Ab initio study of mechanism of forming a spiro-Si-heterocyclic ring compound from Me2SiSi: and formaldehyde

The H2SiSi: and its derivatives(X2SiSi:, X = H, Me, F, Cl, Br, Ph, Ar……) is a new species. Its cycloaddition reactions is a new area for the study of silylene chemistry. The mechanism of the cycloaddition reaction between singlet Me2SiSi: and formaldehyde has been investigated with the CCSD(T)//MP2/6-31G∗ method in article. From the potential energy profile, it could be predict that the reaction has one dominant reaction pathway. The reaction rule presented is that the two reactants firstly form a four-membered Si-heterocyclic ring silylene through the [2+2] cycloaddition reaction. Because of the 3p unoccupied orbital of Si: atom in the four-membered Si-heterocyclic ring silylene and the π orbital of formaldehyde forming a π → p donor–acceptor bond, the four-membered Si-heterocyclic ring silylene further combines with formaldehyde to form an intermediate. Because the Si: atom in intermediate happens sp3 hybridization after transition state, then, intermediate isomerizes to a spiro-Si-heterocyclic ring compound via a transition state. The research result indicates the laws of cycloaddition reaction between Me2SiSi: and formaldehyde, and laid the theory foundation of the cycloaddition reaction between H2SiSi: and its derivatives(X2SiSi:, X = H, Me, F, Cl, Br, Ph, Ar……) and asymmetric π-bonded compounds, which are significant for the synthesis of small-ring and spiro-Si-heterocyclic ring compounds. The study extends research area and enriched the research content of silylene chemistry.