Nitro-ruthenium(II)-arylazoimidazoles: synthesis, spectra, crystal structure and electrochemistry of dinitro-bis{1-alkyl-2-(arylazo)imidazole}ruthenium(II). Nitro-nitroso derivatives and reactivity of the electrophilic {Ru-NO}6 system

Silver ion assisted aquation of blue cis,trans,cis-RuCl2 (RaaiR')(2) (4-6) leads to solvento species, blue-violet cis, trans, cis - [Ru(OH2)(2) (RaaiR')(2)] (ClO4)(2) [RaaiR' = p-R-C6H4-N = N C3H2-NN-1-R' (1-3), abbreviated as N, N'-chelator where N(imidazole) and N(azo) represent N and N', respectively; R = H(a), Me (b), Cl (c) and R' = Me (1 /4 /7 /10), CH2CH3 (2 /5 /8 /11), CH9(2)Ph (3 /6 /9 /12)] that have been reacted with NO2- in warm ethanol resulting violet dinitro complexes of the type, Ru(NO2)(2) (RaaiR')(2) (7-9). The structure in one case, [Ru(NO2)(2) ( HaaiCH(2)Ph)(2)] (9a), has been established by X-ray diffraction as the cis-Ru(NO2)(2) motif along with trans - N, N and cis - N', N' dispositions of the chelator N atoms around the coordination sphere. The nitrite complexes are useful synthons of electrophilic nitrosyls, and on triturating the compounds 7b-9b with conc. HClO4 nitro-nitrosyl derivatives, [Ru(NO2) (NO) (MeaaiR')(2)] (ClO4)(2) (10b-12b), are isolated. The solution structure and stereoretentive transformation in each reaction step have been established by H-1 NMR results. All the complexes exhibit strong MLCT transitions in the visible region. They are redox active and display one metal-centred oxidation and successive ligand- based reductions. The redox potentials of Ru(III) / Ru(II) (E-1/2(M)) of 10b-12b are anodically shifted by similar to0.2 V as compared to those of dinitro precursors 7b-9b. The nu(NO) > 1900 cm(-1) strongly suggests the presence of linear Ru-N-O bonding. The electrophilic behaviour of metal bound nitrosyl has been proved in one case (12b) by reacting with a bicyclic ketone, camphor, containing an active methylene group and an arylhydrazone with an active methine group, and the heteroleptic trischelates thus formed are characterised.