Axial ligand effect on the reaction mechanism of head-to-head pivalamidato-bridged Pt(III) binuclear complex containing an equatorial bromide ligand with acetone

Abstract

The axial ligand substitution reactions of head-to-head (HH) pivalamidato-bridged platinum(III) binuclear complexes containing equatorial Br− ligands, ([(H2O)(NH3)2Pt(μ-pivalamidato)2Pt(Br)2(OH2)]2+ (complex 1) and [(Br)(NH3)2Pt(μ-pivalamidato)2Pt(Br)2(Br)] (complex 2)) with acetone were kinetically investigated in acidic aqueous solutions. Both the complexes reacted with acetone slowly and acetonyl PtIII binuclear complexes were formed in two steps (1 and 2). The observed pseudo first-order rate constants (kobs1) for step 1 of the reactions of complexes 1 and 2 were linearly and quadratically dependent on the excess ligand concentration (CL) at a given [H+], respectively. The rate constants for step 2 in both the reactions were independent of both CL and [H+]. A reaction mechanism involving an intermediate with one π-coordinated acetone molecule was proposed for complex 1, which is similar to those proposed previously for the reactions of HH tetraammine amidato-bridged diplatinum(III) complexes with acetone. In contrast, a reaction mechanism involving an intermediate with two π-coordinated acetone molecules on the axial sites was proposed for complex 2.