Cycloaddition reactions of N-heterocyclic stable silylenes with ethylene and formaldehyde

The cycloaddition reactions of N-heterocyclic silylenes 1–4 with ethylene (C2H4) and formaldehyde (CH2O) molecules were performed at the MP2/6-31G** level of theory, respectively. Full optimizations and frequency analyses were done for the stationary points on the potential energy surface. The intrinsic reaction coordinate (IRC) was also calculated for all the transition states at the same level of theory. The possible cycloaddition mechanisms were investigated and results from various reactions were compared in detail. The theoretical results indicated that the cycloaddition reactions of N-heterocyclic silylenes with C2H4 and CH2O proceeded through a concerted mechanism to form a three-membered ring containing C1, C2 (O), and Si atoms in the products, which was similar to those of simple silylene H2Si. Silylenes 1–4 exhibit some electrophilicity toward C2H4 whereas nucleophilicity toward CH2O leading to the reaction process. Based on the reaction energy barrier and the exothermic energy, the reaction activities of saturated silylene (2) were stronger than those of unsaturated silylenes (1, 3, and 4).