Reaction of Ru(PPh3)3Cl2 with arylazoimidazoles: spectral characterisation and redox studies of [bis-{N(1)-alkyl-2-(arylazo)imidazole}-bis-(triphenylphosphine)]-ruthenium(II) perchlorate

Ru(PPh3)3Cl2 reacts with N(1)-alkyl-2-(arylazo)imidazoles, p-RC6H4N=NC3H2N2X, [RaaiX, R = H(a), Me(b), Cl(c); X = Me(1), Et(2), Bz(3)] under refluxing conditions in EtOH to give [Ru(RaaiX)2(PPh3)2](ClO4)2 · H2O complexes (4–6). RaaiX is a bidentate chelator (N, N′) with N(imidazole), N and N(azo), N′ donor centres. Three isomers are present in the mixture in which the pairs of PPh3, N and N′ occupy cis–cis–trans, cis–trans–cis and cis–cis–cis, positions respectively. The isomers were identified by 1H-n.m.r. spectra. Four signals are observed in the aliphatic zone for N(1)-X; two are of equal intensity at higher δ and the other two signals at lower δ in the ratio 1:0.3:0.2 suggesting the presence of cis–cis–cis, cis–trans–cis and cis–cis–trans-geometry. The complexes display the allowed t2(Ru) → π*(RaaiX) transition. Cyclic voltammetry indicates two consecutive RuIII/II couples along with azo reductions.