Selective Electrocatalytic Oxidation of Ammonia by Ru-dpp Complexes Containing Aromatic Nitrogen Donor as Axial Ligand.

Inspired by the rapid growth of Ru-based complexes as molecular ammonia oxidation catalysts, we propose novel Ru-dpp complexes bearing a nitrogen donor as the axial ligand into the ammonia oxidation catalysts family. Herein, a series of Ru-dpp complexes [Ru(-,',″-dpp)(bpy)(L)]·PF (where Hdpp = 2-[5-(pyridin-2-yl)-1-pyrrol-2-yl]pyridine; bpy = 2,2'-bipyridine; L = pyridine (); 4-methylpyridine (); pyrimidine (); isoquinoline ()) containing aromatic nitrogen donor axial ligand are synthesized and fully characterized by NMR, IR, and ESI-MS. The structural analysis displays that dpp as a pincer ligand coordinates to ruthenium, and nitrogen donor L binds to ruthenium at an axial ligand. The reaction of with ammonia generates ammonia-ligated complexes, which are monitored by NMR and UV-vis spectra. The electrochemical properties are studied by cyclic voltammetry and density functional theory calculation. These titled complexes have good electrocatalytic performances for selective oxidation of ammonia into hydrazine at 0.6 V versus CpFe onset potential. The turnover frequency of NH formation is 326.4-393.4 h, and the faraday efficiency of generating hydrazine exceeds 97%. The N-N formation mechanism via bimolecular coupling of ruthenium amide/imide is proposed. The aminyl character of ruthenium amide intermediate is confirmed by EPR spectra.