Cycloruthenated complexes: pH-dependent reversible cyclometallation and reactions with nitrite at octahedral ruthenium centers.

The pH-dependent reversible cyclometallation and reactions with nitrite in a near-aqueous system of a related set of cyclometallated ruthenium(ii) bipyridyl complexes were investigated in detail. These complexes are [Ru(ppy)(bpy)2]PF6 (, bpy = 2,2'-bipyridine, Hppy = 2-phenylpyridine), [Ru(thpy)(bpy)2]PF6 (, Hthpy = 2-(2-thienyl)pyridine), and [Ru(dfppy)(bpy)2]PF6 (, Hdfppy = 2-(2,4-difluorophenyl)pyridine). As expected, reversible UV-Vis spectra of these three complexes in near-aqueous solutions can be achieved by treating with acid or base, which indicates a pH-dependent reversible cyclometallation. However, the addition of nitrite to acidic solutions of these complexes disturbed the reversible pH-dependent processes. Unexpected ruthenium complexes in the aforementioned system were then isolated and characterized using FT-IR, MS, (1)H NMR, and UV-Vis spectra, indicating that two reaction modes occurred at the ruthenium(ii) centers: (1) the insertion of NO into the ruthenium-aryl bond to form a ruthenium C-nitroso complex; and (2) the coordination of NO with the entire dissociation of one bipyridine to form a {Ru-NO}(6) complex, which is the first example involving the cleavage of Ru-N(∧)N bonds in ruthenium bipyridyl complexes.