Ab initio study of mechanism of forming a spiro-Si-heterocyclic compound involving Ge from (CH3)2Ge=Si: and formaldehyde.

(CH3)2Ge=Si: and its derivatives (X2Ge=Si:, X=H, F, Cl, Br, Ph, Ar) are a new species. Their cycloaddition reaction is a new area for the study of silylene chemistry. The mechanism of the cycloaddition reaction between singlet (CH3)2Ge=Si: and formaldehyde was investigated with the CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has one dominant pathway. The reaction rule presented is that the two reactants first form a four-membered Ge-heterocyclic silylene through the [2+2] cycloaddition reaction. Because of the 3p unoccupied orbital of Si: atom in the four-membered Ge-heterocyclic silylene and the π orbital of formaldehyde forming a π→p donor-acceptor bond, the four-membered Ge-heterocyclic silylene further combines with formaldehyde to form an intermediate product. The Si: atom in the intermediate product is sp3 hybridized after transition state, and this intermediate isomerizes to a spiro-Si-heterocyclic compound involving Ge via a transition state. [ABSTRACT FROM AUTHOR]