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(NBut)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-disilacyclopentadiene3, 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, with1furnishes the related 1,3-disilacyclopentadiene4but with an amidinato silylene pendent attached to the Si=C carbon ring atom.