Theoretical study of mechanism of forming a silapolycyclic compound between methylenesilylene and acetone

摘要

The mechanism of the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and acetone has been investigated with MP2/6-31G~(z.ast) 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 CCSD(T)//MP2/6-31G~* method. From the potential energy profile, we predict that the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and acetone has two competitive dominant reaction pathways. First dominant reaction pathway consists of four steps: (I) the two reactants (R1 R2) first form an intermediate (INT1) through a barrier-free exothermic reaction of 46.2 kJ/mol; (II) intermediate (INT1) then isomerizes to a planar four-membered ring product (P3) via transition state (TS3) with an energy barrier of 47.1 kJ/mol; (III) planar four-membered ring product (P3) further reacts with acetone (R2) to form an intermediate (INT4) which is also a barrier-free exothermic reaction of 40.0 kJ/mol; (IV) intermediate (INT4) isomerizes to a silapolycyclic compound (P4) via transition state (TS4) with an energy barrier of 57.0 kJ/mol. Second dominant reaction pathway consists of three steps: (I) the two reactants (R1, R2) first form a four-membered ring intermediate (INT2) through a barrier-free exothermic reaction of 0.5 kJ/mol; (II) INT2 further reacts with acetone (R2) to form an intermediate (INT5), which is also a barrier-free exothermic reaction of 45.4 kJ/mol; (III) intermediate (INT5) isomerizes to a silapolycyclic compound (P5) via transition state (TS5) with an energy barrier of 49.3 kJ/mol. P4 and P5 are isomeric compounds.