Ab initio Study of Mechanism of Forming a Germanic Hetero-Polycyclic Compound between Germylidene (H2C=Ge:) and Acetone

The mechanism of the cycloaddition reaction of forming a germanic hetero‐polycyclic compound between singlet germylidene (R1) and acetone (R2) has been investigated with CCSD(T)//MP2/6‐31G* method. From the surface energy profile, it can be predicted that the dominant reaction pathway for this reaction consists of three steps: (1) the two reactants (R1, R2) firstly form a twisted four‐membered ring intermediate (INT2); (2) the intermediate (INT2) reacts further with acetone (R2) to give another intermediate (INT4); (3) intermediate (INT4) isomerizes to a hetero‐polycyclic germanic compound (P4) via a transition state TS4. The presented rule of this reaction: the 2+2] cycloaddition effect between the π orbital of germylidene and the π orbital of π‐bonded compounds leads to the formation of four‐membered ring intermediate (INT2). The 4p unoccupied orbital and the lone‐pair sp electrons of Ge in the four‐membered ring intermediate (INT2) react with the π orbital and the antibonding π* orbital of π‐bonded compounds, respectively, forming the π→p and sp→ π* cyclic donor‐acceptor bonds, resulting in the generation of a stable germanic hetero‐polycyclic compound (P4).