Synthesis and characterization of chiral diphosphine platinum(II) VANOL and VAPOL complexes

Reaction of (dppe)PtCO3 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)PtCO3, both complexes adopt the symmetric O,O'-mode. Mismatched complexes with (R,R-chiraphos)-PtCO3 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)Pt2+ fragment indicate that VANOL is the thermodynamically preferred ligand.