Synthesis of homo- and heterocyclic silanes via intermediates with Si=Si bonds

An account is given of our efforts in the synthesis of homo- and heterocyclic silanes via occasionally stable unsymmetrically substituted disilene intermediates of the A(2)Si=Si(A)B type that are accessible from a disila analog of a vinyl lithium. This approach is particularly powerful in the preparation of three-membered rings such as cyclotrisilanes with a residual functionality that can be either electro- or nucleophilic in nature and can even give rise to ring-expanded products with preserved Si=Si moiety. The intermediacy of transient silylenes in some of these transformations is discussed as well as the structural effects of the electronic properties of the residual functional group. The relevance of these studies for the understanding of Si(100) surface annealed species during the epitaxial growth of elemental silicon is pointed out, and the potential of the methodology for the synthesis of unusual polycyclic silicon clusters is noted.