Communications
mixture were removed with a filter syringe and characterized by
solution H NMR spectroscopy and GC-MS over the course of the
nosilanes in toluene has been previously proposed to cause
1
grafting of very densely populated organic groups.[10b] How-
ever, by lowering the concentration of aminorganoosilane and
shortening the reaction times, we have also synthesized
similar site-isolated samples that display efficient catalytic
properties in toluene at lower temperature (Supporting
Information).
reactions. The percentage yields and conversions were determined
from 1H NMR spectra measured in deuterated acetone.
Received: November 8, 2006
Revised: December 22, 2006
Published online: March 13, 2007
In conclusion, we have described the synthesis of the most
efficient mesoporous catalysts reported to date for the Henry
reaction by postgrafting spatially distributed organoamine
groups on mesoporous silica. This was achieved by reacting
excess amounts of aminoorganosilanes in ethanol or by
postgrafting smaller amounts of aminoorganosilanes in tolu-
ene for a short reaction time. Despite the lower number of
catalytic sites, the resulting materials with increased cooper-
ative properties and higher surface areas revealed the most
enhanced catalytic properties. This procedure should allow
the synthesis of various bifunctional catalysts for a number of
other reactions in which cooperative effects by two functional
groups and higher surface areas are required. We have
confirmed that such one-pot synthetic methods allow the
preparation of spatially isolated bifunctional catalysts, which
until now were only attainable through lengthy and costly
multistep methods.[10] In contrast, this approach is very simple,
involving one step, and versatile compared to all previously
reported procedures.
Keywords: bifunctional catalysts · Henry reaction ·
heterogeneous catalysis · mesoporous materials ·
nanostructures
.
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Experimental Section
Postgrafting of spatially isolated organoamines onto mesoporous
silica, MCM-41: MCM-41 was synthesized as reported previously (see
the Supporting Information).[13] The sample of MCM-41 was kept in
an oven at 808C to remove physisorbed water prior to postgrafting.
For AP-E1, MCM-41 (500 mg) was stirred with excess 3-amino-
propyltrimethoxysilane (APTMS; 0.66 g, 3.68 mmol) under reflux in
ethanol (250 mL) at around 788C for 6 h. The solution was filtered,
and the precipitate was washed with dichloromethane (200 mL) and
ethanol (500 mL) and then dried in air. Two other samples were
prepared in toluene, one of which was prepared by stirring MCM-41
(500 mg) with APTMS (0.82g, 3.68 mmol) in toluene (250 mL) at
788C (AP-T1), and the other was prepared similarly but under reflux
at about 1128C (AP-T2). These samples were washed and dried as
above, and the resulting mesoporous samples were characterized
instrumentally (see the Supporting Information for details).
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Henry (nitroaldol) reaction: The Henry reaction was performed
as reported before.[9,14] Typically, the aminofunctionalized mesopo-
rous sample (20 mg) was added to a mixture of p-hydroxybenzalde-
hyde (122 mg, 1 mmol) and nitromethane (10 mL). The reaction
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ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 2879 –2882