Synthesis, Characterization and Catalytic Activity of Rh(I)-complexes with (S)-BINAPO, an Axially Chiral Inducer Capable of Hemilabile P,O-heterobidentate Coordination

The reaction of dinuclear rhodium(I) derivatives of the formula [Rh(DIOL)X]2 with the axially chiral phosphinyl phosphane 2-(diphenylphosphinyl)-2′-(diphenylphosphanyl)-1,1′-binaphthalene ((S)-BINAPO, 1) leads to the formation of cationic complexes [(BINAPO)Rh(DIOL)]+ where the ligand (S)-BINAPO consistently displays a P,O-chelate coordination which is mantained even in solvents of fair polarity. The mononuclear rhodium(I) complexes (S)-2-diphenylphosphanyl-2′-diphenylphosphinyl-1,1′-binaphthalene- (1,5-cyclooctadiene) rhodium tetrafluoroborate (3b) and (S)-2-diphenylphosphanyl-2′-diphenylphosphinyl-1,1′-binaphthalene- (1,4-norbornadiene) rhodium tetrafluoroborate (3c) with 1,5-cyclooctadiene (COD) and 2,5-norbornadiene (NBD) as the diolefin were isolated and characterized. Both show a fluxional behaviour in solution which is due to the mobility of the diolefin rather than to a displacement-recombination of the oxygenated arm of the ligand. The mobility of the 1,4-norbornadiene ligand in 3c is extremely pronounced and the coordinated diolefin flexibility could be frozen only at about 200 K. These complexes are active but poorly stereoselective catalysts for the hydrogenation, hydroboration, and hydroformylation of alkenes.