Mr. Wasihun Menberu Dagnaw

Abstract: DFT computations have been performed to gain insight into the mechanisms of the oxidative azidation of alkanes with H2O2/CF3COOH catalyzed by a non-heme IronII complex, giving azido-alkane. In our work, the catalytical oxidative azidation mechanism includes five major parts, (i) coordination of N3 (ii) formation of ironIV-oxo complex, (iii) hydrogen-atom transfer (HAT), (iv) N3 radical rebound, and (v) regeneration of the catalyst. The detailed characterization of the pathways allows us to have the following key mechanistic findings. The formation of the high-valent ironV-oxo intermediate from the reaction between Cat(II) and H2O2 is the rds with a barrier of 14.1 kcal mol-1 (3TS1 relative to 3INT1) and is endergonic by 45.2 kcal/mol. Note that, experimentally the small kinetic isotope effect also suggested that the hydrogen atom transfer (HAT) step by the high valent iron-oxo intermediate is not the rds. Next, the oxo ligand in 3INT4 with the presence of one CF3COOH molecules abstracts an H-atom from cyclohexane via crossing 3TS2 with a barrier of 9.6 kcal/mol relative to 3INT5, giving an intermediate 4INT6. In 3TS2, the bond lengths of OH (1.415Å), and HC (1.208Å) showed that an H-atom transfer for OH bond formation and alkane radical containing intermediate 3INT6. The calculated kinetics and thermodynamic properties are in good agreement with the available experimental findings. We expect that this study could enrich the field of oxidative C-H activation.

Key words:  FeII(PyBzIm)3 (Cat(II)) complex, oxidative azidation, HAT, DFT calculations

University: CityU

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