Catalytic applications of recyclable silica immobilized NHC-ruthenium complexes

Article abstract of DOI:10.1016/j.tet.2012.10.023

A monosilylated Hoveyda-Grubbs ruthenium alkylidene has been prepared and grafted through the NHC ligand to a mesostructured silica, in refluxing toluene or at room temperature, giving two new organic-inorganic hybrid silica materials M2 and M3, respectiv

Full text of DOI:10.1016/j.tet.2012.10.023

Tetrahedron 69 (2013) 341e348
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Catalytic applications of recyclable silica immobilized
NHCeruthenium complexes
a
,
,
b
b
Amalia Monge-Marcet b, Roser Pleixats a , Xavier Cattoen , Michel Wong Chi Man
*
ꢀ
€
a
ꢀ
ꢀ
Chemistry Department, Universitat Autonoma de Barcelona, Cerdanyola del Valles 08193, Spain
b
ꢁ
Institut Charles Gerhardt Montpellier (UMR 5253 CNRS-UM2-ENSCM-UM1), 8 rue de l’ecole normale, Montpellier 34296, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A monosilylated HoveydaeGrubbs ruthenium alkylidene has been prepared and grafted through
the NHC ligand to a mesostructured silica, in refluxing toluene or at room temperature, giving two
new organiceinorganic hybrid silica materials M2 and M3, respectively. While M3 exhibited good
performances in several metathesis reactions, M2 showed good selectivity in the hydrosilylation of
terminal alkynes, where the b-(Z)-vinylsilane was obtained as major product. Recycling of the supported
catalysts without significant decrease in activity and selectivity was proven for at least three cycles in
both transformations.
Received 26 July 2012
Received in revised form
25 September 2012
Accepted 5 October 2012
Available online 12 October 2012
Keywords:
Supported catalysis
Organosilica
Ó 2012 Elsevier Ltd. All rights reserved.
Olefin metathesis
Alkyne hydrosilylation
NHC ruthenium alkylidene
1. Introduction
Olefin metathesis has been established in the last two decades as
a powerful synthetic tool for the formation of new carbonecarbon
double bonds in a selective manner under mild conditions. This or-
ganometallic transformation has been widely used in organic syn-
thesis, medicinal chemistry, polymer and material science.1e7 The
development of highly active and functional group tolerant well-
defined metal alkylidene catalysts explains the great success of
these reactions in various fields. Nowadays, the most widely used are
the GrubbsI and II and HoveydaeGrubbs I and II rutheniumcomplexes
1a,b and 2a,b, respectively (Fig. 1), which are now commercially
available. Apart from these, scientists have explored a great variety of
modifications on the metal environment in order to tune their sta-
bility, reactivity and selectivity towards certain substrates.8e11
Fig. 1. Rutheniumealkylidene olefin metathesis catalysts.
On the other hand, the recovery and reuse of the catalyst have
become the subject of intense research for economic and envi-
ronmental reasons. To this aim, the immobilization of homoge-
neous ruthenium alkylidene complexes on insoluble supports is
one of the most widely used strategy.4,12e17 Apart from recovery
and recycling, catalyst immobilization presents other advantages,
such as protection against deactivation and decomposition path-
ways, easy separation of the catalyst from the reaction mixture and,
lower metal contamination of the final organic product. In this
context, hybrid silica materials have emerged as an alternative to
the most frequently encountered organic polymers for immobiliz-
ing Grubbs’ catalysts.15e17 Organically modified silica exhibit
chemical, mechanical and thermal stabilities superior to those of
organic polymers and, most often, higher surface areas. These
properties make them versatile matrices for the immobilization of
homogeneous catalysts, either by physical entrapment or by
covalent bonding.18,19 Type 1 and 2 complexes have been covalently
attached to a support via a number of positions within the catalyst
* Corresponding author. Tel.: þ34 93 5812067; fax: þ34 93 5812477; e-mail
addresses: roser.pleixats@uab.es, roser.pleixats@uab.cat (R. Pleixats).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.10.023

342
A. Monge-Marcet et al. / Tetrahedron 69 (2013) 341e348
framework, i.e., through the phosphine or N-heterocyclic carbene
ligands,20e24 via halogen exchange and through chelating or non-
chelating alkylidene moieties. So far, our group has previously re-
ported HoveydaeGrubbs heterogenized metathesis catalysts
through solegel procedures on suitably modified chelating ben-
zylidene ligands.25e27 More recently, we have also described co-
gelification of mono- and disilylated HoveydaeGrubbs complexes
with tetraethoxysilane (TEOS).28e30
materials derived from the solegel cogelification approach were
active and reusable in the hydrosilylation of terminal alkynes.
Following our interest on silica-supported ruthenium alkylidene
complexes for catalytic applications, we report herein the prepara-
tion of two hybrid silica materials by grafting a new monosilylated
HoveydaeGrubbs complex 3 to mesostructured silica M1. We also
present our results on their activity, selectivity and recycling perfor-
mances in olefin metathesis and hydrosilylation of terminal alkynes.
Beyond the metathesis reaction, Grubbs ruthenium alkylidene
complexes have also been found to promote a growing number of
catalytic processes.31 Many of them were observed as side reactions
during metathesis and were attributed to special conditions or
decomposition of the ruthenium catalyst. Nevertheless, some of
these non-metathetic transformations have been optimized and
became useful in organic synthesis. In particular, the hydro-
silylation of terminal alkynes32 to generate vinylsilanes is an in-
teresting alternative application of this type of complexes,31,33e35 as
the regio- and stereochemistry of this metal-catalyzed trans-
formation may be affected by the nature of the metallic species
used.36 Indeed, Grubbs catalysts have been described to promote
2. Results and discussion
2.1. Preparation and characterization of the supported
catalysts
The synthesis of the monosilylated precursor 3 and the prepa-
ration of the corresponding materials M2 and M3 derived thereof
are summarized in Scheme 1. The diaminoalcohol 4 was obtained in
55% yield from commercial mesitylamine and 2,3-dibromo-1-
propanol following a described procedure.40 The hydroxyl group
of 4 was protected in the form of tert-butyldimethylsilyl ether to
give quantitatively the diamine 5, which was reacted with trie-
thylorthoformate in the presence of hydrochloric acid to afford the
dihydroimidazolium salt 6 in 92% yield. The deprotection step to
achieve alcohol 7 was performed with 1-chloroethyl chloroformate
following a mild procedure.41 The successful formation of silylated
carbamate 8 from alcohol 7 and commercial (3-isocyanatopropyl)
triethoxysilane required the presence of a catalytic amount of SmI2
and 1,3-dimethyltetrahydropyrimid-2-one.42 The silylated ruthe-
nium alkylidene complex 3 was obtained by deprotonation of 8
with potassium bis(trimethylsilyl)amide and subsequent treatment
of the in situ generated free carbene with commercial complex 2a.
