Organic-inorganic hybrid silica material derived from a monosilylated Grubbs-Hoveyda ruthenium carbene as a recyclable metathesis catalyst

Article abstract of DOI:10.3390/molecules15085756

The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene complex is described, as well as the preparation and characterization of the corresponding material by sol-gel cogelification with tetraethoxysilane (TEOS) and the assay of this recyclab

Full text of DOI:10.3390/molecules15085756

Molecules 2010, 15, 5756-5767; doi:10.3390/molecules15085756
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Organic-Inorganic Hybrid Silica Material Derived from a
Monosilylated Grubbs-Hoveyda Ruthenium Carbene as a
Recyclable Metathesis Catalyst
Guadalupe Borja 1, Roser Pleixats 1,*, Ramón Alibés 1, Xavier Cattoën 2 and
Michel Wong Chi Man 2
1
Chemistry Department, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, 08193-
Barcelona, Spain
2
Institut Charles Gerhardt Montpellier (UMR 5253 CNRS-UM2-ENSCM-UM1), Architectures
Moléculaires et Matériaux Nanostructurés, Ecole Nationale Supérieure de Chimie de Montpellier, 8
rue de l’école normale, 34296 Montpellier cédex 5, France
* Author to whom correspondence should be addressed; E-Mail: Roser.Pleixats@uab.es;
Tel.: +34-93-581-2067; Fax: +34-93-581-1265.
Received: 28 June 2010; in revised form: 10 August 2010 / Accepted: 18 August 2010 /
Published: 23 August 2010
Abstract: The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene
complex is described, as well as the preparation and characterization of the corresponding
material by sol-gel cogelification with tetraethoxysilane (TEOS) and the assay of this
recyclable supported catalyst in ring-closing diene and enyne metathesis reactions under
thermal and microwave conditions.
Keywords: catalyst immobilization; ring-closing metathesis; organic-inorganic hybrid
material; ruthenium alkylidene; sol-gel process
1. Introduction
Olefin metathesis is a very powerful, mild, efficient, versatile and selective method for the cleavage
and the formation of C-C double bonds, which has been widely used by organic chemists for the
preparation of a great variety of compounds and polymers [1-12]. Ring-closing enyne metathesis has
also been explored in recent years as an atom economical process to provide 1-vinylcycloalkenes from

Molecules 2010, 15
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acyclic enynes [13-19]. The enormous success of metathesis procedures in the academic field during
the last decade is due to the development of several well-defined metal alkylidenes. The second-
generation Grubbs ruthenium catalysts [20] 1b (Figure 1) and especially the Grubbs-Hoveyda catalysts
[21,22] 2a,b (Figure 1) show enhanced reactivity, stability and recovery profiles compared to the first
generation Grubbs catalyst 1a (Figure 1), the chelating ligand playing a crucial role in such improvements.
Figure 1. Ruthenium carbene metathesis catalysts.
On the other hand, the increased robustness and stability of the Hoveyda-Grubbs carbenes facilitates
the preparation of recyclable metathesis catalysts [23-26]. One of the most commonly used recycling
strategies consists of the immobilization of the alkylidene complex on an insoluble polymeric support.
An easy separation of the product and recovery of the catalyst can then be achieved by simple filtration
at the end of the reaction, avoiding time-consuming chromatography. Anchoring of ruthenium
complexes of type 1 and 2 to the polymeric support can be performed via alkylidene exchange
(boomerang-type catalysts). The efficiency of boomerang supported catalysts increases notably when
Hoveyda-type ligands are involved (release-return mechanism) [27]. Insoluble organic polymers have
mainly been used as supports, and in the context of catalyst recycling, it is worth to mention that
hybrid organic-inorganic silica materials show chemical, mechanical and thermal stability superior to
that of organic polymers and, most often, higher surface areas. To date only a few examples of silica-
bound alkylidene complexes have been described [23-26,28-30] and these silica-bound metathesis
catalysts always refer to anchoring the metal containing moiety to pre-formed porous or non-porous
silicas. Despite the fact that sol-gel hydrolytic condensation [31] of suitable organo-alkoxysilanes is a
convenient method to prepare solid hybrid materials with targeted properties [32,33], no precedents are
available in the literature about the formation of a hybrid silica material via such a process starting
from a silylated Grubbs ruthenium-alkylidene complex. We have previously reported preparation of
several efficient and recyclable Grubbs-Hoveyda type heterogenized metathesis catalysts through sol-
gel procedures on suitably modified Hoveyda ligands [34–36]. However, in these cases, the sol-gel
process was first performed on the silylated monomeric ligands and the metal was subsequently
introduced in the synthesized material. Very recently, some of us have also described DFT mechanistic
studies on the catalytic activity and catalyst recovery of these supported catalysts [37].
