Synthesis, characterization and use in enantioselective hydroformylation of (BINAPO)PtCl 2 (BINAPO=2-diphenylphosphino-2′-diphenylphosphinyl-1,1′-binaphthalene), the first chiral catalyst with an atropisomeric hemilabile P,O-heterodonor ligand

Abstract

Platinum(II) complexes with the axially chiral phosphinyl phosphine ( S)-BINAPO ( 1) have been prepared and their behaviour in solution has been studied by 31 P -NMR spectroscopy. Reaction of PtCl 2(PhCN) 2 with 1 in benzene leads to the isolation of a neutral complex, 4, which maintains the P,O-chelate coordination of the ligand even in solvents of low polarity. The hemilabile character of the ligand is apparent from the reactions with DMSO and with carbon monoxide which promote the cleavage of the chelate ring of 4 through displacement of the oxygenated arm. Insertion of tin(II) chloride into the Pt–Cl bond takes readily place at room temperature affording only one of the possible trichlorostannato derivatives ( 6) with complete selectivity. In the presence of SnCl 2, the platinum complex 4 originates a catalyst of remarkable regioselectivity which, in the hydroformylation of styrene, is able to produce in up to 30% e.e. the branched aldehyde as the prevalent product.