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.