Oxygen Activation by Co(II) and a Redox Non-Innocent Ligand: Spectroscopic Characterization of a Radical–Co(II)–Superoxide Complex with Divergent Catalytic Reactivity

Abstract

Bimetallic (Et4N)2[Co2(L)2], (Et4N)2[1] (where (L)(3-) = (N(o-PhNC(O)(i)Pr)2)(3-)) reacts with 2 equiv of O2 to form the monometallic species (Et4N)[Co(L)O2], (Et4N)[3]. A crystallographically characterized analog (Et4N)2[Co(L)CN], (Et4N)2[2], gives insight into the structure of [3](1-). Magnetic measurements indicate [2](2-) to be an unusual high-spin Co(II)-cyano species (S = 3/2), while IR, EXAFS, and EPR spectroscopies indicate [3](1-) to be an end-on superoxide complex with an S = 1/2 ground state. By X-ray spectroscopy and calculations, [3](1-) features a high-spin Co(II) center; the net S = 1/2 spin state arises after the Co electrons couple to both the O2(•-) and the aminyl radical on redox non-innocent (L(•))(2-). Dianion [1](2-) shows both nucleophilic and electrophilic catalytic reactivity upon activation of O2 due to the presence of both a high-energy, filled O2(-) π* orbital and an empty low-lying O2(-) π* orbital in [3](1-).

Spectroscopic and computational studies of reversible O2 binding by a cobalt complex of relevance to cysteine dioxygenase

“…Finally, the cobaltbased approach has allowed us to isolate and spectroscopically characterize a dioxygen-bound adduct (4-O2), which is significant given that iron congeners of this species have eluded detection in both CDO and related model complexes. Furthermore, cobalt(iii)-superoxo intermediates like 4-O2are likely involved in numerous catalytic processes, including the aerobic oxidation of organic compounds 59,60 and oxygenreduction reactions. [61][62][63] To gain a better understanding of the spectroscopic and chemical features of the Co-and Fe-CDO models, density functional theory (DFT) calculations were utilized to generate molecular bonding descriptions, computed spectroscopic parameters, and potential energies surfaces of putative O2 activation mechanisms.…”

Reactivity of a Cobalt(III)–Hydroperoxo Complex in Electrophilic Reactions

“…13 Very recently, the reactivity of an end-on cobalt(II)-superoxo intermediate with a redox non-innocent ligand has been investigated in catalytic deformylation reactions. 14 …”

In Situ Structural Determination of a Homogeneous Ruthenium Racemization Catalyst and Its Activated Intermediates Using X‐Ray Absorption Spectroscopy

“…In seminal work by the group of Lei on copper‐mediated cross‐couplings, XAS was used to show that Cu I species were the catalytically active intermediates in the mixture, whereas Cu II ‐ and Cu 0 ‐species acted as spectators . XAS has also been applied to other elements in attempts to elucidate catalytic species . In the few reports that exist, to the best of our knowledge, the emphasis lies either on the X‐ray absorption near edge structure (XANES) in an operando setup or on accumulated intermediates .…”

“…[10,11] XASh as also been applied to other elements in attempts to elucidate catalytic species. [5,[12][13][14][15][16] In the few reports that exist, to the best of our knowledge,t he emphasis lies either on the X-ray absorption near edge structure (XANES) in an operando setup [17] or on accumulated intermediates. [18,19] Alternatively, studies are performed on very simple systemsw ith high symmetry or under conditions that do not provide time-resolved structurali nformationo fe nough quality.H erein, we report an in situ XAS that allowsf or the structurald etermination of at ransient metal intermediate in ar uthenium-catalysed reaction.…”