Ruthenium Catalyzed Dehydrogenation of Alcohols and Mechanistic Study

We synthesized pyridylamine ligated arene-Ru(II) complexes and employed these complexes for the catalytic acceptorless dehydrogenation of primary alcohols to carboxylic acids. All the synthesized complexes [Ru]-1-[Ru]-10 are characterized using several spectro-analytical techniques, and the structures of complexes [Ru]-1, [Ru]-2, and [Ru]-5 are determined using single crystal X-ray crystallography. Efficient catalytic conversion of primary alcohols to potassium carboxylates or carboxylic acids is achieved in toluene with the quantitative release of hydrogen gas. The studied protocol for carboxylic acid synthesis with hydrogen generation is also employed for a wide range of substrates, including aliphatic alcohols, aromatic alcohols, and heteroaromatic alcohols, to obtain respective carboxylic acids in good yields (up to 86%). The studied arene-Ru catalysts also exhibit superior catalytic activity for the bulk reaction to achieve a turnover number of 1378. Moreover, extensive mass investigations are also performed to elucidate the mechanistic pathway by identifying the crucial catalytic intermediates, including aldehyde and diol coordinated Ru species under the catalytic and controlled reaction conditions.