Hybrid-bridged silsesquioxane as recyclable metathesis catalyst derived from a bis-silylated Hoveyda-type ligand

Article abstract of DOI:10.1002/adsc.200505447

The synthesis of a bis-silylated Hoveyda-type monomer is described as well as the preparation of several organic-inorganic hybrid materials derived from it by a sol-gel process (with and without tetraethyl orthosilicate) and by anchoring to MCM-41. The re

Full text of DOI:10.1002/adsc.200505447

FULL PAPERS
DOI: 10.1002/adsc.200505447
Hybrid-Bridged Silsesquioxane as Recyclable Metathesis Catalyst
Derived from a Bis-Silylated Hoveyda-Type Ligand
a
a,
b,
b
¨
Xavier Elias, Roser Pleixats, * Michel Wong Chi Man, * Joel J. E. Moreau
a
`
`
Chemistry Department, Universitat Autonoma de Barcelona, Cerdanyola del Valles, 08193 Barcelona, Spain
Fax: (þ34)-93-581-1265, e-mail: roser.pleixats@uab.es
b
´ ´
´
´
´
Heterochimie Moleculaire et Macromoleculaire (UMR-CNRS 5076), Ecole Nationale Superieure de Chimie de
´
´
Montpellier, 8 rue de lꢀecole normale, 34296 Montpellier cedex 5, France
Fax: (þ33)-4-6714-7212, e-mail: michel.wong-chi-man@enscm.fr
Received: November 17, 2005; Accepted: February 2, 2006
Supporting Information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: The synthesis of a bis-silylated Hoveyda- complexes covalently bonded to the silica matrix.
type monomer is described as well as the preparation These materials are recyclable catalysts for the ring-
of several organic-inorganic hybrid materials derived closing metathesis reaction of dienes and enynes.
from it by a sol-gel process (with and without tet-
raethyl orthosilicate) and by anchoring to MCM-41.
The resulting materials were treated with second gen- Keywords: catalyst immobilization; metathesis; organ-
eration Grubbsꢀ catalyst to generate second genera- ic-inorganic hybrid materials; ruthenium; sol-gel proc-
tion Hoveyda–Grubbs-type alkylideneruthenium ess
Introduction
via phosphine exchange,[6] via the N-heterocyclic car-
bene ligand,[7] through halogen exchange,[8] or via alky-
Olefin metathesis constitutes a very powerful, mild, effi- lidene exchange (boomerang-type catalysts).[9] The effi-
cient and selective method for the rupture and reforma- ciency of boomerang-supported catalysts increases no-
ꢀ
tion of C C double bonds, widely used by organic chem- tably when Hoveyda-type chelating ligands are
ists for the synthesis of a great variety of compounds.[1] used.[10] Insoluble organic polymers are the supports
Ring-closing enyne metathesis has also been explored most frequently found in the literature, although an-
in recent years, providing 1-vinylcycloalkene derivatives choring to soluble poly(ethylene glycol)[10a–c] and some
from acyclic enynes in an atom economical process.[2] recent examples of silica-bound alkylidene-ruthenium
The enormous success of metathesis reactions during complexes have also been described.[6b,7c–e,8b–d,10f, g,j]
the last decade is due to the development of several
The above-mentioned examples about silica-bound
well-defined metal alkylidenes. The second-generation catalysts refer to anchoring to porous and non-porous
Grubbs ruthenium catalysts[3] 1b, c (Figure 1) and spe- silicas and to glass non-porous monoliths. The sol-gel hy-
cially the Hoveyda–Grubbs catalysts[4] 2a, b (Figure 1) drolytic-condensation[11–13] of suitable organo-alkoxysi-
show enhanced reactivity, stability and recovery profiles lanes is a convenient method to synthesize solid hybrid
compared to the first generation Grubbs catalyst 1a materials with targeted properties.[14–16] Several organo-
(Figure 1), chelating styrenic ligands playing a role in metallic complexes have been immobilized according to
such improvements. In the last years several research this process to generate heterogeneous hybrid cata-
groups have dedicated their efforts to the preparation lysts[17–19] and among these, bridged silsesquioxanes[20,21]
and testing of reusable metathesis catalysts,[5] one of appeared as an efficient route to produce these catalysts
the most used recycling strategies being the immobiliza- with a high and controlled loading of the organics due to
ꢀ
tion of a robust and stable alkylidene complex on a pol- the preserved covalent Si C bonds during the mild hy-
ymeric insoluble support. Filtration at the end of the re- drolysis-condensation reactions.[22] We want to present
action allows an easy separation of the product and re- here our results concerning the preparation, the activity
covery of the catalyst, avoiding time-consuming chro- and the recycling of hybrid organic-inorganic silicas con-
matography. Anchoring of ruthenium alkylidenes of taining
second-generation
Grubbs-Hoveyda-type
type 1 and 2 to the polymeric matrix has been performed ruthenium complexes, in the ring-closing metathesis
Adv. Synth. Catal. 2006, 348, 751 – 762
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Xavier Elias et al.
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Results and Discussion
Monomer Synthesis
The bis-silylated monomer 7 used for the preparation of
hybrid materials was synthesized as summarized in
Scheme 1. Commercial 2,3-dihydroxybenzaldehyde
was treated with two equivalents of iodide 3 in DMF at
508C in the presence of potassium carbonate to afford
the protected diol 4 in 88% yield. Subsequent reaction
with triphenylphosphonium methylide in anhydrous di-
ethyl ether at 08C provided the styrenic compound 5 in
73% yield after column chromatography of the crude
mixture. Standard deprotection of 5 with tetrabutylam-
monium fluoride gave the diol 6 (82% yield after tritura-
tion with petroleum ether), which was treated with two
equivalents of 3-(isocyanatopropyl)triethoxysilane to
afford the desired dicarbamate 7 in 92% yield.
Figure 1. Ruthenium-alkylidene metathesis catalysts.