As observed previously for other silylated ruthenium complexes,30
in spite of the use of a special silica, which was previously dried (see
Experimental section), a certain amount of the silylated complex
was retained during the chromatographic separation, explaining
the significant drop of the yield in the last purification step of 3.
The grafting of complex 3 to a previously prepared39 meso-
structured silica M1 (SBA-15 type)43 was first attempted under
the formation of
products, whereas more classical platinum catalysts induce a great
selectivity towards the
-(E)-vinylsilanes.37,38 Cox and co-workers
b a
-(Z)-vinylsilanes34,35 or -vinylsilanes33 as major
b
have shown that a variety of factors (substrate, solvent, tempera-
ture) can significantly affect the regio- and steroselectivity.35 Al-
though the nature of the active catalyst still remains speculative,
different alternative mechanistic proposals have been suggested;
one of them involving the formation of ruthenium hydride species
in the catalytic cycle.35
The recycling of ruthenium alkylidenes in non-metathetic
transformations has scarcely been reported. To the best of
our knowledge, our report on a family of silica-immobilized phos-
phine-free bidentate N,O-prolinate ruthenium benzylidenes was
the first example on alkyne hydrosilylation.39 These novel catalysts
promoted olefin metathesis or hydrosilylation depending on the
method and conditions under which the complexes were supported
to the silica matrix. While grafting and entrapment procedures gave
active and recyclable catalysts for diene ring closing metathesis, the
Scheme 1. Preparation of materials M2 and M3.

A. Monge-Marcet et al. / Tetrahedron 69 (2013) 341e348
343
classical conditions. A mixture of 3 and M1 was refluxed in anhy-
drous toluene under argon for 24 h then the solid M2 was filtered,
thoroughly washed with dichloromethane and dried overnight
under vacuum at 50 ꢀC. During the process the initial green solution
turned brown, which was interpreted as a sign of a change in the
coordination sphere of ruthenium with the formation of other ru-
thenium species. For this reason, M3 was prepared under milder
conditions.23 In this case, the grafting was performed at room
temperature in anhydrous toluene for 48 h, followed by a Soxhlet
extraction with dichloromethane to ensure the complete removal
of residual complex 3 not covalently bound to the silica support M1.
After filtration and drying overnight under vacuum at 50 ꢀC, M3
was obtained as a green powder. Both materials were fully char-
acterized by 29Si solid state NMR, N2-sorption measurements, TGA
and elemental analysis. Some characterization data of materials
M1eM3 are shown in Table 1.
important increase at low relative pressure corresponding to the
filling of micropores, followed by a sharp increase at p/p0¼0.7
(narrow pore size distribution centred at 60e70 nm) and a final
beak arising from the filling of the voids between particles. As ex-
pected the main difference lays on the BET specific surface area,
higher for the parent material M1 than for the grafted materials M2
and M3. The difference in BET surface area between M2 and M3
might result from the slightly different organic content and also
from a different distribution of organics on the surface. In the case
of M2 some pores may be blocked, and this would affect the
sorption analysis and explain the significant drop in surface area.
2.2. Application in catalysis
The activity of the supported catalysts M2 and M3 was first
evaluated in the ring closing metathesis of diethyl 2,2-
diallylmalonate 9 using 2 mol % of the catalyst in dry and
degassed CH2Cl2 at room temperature under inert atmosphere
(Table 2, entries 1 and 3). In this benchmark reaction we could
observe a clear difference between M2 and M3. While the latter
achieved complete conversion of 9 into the desired cyclopentene 10
in 3 h (Table 2, entry 3), 24 h were needed for M2 to reach full
conversion and compound 10 was accompanied by a small amount
of the undesired cycloisomerization by-product (Table 2, entry 1).
Besides, when the catalyst was reused, M2 underwent rapid de-
activation after the second run (78% yield in 40 h) and could not be
further reused (Table 2, entry 2). On the other hand, the green
material M3 was able to promote this RCM at least for three runs
with a decrease in activity in the third one. The recyclability of M3
in refluxing dichloromethane was not improved (Table 2, compare
entries 3e5 and 6e8), but in toluene at 60 ꢀC the reaction times
were significantly reduced, diene 10 being obtained in almost
quantitative yield within 1 h in the third cycle (Table 2, entries
9e12).
Catalyst deactivation in M2 did not arise from ruthenium
leaching. The metal content in the final organic product 10 after the
first cycle was 217 and 221 ppm for M2 and M3, respectively.
However, hot-filtration test indicated that the ruthenium species
leached were not catalytically active and probably the work-up
procedure (simple cannula filtration) may partially account for
this metal loss. Considering these results, it appears that the colour
of the hybrid silica is a good indicator to determine whether the
appropriate ruthenium ligand environment was maintained during
the immobilization process.
We then decided to extend the application of the more efficient
hybrid material M3 to other ring closing metathesis using common
dienes and an enyne. The reactions were very selective as the
cycloisomerization by-products27 were not detected and only some
remaining starting reactant was observed in the 1H NMR spectrum
when the conversion was not complete. The supported catalyst
promoted the RCM of the more challenging p-toluenesulfonamide
derivatives 11 and 13 to afford quantitatively di- and trisubstituted
olefins 12 and 14, respectively, after treatment in dichloromethane
at room temperature for 24 h (Table 2, entries 12 and 13). Re-
markably, material M3 could be recycled in three consecutive runs
in the formation of the trisubstituted olefin 14 with only a small
decrease in the activity for the last run. Under the same conditions,
meso-diamine 15 was converted into compound 16 with moderate
yield (42%, Table 2, entry 16) and the tetraene 17 gave high yield of
compound 18 arising from a selective double ring-closing me-
tathesis (91%, Table 2, entry 17). Finally the green immobilized
catalyst M3 was also capable of promoting the ring-closing me-
tathesis of enyne 19 in dichloromethane at room temperature to
give the diene 20 in 88% yield (Table 2, entry 18). The release of
volatile ethylene in these diene RCM reactions is the driving force,
which shifts the equilibrium to the productive metathesis. This
Table 1
Characterization data of materials M1eM3
Mat. N2-sorption measurements
TGAb (%) Elemental analysis (%)
SBET (m2/g)
Vpore (cm3/g)
Nc
Sid
Rud
a
M1
M2
M3
730
515
610
1.17
0.94
1.19
d
d
d
d
84.1
86.3
0.49
0.36
45.2
34.8
0.89
0.70
a
Pore volume.
Residual mass in the TGA analysis.
