Thermically and electrochemically induced isomerization of a (Bis(ferrocene)-cyclam)copper(II) complex

The new bis(ferrocene)-cyclam macrocycle 1,8-bis(ferrocenylmethyl)-1,4,8,11-tetraazacyclotetradecane, denoted L, has been synthesized. Two Cull complexes with L have been isolated and characterized from X-ray structure determination and electrochemical studies. These two LCuII 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 I-Cull 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 LCuII 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 LNiII complex was also isolated and characterized by X-ray diffraction analysis and from electrochemical studies.