Interaction of η2‑C2B10H10 and Its Derivatives with Group‑X Transition Metals: A Theoretical Study Using DFT

Carboranes, a unique class of icosahedral boron–carbon clusters, exhibit remarkable thermal stability, hydrophobicity, and bioinertness, making them attractive in diverse applications from drug delivery to organometallic chemistry. Their dehydrogenated derivatives, o-carborenes, serve as versatile ligands, binding transition metals in η1 or η2 modes, giving rise to well-defined carboranyl/η2-carborene complexes across early and late metals. While transition-metal–ligand interactions are traditionally described by the Dewar–Chatt–Duncanson (DCD) model, deviations involving combined dative and electron-sharing (D + E) interactions have been reported for aryne and C60 ligands. Motivated by these precedents, we investigate the bonding in Group X transition metal complexes, TM–(η2-1,2-C2B10H10–nXn) (TM = Ni, Pd, Pt; n = 0–2; X = I, Br, Ph), using NBO, QTAIM, ELF, and EDA-NOCV analyses. These studies reveal that, unlike alkyne/aryne analogues adhering to the DCD model, the o-carborene complexes adopt the D + E bonding paradigm, where TM fragments interact as a cationic fragment with an anionic o-carborene fragment, stabilized by dominant electrostatic contributions complemented by π-sharing. This work highlights the distinctive bonding adaptability of o-carborenes and establishes their role as electronically flexible ligands beyond the scope of classical models.