylimidazolium
The silica/ether slurry solution was left to settle in order to
separate the phases after which the ethereal layer was re-
moved by pipette and the silica was further extracted with
Bis[(trifluoromethyl)sulfonyl]imide ([C mim] ACHTGNUTERNN[UNG NTf ])
2
2
A flame-dried Schlenk flask was charged with ligand
0.011 mmol) and metal(II) triflate (0.010 mmol, 10 mol%).
3
diethyl ether (2ꢄ5 cm ). After extraction fresh diethyl ether
(
3
3
(5 cm ) was added to the silica and the resultant slurry was
To this was added dichloromethane (5 cm ) and [C mim]-
2
3
charged with further portions of either Diels–Alder or Mu-
kaiyama-aldol substrates.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[NTf ] (3.00 g, 2 cm ) and the resulting solution was stirred
2
at room temperature for 5 min. Dichloromethane was then
It should be noted that for reactions conducted in di-
chloromethane, prior to addition of reagents, the time re-
quired to form the active catalyst is critical to achieving re-
producible catalyst performance. As reported by Evans
removed under high vacuum for one hour leaving the active
catalyst dissolved in the ionic liquid. Thereafter, the Diels–
Alder or Mukaiyama-aldol substrates were added. The re-
sulting mixture was stirred at room temperature for the
specified amount of time after which the ionic liquid was ex-
[41]
et al. a 3 h complexation time is typically required to ach-
ieve consistent results. In contrast, for reactions conducted
in the ionic liquid, the catalyst performance does not
depend on the metal-ligand complexation time and reprodu-
cible ee values and conversions were obtained after aging/
complexation for only 5 min.
3
tracted with diethyl ether (3ꢄ5 cm ) in air. Both the Diels–
Alder and Mukaiyama-aldol reactions were worked up as
previously described to afford the unpurified products which
were analysed directly.
1002
asc.wiley-vch.de
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 995 – 1004

Asymmetric Carbon-Carbon Bond Forming Reactions Catalysed by Metal(II) Bis(oxazoline) Complexes
Acknowledgements
Chem. 2006, 118, 272–275; Angew. Chem. Int. Ed.
006, 45, 266–269.
2
This work was supported by an EU Marie Curie Early Stage
Training Site Fellowship, contract number HPMT-GH-00-
[10] O. Jimenez, T. E. Mꢆller, C. Sievers, A. Spirkl, J. A.
Lercher, Chem. Commun. 2006, 2974–2976.
0
0147-03, QUILL and a Portfolio Partnership grant from the
[11] a) V. Polshettiwar, ꢇ. Molnꢈr, Tetrahedron 2007, 63,
6949–6976; b) A. Corma, H. Garcꢂa, A. Leyva, Tetra-
hedron 2004, 60, 8553–8560.
EPSRC. We thank Bayer Material Science for the gift of the
carbon nanotubes.
[
12] a) A. Wolfson, J. F. J. Vankelecom, P. A. Jacobs, Tetra-
hedron Lett. 2003, 44, 1195–1198; b) K. L. Fow, S. Jae-
nicke, T. E. Mꢆller, C. Sievers, J. Mol. Catal. A 2008,
References
2
79, 239–247; c) L.-L. Lou, X. Peng, K. Yu, S. Liu,
Catal. Commun. 2008, 9, 1891–1893; d) U. Hintermair,
T. Hçfener, T. Pullmann, G. Franciꢉ, W. Leitner, Chem-
CatChem 2010, 2, 150–154.
[
1] a) M. Glos, O. Reiser, Org. Lett. 2000, 2, 2045–2048;
b) R. Annunziata, M. Benaglia, M. Cinquini, F. Cozzi,
M. Pitillo, J. Org. Chem. 2002, 67, 3160–3166.
[
[
[
13] L. Lou, K. Yu, F. Ding, W. Zhan, X. Peng, S. Liu, Tetra-
[
2] a) K. Hallman, C. Moberg, Tetrahedron: Asymmetry
hedron Lett. 2006, 47, 6513–6516.
14] M. R. Castillo, L. Fousse, J. M. Fraile, J. I. Garcꢂa, J. A.
Mayoral, Chem. Eur. J. 2007, 13, 287–291.
2
001, 12, 1475–1478; b) M. I. Burguete, J. M. Fraile,
J. I. Garcia, E. Garcia-Verdugo, S. V. Luis, J. A. Mayor-
al, Org. Lett. 2000, 2, 3905–3908; c) S. Orlandi, A.
