Thermically and Electrochemically Induced Isomerization of a (Bis(ferrocene)−cyclam)copper(II) Complex

Abstract

The new bis(ferrocene)−cyclam macrocycle 1,8-bis(ferrocenylmethyl)-1,4,8,11-tetraazacyclotetradecane, denoted L, has been synthesized. Two Cu^II complexes with L have been isolated and characterized from X-ray structure determination and electrochemical studies. These two LCu^II complexes correspond to the type I (ferrocenyl subunits in the same side of the cyclam plane) and type III (ferrocenyl subunits above and below the cyclam plane) isomers. The type I LCu^II complex was synthesized from L and a Cu²⁺ salt, while the type III isomer was obtained by oxidation in air or by comproportionation of the Cu^I complex. The interconversion between type I and type III LCu^II complexes is negligible in acetonitrile and slow in dimethyl sulfoxide but fast via an electrochemical reduction−reoxidation cycle. According to UV−vis and electrochemical characterizations, the type III isomer is thermodynamically more stable and the type I isomer is kinetically favored. A type III LNi^II complex was also isolated and characterized by X-ray diffraction analysis and from electrochemical studies.