Stable Strained Donor-Free\nSilanone and Its Derived\nNHC-Stabilized Disilacyclobutadiene and Cyclic Alkenyl Silylene

The strained silanone <b>2</b> was obtained by\nthe reaction\nof disilacyclobutene <b>1</b> with N<sub>2</sub>O. Silanone <b>2</b> exhibited unprecedented thermal stability in both the solid\nstate and solution. DFT calculations on <b>2</b> revealed that\nthe highly polarized SiO double bond is effectively stabilized\nby its electron delocalization with the unsaturated Si<sub>2</sub>C<sub>2</sub> ring. Treatment of <b>2</b> with 1,3,4,5-tetramethylimidazolin-2-ylidene\nyielded the first Lewis base-stabilized disilacyclobutadiene <b>3</b> via a 1,3-boryl migration. Reaction of <b>2</b> with\nHCCH and Me<sub>3</sub>SiN<sub>3</sub> resulted in the addition of\nC–H and Si–N bonds to the SiO double bond. Interestingly,\nirradiation of <b>2</b> at rt yielded oxosilanes <b>7A</b> and <b>7B</b> in C<sub>6</sub>D<sub>6</sub> and <i>n</i>-hexane, respectively, via the 1,2-boryl migration and ring expansion,\nwhereas photolysis at −60 °C led to the formation of cyclic\nalkenyl silylene <b>8</b>.