Cobalt-Catalyzed Dehydrogenation of Alcohols and Amines

Oxidation reactions belong to the core of the organic chemistry. Acceptorless dehydrogenation circumvents the need for traditional stoichiometric oxidants or sacrificial hydrogen acceptors. However, the high cost of the precious metal catalysts typically used in this process limits its exploitation. In this work, two cheap and simple in situ formed cobalt catalysts are developed, for releasing hydrogen gas from different functional groups. The first catalysts is developed from cobalt(II)bromide, bis[2‐(diisopropylphosphino)‐4‐methylphenyl]amine and zinc metal, and mediates the dehydrogenative coupling of alcohols and amines into imines, with hydrogen gas and water as the only byproducts. The mechanism is investigated with labelled substrates and, according to the results, a cobalt(I) PNP complex is believed to be the catalytically active species that extrudes hydrogen gas from the alcohol through a metal ligand bifunctional pathway. The second catalytic system is developed from cobalt carbonyl, which is believed to undergo thermal decomposition into cobalt nanoparticles. The catalyst was employed for the synthesis of a variety of imines obtained from the acceptorless dehydrogenation of different amines and from the acceptorless dehydrogenative coupling of alcohols and amines. The cobalt nanoparticles are recyclable and have been characterized by transmission electron microscopy.