Organic-inorganic hybrid silica materials containing imidazolium and dihydroimidazolium salts as recyclable organocatalysts for Knoevenagel condensations

Article abstract of DOI:10.1039/b916767f

Organic-inorganic hybrid silica materials containing imidazolium and dihydroimidazolium salts prepared from monosilylated and disilylated monomers by sol-gel methodologies are active and reusable organocatalysts for the Knoevenagel condensation of aromatic aldehydes with malononitrile and ethyl cyanoacetate under solvent-free conditions. Our immobilized systems present higher activities than related homogeneous bis-imidazolium salts, showing the cooperative effect of the matrix surface and the additional advantage of easy recycling. The best performances were obtained with the material derived from polycondensation of a disilylated dihydroimidazolium salt in the absence of tetraethoxysilane (TEOS). The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b916767f

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Organic–inorganic hybrid silica materials containing imidazolium
and dihydroimidazolium salts as recyclable organocatalysts for
Knoevenagel condensations
Montserrat Trilla,a Roser Pleixats,*a Michel Wong Chi Man*b and Catherine Biedb
Received 4th June 2009, Accepted 12th August 2009
First published as an Advance Article on the web 8th September 2009
DOI: 10.1039/b916767f
Organic–inorganic hybrid silica materials containing imidazolium and dihydroimidazolium salts
prepared from monosilylated and disilylated monomers by sol–gel methodologies are active and
reusable organocatalysts for the Knoevenagel condensation of aromatic aldehydes with
malononitrile and ethyl cyanoacetate under solvent-free conditions. Our immobilized systems
present higher activities than related homogeneous bis-imidazolium salts, showing the cooperative
effect of the matrix surface and the additional advantage of easy recycling. The best performances
were obtained with the material derived from polycondensation of a disilylated
dihydroimidazolium salt in the absence of tetraethoxysilane (TEOS).
which would provide some advantages from both the econom-
Introduction
ical and environmental points of view. Immobilization of the
organocatalysts12 to an insoluble polymer matrix allows an easy
separation by filtration, simplifying the work-up procedure and
facilitating the catalyst recovery and reuse. In this sense, some
few reports exist about heterogeneous reusable organocatalysts
for Knoevenagel condensations, such as polystyrene-supported
poly(amidoamine) dendrimers,13 purely organic mesoporous
poly(benzimidazole),14 mesoporous silicas (MCM-41, MCM-48
and SBA-15) with grafted aminopropyl groups, dihydroimida-
zole groups or other organic bases,15 and silica gel or mesoporous
SBA-15 functionalized with imidazolium or pyridinium based
ionic liquids.16
Very recently, we have described the preparation of organic–
inorganic hybrid silica materials containing imidazolium and
bis-dihydroimidazolium salts and their use, together with a
palladium source, as recoverable palladium catalysts for cross-
coupling reactions.17 These reactions were performed in a
mixture of solvents, namely DMF and H2O. Herein we present
the catalytic activity and recyclability of these materials towards
Knoevenagel condensation of aromatic aldehydes with active
methylene compounds under solvent-free conditions. Moreover
we studied the influence of the amount of the organic salt loading
in the materials toward the efficiency of the studied reaction.
Among the carbon–carbon bond forming reactions, the Kno-
evenagel condensation of aldehydes with active methylene
compounds constitute one of the most important synthetic
methods for the preparation of electrophilic trisubstituted
alkenes, which involves a simple operation process and mild
conditions. Traditional homogeneous catalysts include primary
or secondary amines or buffer systems containing ammonia or
amines and the corresponding conjugated acid.1 Some reports
about the use of gem-diamines2 and guanidines3 as organocat-
alysts of this reaction can be found. Other common catalysts
are alkali alkoxides, alkali hydroxides and Lewis acids in liquid
phase systems.1 Solid inorganic bases (zeolites, hydroxyapatite,
sepiolites, hydrotalcites, basic oxides etc.) or solid acids (sulfate-
ion promoted zirconia) have also been employed as hetero-
geneous catalysts.4 Recently, alkylammonium,5 imidazolium6
and guanidium-type7 ionic liquids or other task-specific ionic
liquids8 have been described as promoters of this condensation.
