A Molecular Ce₂@<i>I</i>_<i>h</i>-C₈₀ SwitchUnprecedented Oxidative Pathway in Photoinduced Charge Transfer Reactivity

We report for the first time the versatile Ce2@Ih-C80 building block toward synthesizing a novel electron donor−acceptor conjugate, Ce2@Ih-C80-ZnP (1). A systematic investigation of the charge transfer chemistry documents a reductive charge transfer (i.e., formation of (Ce2@Ih-C80)•−-(ZnP)•+) in nonpolar media (i.e., toluene/THF), while an oxidative charge transfer (i.e., formation of (Ce2@Ih-C80)•+-(ZnP)•−) dominates in polar media (i.e., benzonitrile/DMF). Reduction of the [Ce2]6+ cluster, which is highly localized and collinearly arranged with respect to the quaternary bridge carbon, is sufficiently exothermic in all solvents. Notably weak is the electronic coupling between the [Ce2]6+ cluster and the electron-donating ZnP. The oxidation of C806− and the simultaneous reduction of ZnP, on the other hand, necessitate solvent stabilization. In such a case, the strongly exothermic (Ce2@Ih-C80)•−-(ZnP)•+ radical ion pair state formation is compensated within the framework of a nonadiabatic charge transfer by a C806−/ZnP electronic matrix element, as the sum of good overlap and short distance, that exceeds that for [Ce2]6+/ZnP.