Dehydrogenation of Alcohols to Carboxylic Acid Catalyzed by in Situ-Generated Facial Ruthenium-<b>CPP</b> Complex

Abstract

A selective catalytic system for the dehydrogenation of primary alcohols to carboxylic acids using a facial ruthenium complex generated in situ from the [Ru(COD)Cl₂]_<i>n</i> and a hybrid N-heterocyclic carbene (NHC)-phosphine-phosphine ligand (<b>CPP</b>) has been first reported. The facial coordination model was unveiled by NMR analysis of the reaction mixture. Such a <i>fac</i>-ruthenium catalyst system exhibited high catalytic activity and stability, and a high turnover number of 20 000 could be achieved with catalyst loading as low as 0.002 mol %. The exceedingly high catalyst stability was tentatively attributed to both the anchoring role of NHC and the hemi-lability of phosphines. The catalytic system also features a wide substrate scope. In particular, the facial coordination of <b>CPP</b> ligands was found to be beneficial for sterically hindered alcohols, and ortho-substituted benzylic alcohols and bulky adamantanyl methanol as well as cholesterol were all found to be viable dehydrogenation substrates.