Determined by elemental analysis combustion.
Determined by ICPeMS analysis.
b
c
d
The ruthenium content in the hybrid silicas M2 and M3 was
found to be 0.89 and 0.70 wt %, respectively, corresponding to
a loading of 0.088 mmol gꢁ1 for M2 and 0.069 mmol gꢁ1 for M3.
This relatively low ruthenium content impeded a more detailed
study of the ruthenium coordination sphere by means of 13C solid
state NMR. On the other hand, the 29Si CP MAS solid state NMR
could be performed and exhibited typical Q2, Q3 and Q4 signals
from ꢁ90 to ꢁ115 ppm derived from TEOS condensation. In M2 the
presence of a T1 peak at ꢁ48.9 ppm confirmed the covalent in-
corporation of the organosilane to the silica network. In the case of
M3 the ruthenium loading was too low to allow a clear identifica-
tion of the CeSi covalent bond in the spectrum. However, in-
complete removal of unreacted organosilane was discarded
because of the absence of ungrafted T0 species, which indicated
that the metal present in the material must be covalently integrated
within the silica framework. The texture of the grafted materials
was studied with N2-sorption measurements, which revealed that
the covalent post-functionalization did not affect the meso-
structure of the parent material M1. N2-sorption isotherms show
similar profiles for the three materials (Fig. 2). They display an
Fig. 2. N2-sorption isotherms of M1eM3.

344
A. Monge-Marcet et al. / Tetrahedron 69 (2013) 341e348
Table 2
Catalytic experiments in ring-closing metathesis reactionsa
Entry
Substrate
Product
Catalyst
Cycle
Solvent
T (ꢀC)
t (h)
Conv.b(%)
Yieldb (%)
1
2
3
4
5
6
7
8
M2
M2
M3
M3
M3
M3
M3
M3
M3
M3
M3
1
2
1
2
3
1
2
3
1
2
3
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Toluene
Toluene
Toluene
rt
rt
rt
rt
24
40
3
4
24
3
100
80
100
100
86
100
97
92
97
78
>99
>99
83
>99
97
92
>99
97
rt
Reflux
Reflux
Reflux
60
60
60
4
24
0.5
0.5
0.8
9
10
11
100
100
100
>99
12
M3
1
CH2Cl2
rt
24
100
>99
13
14
15
M3
M3
M3
1
2
3
CH2Cl2
CH2Cl2
CH2Cl2
rt
rt
rt
24
24
24
99
99
90
99
99
90
16
17
M3
M3
1
1
CH2Cl2
rt
rt
24
24
42
91
42
91
CH2Cl2
18
M3
1
CH2Cl2
rt
24
88
88
a
Reaction conditions: Ru (2 mol %), anhydrous and degassed solvent, inert atmosphere, [substrate]¼0.1 M.
b
Determined by 1H NMR spectroscopy. When the yield is lower than the conversion the corresponding cycloisomerization side-product was also obtained.
small olefin was not efficiently trapped inside the pores of a mes-
a surprisingly high selectivity towards the b-Z isomer (92% and 90%
for M2 and M3, respectively) (Table 3, entries 3 and 6).
ostructured silica MCM-41 (pore size 29 A)44 and we assume it can
ꢂ
also diffuse easily in the present larger pores of SBA-15 type silicas.
Having examined the application of M3 in the metathesis re-
action and following our previous studies with immobilized N,O-
prolinate ruthenium benzylidenes,39 we then turned our interest to
the hydrosilylation of terminal alkynes, which constitutes another
application of Grubbs’ ruthenium catalysts. Indeed, complexes 1b31
and 2b33 have already been reported in such hydrosilylation re-
actions to afford a mixture of three compounds resulting from two
Recycling experiments were performed with M2, which could be
recovered and reused in three consecutive runs, without any de-
crease in activity or selectivity being observed (Table 3, entries 3e5).
Ruthenium leaching measured after the first cycle corresponded to
a metal loss of 0.7% of the initial amount of catalyst used. This value is
lower than the leaching value observed during the olefin metathesis
reaction (2.2%) with the same supported catalyst. The hydro-
silylation reaction was also tested with other terminal alkynes and
silanes under the same conditions. With triethoxysilane the trend in
selectivity was maintained despite a small decrease in the major
product amount (85%, Table 3, entry 7). In the reaction between
regioisomers (a and b), with two possible diastereoisomers (E and Z)
for the regioisomer. We first performed the reaction between
b
triethylsilane and phenylacetylene with both homogeneous com-
plexes 1b and 2b in CH2Cl2 at room temperature with a catalyst
loading of 2 mol % (Table 3, entries 1 and 2). Within 24 h, full con-
version was achieved with differences in the vinylsilanes distribu-
1-octyne and triethylsilane, the
product with 86% selectivity, despite an increase of up to 10% for the
formation of the olefin (Table 3, entry 8). The combination
of 1-octyne with triethoxysilane implied a significant change in
selectivity, since and -Z isomers were produced in similar
amounts (Table 3, entry 9).
b-Z isomer remained the major
a
tion. Whereas with complex 1b the major product was the
b-Z
isomer, for 2b the -E olefin was detected as the main product with
b
a
b
91% selectivity. The products ratio was easily calculated taking into
account the characteristic values of vinylsilane coupling constants.45
We then undertook the same reaction with the supported catalysts
M2 and M3 under the same conditions mentioned above. Phenyl-
acetylene was fully converted into a mixture of isomers, with
Interestingly, the behaviour of the hybrid silica M2 was more
similar to the homogeneous Grubbs II catalyst, 1b, than to the
GrubbseHoveyda II catalyst, 2b, since it showed a high preference
for the b-Z isomer with only traces of the a and b-E products (Table

A. Monge-Marcet et al. / Tetrahedron 69 (2013) 341e348
345
Table 3
Catalytic experiments in alkyne hydrosilylationa
Entry
1
Major product
Catalyst
Cycle
1
t (h)
Conv.b(%)
a:b-(E):b
-(Z)b
GrubbseHoveyda II (2b)
24
>99
9:91:0
2
Grubbs II (1b)
1
24
>99
10:25:65
3
4
5
6
M2
M2
M2
M3
1
2
3
1
24
24
24
40
>99
95
99
5:3:92
1:3:96
2:1:97
5:5:90
95
7
M2
1
24
>99
5:9:85
8
9
M2
M2
1
1
24
24
>99
>99
10:4:86
45:14:41
a
Reaction conditions: Ru (2 mol %), dry and degassed CH2Cl2, inert atmosphere, rt, [alkyne]¼[silane]¼0.5 M.
