Small molecule activation by transition metal centers is essential to numerous stoichiometric and catalytic organic transformations in biological and industrial processes. Nature has gone through a course of trial and error to refine the living creatures, processes, and materials over 3.6 billion years. Oxygen-coordinating metal intermediates, such as metal–superoxo, –peroxo, –hydroperoxo, and –oxo species, are frequently invoked as plausible oxidants in the oxidation of organic substrates in the living organisms. Here, we describe our recent results on the synthesis, structural and spectroscopic characterization, and reactivity studies of M-O2 complexes bearing tetraazamacrocyclic n-TMC ligands, where M = Cr, Mn, Fe, Co, and Ni and n = 12, 13, and 14.[1,2] Notably, several novel metal-O2 complexes, demonstrated by x-ray crystal structures to be end-on metal-superoxo and side-on metal-peroxo species, have been thoroughly characterized using various spectroscopic techniques, including resonance Raman and x-ray absorption spectroscopy. The metal ions and the ring size of the supporting ligands are found to be important factors that control the geometric and electronic structures of the metal-O2 complexes (i.e., end-on metal-superoxo vs. side-on metal-peroxo). Reactivity studies performed with the metal-superoxo and -peroxo complexes reveal that the former is capable of conducting electrophilic reactions (e.g., oxygen atom transfer and C-H bond activation of organic substrates), whereas the latter is an active oxidant in nucleophilic reactions (e.g., aldehyde deformylation). A complete intermolecular O2-tranfer from metal(III)-peroxo complexes to a Mn(II) complex has been demonstrated as well.
 J. Cho, S. Jeon, S. A. Wilson, L. V. Liu, E. A. Kang, J. J. Braymer, M. H. Lim, B. Hedman, K. O. Hodgson, J. S. Valentine, E. I. Solomon, W. Nam, Nature 2011, 478, 502-505.
 J. Cho, R. Sarangi, W. Nam, Acc. Chem. Res. 2012, 45, 1321-1330.
- Design of model complexes of metalloenzymes
- Characterization and reactivity studies for biomimetic materials
- Application for medical and environmental materials
Awards and Honors
- 2014 : Co-chair (symposium), The 41st International Coordination Chemistry Conference
- 2013 : Co-chair, International Symposium on Bioinorganic Chemistry
- 2010 : The Distinguished Lectureship Award from the Chemical Society of Japan
- 2008 : Organizing Committee Member, The 4th Asian Biological Inorganic Chemistry Conference