[60]Fullerene–Metal Cluster Complexes: Understanding Novel η 1 and η 2[6:5] Bonding Modes of Metallofullerenes

We performed extensive density functional calculations on various metallofullerene complexes and their polyanions to gain insight into novel η 1 and η 2[6:5] metal (M)–C 60 bonding modes. For L n MC 60 (L = ligand), the η 1 mode is calculated to be the most stable, followed by η 2[6:5] and η 2[6:6] for –3 anions, in contrast to η 2[6:6] >> η 2[6:5] ≈ η 1 for neutral cases. This observation is responsible for the transformation from η 2[6:6] to η 1 for L n M 3 C 60 , such as [Os 3 (CO) 9 C 60 ], upon successive electron reductions. Our energy partitioning analysis (EPA) indicates that the π‐type character of η 2[6:6] is much larger than that of η 2[6:5] . An electron addition decreases the π‐type interaction of both the η 2[6:6] and η 2[6:5] modes by about 35 %, whereas it has little effect on σ‐type interactions. Because of the large proportion of π‐character in η 2[6:6] coordination, the stability of η 2[6:6] coordination decreases steeply as electron reductions continue. On the basis of the EPA results, we could explain why the reaction of [Os 3 (CO) 8 (CNR)(μ 3 ‐η 2[6:6] ,η 2[6:6] ,η 2[6:6] ‐C 60 )] (R = CH 2 Ph) with CNR (4e donor) produces [Os 3 (CO) 8 (CNR)(μ 3 ‐CNR)(μ 3 ‐η 1 ,η 2[6:5] ,η 1 ‐C 60 )]. The η 1 and η 2[6:5] bonding modes of M–C 60 are crucial to fully understand the bonding nature of M–C 60 bonds in exohedral metallofullerene complexes.