Binuclear Cobalt Complex‐Catalyzed Dehydrogenation of Ammonia Borane and Transfer Hydrogenation of Alkenes, Carbonyls and Nitriles: High Efficiency under Mild Conditions

Comprehensive Summary The development of efficient and sustainable catalytic systems based on earth‐abundant metals for hydrogen storage and green organic synthesis represents a significant and urgent challenge. While ammonia borane (AB) is a promising hydrogen carrier, its catalytic dehydrogenation and subsequent transfer hydrogenation have predominantly relied on precious‐metal catalysts, and existing cobalt‐based systems often lack the combination of ultrahigh activity and broad utility. Addressing this gap, this work introduces a well‐defined macrocyclic bispyridyldiimine‐supported binuclear cobalt complex that serves as a highly efficient catalyst for both AB dehydrogenation, achieving high H₂ release and a wide range of AB‐mediated transfer hydrogenation reactions under mild conditions. The system demonstrates exceptional performance by facilitating the reduction of diverse substrates—including alkenes, indoles, nitriles, and carbonyl compounds—in high yields. Its unprecedented activity is highlighted by the transfer hydrogenation of olefins at an ultralow catalyst loading of just 0.01 mol%, and its capability to hydrogenate challenging substrates like indoles at room temperature, overcoming the need for traditional harsh conditions. A key mechanistic insight is the distinct bimetallic advantage: the corresponding mononuclear cobalt complex is catalytically inactive under identical conditions, underscoring that the superior activity arises from the synergistic binuclear structure. These findings establish synergistic binuclear cobalt catalysis as a highly active, and sustainable platform for reductive transformations using AB, fundamentally advancing the field of earth‐abundant metal catalysis.