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) degrees ) with an Si-B bond length of 1.8379(17) A, which is about 10% shorter than typical Si-B single bonds. The silaborene 2 reacted with lithium trimethylsilylacetylide at 60 degrees 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) A) 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.