Approach to the "Missing" Diarylsilylene: Formation, Characterization, and Intramolecular C-H Bond Activation of Blue Diarylsilylenes with Bulky Rind Groups.

The treatment of the bulky Rind-based dibromosilanes, (Rind)SiBr () [Rind = 1,1,7,7-tetra-R-3,3,5,5-tetra-R--hydrindacen-4-yl: EMind (: R = Et, R = Me) and Eind (: R = R = Et)], with two equivalents of BuLi in EtO at low temperatures resulted in the formation of blue solutions derived from the diarylsilylenes, (Rind)Si: (). Upon warming the solutions above -20 °C, the blue color gradually faded, accompanying the decomposition of and yielding cyclic hydrosilanes () via intramolecular C-H bond insertion at the Si(II) center. The molecular structures of the bulky Eind-based and were confirmed by X-ray crystallography. Thus, at -20 °C, blue crystals were formed (Crystal-A), which were identified as mixed crystals of and . Additionally, colorless crystals of as a singular component were isolated (Crystal-B), whose structure was also determined by an X-ray diffraction analysis. Although the isolation of was difficult due to their thermally labile nature, their structural characteristics and electronic properties were discussed based on the experimental findings complemented by computational results. We also examined the hydrolysis of to afford the silanol, (Eind)SiH(OH) ().