Synthesis, Spectra and Electrochemistry of Dinitro-bis-{1-alkyl-2-(arylazo) imidazole} Ruthenium(II). Nitro-nitroso Derivatives and Reactivity of the Electrophilic {Ru-NO}6System

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Ag+ assisted aquation of blue cis-trans-cis-RuCl2(RaaiR′)2 (4–6) leads to the synthesis of solvento species, blue-violet cis-trans-cis-[Ru(OH2)2(RaaiR′)2](ClO4)2 [Raai R′=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), OMe (b), NO2 (c) and R′ = Me (1/4/7/10), CH2CH3 (2/5/8/11), CH2Ph (3/6/9/12)] that have been reacted with NO 2 − in warm EtOH resulting in violet dinitro complexes of the type, Ru(NO2)2(RaaiR′)2 (7–9). 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)(OMeaaiR′)2](ClO4)2 (10b–12b) are isolated. The solution structure and stereoretentive transformation in each step have been established from 1H n.m.r. 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 ~ 0.2 V as compared to those of dinitro precursors, (7b–9b). The ν(NO) >1900 cm−1 strongly suggests the presence of linear Ru–NO 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 tris chelates thus formed have been characterised.