Dehydrogenative oxidation of alcohols using ruthenium (II) complexes

Abstract

A very efficient, highly atom economical and environmentally benign oxidation of secondary alcohols using three different in situ catalyst systems has been demonstrated. All the three catalyst systems were generated from commercially available ruthenium(II)benzenedichloride dimer, dicholro(1,5-cyclooctadiene)ruthenium(II) polymer and ruthenium(II)(p-cymene)dichloride dimer in combination with simple, cheap and eco-friendly hexamethylenetetramine as the additive. Moreover, all the catalyst systems were found to be highly atom economic as they avoid the employment of any stoichiometric hydrogen acceptor. Among all the three catalyst systems, ruthenium(II)(p-cymene)dichloride dimer was found to be very active with a low catalyst loading of 0.5 mol% and a maximum turn over number (TON) of 700 was obtained while using 0.1 mol% of ruthenium(II)(p-cymene)dichloride dimer. Experimental results have shown that the oxidation of alcohols involves dehydrogenative pathway and produces hydrogen as the sole product and suggesting the use of the developed catalyst systems for the release of hydrogen from liquid organic hydrogen carriers. 1H-NMR studies on ruthenium(II)(p-cymene)dichloride dimer system proved that the reaction involves formation of ruthenium-hydride species as the active catalyst.