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

Ring opening of disilacyclopropylidenes provides a possible route to the ye t 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 ba sis 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-disila allenes. This barrier is much smaller than the barrier (42.5 kcal mol(-1)) for the all carbon analogue, cyclo-C3H4ClLi. The differences between the si licon and carbon systems are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.