Will an eta(3)-Si3H3 ligand form sandwich compounds with main group elements?

eta(3)-Si3H3 sandwich compounds 5 and 6, with classical and H-bridged ligan ds, respectively, having the main group elements boron and carbon as centra l atoms are minima at B3LYP/6-311++G(2d,2p). The stability of these systems is assisted by transfer of charge from the ligands to the central atom and is reversed from that of cyclopentadienyl sandwiches. The C and B containi ng pyramidal complexes 7, containing both a eta(3)-Si3H3 and a mu(2)-Si3H3 ligand, are more stable than 5 by 20.7 and 8.5 kcal/mol, respectively. The spiro compounds 8, in which the C and B atoms an sandwiched by two allylic mu(2)-Si3H3 ligands, are still more stable by 29.6 and 21.9 kcal/mol, respe ctively. All three types (face-face, face-side, side-side) of sandwich stru ctures are considered viable targets for synthetic pursuit. The Be complexe s deviate from the C and B analogues because Be is much more electropositiv e. In the preferred cluster structure 9 the Be atom sits in a Si6H6 basket.