(RCM) reaction. These heterogeneous catalysts are ob-
tained as bridged silsesquioxanes from a bis-silylated
Hoveyda-type monomer via the sol-gel process and Preparationof Hybrid Materials and Catalysts
also by anchoring this monomer to a mesostructured
MCM-41.[23]
Four different types of hybrid materials were prepared
To our knowledge there is no example in the literature from bis-silylated compound 7 (Scheme 2). Cogelifica-
reporting the use of a bis-silylated ligand in a sol-gel tion with tetraethoxysilane (40:1 as molar ratio TEOS:
process for the preparation of re-usable metathesis cat- 7) in ethanol at room temperature under nucleophilic
alysts. Grafting does not allow the control of either the conditions (stoichiometric water, 1% molar of ammoni-
loading of organic groups or their distribution, which de- um fluoride as catalyst) afforded 8a, whereas hydrolytic
pends on the number of the surface silanol groups, on the polycondensation of monomer 7 without TEOS in the
diffusion of reagents through the pore channels, and on same nucleophilic conditions gave 8b. Another sol-gel
steric factors, with some organic moieties remaining on condition was tested with neat monomer 7 in order to
the surface of the pores. The co-gelification of the bis-si- get an organized and porous material, using dodecyl-
lylated monomer with TEOS would allow the organic amine both as basic catalyst and surfactant,[24] giving
moiety to be integrated in the matrix, which could result rise to material 8c. Anchoring of 7 to mesostructured
in a supported catalyst different from those prepared by silica MCM-41 was also performed under standard con-
grafting. Moreover, the hydrolysis of this bis-silylated li- ditions (refluxing toluene for 24 h), 8d being obtained.
gand alone (without TEOS) can also afford a hybrid ma- Finally, hydrosilylation of surface hydroxy groups of ma-
terial with a regular and stoichiometric distribution of terials 8a and 8d was achieved by refluxing with excess
the organics throughout the silicate network.
hexamethyldisilazane, leading to 8aSi and 8dSi, respec-
Scheme 1. Preparation of the bis-silylated Hoveyda-type monomer 7.
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Hybrid-Bridged Silsesquioxane as Recyclable Metathesis Catalyst
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Scheme 2. Preparation of hybrid silica materials 8a–d, 8aSi, and 8dSi from 7.
tively. Capping of the silanol groups was performed in quioxanes bearing voluminous organic moieties and was
order to test if improved materials could be obtained, expected for 8b.[21,22] On the contrary, the use of dodecyl-
as these silylated hybrids 8aSi and 8dSi are less hygro- amine failed to give a porous material for 8c, most prob-
scopic than their parent 8a and 8d.
ably due to the existence of interactions between the bis-
The materials were studied by several techniques (13C silylated monomer and the long alkyl chain amine which
and 29Si solid state NMR and BET surface area measure- disfavour the organization of the latter in aqueous solu-
ments).
tion. Those hybrids prepared with TEOS or anchored to
Owing to the high loading of the ligand in 8b and 8c, the MCM-type material (8a, 8aSi, 8d, 8dSi) are highly
the 13C solid state NMR of 8b was performed which ex- porous (546–766 m2/g) as expected.
hibits the chemical shifts characteristic of the organic li-
All materials (8a–d, 8aSi and 8dSi) were charged with
gand (see Figure 2a and Experimental Section). The sig- the metal by treating them with the second generation
ꢀ
nal at 10.8 ppm (Si C) shows the preservation of the co- Grubbs catalyst 1b (0.25 or 1.1 equivs.) in refluxing an-
valently bonded ligand to the silica network.
hydrous and degassed dichloromethane (Scheme 3).
This was confirmed by the 29Si CP-MAS solid state Ruthenium content in materials 9a–d, 9aSi and 9dSi
NMR spectrum of 8c (Figure 2b) in which only the T was determined by ICP (inductively coupled plasma)
units (T1, T2 and T3) are observed. Due to the absence analysis, the results being summarized in Table 2.
of Q units at ꢀ90 to ꢀ120 ppm, we can conclude that
ꢀ
no Si C cleavage occurred during the hydrolysis-con-
densation reactions to prepare the sol-gel materials. In Assay of Supported Catalysts in Diene and Enyne
the case of the materials prepared with TEOS (8a) or Ring-Closing Metathesis Reactions
MCM type (8d) and also the corresponding solids treat-
ed with HMDS (8aSi and 8dSi), Q units are the major Supported catalysts 9 have been tested in the ring-clos-
peaks at about ꢀ100 (Q3) and ꢀ110 (Q4) which are ing metathesis reaction of N,N-diallyl-4-methylbenz-
due to the condensed TEOS part. The signal at around enesulfonamide (10)[25] to give 1-[(4-methylphenyl)sul-
13 ppm in 8aSi and 8dSi corresponds to the SiMe3 fonyl]-2,5-dihydro-1H-pyrrole (11)[25] (Scheme 4). In
ꢀ
unit. This is illustrated by the 29Si solid state NMR of all cases the reaction was performed in dichloromethane
8a (Figure 2c).
(0.05 M for 10) at room temperature, using a 3.5% molar
The 29Si solid state NMR data, some textural proper- concentration of catalyst for the times indicated in Ta-
ties and the ligand loading of hybrid materials 8 are sum- ble 3 (the disappearance of 10 was monitored by GC).
marized in Table 1.
Filtration and evaporation of the solvent afforded pure
Very low surface areas are obtained in the case of the 11, together with small amounts of 10 in some cases
1
two materials 8b and 8c (respectively 7.5 and <1 m2/g). (the molar ratio 11/10 was determined by H NMR).
The low surface area is usual in the case of bridged silses- Heterogeneous catalysts 9 were reused directly in the
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Xavier Elias et al.
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Figure 2. Solid state CP-MAS NMR spectra: (a) 13C spectrum of 8b, (b) 29Si spectrum of 8c
next run, six cycles being performed for each catalyst; are not very significant. Moreover, the decrease in con-
until the fifth run the reaction times were maintained version at the fifth cycle is greater for 9a and 9d than for
the same in order to follow the efficiency of the catalyst 9b and 9c (where TEOS has not been used for the prep-
upon recycling, in the sixth run the reaction was left for aration of the material). The porosity of the material
24 h.
