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

摘要

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 (1, bpy = 2,2'-bipyridine, Hppy = 2-phenylpyridine), [Ru(thpy)(bpy)(2)]PF6 (2, Hthpy = 2-(2-thienyl)pyridine), and [Ru(dfppy)(bpy)(2)]PF6 (3, 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, H-1 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 boolean AND N bonds in ruthenium bipyridyl complexes.