Sol-gel immobilized Hoveyda-Grubbs complex through the NHC ligand: A recyclable metathesis catalyst

Article abstract of DOI:10.1016/j.molcata.2012.01.019

The synthesis of a bis-silylated Hoveyda-Grubbs ruthenium alkylidene complex is described, as well as the preparation via the sol-gel process and the characterization of an organosilica by co-gelification with tetraethyl orthosilicate (TEOS). This material is an active supported catalyst for various metathesis reactions. The recyclability has been proven even for the formation of a trisubstituted olefin. This is the first example of an immobilized Hoveyda-Grubbs' type complex prepared by sol-gel co-gelification from a well-defined ruthenium alkylidene precursor bearing a silylated NHC moiety.

Full text of DOI:10.1016/j.molcata.2012.01.019

Journal of Molecular Catalysis A: Chemical 357 (2012) 59–66
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Sol–gel immobilized Hoveyda–Grubbs complex through the NHC ligand: A
recyclable metathesis catalyst
Amàlia Monge-Marceta,b, Roser Pleixatsa,∗, Xavier Cattoënb, Michel Wong Chi Manb
a Chemistry Department, Universitat Autònoma de Barcelona, 08193-Cerdanyola del Vallès, Barcelona, Spain
b Institut Charles Gerhardt Montpellier (UMR 5253 CNRS-UM2-ENSCM-UM1), 8 rue de l’école normale, 34296 Montpellier, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of a bis-silylated Hoveyda–Grubbs ruthenium alkylidene complex is described, as well
as the preparation via the sol–gel process and the characterization of an organosilica by co-gelification
with tetraethyl orthosilicate (TEOS). This material is an active supported catalyst for various metathesis
reactions. The recyclability has been proven even for the formation of a trisubstituted olefin. This is the
first example of an immobilized Hoveyda–Grubbs’ type complex prepared by sol–gel co-gelification from
a well-defined ruthenium alkylidene precursor bearing a silylated NHC moiety.
Received 5 September 2011
Received in revised form 11 January 2012
Accepted 23 January 2012
Available online 31 January 2012
Dedicated to Prof. Christian Bruneau on
occasion of his 60th birthday.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Catalyst immobilization
Metathesis
Organic–inorganic hybrid silica material
NHC ruthenium complex
Sol–gel process
1. Introduction
intermolecular catalyst–catalyst interactions are inhibited via site
isolation.
Olefin metathesis constitutes one of the most powerful tools for
the formation of carbon–carbon double bonds under mild condi-
tions in a selective manner, and is widely employed nowadays in
both organic and polymer chemistry [1–15]. In the recent years,
ring-closing metathesis of acyclic enynes has also emerged as an
atom economical process to provide 1-vinylcycloalkenes [16–20].
The great success of metathesis reactions in the academic field
can be attributed to the development of well-defined alkylidene
ruthenium catalysts [21–25] 1a–c (Fig. 1) with high activity and
functional group tolerance [26–28]. The second generation Grubbs
catalyst 1b and the Hoveyda–Grubbs catalysts 2a–b [29,30] (Fig. 1)
containing a chelating styrenic ligand instead of a phosphine, led
to enhanced reactivity, stability and recovery profiles compared to
the first generation Grubbs catalyst 1a.
Furthermore, the recovery and recycling are facilitated and
the organic products are obtained with lower contamination by
ruthenium species and without time-consuming chromatography.
Therefore, the recovery and reuse of the catalytic system remains
as a challenge of economic and environmental relevance. Thus,
over the past decade several research groups have prepared and
tested recyclable metathesis catalysts [35–42]. Although several
approaches have been described using conveniently modified solu-
ble ruthenium alkylidene complexes (ionic liquids [43], water [44],
fluorous [45,46] and PEG-tagged materials [47]), one of the most
used strategies consists in the immobilization of a robust and sta-
ble alkylidene complex on a polymeric insoluble support. Filtration
at the end of the reaction allows an easy separation of the product
and the recovery of the catalyst.
Homogeneous catalysts present several drawbacks such as
deactivation through decomposition pathways, difficult recycling
and tedious separation of the catalyst from the organic prod-
ucts [26,27,31–34]. The immobilization of the catalyst onto a
solid support can prevent bimolecular decomposition pathways as
The anchorage of ruthenium alkylidenes of types 1 and 2 to
the polymeric matrix has been performed [37–41] via a num-
ber of positions within the catalyst framework, i.e. via halogen
exchange, through phosphine or alkylidene moieties (boomerang-
type catalysts) and via the N-heterocyclic carbene ligand (NHC)
(permanently immobilized catalysts) [48–50]. Although insoluble
or soluble organic polymers are the most frequently used supports,
it is worth mentioning that hybrid organic–inorganic silica mate-
rials or organically modified silica show chemical, mechanical and
thermal stabilities superior to those of organic polymers and, most
∗
Corresponding author. Tel.: +34 93 581 2067; fax: +34 93 581 2477.
