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 C2-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.

将1,2-双(二苯基膦)乙烷 (dppe)合铂(II)碳酸盐 [(dppe)PtCO₃] 与S-VANOL或S-VAPOL反应，可分别得到(dppe)Pt(S-VANOL)与(dppe)Pt(S-VAPOL)两种配合物。核磁共振(NMR)数据表明，前一配合物中的VANOL配体以C₂对称的O,O′配位模式与金属结合，而VAPOL配体则以C,O配位模式结合，该模式会部分破坏配体的芳香性。当使用(S,S)-手性双膦配体chiraphos合铂(II)碳酸盐 [(S,S-chiraphos)PtCO₃] 合成S-VANOL与S-VAPOL的匹配型配合物时，两种配合物均采取对称的O,O′配位模式。采用(R,R)-手性双膦配体chiraphos合铂(II)碳酸盐 [(R,R-chiraphos)PtCO₃] 制备的失配型配合物中，两种配体均采取C,O配位模式，但无法分离得到S-VANOL对应的配合物。针对(S,S)-手性双膦配体chiraphos合铂(II)阳离子 [(S,S-chiraphos)Pt²+] 开展的S-VANOL与S-VAPOL竞争配位实验显示，VANOL是热力学更具优势的配体。