Reactivity of the Dimer [{RuCl(μ-Cl)(η3:η3‑C10H16)}2] (C10H16 = 2,7-Dimethylocta-2,6-diene-1,8-diyl) toward Guanidines: Access to Ruthenium(IV) and Ruthenium(II) Guanidinate Complexes

The novel bis­(allyl)­ruthenium­(IV) guanidinate complexes [RuCl­{κ2(N,N′)-C­(NR)­(NiPr)-NHiPr}­(η3:η3-C10H16)] (C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl; R = Ph (3a), 4-C6H4F (3b), 4-C6H4Cl (3c), 4-C6H4Me (3d), 3-C6H4Me (3e) 4-C6H4tBu (3f)) have been synthesized by treatment of the dimeric precursor [{RuCl­(μ-Cl)­(η3:η3-C10H16)}2] (1) with 4 equiv of the corresponding guanidine (iPrHN)2CNR (2a–f). The easily separable guanidinium chloride salts [(iPrHN)2C­(NHR)]­[Cl] (4a–f) are also formed in these reactions. Attempts to generate analogous Ru­(IV) guanidinate complexes from (iPrHN)2CNR (R = 2-C6H4Me (2g), 2,4,6-C6H2Me3 (2h), 2,6-C6H3iPr2 (2i)) failed, due probably to the steric hindrance associated with the aryl group in these guanidines. On the other hand, the reaction of the dimer [{RuCl­(μ-Cl)­(η3:η3-C10H16)}2] (1) with (iPrHN)2CN-4-C6H4CN (2j) led to the selective formation of the mononuclear derivative [RuCl2(η3:η3-C10H16)­{NC-4-C6H4-NC­(NHiPr2)2}] (5), in which the guanidine coordinates to ruthenium through the pendant nitrile unit. This result contrasts with that obtained by employing the related Ru­(II) dimer [{RuCl­(μ-Cl)­(η6-p-cymene)}2] (6), whose reaction with 2j afforded the expected guanidinate complex [RuCl­{κ2(N,N′)-C­(N-4-C6H4CN)­(NiPr)-NHiPr}­(η6-p-cymene)] (7). Treatment of 7 with dimer 1 yielded the dinuclear Ru­(II)/Ru­(IV) derivative 8, via cleavage of the chloride bridges of 1 by the CN group of 7. Reductive elimination of the 2,7-dimethylocta-2,6-diene-1,8-diyl chain in [RuCl­{κ2(N,N′)-C­(NR)­(NiPr)-NHiPr}­(η3:η3-C10H16)] (3a–f) readily took place in the presence of an excess of 2,6-dimethylphenyl isocyanide, thus allowing the high-yield preparation of the octahedral ruthenium­(II) compounds mer-[RuCl­{κ2(N,N′)-C­(NR)­(NiPr)-NHiPr}­(CN-2,6-C6H3Me2)3] (9a–f). The structures of [RuCl­{κ2(N,N′)-C­(N-4-C6H4Me)­(NiPr)-NHiPr}­(η3:η3-C10H16)] (3d), [RuCl­{κ2(N,N′)-C­(N-4-C6H4CN)­(NiPr)-NHiPr}­(η6-p-cymene)] (7), and mer-[RuCl­{κ2(N,N′)-C­(N-4-C6H4tBu)­(NiPr)-NHiPr}­(CN-2,6-C6H3Me2)3] (9f), as well as those of the guanidinium chloride salts 4a–c, were unequivocally confirmed by X-ray diffraction methods. In addition, the catalytic behavior of the guanidinate complexes 3a–f and 9a–f in the redox isomerization of allylic alcohols was also explored.