A. Corma et al. / Journal of Catalysis 229 (2005) 322–331
323
cient framework flexibility to accommodate a certain pro-
portion of a large organic component. PMOs prepared from
TEOS and large organosilicon compounds have a periodic
mesoporous channel structure with the organic functional-
ity covalently grafted to the walls. These solids constitute a
logical evolution of those in which MCM-41 has covalently
anchored an organosilicon compound by just a single tether.
Although there must be common properties between these
two solids, PMOs may have larger surface areas and pore
volumes, and the organic component should experience a
larger degree of immobilisation than post-synthetically mod-
ified MCM-41.
We have contributed to the development of functional
PMOs by preparing solids that exhibit a photochemical re-
sponse [10,11] or that are catalytically active [12,13]. In
some cases, the organic precursor was initially enantiomer-
ically pure, and the resulting solid (termed ChiMO, from
Chiral Mesoporous Organosilicas) exhibits optical activity
towards polarised light [14]. In these examples, however,
the content of organic component that can be tolerated in
the solid while it is still forming a MCM-41-like structure
is limited to a level typically below 20 wt%. However, this
content is sufficiently high for most of the applications.
As a continuation of this line of research, we report here
the synthesis and catalytic activity of a PMO containing
a carbapalladacycle complex of the type of compound 1.
These palladium complexes have been reported to be highly
active catalysts for Suzuki–Miyaura cross-coupling in aque-
ous solution and supported in amorphous inorganic ox-
ides [6,15–20].
and the spectra were recorded in a Nicolet 710 instrument
at room temperature after outgassing at the corresponding
temperature under 10−2 Pa. BET surface area and micropore
volume were measured by isothermal nitrogen adsorption
with a Micromeritics ASAP2000, with the use of samples
that were previously sieved (particle size 0.2–1 µm). X-ray
diffraction spectra were recorded in a X’Pert Philips analyser
with a curved monochromator for Cu X-ray radiation, with
the use of automatic divergence and anti-scatter slits and
a mini-proportional Xe detector. The C and N content of
the solids was determined by combustion chemical analysis
with a Fisons CHNSO analyser. We determined the Pd con-
tent by dissolving the silicate in a mixture of HF:HCl:HNO3
conc. (30 mg of solid in ca. 1:1:1 ml), diluting the solu-
tion in water (30 ml), and measuring by quantitative atomic
absorption spectroscopy (Varian SpectrAA 10 plus). Quan-
tification was achieved by a comparison of the response
with a calibration plot. MCM-41 was prepared by hydrother-
mal crystallisation at 100 ◦C, with cetyltrimethyl ammonium
bromide as a structure-directing agent and Aerosil as a silica
source, following a procedure described in detail elsewhere
[21,22].
2.1. Synthesis of the silylated carbapalladacycle
precursor 2
The carbapalladacycle oxime complex was synthesised
as described in Ref. [7]. The complex (730 mg, 2.5 mmol)
was placed in a previously dried double-necked round-
bottomed flask. Then anhydrous THF (25 ml) was added
under a nitrogen atmosphere, and the mixture was magneti-
cally stirred in a preheated oil bath at 65 ◦C under a nitrogen
atmosphere until a dark yellow solution was observed. 3-
Isocyanatepropyltriethoxysilane (1.875 ml, 7.5 mmol) was
slowly added, and the reaction was left to react at 65 ◦C un-
der an inert atmosphere for 24 h. We monitored the course
of the reaction by periodically taking aliquots (0.5 ml) and
following the decrease of the isocyanate band at 2275 cm−1
together with the appearance of the amide bands by IR. At
the final time the mixture was concentrated, hexane (500 ml)
was added, the solution was cooled, and the precursor started
to precipitate as a black solid. The solid was isolated by fil-
tration in vacuo under a nitrogen atmosphere and stored in
a screw-capped vial under argon (1.2 g, 61%). [IR (CDCl3,
cm−1): 3315, 2975, 2930, 2885, 2275, 1768, 1745, 1580,
1580, 1550, 1525, 1460, 1440, 1390, 1375, 1340, 1280,
2. Experimental
The reagents and solvents were obtained from commer-
cial sources and were used without further purification. Gas
chromatographic analyses were performed on a HP 5890
instrument equipped with a 25-m capillary column of 5%
phenylmethylsilicone. GC/MS analyses were performed on
a Agilent 5973N spectrometer equipped with the same col-
umn and operated under the same conditions as the GC.
HPLC-UV analyses were performed with a Varian instru-
ment with an UV diode array detector separating the mixture
through a Kromasil-C18 column (0.4 × 25 cm, pore diam-
eter 5 µm). CH3CN:H2O was used as the mobile phase
1
(50:50 v/v, flow: 0.7 ml min−1). H- and 13C-NMR were
1
recorded in a 300-MHz Bruker Avance instrument, with
CDCl3 or CD3OD as the solvent and TMS as the internal
standard. Diffuse reflectance UV–vis spectra were recorded
on a Cary 5G adapted with a praying mantis accessory, with
BaSO4 as a reference. IR spectra were recorded on a Jasko
460plus spectrophotometer, with the use of sealed greaseless
quartz cells with CaF2 windows. IR spectra were recorded in
transmission mode using self-supported wafers of the PMOs
prepared pressing the solid at 2 tons cm−1 for 15 s. Thermal
treatments were carried out in situ inside the sealed IR cells,
1235, 1200. H NMR δH (ppm, 300 MHz, CDCl3): 8.15
(bs), 6.95 (1H, d), 6.7 (1H, s), 6.55 (1H, d), 5.85 (bs), 3.75
(10H, q), 3.25 (H, s), 2.2 (3H, s), 1.7 (4H, s), 1.25 (15H, t),
0.75 (4H, bs). 13C NMR δC (ppm, 300 MHz, DMSO-d6):
180.1, 158.2, 154.6, 154.1, 130.6, 120.8, 113.0, 58.9, 44.1,
26.0, 23.1, 18.5, 13.2, 7.9. MS (FAB): isotopic distribution
recorded for 2 compatible with 1 Pd (relative % with respect
to the major peak of the peak cluster): m/z 719 (41), 721
(41), 722 (81), 723 (100), 725 (96), 727 (44); other peak
clusters at 645, 503 (loss of one propyldiethoxysilyl group)