Well-defined ruthenium-hexamethylenetetramine complex: Synthesis, characterization, and catalytic activity towards base and acceptor free oxidation of alcohols and amines

A ruthenium hexamethylenetetramine complex [RuCl2(p-cym)HMTA] was prepared in quantitative yield at room temperature for 30 m. NMR and fluorescence spectroscopic studies revealed that the complex is unstable in solution resulting in the decomposition of HMTA unit with the elimination of p-cymene moiety. The newly synthesized complex is very efficient for the conversion of amines and alcohols into imines and ketones, respectively, in the absence of any base/additive/acceptor. The synthetic viabilty of the catalyst was successfully tested for the gram scale synthesis of industrially important product bis(4-chlorophenyl)methanone. The spectroscopic and experimental studies showed that ruthenium-hydride species was formed as active catalyst during the catalytic reactions and oxidation of alcohols and amines follows a dehydrogenative oxidation mechanism. The amount of hydrogen gas evolved during the ruthenium complex catalysed oxidation of diphenylmethanol was estimated to be 92%, implies the potential usage of catalyst in the field of liquid organic hydrogen storage.