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.碳硼烷（Carboranes）是一类独特的二十面体硼碳簇合物，其展现出优异的热稳定性、疏水性与生物惰性，使其在从药物递送至有机金属化学的诸多领域中都极具应用潜力。其脱氢衍生物邻碳硼烯（o-carborenes）作为多用途配体，可通过η1或η2配位模式与过渡金属结合，在早期及后期过渡金属中心均可形成结构明确的碳硼烷基/η2-邻碳硼烯配合物。传统上，过渡金属-配体相互作用以迪瓦尔-查特-邓坎森（Dewar–Chatt-Duncanson, DCD）模型进行阐释，而此前已有研究报道，芳炔（aryne）与C60配体存在兼具配位键与电子共享键（D + E）的相互作用模式。受此类研究先例的启发，本研究针对第X族过渡金属配合物TM–(η2-1,2-C2B10H10–nXn)（其中TM=镍（Ni）、钯（Pd）、铂（Pt）；n=0~2；X=碘（I）、溴（Br）、苯基（Ph））的成键情况展开研究，采用自然键轨道（Natural Bond Orbital, NBO）、量子理论原子分子（Quantum Theory of Atoms in Molecules, QTAIM）、电子定域化函数（Electron Localization Function, ELF）以及能量分解分析-自然价键轨道化学分析（Energy Decomposition Analysis-Natural Orbitals for Chemical Valence, EDA-NOCV）方法。研究结果表明，与遵循DCD模型的炔烃/芳炔类似物不同，邻碳硼烯配合物采用D+E成键范式：过渡金属片段以阳离子形式与带负电的邻碳硼烯片段相互作用，其稳定性主要源于静电相互作用，并辅以π电子共享作用。本研究凸显了邻碳硼烯独特的成键适配性，并确立了其作为超越经典模型范畴的电子柔性配体的地位。