The synthesis and kinetics of isomerization and solvent exchange of the trans-Chloro(dimethyl sulfoxide)bis(ethylenediamine)cobalt(III) ion in dimethyl sulfoxide

Abstract

The synthesis and characterization of trans-[CO(en)₂(Me₂SO)Cl](ClO₄)₂ are described. Its rate of isomerization to the cis isomer has been measured in Me₂SO in the range 293-313 K: k_tc = 1.5₄ × 10^-3s^-1 at 298.2 K, ΔH^‡ = 105 kJ mol^-1, ΔS^‡ = 55 J mol^-1 K^-1. The solvent exchange rate has been measured by ¹H n.m.r. spectroscopy in (CD₃)₂SO at 308.2K: k_ex = k_tt+k_tc = 7.0xl0^-3 s^-1. These and other data show that trans-to-cis isomerization requires solvent exchange, each act of which leads to substantial rearrangement, c. 90% cis (308.2 K). Differences between non-aqueous and aqueous systems in the steric course of substitution are discussed.