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

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