Disilicon‐Mediated Carbon Monoxide Activation: From a 1,2,3‐Trisila‐ to 1,3‐Disilacyclopentadienes with Hypercoordinate λ⁴Si‐λ³C Double Bonds

The facile reaction of the SiPh₂-bridged bis-silylene (LSi:)₂SiPh₂ (L=PhC(NBu^t)₂) with diphenylacetylene affords the unprecedented 1,2,3-trisilacyclopentadiene (LSi)₂(PhC)₂SiPh₂ 1 with a hypercoordinate λ⁴Si-λ³Si double bond. Compound 1 is very oxophilic and consumes three molar equivalents of inert N₂O 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 λ⁴Si-λ³C 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.