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

• [Ru2(μ-O2CMe)4(MeOH)2]+ was disproportionated by hindered phospines.
• Oxidized disproportionation products show the rare Ru(μ-OMe)2(μ-O2CMe)2Ru core.
• On further exposure to methanol, η1-acetates are displaced by η1-methoxides.

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.

Disproportionation of mixed-valent [Ru2(μ-O2CMe)4(MeOH)2]+ was achieved by reaction with either of two phosphines, PCy3 and PCy2Ph, and the two oxidized products isolated. X-ray analysis reveals the products to contain a rare “Ru(μ-OMe)2(μ-O2CMe)2Ru” core. Further exposure of the products, (phosphine)(η1-O2CMe)Ru(μ-OMe)2(μ-O2CMe)2Ru(η1-O2CMe)-(phosphine), to methanol, leads to the displacement of the peripheral η1-bound acetates by methoxide.Figure optionsDownload as PowerPoint slide