(see Table 1) does not seem to be a crucial point, as
As we see in Table 3, the activity of the catalysts to at- the non-porous materials 9b and 9c keepbetter their ef-
tain full conversion in the first cycle follows the se- ficiency upon recycling. If we compare the material 9a,
quence 9c>9b>9a>9d, although the differences found where the organic part has been incorporated by sol-
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Hybrid-Bridged Silsesquioxane as Recyclable Metathesis Catalyst
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Figure 2. (c) 29Si spectrum of 8a.
Table 1. Some analytical and textural data of hybrid materials 8.
8
29Si CP MAS NMR
SBET [m2 gꢀ1
]
Pore Diam. [Š]
mmol 8/g
R3SiO
–
T1
T2
T3
Q2
Q3
Q4
8a
8b
8c
8d
8aSi
8dSi
–
ꢀ57.2
ꢀ64.5
ꢀ101.2
ꢀ109.2
766
7.5
<1
757
672
546
0.136
1.910
1.806
0.332
0.232
0.325
–
–
–
–
13.0
13.5
ꢀ45.3
ꢀ51.6
ꢀ54.4
ꢀ57.0
ꢀ67.2
ꢀ65.0
ꢀ64.71
ꢀ64.2
ꢀ92.3
ꢀ100.9
ꢀ102.0
ꢀ103.0
ꢀ109.9
ꢀ109.7
ꢀ109.9
22–26
46
22
Table 2. Ruthenium content in hybrid materials 9.
though the reaction time in the first cycle is lowered,
the efficiency upon recycling decreases very rapidly.
The ring-closing metathesis reaction to afford 11 has
been performed in the literature with several recyclable
immobilized catalyst types under different conditi-
ons.[9c, e,10a, h,j,26] Mauduit[26a] used imidazolium-tagged
first and second generation Grubbs Ru complexes in
ionic liquid as immobilizing solvent (2.5% molar Ru,
9
% Ru
mmol Ru/g
9a
1.17
0.116
9b
1.82
0.180
9c
9d
0.7125
1.14
0.0705
0.113
9aSi
9dSi
0.5059
0.4992
0.0500
0.0494
BMIM·PF6, 608C, 45 min) obtaining full conversions
[26b]
upto 5 cycles. In a similar work, Yao
(1% molar
Ru, BMIM·PF6-CH2Cl2 1:9, 458C, 1 h, 0.2 M) achieved
17 cycles with conversions from>98% to 90%. Gib-
gel cogelification, with the mesostructured 9d obtained son[26c] reported the encapsulation of a second genera-
by anchorage, the first one is slightly better (lower reac- tion Grubbs catalyst in polystyrene (2.5% molar Ru, wa-
tion time, higher conversion at 24 h in the sixth cycle). ter/methanol 4:1, 508C, 1.5 h) affording 4 cycles with
The silylation of residual Si OH in 8a and 8d before decreasing yields (92% to 40%). Curran[26d] performed
ꢀ
charging with the metal (see Scheme 2 and 9aSi and the reaction with fluorous versions of first and second
9dSi in Table 3) does not improve the materials. Al- generation Grubbs–Hoveyda catalysts (5% molar Ru,
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Xavier Elias et al.
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Scheme 3. Preparation of ruthenium heterogeneous catalysts 9a–d, 9aSi, and 9dSi from the corresponding materials 8.
room temperature, 1 h). But the simplest method to iso-
late and recycle the catalyst is by its immobilization in a
solid insoluble support. Barrett[9c] has anchored a second
generation Grubbs catalyst to polystyrene by the alkyli-
dene moiety and has described 5 cycles with decreasing
conversions (100 to 42%) (2.5% molar Ru, toluene,
508C, 2 h). Nolan[9e] has reported the same type of cata-
lysts anchored to polydivinylbenzene resins, performing
3 cycles (5% molar Ru, dichloromethane, room temper-
ature, 1 h) with modest GC yields (30–38%). By anchor-
ing a second generation Hoveyda–Grubbs catalyst to
silica gel Blechert[10j] reported very recently 4 cycles
with decreasing conversions (>99% to 68%) (0.15%
molar Ru, dichloromethane, room temperature, 1 h).
Our conditions are milder than those used in most of
the precedent works (percentage of catalyst and/or reac-
tion temperature and/or reaction time), the recyclability
being better than in most of the aforementioned solid
supports and similar to (for 9a, 9c, 9d) or better (for
9b) than in the recent work of Blechert.[10j] Although
some recycling strategies involving the reaction per-
formed under homogeneous conditions[10h,26a, b,d, e] re-
main superior, the advantage of simplicity in the separa-
tion procedure must be taken into account.
Then, we also wanted to test the formation of a tetra-
substituted olefin. In our hands, treatment of N,N-bis(2-
methylallyl)-4-methylbenzenesulfonamide (12) with
second generation Grubbs catalyst 1b (3.5% molar) un-
der homogeneous conditions (toluene, 808C, 7 h) gave
90% conversion to 3,4-dimethyl-1-[(4-methylphenyl)-
Scheme 4. Diene and enyne metathesis reactions tested with
recyclable catalysts 9.
refluxing dichloromethane, 2 h) achieving 7 cycles with sulfonyl]-2,5-dihydro-1H-pyrrole (13). When our mate-
full conversions or 5 cycles with conversions upto
rial 9a was used as catalyst under analogous conditions
94%. Recently, Lee[26e] has attached a second generation (3.5% molar of Ru, toluene, 808C) a 77% conversion
Grubbs–Hoveyda catalyst on gold clusters, achieving 4 (1H NMR) was found after 24 h (Scheme 4). The conver-
cycles with full conversions (5% molar Ru, dichlorome- sion decreased to 3% after the same reaction time in the
thane, 408C, 1.5 h). Yao[10a] described soluble polymers second cycle. The catalytic material 9d provided poorer
of first generation Grubbs–Hoveyda catalyst anchored results, givingonly 26% conversion after 24 h of reaction
to PEG used upto 3 cycles (5% molar Ru, refluxing di-
under analogous conditions, no recycling being attempt-
chloromethane, 2 h) with slightly decreasing conver- ed. We should mention that very few reports appear in
sions (96 to 92%). Blechert[10 h] has used a soluble poly- the literature about this challenging ring-closing meta-
mer of a second generation Grubbs–Hoveyda catalyst thesis reaction. K. Grela[10e] found a 45% conversion in
derivative generated by ROMP, achieving 5 cycles a homogeneous process with a modified Hoveyda–
with full conversions (1% molar Ru, dichloromethane, Grubbs second generation catalyst (5% molar Ru, re-
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Hybrid-Bridged Silsesquioxane as Recyclable Metathesis Catalyst
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Table 3. Results for the RCM of 10 to 11 with supported catalysts 9.
