On The Non-Innocence And Reactive Versus Non-Reactive Nature Of Alpha-Diketones In A Set Of Diruthenium Frameworks

alpha-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)(2)Ru-II(mu-2,2 '-pyridil)Ru-II(acac)(2)] (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)(2)Ru-III(mu-L2-)Ru-III(acac)(2)], 1a(rac)/1b(meso), [(bpy)(2)Ru-II(mu-L2-)Ru-II(bpy)(2)](ClO4)(2), [2](ClO4)(2) and [(pap)(2)Ru-II(mu-L2-)Ru-II(pap)(2)](ClO4)(2), [3](ClO4)(2) 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 sigma-donating acac is used as the co-ligand whereas electron rich Ru(ii) is preferred in [2](ClO4)(2) and [3](ClO4)(2) when co-ligands of moderate to strong pi-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 alpha-diketones as a function of their substituents.