【作者】 张毅；

【导师】 王勇；

【作者基本信息】 苏州大学 ， 化学， 2017， 硕士

【摘要】 氨硼烷（NH₃BH₃,AB）因含氢量高（19.6wt.%）、分子量小、热稳定性适中而成为近十年来最具潜力的储氢材料之一。在氨硼烷的催化脱氢反应中,过渡金属催化剂能够显著地降低AB的热解温度,提高水解的放氢速度。因此,探索过渡金属催化AB脱氢反应的机理具有重要的意义。本论文采用密度泛函理论（DFT）,分别研究了过渡金属（Fe,Pd）催化剂催化氨硼烷脱氢的反应机理。研究内容主要包括以下两部分:1.在M06/6-311+G（d,p）–SDD//M06/6-31G（d）–SDD计算水平下,通过密度泛函理论（DFT）计算,我们详细地研究了Fe-POCOP螯合配合物催化的氨硼烷脱氢反应的机理。该反应主要是经过一个配体协助的协同的Fe-C_ipso共活化的机理,其中AB中B原子上的氢转移到Fe中心,同时N原子上的质子转移到C_ipso上。DFT计算和NBO电荷分析都表明当配体C_ipso的对位有一个供电子基MeO时,Fe-POCOP螯合配合物的活性最高且决速步的反应能垒最低,只要17.6 kcal/mol。而反应后期催化剂失活机理的分析表明,失活归因于AB中NH₃的解离。2.在M06L/6-311+G（d,p）–LANL2DZ//M06L/6-31G（d）–LANL2DZ水平下,我们研究了Pd氮杂环卡宾配合物催化的串联的N,N-二甲基氨硼烷（DMAB）脱氢以及烯烃氢化的反应机理。对于脱氢反应,我们提出了四种可能的路径,计算结果表明,脱氢反应是通过N上质子先转移到配体卡宾C上,再经过C–H活化,B–H活化,最后异构化的机理进行的,决速步的能垒有26.0 kcal/mol。另外,在脱氢过程中形成的反式双氢配合物在串联的氢化反应中起了关键的作用。它作为活性催化剂可以经过一个逐步的氢转移机理氢化烯烃,并且只需要跨越19.6 kcal/mol的活化能垒。更多还原

【Abstract】 Ammonia-Borane is considered to be one of the most promising chemical hydrogen storage materials,which has received inordinate attention over the past decade due to the high gravimetric hydrogen storage（19.6 wt%H₂）,low molecular weight and high thermal stability.The pyrolysis temperature of ammonia broane can be lower and the rate of hydrolysis can be faster with transition-metal catalysts.Therefore,theoretical studies on the mechanism of transition metal catalyzed dehydrogenation of ammonia-borane are of great significance.In this thesis,the mechanisms of two kinds of transition metal（Fe and Pd）complexes catalyzed ammonia-borane dehydrogenation reactions have been investigated by the density functional theory（DFT）.The main content of this thesis includes the following two parts:1.A mechanistic investigation on ammonia-borane dehydrogenation catalyzed by the newly developed Iron bis（phosphinite）pincer complexes are reported using density functional theory（DFT）calculations at the M06/6-311+G（d,p）–SDD//M06/6-31G（d）–SDD level of theory.We have shown that AB dehydrogenation proceeds through a ligand-assisted concerted Fe-C_ipso cooperation mechanism,in which the hydrogen atom of B-H moves to metal Fe and proton of N-H transfers to pincer ipso carbon simultaneously.DFT calculations and natural bond orbital（NBO）charge analysis suggest that Fe-POCOP complex with an electron-donating MeO group at the para position to the ipso carbon exhibits the highest catalytic activity with the lowest activation barriers of 17.6 kcal/mol.Moreover,loss of NH₃ from the AB-bound complex leads to the diminished catalytic activity at the late stage of the AB dehydrogenation process.2.The mechanism of tandem dimethylamine-borane（NHMe₂BH₃,DMAB）dehydrogenation and alkene hydrogenation catalyzed by the Pd（0）complex[Pd（NHC）（PCy₃）]（NHC=N-heterocycle carbene）has been presented by density functional theory（DFT）calculations at the M06l/6-311+G（d,p）–LANL2DZ//M06l/6-31G（d）–LANL2DZ level of theory.Four possible NHMe₂BH₃ dehydrogenation pathways have been carefully investigated.Theoretical studies show that the N–H proton transfers to ligated carbene carbon and subsequent C–H and B–H activation is the most kinetically favorable with the lowest activation barrier of 26 kcal/mol.It was found that a trans-dihydride Pd（II）species[Pd（H）₂（NHC）（PCy₃）],formed in the dehydrogenation process plays a key role in the tandem hydrogenation reaction of alkene.In addition,DFT calculations show that the hydrogenation reaction is through a stepwise H transfer mechanism with a barrier of 19.6 kcal/mol in the RDS,which is kinetically and thermodynamically favored.更多还原