Hydrazine as a Reducing Agent in Catalytic Transfer Hydrogenation Processes: Up-to-Date Overview Approaches

Abstract

Transfer hydrogenation serves as an alternative platform to promote facile organic transformation in a selective and clean manner, due to its atomic economy, high efficiency, and sustainability. Hydrazine hydrate is one of the common reducing agents used in the selective transfer hydrogenation/reduction methodologies. Our review offers an overview of hydrazine-mediated synthetic methodologies, catalytic processes, and mechanistic approaches in synthetic organic chemistry. Special emphasis is placed on the selective metal-catalyzed, organocatalytic, and metal-free transfer hydrogenation processes of important organic compound families including: i) nitro compounds, ii) alkenes, alkynes, iii) azides, iv) nitriles, and v) (α,β-unsaturated) carbonyl compounds. For this purpose, the diverse landscape of metal complexes, supported-metal catalysts, photocatalytic systems, and organocatalysts is comprehensively covered. Additionally, various mechanistic approaches to the hydrogen transfer process are highlighted, with a focus on the catalyst structure–activity relationship. This content aims to guide the scientific community in developing more efficient and selective catalytic systems for transfer hydrogenation processes and other (photo)redox organic transformations.