MCM‐41‐Anchored Ni (II) Schiff Base Complex: A Recyclable Catalyst for One‐Pot Multicomponent Synthesis of Tetrahydropyrazolopyridines

ABSTRACT Mesoporous MCM‐41 serves as an ideal support due to its large surface area, ordered pore structure, and thermal resilience. Nickel (II) stands out among transition metals for its abundance, low cost, and adaptable coordination chemistry, making it suitable for immobilization via Schiff base ligands to drive various organic transformations. Motivated by these factors, we prepared a novel MCM‐41‐supported Ni (II) Schiff base catalyst, designated as M41@CP@AnL@Ni ( 1 ). The catalyst 1 was characterized by various techniques and tested for the formation of tetrahydropyrazolopyridines. The synthesis of tetrahydropyrazolopyridines was carried out in a single vessel by combining ethyl acetoacetate, hydrazine hydrate, an aromatic aldehyde, and ammonium acetate under mild conditions. The catalyst 1 demonstrated good catalytic performance and selectivity, afforded product yields of up to 97%, especially with electron‐deficient aryl aldehydes under mild thermal conditions (80 °C). The insignificant metal leaching and the absence of any measurable decline in the activity underscore its operational robustness and superior applicability relative to conventional catalytic systems. A feasible reaction mechanism has been proposed. These findings, in conjunction with the catalyst's observed efficiency, provide strong experimental support for the proposed pathway and highlight the critical involvement of the Ni (II) active site throughout the catalytic cycle.