Carborane acidities

Thomas and Hawthorne have synthesized unimolecular, nanospherical boron-rich dodeca(carboranyl)-substituted closomers (122) (Fig. 71) for their potential application as drug-delivery platforms for BNCT.148 The substituted closomers were synthesized by reacting carborane acid chloride with the dodecahydroxy dodecaborate closomer in methylene chloride by utilizing a threefold excess of the former in triethylamine. The twelve pendant closo-1,2-carborane units in the closomer could... 

AG values of deprotonation are as low as 249-250 kcal mol 1 for HS03F or HF associated with SbF5 or S03. The strongest superacid was found to be dodeca-fluorocarborane acid CBnF12H with a AG of 209 kcal mol 1 even suggesting that the dodeca(trifluoromethyl)carborane acid CBnlCF l H would be below the 200 kcal moL1 level ... 

George Olah published a perspective in which he provided an overview of the research of his group over five decades.1 Christopher Reed surveyed the chemistry of carborane acids, the strongest pure Brpnsted acids known, with a conjugate base that engages in little chemistry.2 These acids are employed to prepare highly acidic carbocations, including protonated benzene, protonated C6o, tertiary carbocations, vinyl cations, and silylium ions. The synthesis and properties of unusual... 

Many carbon acids, upon losing the proton, form carbanions that are stabilized by resonance. Structural reorganization (movement of atoms to different positions within the molecule) may accompany this. Chloroform, HCN, and 1-alkynes do not form resonance-stabihzed carbanions, and these behave kinetically as normal acids.It has been reported that carborane acids, such as H(CHBnH5Cl6), are the strongest isolable (Lewis-free) Brpnsted acids known. 

C. A. Reed, Carborane acids. New strong yet gentle acids for organic and inorganic chemistry. Chem. Commun. 2005, 1669. 

Alternatively, carborane acid chlorides can be prepared from the reaction between lithiocarboranes and phosgene [337). 

Carborane acids are strong acids because their anions have exceptionally weak basicities. This arises from the large size of the anions, the delocalized nature of the negative charge in the [CBn] cluster, and the shield of halide substituents. There is an additional important necessity for preparing such a strong acid this is the... 

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