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Issue 13, 2005
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Carborane acids. New “strong yet gentle” acids for organic and inorganic chemistry

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Abstract

Icosahedral carborane anions such as CHB11Cl11 are amongst the least coordinating, most chemically inert anions known. They are also amongst the least basic, so their conjugate acids, H(carborane), are superacids (i.e. stronger than 100% H2SO4). Acidity scale measurements indicate that H(CHB11Cl11) is the strongest pure Brønsted acid presently known, surpassing triflic and fluorosulfuric acid. Nevertheless, it is also an extremely gentle acid—because its conjugate base engages in so little chemistry. Carborane acids separate protic acidity from anion nucleophilicity and destructive oxidative capacity in the conjugate base, to a degree not previously achieved. As a result, many long-sought, highly acidic, reactive cations such as protonated benzene (C6H7+), protonated C60 (HC60+), tertiary carbocations (R3C+), vinyl cations (R2C[double bond, length as m-dash]C+–R), silylium ions (R3Si+) and discrete hydronium ions (H3O+, H5O2+etc.) can be readily isolated as carborane salts and characterized at room temperature by X-ray crystallography.

Graphical abstract: Carborane acids. New “strong yet gentle” acids for organic and inorganic chemistry

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Article information


Submitted
05 Oct 2004
Accepted
08 Feb 2005
First published
25 Feb 2005

Chem. Commun., 2005, 1669-1677
Article type
Feature Article

Carborane acids. New “strong yet gentle” acids for organic and inorganic chemistry

C. A. Reed, Chem. Commun., 2005, 1669
DOI: 10.1039/B415425H

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