Mandoli, D. Pini, P. Salvadori, Angew. Chem. 2001, 113,
15] S. Doherty, P. Goodrich, C. Hardacre, C. Paun, V. I.
Pꢀrvulescu, Adv. Synth. Catal. 2008, 350, 295–302.
2
587–2589; Angew. Chem. Int. Ed. 2001, 40, 2519–
2
521; d) E. Diez-Barra, J. M. Fraile, J. I. Garcia, E.
[16] P. Goodrich, C. Hardacre, C. Paun, V. I. Pꢀrvulescu, I.
Podolean, Adv. Synth. Catal. 2008, 350, 2473–2476.
[17] a) J. M. Takacs, E. C. Lawson, M. J. Reno, M. A.
Youngman, D. A. Quincy, Tetrahedron: AsymMetry
1997, 8, 3073–3078; b) G. Desimoni, G. Fatia, P. P.
Righetti, Tetrahedron Lett. 1996, 37, 3715–3718;
c) D. A. Evans, J. A. Murray, P. V. Matt, R. D. Norcross,
S. J. Miller, Angew. Chem. 1995, 107, 864–867; Angew.
Chem. Int. Ed. Engl. 1995, 34, 798–800.
Garcia-Verdugo, C. I. Herrerias, S. V. Luis, J. A. Mayor-
al, P. Sanchez-Verdu, J. Tolosa, Tetrahedron: Asymme-
try 2003, 14, 773–778.
[
3] a) R. J. Clarke, I. J. Shannon, Chem. Commun. 2001,
1
936–1937; b) K. Park, S.-W. Kim, T. Hyeon, B. M.
Kim, Tetrahedron: Asymmetry 2001, 12, 2931–2935.
4] a) J. M. Fraile, J. I. Garcia, J. A. Mayoral, T. Tarnai, Tet-
rahedron: Asymmetry 1997, 8, 2089–2092; b) J. M.
Fraile, J. I. Garcia, M. A. Harmer, J. A. Mayoral, J.
Mol. Catal. A 2001, 165, 211–218; c) J. M. Fraile, J. I.
Garcia, J. A. Mayoral, T. Tarnai, M. A. Harmer, J.
Catal. 1999, 186, 214–221; d) P. J. Alonso, J. M. Fraile,
J. Garcia, J. I. Garcia, J. I. Martinez, J. A. Mayoral,
M. C. Sanchez, Langmuir 2000, 16, 5607–5612; e) J. M.
Fraile, J. I. Garcia, C. I. Herreruas, J. A. Mayoral, O.
Reiser, A. Socuellamos, H. Werner, Chem. Eur. J. 2004,
[
[18] P. Carbone, G. Desimoni, G. Faita, S. Filippone, P.
Righetti, Tetrahedron 1998, 54, 6099–6110.
[
[
19] J. Joni, M. Haumann, P. Wasserscheid, Adv. Synth.
Catal. 2009, 351, 423–431.
20] Y. Wan, P. McMorn, F. E. Hancock, G. J. Hutchings,
Catal. Lett. 2003, 91, 145–148.
[
[
21] D. Rechavi, M. Lemaire, Org. Lett. 2001, 3, 2493–2496.
22] D. Rechavi, M. Lemaire, J. Mol. Catal. A 2002, 182,
1
0, 2997–3005; f) J. M. Fraile, J. I. Garcia, M. A.
2
39–247.
Harmer, C. I. Herreuas, J. A. Mayoral, O. Reiser, H.
Werner, J. Mater. Chem. 2002, 12, 3290–3295.
[
23] P. OꢁLeary, N. P. Krosveld, K. P. De Jong, G. van Koten,
R. J. M. K. Gebbink, Tetrahedron Lett. 2004, 45, 3177–
[
5] a) H.-U. Blaser, B. Pugin, in: Chiral Reactions in Heter-
ogeneous Catalysis, (Eds.: G. Jannes, V. Dubois),
Plenum Press, New York, 1995, p 33; b) H.-U. Blaser,
Tetrahedron: Asymmetry 1991, 2, 843–866.
3
180.
[
[
24] H. Wang, X. Xia, P. Liu, J. Gao, P. Ying, J. Xiao, C. Li,
Tetrahedron 2006, 62, 1025–1032.
