Bonding-regulated construction of covalent organic framework-supported frustrated Lewis pairs for 1,4-hydrosilylation of α,β-unsaturated ketones

Abstract

Developing recyclable metal-free catalysts to replace precious metals is a diligent goal, and covalent organic framework-supported frustrated Lewis pairs (COF-FLPs), as heterogeneous catalysts, show promise for this; yet their development is hindered by insufficient stable frameworks and suitable construction strategies. Herein, three COF-FLPs (NBDE-FLP, NBE-FLP and NBDE-QA-FLP) were successfully constructed by covalent, coordination or ionic bonding, respectively. All COF-FLPs exhibited high catalytic activity in the 1,4-hydrosilylation of α,β-unsaturated ketones, with fluoroarylborane covalently grafted NBDE-FLP/NBDE-QA-FLP showing better recyclability than coordinated NBE-FLP. Mechanistic studies revealed distinct catalytic pathways: NBDE-QA-FLP follows a rare B/I⁻ FLP-mediated enolate anion pathway; NBE-FLP uses a B/N FLP-enabled enolate anion pathway; while NBDE-FLP adopts a B/O FLP-driven allylic cation pathway. This means that the bonding regulation of COF-FLPs can not only improve the stability and activity of the catalysts but also regulate the types of acid–base pairs and catalytic pathways, which provide new insights for designing stable heterogeneous COF-FLPs.