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Mononuclear metal-O 2 complexes bearing macrocyclic N-tetramethylated cyclam ligands

Title
Mononuclear metal-O 2 complexes bearing macrocyclic N-tetramethylated cyclam ligands
Authors
Cho J.Sarangi R.Nam W.
Ewha Authors
남원우조재흥
SCOPUS Author ID
남원우scopus
Issue Date
2012
Journal Title
Accounts of Chemical Research
ISSN
0001-4842JCR Link
Citation
vol. 45, no. 8, pp. 1321 - 1330
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
Metalloenzymes activate dioxygen to carry out a variety of biological reactions, including the biotransformation of naturally occurring molecules, oxidative metabolism of xenobiotics, and oxidative phosphorylation. The dioxygen activation at the catalytic sites of the enzymes occurs through several steps, such as the binding of O 2 at a reduced metal center, the generation of metal-superoxo and -peroxo species, and the O-O bond cleavage of metal-hydroperoxo complexes to form high-valent metal-oxo oxidants. Because these mononuclear metal-dioxygen (M-O 2) adducts are implicated as key intermediates in dioxygen activation reactions catalyzed by metalloenzymes, studies of the structural and spectroscopic properties and reactivities of synthetic biomimetic analogues of these species have aided our understanding of their biological chemistry. One particularly versatile class of biomimetic coordination complexes for studying dioxygen activation by metal complexes is M-O 2 complexes bearing the macrocyclic N-tetramethylated cyclam (TMC) ligand.This Account describes the synthesis, structural and spectroscopic characterization, and reactivity studies of M-O 2 complexes bearing tetraazamacrocyclic n-TMC ligands, where M = Cr, Mn, Fe, Co, and Ni and n = 12, 13, and 14, based on recent results from our laboratory. We have used various spectroscopic techniques, including resonance Raman and X-ray absorption spectroscopy, and density functional theory (DFT) calculations to characterize several novel metal-O 2 complexes. Notably, X-ray crystal structures had shown that these complexes are end-on metal-superoxo and side-on metal-peroxo species. The metal ions and the ring size of the macrocyclic TMC ligands control the geometric and electronic structures of the metal-O 2 complexes, resulting in the end-on metal-superoxo versus side-on metal-peroxo structures. Reactivity studies performed with the isolated metal-superoxo complexes reveal that they can conduct electrophilic reactions such as oxygen atom transfer and C-H bond activation of organic substrates. The metal-peroxo complexes are active oxidants in nucleophilic reactions, such as aldehyde deformylation. We also demonstrate a complete intermolecular O 2-transfer from metal(III)-peroxo complexes to a Mn(II) complex. The results presented in this Account show the significance of metal ions and supporting ligands in tuning the geometric and electronic structures and reactivities of the metal-O 2 intermediates that are relevant in biology and in biomimetic reactions. © 2012 American Chemical Society.
DOI
10.1021/ar3000019
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자연과학대학 > 화학·나노과학전공 > Journal papers
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