Synthesis, Structure, and Ammonia Oxidation Catalytic Activity of Ru-NH3 Complexes Containing Multidentate Polypyridyl Ligands

Ammonia (electro)oxidation with molecular catalysts is a rapidly developing topic with wide practical applications ahead. We report here the catalytic ammonia oxidation reaction (AOR) activity using [Ru(tda-kappa-(NO)-O-3)(py)(2)], 2, (tda(2-) is 2,2':6',2 ''-terpyridine-6,6 ''-dicarboxylate; py is pyridine) as a catalyst precursor. Furthermore, we also describe the rich chemistry associated with the reaction of Ru-tda and Ru-tPa (tPa(-4) is 2,2':6',2 ''-terpyridine-6,6 ''-diphosphonate) complexes with NH3 and N2H4 using [RuII(tda-kappa-N3O)(dmso)Cl] (dmso is dimethyl sulfoxide) and [RuII(tPa-kappa-N3O)(py)(2)], 8, as synthetic intermediates, respectively. All the new complexes obtained here were characterized spectroscopically by means of UV-vis and NMR. In addition, a crystal X-ray diffraction analysis was performed for complexes trans-[Ru-II(tda-kappa-N-3)(py)(2)(NH3)], 4, trans-[Ru-II(tda-kappa-N-3)(N-NH2)(py)(2)], 5, cis-[Ru-II(tda-kappa-N-3)(py)(NH3)(2)], 6 (30%), and cis-[Ru-II(tda-k-N-3)(dmso)(NH3)(2)], 7 (70%). The AOR activity associated with 2 and 8 as catalyst precursors was studied in organic and aqueous media. For 2, turnover numbers of 7.5 were achieved under bulk electrolysis conditions at an E-app = 1.4 V versus normal hydrogen electrode in acetonitrile. A catalytic cycle is proposed based on electrochemical and kinetic evidence.

Automated summary

The study presented in this report focuses on investigating the catalytic activity of [Ru(tda-kappa-(NO)-O-3)(py)(2)] as a precursor for the ammonia oxidation reaction (AOR). Spectroscopic characterization of the newly synthesized complexes was performed, along with X-ray diffraction analysis of selected compounds. The study also examined the catalytic cycle proposed based on electrochemical and kinetic evidence, achieving promising turnover numbers under bulk electrolysis conditions in acetonitrile.