Lewis acidic ionic liquids based on imidazolium and pyridinium
chloroaluminates have been used as both solvent and Lewis
acid-type catalysts.9 In other cases, the imidazolium-based ionic
liquids act only as reaction media which allows easy recycling
and other catalysts are required, such as glycine, KOH or
hydrotalcite.10
Organocatalysis has experienced a renewed and growing in-
terest in the last decade.11 The relatively high catalyst loading re-
quired in many of the organocatalytic processes has led a number
of groups to investigate the possibility of the catalyst recycling,
Results and discussion
Preparation of the hybrid materials M1–M4
We summarize in Scheme 1 the synthesis of the monosi-
lylated and disilylated monomers 2 and 3 and the prepa-
ration of hybrid materials M1–M2 and M3–M4 derived
thereof. In both types of materials, two hybrids with dif-
ferent amounts of organic loading were prepared. We al-
ready reported the synthesis of M2–M4.17 Material M1 was
prepared similarly to M2 but with different molar ratio of
2 : TEOS. The following reactant molar ratios were used in the
aDepartment of Chemistry, Universitat Auto`noma de Barcelona,
08193-Cerdanyola del Valle`s, Barcelona, Spain.
E-mail: roser.pleixats@uab.cat; Fax: (+34)-93-5811265
bInstitut Charles Gerhardt Montpellier (UMR 5253
CNRS-UM2-ENSCM-UM1), Architectures Mole´culaires et Mate´riaux
Nanostructure´s, Ecole Nationale Supe´rieure de Chimie de Montpellier,
8 rue de l’e´cole normale, 34296-Montpellier ce´dex 5, France
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Scheme 1 Synthesis of the silylated monomers and hybrid silica materials M1–M4.
Table 1 Physicochemical data of materials M1–M4
ordered structure in the hybrid silica. Contrarily, M4 exhibits
a worm-like mesoporous organization, while M3 is even less
organized with no mesoporosity at all.17 The solid state 29Si
NMR spectra of M1, M2 and M4 show two groups of chemical
shifts: T2 and T3 units at around -61 to -66 ppm, resulting from
the hydrolysis–condensation of the corresponding monomers 2
and 3, and Q units (Q3 and Q4) ranging from -96 to -110 ppm
formed from TEOS. M3 spectrum shows only T2 and T3 units
at -57.3 and -65.6 ppm showing that no Si–C bond cleavage
occurred during the hydrolysis process.
Material
SBET (m2 g-1)
Vp (cm3 g-1)
Dp (nm)
mmol N g-1
M1
M2
M3
M4
477
506
2
0.381–0.388
0.308–0.364
—
3.6–3.4
3.1–2.7
—
1.706
0.585
7.430
0.828
266
0.262–0.253
4.3–4.2
case of M1 : [CMICl]0/[NaBF4]0/[TEOS]0/[2]0/[H2O]0/[HCl]0/
[EtOH]0 = 1.0 : 0.6 : 4.5 : 0.45 : 771 : 38 : 25.
The materials were characterized by solid state CP-MAS 29Si
spectroscopy (and 13C NMR for M1 and M3), surface area
BET measurements, IR and elemental analysis. Some relevant
physicochemical data are given in Table 1. Material M3 prepared
from disilylated 3 without TEOS shows a low surface area as
a result of the voluminous organic fragment in the material
as already observed before.18 The other materials prepared in
the presence of TEOS are mesoporous and present higher SBET
values.
Catalytic activity and recyclability of the hybrid materials
M1–M4 in the Knoevenagel condensation
The catalytic activity of our materials was tested in the
Knoevenagel condensation of malononitrile and ethyl cyanoac-
etate with aromatic aldehydes under solvent-free condi-
tions (Scheme 2). Benzaldehyde, 4-fluorobenzaldehyde and
4-methoxybenzaldehyde were chosen as electrophilic substrates.
The stirred mixture of reagents (1.1 eq. of the active methylene
compound) and catalyst (0.4–1.2% mol of organic ligand)
was heated at 100 ◦C or 130 ◦C for the required time. The
products were obtained after addition of dichloromethane to
the cold reaction mixtures, filtration of the solid material,
drying and evaporation of the filtrate. A more environmentally
friendly solvent could be used based on product solubility.