Determined by 1H NMR spectroscopy, products ratio calculated taking into account the characteristic values of vinylsilanes coupling constants.45
b
3, entries 2e5 and 6e8). As mentioned above, material M2 had
a brown colour instead of the typical green colour of the second
generation HoveydaeGrubbs’ type complexes. Even though the
selectivity in this reaction may strongly depend on the reaction
conditions used, the results obtained in catalysis seem to be in
agreement with the fact that the supported ruthenium complex in
M2 might contain other non-alkylidene ruthenium species. Nev-
ertheless, the green material M3, efficient in olefin metathesis, did
also exhibit a selectivity comparable to M2 (Table 3, entries 3 and 6).
These findings suggest that, under our reaction conditions,
alkylidene ruthenium complexes immobilized within the silica
matrix may decompose or lead to the in situ formation of other
ruthenium species. Although different mechanistic proposals have
been made for the hydrosilylation of alkynes with ruthenium
alkylidenes, the nature of the active catalyst still remains un-
known.31 In phosphine-containing ruthenium complexes, an initial
loss of a phosphine ligand has been suggested. On the other hand,
although second generation metathesis catalysts exhibit high sta-
bility towards a wide range of functional groups1 several de-
composition pathways have been proposed for different ruthenium
alkylidene complexes,46e51 Thus, thermal decomposition of
phosphine-containing Grubbs II catalyst has been described,46,47
leading to dinuclear ruthenium hydride species. It has also been
reported the thermal deactivation of Grubbs II and
HoveydaeGrubbs II-type complexes containing unsubstituted ortho
positions in the N-aryl ring, which lead to the formation of ruth-
eniumearene or carbeneearene bonds.48,49 Other deactivation
processes involve the addition of coordinating ligands or solvents,
such as CO50 or DMF.51 In our case no additives were introduced and
phosphine-free complex 3 does not bear ortho unsubstituted aryl
groups. However, in our hands a transparent degassed green solu-
tion of commercial HoveydaeGrubbs II catalyst became dark green
after one day in refluxing toluene. The 1H NMR spectrum of the
residue showed the characteristic signal of the alkylidene proton,
but a new one corresponding to an aldehydic proton was also vis-
ible, suggesting a certain degree of decomposition under these
drastic thermal conditions. On the other hand, the silanol groups of
mesoporous silica have been found to decrease the longevity of
Grubbs I catalysts, participating in the oxidation of the phosphine
ligands.52,53 Although the change of colour and the different re-
activity indeed suggest that the brown material M2 should contain
both alkylidene and non-alkylidene ruthenium species, the nature
of these species is presently unknown. A transmission electron
microscopy analysis (TEM) of M2 discarded the presence of ruthe-
nium nanoparticles in the material.
Both materials M2 and M3 exhibited an improved selectivity in
the hydrosilylation reaction of phenylacetylene with triethylsilane
when compared with other silica-immobilized catalysts described

346
A. Monge-Marcet et al. / Tetrahedron 69 (2013) 341e348
by us where the selectivity towards the
b
-Z isomer was around
distillation just before use. Spectral data were obtained with the
70%.39 To the best of our knowledge M2 and M3 constitute the first
examples of supported ruthenium alkylidene complexes immobi-
lized within a silica framework through the NHC ligand that have
been applied in alkyne hydrosilylation reactions. Further studies
will be needed to gather a higher level of understanding on the
immobilization process and its influence in the structure of the true
active supported species involved in the catalytic cycle.
following instruments: IR on a Bruker Tensor 27 with ATR Golden
Gate; liquid NMR on Bruker DXP-250 MHz, DPX-360 MHz and
AVANCE-II 400 MHz. Chemical shifts (d, parts per million) were
given using the signal of residual non-deuterated solvent as in-
ternal reference. The abbreviations used are s for singlet, d for
doublet, dd for double doublet, t for triplet, q for quadruplet, sept
for septuplet and m for multiplet. The CP-MAS 29Si solid state NMR
spectra were recorded on a Bruker AV400WB. The repetition time
was 5 s with contact time of 5 ms. Surface areas were calculated by
the BrunauereEmmetteTeller (BET) method from N2-sorption
isotherms carried out on a Micromeritics ASAP2020 analyzer;
materials were degassed for 30 h at 55 ꢀC under vacuum and the
pore size distribution was calculated by the BJH method on the
desorption branch. ESI mass spectra were acquired using a micro-
3. Conclusions
Mesostructured hybrid silica materials containing a second
generation HoveydaeGrubbs ruthenium complex were synthe-
sized by applying a grafting methodology to the corresponding
monosilylated complex through the NHC moiety. Depending on the
synthetic conditions, the activity of the new supported catalysts
differs considerably in two kinds of reactions: ring closing olefin
metathesis and hydrosilylation of terminal alkynes. Under mild
grafting conditions, the supported complex M3 proved active and
recyclable for at least three consecutive runs in diene ring-closing
metathesis reactions to give di- and trisubstituted cycloalkenes.
On the other hand, the material M2 prepared at higher temperature
displayed poorer catalytic properties in the metathesis reaction but,
interestingly, it revealed as an active and highly selective catalyst in
the hydrosilylation of terminal alkynes. In this case, the supported
ruthenium complex exhibited an excellent selectivity towards the
ꢀ
TOF-Q instrument at the Universitat Autonoma de Barcelona. Ele-
ꢀ
mental analyses have been performed at Serveis Científico-Tecnics of
the Universitat de Barcelona by inductively coupled plasma (ICP)
ꢀ
analysis. TGA analysis was done at the Institut de Ciencia dels Ma-
terials de Barcelona.
Material M1,39 2,3-bis(mesitylamino)propan-1-ol 4,40 1,3-
dimesityl-4-[(3-triethoxysilyl)propylcarbamoyloxy]methyl-4,5-di-
hydroimidazolium chloride,842 as well as compounds 11,27 13,27
15,54,55 17,56 and 1927 used as substrates for catalytic tests were
prepared as previously reported. Products 12,27 14,27 16,54,55 18,57
20,27 21,58 22,45 2359 and 2460 have previously been described in
the literature and their spectral and physical data were consistent
with those reported.
formation of the cis
b-olefin (up to 97%). Moreover, in this chemical
transformation M2 was also reusable for three runs without de-
crease of activity and selectivity. We had previously shown that the
immobilization approach could affect the supported catalyst per-
formance. The results presented here indicate that the efficiency of
the supported catalysts may also depend on the preparation con-
ditions since they may presumably influence significantly the metal
coordination environment, which can be qualitatively evaluated
from the supported catalyst colouration. Further studies on this
kind of systems will help gathering a deeper understanding on the
structure of the truly catalytic species within the inorganic support.