Run 9a
9b
9c
9d
9aSi[a]
9dSi[a]
t [h] Conv. [%] t [h] Conv. [%] t [h] Conv. [%] t [h] Conv. [%] t [h] Conv. [%] t [h] Conv. [%]
1
2
3
4
5
6
2
2
2
2
2
>98
>98
92
68
31
1.5 >98
1.5 >98
1.3 >98
2.5 >98
2.5 >98
1.5 >98
1.15 >98
1.0
1.0
1.0
1.0
98
94
68
53
93
1
63
20
10
4
1.15
1.15
1.15
1.15
69
29
13
3
1.5
1.5
1.5
94
81
66
94
2.5
2.5
2.5
91
60
32
38
1.5
1.5
1.5
24
57
24
24
24
24
18
24
23
[a]
A 2% molar Ru was used.
fluxing dichloromethane, 16 h), describing also the first
On the other hand, the ring-closing enyne metathesis
reported attempt to obtain 13 with a supported catalyst was successfully performed on 1-allyloxy-1,1-diphenyl-
(0% conversion, 5% molar Ru, refluxing dichlorome- 2-propyne (14) to give 2,2-diphenyl-3-vinyl-2,5-dihydro-
thane, 16 h). Very recently, Mauduit[26a] describes this re- furan (15) with our heterogeneous catalysts 9a and 9d
action using imidazolium-tagged ruthenium complexes (Scheme 4 and Table 4). Good conversions (ca. 100%)
in room temperature ionic liquids (5% molar Ru, were obtained in very short reaction times (1 to 1.5 h)
BMI·PF6/toluene, 608C, 7 h, 65% conversion in the first with 3.5% molar of catalyst in anhydrous dichlorome-
cycle, 0% conversion in the second cycle). Thus, al- thane at room temperature. If we compare the recycla-
though our results with tetrasubstituted olefin 13 could bility properties of both catalysts in Table 4, material
appear as modest, they constitute the first successful re- 9a, obtained from sol-gel cogelification, was clearly su-
port for the preparation of 13 with a polymer-supported perior to 9d, prepared by anchoring the bis-silylated
catalyst. Few reports can be found about the recyclabil- monomer 8d to mesoporous MCM-41. The efficiency
ity of ruthenium catalysts in the preparation of other tet- of the catalyst 9d was significantly decreased after the
rasubstituted alkenes, such as (Z)-4,5-dimethyl-1-tosyl- third cycle. This enyne ring-closing metathesis process
2,3,6,7-tetrahydro-1H-azepine[10b,26b] and diethyl 3,4-di- has been described in the literature[27,28] using several
methylcyclopent-3-ene-1,1-dicarboxylate.[9e] For the catalysts and homogeneous conditions, but there is no
first substrate, Yao[10b] described 3 cycles using a soluble report about recycling and about using polymer-sup-
second generation Grubbs–Hoveyda carbene complex ported catalysts for the preparation of 15. Our results
immobilized on poly(ethylene glycol) (5% molar Ru, under heterogeneous conditions are even better than
0.4 M, refluxing dichloromethane, 18 h, 82% conversion some homogeneous reports (milder conditions, lower
at the third cycle) and the same author[26b] performed 2 reaction times).
cycles with an imidazolium-tagged second generation
Our catalyst does not bear the classical isopropyl
Hoveyda–Grubbs catalyst (4% molar Ru, BMIM· group present in most of the recyclable Hoveyda-type li-
PF6-CH2Cl2 1:1, 458C, 16 h, 79% and 78% conversion). gands. Lamaty[10c] has also described a soluble-polymer
For the second substrate, Nolan[9e] achieved 4 cycles with bound Ru carbene with the chelating oxygen of the Hov-
modest yields with a second generation Grubbs catalyst eyda ligand directly linked to a polyethylene glycol
anchored to a cross-linked polystyrene through the alky- chain. From the original work of Hoveyda[4a] it appears
lidene ligand (5% molar Ru, toluene, 808C, 3 h, GC that an isopropoxy is better than a methoxy chelating
yields between 36 and 22%).
groupfor the stability and catalytic activity of derived
Ru catalysts, due to the larger steric bulkiness of the for-
mer, which may facilitate dissociation of the oxygen
atom from Ru during initiation. In our case the isopropyl
groupis substituted by an alkylidene chain, which is un-
doubtedly bulkier than a methyl group. Nevertheless, as
classical chelating isopropoxy group could remain the
best choice, further studies are being developed in our
groupwith supported catalysts derived from a sol-gel
bearing this isopropoxy group that will be published in
the near future. Another structural feature of our cata-
lyst deserves also some comment. Blechert has shown[29]
that the presence of a steric bulky group adjacent to the
chelating isopropoxy moiety improves the activity of the
Table 4. Results for the RCM of 14 to 15 with supported cat-
alysts 9.
Run
9a
9d
t [h]
Conv. [%]
t [h]
Conv. [%]
1
2
3
4
5
1.1
1.1
1.1
1.1
1.3
>98
97
95
89
88
1.5
1.5
1.25
1.5
1.5
96
88
72
55
43
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Xavier Elias et al.
FULL PAPERS
multiplet. The CP MAS 29Si solid state NMR spectra were re-
corded on a Bruker FT-AM 400. The repetition time was 5 sec-
onds with contact time of 5 milliseconds. The CP MAS 13C solid
state NMR spectra were recorded on a Bruker FT-AM 400.
