Authentic Sn═B-Double Bonds in Polar Stannaborene Derivatives.

We report on the synthesis of an authentic Sn═B-moiety realized in a stannaborenyl anion and stannaborenium cation. Starting with an oxidative addition of boron tribromide to a stannylene-phosphine Lewis pair [-CH(Ar*BrSn-BBr-PPh)] () [Ar* = CH(2,6-Trip), Trip = 2,4,6-CHPr] was synthesized. Reduction of with magnesium yields the Grignard-type stannaborene [-CH(Ar*Sn═B{PPh}MgBr{thf})] () featuring a Sn═B double bond and a B-Mg interaction. Following an alternative protocol, hydride substitution at yields the tinhydride [-CH(Ar*HSn-BBr-PPh)] (). HBr elimination of in reaction with NHC (NHC = 1,3,4,5-tetramethylimidazol-2-ylidene) gives the carbene and phosphine stabilized stannyl-borylene [-CH(Ar*BrSn-B{PPh}{NHC})] () after simultaneous bromide transfer from boron to tin. In reaction of with Li[Al(OC{CF})] or Na[BAr] in a mixture of -DFB/benzene a stannaborene [-CH(Ar*Sn═B{PPh}{NHC})] [] stabilized by the respective weakly coordinating anion was isolated (Ar = CH-3,5-(CF), -DFB = -difluorobenzene). The phosphine and NHC-supported stannaborenium cation adds ammonia at room temperature under splitting of a N-H bond and formation of Sn-NH and B-H bonds to give [-CH(Ar*{HN}Sn-BH{PPh}{NHC})] ().