E-mail address: roser.pleixats@uab.cat (R. Pleixats).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2012.01.019

60
A. Monge-Marcet et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 59–66
synthesis, the activity and the recycling of a new organosilica mate-
rial derived from a second generation Hoveyda–Grubbs ruthenium
complex bearing a bis-silylated NHC moiety.
L
Ru
O
L
Cl
Cl
Cl
Cl
Ru
Ph
PCy3
2. Experimental
1a L = PCy3
1b L = SIMes
1c L = IMes
2a L = PCy3
2b L = SIMes
2.1. 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%, glyoxal solution 40% (w/w), allylmag-
nesium chloride 2 M solution in anhydrous THF, triethyl ortho-
formate 98%, trichlorosilane, potassium bis(trimethylsilyl)amide
(0.5 M solution in anhydrous toluene), tetrabutylammonium flu-
oride (1 M solution in anhydrous THF) and first generation
Hoveyda–Grubbs catalyst 2a were purchased from Aldrich. The sil-
ica gel for flash chromatography was SiliCycle P60 R12030, with a
particle size of 60.0–75.0 ␮m; a pore volume of 0.8–1.0 mL/g and
6.5–7.5 pH (suspension in 10% water). The silica gel was dried
under a nitrogen flow using a heat gun just before use. Pt Karstedt
catalyst (10% wt in isopropanol) was kindly provided by Rho-
dia. All commercial reagents were used as received except for
trichlorosilane which was purified by distillation then degassed
just before use. Spectral data were obtained with the following
instruments: IR on a Bruker Tensor 27 with ATR Golden Gate; liq-
uid NMR on Bruker DRX-250MHz, DPX-360MHz and AVANCE-II
400MHz. Chemical shifts (ı, ppm) were given using the sig-
nal of residual non-deuterated solvent as internal reference. The
abbreviations used are s for singlet; d for doublet; dd for dou-
ble doublet; ddd for double double doublet; t for triplet; q for
quadruplet and sept for septuplet. The CP-MAS 29Si solid state
NMR spectra were recorded on a Bruker AV400WB. The repeti-
tion time was 5 s with contact time of 5 ms. Surface areas were
calculated by the Brunauer–Emmett–Teller (BET) method from
N2-sorption isotherms carried out on a Micromeritics ASAP2020
analyzer; materials were degassed for 30 h at 55 ◦C under high
vacuum (10 ␮m Hg) and the pore size distribution was calculated
by the BJH method on the desorption branch. ESI mass spectra
were acquired using a microTOF-Q instrument at the Universitat
Autònoma de Barcelona and FAB mass spectra were recorded at
the Universidad de Santiago de Compostela using 3-nitrobenzyl
alcohol as matrix. Elemental analyses have been performed at
Serveis Científico-Tècnics of the Universitat de Barcelona by induc-
tively coupled plasma (ICP) analysis. TGA analysis was done at the
Institut de Ciència dels Materials de Barcelona. Microwave reactions
were conducted on a CEM Discover® Microwave synthesizer. The
machine consists of a continuous focused microwave-power deliv-
ery 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.
The experiments were performed using a stirring option whereby
the contents of the vessel were stirred by means of a rotating mag-
netic plate located below the floor of the microwave cavity and a
Teflon-coated magnetic stir bar in the vessel. The experiments were
carried out with simultaneous cooling, when necessary, by passing
compressed nitrogen through the microwave cavity while heating.
N,N’-(1E,2E)-ethane-1,2-diylidenebis(2,4,6-trimethylaniline) 3
[85], (4R,5S)-N,N’-dimesitylocta-1,7-diene-4,5-diamine 4 [86,87]
and (4S,5R)-4,5-diallyl-1,3-dimesityl-4,5-dihydro-1H-imidazol-3-
ium chloride 5 [86,87], as well as compounds 10 [79], 12 [88], 14
[79], 17 [86,87] and 19 [79] used as substrates for catalytic tests
were prepared as previously reported. Products 9, 11 [79], 13 [79],
15 [79], 18 [86,87], 20 [79] and 22 have previously been described in
N
N
N
N
SIMes
IMes
Fig. 1. Ruthenium-alkylidene olefin metathesis catalysts.
often, higher surface areas, and have emerged as versatile matrices
for supporting homogeneous catalysts, either physically entrapped
or covalently bonded to the matrix [51–53]. In fact, some examples
of silica immobilized alkylidene ruthenium complexes have also
been reported, either by confinement [54,55] or covalent grafting
methods [56–62] through a phosphine [62], a carboxylate ligand
[63–65], the chelating benzylidene [66–70], the NHC [56–61,71] or
through direct Ru–O–Si bonds [72].