We present herein the synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene
complex, the preparation and characterization of the corresponding material by sol-gel cogelification
with tetraethoxysilane (TEOS) and the assay of this supported catalyst in ring-closing diene and enyne
metathesis reactions under thermal and microwave conditions.

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2. Results and Discussion
2.1. Synthesis of the monosilylated monomer and preparation of hybrid silica material M1
The monosilylated monomer 5 required for the synthesis of the hybrid material M1 was prepared as
summarized in Scheme 1. Treatment of the known alcohol 3 [35] with the second generation Grubbs
catalyst 1b in refluxing anhydrous dichloromethane in the presence of CuCl as phosphine scavenger
[22] gave the ruthenium complex 4. This was obtained as a green solid in 70% isolated yield after
1
chromatography of the crude mixture through silica gel and was fully characterized by IR, H-NMR,
13C-NMR and HR-MS. Subsequent reaction of the alcohol 4 with commercial 3-(isocyanatopropyl)-
triethoxysilane in anhydrous dichloromethane at room temperature afforded the desired silylated
carbamate 5 in 78% isolated yield, also as a green solid. Characterization of 5 was accomplished by
1H-NMR, 13C-NMR, ESI-MS and HR-MS-FAB. Bidimensional NMR experiments (1H-1H COSY, 1H-
1
1
1
1H NOESY, H-13C HSQC, H-13C HMBC) allowed the complete assignment of the signals in the H
NMR spectra for both 4 and 5.
Scheme 1. Preparation of monosilylated ruthenium complex 5 and hybrid material M1.
Co-gelification of 5 with TEOS (molar ratio 1:40) was performed in anhydrous ethanol at room
temperature under nucleophilic conditions (one equivalent of water per ethoxy group, 1% molar of
ammonium fluoride as catalyst). The solution gelified overnight and it was allowed to age for five
days. Then, it was washed successively with ethanol and dichloromethane, and the powder was dried
overnight under vacuum at 60 ºC to afford M1 as a green solid (Scheme 1). This material was studied
by several techniques (29Si CP-MAS NMR, N2 adsorption-desorption analysis, elemental analysis,
29
ICP). The Si CP-MAS NMR of M1 confirmed the covalent bonding of the organic moiety to the
matrix by the presence of T2 and T3 signals at -57.0 and -64.1 ppm respectively, in addition to the
characteristic Q2, Q3 and Q4 signals due to the condensed TEOS at -92.9, -102.6 and -111.7 ppm
(Figure 2a). The N2 adsorption-desorption isotherm of M1 is representative of a material with large
mesopores (pore size distribution centered around 120–175 Å), with a total pore volume of

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0.89–0.93 cm3/g and a BET surface area of 332 m2/g (Figure 2b). The ruthenium content was
determined by inductively coupled plasma (ICP) analysis (0.86% w/w, 0.085 mmol Ru/g of material).
The results of elemental analysis revealed a N/Si ratio of 1/20 and a Ru/N ratio of about 1/6. As the
theoretical values should be 1/14 and 1/3 respectively considering a complete condensation of the
monomer, it is likely that incomplete condensation and partial loss of the metal has occurred during the
formation of the material by the sol-gel process.
Figure 2. (a) Solid state CP-MAS 29Si NMR spectrum of M1. (b) N2 sorption isotherm of
M1 and plot of the pore size distribution.
