| Abstract
| - A new class of potent electrophilic “R+” alkylating agents has been developed using weaklynucleophilic carborane anions as leaving groups. These reagents, R(CHB11Me5X6) (R = Me, Et, and i-Pr;X = Cl, Br), are prepared via metathesis reactions with conventional alkylating agents such as alkyl triflates,using the high oxophilicity of silylium ion-like species, Et3Si(carborane), as the driving force to obtainincreased alkyl electrophilicity. The crystal structure of the isopropyl reagent, i-Pr(CHB11Me5Br6), has beendetermined, revealing covalence in the alkyl−carborane bonding. This contrasts with the free i-Pr+carbocation observed when the anion is less coordinating (e.g. Sb2F11-) or with tertiary alkyl centers, as in[tert-butyl][carborane] salts. In solution, the reagents exist as equilibrating isomers with the alkyl group atthe 7−11 or 12 halide positions of the CB11 icosahedral carborane anion. These alkylating agents are soelectrophilic that they (a) react with alkanes at or below room temperature via hydride extraction to producecarbenium ions, (b) alkylate benzene without a Friedel−Crafts catalyst to give arenium ions, and (c) alkylateelectron-deficient phosphorus compounds that are otherwise inert to conventional alkylating agents suchas methyl triflate.
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