Nickel‐Catalyzed Hydrogenation and Dehydrogenation Processes: A Useful Tool in Organic Synthesis

Catalytic hydrogenation and dehydrogenation are fundamental transformations in organic synthesis, traditionally dominated by noble metals. In recent decades, nickel has emerged as a sustainable and cost‐effective alternative due to its rich redox chemistry, broad applicability, and catalytic efficiency. This review comprehensively summarizes the progress in nickel‐catalyzed hydrogenation and dehydrogenation reactions over the past three decades, emphasizing the evolution of catalyst design and mechanistic understanding as well. This review is structured into three major categories based on catalyst type: homogeneous, heterogeneous, and nanoparticle‐supported catalyst. Each section is further divided into direct hydrogenation, transfer hydrogenation, and dehydrogenation reactions, covering a wide range of substrates including alkynes, alkenes, carbonyl compounds, nitroarenes, amines, and alcohols. Structure–activity relationships, mechanistic pathways, and chemoselectivity trends are critically analyzed to provide insights into the role of nickel in these transformations. Challenges and future directions in developing next‐generation nickel catalysts for green and selective transformations are also outlined.