Axial Substitution Reaction of Substituted Pyridine on Chloro(5,10,15,20-tetraphenylporphinato)chromium(III) in Toluene with Special Reference to the Substituent Effect

Abstract

Equilibria and kinetics for the axial substitution reaction of pyridine and substituted pyridines (L) coordinated to chloro(5,10,15,20-tetraphenylporphinato)chromium(III) [Cr(tpp)(Cl)] by 1-methylimidazole as an entering ligand in toluene have been studied spectrophotometrically. Equilibrium constants, rate constants, and activation parameters for the substitution of L from the six-coordinated [Cr(tpp)(Cl)(L)] complex have been obtained. It has been demonstrated that equilibrium constants of the substitution reaction depend on the basicity of the axial ligands and that a good linear relationship between the activation parameters and the basicity of L is in accord with the reaction mechanism with a limiting dissociative activation mode.