Most examples of silica-immobilized Grubbs catalysts refer to
the covalent anchoring of the metal-containing moiety to pre-
formed porous or non-porous silicas, monoliths or mesocellular
foams. So far, little attention has been paid to sol–gel hydrolytic
condensation of organo-alkoxysilanes [73], which is a convenient
method for the preparation of organosilica materials with tar-
geted properties [74,75]. This methodology represents an efficient
route to produce supported catalysts with a high and controlled
loading of the organics as the covalent Si–C bonds are preserved
during the mild hydrolysis-condensation reactions, which results
in supported catalysts different from those prepared by grafting
methods [76–78]. Our research groups have previously reported
the synthesis of several efficient recyclable Hoveyda–Grubbs-type
heterogenized metathesis catalysts through sol–gel procedures on
suitably modified benzylidene ligands [79–81]. However, in these
cases, the sol–gel process was first conducted on the silylated
Hoveyda ligands and the metal was subsequently introduced in
the synthesized material. Very recently, we have also described
the first use of a boomerang-type recyclable supported metathe-
sis catalyst that can proceed under both thermal and microwave
conditions [82]. This catalyst was obtained by co-gelification of
a monosilylated Hoveyda–Grubbs complex with TEOS. Moreover,
DFT mechanistic studies on the catalytic activity and recyclability
of these supported catalysts have been performed [83].
Immobilization approaches involving phosphine, alkylidene
and also alternative X-type ligands replacing the ancillary chlo-
rides suffer from the facts that these ligands are substitutionally
labile: a release-return mechanism is operating [38] or an exchange
between X-type ligands can take place [84]. These strategies are,
thus, more prone to leaching of the metal and bimolecular decom-
position of the in situ formed homogeneous catalytic species.
Heterogenization through functionalized NHC ligands [71] is an
attractive approach as the NHC forms a strong bond to the ruthe-
nium centre and this ligand is the most substitutionally inert. Up to
now there is no precedent of immobilized metathesis catalysts aris-
ing from a sol–gel hydrolytic polycondensation of silylated NHC–Ru
complexes.
Following our studies on recyclable catalysts based on sol–gel
methodologies, we present here our results concerning the

A. Monge-Marcet et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 59–66
61
the literature and their spectral and physical data were consistent
with those reported.
21.3, 21.5, 23.1, 32.1, 58.7, 66.9, 68.9, 75.1, 113.3, 122.6, 123.1,
130.0, 130.4, 138.7, 140.0, 140.4, 140.9, 146.0, 152.4, 211.4, 300.0;
12
FAB-MS: found: 1036.3889, calc. for
1036.3925.
C
49
H80N2O7Si235Cl2Ru:
2.2. Synthesis of the supported catalyst
2.2.3. Preparation of material M1
2.2.1. Synthesis of 1,3-dimesityl-4,5-bis[3-(triethoxysilyl)propyl]-
Under argon atmosphere a solution of complex 7 (0.221 g,
0.214 mmol) and TEOS 98% (1.80 mL, 0.94 g cm−3, 7.96 mmol) in
dry and degassed DMF (4 mL) was prepared in a 25 mL flask.
Under stirring a solution of TBAF (0.090 mL, commercial solution
1 M in anh. THF, 0.090 mmol, 1 mol% F with respect to Si) and
milliQ water (0.627 mL, 34.3 mmol, H2O/EtO = 1) in dry DMF (4 mL)
was added to the first solution (molar ratio 7:TEOS:H2O:TBAF
1:38:160:0.4). The final mixture was stirred at room temperature
for 5 min and then stirring was stopped. A gel was formed after
1 h and was aged for 6 days at room temperature under argon
atmosphere. At this time, the gel was pulverized, filtered, washed
with dry EtOH (3 × 10 mL), dry CH2Cl2 (2 × 10 mL) and finally dried
overnight at 50 ◦C under vacuum (0.7 mbar). The final solid was
crushed to obtain material M1 as a green powder (0.932 g). 29Si
CP-MAS (79.5 MHz) ı = −58.7 (T2), −67.2 (T3), −92.6 (Q2), −102.5
(Q3), −111.5 (Q4). BET surface area: 404 m2 g−1; pore diameter dis-
4,5-dihydroimidazol-1H-ium chloride
(6)
In
a 100 mL sealed Schlenk tube, compound 5 (0.517 g,
1.22 mmol) was dissolved in dry CH2Cl2 (15 mL) under argon
atmosphere. To this solution Karstedt’s catalyst (168 ␮L, 10.4 wt%
Pt solution in isopropanol, 0.080 mmol Pt) and distilled HSiCl3
(3.50 mL, 1.34 g cm−3, 34.7 mmol) were added. After sealing the
Schlenk tube, the reaction mixture was stirred under argon at 40 ◦C
for 20 h. After this time, the excess of HSiCl3 was distilled off.
