Ab initio study on the mechanism of forming a silapolycyclic compound between methylenesilylene and ethene

The mechanism of the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and ethene has been investigated with the MP2/6-31G∗ method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by the CCSD(T)//MP2/6-31G∗ method. From the potential energy profile, it can be predicted that, reaction (3) is the dominant channel of cycloaddition reaction between singlet methylenesilylene and ethene. This reaction consists of four steps: (I) the two reactants first form a three-membered ring intermediate INT through a barrier-free exothermic reaction of 13.3 kJ mol−1; (II) INT then isomerizes to a four-membered ring product P2 via the transition state TS2 with an energy barrier of 32.0 kJ mol−1; (III) P2 further reacts with ethene(R2) to form a silapolycyclic intermediate INT3, which is also a barrier-free exothermic reaction of 11.8 kJ mol−1; (IV) INT3 isomerizes to a silapolycyclic compound P3 via the transition state TS3 with an energy barrier of 1.5 kJ mol−1. This reaction has quite excellent selectivity.