In that way, not only the versatility of the supported catalysts could
be broadened but it would also help in the design of new tandem or
domino transformations starting from a single complex precursor.
This may be important in the development of new silica-based
catalytic systems containing organometallic species, which allow
the reduction of metal contamination in the final organic com-
pound thanks to the immobilization and the affinity of the silica for
some metal complexes.
4.2. 3-(tert-Butyldimethylsilyloxy)-N1,N2-dimesitylpropane-
1,2-diamine (5)
A mixture of compound 4 (3.03 g, 9.29 mmol), imidazole 99%
(1.61 g, 23.4 mmol) and tert-butyldimethylsilyl chloride 98% (1.51 g,
9.84 mmol) was dissolved in dry DMF (30 mL) and stirred overnight
at room temperature under argon. Then water (25 mL) was added
and the product was extracted with petroleum ether (3ꢂ20 mL).
The organic layers were washed with water (2ꢂ20 mL), brine
(2ꢂ15 mL), dried over Na2SO4 and concentrated in vacuo to give the
crude product, which was purified by flash chromatography (10/1
hexane/AcOEt) to give compound 5 (4.07 g, 99%) as a colourless oil.
Rf (10/1 hexane/AcOEt) 0.76; nmax (ATR) 3371, 2953, 2930, 2858,
1486, 1254, 1233, 1009, 938, 634 cmꢁ1
; dH (360 MHz, CDCl3) 6.80
(4H, s, HAr), 3.71 (1H, dd, J 10.0 and 2.5 Hz, OCHH), 3.65 (1H, dd, J
10.0 and 3.6 Hz, OCHH), 3.55 (2H, br s, NH), 3.44 (1H, m, NHCHCH2),
3.25 (1H, dd, J 12.0 and 6.0 Hz, NHCHCHH), 2.89 (1H, dd, J 12.0 and
6.5 Hz, NHCHCHH), 2.27 (6H, s, o/p-CH3), 2.23 (6H, s, o/p-CH3), 2.22
(6H, s, o/p-CH3), 0.89 (9H, s, SiC(CH3)3), 0.04 (3H, s, SiCH3), 0.03 (3H,
s, SiCH3); dC (90 MHz, CDCl3) 144.0, 141.8, 131.2, 130.7, 129.7, 129.6,
129.2, 63.4, 58.1, 50.3, 26.0, 20.7, 20.6, 19.1, 18.5, 18.4, ꢁ5.3, ꢁ5.4.
4. Experimental section
4.1. General
When required, experiments were carried out using standard
high-vacuum and Schlenk techniques. Solvents were degassed,
dried and distilled just before use following standard procedures.
2,4,6-Trimethylaniline 98%, triethylorthoformate 98%, 2,3-dibro-
mo-1-propanol, chloro-tert-butyldimethylsilane, imidazole,1-chlo-
roethyl chloroformate, samarium(II) iodide, 1,3-dimethyltetr-
ahydropyrimidin-2(1H)-one, (3-isocyanatopropyl)triethoxysilane,
potassium bis(trimethylsilyl)amide (0.5 M solution in anhydrous
toluene), first generation HoveydaeGrubbs catalyst 2a, tetraethy-
lorthosilicate (TEOS) and Pluronics P123Ò were purchased from
Aldrich. The silica gel for flash chromatography was SiliCycle P60
4.3. 5-[(tert-Butyldimethylsilyloxy)methyl]-1,3-dimesityl-4,5-
dihydro-1H-imidazol-3-ium chloride, (6)
Compound 5 (4.07 g, 9.23 mmol) was dissolved in triethylor-
thoformate 98% (30 mL, 0.891 g/cm3, 177 mmol) then HCl (870
mL,
concd HCl 37%, 10.3 mmol) was added dropwise. The mixture was
stirred for 3 h at 80 ꢀC under inert atmosphere. After this time, the
crude product was cooled down to 40 ꢀC and the volatiles were
removed under vacuum. To the residue Et2O (40 mL) was added
and the mixture stirred for 1 h at room temperature. During this
time a solid precipitated, which was filtered off and washed with
warm toluene, Et2O and pentane to afford 6 (4.14 g, 92%) as a white
solid. Mp 215e217 ꢀC; nmax (ATR) 2953, 2859,1719,1623,1466,1277,
R12030, with a particle size of 60.0e75.0
mm, a pore volume of
0.8e1.0 mL/g and a pH of 6.5e7.5 (10% suspension in water). The
silica gel was dried under a nitrogen flow using a heat gun just
before use. All commercial reagents were used as received except
for (3-isocyanatopropyl)triethoxysilane, which was purified by
1250, 1219, 1120, 1120, 1036, 1005, 853, 836, 780, 676 cmꢁ1
(250 MHz, CDCl3) 9.22 (1H, s, NCHN), 6.96 (4H, s, HAr), 5.30 (1H, m,
; dH

A. Monge-Marcet et al. / Tetrahedron 69 (2013) 341e348
347
NCHCH2N), 4.82 (1H, m, NCHCHHN), 4.30 (1H, m, NCHCHHN), 3.82
(1H, d, J 12.1 Hz, OCHH), 3.72 (1H, d, J 12.1 Hz, OCHH), 2.44 (12H, m,
o-CH3), 2.29 (6H, s, p-CH3), 0.87 (9H, s, SiC(CH3)3), 0.06 (6H, s,
SiCH3); dC (62.5 MHz, CDCl3)160.3, 140.9, 140.6, 136.5, 135.6, 130.8,
130.5, 130.2, 129.0, 65.6, 60.4, 52.5, 26.4, 21.4, 21.3, 19.2, 18.9, 18.5,
ꢁ4.9, ꢁ5.0.
anhydrous toluene (20 mL) for 24 h. After this time the suspension
was filtered under argon. The solid was washed with dry CH2Cl2
until the filtrates were colourless, then it was dried overnight at
25 ꢀC under vacuum (1.0 mbar) to afford M2 as a brown solid
(0.955 g). [Found: N, 0.49; C, 7.02; H, 0.74; Si, 45.24; Ru, 0.89;
0.088 mmol/g material]; 29Si CP MAS NMR (79.5 MHz) ꢁ48.9 (T1),
ꢁ93.3 (Q2), ꢁ102.6 (Q3), ꢁ112.8 (Q4); BET SBET 515 m2/g, pore di-
ꢂ
4.4. 5-(Hydroxymethyl)-1,3-dimesityl-4,5-
dihydroimidazolium chloride, (7)
ameter distribution centred around 60e80 A, pore volume
0.94 cm3/g; TGA (air, 20 to 700 ꢀC) residual mass 84.08%.