Q3
700
b)
a)
4
3
2
1
0
600
500
400
300
200
100
0
Desorption
400
0
200
Q4
Pore diameter (Å)
Q2
Adsorption
Desorption
T2
T3
-20
-40
-60
-80
-100
-120
-140
-160 ppm
0
0,2
0,4
0,6
0,8
1
Relative pressure
2.2. Catalytic activity and recyclability of the hybrid material M1 in diene and enyne ring-closing
metathesis reactions
The catalytic activity of the material M1 was tested for the ring-closing metathesis reactions on
diene and enyne substrates 6, 7 and 8 (Scheme 2). The results are summarized in Table 1.
Scheme 2. Diene and enyne metathesis reactions tested with hybrid material M1.

Molecules 2010, 15
Table 1. Results for the diene and enyne RCM reactions with hybrid material M1. a
5760
Conversion
Entry
Substrate
Solvent
Heating
T (ºC)
t (h)
Cycle
b
%
1
2
3
4
5
6
7
8
9
10
11
12
13
14
6
6
6
6
6
6
6
7
7
7
7
7
8
8
8
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
--
Conventional
MWc
rt
reflux
60
60
60
60
60
rt
reflux
rt
50
45
reflux
60
60
20
24
1
2
1
2
3
4
5
1
1
1
1
2
1
1
2
100
100
100
97
94
79
0.33
0.33
0.33
0.33
2.33
24
24
24
0.67
4
22
MWc
MWc
MWc
MWc
77
--
94
conventional
--
100d
88
MWc
84e
65f
100
100
64
MWc
conventional
MWc
3
15
15
MWc
a
General conditions: anhydrous and degassed solvent, inert atmosphere, 3.5 mol% of Ru,
b
[substrate] = 0.05 M. Conversion determined by NMR, only the desired product being formed
c
d
unless otherwise stated. Microwave irradiation with PowerMax option enabled. 82% of 10 and
e
18% of the cycloisomerization product 10b. 77% of 10 and 7% of the cycloisomerization product
10b. f 63% of 10 and 2% of the cycloisomerization product 10b.
The intramolecular reaction on diethyl 2,2-diallylmalonate (6), performed in anhydrous and
degassed dichloromethane at room temperature, gave product 9 with a 100% conversion after 20 h,
with no other compound being detectable by NMR. The desired final product 9 was isolated in pure
form after simple filtration and solvent evaporation (entry 1). The recovered catalyst was reused in a
second cycle, but refluxing conditions were required to produce 100% conversion after 24 h (entry 2).
Alternatively, microwave irradiation was used as a means of shortening the reaction times [38,39],
which can be beneficial in order to avoid catalyst decomposition by prolonged heating. Thus, when the
process was performed at 60 ºC under microwave irradiation, the reaction was complete in 20 min and
the catalyst was reused up to 5 runs (entries 3-7). The activity was maintained for the first three cycles.
The conversion decreased in the fourth cycle to 79% for the same reaction time (20 min) and higher
reaction time (140 min) was required to achieve a similar conversion (77%) in the fifth cycle.
Following these studies on the RCM of 6, four different set of conditions were tested for the similar
reaction on N,N-diallyl-p-toluenesulfonamide (7) to afford product 10 (entries 8-12). By performing
the reaction in dichloromethane at room temperature a 94% conversion was achieved after 24 h (entry
8). Complete conversion was attained under refluxing dichloromethane, but thermal heating results in
the formation of a secondary product 10b derived from a cycloisomerization process (entry 9). A
change of solvent from dichloromethane to toluene led to 88% conversion of 7 after 24 h at room
temperature (entry 10). Although secondary product 10b was avoided under these conditions, the
reaction rate was not higher than in dichloromethane at the same temperature. Interestingly by
adopting microwave irradiation at 50 ºC in dichloromethane in similar reaction conditions (entry 11), a
87% conversion was observed after 45 min, although the mixture still contained minor amounts of the
secondary product 10b (77% of 10 and 7% of 10b). The recycling of the catalyst M1 was studied
under microwave irradiation at 45ºC, affording a conversion of 65% after 4 h. The mixture contained

Molecules 2010, 15
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also a minor amount of 10b (2%) (entry 12). Thus, it seems that prolonged heating or irradiation at
higher temperatures must be avoided for the RCM reaction with this substrate 7 and catalyst M1.
