New route to 1-thia-closo-dodecaborane(11), closo-1-SB11H11, and its halogenation reactions. The effect of the halogen on the dipole moments and the NMR spectra and the importance of spin–orbit coupling for the 11B chemical shifts

Abstract

Reaction between nido-B₁₀H₁₄ (1) and elemental sulfur in CHCl₃ in the presence of Et₃N at room temperature, followed by treatment with Et₃N·BH₃ at 170–190 °C, resulted in the isolation of closo-1-SB₁₁H₁₁ (2) in 50% yield. Selected electrophilic halogenation reactions of compound 2 led to the isolation of a series of monohalogenated derivatives of general constitution 12-X-closo-1-SB₁₁H₁₀ (12-X-2, where X = Cl, Br, and I). The structures of 12-Cl-2 and 12-I-2 were determined by an X-ray diffraction analysis and the structures of all compounds were geometry optimised at the RMP2(fc)/6-31G* level. The constitution of all compounds is consistent with the results of mass spectrometry and multinuclear (¹H and ¹¹B) spectroscopy complemented by two-dimensional [¹¹B–¹¹B]-COSY and ¹H{¹¹B(selective)} NMR measurements. Experimental ¹¹B chemical shifts generally show acceptable agreement with theoretical values calculated by GIAO methods, but spin–orbit coupling must be included for nuclei bearing heavy-atom substituents such as Br or I. The dipole moments determined for the B12-X bonds show similarities to those of aliphatic C–X bonds and confirm unambiguously the B12 → S dipole moment orientation in the SB₁₁ cage.