Metallaphotocatalytic Amination of Aryl Chlorides Enabled by Highly Crystalline Acetylene-Based Hydrazone-linked Covalent Organic Frameworks

Abstract

Amination of aryl chlorides by metallaphotocatalysis is highly desired but remained practically challenging. Meanwhile, relying on soluble noble-metal photocatalysts suffers from resource scarcity and structural instability which limit their practical application. Here in, a highly crystalline acetylene-based hydrazone-linked BTH-THFEB COF is reported that enable metallaphotocatalytic amination of aryl chlorides. The non-planar effect of hydrazone linkage and weak interlayer attraction of acetylene bond were minimized by intralayer hydrogen-bonding. As a result, the COF showed not only an improved crystallinity and porosity, but also enhanced optical and electronic properties compared to a COF analogue without hydrogen-bonding. Notably, dual BTH-THFEB/Ni system afforded C─N coupling products from broad aryl chloride substrates in excellent yields (up to 99%) and good functional tolerance. Furthermore, BTH-THFEB is recoverable and reusable for five times photocatalysis cycles. This report demonstrates simple approach to tune the structure-activity relationship in COFs at molecular level.