Otherwise, a competitive cycloisomerization reaction of 7 occurs. Cycloisomerization of a diene in
competition to the expected ring-closing metathesis reaction has been previously reported [40], this
side reaction being mediated by a decomposition product of the initial metathesis catalyst. It is not
unlikely that ruthenium hydride species are involved in such transformations. Finally, an enyne RCM
reaction was assayed with 1-allyloxy-1,1-diphenyl-2-propyne (8) to give the diene 11 (entries 13-15).
Under refluxing dichloromethane a complete conversion was observed after 22 h (entry 13). The
reaction time required for 100% conversion was reduced considerably (3 h) by adopting microwave
irradiation conditions at 60 ºC (entry 14). The recovered material M1 was reused under analogous
conditions to afford 64% conversion after 15 h (entry 15).
After the reaction, the ruthenium contents in the crude products 9 and 10 (Table 1, entries 4 and 8)
corresponded to 353 ppm and 175 ppm, respectively, as determined by ICP analysis. Thus the loss of
ruthenium in M1 during a reaction cycle was 1.9% and 0.8%, respectively.
Comparison of the results presented here with those previously described by us [35], where the sol-
gel process was first performed on the silylated monomeric Hoveyda ligand and the metal was
subsequently introduced in the synthesized material, show that the catalytic activity and recyclability
was superior in our previous work. Diffusion problems could be on the origin of the lower activity of
the herein described M1. Presumably the ruthenium complex is mainly located in the present case
inside the material, being less accessible to the reactants. The requirement of more drastic conditions
and the presence of silanol groups on the material could explain the formation of decomposition
species leading to side reactions or catalyst deactivation [41]. Nevertheless, it is worth to mention that
olefin metathesis with Hoveyda-Grubbs catalysts has been successfully performed in aqueous media,
suggesting the high stability of this type of complexes [42].
3. Experimental
3.1. General
13
1H- and C-NMR spectra were recorded on a Bruker DPX250 or on a Bruker AVANCE-III 400
instrument and the J values are given in Hz. The CP-MAS 29Si solid state NMR spectra were recorded
on a Bruker AV-400-WB at the Servei de Ressonància Magnètica Nuclear of the Universitat
Autònoma de Barcelona. MS (ESI) and HR-MS (ESI) analyses were recorded at the Servei d’Anàlisi
Químic of the Universitat Autònoma de Barcelona on a Hewlett-Packard 5989A instrument. HR-MS
(FAB) analysis was recorded at the Unidad de Espectrometría de Masas of the Universidad de
Santiago de Compostela using 3-nitrobenzyl alcohol as matrix. IR data (KBr) were obtained with a
Thermo Nicolet IR200 spectrophotometer. Elemental analyses have been performed at the Serveis
Científicotècnics of the Universitat de Barcelona, using Inductively Coupled Plasma (ICP) for Ru and
Si. Surface areas were calculated using the Brunauer-Emmett-Teller (BET) method based on N2
adsorption-desorption studies performed on a Micromeritics ASAP2020 analyzer at the Institut Charles
Gerhardt Montpellier, after degassing the material at 55 ºC for 30 h. Microwave reactions were
conducted on a CEM Discover® Microwave synthesizer. The machine consists of a continuous focused

Molecules 2010, 15
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microwave-power delivery system with operator-selectable power output from 0 to 300 W. Reactions
were performed in glass vessels (capacity 10 mL) sealed with a septum. Temperature measurements
were conducted using an infrared temperature sensor mounted under the reaction vessel. All
experiments were performed using a stirring option whereby the contents of the vessel were stirred by
means of a rotating magnetic plate located below the floor of the microwave cavity and a Teflon-
coated magnetic stir bar in the vessel. All experiments were carried out with simultaneous cooling by
passing compressed nitrogen through the microwave cavity while heating (PowerMAX option
enabled). The alcohol 3 was prepared as previously described [34].
