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Identification, Characterization, and Electronic Structures of Interconvertible Cobalt-Oxygen TAML Intermediates

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Title
Identification, Characterization, and Electronic Structures of Interconvertible Cobalt-Oxygen TAML Intermediates
Author(s)
Malik, Deesha D.; Ryu, Wooyeol; Kim, Yujeong; Singh, Gurjot; Jun-Hyeong Kim; Sankaralingam, Muniyandi; Lee, Yong-Min; Seo, Mi Sook; Mahesh Sundararajan; Ocampo, Daniel; Roemelt, Michael; Park, Kiyoung; Kim, Sun Hee; Mu-Hyun Baik; Shearer, Jason; Ray, Kallol; Fukuzumi, Shunichi; Nam, Wonwoo
Publication Date
2024-05
Journal
Journal of the American Chemical Society, v.146, no.20, pp.13817 - 13835
Publisher
American Chemical Society
Abstract
The reaction of Li[(TAML)CoIII]·3H2O (TAML = tetraamido macrocyclic tetraanionic ligand) with iodosylbenzene at 253 K in acetone in the presence of redox-innocent metal ions (Sc(OTf)3 and Y(OTf)3) or triflic acid affords a blue species 1, which is converted reversibly to a green species 2 upon cooling to 193 K. The electronic structures of 1 and 2 have been determined by combining advanced spectroscopic techniques (X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), X-ray absorption spectroscopy/extended X-ray absorption fine structure (XAS/EXAFS), and magnetic circular dichroism (MCD)) with ab initio theoretical studies. Complex 1 is best represented as an S = 1/2 [(Sol)(TAML•+)CoIII-OH(LA)]− species (LA = Lewis/Brønsted acid and Sol = solvent), where an S = 1 Co(III) center is antiferromagnetically coupled to S = 1/2 TAML•+, which represents a one-electron oxidized TAML ligand. In contrast, complex 2, also with an S = 1/2 ground state, is found to be multiconfigurational with contributions of both the resonance forms [(H-TAML)CoIV═O(LA)]− and [(H-TAML•+)CoIII═O(LA)]−; H-TAML and H-TAML•+ represent the protonated forms of TAML and TAML•+ ligands, respectively. Thus, the interconversion of 1 and 2 is associated with a LA-associated tautomerization event, whereby H+ shifts from the terminal −OH group to TAML•+ with the concomitant formation of a terminal cobalt-oxo species possessing both singlet (SCo = 0) Co(III) and doublet (SCo = 1/2) Co(IV) characters. The reactivities of 1 and 2 at different temperatures have been investigated in oxygen atom transfer (OAT) and hydrogen atom transfer (HAT) reactions to compare the activation enthalpies and entropies of 1 and 2. © 2024 American Chemical Society.
URI
https://pr.ibs.re.kr/handle/8788114/15284
DOI
10.1021/jacs.3c14346
ISSN
0002-7863
Appears in Collections:
Center for Catalytic Hydrocarbon Functionalizations(분자활성 촉매반응 연구단) > 1. Journal Papers (저널논문)
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