Characterization of the basicity of mixed oxides obtained from hydrotalcite-like precursors by 13C CP/MAS NMR spectroscopy using nitromethane-reactive adsorption is described. On Lewis bases, featuring acid–base pairs, the nature of adsorbed species namely nitromethane, aci-anion nitromethane, and methazonate salt analogue depends on the relative strength of the basic and acid sites on the pairs. None of these species is obtained using Brønsted bases such as layered double hydroxide (LDH) of the meixnerite type. In that case a formate analogue is proposed to be formed. Heterogeneous base catalysis of the Michael addition of nitromethane to cyclohex-2-en-1-one is studied. A relationship is established between the activity of the catalyst and the 13C CP/MAS NMR chemical shift of the aci-anion nitromethane which is a measure of the basic strength. Discussion of NMR and catalytic results takes into account the respective roles of basicity and of conjugate Lewis acidity. Basicity is needed to form a reactive anion comparable to aci-anion nitromethane, but the higher the stabilization of aci-anion nitromethane by Lewis acidity, the lower the activity. Increasing the basic strength by decreasing the Lewis acidity of the acid–base pairs leads to an increase of activity concomitant with the formation of methazonate as shown by 13C MAS NMR. The efficiency of meixnerite which is the most active and selective catalyst is related not only to its Brønsted basicity but also to its weak Lewis acidity.

Adsorption of nitromethane on oxide surfaces was monitored using 13C CP/MAS NMR. Stabilization of the aci-anion formed by reaction of nitromethane on acid−base pairs was apparent. A linear relationship between the 13C NMR isotropic chemical shift of the methylene group of the adsorbed aci-anion of nitromethane and the heat of adsorption of CO2 measured by microcalorimetry was established. The results suggest that nitromethane constitutes an accurate and effective NMR probe for monitoring the basicity of oxide surfaces.

(−)-Ephedrine, used as a model β-amino alcohol, was covalently anchored on mesoporous micelle templated aluminosilicates (Al-MTS) through nucleophilic substitution of halogenoalkyl(aryl)silane chains previously grafted on the surface. The covalent grafting was performed either by silylation (method a) or by surface sol–gel (method b). The latter method provided higher loading. However, the higher loading lowers the resulting mesoporous volume. The coupling alkyl halide moiety was then substituted with (1R,2S)-(−)-ephedrine. Used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc, these materials showed properties which depend mainly on the grafting method. The best results (activity, enantioselectivity) were obtained with catalysts prepared from supports featuring high initial pore diameter. The effect of the regular porosity on the efficiency and enantioselectivity was shown. Dilution of catalytic sites by alkyl groups and rigidification of the linker were also studied.

New solid chiral auxiliaries are used in the enantioselective alkylation of benzaldehyde with diethylzinc. These auxiliaries are obtained by direct immobilization of their homogeneous counterparts, (−)-ephedrine and (−)-O-methyl-ephedrine, on the surface of mesoporous micelle templated silicates and aluminosilicates. Hybrid materials are characterized, and the interactions between the heteroatoms of the organic compounds and the surface are studied by FTIR spectroscopy. Efficiency of such hybrid solids is discussed.

Heterogeneous enantioselective alkylation of benzaldehyde with diethylzinc was performed using (-)-ephedrine grafted on mesoporous micelle templated aluminosilicates or silicates, as chiral auxiliary. Supports were characterized by a regular mesoporosity and a same initial pore diameter. Immobilization of the chiral aminoalcohol was performed through covalent anchoring of 3-halogenopropyltrimethoxysilane (XPTMS) and substitution of the halogen by (-)-ephedrine. Comparison of the efficiency of the catalysts was carried out. Results were analyzed taking into account the accessibility to the catalytic sites by changing their density (decrease of XPTMS concentration, spacing of the sites by alkyl goups) and the effect of the uncovered mineral surface on activities and enantioselectivities.

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Covalent immobilization of (1R,2S)-(−)-ephedrine, used as a model molecule of β-aminoalcohols, on the surface of MCM-41-type mesoporous aluminosilicates, performed by a new sol–gel method, leads to chiral auxiliaries which show greatly enhanced rates and ee's compared to those reported up to now in the enantioselective addition of diethylzinc to benzaldehyde.

Infrared spectroscopy of isocyanic acid generated insitu by the thermal decomposition of nitromethane provides an efficient and easy method to probe the basic strength of the surface of oxides. The frequencies of the adsorbed isocyanate species are directly correlated with the heats of adsorption of carbon dioxide determined by microcalorimetry.

