Theoretical study of protonation of the B 10 H 10 2− anion and subsequent hydrogen removal due to substitution reaction in acidic medium

The protonation of B 10 H 10 2− in the presence of acetonitrile molecules has been studied using the Density Functional Theory on the B3LYP/6-31G ∗ and more flexible B3LYP/6-311++G ∗∗ levels. The B 10 H 10 2− anion was surrounded by twenty acetonitrile molecules CH 3 CN to complete the first sphere of solvation, and H + was added to the system. The protonation of B 10 H 10 2− is regarded as a proton H ∗ transfer from a nitrogen atom of protonated acetonitrile CH 3 CN⋅H + to a facet of a boron cluster, accompanied by overcoming a small activation barrier of ca. 4.9 kcal/mol. The proton affinity (PA) of B 10 H 10 2− in the presence of solvent molecules is ca. 8.7 kcal/mol, which is much lower than that of the “bare” B 10 H 10 2− . The effect of a solvent presence upon the isomerism of B 10 H 11 − was studied, and it was shown that the local configuration of acetonitrile molecules facilitates the existence of BH 2 -isomers for B 10 H 11 − . The removal of H 2 from the formed B 10 H 11 − ⋅20CH 3 CN species was also investigated. In contrast to the “bare” B 10 H 11 − that features different activation barriers for H 2 removal from vertices with initial coordination number 6 or 5, the solvation facilitates this process only for the coordination number 6, while the other leads to the deprotonation of B 10 H 11 − back to B 10 H 10 2− . Estimated energy barrier value for hydrogen removal is ca. 23.6 kcal/mol, which equals to boiling conditions in the case of actual experiment. One of the nearest CH 3 CN molecules substitutes instead of H 2 giving B 10 H 9 (NCCH 3 ) − . This reaction shows an exothermic effect of ca. 16.1 kcal/mol.