INFLUENCE OF SUBSTITUENTS AND LIGANDS OF VARIOUS COBALT(II) PORPHYRIN DERIVATIVES COORDINATELY BONDED TO SILICA ON THE OXIDATION OF MERCAPTAN

Cobalt(II) phthalocyanines with either electron-withdrawing or -donating substituents as well as cobalt(II) naphthalocyanine and cobalt(II) tetraphenylphorphyrin are coordinatively bonded to different types of modified silica. The catalytic activities in the oxidation of 2-mercaptoethanol of the different supported porphyrins are compared. The influence (i) of the substituents, correlating with their Hammett constants sigma(p), and (ii) of the ligand types, correlating with their HOMO-LUMO energy gap, are discussed on the basis of the metal LUMO orbital energy. A mechanism is proposed, considering that only one coordination site is offered by the catalyst for the mediation of the electron transfer between the reactants in the redox process. The fine structure of the UV-Vis spectra is referred to as Mie scattering.