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 form ation of cationic complexes [(BINAPO)Rh(DIOL)](+) where the ligand (S)-BINA PO 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-cyclooctad iene) rhodium tetrafluoroborate (3b) and (S)2-diphenylphosphanyl-2'-dipheny lphosphin rhodium tetrafluoroborate (3c) with 1,5-cyclooctadiene (COD) and 2,5-nobornadiene (NBD) as the diolefin were isolated and characterized. Bot h show a fluxional behaviour in solution which is due to the mobility of th e diolefin rather than to a displacement-recombination of the oxygenated ar m of the ligand. The mobility of the 1,4-norbornadiene ligand in 3c is extr emely pronounced and the coordinated diolefin flexibility could be frozen o nly at about 200 K. These complexes are active but poorly stereoselective c atalysts for the hydrogenation, hydroboration, and hydroformylation of alke nes.