Computational study of the release of H2 from ammonia borane dimer (BH3NH3)2 and its ion pair isomers
Computational study of the release of H2 from ammonia borane dimer (BH3NH3)2 and its ion pair isomers
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DOI：
10.1021/jp0732007
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发表时间：
2007-09-13
影响因子：
2.9
通讯作者：
Dixon, David A.
中科院分区：
文献类型：
--
作者：
Nguyen, Vinh Son;Matus, Myrna H.;Dixon, David A.
高层次的电子结构计算已被用来映射出的势能面的相关部分的释放H-2的氨硼烷，BH 3 NH 3（AB）的二聚体。在二阶微扰MP2水平上采用相关一致的aug-cc-pVTZ基组，优化了稳定点的几何构型.在这些点上使用耦合簇CCSD（T）理论计算相对能量，相关一致的基组至少达到aug-cc-pVTZ水平，在某些情况下外推到完整的基组极限。结果表明，有一些可能的二聚体涉及不同类型的氢键相互作用。最稳定的气相（AB）（2）二聚体由头-尾环状构象产生，并且相对于两个AB单体稳定14.0 kcal/mol。（AB）（2）可以通过几条直接途径生成一个或两个H-2分子，能垒范围为44 - 50 kcal/mol。乙硼烷离子对异构体的二氨化物[BH 4-][NH 3BH 2NH 3 +]（DADB）比（AB）（2）稳定性低10.6 kcal/mol，并且可以通过克服类似于26 kcal/mol的能垒由两个AB单体形成。DADB也可以通过将两个NH3分子连续添加到B2 H6以及通过AB与分离的BH 3和NH3分子的缩合来产生。从DADB中消除H-2的途径的特征在于20.1 kcal/mol的较小的能垒。交替离子对[NH 4 +][BH 3 NH 2BH 3-]的计算值为16.4 kcal/mol，高于（AB）（2），并以17.7 kcal/mol的能垒进行H-2释放。从两种离子对异构体中消除H-2产生链BH 3 NH 2BH，NH3作为产物。我们的研究结果表明，中性二聚体将发挥次要作用，从氨硼烷中释放H-2，从离子对实验观察到的离子液体和固体状态的主导作用。
High-level electronic structure calculations have been used to map out the relevant portions of the potential energy surfaces for the release of H-2 from dimers of ammonia borane, BH3NH3 (AB). Using the correlation-consistent aug-cc-pVTZ basis set at the second-order perturbation MP2 level, geometries of stationary points were optimized. Relative energies were computed at these points using coupled-cluster CCSD(T) theory with the correlation-consistent basis sets at least up to the aug-cc-pVTZ level and in some cases extrapolated to the complete basis set limit. The results show that there are a number of possible dimers involving different types of hydrogen-bonded interactions. The most stable gaseous phase (AB)(2) dimer results from a head-to-tail cyclic conformation and is stabilized by 14.0 kcal/mol with respect to two AB monomers. (AB)(2) can generate one or two H-2 molecules via several direct pathways with energy barriers ranging from 44 to 50 kcal/mol. The diammoniate of diborane ion pair isomer, [BH4-][NH3BH2NH3+] (DADB), is 10.6 kcal/mol less stable than (AB)(2) and can be formed from two AB monomers by overcoming an energy barrier of similar to 26 kcal/mol. DADB can also be generated from successive additions of two NH3 molecules to B2H6 and from condensation of AB with separated BH3 and NH3 Molecules. The pathway for H-2 elimination from DADB is characterized by a smaller energy barrier of 20.1 kcal/mol. The alternative ion pair [NH4+][BH3NH2BH3-] is calculated to be 16.4 kcal/mol above (AB)(2) and undergoes H-2 release with an energy barrier of 17.7 kcal/mol. H-2 elimination from both ion pair isomers yields the chain BH3NH2BH,NH3 as product. Our results suggest that the neutral dimer will play a minor role in the release of H-2 from ammonia borane, with a dominant role from the ion pairs as observed experimentally in ionic liquids and the solid state.