Comparative Study on ortho-C–H vs ortho-C–X (X = C, Cl, S) Bond Activation in ortho-Caromatic–N Bond Fusion in Substituted Anilines Using Ruthenium(II) Mediators: Isolation and Characterization of Unusual Ru2 Complexes

The chemical reactions of a selection of ortho-mono- and disubstituted anilines with two ruthenium polyene mediator complexes, CpRuIICl­(PPh3)2 (Cp = cyclopentadienyl anion) and (Bnz)2RuII2Cl4 (Bnz = benzene), have been undertaken with a primary aim to make a comparison between ortho-C–H and ortho-C–X (X = Cl, C, S) bond activation processes in ortho-C–N bond fusion reactions. The reaction of ortho-monosubstituted anilines, viz., 2-chloroaniline (HL1a), 2-methylaniline (HL1c), and 2-methylthioaniline (HL1b), with CpRuIICl­(PPh3)2 yielded mononuclear complexes [CpRuIIL2a–cCl] (1, 3, and 5), containing in situ generated ligands N-(aryl)-ortho-quinonediimine, L2a–c, along with anilido-bridged RuIII2 complexes (2, [CpClRuIII{μ-η2-(L1a)}]2; 4, [CpClRuIII{μ-η2-(L1c)}]2; and [6]­Cl2, [CpRuIII{μ-η21-(L1b)}]2), respectively. The new ligands, L2a–c are formed via ortho-C–H bond activation reactions, whereas ortho-C–X bonds remained unaffected. However, the ortho-C–Cl bond activation reaction is also noted in the reaction between CpRuIICl­(PPh3)2 and ortho-disubstituted aniline 2,6-dichloroaniline (HL3a) in more forceful conditions. The ruthenium­(III) binuclear complex [CpRuIII{μ-η21-(L3a)}­(μ-η21-L2d)­(μ-η2-acetate)­RuIIICl]­Cl, [7]­Cl, of an in situ generated N-(2,6-dichlorophenyl)-6-chloro-ortho-quinonediimine ligand, L2d, has been isolated from the above reaction. The ligand L2d coordinates in a η2-binding mode through an imine (NH) nitrogen atom. The coordination mode of 2,6-dichloroanilide, (L3a), in [7]Cl is unusual in that an aromatic-C–Cl group is coordinated to a Ru­(III) center, and it represents the first authentic crystallographic evidence of such a coordination mode in a transition metal complex. Similar reactions on a redox-inert mediator complex, (Bnz)2RuII2Cl4 (Bnz = benzene), with the aforesaid aromatic amines failed to result in ortho-C–N bond fusion reactions and afforded the mononuclear anilino complexes and an anilido-bridged RuII2 compound, [9]­Cl2. The complexes have been characterized by using a host of physical methods as well as single-crystal X-ray structure determination. Their redox and spectroscopic properties have been thoroughly characterized by cyclic voltammetry and UV–vis and electron paramagnetic resonance spectroscopy. Density-functional theory calculations were employed to confirm their structural features and to support the spectral and redox properties.