Modulating β‐Keto‐enamine‐Based Covalent Organic Frameworks for Photocatalytic Atom‐Transfer Radical Addition Reaction

The atom‐transfer radical addition (ATRA) reaction simultaneously forges carbon‐carbon and carbon‐halogen bonds. However, frequently‐used photosensitizers such as precious transition metal complexes, or organic dyes have limitations in terms of their potential toxicity and recyclability. Three β‐ketoenamine‐linked covalent organic frameworks (COFs) from 1,3,5‐triformylphloroglucinol and 1,4‐phenylenediamines with variable transient photocurrent and photocatalytic activity have been prepared. A COF bearing electron‐deficient Cl atoms displayed the highest photocatalytic activity toward the ATRA reaction of polyhalogenated alkanes to give halogenated olefins under visible light at room temperature. This heterogeneous photocatalyst exhibited good functional group tolerance and could be recycled without significant loss of activity. Atom‐transfer radical addition reactions have been achieved by using covalent organic frameworks as visible‐light photoredox catalysts without the need for transition metals, sacrificial agents, or base. Simple modification of the monomers enables the photocatalytic activity to be tuned.