Two bioinspired hydroxo-bridged diferric complexes 6 and 7 with N4-donor ligands of the PDP type (PDP=N,N′-bis(pyridin-2-ylmethyl)-2,2′-bipyrrolidine), differing by substituents at the pyridine rings (4-NMe2 in 7 vs. 3,5-Me2-4-OMe in 6), efficiently catalyze the enantioselective alkene epoxidation with H2O2 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 aAA (S=3/2, g1, g2=3.69, g3=1.96), whereas catalyst systems based on complex 6 exhibit the low-spin perferryl intermediate 6 aAA (S=1/2, g1=2.07, g2=2.01, g3=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 aAA, demonstrate higher enantioselectivity (% ee) in the epoxidation of chalcone. The origin of the unprecedented high-spin state of the perferryl intermediate is discussed.

Язык оригиналаанглийский
Страницы (с-по)5345-5352
Число страниц8
Номер выпуска21
СостояниеОпубликовано - 7 ноя 2019

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