Observation of Room Temperature B–Cl Activation of the HCB₁₁Cl₁₁^– Anion and Isolation of a Stable Anionic Carboranyl Phosphazide

Abstract

The perchlorinated carba-closo-dodecaborate anion is typically inert toward B-Cl functionalization. We present here the observation of two competing reactions that occur with this anion at ambient temperature. When this molecule is treated with n-BuLi and subsequently reacted with tosyl azide, a cycloaddition occurs and results in chloride substitution at a B-Cl vertex. The competing and dominant pathway is a substitution reaction to form the azide N3CB11Cl11(-). This rare anionic carboranyl azide reacts with PPh3 in FC6H5 to afford a stable anionic phosphazide. When dissolved in tetrahydrofuran, the phosphazide is in equilibrium with free PPh3 and N3CB11Cl11(-). Both the triazole and phosphazide are characterized by single-crystal X-ray diffraction, NMR and IR spectroscopy, and high-resolution mass spectrometry.

Nonclassical Applications of closo-Carborane Anions: From Main Group Chemistry and Catalysis to Energy Storage

“…Triazole radical anions eluded isolation for many decades until a carborane-substituted derivative provided ready access to this interesting family of reactive compounds (Scheme ). A novel “click-like” reaction between [Li + ]­[3Cl 11 ] and azides Ph-N 3 was discovered to access triazole 101 , , which possesses aromatic characteristics inside and outside the cluster core (Scheme ). Notably, these reactions were demonstrated to be effective for various azides (for N 3 -R, R = Ph, 4-FC 6 H 4 , 4-MeOC 6 H 4 , 2-MeC 6 H 4 , or Ad) .…”

Kinetic and mechanistic studies of the Staudinger reduction: On the chemistry of aryl phosphazides

“…In principle, protonation may occur at either N α or N γ : N γ in phosphazides and is known to be susceptible to electrophilic attack by species such as acyl halides, [ 8,34 ] and crystal structure data suggests that both sites can interact with cationic and electrophilic species, such as metal complexes and boranes. [ 7,35 ]…”

“…principle, protonation may occur at either N α or N γ : N γ in phosphazides and is known to be susceptible to electrophilic attack by species such as acyl halides, [8,34] and crystal structure data suggests that both sites can interact with cationic and electrophilic species, such as metal complexes and boranes. [7,35] An alternative involving protonation of the N-oxide group has precedent in the literature with strong acids, [36] but the N-oxide group is not considered basic enough to appreciably deprotonate water. [37] Stabilized phosphazides (2,6-dinitrophenyl species) have pK a values for their conjugate acids in the range 9-11 in nitromethane, [38] making the phosphazide a reasonable site for protonation.…”