Thus, analogous results can be achieved using ethanol as green
organic21 extracting solvent. The recovered catalytic materials
were washed and dried prior to their reuse in subsequent runs.
The same reaction conditions and the same reaction times were
M1 presents a nitrogen sorption isotherm of type IV according
to IUPAC (Fig. 1(b)) and its powder X-ray diffraction (PXRD)
exhibits a sharp diffraction peak indicating an organised meso-
porous structure but with less defined periodicity as in M2
as expected (Fig. 1(a)).19 PXRD of the more diluted material
M2 (ratio 1 : 40)17 exhibits a 2D hexagonal mesopore structure
(MCM-41 type) as expected.20 This fact indicates that higher
dilution of the organic monosilylated moiety favors a more
Fig. 1 (a) PXRD of M1; (b) N2 sorption isotherm of M1 and plot of
the pore size distribution.
Scheme 2 Knoevenagel condensations catalyzed by hybrid materials
M1–M4.
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Table 2 Knoevenagel condensations catalyzed by M1–M4, and blank experiments
Entry
X
Y
M (% mol)
T (◦C)
t (h)
Product
% in consecutive cycles
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
H
H
F
OMe
H
F
H
F
OMe
F
H
F
H
H
F
OMe
H
H
H
CN
CN
CN
CN
COOEt
COOEt
CN
CN
CN
COOEt
CN
CN
CN
CN
CN
CN
COOEt
CN
CN
M3 (0.4)
M3 (1.2)
M3 (1.2)
M3 (1.2)
M3 (1.2)
M3 (1.2)
M1 (0.8)
M1 (0.8)
M1 (0.8)
M1 (0.8)
M2 (0.8)
M2 (0.8)
M4 (0.4)
—
100
100
100
100
130
130
100
100
100
130
100
100
100
100
100
100
130
100
100
130
6
2
4
4
2
2
6
15
16
16
6
16
6
4
4
5
6
7
8
4
5
6
8
4
5
4
4
5
6
7
4
4
7
93/95/97/96/99a
96/94/94/92/95a
97/100/97/95/100a
99/81/77/66/75b
100/81/94/79/42b
97/100/57/38/31b
98/97/100/97/96a
73/74/72/72/71a
100/96/98/93/97a
98/97/76/53/42b
80/76/75/72/84a
60/59/66/58/71a
76/68/67/64/61a
8b
6
—
—
—
16
16
4
6
22
4
5b
11b
2b
MCM-41
9 (1.2)
9 (1.2)
32b
98a
H
COOEt
66b
a Isolated yields. b Calculated yields based on NMR integration.
maintained in five consecutive cycles with the same batch of
catalyst to assess its recyclability.
entries 13 and 1). Thus, higher dilution of the organic moiety
into the inorganic matrix is detrimental, probably due, in part,
to the need of high amounts of solid for the diluted material.
The number of catalytic centers can be estimated from the
elemental analysis and BET surface area (see Table 1). Material
M3 prepared without TEOS gives an elemental analysis of
7.43 mmol of N/g, which corresponds to a 3.715 mmol of
dihydroimidazolium sites per g of solid material. Material
M4 prepared with 80 molar equivalent of TEOS has almost
10 times less sites per g (0.828 mmol N/g; 0.414 mmol of
dihydroimidazolium sites per g of solid material). Although we
are using similar molar amount of organic ligand (compare,
for instance, entry 1 with entry 13 of Table 2), M3 has a higher
density of active sites on a smaller surface area and hence has the
organic ligands quite close, whereas in M4 the organic ligands
are spread (or diluted) in the silica matrix formed by the added
TEOS. The fact that M3 provides the best results is probably due,
in part, to a cooperative effect between neighboring centers.
Blank experiments were also performed. Compounds 4, 5,
6 and 7 were obtained in very low yields (2 to 11%) upon
prolonged heating in the absence of any catalyst (entries 14–
17). Mesostructured silica MCM-41 containing no organic
moiety gave a 32% NMR yield of compound 4 under the
same conditions used for catalysts M1–M4 (compare entry 18
with entries 1, 7, 11 and 13). This makes clear that, although
the surface of the silica support can itself play a role on the
catalytic activity, the imidazolium and dihydroimidazolium salts
anchored to the silica matrix display a crucial catalytic effect.
