Mechanisms of thermal rearrangement of diarylbis(pyridine)platinum(II) complexes: Reductive carbon-carbon elimination versus hydrogen transfer

Article abstract of DOI:10.1021/om00102a003

Thermolytic behavior in solution of a series of complexes cis-(py)₂Pt(4-C₆H₄R)₂ (R = H, CMe₃, CF₃; py = pyridine) has been examined. When R = CMe₃, thermolytic rearrangement generates biaryl via unimolecular reductive elimination without prerequisite ligand dissociation. Arene elimination is an important, temperature-dependent, competitive reaction, which is suppressed by deuteriation of either aryl or pyridine ligands. Comparison with photolytic rearrangement of Hg(4-C₆H₄CMe₃)₂ indicates that Pt-C homolysis is not a significant contributor. A mechanism is indicated in which successive, reversible H transfers from pyridine and aryl ligands may occur, the latter resulting in a rare example of aryl group isomerization prior to elimination. For R = H, similar mechanistic competition is observed, but when R = CF₃, concerted mononuclear reductive elimination is the only significant pathway. Its activation parameters suggest conformational restriction in the transition state. Metallic Hg alters the rearrangement pattern but not by scavenging heterogeneous byproducts.