Are disilacyclopropylidenes and their carbenoids good precursors for the unknown 1,3-disilaallenes?

Ring opening of disilacyclopropylidenes provides a possible route to the yet unknown 1,3-disilaallenes. To examine the feasibility of this reaction we studied computationally the potential energy surfaces for the elimination of LiCl from cyclo-CSi2H4ClLi (and for comparison also for cyclo-C3H4ClLi), which serve as models for the corresponding substituted systems. On the basis of ab initio molecular orbital calculations at the MP2/6-31G(d)//MP2/6-31G(d)+ZPE level we predict that the activation energy for the conversion of cyclo-CSi2H4ClLi to 1,3-disilaallene (+LiCl) is only 6.5 kcal mol−1, making this reaction a promising strategy for the synthesis of 1,3-disilaallenes. This barrier is much smaller than the barrier (42.5 kcal mol−1) for the all carbon analogue, cyclo-C3H4ClLi. The differences between the silicon and carbon systems are discussed.