Transmetalation of arylpalladium and platinum complexes. Mechanism and factors to control the reaction

This article reviews recent studies on intra- and intermolecular transfer of the aryl ligand bonded to Pd(II) and Pt(II). Cationic arylpalladium complexes with bpy and THF ligands undergo intermolecular aryl group transfer to produce biaryl via a diarylpalladium intermediate. This reaction is applied to cyclization of cationic dinuclear arylpalladium complexes, affording the crown ether derivative with biphenylene units. Analogous arylplatinum complexes do not form diaryl complexes via transmetalation, while they react with CO and phenylallene to cause replacement of the coordinated solvent and insertion of the small molecules into the Pt–C bond, respectively. Conproportionation of PtCl2(cod) and PtPh2(cod) produces PtCl(Ph)(cod), which is induced by dissociation of a Cl ligand from the former complex. PtCl2(cod) reacts also with diarylplatinum complexes with bpy and dppe. Disproportionation of PtPh(CH2COMe)(cod) and conproportionation of PtPh2(cod) and Pt(CH2COMe)2(cod) take place at 50 °C, but the rates of apparently reversible reactions differ from each other. Addition of OH− to a solution of PtI(Ph)(cod) causes intermolecular phenyl ligand transfer to produce PtPh2(cod). The dinuclear intermediate complex with bridging OH ligand is prepared from an independent route and fully characterized. The complex causes transmetalation of aryl group of aryl boronic acid.