Nguyen Minh Tho, Nguyen Vinh Son, Matus Myrna H, Gopakumar G, Dixon David A
Department of Chemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, USA.
J Phys Chem A. 2007 Feb 1;111(4):679-90. doi: 10.1021/jp066175y.
Electronic structure calculations using various methods, up to the coupled-cluster CCSD(T) level, in conjunction with the aug-cc-pVnZ basis sets with n = D, T, and Q, extrapolated to the complete basis set limit, show that the borane molecule (BH3) can act as an efficient bifunctional acid-base catalyst in the H2 elimination reactions of XHnYHn systems (X, Y = C, B, N). Such a catalyst is needed as the generation of H2 from isoelectronic ethane and borane amine compounds proceeds with an energy barrier much higher than that of the X-Y bond energy. The asymptotic energy barrier for H2 release is reduced from 36.4 kcal/mol in BH3NH3 to 6.0 kcal/mol with the presence of BH3 relative to the molecular asymptote. The NH3 molecule can also participate in a similar catalytic process but induces a smaller reduction of the energy barrier. The kinetics of these processes was analyzed by both transition-state and RRKM theory. The catalytic effect of BH3 has also been probed by an analysis of the electronic densities of the transition structures using the atom-in-molecule (AIM) and electron localization function (ELF) approaches.
使用各种方法进行的电子结构计算，直至耦合簇CCSD(T)水平，并结合n = D、T和Q的aug-cc-pVnZ基组，外推至完整基组极限，结果表明硼烷分子（BH3）在XHnYHn体系（X、Y = C、B、N）的H2消除反应中可作为一种高效的双功能酸碱催化剂。由于从等电子乙烷和硼烷胺化合物生成H2的过程中，其能垒远高于X - Y键能，因此需要这样一种催化剂。相对于分子渐近线，在有BH3存在的情况下，H2释放的渐近能垒从BH3NH3中的36.4 kcal/mol降低至6.0 kcal/mol。NH3分子也可参与类似的催化过程，但导致的能垒降低较小。通过过渡态理论和RRKM理论对这些过程的动力学进行了分析。还使用分子中的原子（AIM）和电子定位函数（ELF）方法对过渡结构的电子密度进行分析，从而探究了BH3的催化作用。