Compound 6 (2.03 g, 4.17 mmol) was dissolved in MeOH (4 mL)
and to this solution 1-chloroethyl chloroformate 97% (0.470 mL,
1.31 g/cm3, 4.45 mmol) was added dropwise. The final mixture was
stirred overnight at room temperature and after this time, the
volatiles were removed in vacuo and the residue was treated with
Et2O (5 mL). A solid precipitated, which was filtered off and washed
with Et2O and pentane until it turned colourless affording com-
pound 7 (1.46 g, 94%) as a white solid. Mp: 237e242 ꢀC; nmax (ATR)
3194, 2918, 1670, 1626, 1481, 1379, 1267, 1217, 1102, 1034, 981, 852,
4.7. Hybrid silica material M3
In a 25 mL Schlenk tube under argon, compound 3 (0.057 g,
0.063 mmol) and mesostructured silica M1 (0.680 g, 11.3 mmol)
were stirred together in anhydrous toluene (12 mL) at room tem-
perature for 48 h. After this time the suspension was filtered off
under argon and the solid was washed with dry CH2Cl2 with
a Soxhlet apparatus for 48 h under argon atmosphere. Then the
solid was dried overnight at 25 ꢀC under vacuum (1.0 mbar) to
afford M3 (0.650 g) as a green solid. [Found: N, 0.36; C, 4.68; H,
0.91; Si, 34.84; Ru, 0.70; 0.069 mmol/g material]; 29Si CP MAS NMR
(79.5 MHz) ꢁ92.6 (Q2), ꢁ102.6 (Q3), ꢁ112.6 (Q4), signals corre-
sponding to the T peaks could not be observed due to the low
complex loading in the final material; BET SBET 610 m2/g, pore di-
728, 668 cmꢁ1
; dH (360 MHz, CDCl3) 8.89 (1H, br, OH), 8.32 (1H, s,
NCHN), 6.90 (4H, m, HAr), 4.78 (2H, m, NCHCHHN), 4.34 (1H, m,
NCHCHHN), 3.80 (1H, m, HOCHH), 3.50 (1H, m, HOCHH), 2.42e2.25
(18H, m, o/p-CH3); dC (90 MHz, CDCl3) 176.1, 158.9, 140.4, 140.3,
136.8, 136.2, 134.6, 130.5, 130.1, 129.7, 128.7, 66.0, 58.2, 52.6, 22.5,
21.0, 18.3, 18.0, 17.7.
ꢂ
ameter distribution centred around 50e70 A, pore volume
1.19 cm3/g; TGA (air, 20 to 700 ꢀC) residual mass 86.33%.
4.5. Silylated ruthenium complex (3)
4.8. General procedure for catalytic tests in metathesis
reactions
In a 25 mL Schlenk tube under argon, compound 8 (0.300 g,
0.484 mmol) was dissolved in dry and degassed toluene (4 mL). To
this solution KHMDS (1.00 mL, commercial solution 0.5 M in dry
toluene, 0.50 mmol) was added and the mixture was stirred for
10 min at room temperature, while a fine precipitate appeared. To
this suspension a solution of first generation HoveydaeGrubbs
catalyst, 2a (0.160 g, 0.266 mmol) in dry and degassed toluene
(6 mL) was transferred via a cannula and the final mixture was
stirred for 3 h at 80 ꢀC under argon. After this time, the reaction
mixture was cooled down to room temperature and the volatiles
were removed in vacuo. To the residue dry and degassed CHCl3
(10 mL) was added and the solution was stirred for 16 h at room
temperature under argon. Finally the solvent was removed in vacuo
and the crude product was purified by flash chromatography
(hexane/AcOEt 8/2) to afford 3 (0.065 g, 27%) as a sticky green solid.
nmax (ATR) 3331, 2924,1632,1563,1478,1386,1261,1196,1166,1075,
In a 10 mL tube, the supported catalyst (0.002 mmol Ru) was
dried for 1 h under vacuum (1.0 mbar). Then a solution of diene
(0.1 mmol) in dry and degassed solvent (1 mL) was transferred via
a cannula to the tube containing the catalyst under argon. The
resulting suspension was stirred at the target temperature and the
conversion was monitored by GC until the end of the experiment.
At this time, the stirring was stopped, the material was left to settle
and the solution was filtered via a cannula under nitrogen. The
recovered catalyst was washed with dry and degassed solvent
(3ꢂ3 mL), dried under vacuum and directly used in the next cycle.
The filtrates were concentrated under reduced pressure to afford
the corresponding RCM product, whose yield was determined by
1H NMR spectroscopy.
942, 796 cmꢁ1
;
dH (360 MHz, CDCl3) 16.52 (1H, s, Ru]CH), 7.48 (1H,
4.9. Spectral data of compound 1857
t, J 7.6 Hz, C6HH3), 7.05 (4H, br, C6Me3H2), 6.90 (1H, d, J 7.2 Hz,
C6HH3), 6.85 (1H, t, J 7.6 Hz, C6HH3), 6.79 (1H, d, J 7.2 Hz, C6HH3),
5.34 (1H, br, NHCOO), 4.90 (1H, sept, J 5.8 Hz, OCH(CH3)2), 4.57 (1H,
m, NCHCH2),4.30 (1H, t, J 11.2 Hz, NCHHCHN), 4.22 (1H, dd, J 8.3 and
4.0 Hz, NCHHCHN), 4.14 (1H, dd, J 11.3 and 4.0 Hz, CHHO), 3.97 (1H,
t, J 9.0 Hz, CHHO), 3.80 (6H, q, J 6.8 Hz, OCH2CH3), 3.13 (2H, m,
OCONHCH2), 2.60e2.25 (18H, m, o/p-CH3), 1.58 (2H, m, CH2CH2Si),
1.25 (6H, m, OCH(CH3)2), 1.21 (9H, t, J 6.8 Hz, OCH2CH3), 0.59 (2H, m,
CH2Si); dC (62.5 MHz, CDCl3) 298.1, 155.9, 144.9, 138.6, 129.5, 129.4,
122.5, 122.0, 112.6, 77.1, 74.7, 58.2, 43.2, 35.5, 34.5, 29.4, 26.7, 26.6,
26.1, 26.0, 25.9, 23.0, 20.8, 18.0, 7.2, the signal corresponding to NCN
around 210 ppm was not observed due to its low intensity; MS m/z
Oil; dH (360 MHz, CDCl3): 5.81 (4H, s, CH¼CH), 3.78 (8H, s, CH2);
MS m/z 200 (Mþ, 2), 132 (7), 69 (34), 68 (100), 41 (50).
