cs6b01473_si_001.pdf (398.42 kB)
Dramatic Effect of Carboxylic Acid on the Electronic Structure of the Active Species in Fe(PDP)-Catalyzed Asymmetric Epoxidation
journal contribution
posted on 2016-07-11, 00:00 authored by Alexandra
M. Zima, Oleg Y. Lyakin, Roman V. Ottenbacher, Konstantin P. Bryliakov, Evgenii P. TalsiThe
electronic structure of the iron–oxygen intermediates
responsible for catalytic transformations in the biomimetic catalyst
systems [((S,S)-PDP)FeII(OTf)2]/H2O2/RCOOH has been found
to be strongly dependent on the structure of the carboxylic acid RCOOH.
For carboxylic acids with primary and secondary α-carbon atoms
(acetic acid, butyric acid, caproic acid), the active species exhibit
electron paramagnetic resonance (EPR) spectra with large g-factor anisotropy (g1 = 2.7, g2 = 2.4, g3 = 1.7),
whereas for those with tertiary α-carbon atoms (2-ethylhexanoic
acid, valproic acid, 2-ethylbutyric acid), the active species display
EPR spectra with small g-factor anisotropy (g1 = 2.07, g2 = 2.01, g3 = 1.96). The EPR spectra of the latter intermediates
are very similar to those of the intermediates previously assigned
to oxoiron(V) species. The systems featuring intermediates of the
second type ensure higher enantioselection in the epoxidation of electron-deficient
olefins.