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DFT-based comparison between mechanistic aspects of amine and alcohol oxidation mediated by IBX
Density functional theory was utilized to investigate plausible mechanisms for amine and alcohol oxidation by an iodine(V) hypervalent reagent (IBX). In this contribution, we found that amine and alcohol oxidation both proceed by similar mechanisms. The reactions initiate from ligand exchange to give four coordinate intermediates followed by a redox process giving an iodine(III) species and oxidized substrates. Interestingly, for both the ligand-exchange and the redox steps a hypervalent twist is required for the reaction to proceed via an energetically more accessible route. The ligand-exchange process was found to be mediated by a proton-shuttling agent such as water, a second IBX, or a second substrate. While the ligand-exchange step for both amine and alcohol occurs with almost identical activation energy (particularly when water is considered as the shuttling agent), the redox step for the amine takes place with much lower activation energy than that for the alcohol. Finally, we ascertained that five coordinate amide iodine(V) complexes are unreactive toward redox reactions due to the fact that in such cases two electrons from the coordinated amide are required to occupy a 3c–4e σ* orbital which is too high in energy to be reachable.
Funding
Australian Research Council
University of Wollongong
History
Publication title
Journal of Organic ChemistryVolume
85Pagination
515-525ISSN
0022-3263Department/School
School of Natural SciencesPublisher
Amer Chemical SocPlace of publication
1155 16Th St, Nw, Washington, USA, Dc, 20036Rights statement
© 2019 American Chemical SocietyRepository Status
- Restricted