Density functional theory calculations were used to elucidate the mechanism of aziridination involving ethylene and model catalytic nitrenoids, ClMNHCl (MTiZn). Using the BP86/CEP-31G(d) level of theory, the Gibbs free energy changes for each reaction step were calculated, and transition states were found for the proposed mechanisms. It was concluded that the metal plays a key role in determining the reaction pathway. The “late” 3d metals Zn and Cu undergo a two-step mechanism while the “middle” 3d metals (Ni, Co, Fe) undergo a three-step mechanism including an additional isomerization. Surprisingly, these middle 3d metals also exhibit two competitive pathways: the “imide” pathway and the “amide” pathway. Overall, this research suggests that the model catalysts are promising candidates for olefin aziridination under mild conditions and worthy of further investigation.