The residue was dissolved in dry CH2Cl2 (15 mL) and the mixture
was cooled to 0 ◦C. At this temperature a mixture of anhydrous
EtOH/NEt3 (1/1, v/v, 9 mL) was added slowly and the mixture
was stirred at room temperature for 2 h. The volatiles were then
removed under vacuum, the residue was treated with dry toluene
and filtered to separate the ammonium salt. Filtrates were concen-
trated under vacuum and dry pentane was added to precipitate
the desired product, which was separated by filtration and further
washed with pentane until it became white. Pure 6 was isolated
as a white solid after drying under vacuum (0.573 g, 65%). Mp:
149–151 ◦C. IR: (ATR)/cm−1 2972, 2922, 2880 and 2806 (CH), 1620,
1602, 1482, 1458, 1388, 1272, 1166, 1100, 1076, 950, 788, 746;
ıH (360 MHz, CDCl3) 0.51 (4H, m, CH2Si), 1.14 (18H, t, J 6.8 Hz,
OCH2CH3), 1.73 (4H, br s, CH2CH2Si), 1.85 (4H, br s, CH2CH2CH2Si),
2.25 (6H, s, Ar-CH3), 2.35 (6H, s, Ar-CH3), 2.46 (6H, s, Ar-CH3),
3.69 (12H, q, J 6.8 Hz, OCH2CH3), 4.62 (2H, br s, CH), 6.91 (2H, s,
C6H2Me3), 6.95 (2H, s, C6H2Me3), 10.68 (1H, s, NCHN); ıC (90 MHz,
CDCl3) 10.8, 18.4, 18.9, 19.3, 20.7, 21.1, 30.2, 58.5, 66.1, 130.0, 130.4,
130.5, 134.6, 135.8, 140.0, 160.4; ESI-MS: found: 715.4547, calc. for
˚
tribution centred around 30–40 A, average pore diameter (4 V/A,
3
BET): 22.7 A; pore volume: 0.23 cm g−1. EA: found N, 5.00; C,
˚
19.12; H, 3.83; Si, 25.8; Ru, 1.15 (0.113 mmol/g material). Calc. for
C
37H49Cl2N2O1Ru·2SiO1.5·38SiO2 (considering complete conden-
sation): N, 0.87; C, 13.82; H, 1.52; Si, 36.62; Ru, 3.14. The N content
in the material M1 was higher than expected. This could be due
to the solvent used in the sol–gel process (DMF). Residual solvent
remaining in the material despite the overnight drying under vac-
uum at 50 ◦C would explain that the nitrogen content was higher
than expected.
2.3. Typical procedure for the catalytic tests
C39H67N2O6Si2: 715.4532.
In a 10 mL tube under argon atmosphere, supported catalyst
M1 (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 sol-
vent (1 mL) was transferred via a cannula to the tube containing
the catalyst. The resulting suspension was stirred at the tem-
peratures and for the times indicated in the tables. Conversion
was monitored by GC and when all starting material was con-
sumed, the stirring was stopped, the material was left to settle
and the solution was filtered under a nitrogen atmosphere. The
catalyst was washed with dry and degassed solvent (3 × 3 mL),
dried under vacuum and directly used in the next cycle. The fil-
trates were concentrated under reduced pressure to afford the
corresponding product, whose yield was determined by 1H NMR
spectroscopy.
