The rapid progress in the chemistry of carboranes and other polyhedral boron compounds makes the development of methods for the synthesis of their various functional derivatives a high priority. The formation of cyclic oxonium derivatives followed by the ring opening is one of the most efficient methods for the preparation of these compounds. This review addresses the data on the use of the nucleophilic ring opening of cyclic oxonium derivatives based on cobalt and iron bis(dicarbollides), which have been extensively studied in recent years. Reactions involving O-, N-, S-, P- and C-nucleophiles are considered as a route to the targeted synthesis of a wide range of organic boron derivatives, in particular various boron-containing biologically active compounds. Possible applications of the reaction products are discussed.The bibliography includes 197 references.

Substituted undecahydrido-closo-dodecaborates [B₁₂H₁₁NR₂]²⁻ have potential use in materials and drugs, but have presented a synthetic challenge. Microwave-assisted palladium-catalyzed amination of iodo-dodecaborate [B₁₂H₁₁I]²⁻ allows mild and reproducible formation of B–N bonds with aromatic amines, HN-containing heteroaromatics, and amides. The reaction allows general access to amides, reproducible reactions to dodecaborate-substituted anilines, and, for the first time, the substitution of dodecaborate with HN-containing heterocycles.

The 1,4-dioxane derivative of cobalt bis(dicarbollide) reacts with dialkylsulfides and triphenylphosphine to give the corresponding sulfonium and phosphonium derivatives [8-L(CH₂CH₂O)₂-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] (L = SMe₂, S(CH₂CH₂)₂O, PPh₃). The treatment of the triphenylphosphonium derivative with sodium hydroxide results in contraction of the side chain with formation of [8-HOCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻. The same product was obtained by treatment of the dimethylsulfonium derivative with the poorly nucleophilic base t-BuOK, whereas the stronger nucleophiles induce the sulfur demethylation to give [8-MeS(CH₂CH₂O)₂-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻. The alcohol was used for the synthesis of a series of other short-spacer functional derivatives [8-XOCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻ (X = NH₂, SH, N₃). A similar contraction of the disclosed 1,4-dioxane ring via the reactions with SMe₂ and PPh₃ can be used for the synthesis of short-spacer functional derivatives of nido-carborane, whereas the 1,4-dioxane derivatives of closo-decaborate and closo-dodecaborate anions, being stronger electron donors, are more stable and do not react with dimethylsulfide and triphenylphosphine.

A simple and efficient method was developed for the one-pot synthesis of 3-aryl derivatives of ortho-carborane with sensitive functional groups using 3-iodo-ortho-carborane and aryl zinc bromides that were generated in situ. A series of 3-aryl-ortho-carboranes, including those containing nitrile and ester groups, 3-RC₆H₄-1,2-C₂B₁₀H₁₁ (R = p-Me, p-NMe₂, p-OCH₂OMe, p-OMe, o-CN, p-CN, o-COOEt, m-COOEt, p-COOEt) was synthesized using this approach. The solid-state structures of 3-RC₆H₄-1,2-C₂B₁₀H₁₁ (R = p-OMe, o-CN, and p-CN) were determined by single crystal X-ray diffraction. The intramolecular hydrogen bonding involving the ortho-substituents of the aryl ring and the CH and BH groups of carborane was discussed.

An unusual reactivity of 9-iodo-nido-carborane [9-I-7,8-C₂B₉H₁₁]⁻towards nucleophiles under strong basic conditions was revealed.

The simple and efficient method was developed for the one-pot synthesis of B-substituted aryl derivatives of ortho-carborane with functional groups sensitive to organolithium and organomagnesium reagents using 9-iodo-ortho-carborane and generated in situ organozinc compounds. The method proposed was used to prepare a series of 9-aryl-ortho-carboranes, including those containing nitrile and ester groups, 9-RC₆H₄-1,2-C₂B₁₀H₁₁ (R = p-Me, p-NMe₂, p-OCH₂OMe, o-OMe, p-OMe, o-CN, p-CN, o-COOEt, m-COOEt, and p-COOEt). It was demonstrated that the same approach can be used for synthesis of diaryl derivatives of ortho-carborane 9,12-(RC₆H₄)₂-1,2-C₂B₁₀H₁₀ (R = H, p-Me). The solid-state structures of 9-RC₆H₄-1,2-C₂B₁₀H₁₁ (R = p-NMe₂, p-OCH₂OMe, o-OMe, o-CN, p-CN, m-COOEt, and p-COOEt) and 9,12-(p-MeC₆H₄)₂-1,2-C₂B₁₀H₁₀ were determined by single crystal X-ray diffraction.