The synthesis and properties of the nitrilium derivatives of closo-dodecaborate [B12H12]²⁻, closo-decaborate [B10H10]²⁻, cobalt bis(dicarbollide) [3,3’-Co(1,2-C2B9H11)2]⁻, nido-decaborate [B10H14]²⁻ and nido-carborane [7,8-C2B9H12]⁻ are reviewed.

Nucleophilic addition reactions to the activated triple bond of the nitrilium derivatives of the closo -dodecaborate anion were studied.

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-(CH₂)₄O-7,8-C₂B₉H₁₁] and [10-O(CH₂CH₂)₂O-7,8-C₂B₉H₁₁] with various nucleophiles was developed. Both cyclic oxonium derivatives can be obtained as single isomers by reaction of the parent anion [7,8-C₂B₉H₁₂]^- 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.

A number of new nido-carboranyl amidines 10-R(CH₂)_nNHC(Et)HN-7,8-C₂B₉H₁₁ (n = 2, R = OH, OMe, and NMe₂; n = 3, R = OH) were synthesized by the nucleophilic addition of amino alcohols and N,N-dimethylethylenediamine to the highly activated –CN⁺– triple bond of the 10-propionitrilium derivative of nido-carborane. A similar reaction of 10-EtCN-7,8-C₂B₉H₁₁ with ethylenediamine unexpectedly resulted in the cleavage of the CN bond to form the ammonium derivative 10-H₃N-7,8-C₂B₉H₁₁. The complexation of the synthesized carboranyl amidines 10-MeO(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ and 10-Me₂N(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ with nickel and palladium phosphine complexes [(Ph₃P)₂MCl₂] (M = Ni, Pd) was studied. The reactions with 10-MeO(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ result in half-sandwiched metallacarborane complexes with the retention of one triphenylphosphine ligand [3-Ph₃P-3-(8-MeOCH₂CH₂NC(Et)NH)-3,1,2-MC₂B₉H₁₀], while the reactions with 10-Me₂N(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ proceed with the complete loss of the phosphine ligands and lead to the formation of complexes with the η⁵:κ²(N,N′)-coordinated carboranyl amidine ligand [3,3-(8-Me₂NCH₂CH₂NC(Et)NH)-3,1,2-MC₂B₉H₁₀]. The crystal molecular structures of the synthesized complexes were determined by single crystal X-ray diffraction.

This review summarizes data on the main types of charge-compensated nido-carborane derivatives. Compared with organic analogs, onium derivatives of nido-carborane have increased stability due to the stabilizing electron-donor action of the boron cage. Charge-compensated derivatives are considered according to the type of heteroatom bonded to a boron atom.