Carboranes as Lewis Acids: Tetrel Bonding in CB11H11 Carbonium Ylide

Abstract

High-level quantum-chemical computations (G4MP2) are carried out in the study of complexes featuring tetrel bonding between the carbon atom in the carbenoid CB11H11—obtained by hydride removal in the C-H bond of the known closo-monocarbadodecaborate anion CB11H12(−) and acting as Lewis acid (LA)—and Lewis bases (LB) of different type; the electron donor groups in the tetrel bond feature carbon, nitrogen, oxygen, fluorine, silicon, phosphorus, sulfur, and chlorine atomic centres in neutral molecules as well as anions H(−), OH(−), and F(−). The empty radial 2pr vacant orbital on the carbon centre in CB11H11, which corresponds to the LUMO, acts as a Lewis acid or electron attractor, as shown by the molecular electrostatic potential (MEP) and electron localization function (ELF). The thermochemistry and topological analysis of the complexes {CB11H11:LB} are comprehensively analysed and classified according to shared or closed-shell interactions. ELF analysis shows that the tetrel C⋯X bond ranges from very polarised bonds, as in H11B11C:F(−) to very weak interactions as in H11B11C⋯FH and H11B11C⋯O=C=O.