The trans-labilization of nitric oxide in Ru-II complexes by C-bound imidazoles

The synthesis, characterization and reactivity of trans-[NO(L)(NH3)(4)Ru]Cl -3 (L = imidazole, theophylline and caffeine) are presented. H-1 NMR spectr oscopy indicates that the imidazole ligands are coordinated to the Ru-II th rough a carbon atom (im kappa (2) 1,3Me(2)Xan kappa (8) and 1,3,7Me(3)Xan k appa (8)). The nitrosyl stretching frequencies (v(NO) congruent to 1913 cm( -1)) suggest the coordinated nitrosyl has substantial NO+ character. The co mplexes undergo a single-electron reduction (E-degrees congruent to - 0.50 V versus Ag/AgCl), which involves the coordinated nitrosyl. Dissociation of NO. in the reduced species is facilitated by the trans-imidazolylidene lig and. The lower than expected reduction potentials of these complexes may ac count for their inactivity in evoking neuronal firing in the hippocampus by releasing NO following reduction. (C) 2001 Elsevier Science B.V. All right s reserved.