Radiolytic Reduction of Rhodium Porphyrins. Chain Reaction in Alkaline 2-Propanol

Rhodium(II) tetramesitylporphyrin (Rh{sup III}TMP) undergoes radiolytic reduction in deoxygenated alkaline alcohol solutions to produce a transient Rh{sup II}TMP and then a stable Rh{sup I}TMP. When the solvent was 2-PrOH and the KOH concentration was $$LS@0.02 mol L{sup -1}, the radiolytic yield of reduction was considerably higher than the total yield of reducing radicals, indicating a chain reaction. The chain propagation process is suggested to be a reaction of the intermediate Rh{sup II}TMP with the solvent and the base to yield Rh{sup I}TMP and an additional reducing radical, (CH{sub 3}){sub 2}CO{sup -}. No chain reaction was observed with $$LB@KOH$RB > 0.01 mol L{sup -1} or when the solvent was MeOH. With pyridine as an axial ligand, reduction occurs on the porphyrin ring to yield Rh{sup III}TMP{sup -}, which then yields the stable Rh{sup I}TMP. Further radiolytic reduction of Rh{sup I}TMP in 2-PrOH takes place at the porphyrin ring to yield the chlorin and more highly reduced products. 25 refs., 2 figs., 1 tab.