4.10. General procedure for catalytic tests in hydrosilylation
reactions
In a 10 mL tube, the supported catalyst (0.004 mmol Ru) was
dried for 1 h under vacuum (1.0 mbar). Then dry and degassed
CH2Cl2 (0.4 mL) was transferred with a syringe to the tube con-
taining the catalyst under argon. To the resulting suspension, the
corresponding silane (0.21 mmol) and alkyne (0.21 mmol) were
added and the mixture was stirred at room temperature under
argon. The reaction was monitored by TLC until the end of the
experiment. The stirring was stopped, the material was left to settle
and the solution was filtered via a cannula under nitrogen. The
recovered catalyst was washed with dry and degassed CH2Cl2
(3ꢂ3 mL), dried in vacuo and directly used in the next cycle. The
filtrates were concentrated under reduced pressure to afford the
(ESI) 926.2 (11, MþNaþ), 834.3 (48), 742.3 (22.0), 668.4 (100), 584.4
12
(49.5); HRMS (ESI) found 926.2676. [
requires 926.2648.
C
H61 35Cl2N3O6RuSiþNa]þ
42
4.6. Hybrid silica material M2
In a 50 mL Schlenk equipped with a DeaneStark apparatus
under argon atmosphere, compound 3 (0.101 g, 0.111 mmol) and
mesostructured silica M1 (0.982 g, 16.4 mmol) were refluxed in
corresponding vinylsilane mixture. Yield and
a/b-E/b-Z ratios were
determined by 1H NMR spectroscopy.

348
A. Monge-Marcet et al. / Tetrahedron 69 (2013) 341e348
4.11. Spectral data of the stereoisomers mixture 2359
20. Mayr, M.; Mayr, B.; Buchmeiser, M. R. Angew. Chem., Int. Ed. 2001, 40, 3839.
21. Schuerer, S. C.; Gessler, S.; Buschmann, N.; Blechert, S. Angew. Chem., Int. Ed.
2000, 39, 3898.
22. Pruehs, S.; Lehmann, C. W.; Fuerstner, A. Organometallics 2004, 23, 280.
23. Allen, D. P.; Van Wingerden, M.; Grubbs, R. H. Org. Lett. 2009, 11, 1261.
dH (360 MHz, CDCl3) (Z)-23 6.38 (1H, dt, J 14.2 Hz, J 7.4 Hz,
b
CH2CH]CH), 5.38 (1H, d, J 14.2 Hz, SiCH]CH), 2.09 (2H, m,
CH2CH]CH), 1.37e1.26 (8H, m, CH]CHCH2CH2CH2CH2CH2CH3),
0.95 (9H, t, J 7.9 Hz, SiCH2CH3), 0.89 (3H, t, J 6.8 Hz, CH2CH2CH3,
partially overlap with the previous signal), 0.58 (6H, q, J 7.9 Hz,
ꢁ
ꢁ
24. Karame, I.; Boualleg, M.; Camus, J.-M.; Maishal, T. K.; Coperet, C.; Corriu, R. J. P.;
ꢁ ꢁ
Jeanneau, E.; Mehdi, A.; Reye, C.; Veyre, L.; Thieuleux, C. Chem.dEur. J. 2009, 15,
11820.
25. Elias, X.; Pleixats, R.; Wong Chi Man, M.; Moreau, J. J. E. Tetrahedron 2008, 64,
6770.
SiCH2CH3);
CH]CHSi);
rest of signals of
b
a
(E)-23 6.03 (1H, m, CH]CHSi), 5.53 (1H, d, J 18.7 Hz,
-23 5.62 (1H, br, CHH]C), 5.28 (1H, br, CHH]C), the
(E)-23 and -23 are masked by the (Z)-23 isomer.
26. Elias, X.; Pleixats, R.; Wong Chi Man, M.; Moreau, J. J. E. Adv. Synth. Catal. 2007,
349, 1701.
b
a
b
27. Elias, X.; Pleixats, R.; Wong Chi Man, M.; Moreau, J. J. E. Adv. Synth. Catal. 2006,
348, 751.
€
28. Borja, G.; Pleixats, R.; Alibes, R.; Cattoen, X.; Wong Chi Man, M. Molecules 2010,
4.12. Spectral data of the stereoisomers mixture 2460
15, 5756.
€
29. Monge-Marcet, A.; Pleixats, R.; Cattoen, X.; Wong Chi Man, M. Catal. Sci.
Technol. 2011, 1, 1544.
30. Monge-Marcet, A.; Pleixats, R.; Cattoen, X.; Wong Chi Man, M. J. Mol. Catal. A:
dH (360 MHz, CDCl3)
b(Z)-24 6.52 (1H, dt, J 14.4 Hz, J 7.4 Hz,
€
CH2CH]CH), 5.28 (1H, d, J 14.4 Hz, SiCH]CH), 3.81 (6H, q, J 6.8 Hz,
SiOCH2CH3), 2.29 (2H, m, CH2CH]CH), 1.44e1.39 (m, 8H, CH]
CHCH2CH2CH2CH2CH2CH3), 1.23 (9H, t, J 6.8 Hz, SiOCH2CH3), 0.87
(3H, t, J 6.8 Hz, CH2CH2CH3);
5.71 (1H, br, CHH]C), 5.62 (1H, br, CHH]C), 2.14 (2H, t, J 7.9 Hz,
Chem. 2012, 357, 59.
31. Alcaide, B.; Almendros, P.; Luna, A. Chem. Rev. 2009, 109, 3817.
32. Marciniec, B.; Maciejewski, H.; Pietraszuk, C.; Pawluc, P. In Hydrosilylation: A
Comprehensive Review on Recent Advances; Marciniec, B., Ed.; Advances in
Silicon Science Series; Springer: Berlin, 2009; Vol. 1, Chapter 2.
33. Menozzi, C.; Dalko, P. I.; Cossy, J. J. Org. Chem. 2005, 70, 10717.
34. Maifeld, S. V.; Tran, M. N.; Lee, D. Tetrahedron Lett. 2005, 46, 105.
b(E)-24 5.40 (1H, m, CH]CHSi); a-24
CH2CH]CH), the rest of signals of
by the (Z)-24 isomer.
b
(E)-24 and
a-24 were masked
ꢁ
35. Arico, C. S.; Cox, L. R. Org. Biomol. Chem. 2004, 2, 2558.
b
ꢁ
ꢁ
36. Gordillo, A. I.; Forigua, J.; Lopez-Mardomingo, C.; de Jesus, E. Organometallics
2010, 30, 352.
37. For a recent example of heterogeneous catalytic hydrosilylation of alkynes with
platinum catalysts, see: Alonso, F.; Buitrago, R.; Moglie, Y.; Ruiz-Martinez, J.;
Acknowledgements
ꢁ
Sepulveda-Escribano, A.; Yus, M. J. Organomet. Chem. 2011, 696, 368.
