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A new approach to synthesis of functional derivatives of 7,8-dicarba-nido-undecaborate anion based on ring-opening of its cyclic oxonium derivatives [10-(CH 2 ) 4 O-7,8-C 2 B 9 H 11 ] and [10-O(CH 2 CH 2 ) 2 O-7,8-C 2 B 9 H 11 ] with various nucleophiles was developed. Both cyclic oxonium derivatives can be obtained as single isomers by reaction of the parent anion [7,8-C 2 B 9 H 12 ] -with mercury(II) chloride in the corresponding solvents. Mechanism of formation of the cyclic oxonium derivatives of 7,8-dicarba-nido-undecaborate anion was proposed. A series of 7,8-dicarba-nido-undecaborate derivatives with terminal carboxylic and azide functions were prepared by the ring-opening reactions of the cyclic oxonium derivatives with substituted phenolate and azide ions, respectively.

Reactions of the iodonium derivative of cobalt bis(dicarbollide) anion [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] with Lewis bases in aromatic solvents were studied. The reactions proceed through the iodonium bridge opening, and the structure of the reaction products depends strongly on the nature of the Lewis base and solvent used. The reactions with conventional Lewis bases (L) give the corresponding products of Lewis base addition, [8-L-8′-I-3,3′-Co(1,2-C2B9H10)2], whereas the reactions with sterically hindered Lewis bases (L*) result in activation of the C−H bond of the aromatic solvent with formation of the corresponding aryl derivatives [8-Ar-8′-I-3,3′-Co(1,2-C2B9H10)2]−. Activated arenes, such as toluene, could react with [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] without Lewis bases, whereas strongly deactivated arenes do not give C−H activation products even in the presence of sterically hindered Lewis bases.