On the non-innocence and reactive versus non-reactive nature of α-diketones in a set of diruthenium frameworks.

α-Diketones are an important class of building blocks employed in many organic synthetic reactions. However, their coordination chemistry has rarely been explored. In light of this, our earlier report on [(acac)Ru(μ-2,2'-pyridil)Ru(acac)] (acac = acetylacetonate) showcased the sensitivity of a diketone fragment towards oxidative C-C cleavage. Following the lead, the synthesis of similar but stable diketo fragments containing diruthenium compounds was attempted. Three diruthenium compounds with the bridge 1,2-bis(2-hydroxyphenyl)ethane-1,2-dione (L) were prepared: diastereomeric [(acac)Ru(μ-L)Ru(acac)], 1a(rac)/1b(meso), [(bpy)Ru(μ-L)Ru(bpy)](ClO), [2](ClO) and [(pap)Ru(μ-L)Ru(pap)](ClO), [3](ClO) with ancillary ligands of different donating/accepting characteristics. The metal is stabilised in different oxidation states in these complexes: Ru(iii) is preferred in 1a/1b when σ-donating acac is used as the co-ligand whereas electron rich Ru(ii) is preferred in [2](ClO) and [3](ClO) when co-ligands of moderate to strong π-accepting properties are employed. The oxidative chemistry of these systems is of particular interest with respect to the participation of varying bridging-ligands which contain phenoxide groups. On the other hand, the reduction processes primarily resulting from the metal or the ancillary ligands are noteworthy as the normally reducible 1,2-diketo- group remains unreduced. These results have been rationalised and outlined from thorough experimental and theoretical investigations. The results presented here shed light on the stability of metal coordinated α-diketones as a function of their substituents.