Isolable Spirocyclic Silylone: π-Delocalized Spiro[3.3]heptasila-2,6-diylidone.

Strained cyclic tetrylones are important synthons due to various synthetic applications. Connecting two cyclic tetrylone rings through a single shared quaternary group 14 element atom to form a spirocyclic molecule has been unexplored both theoretically and experimentally. The formation of a spirocyclic motif has been a synthetic challenge. In contrast, the reaction of amidinato disilicon(I) 1 , (Me 3 P) 2 SiCl 4 , and KC 8 afforded π-delocalized spiro[3.3]heptasila-2,6-diylidone 2 and tetrasilacyclobutadiene byproducts 3 and 4 . Compound 2 is the smallest spirocyclic tetrylone derivative, which is composed of a σ-type lone pair and delocalized π bond in each all-silicon spirocyclic ring. The electronic property is supported by its coordination with a W(CO) 5 moiety.