Unprecedented examples of double-addition of aromatic amines across a ruthenium(II)-coordinated nitrile function: Isolation and X-ray structures of ruthenium complexes of amidinate and cyclometalated amidine

The present report examplifies a novel type of aromatic amine addition reactions at a ruthenium(II) complexed acetonitrile. The electrophilic cationic complex, cis-[L2Ru(CH3CN)2](ClO4)2 (1) [L = 2-(phenylazo)pyridine] reacts with aromatic primary amines only in neat to produce a violet amidinate complex, [L2Ru–N(Ar)–C(CH3)–N(Ar)]+ (2) of ruthenium(II). Along with it a blue ortho-metalated ruthenium(II) amidine complex, [L2Ru–N(H)double bond; length as m-dashC(CH3)–N(H)Ar]+ (3) is also formed. X-ray structures of the two representative complexes are reported. The transformation 1 → 2 is unprecedented, involves multiple steps and occurs with addition of two equivalents of ArNH2 across a coordinated nitrile function. In this complex, amidinate ligand binds to ruthenium(II) center as a σ,σ symmetrical bidentate chelate. The formation of 3 is a combination of nucleophilic amine addition and cyclometalation. 1H and 13C NMR spectra of the products are examined, which are consistent with their formulations and structures. Optical spectra and redox properties of the newly synthesized complexes are reported. Visible range spectra of 2 and 3 are dominated by moderately intense metal-to-ligand charge transfer transitions. The complexes show multiple redox responses. The anodic potential response occurs at a high positive potential, which is attributed to a Ru(II)/Ru(III) couple. The cathodic potential responses are due to reductions of the coordinated diazo ligands.