Mechanism of redox reactions between SO3 center dot- radicals and transition-metal macrocyclic complexes: Oxidative addition to the ligand and outer-sphere electron transfer

Reactions of SO3.- radicals with complexes of Ni(II and I) and Cu(II and I) were investigated under anaerobic conditions. Reactions of CuCR+, Cu(TIM)( +), and Ni(Me-6[14]dieneN(4))+ with SO3.- radicals were investigated by tim e-resolved spectroscopy. The kinetics of the processes is in accordance wit h an outer-sphere electron-transfer mechanism. Intermediates with a ligand- radical nature were observed in SO3.- reactions with Cu(2,9-dimethyl-1, 10- phenanthroline)(2)(+), Cu(Me-6[14]dieneN(4))(2+), NiCR2+, or NiCRH42+. Two products were isolated in the reaction of NiCR2+ with SO3.- radicals, one p roduct with a sulfonated macrocycle and the other product with one addition al double bond in the macrocycle. These products confirmed the attack of th e ligand by SO3.- radicals and the formation of intermediates with a ligand -radical nature. A mechanism based on the oxidative addition of SO3.- radic als to the ligand accounts also for the kinetics of product formation.