Catalyst design strategies for controlling reactions in microporous and mesoporous molecular-sieves

Catalytically active transition-metal ions in high oxidation states (Co-III, Mn-III. Fe-III), have been designed on high-area, molecular-sieve, aluminophosphate microporous solids for the aerobic oxyfunctionalisation of a variety of saturated hydrocarbons. Certain metal-substituted molecular-sieves permit only end-on approach of linear alkanes to the active centres, thereby favouring enhanced reactivity either at one or both of the terminal methyl groups. The size and shape of the pores of the solid molecular-sieve ensure that the oxidations, which proceed by a free-radical mechanism, take place in a highly shape-selective mariner in the restricted environment of the catalytically active sites. Anchored bimetallic nanoparticle catalysts display high activity for the low-temperature, selective hydrogenation of cyclic polyenes under solvent-free conditions, and chiral catalysts, derived from 1,1'-bisdiphenylphosphinoferrocene, and anchored within mesoporous silica, display a remarkable increase in both enantioselectivity, and activity, in the hydrogenation of E-alpha-phenyl cinnamic acid and ethyl nicotinate, when compared to an analogous homogeneous model compound. (C) 2002 Elsevier Science B.V. All rights reserved.