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Mechanistic Insights into Fe Catalyzed α‐C−H Oxidations of Tertiary Amines
Author(s) -
Legacy Christopher J.,
Hope Taylor O.,
Gagné Yohann,
Greenaway Frederick T.,
Frenette Mathieu,
Emmert Marion H.
Publication year - 2021
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202001382
Subject(s) - chemistry , catalysis , electron paramagnetic resonance , kinetic isotope effect , selectivity , amine gas treating , kinetics , reaction mechanism , substrate (aquarium) , isotopic labeling , combinatorial chemistry , photochemistry , radical , hydrolysis , organic chemistry , physics , oceanography , deuterium , nuclear magnetic resonance , quantum mechanics , geology
We report detailed mechanistic investigations of an iron‐based catalyst system, which allows the α‐C−H oxidation of a wide variety of amines. In contrast to other catalysts that effect α‐C−H oxidations of tertiary amines, the system under investigation exclusively employs peroxy esters as oxidants. More common oxidants (e. g. t BuOOH) previously reported to affect amine oxidations via free radical pathways do not provide amine α‐C−H oxidation products in combination with the described catalyst system. The investigations described herein employ initial rate kinetics, kinetic profiling, DFT calculations as well as Eyring, kinetic isotope effect, Hammett, ligand coordination, and EPR studies to shed light on the Fe catalyst system. The obtained data suggest that the catalytic mechanism proceeds through C−H abstraction at a coordinated substrate molecule. This rate‐determining step occurs either through an Fe(IV) oxo pathway or a 2‐electron pathway at an Fe(II) intermediate with bound oxidant. DFT calculations indicate that the Fe(IV) oxo mechanism will be the preferred route of these two possibilities. We further show via kinetic profiling and EPR studies that catalyst activation follows a radical pathway, which is initiated by hydrolysis of PhCO 3 t Bu to t BuOOH. Overall, the obtained mechanistic data support a non‐classical, Fe catalyzed pathway that requires substrate binding, inducing selectivity for α‐C−H functionalization.