Immobilization of rhodium complexes in chiral organic-inorganic hybrid materials

Two new alkoxysilylated derivatives of (-)-(1R,2R)-1,2-diaminocyclo-hexane: M = N-[(triethoxysilyl) propyl] - (-)- (1R, 2R)-1,2-diaminocyclohexane and B = N,N'-bis [(triethoxysilyl)propyl]-(-)-(1R,2R)-1,2-diaminocyclohexane h ave been synthesized. Their complexation with [Rh(cod)Cl](2) in the presenc e of TEOS = Si(OEt)(4), followed by sol-gel hydrolysis-condensation, afford ed new catalytic chiral hybrid materials. Evidence for the presence of the organic moieties complexed by rhodium in these solids was obtained by UV-vi sible spectroscopy, FT-IR studies, solid state C-13 and Si-29 CP-MAS NMR an alysis, energy-dispersive X-ray (EDX) techniques, and elemental analysis. T he nitrogen sorption studies and BET analyses ranged these solid gels from nonporous to highly porous materials. The catalytic activities and selectiv ities of the solid materials have been studied in the asymmetric hydrogen-t ransfer reduction of prochiral ketones and compared to that of the homogene ous rhodium complexes of the ligands M and B. The hybrid materials appeared interesting supports for enantioselective heterogeneous catalysis leading to chiral alcohols with ee up to 58% in the reduction of acetophenone and u p to 98% in the case of the more hindered related ketones. The catalytic pr operties as a function of the nature of chiral hybrid solid are discussed. (C) 2000 Wiley-Liss, Inc.