Dehydrogenative oxidation of alcohols using ruthenium (II) complexes

A very efficient, highly atom economical and environmentally benign oxidation of secondary alco-hols using three different in situ catalyst systems has been demonstrated. All the three catalyst sys-tems 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 sys-tems were found to be highly atom economic as they avoid the employment of any stoichiometric hydro-gen 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 sys-tem proved that the reaction involves formation of ruthenium-hydride species as the active catalyst.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

A highly efficient oxidation of secondary alcohols has been achieved using three different in situ catalyst systems, all of which are environmentally friendly and highly atom economical. These catalyst systems were generated from commercially available ruthenium(II)benzenedichloride dimer, dichloro(1,5-cyclooctadiene)ruthenium(II) polymer, and ruthenium(II)(p-cymene)dichloride dimer, in combination with the additive hexamethylenetetramine. The catalyst systems showed high activity even at low catalyst loadings, and the oxidation reactions proceeded via a dehydrogenative pathway to produce hydrogen as the sole product. The developed catalyst systems have potential applications in the release of hydrogen from liquid organic hydrogen carriers.