Superacidity of Boron Acids H₂(B₁₂X₁₂) (X=Cl, Br)

Abstract

Acid remarks: The anhydrous diprotic boron acids H2(B12X12) (X=Cl, Br; see picture, B orange, X green) are the first examples of diprotic superacids and may be the strongest acids yet isolated. Both protons protonate benzene to give benzenium ion salts that are stable at room temperature. These acids owe their existence to the stability of the icosahedral B12 cluster with its dinegative charge buried beneath a layer of halide substituents.magnified image

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…[262] At the Acidity Limit:C arborane-Based Neutral Acids: Thes trongest known Brønsted acids belong to the H[WCA] family,w here WCA is ac arborane anion, and are typically synthesized through the reaction of the silylated carborane anion with HCl [see Eq. [107,110] Furthermore,b oth protons of H 2 -(B 12 Cl 12 )w ere demonstrated to be capable of protonating benzene,t hus making its Brønsted acidity comparable with that of the H(HCB 11 Cl 11 )a cid. [236,260] Thes trength of the Brønsted acid is increased as the carborane anion becomes less coordinating and, as ar esult, the strongest neutral acid may be H(HCB 11 F 11 ) [236] closely followed by its chloride-containing relative H(HCB 11 Cl 11 ).…”

“…[10] However, more recently,adduct formation between ac omparatively mild Brønsted acid and as trong Lewis acid has also been demonstrated to provide highly Brønsted acidic systems. [11,107,110,236,250] [11,107,110,236,250] …”

“…(10) above]. [107] Thef luoride-containing analogue H 2 (B 12 F 12 )h as,h owever,o nly been reported as its dihydronium salt (H 3 O) 2 [B 12 F 12 ]. [11] These highly potent Brønsted acids are able to quantitatively protonate extremely weak bases such as linear alkanes, [236] thereby giving rise to tertiary carbocations through facile 1,2-shifts of primary or secondary carbocations of benzene [263,264] and fullerenes [265] at the one equivalent level.…”

Investigations on a series of novel ionic liquids containing the [closo-B12Cl12]2− dianion

“…35 Thereby, we can conclude that both the higher symmetry and the enhanced electrostatic forces in [closo-B 12 Cl 12 ] 22 dianion containing salts led to an increased lattice energy, and of course, the higher melting points. Inspired by this, we may predict that the monocharged analog of [closo-B 12 Cl 12 ] 22 dianion, namely the [CHB 11 Cl 11 ] 2 anion, 24 would have the potential to form the corresponding lowest melting point boron cluster anion salts due to its monovalent anion.…”

Rhodium(III)‐Catalyzed Alkenylation–Annulation of closo‐Dodecaborate Anions through Double B−H Activation at Room Temperature

“…Steric factors played acrucial role in the formation of 3.W hen the methyl group on the phenyl ring was changed from the para to the meta position, the yield of the isolated product 3 decreased from 85 to 77 %; with the methyl group in the ortho position, the desired product was not obtained (entries 2-4). For 3a,the specific bond distances for the five-membered ring are B1ÀB2 1.713(4), B1ÀN1 1.517(3), N1ÀC1 1.325(3), C1ÀO 1.320(3), OÀB2 1.508 (3). On the other hand, thiophenyl-substituted diacetylene served as as uitable substrate,a se xemplified by the synthesis of 3p in 67 %yield (entry 16).…”