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

Abstract

2,3,4.5-Tetracarba-m'do-hexaboranes(6), Exchange Reactions, NMR Spectra 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 E t3BH leads to the 1,2,3,4,5-pentaalkyl-2,3,4,5-tetracarba-/7/do-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 E tB B r, and (Z)-l,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 l,l-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-tetracarbam do-hexaborane(6) 11 was isolated in low yield (<5%) from the reaction between 9 and BBr3 (slight excess).

PENTAALKYL-6-DIPHENYLPHOSPHINO-2,3,4,5-TETRACARBA-NIDO-HEXABORANES(6)

“…"B-and 31P NMR spectra serve as excellent tools for monitoring the progress of the reaction and determining the product distribution. As an example, Figure 2 shows that the formation of 4-carb-P(BH3)Ph2 is readily evident from the IlB NMR spectra, and that both P-B bonds in this borane adduct are kinetically stable in the presence of a large excess of BH3-THE In the 31P NMR spectra the formation of the P-B 6"P 6I3C I3C NMR signals for the C(2,5)-and sharp signals for the C(3,4) atoms as doublets owing to 3J(31P,13C (3,4)). By selective heteronuclear I3C{'H, I'B} triple resonance experiments, the broad 13C(2,5) NMR signals become sharp doublets owing to 2J(31P, I3C(2,5)) ( Figure 2).…”

Pentaalkyl-6-Triorganostannyl-2,3,4,5-Tetracarba-Nido-Hexaboranes(6)

“…A 2:1 mixture of the isomers 2,4-dimethyl-1,3,5-triethyl-and 2,5-dimethyl-1,3,4-triethyl-2,3,4,5-tetracarba-n/cfo-hexaboranes(6) [1] served as starting materials. These were converted into carb-Br 2 + 2' [4], The THF solutions of Me 3 SnLi [10] and Ph 3 SnLi [11] were prepared following literature procedures. The reactions 4.3 to 4.7 were carried out in NMR tubes.…”

“…Following again the literature procedure [4], 1 + 1' were converted selectively to 2 + 2' by treatment with boron tribromide [Eq.(2)]. In the following the 6-substituted carboranyl moieties are abbreviated as carb.…”

“…Only recently, the synthesis of tetraalkyl-1,6-dibromo- [3] and pentaalkyl-6-bromo-derivatives [4] was reported, together with the corresponding B-Η derivatives, and the basic structure of such alkylated carbaboranes determined by an X-ray diffraction analysis of another pentamethyl derivative with the N-bonded Fe 2 (CO) 6 -p-SN fragment in 6-position [5], Various polyhedral boranes are known in which triorganostannyl groups are linked to boron either in bridging or in terminal position [6]. The synthetic potential of simple stannylboranes [7] is increasing since it was found that compounds such as Me 3 SnB(NEt 2 ) 2 can be used in the palladium-catalyzed stannylboration of alkynes [8], Therefore, we report in the present work on the synthesis of pentaalkyl-6-triorganostannyl-2,3,4,5-tetracarba-n/dohexaboranes(6) 3, together with the results of a first screening of the reactivity of 3 towards various element halides.…”

One‐Pot Synthesis of 1,6‐Diiodo‐2,3,4,5‐tetracarba‐nido‐hexaboranes(6) and Mechanistic Studies on the Reaction System Alkynes/BI3/NaK2.8

“…Wrackmeyer et al were able to obtain 1,6‐dibromo‐2,3,4,5‐tetracarba‐ nido ‐hexaboranes(6)5a in high yield by treating 1,4,6,9‐tetraalkyl‐3,8diethyl‐2,7‐bis(diethylboryl)‐5‐stannaspiro[4.4]nona‐1,3,6,8tetraenes with BBr 3 . They also studied the reactions between the peralkylated 2,3,4,5‐tetracarba‐ nido ‐hexaboranes(6) and an excess of BBr 3 (and BI 3 ), whereby the corresponding B6‐halo substituted carboranes were formed 5b. Nucleophilic substitution reactions of such B‐halo carboranes were found to replace the basal B6‐halogen atom to give the corresponding carboranes with organyl,5c stannyl5d and diphenylphosphanyl5e groups as well as, in the 1,6‐dibromo case, an N ‐bonded [Fe 2 (CO) 6 (μ‐SN)] substituent in the 6‐position 5f.…”