Theoretical investigation of the mechanism of forming a silicic bis-heterocyclic compound between dichlorosilylenesilylene [Cl 2 Si = Si:] and ethylene

Abstract

The mechanism of the cycloaddition reaction between singlet state unsaturated silylene dichlorosilylenesilylene [Cl₂Si = Si:] and ethylene, which generates a silicic bis-heterocyclic compound, has been investigated with the CCSD(T)// MP2/6-31G^* method. The calculations show that the dominant reaction pathway consists of three steps. (I) The 3p unoccupied orbital of the Si atom in dichlorosilylenesilylene [Cl₂Si = Si:] (R1) and the π-orbital of ethylene (R2) firstly form a π → p donor–acceptor bond, which makes the two reactants generate a three-membered cyclic intermediates (INT) through a barrier-free exothermic reaction of 127.7 kJ mol⁻¹. (II) INT then isomerises to a four-membered cyclic silylene (P1) by the ring-expansion effect, which is via a transition state (TS1) with an energy barrier of 6.4 kJ mol⁻¹. (III) sp³ hybridisation of the Si atom finally makes P1 react directly with ethylene to form a silicic bis-heterocyclic compound (P2) without any intermediates and transition states, and this step is also a barrier-free exothermic reaction of 138.6 kJ mol⁻¹.