KINETICS OF SULFOXIDE DISPLACEMENT BY 2,2'-BIPYRIDINE IN CIS-DIPHENYL, DIMETHYL AND DICHLORO-BIS(DIMETHYL SULFOXIDE)PLATINUM(II) IN ACETONITRILE

The kinetics of the reaction cis-[PtR2(Me2SO)2] + bpy --> [PtR2(bpy)] + 2Me2SO (R = CH3, C6H6; bpy = 2.2'-bipyridine) have been studied in the coordinating solvent acetonitrile, where sulfoxide complexes are in equilibrium with the solvento species cis-[PtR2(Me2SO)(CH3CN)]. Rate data obey the relationship k(obs) = k1k3[L-L]/k'-1 + k-1[Me2SO] + k3[L-L] which implies that both starting materials and their solvato counterparts in equilibrium generate, in a dissociative way, a common intermediate [R2Pt(Me2SO)] at a similar rate. The relative efficiency of three different nucleophiles bpy, Me2SO and CH3CN in capturing the reactive species [R2Pt(Me2SO)] shows that the latter maintains a reasonable discriminating ability also in CH3CN. In contrast, cis-[Pt(Me2SO)Cl2] does not undergo any solvolysis in CH3CN and, in its reaction with chelating bpy, substitutes both sulfoxides in the usual associative mode of activation.