Synthesis of silica-supported chiral ferrocenylphosphine ligands and their application in some stereoselective reactions

Abstract

Synthesis of new BPPFA analogues, having exchanged one of the N-methyl groups for a long (–C₁₀H₂₀–) or short (–C₄H₈–) alkyl chain with a terminal methoxycarbonyl group, and their immobilization on silica are described. Immobilization resulted in considerable lowering of the reaction rates as well as stereoselectivity in hydrogenation reactions. On the other hand, both homogeneous 3a as well as immobilized ligand 6a with a longer spacer (–C₁₀H₂₀–) have activities and enantioselectivities in allylic nucleophilic substitution comparable to the known BPPFA ligand. This is true also for homogeneous ligand 3b with a shorter chain (–C₄H₈–), but its immobilization resulted in a big drop of activity as well as selectivity.