Effect of Nature of Substituents on Coordination Properties of Mono- and Disubstituted Derivatives of Boron Cluster Anions [BnHn]2– (n = 10, 12) and Carboranes with exo-Polyhedral B–X Bonds (X = N, O, S, Hal)

This review systematizes data on the coordination ability of mono- and disubstituted derivatives of boron cluster anions and carboranes in complexation with transition metals. Boron clusters anions [BnHn]2–, monocarborane anions [CBnHn–1]–, and dicarboranes [C2BnHn–2] (with non-functionalized carbon atoms) (n = 10, 12) containing the B–X exo-polyhedral bonds (X = N, O, S, Hal) are discussed. Synthesis and structural features of complexes known to date are described. The effect of complexing metal and substituent attached to the boron cage on the composition and structures of the final complexes is analyzed. It has been established that substituted derivatives of boron cluster anions and carboranes can act as both ligands and counterions. A complexing agent can coordinate substituted derivatives of the boron cluster anions due to three-center two-electron 3c2e MHB bonds, by the substituent functional groups, or a mixed type of coordination can be realized, through the BH groups of the boron cage and the substituent. As for B-substituted carboranes, complexes with coordinated substituents or salts with non-coordinated carborane derivatives have been isolated; compounds with MHB bonding are not characteristic of carboranes.

Non-Covalent Interactions in the Crystal Structures of Perbrominated Sulfonium Derivatives of the closo-Decaborate Anion

A new series of compounds based on perbrominated disubstituted sulfonium derivatives of the closo-decaborate anion (n-Bu₄N)[2-B₁₀Br₉SR₂] (R = n-Pr, i-Pr, n-Bu, n-C₈H₁₇, n-C₁₂H₂₅, n-C₁₈H₃₇) was obtained, characterised by modern physicochemical methods of analysis. According to the results of an X-ray diffraction study, some of the anions and solvate molecules were disordered. The cations (n-Bu₄N)⁺ and anions [2-B₁₀Br₉SR₂]^- were associated via C-H…Br and H…H contacts. In addition, Br…Br interactions between anions were revealed. The role of these contacts was analysed in terms of Hirshfeld surface analysis, QTAIM theory and the NCI method using quantum chemical calculations. An increase in the size of the alkyl R moiety led to significant strengthening of the total energy of H…H interactions. In the case of R = -n-C₁₈H₃₇, a parallel mutual orientation of alkyl moieties was established that was similar to the packing of salts of fatty acids. The nature of C-H…Br and Br…Br interionic interactions was found to be attractive, in contrast to the repulsive nature of intermolecular Br…Br interactions.

Synthesis of Perchlorinated Sulfonium Derivatives of closo-Decaborate Anion [2-B10Cl9SR2]- (R = i-C3H7, n-C3H7, n-C4H9, n-C8H17, n-C12H25, n-C18H37, CH2Ph, and cyclo-S(CH2)4)

A method for obtaining perchlorinated di-S,S-substituted derivatives of the closo-decaborate anion with various alkyl groups has been developed: [B₁₀Cl₉SR₂]^- (R= i-C₃H₇, n-C₃H₇, n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅, n-C₁₈H₃₇, CH₂Ph, and cyclo-S(CH₂)₄). The method is based on the preparation of the sulfonium-substituted anion [B₁₀H₉SR₂]^- by alkylation of the anion [B₁₀H₉SH]^2- with bromoalkanes (i-C₃H₇Br, n-C₃H₇Br, n-C₄H₉Br, n-C₈H₁₇Br, n-C₁₂H₂₅Br, n-C₁₈H₃₇Br, PhCH₂Br, and BrCH₂(CH₂)₂CH₂Br) followed by the cluster chlorination with sulfuryl chloride SO₂Cl₂ in acetonitrile. The process proceeds until the hydrogen atoms in the boron cluster are completely replaced with chlorine and completes within 60 h. It has been found that the melting point of salts ((C₄H₉)₄N)[B₁₀Cl₉SR₂] (R= i-C₃H₇, n-C₃H₇, n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅, and n-C₁₈H₃₇) strongly depends on the length of the hydrocarbon chain of the substituent R.