A Thienothiophene-Based Olefin-Linked Covalent Organic Framework for the Metal-Free Photocatalytic Oxidative Coupling of Amines

Abstract

The oxidative coupling of amines is a useful way to prepare many diverse compounds for the pharmaceutical and chemical industries. Covalent organic frameworks (COFs), a crystalline class of porous polymers, have emerged as promising heterogeneous photocatalysts that can accomplish this transformation under metal-free conditions due to their excellent photochemical stability and tunable electronic properties. Herein, we report the optoelectronic and photocatalytic properties of an olefin-linked COF containing thienothiophene (TT) and 2,4,6-trimethyl-1,3,5-triazine (TMT) units. The TT-TMT-COF exhibited a narrow band gap with extended light absorption and excellent charge separation, making it useful for the oxidative coupling of various benzylamines. The TT-TMT-COF exhibited fast reaction times, excellent recyclability, and conversions as high as ∼99%. The reactivity of TT-TMT-COF was on par or significantly better than that of a few small molecule 2,4,6-tris((E)-2-(thieno[3,2-b]thiophen-2-yl)vinyl)-1,3,5-triazine (TT-TMT) and 2,4,6-tris((E)-2-(thiophen-2-yl)vinyl)-1,3,5-triazine (Thio-TMT) homogeneous catalytic systems containing similar functional units. This work further highlights the ability of the COF to perform useful and efficient catalytic transformations in a sustainable manner.