Regioselective Coordination of Re₂(CO)₁₀ to Y@C_2v(9)‑C₈₂: An Unprecedented η¹ Complex Stabilized by Intramolecular Electron Transfer

The prototypical η¹-coordinated complexes of endohedral metallofullerenes (EMFs) have never been reported because of their low stability. Herein, we have developed a highly efficient radical-coupling strategy by performing a regioselective photochemical reaction of a rhenium complex (1) with the paramagnetic Y@C_2v(9)-C₈₂ to form an unprecedented η¹-coordinated complex with high stability: namely, Re­(CO)₅-η¹-Y@C_2v(9)-C₈₂ (2). X-ray results demonstrate that the rhenium moiety coordinates to a [5,6,6]-carbon atom on the cage via a single Re–C σ bond. Vis–NIR results suggest that 2 displays an absorption curve that is identical with the monoanion of metallofullerene [Y@C_2v(9)-C₈₂]⁻, confirming unambiguously that one electron is transferred from the rhenium center to Y@C_2v(9)-C₈₂. This is also confirmed by an ESR study showing the diamagnetic properties of 2. Surprisingly, our electrochemical results reveal that 2 possesses a redox behavior similar to that of pristine Y@C_2v(9)-C₈₂. Thus, we have presented a useful methodology for the synthesis of EMF-based molecular building blocks with the same electrochemical properties but different electronic configurations (e.g., open shell versus closed shell).