2.2.2. Synthesis of bis-silylated ruthenium complex (7)
In a 50 mL Schlenk tube, compound 6 (0.549 g, 0.730 mmol)
was dissolved in dry and degassed toluene (10 mL). Under argon
atmosphere, KHMDS (2.0 mL, commercial 0.5 M solution in dry
toluene, 1.0 mmol) was added and the resulting solution stirred
at room temperature for 10 min, during this time a fine precip-
itate appeared. To this suspension, a solution of 1st generation
Hoveyda–Grubbs catalyst 2a (0.299 g, 0.498 mmol) in dry and
degassed toluene (7 mL) was transferred via a cannula. Then the
Schlenk tube was sealed and the mixture was stirred under argon
atmosphere at 80 ◦C for 3 h. Then, the crude product was cooled
down to room temperature and volatiles were removed under
vacuum. The brown residue was treated with dry and degassed
chloroform at room temperature for 16 h. After this time, the
initial brown colour turned green and the solvent was removed
under vacuum. The residue was purified by flash chromatog-
raphy using hexane/AcOEt as eluent (6/1, these solvents were
previously dried), to afford 7 as a sticky green solid (0.105 g,
20%). IR: (ATR)/cm−1 2923 and 2853 (CH), 1589, 1476, 1450,
1410, 1382, 1291, 1257, 1100 (Si–O–Si), 1075, 1034, 939, 849,
796, 744; ıH (400 MHz, CDCl3) 0.50 (4H, m, CH2Si), 1.10 (18H,
t, J 6.8 Hz, OCH2CH3), 1.14 (6H, br s, CH(CH3)2), 1.19–1.50 (8H,
m, CH2CH2CH2Si), 2.26 (6H, s, Ar-CH3), 2.29 (3H, s, Ar-CH3),
2.37 (3H, s, Ar-CH3), 2.46 (3H, s, Ar-CH3), 2.56 (3H, s, Ar-CH3),
3.65 (12H, q, J 6.8 Hz, OCH2CH3), 4.32 (2H, m, NCHCHN), 4.79
(1H, sept, J 6.8 Hz, CH(CH3)2), 6.68 (1H, d, J 8.4 Hz, C6H3H), 6.77
(1H, t, J 7.2 Hz, C6H3H), 6.85 (1H, dd, J 7.6, 1.6 Hz, C6H3H),
6.93–6.97 (4H, m, C6H2Me3), 7.40 (1H, ddd, J 8.4, 7.6, 1.6 Hz,
C6H3H), 16.5 (1H, s, Ru = CH); ıC (63 MHz, CDCl3) 11.3, 18.7,
All catalytic reactions have previously been tested by us using
the second generation Hoveyda–Grubbs’ catalyst reaching com-
plete conversions in 1–16 h.
2.4. Spectral data
(1R,2S)-N1,N2-dimesitylcyclohex-4-ene-1,2-diamine (16). IR:
(ATR)/cm−1 3361 (NH), 3025 (Csp2), 2916 and 2853 (CH), 1477,
1441, 1260, 1237, 1076, 1029, 851, 799, 756, 743, 672, 663; ıH
(360 MHz, CDCl3) 2.01 (2H, dd, J 16.5, 4.5 Hz, CHCHH), 2.17 (2H,
dd, J 16.5, 4.5 Hz, CHCHH), 2.23 (6H, s, p-CH3), 2.70 (12H, s, o-CH3),
3.70 (2H, t, J 5.04 Hz, NHCH), 3.83 (1H, br s, NH), 5.64 (2H, br s,
CH CH), 6.81 (4H, s, C6H2Me3); ıC (90 MHz, CDCl3) 19.3, 20.6, 29.5,
53.8, 125.5, 129.3, 129.7, 130.7, 141.9; ESI-MS: found: 349.2643
(M+H)+, calc. for C24H33N2: 349.2638.

62
A. Monge-Marcet et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 59–66
160
140
120
100
80
60
40
adsorption
desorption
20
0
0,0
0,2
0,4
0,6
0,8
1,0
Fig. 2. 29Si CP-MAS solid state NMR of hybrid silica material M1.
Relative Pressure (p/p°)
3. Results and discussion
3.1. Preparation of the organosilica material
0,6
0,5
0,4
0,3
0,2
0,1
0,0
The synthesis of the bis-silylated ruthenium-complexed pre-
cursor 7 and the preparation of the corresponding material M1
are summarized in Scheme 1. The reaction of commercial mesity-
lamine with glyoxal following a reported procedure [85] provided
compound 3 in nearly quantitative yield. Subsequent allylation
of this bis-imine with commercial allylmagnesium chloride in
dry THF afforded a mixture of meso and dl isomers from which
the pure meso-diamine 4 was obtained in 51% yield after crys-
tallization [80]. The diallyl dihydroimidazolium chloride 5 was
obtained from 4 in 92% yield under standard cyclization condi-
tions with ethyl orthoformate [86]. Hydrosilylation of 5 with HSiCl3
with Pt catalyst followed by treatment with ethanol/NEt3 yielded
the bis(triethoxy)silylated imidazolium salt 6 (overall 65% yield).
Ruthenium complex 7 was prepared by deprotonation of 6 with
potassium bis(trimethylsilyl)amide and by treatment of the in situ
generated free carbene with commercial complex 2a. Although
special silica gel and dried solvents were used in a rapid chro-
matographic separation (see Section 2.1), some silylated complex
was retained and a significant drop of the yield occurred during
the purification step. Co-gelification of 7 with TEOS (molar ratio
1:38) was performed under argon atmosphere in anhydrous DMF
at room temperature under nucleophilic conditions (stoichiometric
amount of water, 1 mol% of tetrabutylammonium fluoride as cat-
alyst). The solution gelified after 1 h and was aged for six days at
room temperature under argon atmosphere. Then, it was filtered,
washed successively with dry ethanol and dichloromethane until
the filtrates showed no colour, and the powder was dried overnight
under vacuum at 50 ◦C to afford M1 as a green solid.