ꢁ
We thank financial support from Ministerio de Ciencia e Innovacion
(MICINN) of Spain (Project CTQ2009-07881/BQU and a grant to A.M.-
M.), Consolider Ingenio 2010 (Project CSD2007-00006), Generalitat
de Catalunya (Project SGR2009-01441), CNRS and the Agence Natio-
nale de la Recherche (ANR-07-CP2D-11-02 MESORCAT).
38. For a recent example of heterogeneous catalytic hydrosilylation of alkynes with
ꢁ
platinum catalysts, see: Alonso, F.; Buitrago, R.; Moglie, Y.; Sepulveda-Escri-
bano, A.; Yus, M. Organometallics 2012, 31, 2336.
€
39. Monge-Marcet, A.; Pleixats, R.; Cattoen, X.; Wong Chi Man, M. J. Sol-Gel Sci.
Technol. http://dx.doi.org/10.1007/s10971-011-2610-9.
40. Mayr, M.; Buchmeiser, M. R.; Wurst, K. Adv. Synth. Catal. 2002, 344, 712.
41. Yeom, C.-E.; Kim, Y. J.; Lee, S. Y.; Shin, Y. J.; Kim, M. Tetrahedron 2005, 61, 12227.
€
42. Kohler, K. WO Patent 2007/017041, 2007.
References and notes
43. Lettow, J. S.; Han, Y. J.; Schmidt-Winkel, P.; Yang, P.; Zhao, D.; Stucky, G. D.; Ying,
J. Y. Langmuir 2000, 16, 8291.
44. Wu, T.-M.; Wu, G.-R.; Kao, H.-M.; Wang, J.-L. J. Chromatogr., A 2006, 1105, 168.
45. Chautan, M.; Hauck, B. J.; Keller, L. P.; Boudjouk, P. J. Organomet. Chem. 2002,
645, 1.
1. Grubbs, R. H. Handbook of Metathesis; Wiley-VCH: Weinheim, 2003; Vol. 1e3.
2. Vougioukalakis, G. C.; Grubbs, R. H. Chem. Rev. 2010, 110, 1746.
3. Nolan, S. P.; Clavier, H. Chem. Soc. Rev. 2010, 39, 3305.
46. Hong, S. H.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2004, 126, 7414.
47. Hong, S. H.; Wenzel, A. G.; Salguero, T. T.; Day, M. W.; Grubbs, R. H. J. Am. Chem.
Soc. 2007, 129, 7961.
4. Hoveyda, A. H.; Gillingham, D. G.; Van Veldhuizen, J. J.; Kataoka, O.; Garber, S.
B.; Kingsbury, J. S.; Harrity, J. P. A. Org. Biomol. Chem. 2004, 2, 8.
5. Chauvin, Y. Adv. Synth. Catal. 2007, 349, 27 (Nobel Lecture 2005).
6. Grubbs, R. H. Adv. Synth. Catal. 2007, 349, 34 (Nobel Lecture 2005).
7. Schrock, R. R. Adv. Synth. Catal. 2007, 349, 41 (Nobel Lecture 2005).
48. Hong, S. H.; Chlenov, A.; Day, M. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 2007,
46, 5148.
ꢁ
49. Vehlov, K.; Gessler, S.; Blechert, S. Angew. Chem., Int. Ed. 2007, 46, 8082.
50. Herbert, M. B.; lan, Y.; Keitz, B. K.; Liu, P.; Endo, K.; Day, M. W.; Houk, K. N.;
Grubbs, R. H. J. Am. Chem. Soc. 2012, 134, 7861.
8. Tzur, E.; Szadkowska, A.; Ben-Asuly, A.; Makal, A.; Goldberg, I.; Wozniak, K.;
Grela, K.; Lemcoff, N. G. Chem.dEur. J. 2010, 16, 8726.
9. Kress, S.; Blechert, S. Chem. Soc. Rev. 2012, 41, 4389.
ꢁ
51. Mallagaray, A.; Mohammadiannejad-Abbasabadi, K.; Medina, S.; Domínguez,
10. Borre, E.; Caijo, F.; Rix, D.; Crevisy, C.; Mauduit, M. Chem. Today 2008, 26, 89.
ꢁ
G.; Perez-Castells, J. Org. Biomol. Chem. 2012, 10, 6665.
11. Hoveyda, A. H.; Malcolmson, S. J.; Meek, S. J.; Zhugralin, A. R. Angew. Chem., Int.
€
52. Polarz, S.; Volker, B.; Jeremias, F. Dalton Trans. 2010, 39, 577.
Ed. 2000, 49, 34.
53. Staub, H.; Guillet-Nicolas, R.; Even, N.; Kayser, L.; Kleitz, F.; Fontaine, F.-G. Chem.
dEur. J. 2011, 17, 4254.
54. Weigl, K.; Kohler, K.; Dechert, S.; Meyer, F. Organometallics 2005, 16, 4049.
12. Deshmukh, P. H.; Blechert, S. Dalton Trans. 2007, 2479.
13. Diesendruc, C. E.; Tzur, E.; Lemcoff, N. G. Eur. J. Inorg. Chem. 2009, 4185.
14. Buchmeiser, M. R. New J. Chem. 2004, 28, 549.
15. Coperet, C.; Basset, J.-M. Adv. Synth. Catal. 2007, 349, 78.
16. Clavier, H.; Grela, K.; Kirshning, A.; Mauduit, M.; Nolan, S. P. Angew. Chem., Int.
€
ꢁ
55. Weigl, K. PhD dissertation, University of Kaiserlautern, 2006.
ꢁ
~
56. Cerezo, S.; Cortes, J.; Moreno-Manas, M.; Pleixats, R.; Roglans, A. Tetrahedron
1998, 54, 14869.
Ed. 2007, 46, 6786.
17. Buchmeiser, M. R. Chem. Rev. 2009, 109, 303.
18. Zamboulis, A.; Moitra, N.; Moreau, J. J. E.; Cattoen, X.; Wong Chi Man, M.
J. Mater. Chem. 2010, 42, 9322.
19. Ciriminna, R.; Cara, P. D.; Sciortino, M.; Pagliaro, M. Adv. Synth. Catal. 2011, 353, 677.
ꢀ
57. Santamaria, A. PhD dissertation, Universitat Autonoma de Barcelona, 2002.
€
58. Hu, J. J.; Li, F.; Hor, T. S. A. Organometallics 2009, 2, 1212.
59. Takeuchi, R.; Nitta, S.; Watanabe, D. J. Org. Chem. 1995, 60, 3045.
60. Foltynowicz, Z.; Marciniec, B. J. Organomet. Chem. 1989, 376, 15.