Photocatalytic Transfer Hydrogenation of Nitriles to Primary Amines over a Pd Nanocube-Modified Poly(heptazine imide) Catalyst

Abstract

Hydrogenation reactions are integral to the fine chemical, pharmaceutical, and petrochemical industries. However, achieving efficient and selective hydrogenation under mild conditions without stoichiometric reductants or high-pressure hydrogen remains a significant challenge. While photocatalytic transfer hydrogenation offers a sustainable alternative, its application has been largely restricted to the reduction of C=C, C≡C, and C=O bonds. In this work, we expand the scope of this strategy to nitrile groups (C≡N) by developing a novel catalyst (C-Pd-PHI) based on palladium cubic nanoparticles supported on poly(heptazine imide). The experimental results indicate that the Pd nanocubes primarily expose the (100) crystal facets and exhibit a strong interaction with the PHI support, which facilitates the formation of Pd–H species through protonation. Concurrently, the relatively weak binding affinity of the Pd nanocubes toward hydrogen intermediates promotes the desorption and release of hydrogen gas, which effectively suppresses over-hydrogenation reactions. Given the aforementioned properties, with 2-(3-chloro-5-(trifluoromethyl)pyridin-2-yl)acetonitrile employed as the model substrate, the C-Pd-PHI exhibits a substrate conversion efficiency of 73% and a target amine selectivity of 79% under visible light irradiation. Notably, after undergoing five consecutive catalytic cycles, the selectivity of the target amine remains stable at 75%. This work underscores the critical role of nanocrystal facet engineering in photocatalyst design and provides new ideas for sustainable transfer hydrogenation reactions.