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

Abstract The facile reaction of the SiPh 2 ‐bridged bis‐silylene (LSi:) 2 SiPh 2 (L=PhC(NBu t ) 2 ) with diphenylacetylene affords the unprecedented 1,2,3‐trisilacyclopentadiene (LSi) 2 (PhC) 2 SiPh 2 1 with a hypercoordinate λ 4 Si−λ 3 Si double bond. Compound 1 is very oxophilic and consumes three molar equivalents of inert N 2 O 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 λ 4 Si‐λ 3 C 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.