Mechanism and stereoselectivity of benzylic C-H hydroxylation by Ru-porphyrin: a computational study.
Org Biomol Chem
; 18(2): 346-352, 2020 01 02.
Article
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| MEDLINE
| ID: mdl-31845954
ABSTRACT
The mechanism and origin of the stereoselectivity of asymmetric benzylic C-H hydroxylation by Ru-porphyrin were elucidated with density functional theory calculations. The reaction proceeds via a hydrogen-atom abstraction/oxygen-rebound pathway, wherein a high-valent ruthenium-oxo species abstracts a hydrogen atom from ethylbenzene to generate a radical pair intermediate, followed by the oxygen-rebound process to form 1-phenylethanol. The hydrogen-atom abstraction step is the rate- and stereoselectivity-determining step. Based on the mechanistic model, the computed stereoselectivity is in agreement with the experimental observations. Analysis of the distortion/interaction model suggests that stereoselectivity is determined by both the distortion energy of the ethylbenzene and the interaction energy between the ethylbenzene and the chiral Ru-porphyrin. The steric repulsion between the phenyl group of ethylbenzene and the bulky substituent of Ru-porphyrin is the leading cause of chiral induction.
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MEDLINE
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En
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Org Biomol Chem
Asunto de la revista:
BIOQUIMICA
/
QUIMICA
Año:
2020
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Article