The Telluraboranes closo‐TeB₅Cl₅ and closo‐TeB₁₁Cl₁₁ with Exceptionally Long Body Diagonals: Synthetic and Bonding Motifs for Innovative Octahedral and Icosahedral Geometries

Abstract

Six-vertex closo-TeB 5 Cl 5 (1) and twelve-vertex closo-TeB 11 Cl 11 (2) telluraboranes have been prepared via copyrolysis of B 2 Cl 4 with TeCl 4 in vacuo at temperatures between 360 °C and 400 °C. Both compounds are sublimable, offwhite solids, and they have been characterized by one-and two-dimensional 11 B NMR and high-resolution mass spectroscopy. Both ab initio/GIAO/NMR and DFT/ZORA/NMR computations support octahedral and icosahedral geometries for 1 and 2, respectively, as expected due to their closo-electron counts. The octahedral structure of 1 has been confirmed by single-crystal X-ray diffraction on an incommensurately modulated crystal. The corresponding bonding properties have been analyzed in terms of the intrinsic bond orbital (IBO) approach. 1 is the first example of a polyhedral telluraborane with a cluster size smaller than 10 vertices.

Chlorinated polyhedral selenaboranes revisited by joint experimental/computational efforts: the formation of closo-1-SeB9Cl9 and the crystal structure of closo-SeB11Cl11

“…The 11 B experimental and computed chemical shifts of 1a and 1b have already been given in our previous report, but as experimental ones without specifications. In analogy with closo -TeB 5 Cl 5 , 12 the 11 B NMR spectrum of 1a shows the reported two broad signals in a 1 : 4 ratio at 23.2 ppm ( h 1/2 ≈ 110 Hz) for B(6) and at 4.6 ppm for B(2–5) with the expected cross-peak in the COSY 11 B 11 B NMR spectrum. The latter signal resolves to a quartet either by homodecoupling or by applying the Lorentz–Gaussian transformation with a 1 J ( 11 B 11 B) of 27 Hz (the computed J value is 30.6 Hz, see below and the ESI†), thereby indicating coupling with B(6).…”

“…The chemical shifts and assignments of 2 are in agreement with those established for the corresponding parent selenaborane closo-1-SeB 9 H 9 , 7f namely −19.9 ppm (B(6-9)), −5.4 ppm (B(2-5)) and +73.3 ppm (B(10)), with the last one representing an extreme value of antipodal deshielding. This effect has already been explained in relation to the δ( 11 B) of B(10) in closo-1-SB 9 H 9 to the much less pronounced downfield chemical shift of B (12) in closo-SB 11 H 11 . 17 The mass spectrum of selenaborane 2 exhibits a strong parent ion envelope with minor cut-offs, indicating the stepwise abstraction of BCl 2 and BCl 3 fragments, whose intensity patterns are consistent with the calculated spectra based on natural isotopic abundances.…”

“…The above B3LYP/6-311+G** geometry of 2 has also been used in NMR shift computations using the GIAO-PBE1PBE model chemistry with the same basis set as in the derivation of the molecular geometry of 2 , likewise successfully utilized in previous studies. 12,20 The most striking feature of the molecular geometry of 2 is the considerable expansion of the square belt adjacent to selenium (see Fig. 1), with the analogical pentagonal belt adjacent to Se in 1b exhibiting the same pattern.…”

“…It has been shown in all previous formations of heteroboranes via co-pyrolysis of B 2 X 4 with elemental halides in vacuo that the incorporation of heteroatoms can only occur in the gas phase, 10,12 and therefore the temperature during pyrolysis has to be high enough to vaporize both starting components, but not too high to cause the thermal degradation of the prospected heteroborane products ( e.g. as a reverse reaction of eqn (4)).…”

“…In addition, it was our intention to extend the still quite limited spectroscopic data of closo -SeB 5 Cl 5 and closo -SeB 11 Cl 11 available so far to allow comparisons with the data of the very recently reported related octahedral and icosahedral closo -telluraboranes. 12…”