Desorption
10
100
1000
Pore Diameter (Å)
Fig. 3. N2-sorption isotherm and pore size distribution of M1.
The ruthenium content was determined by inductively coupled
plasma (ICP) analysis (1.15%, w/w, 0.113 mmol Ru/g of material).
As the results of elemental analysis revealed a Ru/Si ratio of 1/81,
whereas the theoretical value should be 1/40 (considering a com-
plete condensation) it is likely that incomplete condensation (as
determined by the 29Si solid state NMR in Fig. 2) and partial loss
of the metal have occurred during the formation of the material by
the sol–gel process.
This material was characterized by 29Si solid state NMR, N2-
adsorption–desorption experiments, TGA and elemental analysis.
The 29Si CP-MAS NMR (Fig. 2) of M1 confirmed the covalent bond-
ing of the organic moiety to the silica matrix by the presence of T2
and T3 signals at −58.7 and −67.2 ppm, respectively, in addition to
the characteristic Q2, Q3 and Q4 signals corresponding to the con-
densed TEOS at −92.6, −102.5 and −111.5 ppm. The high dilution
of the organic moiety in the inorganic matrix precluded the obser-
vation of the corresponding absorptions in solid state 13C NMR and
IR spectra.
3.2. Activity and recyclability of the supported catalyst
The supported catalyst M1 has been tested in the ring closing
metathesis (RCM) reactions of several dienes and one enyne, as well
as in the cross metathesis (CM) of styrene. All the reactions were
performed in dry and degassed solvents under inert atmosphere
using a 2 mol% of the catalyst for the times indicated in Table 1.
Filtration of the insoluble catalyst and evaporation of the solvent
from the filtrates afforded the desired products, together with cer-
tain amounts of starting compound when incomplete conversions
were observed.
The N2 adsorption–desorption isotherm (Fig. 3) of M1 is
representative of a material with an important contribution of
micropores, and a sharp distribution of mesopore sizes; the pore
Heterogeneous catalyst M1 promoted the ring-closing metathe-
sis reaction of common terminal dienes, such as diethyl
2,2ꢀ-diallylmalonate (8) and N,N’-diallyl p-toluenesulfonamide
˚
diameter distribution (Fig. 3) is centred around 30–40 A, with a total
pore volume of 0.23 cm3 g−1 and a BET surface area of 404 m2 g−1
.

A. Monge-Marcet et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 59–66
63
NH2
1. CH2=CHCH2MgCl
anh. THF, -94 ºC to r.t.
O
O
N
N
NH HN
2. Crystallization
51%
iPrOH/H2O
98%
3
meso-4
1. HSiCl3
Karstedt cat.
Si(OEt)3
(EtO)3Si
HC(OEt)3, NH4Cl
anh. CH2Cl2, 45 ºC
N
N
N
N
2. anh. EtOH/NEt3
anh. CH2Cl2
140 ºC
92%
Cl
Cl
5
6
65%
SiO1.5
O1.5Si
Si(OEt)3
(EtO)3Si
· 19 SiO2
· 19 SiO2
N
N
N
N
1. 2a, KHMDS
anh. toluene, 80 ºC
38 TEOS
Cl
Cl
Cl
Cl
cat. TBAF, H2O
Ru
Ru
O
O
2. anh. CHCl3
20%
anh. DMF
7
M1
Scheme 1. Preparation of the hybrid silica material M1.
test in toluene1 ensured that all catalytic activity arose from the
heterogenized alkylidene complex present in M1. Additional exper-
iments were performed with lower amounts of catalyst. Thus the
reaction of 8 with M1 (0.4 mol%) in dichloromethane for 24 h gave
81% yield of 9 at room temperature and 93% under refluxing con-
ditions (TON 202 and 232, respectively). Compound 9 was also
obtained in 87% yield after 10 min in CH2Cl2 under microwave
activation (120 ◦C, 1 mol% Ru).
Following these encouraging results, we next focused on the
evaluation of the recovery and reuse of supported catalyst M1. Thus,
recycling experiments were performed with substrates 8, 12 and
21 (Table 2).
