ELECTROCHEMICAL MONITORING OF VALENCE-BOND ISOMERS INTERCONVERSION INBIPYRIDYL-C-61(PERPENDICULAR-TO) ANIONS

Electrochemical, quantum chemical, and spectroscopic techniques are us ed to study the dynamics of the reduction of bpy-C-61. A thorough inve stigation of the temperature and scan rate dependence of the cyclic vo ltammetry peaks coupled with numerical simulations clearly reveals tha t the trianion and the tetraanion undergo two chemical reactions accor ding to the same parallel ECE mechanism. Quantum chemical calculations show that three isomers are quasi equienergetic in the charged states and support the hypothesis that triply and quadruply reduced bpy-C-61 undergoes facile conversion among three of its structural isomers, i. e., [5,6]-closed bpy-C-61, [5,6]-open bpy-C-61, and [6,6]-closed bpy-C -61. Substituent and/or solvent effects may effectively reverse the ro les of [5,6]-closed bpy-C-61 and [6,6]-closed bpy-C-61. As for [5,6]-c losed isomer, it is the first time that its existence is proposed on t he basis of the observation of a redox process. The six reduction peak s of C-60 have been observed for the first time in a pure solvent (THF , -60 degrees C), and the cyclic voltammetry peaks of the fullerene mo iety and the bpy fragment have been assigned.