Disilicon-Mediated Carbon Monoxide Activation: From a 1,2,3-Trisila- to 1,3-Disilacyclopentadienes with Hypercoordinate λSi-λC Double Bonds.

The facile reaction of the SiPh-bridged bis-silylene (LSi:)SiPh (L=PhC(NBu)) with diphenylacetylene affords the unprecedented 1,2,3-trisilacyclopentadiene (LSi)(PhC)SiPh 1 with a hypercoordinate λSi-λSi double bond. Compound 1 is very oxophilic and consumes three molar equivalents of inert NO to form the bicyclic oxygenation product 2 through O-atom insertion in the Si=Si and Si-Si bonds. Strikingly, 1 can completely split the C≡O bonds of carbon monoxide under ambient conditions (1 atm, room temperature), yielding the 1,3-disilacyclopentadiene 3, representing the first hypercoordinate example of a cyclosilene with a λSi-λC double bond. Likewise, reaction of Xyl-NC (Xyl=2,6-dimethylphenyl), an isocyanide isoelectronic with CO, with 1 furnishes the related 1,3-disilacyclopentadiene 4 but with an amidinato silylene pendent attached to the Si=C carbon ring atom.