In all cases the recyclability of the catalyst was demon-
strated. In the styrene self-metathesis, the catalyst was reused in
dichloromethane at room temperature for four cycles, with quan-
titative yields of trans-stilbene 22 in the first three cycles (Table 2,
entries 1–3; TON = 150 in total after 3 cycles). Recycling of material
M1 in the ring-closing metathesis of diethyl 2,2ꢀ-diallylmalonate
(8) was carried out for 5 cycles under two different conditions,
i.e. in toluene at 60 ◦C and in hexane at 40 ◦C, with very good
isolated yields until the fourth cycle (Table 2, entries 5–9 and
10–14). The formation of the cycloisomerization by-product was
not detected when performing the reaction in toluene at 60 ◦C,
(10), to give the disubstituted olefins 9 and 11 with excellent
yields under different reaction conditions (in dichloromethane
at rt, in toluene at 60 ◦C, in hexane at 40 ◦C) (Table 1, entries 1
and 2). Reactions were very selective as the cycloisomerization
by-products [79] were not detected and only minor amounts of
remaining starting reactant were observed in the 1H NMR spectrum
of the crude mixture when the conversion was not complete. As
expected, more challenging substrates, like p-toluenesulfonamide
derivatives 12 and 14 that afford respectively tri- and tetrasub-
stituted olefins 13 and 15 (Table 1, entries 3 and 4) required
either longer reaction times or higher temperature to achieve rea-
sonable conversions. Organosilica M1 was next examined in the
RCM of the meso-diamine 4 and the 4,5-diallylimidazolium salt
17 [86], which remarkably afforded the new 4-cyclohexenyl-1,2-
diamine 16 and the bicyclic tetrafluoroborate salt 18, respectively,
in moderate yields (Table 1, entries 5 and 6). Finally, the immo-
bilized catalyst M1 was also active in the RCM of the enyne 19
to give diene 20 (Table 1, entry 7) and in the cross metathe-
sis of styrene (21), showing high selectivity for the formation of
trans-stilbene (22) (E/Z ratio higher than 99/1; Table 1, entry 8).
Some reduced activity was obtained with this immobilized catalyst
compared with the analogous homogeneous alkylidene. Neverthe-
less, some reaction times have not been optimized. For instance,
the conversion of 8 in CH2Cl2 at rt (entry 1) was 56% after 6 h
(TON = 28, TOF = 4.7 h−1) and 99% after 24 h (GC monitoring). Under
the same conditions, diene 12 (entry 3) gave GC conversions of 57%
after 5 h (TON = 28.5, TOF = 5.7 h−1), 89% after 18 h and 92% after
24 h.
1
Hot-test was performed in the reaction of 8 in toluene at 60 ◦C. After 5 min (54%
conversion), half of the reaction was filtered through a number 4 sintered glass-filter.
After additional 60 min reaction time, the suspension containing M1 proceeds to 95%
conversion, whereas the filtrates showed no further reactivity. The determination of
the ruthenium leaching was performed in the reaction of 8 in hexane at 40 ◦C. After
complete conversion the reaction was filtered through number 4 sintered glass-
filter and from the evaporated filtrates, the ruthenium content was determined by
ICP. For practical reasons, in recycling catalytic tests filtration after each cycle was
done through a cannula equipped with two filtering number 2 Whatman papers.
After the reaction, the ruthenium content in the crude product
9 (Table 1, entry 1) was determined by ICP-MS analysis and only a
loss of 0.2% ruthenium was found with respect to the initial amount
of ruthenium added as catalyst. Leaching and also the work-up pro-
cess (filtration) may account for this loss. Moreover, a hot-filtration

64
A. Monge-Marcet et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 59–66
Table 1
Catalytic activity of supported catalyst M1 in different metathesis reactions.a
Entry
1
Substrate
Product
Time (h)
Yield (%)b
24c
>99
>99
>99
EtOOC
COOEt
EtOOC
COOEt
0.5d
0.5e
8
9
2
24c
5d
>99
94
57
Ts
N
Ts
N
24e
11
10
Ts
N
13
15
Ts
3
4
5
48c
24f
>99
33
N
12
Ts
N
Ts
N
14
48c
2g
23
49
41
16
3f
16
24e
MesHN
MesN
NHMes
MesHN
MesN
NHMes
4
18
17
NMes
6
7
48c
49
NMes
BF4
BF4
48c
5d
>99
96
O
O
Ph
Ph
20
Ph
Ph
Ph
19
Ph
Ph
8h
24c
>99
21
22
a
Under argon atmosphere, in dry and degassed solvent, 2 mol% of Ru, [substrate] = 0.1 M.
b
c
d
e
f
Determined by 1H NMR spectroscopy.
In CH2Cl2 at room temperature.
In toluene at 60 ◦C.
In hexane at 40 ◦C.
In toluene at 80 ◦C.
g
h
Under microwave activation at 120 ◦C with PowerMax option not enabled.
E/Z ratio > 99/1.
although some loss of activity was observed in the last two runs
(Table 2, entries 8–9), as longer reaction times were needed to reach
90% conversion. With hexane as solvent, a small amount of cycloi-
somerization product could be detected after the first cycle (2%).
