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 [ o -C 6 H 4 (Ar*BrSn-BBr 2 -PPh 2 )] ( 2a ) [Ar* = C 6 H 3 (2,6-Trip) 2 , Trip = 2,4,6-C 6 H 2 i Pr 3 ] was synthesized. Reduction of 2a with magnesium yields the Grignard-type stannaborene [ o -C 6 H 4 (Ar*Sn═B{PPh 2 }MgBr{thf})] 2 ( 3 ) 2 featuring a Sn═B double bond and a B-Mg interaction. Following an alternative protocol, hydride substitution at 2a yields the tinhydride [ o -C 6 H 4 (Ar*HSn-BBr 2 -PPh 2 )] ( 4a ). HBr elimination of 4a in reaction with Me NHC ( Me NHC = 1,3,4,5-tetramethylimidazol-2-ylidene) gives the carbene and phosphine stabilized stannyl-borylene [ o -C 6 H 4 (Ar*BrSn-B{PPh 2 }{ Me NHC})] ( 5 ) after simultaneous bromide transfer from boron to tin. In reaction of 5 with Li[Al(OC{CF 3 } 3 ) 4 ] or Na[BAr F 4 ] in a mixture of o -DFB/benzene a stannaborene [ o -C 6 H 4 (Ar*Sn═B{PPh 2 }{ Me NHC})] + [ 6 ] stabilized by the respective weakly coordinating anion was isolated (Ar F = C 6 H 3 -3,5-(CF 3 ) 2 , o -DFB = o -difluorobenzene). The phosphine and NHC-supported stannaborenium cation 6 adds ammonia at room temperature under splitting of a N-H bond and formation of Sn-NH 2 and B-H bonds to give [ o -C 6 H 4 (Ar*{H 2 N}Sn-BH{PPh 2 }{ Me NHC})] + ( 7 ).