Oxidation-Induced Nucleophilic Substitution at 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 impressively 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 reaction mechanism is oxidation-induced nucleophilic substitution. The hydride anion at the B(12) position is abstracted by oxoammonium oxidant with favorable energy (the ∆∆G^‡ was 4.2 kcal/mol favored to the meta-B–H bonds), 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.