Novelty in Transfer Hydrogenation and Related Reactions Catalyzed by Ruthenium Catalysts

Transfer hydrogenation (TH) is a straightforward transformation for the reduction of carbonyl compounds to alcohols using suitable hydrogen donors under mild reaction conditions. Conversely, carbonyl compounds can be obtained by alcohols by means of hydrogen acceptors without the use of hazardous oxidants. As a result of the reversibility of the TH, borrowing hydrogen transformations, namely C-C and C-N forming reactions, can be achieved via C-H activation. In order to have access to selective catalytic processes, the development of well-defined homogenous catalysts, obtained through a fine tuning of non-innocent ligands via metal-ligand cooperativity, is a current research target.1 In addition, high catalyst productivity is a critical factor for applications and relies on the design of robust catalysts. This presentation deals with the preparation of ruthenium complexes, containing bidentate and pincer ligands, which display high activity in the TH of carbonyl compounds, Oppenauer-type alcohol oxidation, alcohol racemization, hydrogenation, dehydrogenation, amine alkylation and photochemical TH reactions (Figure 1). Mechanistic studies indicates that Ru-hydrides and Ru-alkoxides are key species involved in the catalytic processes.