Bonding-Regulated Construction of Covalent Organic Framework-Supported Frustrated Lewis Pairs for 1,4-Hydrosilylation of α,β-Unsaturated Ketone

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 showed 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. It means that the bonding-regulated 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 provides new insights for designing stable heterogeneous COF-FLPs.