Exceedingly Fast Oxygen Atom Transfer to Olefins via a Catalytically Competent Nonheme Iron Species

Abstract

The reaction of [Fe(CF3 SO3 )2 (PyNMe3 )] with excess peracetic acid at -40 °C leads to the accumulation of a metastable compound that exists as a pair of electromeric species, [Fe(III) (OOAc)(PyNMe3 )](2+) and [Fe(V) (O)(OAc)(PyNMe3 )](2+) , in fast equilibrium. Stopped-flow UV/Vis analysis confirmed that oxygen atom transfer (OAT) from these electromeric species to olefinic substrates is exceedingly fast, forming epoxides with stereoretention. The impact of the electronic and steric properties of the substrate on the reaction rate could be elucidated, and the relative reactivities determined for the catalytic oxidations could be reproduced by kinetic studies. The observed fast reaction rates and high selectivities demonstrate that this metastable compound is a truly competent OAT intermediate of relevance for nonheme iron catalyzed epoxidations.

Catalytic Applications of Pyridine‐Containing Macrocyclic Complexes

“…Complex 14 was also a competent catalyst in alkene epoxidation with peracetic acid . All experimental evidence provided by Costas and co‐workers was in agreement with complex 15 being the active species in oxygen atom transfer (OAT) with alkenes.…”

“…Complex 14 was also a competent catalyst in alkene epoxidation with peracetic acid. [46] All experimental evidence provided by Costas and co-workers was in agreement with complex 15 being the active species in oxygen atom transfer (OAT) with alkenes. Active species 15 exhibited rates in OAT reactions with cyclooctene three to four orders of magnitude higher than those reported for the ferryl(IV) intermediates of ligands 10 [39] and 11.…”

Acid‐Triggered O−O Bond Heterolysis of a Nonheme FeIII(OOH) Species for the Stereospecific Hydroxylation of Strong C−H Bonds

“…[38,39] Physical methods. Reagents and solvents used were of commercially available reagent quality unless otherwise stated.…”

“…PyNMe 3 and [Fe II (OTf) 2 (PyNMe 3 )] (1)w ere prepared following previously described procedures. [38,39] Physical methods. High resolution mass spectra (HRMS) were recorded on aB ruker MicrOTOF-Q IITM instrument using ESI or Cryospray ionization sources at Serveis Tcnics of the University of Girona.…”

“…[38] 2 provedt o be highly active for the oxidation of alkanes with strong CÀH bondsa nd alkenes, leading to the fastest oxidation rate described so far for synthetic iron-oxygen systems (k cyclohexane = 2.8 m À1 s À1 at À40 8C, k cyclooctene = 375 m À1 s À1 at À60 8C). [38,39] On the basis of at horough EPR spectroscopic analysis, 2 was assigned as am ixture of two components in fast equilibrium:a major component corresponding to [Fe V (O)(OAc)(PyNMe 3 )] 2 + (40 %) and am inor species regardeda s[ Fe III (OOAc)(PyNMe 3 )] 2 + (5 %). Both EPR active species followed the kinetic trace of the 490 nm chromophorei nt he presencea nd absence of alkane or alkene substrate, thus indicating their direct relationship with the active species responsible fort he oxidatione vent.…”