A Stable Silaborene: Synthesis and Characterization

A stable silicon−boron doubly bonded compound, silaborene (2), was synthesized by the reaction of 1,1-dilithiosilane (1) with dichloro(2,2,6,6-tetramethylpiperidino)borane in toluene. The X-ray crystallographic analysis of 2 revealed that the >SiB−N< framework is almost linear (176.87(13)°) with an Si−B bond length of 1.8379(17) Å, which is about 10% shorter than typical Si−B single bonds. The silaborene 2 reacted with lithium trimethylsilylacetylide at 60 °C in DME to give the corresponding silaborenide (4-·[Li(dme)3]+), whose reddish-orange crystals were isolated as the solvent separated ion pair. The X-ray analysis of 4-·[Li(dme)3]+ showed that the Si−B bond length (1.933(3) Å) is longer than that of 2, but still shorter than typical Si−B single bonds. These structural features indicate that 4- has double bond character involving the >SiB<- resonance structure.