Catalytic and stoichiometric C[sbnd]H oxidation of benzylalcohols and hydrocarbons mediated by nonheme oxoiron(IV) complex with chiral tetrapyridyl ligand

Dóra Lakk-Bogáth, Balázs Kripli, Bashdar I. Meena, G. Speier, J. Kaizer

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Bioinspired chiral iron(II) complex [((R)-(−)-N4Py*)Fe II (CH 3 CN)] 2+ (1) (N4Py* = N,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine) has been shown to efficiently catalyze the benzylic C[sbnd]H oxidation of ethylbenzene with tert-butyl hydroperoxide (TBHP), H 2 O 2 , and meta-chloroperoxybenzoic acid (mCPBA) resulting in enantiomerically enriched 1-phenylethanol up to 12.5% ee and the corresponding acetophenone, where the [Fe IV (N4Py*)(O)] 2+ (2) intermediate has been detected by UV/Vis spectrometry. The stoichiometric oxidation of benzyl alcohol and various hydrocarbon derivatives including the asymmetric hydroxylation of ethylbenzene with 2 has also been investigated. Detailed kinetic, and mechanistic studies (kinetic isotop effect (KIE) of 31 and 38, and Hammett correlation with ρ = −0.32 and −0.98 for PhCH 2 OH and PhCH 3 , respectively, and the linear correlation between the normalized bimolecular reaction rates and bond dissociation energies (BDE CH )) lead to the conclusion that the rate-determining step in these reactions above involves hydrogen-atom transfer between the substrate and the Fe(IV)-oxo species. The stoichiometric 2-mediated hydroxylation of ethylbenzene affords 1-phenylethanol in up to 33% ee, suggesting clear evidence for the involvement of the oxoiron(IV) species in the enantioselective step. The moderate enantioselectivity may be explained by the epimerization of the long-lived substrate radical before the rebound step (non-rebound mechanism, where k ep > k reb ). The kinetic resolution of the resulting chiral alcohol due to its metal-based overoxidation process into acetophenone in the catalytic metal-based ethylbenzene oxidation can be excluded.

Original languageEnglish
Pages (from-to)165-170
Number of pages6
JournalInorganic Chemistry Communications
Volume104
DOIs
Publication statusPublished - Jun 1 2019

Keywords

  • Asymmetric hydroxylation
  • Biomimetic oxidation
  • C-H activation
  • Chiral iron complex
  • Kinetics

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Fingerprint Dive into the research topics of 'Catalytic and stoichiometric C[sbnd]H oxidation of benzylalcohols and hydrocarbons mediated by nonheme oxoiron(IV) complex with chiral tetrapyridyl ligand'. Together they form a unique fingerprint.

  • Cite this