Cooperativity between the surface and active site in hybrid
organic–inorganic heterogeneous catalysts has been previously
reported.22 Finally, we compared the activity of our immobilized
systems with that of a related homogeneous bis-imidazolium
salt 9 (Fig. 2) which we recently described.23 Compound 4 was
prepared in 98% isolated yield after 22 h at 100 ◦C in the
presence of 1.2% mol of 9 (Table 2, entry 19) and the acrylate
derivative 7 in 66% NMR yield after 4 h at 130 ◦C (Table 2,
The first essays were performed with catalytic material M3
(Table 2, entries 1–6). As it was prepared without the addition
of TEOS, it has a much higher content of organic moiety per
gram of material and less amount of this solid has to be added. In
practice, this is quite advantageous for a solvent-free procedure.
The reactions of aromatic aldehydes with malononitrile were
performed at 100 ◦C (entries 1–4), requiring between 2 and 6 h
to be completed, depending on the amount of catalyst (compare
entries 1 and 2) and the aldehyde used. The electronic character
of the substituent on the aldehyde does not seem to have a sig-
nificant influence on the first cycle, reactions with benzaldehyde
proceeding faster than those with substituted ones (compare
entries 2, 3 and 4). However, with 4-methoxybenzaldehyde as the
electrophile, this catalyst was found less effective in the recycling
(entry 4), whereas no decrease in activity was observed in the
other cases in five consecutive cycles (entries 1–3). Less reactive
ethyl cyanoacetate required higher temperatures (130 ◦C) when
treated with benzaldehyde and 4-fluorobenzaldehyde (entries 5–
6), the yields of product decreasing after the third or fourth cycle
for the same reaction time.
Next, the material M1 was tested (Table 2, entries 7–10). An
amount of 0.8% mol of this monocationic organic ligand would
be equivalent to the 0.4% mol used for the biscationic organic
ligand present in M3 (compare entries 7 and 1). Again, the
reaction was slower with substituted benzaldehydes (compare
entries 8 and 9 with entry 7), although good to excellent activity
and recyclability upon five runs was found. Treatment of ethyl
cyanoacetate with 4-fluorobenzaldehyde at 130 ◦C for 16 h gave
nearly complete conversion, although the yields decreased upon
recycling (entry 10) as observed before (entry 6).
Material M2 (1 : 40) was inferior to M1 (1 : 10) (compare
entries 11 and 12 with entries 7 and 8 for the same reactions
performed under analogous conditions). In the same way, M4
(with TEOS) performed less than M3 (without TEOS) (compare
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moter in Knoevenagel condensations; however no mechanistic
details were mentioned by the authors. From these facts, it is
clear that although the chloride-based nucleophilic mechanism
can not be excluded in our chloride dihydroimidazolium salts,
another alternative reaction pathway is required to account for
the results with other anions. We think that the catalytic activity
is more likely related to the relative acidity of C-2 hydrogens
of the imidazolium and dihydroimidazolium salts. The better
catalytic performance of M3 which has been associated before
to its higher density of active sites and to a cooperative effect
between neighboring centers would be in accordance with
our mechanistic proposal of concomitant activation of both
nucleophilic and electrophilic reagents through their interaction
with proximal dihydroimidazolium moieties.
Fig. 2 Homogeneous catalyst 9 for Knoevenagel condensation.
entry 20). These results are inferior to those obtained with
materials M1–M4 (compare entry 19 with entries 2, 7, and entry
20 with entry 5), which have the additional advantage of easy
recovery and recycling. This fact would be in accordance with
the above mentioned cooperativity effect.
Compounds 7 and 8 were each obtained as a single stereoiso-
1
mer (GLC) and their H NMR spectra were coincident with
Conclusions
those described for the isomers with (E) configuration.24,25
Moreover, observed experimental values show good accordance
with the estimated values26 for the olefinic protons of (E) isomers
7 and 8; the (Z) isomers should present these protons at higher
fields.
