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

Dalton Transactions Pub Date: 2020-12-08 DOI: 10.1039/D0DT03400B

Abstract

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)2RuII(μ-2,2′-pyridil)RuII(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)2RuIII(μ-L2?)RuIII(acac)2], 1a(rac)/1b(meso), [(bpy)2RuII(μ-L2?)RuII(bpy)2](ClO4)2, [2](ClO4)2 and [(pap)2RuII(μ-L2?)RuII(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 σ-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 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.

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