The Possible Aromatic Conjugation via the Different Edges of (Car)Borane Clusters: Can the Relationship Between 3D and 2D Aromatic Systems Be Reconciled?

The possible aromatic conjugation between 3D and 2D aromatic units is in the focus since the synthesis of benzocarborane. It has been showed that in the 3D aromatic icosahedral 1,2-dicarba-closo-dodecaborane systems fused with 2D aromatic rings a global 3D/2D aromaticity does not exist. Despite this fact during the last years several studies proposed interactions between 2D and 3D moieties. Herein, while tuning the size and the effective charge of the (car)borane systems, we demonstrate that global aromatic character can be excluded in any investigated cases, and the detectable conjugative properties can be explained the effect of the well-known negative hyperconjugation. The interaction between the 2D and 3D units in the (car)borane-fused 2D ring systems was investigated computationally. Although aromatic conjugation can be excluded, other factors, such as negative hyperconjugation and ring strain, play a crucial role in the overall stability of these systems and should be taken into account during their investigation. image