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 CuII 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 LCuII 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 CuI 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.