Metal-free CO2 fixation: conversion of epoxides to cyclic carbonates by a highly efficient bifunctional boron-tethered N-heterocyclic nitrenium catalyst.

Abstract

The development of sustainable, metal-free catalytic platforms for the chemical fixation of carbon dioxide (CO₂) into value-added products remains a formidable challenge. Herein, we report the rational design of a highly efficient bifunctional organoboron catalyst, featuring a Lewis acidic boron center tethered to an N-heterocyclic nitrenium ion, for the solvent-free cycloaddition of CO₂ to epoxides. This system exhibits enhanced catalytic activity and recyclability, delivering a broad range of cyclic carbonates in excellent yields under neat conditions. Thorough mechanistic studies reveal the key transient intermediates in the reaction pathway. Notably, our catalyst demonstrates the highest activity among the metal-free systems reported to date for the coupling of CO₂ to propylene oxide under ambient conditions (TOF = 12.4 h^-1, 25 °C, 1 bar), establishing this organoboron framework as a remarkably robust and green catalyst.