Theoretical Study On The Mechanism Of Cycloaddition Reaction Of Germylene Germylene And Its Derivatives

In this paper, in order to study the mechanism of cycloaddition reaction,we chose thegermylene germylene and its derivatives react with ethylene, formaldehyde, acetone andethylal as the models. finally the result reveal the rules of cycloaddition reactionsbetween germylene germylene or its derivatives and the symmetric or asymmetricπ-bonded compounds.In this study, the Gaussian98package is used, the MP2and B3LYP calculationmethods and the reasonable basis sets (6-31G*，6-311++G**) have been implemented tooptimized all points(the corresponded molecular geometries) on the reaction profile, then,CCSD(T) calculation and vibrational analysis are done for them. From the result ofvibrational analysis,we can know each configuration and the transition state between themis correct or not. The calculated results with IRC to find further proof of the transition stateis correct.We chose the the cycloaddition reactions between germylene germylene, dimethyl-germylene germylidene and ethylene as the models to study the mechanisms of thereactions, as a result, we can predict that these reactions have only one dominant reactionpathway and the mechanism of them are similarily. the finally result is that: at the first, aGe-heterocyclic four-membered ring germylene is formed through the [2+2] cycloadditionbetween two reactants (R1, R2), next, the4p unoccupied orbital of the Ge: atom in thisfour-membered ring germylene reacts with the π-orbital of ethylene,forming a π→pdonor–acceptor bond, leading to the formation of intermediate. Finally the intermediate isisomerized to a spiro-heterocyclic ring compound via the transition state.Study on the mechanisms of the cycloaddition reactions between germylenegermylene, dimethyl-germylidene germylidene and ethylal, acetone, the result indicatethat these reactions have only one dominant reaction pathway and the mechanism of themare similarily. Conclusion: at the first, a Ge-heterocyclic four-membered ring germyleneis formed through the cycloaddition reaction between two reactants. However, Ge: atomin this four-membered ring germylene have4p unoccupied orbital, so the4p unoccupiedorbital of the Ge: atom reacts with the π-orbital of formaldehyde, ethylal or acetone,as aresult, an intermediate is formed, and then the intermediate is isomerized to a spiro-heterocyclic ring compound via the transition state, At the same time, cycloadditionreactions between germylene germylene and ethylal, acetone, formaldehyde, respectivelyor cycloaddition reaction between dimethyl-germylidene germylidene andformaldehyde,due to the ring tension,the Ge-heterocyclic four-membered ring germyleneisomerized to a spiro-heterocyclic four-membered ring compound.