3.2. Preparation of the Grubbs-Hoveyda ruthenium alkylidenic complex 4
Complex 1b (1.852 g, 2.18 mmol) and CuCl (216 mg, 2.18 mmol) were weighed into a Schlenk
flask under an inert atmosphere and dissolved in anhydrous CH2Cl2 (42.5 mL). A solution of 3
(500 mg, 2.12 mmol) in anhydrous CH2Cl2 (45 mL) was added. The mixture was refluxed for 2 h
under argon atmosphere (1H-NMR monitoring), as initial deep red colour turned green. From this point
forth, all manipulations were carried out in air with reagent-grade solvents. The reaction mixture was
concentrated under vacuum to give a dark green solid residue, which was dissolved in a minimal
volume of 1:1 pentane/CH2Cl2. The solution was passed through a pipette containing a plug of cotton
and purified by column chromatography through silica gel. Elution with CH2Cl2 to CH2Cl2/MeOH
1
(98:2), removal of solvent and drying afforded 4 as a bright green solid (1.04 g, 70%). H-NMR
(CDCl3, 250 MHz) δ (ppm): 16.45 (s, 1H, Ru=CH), 7.10 (m, 1H, aromatic CH), 7.07 (s, 4H, mesityl
aromatic CH), 6.68 (d, 1H, aromatic CH, J = 9.3 Hz), 6.47 (d, 1H, aromatic CH, J = 3.0 Hz), 4.81
(sept, 1H, -CH(CH3)2, J = 6.0 Hz), 4.18 (m, 4H, -N-CH2-CH2-N-), 4.03 (t, 2H, -O-CH2-CH2-CH2-OH,
J = 5.8 Hz), 3.85 (q, 2H, -O-CH2-CH2-CH2-OH, J = 5.5 Hz), 2.47 (s, 12H, mesityl CH3), 2.40 (s, 6H,
mesityl CH3), 2.01 (quint, 2H, -O-CH2-CH2-CH2-OH, J = 5.9 Hz), 1.70 (t, 1H, -OH, J = 5.3 Hz), 1.24
(d, 6H, -CH(CH3)2, J = 5.8 Hz). 13C-NMR (CDCl3, 100.6 MHz) δ (ppm): 296.3 (Ru=CH), 211.3 (Ru-
NHC), 154.2 (aromatic C), 146.7 (aromatic C), 145.6 (aromatic C), 138.9 (mesityl C), 129.4 (mesityl
CH), 115.8 (aromatic CH), 113.3 (aromatic CH), 108.0 (aromatic CH), 75.0 (-CH(CH3)2), 66.7 (-O-
CH2-CH2-CH2-OH), 60.5 (-O-CH2-CH2-CH2-OH), 51.6 (-N-CH2-CH2-N-), 32.1 (-O-CH2-CH2-CH2-
OH), 21.2 (mesityl CH3 + -CH(CH3)2). IR ν (cm-1) (KBr): 3448, 2923, 1688, 1488, 1258, 1214, 855.
m.p (ºC): 199 (dec.). HR-MS (ESI) Calcd. for [C34H44Cl2N2O3RuNa]+: 723.1652; Found: 723.1668.
