The process of protonation of [2,6-B₁₀H₈O₂CCH₃]⁻ was investigated both theoretically and experimentally. The most suitable conditions for protonation of the derivative [2,6-B₁₀H₈O₂CCH₃]⁻ were found. The process of protonation was carried out in the presence of an excess of trifluoromethanesulfonic acid CF₃SO₃H at room temperature in dichloromethane solution. The structure of the resulting complex [2,6-B₁₀H₈O₂CCH₃*H^fac]⁰ was established using NMR data and the results of DFT calculations. An additional proton atom H^fac was found to be localized on one of the facets that was opposite the boron atom in a substituted position, and which bonded mainly with one apical boron atom. The main descriptors of the B-H^fac bond were established theoretically using QTAIM and NBO approaches. In addition, the mechanism of [2,6-B₁₀H₈O₂CCH₃]⁻ protonation was investigated.

A comprehensive study focused on the preparation of disubstituted carboxonium derivatives of closo-decaborate anion [2,6-B₁₀H₈O₂CC₆H₅]⁻ was carried out. The proposed synthesis of the target product was based on the interaction between the anion [B₁₀H₁₁]⁻ and benzoic acid C₆H₅COOH. It was shown that the formation of this product proceeds stepwise through the formation of a mono-substituted product [B₁₀H₉OC(OH)C₆H₅]⁻. In addition, an alternative one-step approach for obtaining the target derivative is postulated. The structure of tetrabutylammonium salts of carboxonium derivative ((C₄H₉)₄N)[2,6-B₁₀H₈O₂CC₆H₅] was established with the help of X-ray structure analysis. The reaction pathway for the formation of [2,6-B₁₀H₈O₂CC₆H₅]⁻ was investigated with the help of density functional theory (DFT) calculations. This process has an electrophile induced nucleophilic substitution (EINS) mechanism, and intermediate anionic species play a key role. Such intermediates have a structure in which one boron atom coordinates two hydrogen atoms. The regioselectivity for the process of formation for the 2,6-isomer was also proved by theoretical calculations. Generally, in the experimental part, the simple and available approach for producing disubstituted carboxonium derivative was introduced, and the mechanism of this process was investigated with the help of theoretical calculations. The proposed approach can be applicable for the preparation of a wide range of disubstituted derivatives of closo-borate anions.

Borylated carboxonium ions based on closo-dodecaborate anions were obtained. The nature of the interaction between the cluster cage and the organic moiety was analysed theoretically.

A theoretical investigation of mono-methyl derivatives of closo-borate anions of the general form [B_nH_nCH₃]^2– (n = 6, 10, 12) and monocarboranes [HCB_nH_nCH₃]⁻ (n = 5, 9, 11) was carried out. An analysis of the main bonding descriptors of exo-polyhedral B–C bonds was performed using the QTAIM (quantum theory of “Atoms in Molecules”), ELF (electron localisation function), NBOs (natural bond orbitals) analyses and several other approaches for the estimation of B–C bond orders (viz. Laplacian bond order (LBO), fuzzy bond order (FBO) and Mayer and Wiberg formalisms). Based on the data obtained on electron density descriptors, it can be concluded that orbital interaction increases with increasing boron cluster size. The present investigation provides a better understanding of exo-polyhedral B–C bond phenomena in boron cluster systems. The data obtained can be used to estimate B–C bond strength, which can be useful for studies devoted to the synthesis and properties of boron cluster systems.

A theoretical modelling of the interaction process between a protonated complex of carboxonium derivative [2,6-B₁₀H₈O₂CCH₃*H^fac]⁰ and acetonitrile molecule CH₃CN was carried out. As a result of the process, a trisubstituted [B₁₀H₇O₂CCH₃(NCCH₃)]⁰ derivative was formed. This reaction has an electrophile-induced nucleophilic substitution (EINS) mechanism. The main intermediates and transition states of the substitution process were established. As in the case of all previously investigated EINS processes, the key intermediate was an anion with a dihydrogen H₂ fragment attached to one boron atom (B(H₂) structure motif). The process of nucleophilic substitution can proceed on a different position of the cluster cage. The main potential pathways were assessed. It was established that substitution on the B₄ position of the cluster cage was the most energetically favourable, and the [2,4,6-B₁₀H₇O₂CCH₃(NCCH₃)]⁰ isomer was formed.

This paper reports on a theoretical investigation of the bond dissociation energies of B–H and B–F interactions of closo-borate anions [B_nH_n−1X]²⁻ (n = 6, 10 and 12; X = H and F), in which homolytic and heterolytic bond breaking cases were considered, and the main trends in bond dissociation energy values were analysed. The wB97X-D3/TZVPP level of theory was applied for geometry optimisation of the molecular species under consideration. DLPNO-CCSDT/CBS single-point calculations were made to ensure an accurate estimation of the target systems’ electronic energy. The correlations between the value of the bond dissociation energy and variables such as electron density descriptors of B–H and B–F interactions and frontier orbital energies (HOMO, SOMO and LUMO) were established.