Aerobic oxidative dehydrogenation of coordinated imidazoline units of pincer ruthenium complex

A new pincer ruthenium complex (1; [RuL1(tpy)](PF6); L1 = 1,3-di(2-imidazoline-2-yl)benzene, tpy = 2,2′:6′,2″-terpyridine) having a κ3NCN pincer ligand with two imidazoline units and related ruthenium complexes were synthesized and characterized. The imidazoline units of 1 were oxidized in air to give an imidazole-ligated pincer complex (2; [RuL2(tpy)](PF6); L2 = 1,3-di(2-imidazolyl)benzene). Results of the 1H NMR spectroscopic and cyclic voltammetric studies of the complexes indicate that the σ-donor character of the pincer ligand of 1 induces the Ru-promoted oxidative dehydrogenation of coordinated imidazoline moieties to imidazole units with oxygen in air.