Unraveling the reaction pathways of cyclotrisilenes: a computational analysis

Cyclotrisilenes can pursue four types of reaction pathways with unsaturated substrates: π-addition, σ-insertion, exocyclic σ-insertion, and ring-opening reactions. A computational investigation of all these reaction pathways of 1,2,3,3-tetramethyl cyclotrisilene c-Si₃Me₄ (I) and 1,2-bis(trimethylsilyl)-3,3-dimethyl cyclotrisilene c-Si₃Me₂(SiMe₃)₂ (II) with phenylacetylene (R1) and benzaldehyde (R2) is carried out. The reaction pathways are found to be significantly influenced by the substituents attached to the cyclotrisilene ring. Both the π-addition and the σ-insertion reactions proceed with moderate activation energy and high exoergicity, and the electronic nature of the functional group is crucial in deciding the favorable pathway. The exocyclic σ-insertion reactions are found to possess a huge energy barrier, irrespective of the steric and electronic nature of cyclotrisilenes and the substrates. While the course of the reaction and the viability of the ring-opening reaction with phenylacetylene are impacted by the nature of cyclotrisilene, the ring-opening reactions of I and II with benzaldehyde are both highly endoergic.