AXIAL SUBSTITUTION-REACTION OF SUBSTITUTED PYRIDINE ON ORO(5,10,15,20-TETRAPHENYLPORPHINATO)CHROMIUM(III) IN TOLUENE WITH SPECIAL REFERENCETO THE SUBSTITUENT EFFECT

Equilibria and kinetics for the axial substitution reaction of pyridin e and substituted pyridines (L) co-ordinated to oro(5,10,15,20-tetraph enylporphinato)chromium(III) [Cr(tpp)(Cl)] by 1-methylimidazole as an entering ligand in toluene have been studied spectrophotometrically. E quilibrium constants, rate constants, and activation parameters for th e substitution of L from the six-coordinated [Cr(tpp)(Cl)(L)] complex have been obtained. It has been demonstrated that equilibrium constant s of the substitution reaction depend on the basicity of the axial lig ands and that a good linear relationship between the activation parame ters and the basicity of L is in accord with the reaction mechanism wi th a limiting dissociative activation mode.