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

• Published in: Inorganic chemistry 2024-05, Vol.63 (22), p.10312-10323
• Main Authors: Seikh, Liton, Sutradhar, Subhankar, Dhara, Suman, Bera, Sudip Kumar, Panda, Sanjib, Paine, Tapan Kanti, Lahiri, Goutam Kumar
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.4c01029

This article demonstrated the redox-noninnocent phenylene-linked bis­(β-diketiminate) (L2–)-bridged first example of isomeric diruthenium­(III)-acac species (acac = acetylacetonate) and its ability to activate dioxygen. The coordination of deprotonated L2– to the {Ru­(acac)2} in bis­(bidentate) mode led to isomeric {(acac)2RuIII}2(μ-L2–) (S = 1, 1-trans/1-cis, green). 1 displayed Ru­(III)-based anisotropic EPR in CH3CN but without the resolution of the forbidden (ΔM s = 2) g 1/2 signal at 77 K. 1-cis, however, slowly transformed to the energetically favored 1-trans form. 1 underwent two-step oxygenation at the Cβ sites of L2– to form the β-diketiminate/α-ketodiimine (L′ –)-bridged mixed valent (acac)2RuIII(μ-L′ –)­RuII(acac)2 (2, S = 1/2, pink) followed by bis­(α-ketodiimine) (L″)-bridged isovalent (acac)2RuII(μ-L″)­RuII(acac)2 (3, S = 0, red). The role of O2 toward 1 → 2/3 was corroborated by 18O2 labeling experiment. Redox steps of 1–3 varied as a function of isomeric identity, bridge, and metal oxidation state. The calculated MOs and Mulliken spin densities attributed to the noninnocence of L2–, L′ –, and L″ in the respective complexes. Spectrophotometric monitoring of 1 → 2 revealed pseudo-first-order rate constants (105 k s–1) of 1.8 (303 K), 3.5 (313 K), 7.7 (323 K), and 17.0 (333 K) and ΔH ⧧/ΔS ⧧/ΔG ⧧ of 14.3 kcal mol–1/–33.1 cal mol–1 K–1/24.2 kcal mol–1 (298 K), respectively. Moreover, characterization of the short-lived blue intermediate obtained during the conversion of 1 → 2/3 upon exposure to O2 supported its valence tautomeric form ( VT 1, RuIII-L2–-RuIII ↔ RuIII-L•–-RuII, S = 1), which in effect facilitated oxygen activation at the ligand backbone.