Boron-11 and proton nuclear magnetic resonance study of anti-B18H22 and its anions, anti-[B18H21]– and anti-[B18H20]2–. The crystal and molecular structure of [NMe4]2[anti-B18H20]

Abstract

The neutral borane anti-B₁₈H₂₂(1), and its mono- and di-anions, in [C₁₀H₆(NMe₂)₂H][anti-B₁₈H₂₁](2) and [NEt₄]₂[anti-B₁₈H₂₀](3) respectively, have been characterized by two-dimensional [¹¹B–¹¹B]-COSY, [¹H–¹H]-COSY, and ¹H-{¹¹B(selective)} n.m.r. spectroscopy, and by [¹H–¹¹B] shift correlations. Deprotonation of compound (1) is shown to occur with the loss of the bridging hydrogen atoms associated with the conjuncto-boron atoms. A single-crystal X-ray diffraction analysis of [NMe₄]₂[anti-B₁₈H₂₀](4) showed the crystals to be monoclinic, space group P2₁/c, with a= 693.6(1), b= 1 601.6(3), c= 1 131.6(2) pm, β= 102.07(1)°, and Z= 2. The borane anion lies on the crystallographic centre of symmetry and the solid-state structure confirms that obtained from n.m.r. spectroscopy.