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

Abstract

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)Å, α= 86.51(2), β= 72.89(2), and γ= 85.59(2)°.