Ab initio study on the mechanism of cycloaddition reaction between H2Si=Si: and formaldehyde

Abstract

The mechanism of the cycloaddition reaction between singlet H2Si=Si: and formaldehyde has been investigated with the CCSD(T)//MP2/6-31G* method. From the potential energy profile, it could be predicted that the reaction has three competitive dominant reaction pathways. The reaction rules presented is that the 3p unoccupied orbital of the Si: atom in H2Si=Si: inserts the π orbital of formaldehyde from the oxygen side, resulting in the formation of an intermediate. Isomerization of the intermediate further generates a four-membered ring silylene (the H2Si–O in the opposite position). In addition, the [2+2] cycloaddition reaction of the two π-bonds in H2Si=Si: and formaldehyde also generates another four-membered ring silylene (the H2Si–O in the syn-position). Because of the unsaturated property of the Si: atom in the two four-membered ring silylenes, the two four-membered ring silylenes could further react with formaldehyde, generating two silicic bis-heterocyclic compounds. Simultaneously, the ring strain of the four-membered ring silylene (the H2Si–O in the syn-position) makes it isomerize to a twisted four-membered ring product.