Harnessing a Nickel-Immobilized Nitrogen-Rich Covalent Organic Polymer for Nitroarene Hydrogenation and Hantzsch Condensation

Nitrogen-rich covalent organic polymers are attractive supports for stabilizing metal nanoparticles (NPs) owing to their high surface area, tunable porosity, and abundant coordination sites. Herein, a triazine-based covalent organic polymer, named CPMP, was developed for immobilizing Ni NPs, affording a mesoporous hybrid material, Ni@CPMP, which showed efficient activity for the aqueous NaBH 4 -mediated hydrogenation of nitroarenes, with rapid reduction of 4-NP and 2-NA giving apparent rate constants of 2.0 × 10 –2 s –1 and 1.40 × 10 –2 s –1, respectively. Kinetic studies suggested that the reaction follows a Langmuir–Hinshelwood pathway involving surface adsorption of both nitroarene and hydride species. The catalyst exhibited high chemoselectivity and wide functional group tolerance, enabling synthesis of value-added amines as well as gram-scale synthesis of pharmaceutically relevant compounds. Beyond this, Ni@CPMP also demonstrated catalytic efficiency in the solvent-free Hantzsch multicomponent condensation for the synthesis of polyhydroquinoline derivatives in excellent yields, with structural confirmation by single-crystal X-ray diffraction (SCXRD) analysis. The enhanced catalytic performance is attributed to the uniform dispersion of Ni NPs within the polymer matrix, which improves active-site accessibility, substrate adsorption, and catalyst stability. The catalyst also demonstrated recyclability over multiple cycles. In addition, green metrics highlights the sustainability of both catalyst synthesis and catalytic process. This work establishes Ni@CPMP as a sustainable and multifunctional polymer-supported catalyst for pollutant reduction and heterocyclic synthesis.