In this contribution, the effect of the structure of the catalytic additive – carboxylic acid – on the catalytic performance of the iron based catalyst [(PDP)Fe(OTf)2], 2 (PDP = N,N′-bis(2-pyridylmethyl)-(S,S)-2,2′-bipyrrolidine) in the selective aromatic oxidation of alkylbenzenes with H2O2 is presented. Eight (linear and branched) carboxylic acids have been tested; in the presence of 2-ethylhexanoic acid, the system [(PDP)Fe(OTf)2]/RCOOH/H2O2 has demonstrated the highest substrate conversion and the highest selectivity for oxygen incorporation into the aromatic ring (up to > 99%) at the same time. Low-temperature EPR spectroscopic study of the system [(PDP)Fe(OTf)2]/2-ethylhexanoic acid/H2O2 witness the presence of the low-spin perferryl intermediate 2aEHA with small g-factor anisotropy (g1 = 2.069, g2 = 2.007, g3 = 1.963), which directly reacts with benzene at −80 °C with the rate constant k2 = 0.6 M−1s−1, and with toluene with k2 > 1 M−1s−1, thus giving evidence for its key role in the selective oxygenation of aromatic substrates.
|Журнал||Journal of Organometallic Chemistry|
|Состояние||Опубликовано - 15 сент. 2018|