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: ktc = 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: kex = ktt+ktc = 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.