Gao Yanhong, Szathmári Balázs, Buzsáki Dániel, Kelemen Zsolt
Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest, H-1111, Hungary.
HUN-REN Wigner Research Centre for Physics, P.O. Box 49, Budapest, H-1525, Hungary.
Chemistry. 2025 Jul 22;31(41):e202501806. doi: 10.1002/chem.202501806. Epub 2025 Jun 27.
Over the past few decades, considerable attention has been devoted to explore the electronic interactions of various substituents with 3D aromatic carboranes. In the case of substituents possessing available p-orbitals, conjugation between the π-system and the σ-framework of the carborane is possible via negative hyperconjugation, where electron density from a filled π-orbital overlaps with an adjacent σ* orbital. However, this is inherently a local effect, which was further bolstered by the fact that aromatic conjugation between planar (2D) π-systems and the 3D aromatic carborane cage does not exist. Nevertheless, recent studies have raised the intriguing possibility that 3D aromatic carboranes may function as σ-conjugated bridges, enabling electronic communication between spatially separated π-systems. Herein, we investigated the potential conjugation of various substituents with or through carborane systems to better understand the nature of the possible interaction. We demonstrated that significant delocalization through the carborane cluster can be achieved only in the case of radical systems; however, this type of interaction is not a unique feature of carboranes, as similar behavior can also be observed in saturated hydrocarbons.
在过去几十年里，人们投入了大量精力来探索各种取代基与三维芳香碳硼烷的电子相互作用。对于具有可用p轨道的取代基而言，通过负超共轭作用，碳硼烷的π体系与σ骨架之间有可能发生共轭，即填充的π轨道中的电子密度与相邻的σ*轨道重叠。然而，这本质上是一种局部效应，而且平面（二维）π体系与三维芳香碳硼烷笼之间不存在芳香共轭这一事实进一步强化了这一点。尽管如此，最近的研究提出了一个有趣的可能性，即三维芳香碳硼烷可能充当σ共轭桥，实现空间分离的π体系之间的电子通信。在此，我们研究了各种取代基与碳硼烷体系或通过碳硼烷体系发生共轭的可能性，以更好地理解可能存在的相互作用的本质。我们证明，只有在自由基体系中才能通过碳硼烷簇实现显著的离域；然而，这种相互作用并非碳硼烷所独有，因为在饱和烃中也能观察到类似的行为。
