A Stable Fused Bicyclic Disilene as a Model for Silicon Surface

We synthesized the first fused bicyclic disilene 1 representing topologically a partial structure of the Si(001) surface up to the third layer. In the solid state, the five-membered rings adopt the envelope conformation, and the SiSi double bond in 1 exists in the slightly cis-bent form (bent angle θ is 3.6°) compared to that of the highly cis-bent dimer on the Si(001) surface. Highly symmetric 1H NMR spectral pattern of 1 remains even at −80 °C, indicating the facile ring flipping of the bicyclic skeleton in solution. While syn-adduct was obtained in the reaction of 1 with water, anti-addition of chlorine atoms across the SiSi double bond in 1 was observed in the reaction with carbon tetrachloride. The structural characteristics of the 9,10-phenanthrenequinone adduct 7 are in good accord with those of the proposed structure of the 9,10-phenanthrenequinone molecule adsorbed on the Si(001) surface.