116910-66-8Relevant articles and documents
nido-Carborane building-block reagents. 4. Regiospecific substitution at boron in 2,3-R2C2B4H6 Cages. Evidence for intramolecular C-H?Hbridge interactions in 2,3-R2C2B4H5-4-R′ derivatives
Davis Jr., James H.,Grimes, Russell N.
, p. 4213 - 4219 (2008/10/08)
Reactions of nido-2,3-R2C2B4H5- ions (R = ethyl, benzyl) with organic halides (R′X) generate B(4)-substituted derivatives together with the B(6)-substituted enantiomers. The formation of the R2C2B4H5-4-R′ products (R′ = Me, Et, CH2Ph, (CH2)3Ph, CH2C6H4Me) is proposed to occur via R2C2B4H5-μ(4,5)-R′ bridged intermediates, which rapidly rearrange to the 4-substituted species. The reaction occurs cleanly, with ≤1% contamination by other geometric isomers, and thus furnishes a useful regiospecific synthetic route to B-monosubstituted derivatives. In all cases examined, the products are air-stable liquids of low volatility that can be employed as building-block units in the synthesis of organometallic complexes and oligomers. Proton NMR spectra of several of the 2,3,4-trisubstituted products, supported by NOE experiments, indicate spin coupling between a C-CH2 methylene proton and a B-H-B bridging hydrogen. The triethyl and tribenzyl derivatives were bridge-deprotonated by NaH, complexed to Fe2+, and oxidatively fused to produce the hexasubstituted R6C4B8H6 carboranes, although the reaction was sluggish compared to those of the parent C,C′-disubstituted carboranes. The fused compounds are nonfluxional in solution, as determined from NMR spectra.
