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

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 Pt^III binuclear complexes were formed in two steps (1 and 2). The observed pseudo first-order rate constants (k_obs1) for step 1 of the reactions of complexes 1 and 2 were linearly and quadratically dependent on the excess ligand concentration (C_L) at a given [H⁺], respectively. The rate constants for step 2 in both the reactions were independent of both C_L 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.