Reduction and Alkylation of Rhodium Porphyrins in Alcohol Solutions. Radiation Chemical and Photochemical Studies

Abstract

Radiolytic reduction of chlororhodium(III) tetramesitylporphyrin (ClRhIIIP) in alcohol solutions forms a transient RhIIP, which reacts to yield different products under different conditions. In alkaline 2-propanol the product is RhIP-, in weakly acidic conditions HRhIIIP is formed, and under strongly acidic conditions the main products of radiolysis are the alkylated rhodium complexes, R−RhIIIP. The latter products are formed by reaction of RhIIP with alkyl radicals (R•) that are produced in the irradiated solvent (R• = •CH3 and (CH3)2C•OH in 2-propanol). UV photolysis of ClRhIIIP in acetone/2-propanol solutions led to formation of HO(CH3)2C−RhIIIP. One-electron reduction of CH3−RhIIIP occurs at the porphyrin ligand to produce a transient π-radical anion, CH3−RhIIIP•-. In alkaline solution, this transient eliminates •CH3 to form the stable RhIP-, but in neutral or acidic solutions, it undergoes disproportionation, promoted by protonation on the macrocycle, to form CH3−RhIII−chlorin and then CH3−RhIII−isob...