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High‐Spin and Low‐Spin Perferryl Intermediates in Fe(PDP)‐Catalyzed Epoxidations
Author(s) -
Zima Alexandra M.,
Lyakin Oleg Y.,
Bryliakov Konstantin P.,
Talsi Evgenii P.
Publication year - 2019
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.201900842
Subject(s) - catalysis , chemistry , peracetic acid , epoxide , medicinal chemistry , alkene , pyridine , cyclohexene , enantioselective synthesis , stereochemistry , cyclohexane , photochemistry , organic chemistry , hydrogen peroxide
Abstract Two bioinspired hydroxo‐bridged diferric complexes 6 and 7 with N 4 ‐donor ligands of the PDP type (PDP=N,N′‐bis(pyridin‐2‐ylmethyl)‐2,2′‐bipyrrolidine), differing by substituents at the pyridine rings (4‐NMe 2 in 7 vs. 3,5‐Me 2 ‐4‐OMe in 6 ), efficiently catalyze the enantioselective alkene epoxidation with H 2 O 2 and peracetic acid in the presence of a carboxylic acid additive (up to 99 catalyst turnover numbers, TON, toward epoxide, up to 94 % ee ). Catalyst systems based on complex 7 display the high‐spin perferryl intermediate 7 a AA ( S =3/2, g 1 , g 2 =3.69, g 3 =1.96), whereas catalyst systems based on complex 6 exhibit the low‐spin perferryl intermediate 6 a AA ( S =1/2, g 1 =2.07, g 2 =2.01, g 3 =1.96). The S =3/2 and the S =1/2 intermediates directly react with cyclohexene and cyclohexane at low temperatures (−40 °C and −85 °C, respectively). The catalyst systems, exhibiting less reactive intermediate 7 a AA , demonstrate higher enantioselectivity (% ee ) in the epoxidation of chalcone. The origin of the unprecedented high‐spin state of the perferryl intermediate is discussed.