Extending the Chemistry of Hexamethylenetetramine in Ruthenium-Catalyzed Amine Oxidation

Abstract

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.

Aerobic dehydrogenation of amines to nitriles catalyzed by triazolylidene ruthenium complexes with O2 as terminal oxidant

“…The catalytic activity is comparable to that reported for simpler systems like [Ru(cym)Cl 2 ] 2 . 30,31 Control experiments indicate that under identical conditions (i.e. 150°C in 1,2-dichlorobenzene), the activity of this simple complex is indeed comparable to that of complex 7, despite the different ligand set of the two ruthenium species.…”

“…26 More recently, different N-chelated ruthenium complexes [27][28][29] as well as simple [Ru(arene)Cl 2 ] 2 complexes have been demonstrated to be highly competent in amine dehydrogenation. 30,31 Herein we describe new ruthenium(II) complexes featuring a range of functionalized triazolylidene ligands and their catalytic activity in amine oxidation. This subclass of N-heterocyclic carbene (NHC) ligands 32,33 is particularly attractive due to the strong σ-donor capability and easy synthetic accessibility through versatile "click chemistry".…”

Synthesis, characterization, catalytic and biological application of half-sandwich ruthenium complexes bearing hemilabile (κ2-C,S)-thioether-functionalised NHC ligands

“…26 Very recently, the combination of an external base/hydride source (hexamethylenetetramine) and the [Ru(p-cym)Cl2]2 pre-catalyst, reported by Mathaiah et al, generate good nitrile selectivity even for benzylamine derivatives. 27 Finally, various well defined monodentate NHC-Ru catalysts have been developed by Mata et al for this transformation albeit with moderate nitrile selectivity. 28 In this context, we wondered if the straight formation of coordinatively more rigid cationic complexes using bidentate NHC ligands instead of triphenylphosphine could generate more active and robust catalysts.…”

Methods of Nitriles Synthesis from Amines through Oxidative Dehydrogenation

“…Later, Taube and co‐workers carried out a detailed study on the oxidation of different types of amine ligands coordinated to ruthenium centers . Based on these initial findings, numerous ruthenium catalyzed methods have been reported for the ODH of amines to nitriles (Table ) …”

“…utilized commercial ruthenium(II) benzene dichloride dimer complex and hexamethylenetetramine to generate an active site of the [Ru(benzene)(H) 2 ] in situ for the AD of both primary and secondary amines. The role of hexamethylenetetramine was as a hydride donor in the above process . Various ruthenium complexes reported for the AD of amines are shown in Scheme .…”