Photodriven dehalogenative homocoupling for the synthesis of bibenzyl promoted by frustrated Lewis pairs on boron-doped carbon nitride

Abstract

Dehalogenative homocoupling for bibenzyl synthesis in heterogeneous systems often requires metal co-catalysts that suffer from acid-induced deactivation, while homogeneous metal-free frustrated Lewis pairs (FLPs) offer alternative dehalogenation pathways; their recyclability remains challenging. To bridge this gap, we introduce dual defects via boron doping in carbon nitride to construct FLPs for efficient activation of C–X (X = Br, Cl) bond cleavage in benzyl halides to generate benzyl radicals and halogen atoms. Alcohols act as hydrogen donors, scavenging halogen atoms via hydrogen atom transfer (HAT) to form HX and alkoxy radicals, which subsequently regenerate through photocatalytic reduction. The mechanism suppresses side reactions (such as the etherification pathway) to achieve high selectivity for the homocoupling product. Mechanistic investigations verify both the activation effect of FLPs on dehalogenation and the transformation processes of reaction intermediates. The optimal photocatalyst (BCN-0.6) achieves broad substrate applicability with excellent yields (yield up to 91%) and maintains 95% activity over eight cycles. This work highlights the successful transplantation of homogeneous FLP chemistry into a heterogeneous platform for organic synthesis.