Dissociation of Bipyridine and Coordination with Nitrosyl: Cyclometalated Ruthenium Nitrosyl Complex.

A novel family of ruthenium nitrosyl complexes [Ru(bpy)(C ∧ N)(MeCN)NO](PF 6 ) 2 ( 2a - 2e , bpy = 2,2'-bipyridine, HC ∧ N = 2-phenylpyridine and its derivatives) has been prepared by reacting cyclometalated ruthenium complexes [Ru(bpy) 2 (C ∧ N)][PF 6 ] ( 1a - 1e ) with NO + , which were comprehensively characterized by mass, IR, NMR, and UV-vis spectra as well as the single-crystal X-ray structure determinations. Herein, the coordination geometry of Ru atoms in 2a - 2e is a distorted octahedron and {Ru II -NO + } 6 is present in these complexes. Theoretical calculations suggest that the reactions involving dissociation of one bipyridine and coordination with NO + proceed spontaneously (Δ G < 0) and the transformation from 1a - 1e to the intermediates is dominated by substituents (Δ G RI varies from -1.19 to -1.53 eV), which influence the binding energy between Ru(II) and NO + in complexes 2a - 2e (-89.42 to -101.17 kcal/mol) and thus control the photorelease of NO on a certain scale. The weak absorption bands in the visible region could be attributed to the contribution of dπ(Ru II ) → π*(NO + ), which were enhanced greatly under light, indicating the possible release of NO. The photoinduced NO, as well as singlet oxygen ( 1 O 2 ), was then confirmed by EPR spectra, and the amount of NO released from 2a - 2e was estimated via Griess reagent assay. The cytotoxicity of these complexes with or without visible light irradiation was also investigated using an MTT assay.