Synthesis and Characterization of Chiral Diphosphine Platinum(II) VANOL and VAPOL Complexes

Reaction of (dppe)PtCO 3 with S -VANOL or S -VAPOL yielded (dppe)Pt( S -VANOL) and (dppe)Pt( S -VAPOL), respectively. NMR data indicate that the VANOL ligand in the former complex adopts a C 2 -symmetric O,O‘-bound form, while the VAPOL ligand binds to the metal in a C,O-binding mode that partially disrupts the ligand aromaticity. When matched complexes of S -VANOL and S -VAPOL were synthesized with ( S, S -chiraphos)PtCO 3, both complexes adopt the symmetric O,O‘-mode. Mismatched complexes with ( R, R -chiraphos)PtCO 3 have both ligands adopting the C,O-binding mode; however, the S -VANOL complex could not be isolated. Competition experiments between S -VANOL and S -VAPOL for the ( S, S -chiraphos)Pt 2+ fragment indicate that VANOL is the thermodynamically preferred ligand.