Theoretical Study on the Mechanism of the Cycloaddition Reaction between Methylidenesilene and Ethylene

The mechanism of a cycloaddition reaction between singlet methylidenesilene and ethylene has been investigated with MP2/6-31G∗︁ and B3LYP/6-31G∗︁ methods, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Energies of the involved conformers were calculated by CCSD(T)//MP2/6-31G∗︁ and CCSD(T)//B3LYP/6-31G∗︁ methods, respectively. The results show that the dominant reaction pathway of the cycloaddition reaction is that a complex intermediate is firstly formed between the two reactants through a barrier-free exothermic reaction of 13.3 kJ/mol, and the complex is then isomerized to a four-membered ring product P2.1 via a transition state TS2.1 with a barrier of 32.0 kJ/mol.