Kinetics of the displacement of cyclobutane-1,1-dicarboxylate from diammine(cyclobutane-1,1-dicarboxylato)platinum(II) in aqueous solution

Abstract

The displacement of 1,1-cyclobutanedicarboxylate (cbdca^2–) from [Pt(NH₃)₂(cbdca)] has been studied in aqueous solution. In the presence of acid the process resembles the successive displacement of two monodentate carboxylates. The first (ring-opening) stage follows the rate law k_obs.=(k₀+k₁k₀[H⁺])(1 +k₀[H⁺])^–1, k₀= 8 × 10^–5 s^–1, K₀= 0.6 dm³ mol^–1, k₁= 8.0 × 10^–4 s^–1 at 25 °C, while the second follows the simple relationship k_obs.=k[H⁺], k= 1.61 × 10^–4 dm³ mol^–1 s^–1 at 25 °C. In the absence of acid and other nucleophiles the complex is inert and in the presence of chloride the displacement of ligand follows a first-order dependence on [Cl^–], k_obs.=k_Cl[Cl^–]. At 80 °C, k_Cl= 1.32 × 10^–4 dm³ mol^–1 s^–1. The chelate differs from the bis-monodentate carboxylate species in the great importance of the reverse, ring-closing process, which can be prevented in the presence of acid.