Hoveyda-type Ru catalysts. Our catalysts 9 present an
additional groupon this position, which should contrib-
ute to enhance their activity.
ꢀ
Surface areas were determined by the Brunauer–Emmett
Teller (BET) method on a Micromeritics Gemini III 2375 ana-
lyzer, and the average pore diameter was calculated by the BJH
method. ESI mass spectra were acquired using a Navigator
quadrupole instrument, operating in the positive ion mode
(ESþ) at a probe tip voltage of 3 kV. HR-MS have been deter-
mined at SCAI-Unidad de Espectrometría de Masas at the
Conclusion
In summary, we have described the synthesis of a bis-si-
lylated Hoveyda-type monomer, the preparation of sev-
eral hybrid organic-inorganic materials by sol-gel meth-
odologies (with andwithout TEOS) and by anchorage to
mesoporous MCM-41, then the preparation of the cor-
responding second-generation Grubbs–Hoveyda-type
ruthenium complexes and their evaluation as recyclable
catalysts in the ring-closing metathesis reactions of di-
enes and enynes. The RCMon N,N-diallyl-4-methylben-
zenesulfonamide offers milder conditions and better re-
sults than previous works based on catalysts anchored to
insoluble solid supports. The RCM on a more challeng-
ing substrate, N,N-bis(2-methylallyl)-4-methylbenzene-
sulfonamide, gives rise to a tetrasubstituted alkene. Al-
though recyclability has not been achieved in this case,
there is no successful precedent in the literature about
recycling for this substrate. Our materials are good recy-
clable catalysts for the ring-closing enyne metathesis
performed on 1-allyloxy-1,1-diphenyl-2-propyne. This
is the first case described in the literature about recy-
cling in a ring-closing enyne metathesis reaction. In all
cases, materials prepared from the sol-gel are superior
to those coming from anchorage to mesostructured sili-
ca. Further investigations are underway with other
´
Universidad de Cordoba. Elemental analyses have been per-
`
formed at the Servei dꢀAnalisi Química of the Universitat Au-
tonoma de Barcelona or at the Serveis Científico-Tecnics of the
Universitat de Barcelona. The content of ruthenium was deter-
`
`
`
mined at the Serveis Científico-Tecnics of the Universitat de
Barcelona by inductively coupled plasma (ICP) analysis.
1-(tert-Butyldimethylsiloxy)-3-iodopropane (3)[30] was pre-
pared in two steps from 3-chloro-1-propanol as reported.[31]
Mesostructured silica MCM-41 was prepared following the
standard procedure.[23] Methyltriphenylphosphonium iodide
was synthesized from methyl iodide and triphenylphosphine.
The diene 12[10e,27] and enyne 14[27,28] have been mentioned in
the literature but no spectroscopic data were described.
Synthesis of 2,3-Bis(3-tert-
butyldimethylsiloxypropoxy)benzaldehyde (4)
Potassium carbonate (14.38 g, 100 mmol) and iodide 3 (12.02 g,
40.0 mmol) were added to a stirred solution of 2,3-dihydroxy-
benzaldehyde (2.85 g, 20.0 mmol) in DMF (150 mL). The mix-
ture was stirred overnight at 508C under argon. Upon cooling
at room temperature water was added (150 mL) and the solu-
structurally modified ligands in order to get better activ- tion was extracted with petroleum ether (3ꢁ100 mL). The
combined organic layers were washed with water (100 mL)
and with saturated aqueous NaCl (75 mL), dried over anhy-
drous Na2SO4 and concentrated under vacuum to afford 4 as
a brown oil pure enough to carry out the next step; yield:
8.50 g (88%). Further purification can be accomplished by col-
umn chromatography through silica gel (hexane and hexane/
AcOEt, 20:1 as eluents).
ity and also to achieve high surface area and highly po-
rous materials using appropriate structuring templates
with a view to improve the efficiency of these catalysts.
Bridged silsesquioxanes appear to be good alternatives
for the immobilization of the Hoveyda-type catalyst.
Experimental Section
Synthesis of 2,3-Bis(3-tert-
butyldimethylsiloxypropoxy)styrene (5)
General Remarks
When required, experiments were carried out with standard
high-vacuum and Schlenk techniques. Solvents were dried
and distilled just before use. Ammonium fluoride and N,N-
bis(trimethylsilyl)amine were purchased from Aldrich, 3-(tri-
ethoxysilyl)propyl isocyanate was purchased from Lancaster,
tetraethyl orthosilicate, potassium tert-butoxide, 2,3-dihydroxy-
benzaldehyde and tetrabutylammonium fluoride were pur-
chased from Acros. The second-generation Grubbs catalyst
has been purchased from Aldrich and also from Acros. Spectral
data were obtained in the following spectrophotometers: IR
Bruker Tensor 27 with ATR Golden Gate; solution NMR
Bruker AC-250 (1H and 13C). Chemical shifts (d, ppm) were
referenced to Me4Si (1H, 13C). The abbreviations used are s
for singlet, d for doublet, dd for double doublet, t for triplet,
q for quartet, quint for quintuplet, sept for septet and m for
Potassium tert-butoxide (3.8 g, 33.2 mmol) was added to a sus-
pension of methyltriphenylphosphonium iodide (13.7 g,
33.9 mmol) in anhydrous diethyl ether (120 mL) and the mix-
ture was stirred at 08C under argon for 15 min. A solution of
aldehyde 4 (8.0 g, 16.6 mmol) in anhydrous diethyl ether
(50 mL) was added and the mixture was allowed to stir at
08C under argon for one hour and then at room temperature
for 3 h. Water (200 mL) was added and the organic layer was
separated. The aqueous phase was extracted with diethyl ether
(2ꢁ100 mL), the combined organic layers were washed with
water (100 mL) and saturated aqueous NaCl (50 mL), dried
over anhydrous Na2SO4 and concentrated under vacuum.
The residue was chromatographed through silica gel (hexane/
AcOEt 30:1 as eluent) to afford 5 as a pale yellow oil; yield:
5.8 g (73%).
