Redox-Active Carboranyl Diphosphine as an Electron and Proton Transfer Agent.

In this work, we report the first example of the PCET reactivity for a boron cluster compound, the zwitterionic -carboranyl diphosphonium derivative 7-P(H)Bu-10-P(H)Pr--CBH. This main-group reagent efficiently transfers two electrons and two protons to quinones to yield hydroquinones and regenerate a neutral -carboranyl diphosphine, 1-PBu-2-PPr--CBH. As we have previously reported the conversion of this -carboranyl diphosphine into the zwitterionic derivative upon reaction with main group hydrides, the transformation reported herein represents a complete synthetic cycle for the metal-free reduction of quinones, with the redox-active carboranyl diphosphine scaffold acting as a mediator. The proposed mechanism of this reduction, based on p determination, electrochemical studies, and kinetic isotope effect determination, involves the electron transfer from the - cluster to the quinone coupled with the delivery of protons.