Isolable Boron Persulfide: Activation of Elemental Sulfur with a 2‐Chloro‐Azaborolyl Anion

Abstract

The novel boron persulfide 2 LB(η(2) -S2 ) (L=[ArNC(R)CHC(R)](-) ; Ar=2,6-Me2 C6 H3 , R=tBu) was obtained by the reaction of the 2-chloro-azaborolyl anion 1 (LBCl)K(THF) with 0.25 equiv of elemental sulfur (S8 ). Persulfide 2 is labile in solution and could be converted to the cyclic tetrasulfide LBS4 (3) and hexasulfide LBS6 (4) in the presence of sulfur at room temperature and 50 °C, respectively. Desulfination of 2 with triphenylphosphine resulted in the formation of the thioxoborane LB=S (5). Alternatively, 3 and 4 could be obtained by the reaction of 1 with an excess of sulfur. Structural analysis of 2 disclosed the relatively long S-S bond of 2.1004(8) Å due to the lone-pair repulsions of the two sulfur atoms, as disclosed by DFT calculations.

Reactivity of the 2‐Chloroazaborolyl Anion

“…The geometry of the boron atom can be best described as distorted tetrahedral. The B–S bond lengths [1.908 and 1.907(18) Å] are very close to those reported for the known boron polysulfides LBS 6 [1.899 and 1.948(2) Å], but they are significantly longer than those in the three‐coordinate boron compounds containing a B–SR bond (1.770–1.805 Å) …”

“…Furthermore, the calculations have also disclosed that one electron is localized at the boron center and the other unpaired electron is delocalized over the five‐membered ring in the triplet state. More recently, the first boron persulfide was synthesized by the activation of elemental sulfur with 1 . These results prompted us to continually investigate its reactivity and to generate the proposed intermediate.…”

Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

“…Further investigations led to the synthesis of several chalcogenboranes exhibiting multiple bonds, B=X (X= O, S, Se, and Te) [15–27] . In this regard, Frank et al.…”

Synthesis and Structural Characterization of Carbene-Stabilized Carborane-Fused Azaborolyl Radical Cation and Dicarbollyl-Fused Azaborole

“…On the other hand, we wondered if 1 could be oxidized by elemental sulfur via two-electron oxidation to give “BS”-containing compounds. , To this end, treatment of 1 with 0.25 equiv of elemental sulfur in THF at room temperature afforded the unprecedented zwitterionic salt 3 as orange-red crystals in 31% yield (Scheme ). The 11 B NMR spectrum of the cage exhibited a 1:1:1:1:1:1:1:1:1 pattern, ranging from 5.3 to −25.1 ppm, indicating the formation of a nido -C 2 B 9 species.…”