Theoretical study of protonation of the B12H122− anion and subsequent hydrogen loss from the B12H13−: Effect of the medium

Protonation of B12H122− in the presence of acetonitrile molecules has been studied using density functional theory on the B3LYP/6-31+G* and more flexible B3LYP/6-311++G** levels. The B12H122− anion has been surrounded with twelve acetonitrile molecules according to the “supermolecular” approach and H+ was added to the system. Protonation of B12H122− is considered as a proton H* transfer from a nitrogen atom of protonated acetonitrile CH3CN⋅H+ to a facet BBB of a boron cluster. Calculated Proton Affinity (PA) of B12H122− in the presence of solvent molecules is ∼0.4 kcal/mol. This is much lower than that reported previously for bare B12H122− and is within the error of B3LYP calculation. Removal of H2 from the previously formed B12H13−⋅12CH3CN has been studied. The estimated value of the energy barrier for hydrogen removal is ∼11.1 kcal/mol. BH2-isomer of B12H13−⋅12CH3CN is in the ground state and is the starting reagent for calculating the elementary reaction of H2 removal. Both B12H13−⋅12CH3CN systems either with BH2-form of B12H13− or with an additional H* located on the triangular facet BBB have similar energies with the preference (∼5.2 kcal/mol) of the BH2-form. Total energy needed for hydrogen removal and generation of the B12H11− anion with a vacant “hole” is moderate. Once the energy barrier has been overcome, the reaction becomes endothermic. IR spectra for a solvated B12H122− anion in the presence of H+ (either close to one of CH3CN molecules or as a part of B12H13−) have been calculated and compared with IR spectra of [(CH2Naph)Ph3P]2B12H12 and (Bu4N)2B12H12 in acetonitrile and/or CF3COOH solutions. Splitting of ν(B−H) band of the B12H122− anion is treated by a solvate model.