The preparation of novel nitrilium derivatives of closo-dodecaborate anion [B₁₂H₁₁NCR]⁻, R = n-C₃H₇, i-C₃H₇, 4-C₆H₄CH₃, 1-C₁₀H₇ is described. Target compounds were obtained in good yields (up to 73%). The synthesis of target borylated nitrilium derivatives was characterised by the simplicity of the chemical apparatus and the absence of the necessity for the purification of desired compounds. The crystal structures of previously obtained [B₁₂H₁₁NCCH₃]⁻ and novel [B₁₂H₁₁NCC₃H₇]⁻ were established with the help of X-ray structure analysis. DFT-analysis of several nitrilium derivatives [B₁₂H₁₁NCR]⁻, R = CH₃, C₃H₇, 4-CH₃C₆H₄ was carried out. The main peculiarities of the C≡N bond of the exo-polyhedral substituent were revealed in terms of bond lengths, bond orders and atomic charges. The LUMO orbitals of the systems considered were examined for understanding of the electrophilic nature of the nitrilium derivatives of the closo-dodecaborate anion.