In summary, several hybrid silica materials containing imi-
dazolium and dihydroimidazolium salts in different dilutions
have been easily and efficiently prepared in a few steps from
commercial sources using template-based sol–gel methodologies
from the corresponding mono- and disilylated monomers. These
materials are good recyclable catalysts for the Knoevenagel
condensation between active methylene compounds and aro-
matic aldehydes in solvent-free conditions, providing a green and
sustainable route to electrophilic trisubstituted alkenes. The im-
mobilized catalysts show higher activities for this transformation
than other related homogeneous bis-imidazolium salts and are
also much more active than non-functionalized mesostructured
MCM-41, which presents some residual activity. This suggests
a certain degree of cooperativity between the surface of the
inorganic matrix and the active sites and underlines the crucial
role of the organic moiety. Moreover, better performance was
observed from the hybrid catalysts with higher organic loading,
showing that the predominant factor is the concentration of
the organics rather than the porosity in the materials, at least
from these trials in neat conditions. The material obtained
from polycondensation of a disilylated dihydroimidazolium salt
in the absence of TEOS gave the best results, no precedents
being available for this type of organocatalyst for Knoevenagel
reaction.
The mechanism of the condensation under our conditions is
presently unknown as no classic basic catalysis can be claimed
with no basic centers being present here as in common catalysts
such as amines, imidazole or dihydroimidazole, and as no
external base was added. Speculations may be drawn from
the relatively high acidity of the proton at the C-2 position
of the imidazolium and dihydroimidazolium salts (these salts
are precursors of N-heterocyclic carbenes), which could be
the origin of the catalysis through activation of both the
electrophile and the active methylene compound by hydrogen
bond formation with the carbonyl group of the aldehyde and
the cyano and/or ester group of the pre-nucleophile. Like in
classic acid-catalyzed aldol-type reactions the process proba-
bly takes place through an “enol-type” intermediate. Inferior
results obtained with ethyl cyanoacetate when compared with
malononitrile (entry 4 vs. entry 2 of Table 2) can be related
to the lower nucleophilic activity of the ethyl cyanoacetate
compared with malononitrile. Attempts to detect some adducts
resulting from the interaction of the aldehydes, ethyl cyanoac-
etate and malononitrile with the bis-imidazolium iodide 9 by
ESI-MS (electrospray ionization mass spectrometry) at different
temperatures were, however, unsuccessful (binary mixtures of
catalyst/electrophile, catalyst/nucleophile and ternary mixtures
catalyst/nucleophile/electrophile were tested on ESI-MS). A
very recent work27 postulates that chloride anions associated
with soft cations (like tetraalkyl ammoniums, alkyl imidazoli-
ums and alkylpyridiniums) act as catalysts for the Knoevenagel
condensations through an alternative nucleophilic pathway. The
authors attribute the enhanced nucleophilicity of the chloride
anion to a softness/hardness mismatch between the anion
and cation. Under the conditions used by the authors, using
acetonitrile as solvent at 80 ◦C, ammonium salts with bromide
anion and imidazolium salts with tetrafluoroborate anion did
not catalyze the reaction. Most of this work deals, however, with
tetraalkylammonium salts. In sharp contrast with these results,
in our hands, bis-imidazolium iodide 9 effectively catalyzed the
reaction in solvent-free conditions (entries 19 and 20 of Table 2)
and [bmim][BF4] has been reported6 to act as solvent and pro-