25] Y. Nishiuchi, H. Nakano, Y. Araki, R. Sato, R. Fujita,
K. Uwai, M. Takeshita, Bull. Chem. Soc. Jpn. 2009, 77,
[
6] a) M. Haumann, A. Riisager, Chem. Rev. 2008, 108,
1
474–1497; b) C. Van Doorslaer , J. Wahlen, P. Mert-
ens, K. Binnemans, D. De Vos, Dalton Trans. 2010, 39,
377–8390; c) S. Werner, M. Haumann, P. Wassersc-
1
323–1331.
26] M. Struder, H-U. Blaser, C. Exner, Adv. Synth. Catal.
003, 345, 45–65.
27] C. Baleizo, B. Gigante, H. Garcia, A. Corma, Tetrahe-
dron 2004, 60, 10461–10468.
28] C. E. Song, D. H. Kim, D. S. Choi, Eur. J. Chem. 2006,
[
[
[
[
[
[
8
2
heid, Annual Review of Chemical and Biomolecular
Engineering 2010, 1, 203–230.
[
7] a) C. P. Mehnert, R. A. Cook, N. C. Dispenziere, M.
Afeworki, J. Am. Chem. Soc. 2002, 124, 12932–12933;
b) Y. Yang, H. Lin, C. Deng, J. She, Y. Yuan, Chem.
Lett. 2005, 34, 220–221; c) A. Riisager, K. M. Eriksen,
P. Wasserscheid, R. Fehrmann, Catal. Lett. 2003, 90,
1
5, 2927–2935.
29] N. A. Caplan, F. E. Hancock, F. King, G. J. Hutchings,
J. Chem. Soc. Perkin Trans. 2 2001, 1714–1723.
30] G. Gbery, A. Zsigmond, K. J. Balkus, Catal. Lett. 2001,
1
49–153; d) A. Riisager, P. Wasserscheid, R. van Hal,
7
4, 77–80.
R. Fehrmann, J. Catal. 2003, 219, 452–455.
31] J. Garcia, B. Lopez-Sanchez, J. Mayoral, E. Pires, I. Vil-
[
[
8] A. Riisager, B. Jorgensen, P. Wasserscheid, R. Fehr-
lalba, J. Catal. 2008, 258, 378–385.
[32] Y. N. Novikov, M. E. Vol’pin, Physica B+C 1981, 105,
mann, Chem. Commun. 2006, 994–996.
9] a) C. P. Mehnert, R. A. Cook, E. J. Mozeleski, Chem.
Commun. 2002, 3010–3011; b) S. Miao, B. Han, J.
Huang, T. Jiang, Z. Liu, Z. Sun, J. Zhang, Angew.
471–477.
Adv. Synth. Catal. 2011, 353, 995 – 1004
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1003

P. Goodrich et al.
FULL PAPERS
[
33] M. Antonietti, D. Kuang, B. Smarsly, Y. Zhou, Angew.
[37] M. Ruta, I. Yuranov, P. J. Dyson, G. Laurenczy, L.
Kiwi-Minsker, J. Catal. 2007, 247, 269–276.
Chem. 2004, 116, 5096–5100; Angew. Chem. Int. Ed.
2
004, 43, 4988–4992.
34] B. K. Price, J. L. Hudson, J. M. Tour, J. Am. Chem. Soc.
005, 127, 14867–14870.
35] T. Fukushima, T. Aida, Chem. Eur. J. 2007, 13, 5048–
058.
[38] P. Bonhꢊte, A. P. Dias, N. Papageorgiou, K. Kalyana-
sundaram, M. Grꢋtzel, Inorg. Chem. 1996, 35, 1168–
1178.
[
[
[
2
[39] C. G. Oh, Y. k. Baek, S. K. Ihm, Adv. Mater. 2005, 17,
2
70–273.
40] Y. J. Han, J. M. Kim, G. D. Stucky, Chem. Mater. 2000,
2, 2068–2069.
41] D. A. Evans, S. Miller, T. Lectka, P. von Matt, J. Am.
Chem. Soc. 1999, 121, 7559–7573.
5
[
[
36] C. A. Nieto de Castro, M. J. V. LourenÅo, A. P. C. Ri-
beiro, E. Langa, S. I. C. Vieira, P. Goodrich, C. Harda-
cre, J. Chem. Eng. Data, 2010, 55, 653–661.
1
1004
asc.wiley-vch.de
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 995 – 1004