Synthesis of Pentaalkyl-6-bromo-2,3,4,5-tetracarba-nido-hexaboranes(6)

Abstract

Peralkylated 2,3,4,5-tetracarba-mdo-hexaboranes(6) 1 react with boron tribromide, BBr₃, via selective exchange of the alkyl substituent in 6-position to give the corresponding new 6- bromo derivatives 2 in quantitative yield. The 6-iodo derivatives 2(1) can be prepared in the same way using BI₃. Treatment of the carbaboranes 2 with Li Et₃BH leads to the 1,2,3,4,5- pentaalkyl-2,3,4,5-tetracarba-inido-hexaboranes(6) 3. 1,3,4,6-Tetraethyl-2,3,4,5-tetracarbaw do-hexaborane(6) 4 reacts with BBr₃ via degradation of the carbaborane cage to give EtBBr₂, and (Z)-1,4-bis [bis(dibromoboryl)]-3-hexene 5. A new bis(diethylboryl)-substituted dialkenyl(bromo)borane 8 was prepared, but attem pts failed to convert it into a 1-bromo- or 6-bromo-mdo-C₄B₂-carbaborane. Treatment of 1,1-dialkyl-3-diethylboryl-4-ethylstannoles 9 with a large excess of BBr₃ also affords 5, whereas 6-bromo-l,3,4-triethyl-2,3,4.5-tetracarbamdo- hexaborane(6) 11 was isolated in low yield (<5%) from the reaction between 9 and BBr₃ (slight excess)