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FULL PAPERS
(1 mmHg, room temperature, 15 h), furnishing 8b as a white
powder; yield: 0.231 g.
Synthesis of 2,3-Bis(3-hydroxypropoxy)styrene (6)
A solution of tetrabutylammonium fluoride (10.42 g, 32 mmol)
in anhydrous THF (25 mL) was added under argon to a stirred
solution of 5 (4.013 g, 8.35 mmol) in anhydrous THF (25 mL)
at 08C. The mixture was allowed to stir overnight at room tem-
perature under argon. Water was added (100 mL) and extrac-
tions with distilled diethyl ether (3ꢁ60 mL) were performed.
The combined organic layers were washed with water (2ꢁ
50 mL) and saturated aqueous NaCl (50 mL), dried over anhy-
drous Na2SO4 and concentrated under vacuum. The oily resi-
due was washed three times by trituration with petroleum
ether atroom temperature for 1 h. After removing of the super-
natant the residual oil was dried under vacuum to afford 6;
yield: 1.72 g (82%).
Preparationof Hybrid Material 8c
A solution of dodecylamine (0.041 g, 0.22 mmol) in ethanol
(0.3 mL) was added to distilled and deionized water (3 mL)
and stirred for 30 minutes. A solution of 7 (0.373 g, 0.5 mmol)
in anhydrous ethanol (0.2 mL) was added and then more water
(2 mL). The mixture was stirred at room temperature for 24 h.
The formed solid was filtered and left to dry at air overnight.
Then it was powdered and extracted with ethanol in a Soxhlet
for 48 h. The solid was washed with ethanol and dried at atmos-
pheric pressure, affording 8c as a white powder; yield: 0.197 g.
Synthesis of O-{3-[2-(3-
triethoxysilylpropylcarbamoyloxypropoxy)-6-
vinylphenoxy]propyl} N-(3-
Preparationof Hybrid Material 8d
Triethoxysilylpropyl)carbamate (7)
Mesostructured MCM-41 (0.480 g, 8 mmol SiO2) was added to
a solution of 7 (0.148 g, 0.198 mmol) in toluene (10 mL). The
mixture was refluxed for 24 h with a Dean–Stark apparatus.
The solid was filtered and washed successively with toluene
(twice), ethanol (3 times) and acetone (twice), then it was dried
at 708C at atmospheric pressure, affording 8d as a white pow-
der; yield: 0.547 g.
Freshly distilled 3-(triethoxysilyl)propyl isocyanate (2.4 mL,
0.99 g/mL, 9.6 mmol) was added dropwise via syringe under ar-
gon to compound 6 (0.88 g, 3.49 mmol). The homogeneous
mixture was stirred under argon at room temperature for 4
days, then at 508C overnight (1H NMR monitoring). Anhy-
drous diethyl ether was added and the solution was filtered un-
der nitrogen atmosphere. The solvent was removed under vac-
uum and excess isocyanate was distilled off (1008C, 1.7 mbar).
Anhydrous diethyl ether (10 mL) was added to the residue, the
solution was filtered under nitrogen atmosphere and the sol-
vent was evaporated, to give 7 as an oil; yield: 2.40 g (92%).
Preparationof Hybrid Material 8aSi
A suspension of 8a (0.157 g) in N,N-bis(trimethylsilyl)amine
(10 mL) was refluxed under argon for 24 h. After cooling, the
solid was filtered and washed with ethanol (3 times), acetone
(3 times) and diethyl ether (3 times), then it was dried under
vacuum (1 mmHg, 608C, 15 h), affording 8aSi as a white pow-
der; yield: 0.155 g.
Preparationof Hybrid Material 8a
A solution of ammonium fluoride (82 mL of a 1 M solution,
0.082 mmol of fluoride, 4.56 mmol of water) and distilled and
deionized water (0.45 mL, 25 mmol) in anhydrous ethanol
(4 mL) was added to a solution of 7 (0.147 g, 0.20 mmol) and
TEOS (1.693 g, 8.14 mmol) in anhydrous ethanol. The mixture
was stirred manually for a minute to get a homogeneous solu-
tion and was left at room temperature without stirring. Gela-
tion occurred after a few minutes and the gel was allowed to
age for 5 days, after which it was powdered and washed succes-
sively several times with water and then with ethanol. The solid
was dried under vacuum (1 mm Hg, room temperature, 15 h),
Preparationof Hybrid Material 8dSi
A suspension of 8d (0.170 g) in N,N-bis(trimethylsilyl)amine
(10 mL) was refluxed under argon for 24 h. After cooling, the
solid was filtered and washed with ethanol (3 times), acetone
(3 times) and diethyl ether (3 times), then it was dried under
vacuum (1 mmHg, 608C, 15 h), affording 8dSi as a white pow-
der; yield: 0.168 g.
affording 8a as a white powder; yield: 0.609 g.
Preparationof Hybrid Material 8b
Preparationof Hybrid Catalyst 9a
A solution of ammonium fluoride (50 mL of a 0.1 M solution,
0.005 mmol of fluoride, 2.8 mmol of water) and distilled and
deionized water (10 mL, 0.56 mmol) in anhydrous ethanol
(0.25 mL) was added to a solution of 7 (0.372 g, 0.5 mmol) in
anhydrous ethanol (0.25 mL). The mixture was stirred manual-
ly for a minute to get a homogeneous solution and was left at
room temperature without stirring. Gelation occurred after
one night and the gel was allowed to age for 6 days, after which
it was powdered and washed successively with water (twice)
and ethanol (5 times). The solid was dried under vacuum
Anhydrous and degassed dichloromethane (6 mL) was added
under argon to a stirred mixture of 8a (0.375 g, 0.272 mmol
N/g, 0.051 mmol) and 1b (0.0476 g, 0.0561 mmol, 1.1 equivs.)
and the mixture was refluxed under argon overnight. The solid
was filtered, washed several times with 5 mL portions of anhy-
drous dichloromethane until the filtrate had no color, and dried
under vacuum (1 mm Hg, room temperature, 15 h) to obtain 9a
as a pale brown powder; yield: 0.321 g; elemental analysis
found: N 1.15, Ru (ICP) 1.17.
