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

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Abstract
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.