Theoretical study of mechanism of cycloaddition reaction between dichloro-germylene carbene (Cl_2Ge=C:) and aldehyde

摘要

The mechanism of the cycloaddition reaction between singlet dichloro-germylene carbene and aldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero-point energy and CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (A) consists of four steps: (1) the two reactants (R1, R2) first form an intermediate INT2 through a barrier-free exothermic reaction of 142.4 kJ/mol; (2) INT2 then isomerizes to a four-membered ring compound P2 via a transition state TS2 with energy barrier of 8.4 kJ/mol; (3) P2 further reacts with aldehyde (R2) to form an intermediate INT3, which is also a barrier-free exothermic reaction of 9.2 kJ/mol; (4) INT3 isomerizes to a germanic bis-heterocyclic product P3 via a transition state TS3 with energy barrier of 4.5 kJ/mol. The process of channel (B) is as follows: (1) the two reactants (R1, R2) first form an intermediate INT4 through a barrier-free exothermic reaction of 251.5 kJ/mol; (2) INT4 further reacts with aldehyde (R2) to form an intermediate INT5, which is also a barrier-free exothermic reaction of 173.5 kJ/mol; (3) INT5 then isomerizes to a germanic bis-heterocyclic product P5 via a transition state TS5 with an energy barrier of 69.4 kJ/mol.