NEW WEAKLY COORDINATING ANIONS .2. DERIVATIZATION OF THE CARBORANE ANION CB11H12-

Of all the known classes of weakly coordinating anions (oxy anions, fl uoro anions, tetraarylborates, carbanions, polyoxometalates, and carbo ranes), it is the carboranes that are perhaps most suited to further d erivatization. With the ultimate goal of making the 12-vertex closo-ca rborane CB11H12- larger, more versatile, more chemically inert, less c oordinating, less nucleophilic, and more soluble in low dielectric sol vents, 13 new derivatives have been synthesized. C-Lithiation of CB11H 12- followed by treatment with alkyl, silyl, or phosphine halides lead s to the 1-ethyl, 1-(triphenylsilyl), 1-(trifluoromethyl), 1-(diphenyl phosphino), and 1-benzyl derivatives and a mixture of the 7-(pentafluo rophenyl) and 12-(pentafluorophenyl) derivatives. In general, conditio ns for high regiospecificity can be found. Conditions for the controll ed halogenation of CB11H12- with halogens and/or N-halosuccinimides ha ve been developed such that good syntheses of the 12-bromo, 7,12-dibro mo, 12-chloro, and 7,12-dichloro derivatives can be achieved. The pare nt anion can also be derivatized in the 12-position with mercury(II)ac etate or trifluoroacetate. Treatment of the 12-mercurated derivative w ith iodine gives the 7,12-diiodo derivative. All derivatives have been extensively characterized by B-11 NMR spectroscopy. The 12-bromo deri vative has been characterized as its cesium and silver salts by single -crystal X-ray crystallography.