Well-Defined Iron Catalysts for the Acceptorless Reversible Dehydrogenation-Hydrogenation of Alcohols and Ketones

Acceptorless dehydrogenation of alcohols, an important organic transformation, was accomplished with well-defined and inexpensive iron-based catalysts supported by a cooperating PNP pincer ligand. Benzylic and aliphatic secondary alcohols were dehydrogenated to the corresponding ketones in good isolated yields upon release of dihydrogen. Primary alcohols were dehydrogenated to esters and lactones, respectively. Mixed primary/secondary diols were oxidized at the secondary alcohol moiety with good chemoselectivity. The mechanism of the reaction was investigated using both experiment and DFT calculations, and the crucial role of metal–ligand cooperativity in the reaction was elucidated. The iron complexes are also excellent catalysts for the hydrogenation of challenging ketone substrates at ambient temperature under mild H<sub>2</sub> pressure, the reverse of secondary alcohol dehydrogenation.