Diastereoselective synthesis of N-(p-tosylsulfonyl)-2-phenylaziridine over a novel magnetically recyclable Cu(II) catalyst accompanied with the N-inversion assessment at DFT.

An experimental and theoretical study has been carried out on diastereoselective aziridation of styrene over a magnetically recyclable copper(II) catalyst: Cu(acac)2/NH2-T/SiO2@Fe3O4NPs. The turnover number (TON) of our heterogeneous catalyst appears considerably higher than that reported for the homogeneous Cu(acac)2. Successive applications of solid Cu(acac)2/NH2-T/SiO2@Fe3O4NPs have a slight effect on its catalytic activity. Between anticipated cis and trans diastereomeric products, formation of only one is suggested by NMR. Even though, the trans-invertomer appears thermodynamically more stable at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G+G* level, we propose formation of the kinetically more stable cis-invertomer due to π-stacking between the tosyl group and the phenyl of styrene. The possibility of cis-trans conversion is ruled out by the high energy barrier of > 76.9 kcal/mol probed in toluene, CCl4, C7H16, DMSO, CH3CN, and H2O.

Stabilization of carbenes via α-ylide substitutions: a computational quest for new divalents at DFT.

In our continued quest for novel stable carbenes, silylenes, and germylenes, here we compare and contrast multiplicities and relative stabilities of carbenes affected with four different α-ylides. The latter include carbon, immonium, phosphorus, and sulfur ylides substituted at the alpha positions of carbenes with acyclic, cyclic and cyclicunsaturated structural frameworks. Related thermodynamic data are calculated at B3LYP/6-311++G**//B3LYP/6-31+G* and B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G* levels. Investigations reveal the enlargement of the singlet-triplet energy gaps (ΔΕs-t) in the order of immonium > phosphorus > sulfur > carbon. The observed trend, which is taken as an indication of stability, is thoroughly analyzed by applying appropriate isodesmic reactions which differentiate the substituent effects on each of our singlet or triplet carbene. The effect of unsaturation is also probed in each series of the ylide carbenes. The reactivity of the species is discussed in terms of nucleophilicity and electrophilicity.