The role of base catalysts (CsNaX zeolite, hydrotalcite, triethylamine and pyridine derivatives) upon the regioselectivity of the Pudovik reaction is studied. The unexpected synthesis of stable 1,2-dihydropyridine phosphonate derivatives via a one-pot addition reaction under mild conditions is described.

Chiral hybrid organic–inorganic materials were prepared by anchoring optically active β-aminoalcohols such as (−)-ephedrine on MCM-41 type silica as a member of micelle-templated silicas (MTS). Silylation of the surface was performed with halogenopropyltrimethoxysilane. Then, (−)-ephedrine was anchored through halogen substitution. These materials were used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc. This work deals with the study of the various factors such as accessibility to the catalytic sites and coverage of the inorganic surface, which affect their efficiency (activity, selectivity and enantioselectivity).

Cs(2)O in the supercages of Cs-impregnated X and Y zeolites attacks the siliceous portions of the lattice (siloxane bridges), with formation of (Si-O-Cs(+))(2) groups which allow the occlusion (reversible at high temperature) of CO in the sodalite units, as indicated by the formation of an IR band at 2150 cm(-1).

The activity of basic species generated in zeolite CsNaX or CsNaY by cesium acetate impregnation and calcination under a synthetic air flow has been investigated. The Knoevenagel condensation of benzaldehyde and ethylcyanoacetate was used as a model reaction. The evaluation of the number of basic sites was carried out by CO2 TPD. Correlations between initial rates and number of basic sites allowed the determination of the TOF for the modified zeolites. It depends mainly on the host zeolite composition. Moreover, activity varies strongly with crystallinity especially for zeolites Y at high loadings.

This paper reviews recent works on the design of immobilized transition-metal ligands on solid supports. After an overview of some results concerning ligand anchorage on polymeric supports and encapsulation of transition-metal complexes inside layered or zeolitic minerals, the grafting of ligands onto the silicic wall surface of micelle-templated silicas (MTS) is reported. MTS silicas featuring a regular mesoporous system of pore-monodispersed size and exhibiting larger pores than zeolites, provide a new opportunity to allow anchorage of organic moieties through the silanation procedure. Mn(III) Salpr and tSalpr complexes bound onto the MTS surface are active in epoxidation reaction using PhIO as oxygen donor. Anchorage of (1R,2S)-ephedrine has been also investigated with the aim to obtain benefit from the MTS structure effect. These new supported chiral catalysts are active in alkylation of benzaldehyde with diethylzinc although less enantioselective than the corresponding homogeneous catalyst. The effect of dispersion of active sites and of surface passivation has been investigated and discussed in terms of the nature of the support surface. (C) 1998 Elsevier Science S.A. All rights reserved.

This paper reviews recent works on the design of immobilized transition-metal ligands on solid supports. After an overview of some results concerning ligand anchorage on polymeric supports and encapsulation of transition-metal complexes inside layered or zeolitic minerals, the grafting of ligands onto the silicic wall surface of micelle-templated silicas (MTS) is reported. MTS silicas featuring a regular mesoporous system of pore-monodispersed size and exhibiting larger pores than zeolites, provide a new opportunity to allow anchorage of organic moieties through the silanation procedure. Mn(III) Salpr and tSalpr complexes bound onto the MTS surface are active in epoxidation reaction using PhIO as oxygen donor. Anchorage of (1R,2S)-ephedrine has been also investigated with the aim to obtain benefit from the MTS structure effect. These new supported chiral catalysts are active in alkylation of benzaldehyde with diethylzinc although less enantioselective than the corresponding homogeneous catalyst. The effect of dispersion of active sites and of surface passivation has been investigated and discussed in terms of the nature of the support surface.

The synthesis and characterization of a chiral amino-alcohol ((1R-2S)ephedrine) immobilized on MCM-41 type mesoporous silicas (MTS : Micelle Template Silicas) are described. The activity of these supported catalysts in the enantioselective addition of diethylzinc to benzaldehyde are reported, and compared with those obtained with the corresponding silica gel supported catalysts. The observed differences are discussed in terms of the nature of the grafting which depends on the support structure.

MCM-41 type silica surfaces were grafted with primary amino groups through silanation process. Tertiary amino groups covalently bound to the surface were prepared through displacement of previously anchored halogen atom by piperidine. The catalytic activities of the immobilized amino groups were studied in the Knoevenagel condensation of benzaldehyde with ethylcyanoacetate. The mechanism of the catalyst action is discussed