Ruthenium nitrosyl complexes with the molecular framework [RuII(dmdptz)(bpy)(NO)]n+ (dmdptz: N,N-dimethyl-4,6-di(pyridin-2-yl)-1,3,5-triazin-2-amine and bpy: 2,2′-bipyridine). Electronic structure, reactivity aspects, photorelease, and scavenging of NO

Abstract

Two mononuclear ruthenium nitrosyl complexes with a nitrogen-rich ligand coordinated molecular framework, [Ru^II(dmdptz)(bpy)(NO)]ⁿ⁺ (dmdptz: N,N-dimethyl-4,6-di(pyridin-2-yl)-1,3,5-triazin-2-amine and bpy: 2,2′-bipyridine), Enemark and Feltham notation {RuNO}⁶, [4]³⁺ (n = 3), and {RuNO}⁷, [4]²⁺ (n = 2), have been synthesized by sequential pathways from a chloro precursor [Ru^II(dmdptz)(bpy)(Cl)]⁺ [1]⁺via an acetonitrile complex [Ru^II(dmdptz)(bpy)(CH₃CN)]²⁺ [2]²⁺ and a nitro complex [Ru^II(dmdptz)(bpy)(NO₂)]⁺ [3]⁺. Single crystal X-ray structures of [1](ClO₄) and [3](ClO₄) have been successfully elucidated. A substantial low stretching frequency ν(NO) band of [4]³⁺ at 1914 cm⁻¹ due to the influence of a pyridyl-substituted s-triazine ligand suggests the moderately electrophilic nature of NO. Density functional theory calculated trans-angles (Ru1–N6–O1) of 176.713° and 141.745° in [4]³⁺ and [4]²⁺ indicate linear and bent coordination modes of NO to central ruthenium, respectively. A noticeable shift in ν(NO) (solid) (Δν = 364 cm⁻¹) which has been observed on moving from [4]³⁺ to [4]²⁺ is good evidence for NO-centered one-electron reduction with {RuNO}⁶ to {RuNO}⁷ bonding alteration. The redox properties of [4]³⁺ have been studied with precursor complexes. The electrochemical conversion of [4]³⁺ to [3]⁺ has been performed in the presence of 0.5 M NaOH solution. Both [4]³⁺ and [4]²⁺ facilitate the photocleavage of the Ru–NO bond on exposure to a xenon 200 W visible light source with first-order rate constants k_NO of 8.44 × 10⁻³ min⁻¹ (t_1/2 = 82 min) and 4.64 × 10⁻² min⁻¹ (t_{1/2 =} 15 min), respectively. Light-triggered release of NO has been captured by a biologically relevant target protein, reduced myoglobin, as an Mb–NO adduct.