4-二甲基对巯基苯胺吸附于银簇上的光诱导催化偶联反应机理研究

Reaction mechanism study on the photo-driven catalytic coupling reaction of 4-dimethylaminobenzenethiol on the silver cluster

采用密度泛函理论(DFT)中的B3LYP方法对4-二甲基对巯基苯胺吸附在Ag簇上催化偶联生成4,4’-二巯基偶氮苯(4,4’-DMAB)的反应机理进行理论研究.对比研究了暗反应条件下和光照条件下4-二甲基对巯基苯胺吸附在Ag簇上发生催化偶联生成4,4’-二巯基偶氮苯(4,4’-DMAB)的反应机理.为了了解4-二甲基对巯基苯胺中的巯基端S原子吸附在银簇上对反应的影响,比较研究了4-二甲基对巯基苯胺中的N和S原子同时吸附和仅N原子吸附在银簇上两种条件下的化学反应机理.用自然键轨道(NBO)理论和分子中的原子理论(AIM)分析了分子轨道间相互作用和成键特征.研究结果发现:该反应的关键在于氨基端两个甲基的脱去,在暗反应和光照条件下,两端吸附时第二个甲基脱去所需活化能均很高,分别为57.95、63.88 kcal/mol,表明光照在反应中没起到催化作用.暗反应条件下巯基端吸附起到助催化作用,反应为两端协同催化过程.光照条件下银簇两端协同催化过程表现得不明显.

The catalytic coupling reaction mechanisms have been investigated about the transformation P - amino- thiophenol （PATP） and 4 - dimethylaminobenzenethiol （4 - DMABT） to 4,4＇ - dimercaptoazobenzene （4,4＇ - DMAB） on silver cluster by density functional theory （DFF） using B3LYP method. The transformation mecha- nisms of PATP and 4 -DMABT to 4,4＇ -DMAB on silver cluster have been investigated under the conditions of dark reaction and visible light respectively. In order to understand how adsorption of the 4 - DMABT on silver cluster affected this reaction, the relevant chemical reaction mechanism has been studied with N and S atomic ad- sorption of aniline or only N atomic adsorption on silver clusters. Interaction between molecular orbitals and the bond character were analyzed by Natural Bond Orbital Theory （NBO） and Atoms in the molecule theory （AIM）. The results show that： The key lies in the reaction of demethylation on the amino terminus, under dark reaction and visible light condition, the activation energy of removing the second methyl, both were very high, which are 57.95 and 63.88 kcal/mol respectively, indicating that the light did not play a catalytic role in the reaction, it is indicated that thiol - end adsorption help catalytic effect and the this reaction is a two - end concerted catalysis process. But under visible light condition, silver clusters two - end concerted catalysis is not obvious.