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Hexamethylenetetramine (HMTA) is one of the most versatile and most utilized nitrogen-containing heterocyclic compounds in academia and industry. Most of the reactions involving HMTA employ stoichiometric or excess amounts of acid, which hamper the sustainability of the reactions. Herein, we report the first example of the ruthenium-mediated decomposition of HMTA at room temperature, supported by a detailed mechanistic study using thermogravimetric analysis/differential thermal analysis, variable-temperature NMR, UV–vis spectroscopy, and density functional theory techniques. The mechanism study also involves a comparison of the decomposition of HMTA, protonated HMTA, [RuCl3(HMTA)], and [FeCl3(HMTA)], which revealed that [RuCl3(HMTA)] decomposes at the lowest temperature and has the lowest HOMO–LUMO band gap of 2.66 eV. The ruthenium-induced decomposition of HMTA is successfully used as a tool to increase the sustainability of the Sommelet reaction as it employs simple RuCl3·nH2O as a catalyst in as low as 0.5 mol % concentration in aqueous medium. The developed methodology is found to be very selective and efficient even for the very challenging substrates, namely, aliphatic aldehydes and substrates with electron-withdrawing substituents. The findings of this work are the first of its kind in which ruthenium is employed in the Sommelet reaction and also provide a possible platform to improve the sustainability of all reactions involving HMTA as a reactant/reagent.

A very efficient, highly atom economical, and environmentally benign oxidation of primary and secondary amines using an in situ catalyst system generated from commercially available ruthenium(II) benzene dichloride dimer and hexamethylenetetramine has been demonstrated. Mechanistic studies revealed that hexamethylenetetramine acted as a source of hydride to generate the active ruthenium hydride catalyst and amine oxidation involves a dehydrogenative pathway. In comparison to reported catalyst systems for the dehydrogenative oxidation of amines, this synthetic protocol makes use of a simple ruthenium precursor and a cheaper additive; it is very selective, leading to the exclusive formation of nitrile/imine compounds. Further, it releases hydrogen as the only side product, suggesting the potential application of the developed catalyst system in hydrogen storage.

Amides are synthesized directly from alcohols and amines in high yields using an in situgenerated catalyst from easily available ruthenium complexes such as the pcymeneruthenium dichloride dimer, RupcymemeCl22, or the benzeneruthenium dichloride dimer, RubenzeneCl22, an Nheterocyclic carbene NHC ligand, and a nitrogen containing Ltype ligand such as acetonitrile. The phosphinefree catalyst systems showed improved or comparable activity compared to previous phosphinebased catalytic systems. The in situgenerated catalyst from RubenzeneCl22, an NHC ligand, and acetonitrile showed excellent activity toward reactions with cyclic secondary amines such as piperidine and morpholine.

The combination of RuH2(PPh3)4with NHC, MeCN, and NaH provides an efficient system which allows direct synthesis of amides from either alcohols or aldehydes.

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