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FULL PAPERS
Preparationof Hybrid Catalyst 9b
Synthesis of N,N-Diallyl-4-methylbenzenesulfonamide
(10)
Anhydrous and degassed dichloromethane (5 mL) was added
under argon to a stirred mixture of 8b (0.0995 g, 3.82 mmol
N/g, 0.190 mmol) and 1b (0.0409 g, 0.0482 mmol, 0.25 equivs.)
and the mixture was refluxed under argon overnight. The solid
was filtered, washed several times with 5 mL portions of anhy-
drous dichloromethane until the filtrate had no color, and dried
under vacuum (1 mmHg, room temperature, 15 h) to obtain 9b
as a green powder; yield: 0.0879 g; Ru 1.82% (ICP).
A stirred mixture of 4-methylbenzenesulfonamide (3.17 g,
18.2 mmol), allyl bromide (6 mL, 1.398 g/mL, 68.6 mmol) and
potassium carbonate (11.9 g, 85.4 mmol) in acetonitrile
(100 mL) was heated under pressure at 1008C for 24 h in a
closed reactor. The mixture was filtered and the solvent from
filtrate was evaporated to give 10[25] as an oil; yield: 4.47 g
(98%).
Preparationof Hybrid Catalyst 9c
Ring-Closing Metathesis Reaction on N,N-Diallyl-4-
methylbenzenesulfonamide (10) with Supported
Catalysts 9. Synthesis of 1-[(4-Methylphenyl)sulfonyl]-
2,5-dihydro-1H-pyrrole (11). Typical Experimental
Anhydrous and degassed dichloromethane (4 mL) was added
under argon to a stirred mixture of 8c (0.0848 g, 3.614 mmol
N/g, 0.153 mmol) and 1b (0.0321 g, 0.0378 mmol, 0.25 equivs.)
and the mixture was refluxed under argon overnight. The solid Procedure
was filtered, washed several times with 5 mL portions of anhy-
A solution of 10 (0.1004 g, 0.399 mmol) in anhydrous and de-
drous dichloromethane until the filtrate had no color, and dried
under vacuum (1 mmHg, room temperature, 15 h) to obtain 9c
as a pale green powder; yield: 0.0677 g; elemental analysis
found: N 4.365, Ru (ICP) 0.7125.
gassed dichloromethane (8 mL) was added under nitrogen to
9a (0.1204 g, 0.116 mmol Ru/g, 0.0140 mmol Ru) and the mix-
ture was stirred under argon at room temperature for 2 h (GC
monitoring). The mixture was filtered under nitrogen atmos-
phere with a cannula and the solid was washed 4 times with
8 mL portions of anhydrous dichloromethane. The combined
filtrates were evaporated to afford 11;[25] yield: 0.096 g (the mo-
lar ratio 11/10 by 1H NMR was 53/1, 98% conversion). The sol-
id catalyst 9a was dried and reused in the next run.
Preparationof Hybrid Catalyst 9d
Anhydrous and degassed dichloromethane (10 mL) was added
under argon to a stirred mixture of 8d (0.2997 g, 0.664 mmol N/
g, 0.0995 mmol) and 1b (0.0875 g, 0.103 mmol, 1.04 equivs.)
and the mixture was refluxed under argon overnight. The solid
was filtered, washed several times with 5 mL portions of anhy-
drous dichloromethane until the filtrate had no color, and dried
under vacuum (1 mmHg, room temperature, 15 h) to obtain 9d
as a pale brown powder; yield: 0.3011 g; elemental analysis
found: C 15.60, H 2.46, N 1.25, Ru (ICP) 1.14.
The same conditions were adopted for the other catalysts
9b–d, 9aSi, 9dSi except for the reaction times that are summar-
ized in Table 3 together with the attained conversions.
Synthesis of N,N-Bis(2-methylallyl)-4-
methylbenzenesulfonamide (12)
A stirred mixture of 4-methylbenzenesulfonamide (1.58 g,
9.04 mmol), 3-bromo-2-methylpropene (2.6 mL, 1.339 g/mL,
25.01 mmol) and potassium carbonate (4.75 g, 34 mmol) in
acetonitrile (50 mL) was heated under pressure at 1108C for
48 h in a closed reactor. The cooled mixture was filtered and
the solvent from filtrate was evaporated to give 12 as a pale yel-
low oil; yield: 2.45 g (97%).
Preparationof Hybrid Catalyst 9aSi
Anhydrous and degassed dichloromethane (2.2 mL) was add-
ed under argon to a stirred mixture of 8aSi (0.0842 g,
0.464 mmol N/g, 0.0195 mmol) and 1b (0.017 g, 0.020 mmol,
1.02 equivs.) and the mixture was refluxed under argon over-
night. The solid was filtered, washed several times with por-
tions of 2.5 mL of anhydrous dichloromethane until the filtrate
had no color, and dried under vacuum (1 mmHg, room temper-
ature, 15 h) to obtain 9aSi as a pale brown powder; yield:
0.0722 g; elemental analysis found: N 1.18, Ru (ICP) 0.506.
Ring-Closing Metathesis Reaction on N,N-Bis(2-
methylallyl)-4-methylbenzenesulfonamide (12) with
Supported Catalysts 9. Synthesis of 3,4-Dimethyl-1-
[(4-methylphenyl)sulfonyl]-2,5-dihydro-1H-pyrrole
(13). Typical Experimental Procedure
Preparationof Hybrid Catalyst 9dSi
A solution of 12 (0.0744 g, 0.266 mmol) in anhydrous and de-
gassed toluene (5.5 mL) was added under nitrogen to 9a
(0.0805 g, 0.116 mmol Ru/g, 0.00934 mmol Ru) and the mix-
ture was stirred under argon at 808C for 24 h (GC monitoring).
