Areneruthenium(II) carboxylates: reactions with ligands and the X-ray structure of the p-cymene pyrazine complex [Ru(η-p-MeC6H4CHMe2)Cl(pyz)2]PF6

The preparation of monomeric areneruthenium(II) acetates and trifluoroacetates [Ru(η-arene)X(O2CR)] and [Ru(η-arene)(O2CR)2](X = Cl or Br; R = Me or CF3; arene = C6H6, p-MeC6H4CHMe2, C6H3Me3-1,3,5, C6H2Me4-1,2,4,5, or C6Me6)(not all possible combinations) from the corresponding dihalides [{Ru(η-arene)X2}2] is described. Infrared spectra suggest that the complexes [Ru(η-arene)X(O2CR)] contain a bidentate carboxylate group and that [Ru(η-arene)(O2CR)2] contain one bi- and one uni-dentate carboxylate group, which are apparently equivalent on the n.m.r. time-scale at room temperature. Reaction of trifluoroacetic acid with [{Ru(η-C6Me6)Cl2}2] gives a complex of empirical formula Ru(η-C6Me6)Cl(O2CCF3)·CF3CO2H which may be a salt [(η-C6Me6)Ru(η-Cl)2(µ-O2CCF3)Ru(η-C6Me6)][H(O2CCF3)2]·CF3CO2H. Triphenylphosphine converts [Ru(η-C6Me6)(O2CR)2](R = Me or CF3) into [Ru(η-C6Me6)(O2CR)2(PPh3)] in which both carboxylate groups are unidentate. The trifluoroacetate group is completely displaced from [Ru(η-C6H6)Cl(O2CCF3)] by pyridine (py) or ethyldiphenylphosphine to give [Ru(η-C6H6)ClL2]+(L = py or PEtPh2), isolated as PF6– or BPh4– salts. The potentially binucleating ligands pyrazine (pyz), 4,4′-bipyridyl, and 1,3-dithiane react either with [Ru(η-C6H6)Cl(O2CCF3)] or with [{M(η-p-MeC6H4CHMe2)Cl2}2](M = Ru or Os) in the presence of NH4PF6 or NaBPh4 in methanol to give [M(η-arene)ClL2]+ salts in which only one donor atom of the ligand is co-ordinated, but pyz and [{Ru(η-p-MeC6H4CHMe2)Cl2}2] react in dry tetrahydrofurane to give the pyrazine-bridged species {Ru(η-p-MeC6H4CHMe2)Cl2}2(µ-pyz). The structure of the complex [Ru(η-p-MeC6H4CHMe2)Cl(pyz)2]PF6 has been verified by X-ray analysis. The crystals are triclinic, space group P, with a= 9.265(2), b= 9.684(4), c= 12.969(2)A, α= 86.51(2), β= 72.89(2), and γ= 85.59(2)°.