BINAP-Ru and -Rh catalysts covalently immobilised on silica and their repeated application in asymmetric hydrogenation

We present the facile immobilization of a chiral diphosphine ligand, BINAP, on a silica (high pore vol., low surface area). The protected ligand has been immobilized as a phosphine oxide and deprotected on the surface to prevent side reactions of unprotected phosphines with surface silanol groups. The resulting diphosphine ligand on silica was converted to both rhodium and ruthenium complexes. The novel materials were characterised using solid-state IR-DRIFT and 29Si and 31P CP-MAS NMR techniques as well as elemental content measurements. Ruthenium and rhodium catalyzed asym. hydrogenation of various enamides, .beta.-keto-esters and arom. ketones is presented using immobilized BINAP ligands. The repeated use of the immobilized catalyst in five recycles demonstrates homogeneous' catalysis with heterogeneous' catalysts, thus reducing solvent waste, and loss of precious metal and or ligand.