A mechanistic investigation on the formation and rearrangement of silaspiropentane: A theoretical study

The formation of silaspiropentane from addition of singlet silacyclopropylidene 1 and silacyclopropylidenoid 8 to ethylene has been investigated separately at the B3LYP, X3LYP, WB97XD, and M05–2X theories using the 6–31+G(d,p) basis set. The silacycloproylidenoid addition follows a stepwise route. In contrast, a concerted mechanism occurs for silacyclopropylidene addition. Moreover, the intramolecular rearrangements of silaspiropentane 9 to methylenesilacyclobutane 11 and 2-silaallene?+?ethylene 12 have been studied extensively. The required energy barrier for the isomerization of 9 to 10 was determined to be 44.0 kcal mol^?1 at the B3LYP/6–31+G(d,p) level. After formation of 10, the rearrangement to methylenesilacyclobutane 12 is highly exergonic by ?15.9 kcal mol^?1, which makes this reaction promising. However, the conversion of 9 to 11 is calculated to be quite endergonic, by 26.5 kcal mol^?1.