3.3. Preparation of the monosilylated Grubbs-Hoveyda ruthenium alkylidenic complex 5
Freshly distilled 3-isocyanatopropyltriethoxysilane (54 µL, 0.99 g/mL, 0.216 mmol) was added
under argon to 4 (150 mg, 0.214 mmol) in anhydrous dichloromethane (0.5 mL). The mixture was
stirred under argon at room temperature for 4 days. The solvent was removed under vacuum. The
1
residue was washed with anhydrous pentane to afford 5 (231 mg, 64%) as a green solid. H-NMR
(CDCl3, 400 MHz) δ (ppm): 16.44 (s, 1H, Ru=CH), 7.06 (m, 5H, mesityl CH + aromatic CH), 6.67 (d,
1H, aromatic CH, J = 8.0 Hz), 6.45 (d, 1H, aromatic CH, J = 8.0 Hz), 4.80 (septet, 1H, -CH(CH3)2,
J = 6.0 Hz), 4.17 (m, 4H, -N-CH2-CH2-N-), 4.03-3.92 (m, 4H, -O-CH2-CH2-CH2-O-), 3.81 (q, 6H, -O-
CH2-CH3, J = 7.6 Hz), 3.17 (m, 2H, -NH-CH2-CH2-CH2-Si(OEt)3), 2.46 (s, 12H, mesityl CH3), 2.39 (s,

Molecules 2010, 15
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6H, mesityl CH3), 2.06-2.00 (m, 2H, -O-CH2-CH2-CH2-O-), 1.63 (m, 2H, -NH-CH2-CH2-CH2-
Si(OEt)3), 1.22 (m, 15H, -CH(CH3)2 + -O-CH2-CH3), 0.63 (m, 2H, -NH-CH2-CH2-CH2-Si(OEt)3).
13C-NMR (CDCl3, 100.6 MHz) δ (ppm): 296.3 (Ru=CH), 211.4 (Ru-NHC), 154.3 (aromatic C), 146.8
(aromatic C), 145.6 (aromatic C), 138.9 (mesityl C), 129.5 (mesityl CH), 115.8 (aromatic CH), 113.2
(aromatic CH), 108.1 (aromatic CH), 75.0 (-CH(CH3)2), 66.7 (-O-CH2-CH2-CH2-O- or -O-CH2-CH2-
CH2-O-), 60.5 (-O-CH2-CH2-CH2-O- or -O-CH2-CH2-CH2-O ), 58.6 (-O-CH2-CH3), 51.6 (-N-CH2-
CH2-N-), 43.1 (-NH-CH2-CH2-CH2-Si(OEt)3), 32.2 (-O-CH2-CH2-CH2-O-), 22.4 (-NH-CH2-CH2-CH2-
Si(OEt)3), 21.1 (mesityl CH3 + -CH(CH3)2), 18.4 (-O-CH2-CH3). 7.7 (-NH-CH2-CH2-CH2-Si(OEt)3).
ESI-MS m/z (rel. int. %): [M–Cl]+ 912.3 (100), [M–2Cl]+ 876.4 (33.5). HR-FAB: Calcd for
[C44H65Cl2N3O7RuSi]+: 947.3012; Found: 947.3004.
3.4. Preparation of the organic-inorganic hybrid silica material M1 derived from 5
A solution of ammonium fluoride (80 μL of a 1 M solution, 4.44 mmol H2O, 0.08 mmol NH4F) and
distilled and deionized water (490 μL, 27.22 mmol) in anhydrous EtOH (2.8 mL) was added to a
solution of 5 (184 mg, 0.194 mmol) and TEOS 98% (1.620 g, 7.62 mmol) in anhydrous EtOH
(5.2 mL). The mixture was manually shaken for a minute to get a homogeneous solution and was left
at room temperature without stirring. During the night gelification occurred and the gel was aged for 5
days. It was then powdered and washed successively several times with ethanol and then with
dichloromethane. The solid was dried under vacuum (1 mmHg, 60 ºC, overnight), yielding M1 as a
dark green powder (603 mg). 29Si-NMR (79.5 MHz, CP-MAS) δ (ppm): -57 (T2), -64.1 (T3),
-92.9 (Q2), -102.6 (Q3), -111.7 (Q4). EA Calcd. for C38H50Cl2N3O4RuSiO1.5·40SiO2 (considering
complete condensation): 14.09% C, 1.56% H, 1.30% N, 2.19% Cl, 3.12% Ru, 35.54% Si. Found:
9.60% C, 2.55% H, 0.75% N, 1.00% Cl, 31.19% Si. ICP: 0.86%Ru (0.085 mmol Ru/g material). SBET
332 m²/g; pore diameter: 103–111 Å; pore volume: 0.93–0.89 cm³/g.
