Stable Strained Donor-Free Silanone and Its Derived NHC-Stabilized Disilacyclobutadiene and Cyclic Alkenyl Silylene

The strained silanone <b>2</b> was obtained by the reaction of disilacyclobutene <b>1</b> with N₂O. Silanone <b>2</b> exhibited unprecedented thermal stability in both the solid state and solution. DFT calculations on <b>2</b> revealed that the highly polarized Si═O double bond is effectively stabilized by its electron delocalization with the unsaturated Si₂C₂ ring. Treatment of <b>2</b> with 1,3,4,5-tetramethylimidazolin-2-ylidene yielded the first Lewis base-stabilized disilacyclobutadiene <b>3</b> via a 1,3-boryl migration. Reaction of <b>2</b> with HCCH and Me₃SiN₃ resulted in the addition of C-H and Si-N bonds to the Si═O double bond. Interestingly, irradiation of <b>2</b> at rt yielded oxosilanes <b>7A</b> and <b>7B</b> in C₆D₆ and <i>n</i>-hexane, respectively, via the 1,2-boryl migration and ring expansion, whereas photolysis at -60 °C led to the formation of cyclic alkenyl silylene <b>8</b>.