Synthesis and investigation of the boron cluster anion [7-(2′-pyridyl)-7,8-nido-dicarbaundecaborate] and its protonated form

Abstract

The structurally chiral [7-(2′-pyridyl)-7,8-nido-C₂B₉H₁₁]⁻, [1]⁻, anion was prepared by a partial degradation reaction of 1-(2′-pyridyl)-1,2-closo-C₂B₁₀H₁₁. From this anion a protonated specie, H[7-(2′-pyridyl)-7,8-nido-C₂B₉H₁₁] 2, and a tetramethylammonium salt, [NMe₄][7-(2′-pyridyl)-7,8-nido-C₂B₉H₁₁], [NMe₄][1] can be obtained. The ¹H{¹¹B} DNMR study on 2 in the temperature range from 298 to 203 K identified the weakly basic nitrogen atom in the pyridine ring as the proton accepting site in solid state and low temperature and revealed pronounced weakening of the nitrogen–proton interaction while the temperature increases. Capillary electrophoresis and X-ray diffraction confirmed the pyridine nitrogen atom as the proton binding site. Separation of the electrophoretically pure racemic [7-(2′-pyridyl)-7,8-nido-C₂B₉H₁₁]⁻ ion into two peaks by the chiral selector β-cyclodextrine has been achieved.