Experimental
The 1H and 13C NMR spectra were recorded on a Bruker
DPX250 and the J values are given in Hz. ESI-MS analyses
were recorded at the Universitat de Girona on an Esquire
6000 Ion Trap Mass Spectrometer (Bruker) equipped with an
electrospray ion source. The instrument was operated either in
the positive ESI(+) or in the negative ESI(-) ion mode. The
samples (5 mL) were introduced into the mass spectrometer
ion source through an Agilent HPLC with a mobile phase
flow of 100 mL/min (80/20 v/v CH3CN/H2O). Nitrogen was
employed as both a drying and nebulizing gas. IR data were
obtained with a Perkin-Elmer (System 2000 FT-IR) spectropho-
tometer. The CP-MAS 13C and 29Si solid state NMR spectra
were recorded on a Bruker AV-400-WB and on a Bruker
FT-AM 400. Surface areas were determined by the Brunauer–
Emmett–Teller (BET) method on a Micromeritics Tristar 3000
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analyzer, and the average pore diameter was calculated by the
BJH method. Elemental analyses have been performed at the
Serveis Cientificote`cnics of the Universitat de Barcelona. X-Ray
diffraction experiments were carried out on solid powders in
1 mm diameter glass capillaries, in the Laboratoire des Collo¨ıdes,
Verres et Nanomate´riaux (UMR5587), Universite´ de Montpellier
II, France, working in a transmission configuration. A copper
rotating anode X-ray source (functioning at 4 kW) with a
multilayer focusing “Osmic” monochromator giving high flux
(108 photons sec-1) and punctual collimation was employed. An
“Image plate” 2D detector was used. Diffraction curves were
obtained giving diffracted intensity as a function of the wave
vector q. Diffracted intensity was corrected by exposition time,
transmission and intensity background coming from diffusion
by an empty capillary. Compounds 1, 2 and 3 and materials
M2–M4 were prepared as described.17
The following compounds were obtained by an analogous
procedure (see Scheme 2 and Table 2 for modifications in
the reagents, reaction temperature, reaction time, catalyst and
yields).
2-(4-Fluorobenzylidene)malononitrile (5)
Mp 125–126 ◦C (lit.,28 125–126 ◦C); IR nmax (ATR)/cm-1 3036,
2229 (CN), 1594, 1574, 1505, 1415, 1304, 1238, 1161, 1107, 836,
615; dH (250 MHz; CDCl3; Me4Si) 7.22 (2 H, d, J 8.7), 7.73 (1
=
H, s, CH–), 7.96 (2 H, m).
2-(4-Methoxybenzylidene)malononitrile (6)
Mp 113–114 ◦C (lit.,28 113–114 ◦C); IR nmax (ATR)/cm-1 3028,
2219 (CN), 1603, 1568, 1556, 1509, 1367, 1317, 1276, 1179, 1019,
832, 609; dH (250 MHz; CDCl3; Me4Si) 3.91 (3 H, s, OCH3),
=
7.01 (2 H, d, J 9.0), 7.65 (1 H, s, CH–), 7.91 (2 H, d, J 9.0);
Preparation of material M1
dc (62.5 MHz; CDCl3; Me4Si) 56.1, 113.6, 114.7, 115.4, 124.4,
1-Cetyl-3-methylimidazolium chloride (1.635 g, 4.767 mmol),
sodium tetrafluoroborate (0.333 g, 2.972 mmol), hydrochloric
acid (15 mL of conc. HCl, 0.181 mol HCl, 0.624 mol of water)
and distilled and deionized water (55 mL, 3.053 mol) were mixed
and stirred together at 40 ◦C. In a few minutes an emulsion
was formed. A solution of the silylated monomer 2 (1.113 g,
2.147 mmol) and TEOS (4.583 g, 0.0216 mol) in absolute ethanol
(7 mL, 0.120 mol) was added over the emulsion and stirred
133.8, 159.2, 165.1.
(E)-Ethyl-2-cyano-3-phenylacrylate (7)
Mp 45–46 ◦C (lit.,7 46–47 ◦C); IR nmax (ATR)/cm-1 3029, 2981,
2223 (CN), 1722 (CO), 1605, 1444, 1296, 1253, 1200, 1088, 1009,
766, 683; dH (250 MHz; CDCl3; Me4Si) 1.41 (3 H, t, J 7.0, –
OCH2–CH3), 4.40 (2 H, q, J 7.0, –OCH2–CH3), 7.54 (3 H, m),
7.99 (2 H, m), 8.26 (1 H, s, CH–); dc (62.5 MHz; CDCl3; Me4Si)
14.4, 63.0, 103.3, 115.8, 129.6, 131.4, 131.8, 133.6, 155.3, 162.8.
◦
together at 40 C for one day. The resulting white powder was
=
filtered, washed twice with water and three times with ethanol.
