Compromising the metal-metal bond in diruthenium(II,III) tetraacetate: Reaction of [Ru₂(μ-O₂CMe)₄(MeOH)₂]⁺ with phosphines to form 'Ru(μ-O₂CMe)₂(μ-OMe)₂Ru' cores

The anaerobic reactions of mixed-valent [Ru₂(μ-O₂CMe)₄(MeOH)₂]⁺ with two sterically demanding phosphines, PCy₃ (Cy = cyclohexyl) and PCy₂Ph (Ph = phenyl), were carried out and an apparent disproportionation reaction occurred in each case. The two corresponding oxidized, Ru₂(III,III) complexes, [(PCy₃)(η¹-O₂CMe)Ru(μ-OMe)₂(μ-O₂CMe)₂Ru(η¹-O₂CMe)(PCy₃)]2MeOH, 1, and [(PPhCy₂)(η¹-O₂CMe)Ru(μ-OMe)₂(μ-O₂CMe)₂Ru(η¹-O₂CMe)(PPhCy₂)]2.5MeOH, 3, were found not to contain the typical μ-oxo bridge and maintained a single Ru-Ru bond. Both complexes show a rare transoid configured 'Ru(μ-O₂CMe)₂(μ-OMe)₂Ru' core with the remainder of the Ru coordination sphere containing a monodentate phosphine and a monodentate acetate group. This type of core has only been seen once before, in 2004, by Cotton and coworkers in trans-[Ru₂(μ-OMe)₂(μ-O₂CMe)₂(η¹-DAniF)₄]Cl₂, 5, (DAniF^- = N,N′-di(p-anisyl)formamidinate). Further reaction of complexes 1 and 3 in methanol led to slow displacement of the monodentate acetate groups for monodentate methoxides as is shown in the structure of complexes [(PCy₃)(η¹-O₂CMe)Ru(μ-OMe)₂(μ-O₂CMe)₂Ru(η¹-OMe)(PCy₃)]3.5MeOH, (2), and [(PPhCy₂)(η¹-OMe)Ru(μ-OMe)₂-(μ-O₂CMe)₂Ru(η¹-OMe)-(PPhCy₂)]·2MeOH, 4, which maintain this rare core. All complexes were characterized by elemental analysis, IR spectroscopy, ¹H NMR and single crystal X-ray diffraction.