Ab initio study of mechanism of forming a spiro-Ge-heterocyclic ring compound from H2GeGe: and formaldehyde

The mechanism of the cycloaddition reaction between singlet H2GeGe: 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 one dominant reaction pathway. The reaction rule presented is that the [2 + 2] cycloaddition reaction between two reactants firstly generates a four-membered Ge-heterocyclic ring germylene. Because the 4p unoccupied orbital of Ge: atom in the four-membered Ge-heterocyclic ring germylene and the π orbital of formaldehyde form a π → p donor–acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with formaldehyde to form an intermediate. Because the Ge: atom in intermediate happens sp3 hybridization after transition state, then, intermediate isomerizes to a spiro-Ge-heterocyclic ring compound via a transition state. The research result indicates the laws of cycloaddition reaction between H2GeGe: and its derivatives(X2GeGe:, X = F, Cl, CH3, Ph, Ar…) and the asymmetric π-bonded compounds, which is significant for the synthesis of small-ring and spiro-Ge-heterocyclic compounds. The study extends research area and enriches the research content of germylene chemistry.