A computational investigation of the retrocyclization reaction of silacyclo-but-2-enes to 1-silabuta-1,3-dienes: Focus on the effect of the substituents

Substituent effects on the reaction profile of the thermal retrocyclization reaction of silacyclobut-2-enes to 1-silabuta-1,3-dienes were studied using B3LYP hybrid density functional theory as well as CCSD and CCSD(T) ab initio calculations. Several different substituents (-CF3, -SiH3, -CN, -OCH3, -OH, and -NH2) were used to investigate their effects on the relative energies of the transition states of the retrocyclization reaction as well as of the 1-silabutadiene products. It was found that π-donor groups at the 4-position greatly reduce the energy barriers, and also stabilize the 1-silabutadienes relative to the silacyclobut-2-enes. Silyl substituents at the silicon atom will facilitate the reaction when compared to alkyl substituents. The results thus indicate that the ring-opening reaction of 4,4-disubstituted 1,1-disilylsilacyclobut-2-enes with π-donor substituents are particularly suitable entries for formation of 1-silabutadienes of low relative energy.