Sequential Oxygenation of Bis(β-diketiminate) on a Selective Diruthenium Platform.

This article demonstrated the redox-noninnocent phenylene-linked bis(β-diketiminate) (L)-bridged first example of isomeric diruthenium(III)-acac species (acac = acetylacetonate) and its ability to activate dioxygen. The coordination of deprotonated L to the {Ru(acac)} in bis(bidentate) mode led to isomeric {(acac)Ru}(μ-L) ( = 1, -/- ). displayed Ru(III)-based anisotropic EPR in CHCN but without the resolution of the forbidden (Δ = 2) signal at 77 K. -, however, slowly transformed to the energetically favored - form. underwent two-step oxygenation at the C sites of L to form the β-diketiminate/α-ketodiimine (L)-bridged mixed valent (acac)Ru(μ-L)Ru(acac) (, = 1/2, ) followed by bis(α-ketodiimine) (L)-bridged isovalent (acac)Ru(μ-L)Ru(acac) (, = 0, ). The role of O toward → / was corroborated by O labeling experiment. Redox steps of - varied as a function of isomeric identity, bridge, and metal oxidation state. The calculated MOs and Mulliken spin densities attributed to the noninnocence of L, L, and L in the respective complexes. Spectrophotometric monitoring of → revealed pseudo-first-order rate constants (10 s) of 1.8 (303 K), 3.5 (313 K), 7.7 (323 K), and 17.0 (333 K) and Δ/Δ/Δ of 14.3 kcal mol/-33.1 cal mol K/24.2 kcal mol (298 K), respectively. Moreover, characterization of the short-lived intermediate obtained during the conversion of → / upon exposure to O supported its valence tautomeric form (, Ru-L-Ru ↔ Ru-L-Ru, = 1), which in effect facilitated oxygen activation at the ligand backbone.