Oxidation-induced nucleophilic substitution at the electron-rich B(12) vertex in [CB11H12]− under catalyst-free conditions†

Abstract

Highly regioselective B(12) substitutions of the monocarborane anion [CB₁₁H₁₂]⁻ has been a challenge. Here, we synthesized a stable B–O–N zwitterionic compound with an impressive yield (isolated yield up to 98%) and excellent regioselectivity at the B(12) position under catalyst-free conditions. The kinetics, substituent effect, and capture experiments are paired with theoretical calculations, showing that the reaction mechanism is oxidation-induced nucleophilic substitution. The hydride anion at the B(12) position is abstracted by an oxoammonium oxidant with lower cleavage energy of 4.2 kcal mol⁻¹ than B(7–11) positions, thereby changing the electronegativity upon the conversion of [CB₁₁H₁₂]⁻ to neutral [CB₁₁H₁₁], in turn giving very high regioselectivity for nucleophilic substitution. This work presents an effective method for synthesizing B(12) oxygen derivatives of the [CB₁₁H₁₂]⁻ anion.