Properties of the C,C′-dimethylpentahydro-4,5-dicarba-nido-hexaborate-(1–) ion, C2Me2B4H5–, and its reactions with halogen species

Abstract

The nature of the anion, C₂Me₂B₄H₅^–, prepared by the action of alkali metal hydrides, or alkyls, on C,C′-dimethyl-4,5-dicarba-nido-hexaborane(8) C₂Me₂B₄H₆, has been clarified from a study of its ¹¹B n.m.r. spectrum over the temperature range 308–373 K. The anion reacts with iodine monochloride to yield 2-ClC₂Me₂B₄H₅ and 3-ClC₂Me₂B₄H₅(in a 3 :1 ratio), while bromine yields the 3-substituted isomer, 3-BrC₂Me₂B₄H₅, as the major product. Bridge halogen derivatives are believed to be intermediates in these reactions. The 220 MHz ¹H n.m.r. spectrum of the parent carborane, C₂Me₂B₄H₆, is also described to illustrate the potential advantage of using such spectra in studies on these compounds.