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

Area of Science:

• Organometallic Chemistry
• Boron Cluster Chemistry
• Redox Catalysis

Background:

• Proton-Coupled Electron Transfer (PCET) is crucial in chemical reductions.
• Metal-free catalytic systems are highly sought after for sustainable chemistry.
• Boron clusters offer unique electronic properties for redox activity.

Purpose of the Study:

• To report the first example of PCET reactivity in a boron cluster compound.
• To demonstrate a complete metal-free synthetic cycle for quinone reduction.
• To investigate the mechanism of quinone reduction mediated by a carboranyl diphosphine.

Main Methods:

• Synthesis and characterization of a zwitterionic nido-carboranyl diphosphonium derivative.
• Electrochemical studies to probe redox potentials.
• pKa determination and kinetic isotope effect studies to elucidate the reaction mechanism.

Main Results:

• The zwitterionic nido-carboranyl diphosphonium compound efficiently reduces quinones to hydroquinones via PCET.
• The reaction regenerates a neutral closo-carboranyl diphosphine, completing a catalytic cycle.
• The mechanism involves coupled electron transfer from the boron cluster and proton delivery.

Conclusions:

• A novel boron cluster compound exhibits efficient PCET reactivity for quinone reduction.
• This work establishes a complete metal-free synthetic cycle using a redox-active carboranyl diphosphine scaffold.
• The findings open new avenues for designing metal-free catalysts based on boron clusters.