The monocarba-closo-dodecaborate anion [HCB11H11] À (Fig. 1) and its derivatives [HCB11X11] À (from here on: carborane anions; X= H, Me, Hal) are a potentially very advantageous class of weakly coordinating anions (WCA). 1, 2 While other types of WCA (most common are probably the fluorinated tetraarylborates) 3 possess similarly weak basicity and nucleophilicity, 4 carborane anions are inimitable in their robustness. The combination of these properties uniquely empowers carboranes to sustain both the integrity and the reactivity of even the most potent Lewis or Brønsted acids. 5–7 The acid H [HCB11Cl11] is the strongest reported Brønsted acid to date, yet it is stable to sublimation at 200 1C. 8 Carborane anions allowed isolation of discrete salts of vinyl, 9 tert-butyl, 10 and fullerene11 cations. The Me [HCB11Me5Br6] reagent is several orders of magnitude more reactive than methyl triflate. 12 Carborane anions have allowed for solution chemistry of silylium (R3Si+) cations5, 13, 14 and even for the isolation of a discrete silylium cation in the solid state. 15 Our interest in carborane anions stems from their matchless performance in silylium-and aluminium-catalyzed16 C–F activation. 17 In spite of their advantages, carborane anions are still in the process of making the transition ‘‘from exotica to specialty chemicals’’as formulated by Reed in 1998. 2 A major obstacle to wider adoption of carborane anions as WCA’s of choice have been the arduous synthetic routes. In this communication, we report dramatically simplified syntheses of undecahalogenated carborane anions, arguably the most desirable members of the family because of their highest robustness and least basicity. 4 Syntheses of fluorinated (or trifluoromethyl-substituted) carboranes require the use of F2 gas, which involves nontrivial setup and training. 18, 19 Chlorination, bromination, and iodination of carboranes are also accomplished using elemental halogens (or ICl). 1 The heavier halogens are progressively less hazardous, however brominated and especially iodinated carboranes suffer from poor solubility and are more coordinating than their chlorinated analogs.[HCB11H11] À has been described as aromatic in three dimensions. 20 Its halogenation has been mechanistically likened to classical electrophilic aromatic substitution and proceeds first at the ‘‘para’’position, followed by the ‘‘meta’’belt, and finally, by the ‘‘ortho’’belt. 1 Hexahalogenation (Cl, Br, I) can be performed selectively. 2, 21 However, successful execution of the hexahalogenation syntheses requires real-time monitoring of the reaction by 11B NMR for hours or days, while, especially in the case of hexachlorination, deviations from the scale and conditions of the optimized procedure often result in loss of selectivity and overhalogenation. Undecachlorination takes place with ICl in triflic acid after several days at> 200 1C. 8, 22 This is a consistently reproducible synthesis, but it requires a $3000 pressure-and reagent-resistant reactor for a 2 g batch capacity, and a rather extensive workup. Undecabromination has been reported to take place under similarly harsh conditions on a small scale in a sealed tube with Br2 in triflic acid. 22 Undecachlorination of [MeCB11H11] À proceeded under less draconian conditions with Cl2 in hot glacial acetic acid after a week, 22 but it required the extra methylation step which furthermore precludes the potentially attractive subsequent functionalization at the carbon site.

We were interested in developing methods for halogenation that ideally (a) are reproducible and insensitive to minor variations in conditions, ie,‘‘foolproof’’;(b) are scalable;(c) do not require monitoring of the course of …