Theoretical study on the mechanism of cycloaddition reaction between silylene carbene and formaldehyde

The mechanism of the cycloaddition reaction between singlet silylene carbene and formaldehyde has been investigated with 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 CCSD(T)//MP2/6-31G∗ method. From the potential energy profile, it can be predicted that the two competitive dominant reaction pathways of the cycloadditional reaction between singlet silylene carbene and formaldehyde are reaction 4 and reaction 5. Reaction 4 consists of three steps: the two reactants (R1, R2) firstly form a twist four- membered ring intermediate INT4 through a barrier-free exothermic reaction, this intermediate INT4 then isomerizes to a four-membered ring compound P4 via a transition state TS4. subsequently, the compound P4 isomerizes to product P4.2 via a transition state TS4.2, which results from the hydrogen transfer. The process of reaction 5 is as following: on the basis of P4 formed from the reaction 4 between R1 and R2, P4 further reacts with formaldehyde (R2) to form the intermediate INT5 through a barrier-free exothermic reaction, then INT5 isomerizes to a silicic bis-heterocyclic compound P5 via a transition state TS5.