Selective Carbonyl Reduction in Unsaturated Esters and Aldehydes by Transfer Hydrogenation.

Catalytic transfer hydrogenation (TH) is an alternative to the industrially relevant hydrogenation of carbonyl compounds, dismissing the use of pressurized reactors. Herein, we compare ruthenium and osmium pincer complexes as catalysts for the selective carbonyl reduction of the renewable methyl 10-undecenoate, myrtenal, and cinnamaldehyde. Their selective carbonyl reduction is challenging because they also have a C-C double bond susceptible to reduction or isomerization. The osmium complexes, used for the first time in TH, showed considerably better activity and selectivity than the ruthenium ones. The reactions were carried out at temperatures as low as 35 °C at short reaction times, and a solvent screening demonstrated that anisole, which has a high sustainability score, is also the most efficient solvent for these reactions. Finally, renewable ethanol was employed as a sacrificial hydrogen source, circumventing the use of the usually high-carbon-footprint dihydrogen.