Molecular mechanism for H2 release from BH3NH3, including the catalytic role of the Lewis acid BH3.
Molecular mechanism for H2 release from BH3NH3, including the catalytic role of the Lewis acid BH3.
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DOI：
10.1021/jp066175y
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发表时间：
2007-02
期刊：
影响因子：
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通讯作者：
M. Nguyen;V. S. Nguyen;M. Matus;G. Gopakumar;D. Dixon
中科院分区：
文献类型：
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作者：
M. Nguyen;V. S. Nguyen;M. Matus;G. Gopakumar;D. Dixon
电子结构计算采用多种方法，结合aug-cc-pVnZ基组（n = D，T，Q），在耦合簇CCSD（T）水平上，外推到完全基组极限，表明硼烷分子（BH 3）在XHnYHn（X，Y = C，B，N）体系的H2消除反应中可以作为有效的双功能酸碱催化剂.需要这样的催化剂，因为从等电子乙烷和硼烷胺化合物产生H2以远高于X-Y键能的能垒进行。的渐近能量势垒为H2释放从36.4千卡/摩尔的BH 3 NH3减少到6.0千卡/摩尔的BH 3的存在下，相对于分子的渐近线。NH3分子也可以参与类似的催化过程，但引起能量势垒的较小降低。用过渡态和RRKM理论分析了这些过程的动力学。BH 3的催化作用也被探测的过渡结构的电子密度的分析，使用原子在分子（AIM）和电子局域化功能（ELF）的方法。
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.