Synthesis and incorporation of 4-triethoxysilyl-1,2-bis(diphenylphosphino)benzene into silica gel and solgel polymers: Preparation and utilization of recyclable catalysts for alkene hydroformylation and methanol homologation

A chelating phosphine monomer, 4-triethoxysilyl-1,2-bis(diphenylphosphino)benzene ( 9 ), was prepared in three steps from 2,4-dibromoiodobenzene. Attachment of 9 to the surface of commercial silica gel, followed by chelation of rhodium, gave a catalyst which showed both undiminished activity (turnover rates of 90 atom^?1 h^?1) and no loss of rhodium over five recycles in the hydroformylation of styrene. Complexation of cobalt afforded a catalyst for the homologation of methanol. Monomer 9 could be incorporated into a solgel polymer produced from silicic acid in tetrahydrofuran, but low rhodium uptake and low catalytic activity suggested that few phosphine sites were available to the rhodium. The catalytically-active species were modeled by the synthesis of cobalt and rhodium complexes containing 1,2-bis(diphenylphosphino)benzene.