The solid M1 was obtained after template removal by soxhlet
extraction with acetone for one day, powdering and drying
◦
under vacuum at 70 C during 6 h (1.786 g). SBET: 477 m2 g-1;
(E)-Ethyl 2-cyano-3-(4-fluorophenyl)acrylate (8)
pore diameter: 3.65–3.37 nm; pore volume: 0.381–0.388 cm3 g-1;
IR nmax(KBr)/cm-1 3316 (s and br), 1611, 1564, 1549, 1486,
1455, 1082 (vs and br), 957, 803, 577, 469; 29Si CP-MAS NMR
(79.5 MHz): d -66.2 (T3), -100.3 (Q3), -109.7 (Q4). 13C CP-
MAS NMR (100.62 MHz): d 10.3, 17.7, 26.2, 41.2, 51.4, 127.0,
Mp 94–95 ◦C (lit.,24 96–97 ◦C); IR nmax (ATR)/cm-1 3035, 2297,
2226 (CN), 1714 (CO), 1594, 1262, 1226, 1162, 1087, 837, 763;
d
H (250 MHz; CDCl3; Me4Si) 1.42 (3 H, t, J 7.0, –OCH2–CH3),
4.40 (2 H, q, J 7.0, –OCH2–CH3), 7.21 (2 H, dd, J 8.6 and
=
8.4), 8.05 (2 H, dd, J 8.5 and 5.3), 8.23 (1 H, s, CH–); dc
131.9, 135.8, 141.5. Anal. (%) calculated for C15H20N2Si11O21.5
I
(62.5 MHz; CDCl3; Me4Si) 14.4, 63.1, 102.8, 115.7, 117.0 (d,
(assuming total condensation and no halide anion exchange) N
2.78, C 17.87, H 2.00; found: N 2.39, C 16.51. The hydrolysis
and condensation is never complete in these hybrid materials
(see, for instance, the presence of Q3 signals in 29Si CP-MAS
NMR).
4
3
2JCF 22.0), 128.1 (d, JCF 3.2), 133.9 (d, JCF 9.1), 153.8, 162.7,
165.7 (d, 1JCF 255.7).
When some amount of starting reagent was detected in the
NMR spectrum of the crude mixture, together with the final
product, the yield was calculated from the molar ratio of the
compounds in the mixture (derived from NMR integration),
the weight of the crude mixture and the molecular weight of
the compounds present in the mixture. We do not use the NMR
conversion because starting reagents can be partially evaporated
under reduced pressure.
Preparation of 2-benzylidenemalononitrile (4). Typical procedure
A mixture of freshly distilled benzaldehyde (470 mL, 1.04 g mL-1,
4.61 mmol), malononitrile (330 mL, 1.049 g mL-1, 5.24 mmol)
and M3 (0.0297 g, 7.430 mmol N g-1, 0.0552 mmol of bis-
dihydroimidazolium ligand) was stirred at 100 ◦C for 2 h (GLC
monitoring). Dichloromethane was added to the cold mixture,
the catalyst M3 was filtered, the filtrate was dried with anhydrous
sodium sulfate and the solvent◦ was evaporated to give pure
4 (0.684 g, 96%). Mp 80–82 C (lit.,7 80–81 ◦C); IR nmax
(ATR)/cm-1 3032, 2222 (CN), 1588, 1565, 1449, 1215, 754, 677,
615; dH (250 MHz; CDCl3; Me4Si) 7.55 (2 H, t, J 7.4), 7.64 (1 H,
Acknowledgements
We acknowledge financial support from MEC/MICINN of
Spain (Project CTQ2006-04204/BQU), Consolider Ingenio
2010 (Project CSD2007-00006), Generalitat de Catalunya
(Projects SGR2005-00305 and SGR 2009-1441), from the
CNANO and the CNRS. We thank A. Roglans and A. Pla-
Quintana for the ESI-MS analyses and P. Dieudonne´ for PXRD
data.
=
t, J 7.4), 7.79 (1 H, s, CH–), 7.91 (2 H, d, J 7.0). The catalytic
material M3 was washed with water, ethanol and diethyl ether,
and dried under vacuum (2 mm Hg) to be reused in the next run.
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