The mixture was filtered under nitrogen atmosphere with a
cannula and the solid was washed 4 times with 5.5 mL portions
of anhydrous dichloromethane. The combined filtrates were
evaporated to afford 13; yield: 0.073 g (the molar ratio 13/12
Anhydrous and degassed dichloromethane (3.5 mL) was add-
ed under argon to a stirred mixture of 8dSi (0.0900 g,
0.650 mmol N/g, 0.0292 mmol) and 1b (0.0252 g,
0.0297 mmol, 1.01 equivs.) and the mixture was refluxed under
argon overnight. The solid was filtered, washed several times
with 4 mL portions of anhydrous dichloromethane until the fil-
trate had no color, and dried under vacuum (1 mmHg, room
temperature, 15 h) to obtain 9dSi as a pale brown powder;
yield: 0.0797 g; elemental analysis found: N 1.40, Ru (ICP) 0.50.
1
1
by H NMR was 3.4/1, 77% conversion). H and 13C NMR
data of 13 were coincident with those described for this com-
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Hybrid-Bridged Silsesquioxane as Recyclable Metathesis Catalyst
FULL PAPERS
pound in the literature.[32] The solid catalyst 9a was dried and
reused in the next run.
1998, 133, 29; g) K. J. Ivin, J. Mol. Catal. A 1998, 133,
1; h) Ch. Pariya, K. N. Jayaprakash, A. Sarkar, Coord.
Chem. Rev. 1998, 168, 1; i) M. E. Maier, Angew. Chem.
Int. Ed. 2000, 39, 2073; j) A. Fürstner, Angew. Chem.
Int. Ed. 2000, 39, 3012; k) R. Roy, S. K. Das, Chem. Com-
mun. 2000, 519; l) M. R. Buchmeiser, Chem. Rev. 2000,
100, 1565; m) T. M. Trnka, R. H. Grubbs, Acc. Chem.
Res. 2001, 34, 18; n) A. H. Hoveyda, R. R. Schrock,
Chem. Eur. J. 2001, 7, 945; o) F. X. Felpin, J. Lebreton,
Eur. J. Org. Chem. 2003, 3693; p) M. D. McReynolds,
J. M. Dougherty, P. R. Hanson, Chem. Rev. 2004, 104,
2239; q) A. Deiters, S. F. Martin, Chem. Rev. 2004, 104,
2199; r) R. H. Grubbs, Tetrahedron 2004, 60, 7117; s) H.
Katayama, F. Ozawa, Coord. Chem. Rev. 2004, 248,
1703; t) D. Astruc, New. J. Chem. 2005, 29, 42.
Synthesis of 1-Allyloxy-1,1-diphenyl-2-propyne (14)
To a suspension of NaH 60% (0.198 g, 4.95 mmol, 1.04 equivs.)
in DMF (100 mL) at 08C were added successively 1,1-diphen-
yl-2-propyn-1-ol (0.999 g, 4.75 mmol) and allyl bromide
(1.6 ml, 1.398 g/ml, 18.3 mmol). The mixture was allowed to
stir at room temperature under Ar overnight. Water was added
(150 mL) and extractions with distilled diethyl ether (3ꢁ
100 mL) were performed. The combined organic layers were
washed with water (50 mL) and saturated aqueous NaCl
(50 mL), dried over anhydrous Na2SO4 and concentrated un-
der vacuum. The residue was chromatographed through silica
gel (hexane/AcOEt, 19:1 as eluent) to afford 14 as a pale yel-
low oil; yield: 0.992 g (84%).
[2] For reviews on enyne metathesis and its use in organic
synthesis: a) M. Mori, Top. Organomet. Chem. 1998, 1,
133; b) C. S. Poulsen, R. Madsen, Synthesis 2003, 1;
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for a one-pot enyne metathesis-Diels–Alder process de-
Ring-Closing Metathesis Reaction on 1-Allyloxy-1,1-
diphenyl-2-propyne (14) with Supported Catalysts 9.
Synthesis of 2,2-Diphenyl-3-vinyl-2,5-dihydrofuran
(15). Typical Experimental Procedure
˜
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A. Santamaria, Synlett 2001, 1784.
[3] a) M. Scholl, S. Ding, C. W. Lee, R. H. Grubbs, Org. Lett.
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[4] a) J. S. Kingsbury, J. P. A. Harrity, P. J. Bonitatebus Jr,
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A solution of 14 (0.0631 g, 0.254 mmol) in anhydrous and de-
gassed dichloromethane (5 mL) was added under nitrogen to
9a (0.0766 g, 0.116 mmol Ru/g, 0.00889 mmol Ru) and the mix-
ture was stirred under argon at room temperature for 65 mi-
nutes (GC monitoring). The mixture was filtered under nitro-
gen atmosphere with a cannula and the solid was washed 4
times with 5 mL portions of anhydrous dichloromethane. The
combined filtrates were evaporated to yield 15 whose spectro-
scopic data were coincident with that reported in the litera-
ture;[27] yield: 0.066 g (100% conversion by 1H NMR). The solid
catalyst 9a was dried and reused in the next run.
The same conditions were adopted for the other catalyst 9d
except the reaction time (1.5 h). The results are summarized in
Table 4.
[5] See the review article and references cited therein: M. R.
Buchmeiser, New. J. Chem. 2004, 28, 549.
[6] a) S. T. Nguyen, R. H. Grubbs; J. Organomet. Chem.
1995, 497, 195; b) F. Verpoort, P. Jacobs, D. De Vos, K.
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See Supporting Information for characterization data of
compounds 4–8, 12 and 14.
[7] a) S. C. Schürer, S. Gessler, N. Buschmann, S. Blechert,
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Acknowledgements
Financial support from the Ministry of Science and Technology
ofSpain, Generalitat de Catalunya and Universitat Auto noma
de Barcelona (Projects BQU2002-04002, SGR2001-00181,
PNL2005-10), from the French Ministry of Research and Tech-
nology and from the CNRS is gratefully acknowledged.
`
[8] a) P. Nieczypor, W. Buchowicz, W. J. N. Meester,
F. P. J. T. Rutjes, J. C. Mol, Tetrahedron Lett. 2001, 42,
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Xavier Elias et al.
FULL PAPERS
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