A Cationic NHC‐Supported Borole

This work describes the synthesis and characterization of a highly reactive cationic borole. Halide abstraction with Li{Al[OC(CF(3))(3)](4)} from the NHC‐chloroborole adduct yields the first stable NHC‐supported 1‐((Me)NHC)‐2,5‐(SiMe(3))(2)‐3,4‐(Ph*)(2)‐borole cation. Electronically, it features both a five‐membered cyclic conjugated 4 π‐electron system and a cationic charge and thus resembles the yet elusive cyclopentadienyl cation. The borole cation was characterized crystallographically, spectroscopically (NMR, UV/Vis), by cyclovoltammetry, microanalysis and mass‐spectrometry and its electronic structure was probed computationally. The cation reacts with tolane and reversibly binds carbon monoxide. Direct comparison with the structurally related, yet neutral, 1‐mesityl borole reveals strong Lewis acidity, reduced HOMO–LUMO gaps, and increased anti‐aromatic character.