:
3.5. Ring-closing metathesis reaction on diethyl 2,2-diallylmalonate (6) with hybrid silica material M1
3.5.1. Under conventional conditions. Typical procedure (Table 1, entry 1)
A solution of 6 (25 mg, 0.104 mmol) in anhydrous and degassed dichloromethane (2.1 mL) was
added under nitrogen to M1 (43 mg, 0.085 mol Ru/g, 0.0037 mmol Ru) placed in a Schlenk tube and
the mixture was stirred under inert atmosphere at room temperature for 20 h (GC monitoring). The
mixture was filtered under nitrogen atmosphere with a cannula and the solid was washed several times
with 2 mL portions of anhydrous dichloromethane. The combined filtrates were evaporated to give
1
pure 9 (19.3 mg, 100% conversion by H-NMR), whose spectroscopic data were coincident with that
reported in the literature [43]. 1H-NMR (CDCl3, 360 MHz) δ (ppm): 5.60 (m, 2H), 4.19 (q, J = 7.2 Hz,
4H), 3.00 (m, 4H), 1.24 (t, J = 7.2 Hz, 6H).

Molecules 2010, 15
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3.5.2. Under microwave irradiation. Typical procedure (Table 1, entry 3)
A solution of 6 (25 mg, 0.104 mmol) in anhydrous and degassed dichloromethane (2.1 mL) was
added under nitrogen to M1 (43 mg, 0.085 mol Ru/g, 0.0037 mmol Ru) placed in a microwave vessel
which was sealed, placed in the microwave cavity and irradiated to 60 ºC (PowerMax option enabled)
for 20 min (GC monitoring). The mixture was filtered under nitrogen atmosphere with a cannula and
the solid was washed several times with 2 mL portions of anhydrous dichloromethane. The combined
filtrates were evaporated to give pure 9 (23.4 mg, 100% conversion by 1H-NMR). The catalyst M1 was
dried and reused in a next cycle. Compounds 10 [34] and 11 [34] were obtained from 7 and 8,
respectively, by analogous procedures under the conditions described in Table 1.
4. Conclusions
We have synthesized and characterized a monosilylated Grubbs-Hoveyda ruthenium alkylidene
complex, as well as the corresponding material M1 made by sol-gel cogelification with
tetraethoxysilane (TEOS). This material has been assayed as a recyclable catalyst in the ring-closing
metathesis reactions of some selected dienes and enynes. Good results have been obtained for the first
cycle in dichloromethane at room temperature for dienes 6 and 7 and under refluxing conditions for
enyne 8. Notably, considerable improvement has been achieved under microwave irradiation
conditions. Thus, drastic reduction of the reaction time favoured the recyclability of the material.
Under these conditions up to five cycles have been performed on diene 7 to afford 10 in a very fast and
clean reaction. Supported catalyst M1 is, to our knowledge, the first case described in the literature of
a heterogeneous metathesis catalyst prepared by sol-gel co-gelification from a silylated
ruthenium alkylidene.
Acknowledgements
We acknowledge financial support from MICINN of Spain (Projects CTQ2009-07881/BQU and
CTQ2007-60613/BQU), Consolider Ingenio 2010 (Project CSD2007-00006) and Generalitat de
Catalunya (Project SGR2009-01441 and a grant to G. B.). Nirmalya Moitra (ICGM) is gratefully
acknowledged for performing the N2 sorption experiment.
References and Notes
1. Grubbs, R.H., Ed. Handbook of Metathesis, 1st ed.; Wiley-VCH: Weinheim, Germany, 2003;
Volume 1-3.
2. Armstrong, S.K. Ring Closing Diene Metathesis in Organic Synthesis. J. Chem. Soc., Perkin
Trans. 1 1998, 371-388.
3. Fürstner, A. Olefin Metathesis and Beyond. Angew. Chem. Int. Ed. 2000, 39, 3012-3043.
4. Deshmukh, P.H.; Blechert, S. Alkene metathesis: the search for better catalysts. Dalton Trans.
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