Probing Transition Metal–Fullerene Bonds: EDA–NOCV Analyses

Understanding the bonding interactions between transition metals (TM) and fullerenes (C60) is crucial for advancing materials science and catalysis. Herein, we conducted an in-depth analysis using natural bond orbital (NBO) and energy decomposition analysis–natural orbital for chemical valence (EDA–NOCV) at the BP86-D3(BJ)/TZP level of theory. We investigated complexes of Ta, Mo, Fe, Co, Ir, Ni, Pd, and Pt with fullerene, exploring bonding scenarios across different electronic states. Results revealed distinct bonding preferences between distinct TM–(η2-C60) complexes. Interestingly, four out of ten (4/10) (TM = Fe, Ir, Pd, and Pt) exhibited dative interactions akin to the Dewar–Chatt–Duncanson (DCD) model, which is followed by TM–olefin complexes, whereas others showed a deviation from the DCD model trend. They show mixed interaction with a dative σ bond from LTM+ ← (η2-C60)− and a π e-sharing bond as LM+ ↔ (η2-C60)− (D + E bonding) in their charged fragments. 1-Ta and 6-Ni favor both the bonding models with minimal ΔEorb difference. The NOCV results showed π backdonation (50%–70%) and π e-sharing (54.2%–63.8%) dominated over σ donation. Paramagnetic 4a-Co and 4b-Co displayed triplet cobalt and doublet fullerene bonding, aligned with spin density distributions. These insights improve our understanding of bonding behavior to enable targeted design strategies in catalysis and materials science.