An Overview on Transition Metal Catalyzed Ammonia Generation Through N─N Bond Cleavage of Hydrazine.

Transition metal-catalyzed cleavage of bonds is essential in catalytic transformations, particularly the activation of C─C, C─S, and C─N bonds, which have been widely examined in the literature. Despite its importance, the selective breakage of the N─N single bond of hydrazine and its derivatives to generate ammonia or amine-based derivatives, aided by a transition metal catalyst, stands out with a number of literatures at the present time. This 2e/2H process to generate ammonia from hydrazine through N─N bond cleavage is emerging as an attractive alternative to traditional nitrogen fixation methods. Transition metal catalysts are essential in promoting this transformation by selectively activating and cleaving the N─N bond of hydrazine through the disproportionation or reduction pathway, enabling efficient ammonia synthesis under mild circumstances. This review provides a comprehensive investigation of transition metal-catalyzed ammonia formation from hydrazine, focusing on the N─N bond cleavage, the specific ligand designs, the role of the metal center, and the associated mechanistic pathways.