Carboxonium Derivatives of closo-Decaborate Anion [2,6-B₁₀H₈O₂CC₆H₄R]^– Based on Aromatic Carboxylic Acids: Synthesis and Physicochemical Properties

The series of carboxonium derivatives of the closo-decaborate anion of the general form [2,6-B₁₀H₈O₂CC₆H₄R]^–, where R = F, CH₃, C₃H₇, and C₆H₅, were prepared. To obtain the target systems, the reaction between the [B₁₀H₁₁]^– anion and aromatic carboxylic acids was used. This process took place in two stages through the formation of a monosubstituted derivative of the general form [2-B₁₀H₉OC(OH)C₆H₄R]^–, where R = F, CH₃, C₃H₇, and C₆H₅, followed by intramolecular cyclization, leading to the formation of the target disubstituted carboxonium derivatives. The structure of the [2,6-B₁₀H₈O₂CC₆H₄-C₆H₅]^– anion was determined by single-crystal X-ray diffraction. The resulting carboxonium derivatives are capable of protonation to form neutral systems of the general form [2,6-B₁₀H₈O₂CC₆H₄R(H^fac)]⁰, where R = F, CH₃, C₃H₇, C₆H₅. When a protonated carboxonium derivative of acetonitrile is added to a solution, a trisubstituted derivative of the general form [B₁₀H₇O₂CC₆H₄R(NCCH₃)]⁰ is formed.