Cycloaddition reactions of silacyclopropylidenoids to ethylene

The cycloaddition reactions of silacyclopropylidenoids (C 2H 4SiXLi, X = F, Cl, Br) to ethylene have been investigated separately to gain insights into halogen and solvation effects on the energetic of the proposed reactions at the B3LYP/6–311+G(d,p) level of theory. The calculations reveal that the addition of silacyclopropylidenoids to ethylene occurs via stepwise mechanisms. The required initial energy barriers for the conversion of silacyclopropylidenoids to silaspiropentanes are determined to be ΔG = 77.4 kJ/mol, 9.6 kJ/mol, and 9.2 kJ/mol for F, Cl, and Br, respectively. Furthermore, the gas phase calculations show that the reactions are not spontaneous at room temperature, whereas those of THF solvated models indicate that the formations of silaspiropentanes are spontaneous in the cases of X = Br and Cl. Additionally, the findings show that the silacyclopropylidene addition to ethylene is determined to be exergonic in both gas and THF phases by ΔG = –42.6 kJ/mol and –39.3 kJ/mol, respectively.