Structure and Kinetics of Oxidation of Amphiphilic Nickel(II) Pentaazamacrocycles by Peroxodisulfate and by a Nickel(III) Pendant-Arm Macrocycle

Three nickel(II) pentaazamacrocycles bearing pendant alkyl tails have been synthesized,and the crystal structure of one (bearing an octyl tail) is reported. The redox potentials of the complexes, for oxidation of the nickel(II) centre, is 0.72 V (versus S.H.E.) in all cases, indicating that the pendant alkyl tails have no effect on the redox site. The kinetics of oxidation of the complexes by peroxodisulfate, S₂O₈ ^2- and by aqua(5, 5, 7,12, 12, 14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato)nickel(III),Ni(hmca)(OH₂)]²⁺ have been studied. Oxidation by S₂O₈ ^2- occursby ion-pairing of the reactants, followed by electron transfer with concomitant peroxo bond fissure. Oxidation by Ni(hmca)(OH₂)]²⁺ occurs by an outer sphere electron transfer process. Redox kinetics at the nickel centre provides a probe for supramolecular interactions at the pendant tails in such complexes.