However, the recycling was more efficient in this solvent, as the sig-
nificant drop in the activity of M1 was not observed until the fifth
cycle (TON = 141 in total after 3 cycles). With the more challenging
substrate 12, the reuse of M1 was also possible in dichloromethane
at room temperature for at least 3 runs (Table 2, entries 15–17),
even though it required longer reaction times and the decrease in
the catalytic activity could be observed in the fourth cycle (Table 2,
entry 18) (TON = 134 in total after 3 cycles).
Comparison of the results obtained here with those derived from
a catalyst where a well-defined silylated Hoveyda–Grubbs’ com-
plex was immobilized through the benzylidene ligand by sol–gel
process, shows that M1 exhibits a better catalytic activity than
the material previously described by us [82]. Indeed, in the ring
closing metathesis of dienes 8, 10 and enyne 19, similar or higher
conversions were achieved for the same reaction times, but at
lower temperature and with lower catalyst loading (2 mol% of M1
vs 3.5 mol% previously reported [82]). In terms of recyclability,
M1 showed similar performances, and there is no need for using
microwave activation in the present case.
In our former work [79–81], the metal was introduced after
immobilizing the Hoveyda ligands by sol–gel procedures. The
resulting supported catalysts showed better activity and recycla-
bility than M1, since they could be reused for more cycles in
shorter reaction times. In these cases, a release–return mecha-
nism is operating, the catalytic activity arising from homogeneous
species formed in the course of the reaction. In the case of the
present M1 catalyst, immobilized through the less labile NHC-
ligand, the metathesis process occurs in a heterogeneous fashion,
which implies higher reaction times due to diffusion problems. The
ruthenium complex is mainly located inside the material, and is less
accessible to the reactants. In order to prove the stability towards
fluoride sol–gel catalyst, we submitted the commercial second
generation Hoveyda–Grubbs catalyst to analogous conditions of
the sol–gel co-gelification for one day (in dry DMF under argon

A. Monge-Marcet et al. / Journal of Molecular Catalysis A: Chemical 357 (2012) 59–66
65
Table 2
Recycling performance of M1.a
Entry
Substrate
Product
Cycle
Time (h)
Yield (%)b
1
2
3
4
1c
2c
3c
4c
24
24
30
48
>99d
>99d
>99d
Ph
Ph
Ph
21
22
62d
5
6
7
8
9
1e
2e
3e
4e
5e
0.5
0.8
2
16
24
99
97
89
94
83
EtOOC
COOEt
EtOOC
EtOOC
9
10
11
12
13
14
1f
2f
3f
4f
5f
0.5
1.1
1.5
2
95g
97g
89g
78g
88g
24
15
16
17
18
1c
2c
3c
4c
48
48
48
48
99
93
76
21
Ts
N
Ts
N
12
13
a
Reactions performed in dry and degassed solvent; [substrate] = 0.1 M; 2 mol% Ru.
b
c
d
e
f
Determined by 1H NMR spectroscopy.
In CH2Cl2 at rt.
E/Z ratio > 99/1.
In toluene at 60 ◦C.
In hexane at 40 ◦C.
g
A 2% of cycloisomerization by-product was observed.
atmosphere at room temperature, in the presence of TEOS and TBAF
but in the absence of water). The alkylidene complex was recov-
ered in 50% yield after column chromatography and it was present
in another fraction mixed with silicon species.
substrates up to 5 runs and remarkably, no significant loss of activ-
ity was observed during the first 3 cycles, even for the formation
of a trisubstituted olefin. Further investigations are currently in
progress in order to get well-defined supported catalysts with
better reusability.
Recently Grubbs has reported the immobilization of a monosi-
lylated NHC–ruthenium complex by grafting on preformed silica
[60] which was efficient in a number of ring closing metathesis
reactions and was reused for 8 cycles in the RCM of 8, using 0.75%
mol of supported catalyst in C6H6 at 30 ◦C, achieving conversions
around 70–80% in 2 h for the first 4 cycles. A reaction time of 12 h
was required for complete conversion in the fifth run. Material M1
shows similar recyclability under our conditions (see Table 2), since
it could be recovered and reused in the RCM of 8 for four consecu-
tive cycles of up to 2 h with excellent conversions (Table 2, entries
5–7 and 10–13). Moreover and to the best of our knowledge recy-
cling of silica supported metathesis catalysts has not been described
in the RCM of the more challenging substrate 12 to form a trisub-
stituted olefin under mild conditions (3 cycles in CH2Cl2 at room
temperature, Table 2, entries 15–17).
Acknowledgements
We acknowledge financial support from Ministerio de Ciencia
e Innovación (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) and the
Agence Nationale de la Recherche (ANR-07-CP2D-11-02 MESORCAT).
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