Proton Reduction Catalyst-Grafted Covalent Organic Frameworks for Visible-Light-Driven Acceptorless Dehydrogenation of Cyclic Amines

The development of sustainable, noble-metal-free photocatalytic systems for acceptorless dehydrogenation (ADH) of cyclic amines remains a significant challenge. Herein, we report a novel heterogeneous photocatalyst constructed by covalently grafting a cobaloxime-based proton reduction catalyst onto a photosensitive covalent organic framework (PT-COF). The tailored PT-COF scaffold, featuring a donor–acceptor architecture and uncondensed amino groups, serves as both an efficient visible-light harvester and a porous support for cobalt active sites. The resulting Co-PT-COF hybrid exhibits excellent photocatalytic activity for the ADH of a wide range of cyclic amines, affording the corresponding N-heteroarenes in 62–95% yields under an Ar atmosphere at 28 °C with blue LED irradiation for 12 h in water. Notably, the catalyst demonstrates outstanding recyclability over five consecutive cycles with minimal loss of activity or cobalt leaching. Comprehensive photoelectrochemical and spectroscopic studies reveal that enhanced charge separation and efficient electron transfer from the photoexcited COF to the cobalt centers underpin the superior performance. Mechanistic investigations, including in situ EPR spectroscopy, confirm the involvement of α-amino radical intermediates in the catalytic cycle. This work establishes a sustainable platform for solar-driven dehydrogenation chemistry and provides a versatile blueprint for integrating molecular catalysts with photoactive frameworks.