Reaction Mechanism Study On The Photo-driven Catalytic Coupling Reaction Of P-aminothiophenol And4-dimethylaminobenzenethiol On The Silver Cluster

The catalytic coupling reaction mechanism have been investigated about thetransformation P-aminothiophenol (PATP) and4-dimethylaminobenzenethiol (4-DMABT) to4,4′-dimercaptoazobenzene (4,4′-DMAB) on silver cluster by density functional theory (DFT) usingBecke’s three-parameter nonlocal exchange functional and the Lee, Yang, and Parr nonlocalcorrelation functional (B3LYP).In view of the effect of visible light, the transformation mechanism of P-aminothiophenol (PATP)and4-dimethylaminobenzenethiol (4-DMABT) to4,4′-dimercaptoazobenzene (4,4′-DMAB) onsilver cluster have been investigated under the condition of dark reaction and visible lightrespectively. In order to understand adsorption of the PATP and its simple derivative,4-DMABT, onsilver cluster whether affected goal response, the relevant chemical reaction mechanism has beenstudied with N and S atomic adsorption of aniline or only N atomic adsorption on silver clusters.Firstly, the geometries of the reactants, transition states, intermediates and products were optimizedat the6-311+G (d,p) level. vibrational frequency、energy and intrinsic reaction coordinate (IRC)calculation proved the reasonability of intermediates and transition states. Interaction betweenmolecular orbitals and the bond character were analyzed by Natural Bond Orbital Theory (NBO)and Atoms in the molecule theory (AIM).The catalytic coupling reaction mechanism of PATP adsorbed on silver cluster (Ag5) had beenexplored. It is true that the key of the counterpart reaction is the dissociation of two hydrogen atomson amino. Compared with the condition of dark reaction, the activation energies on dissociation oftwo hydrogen atoms both were reduced with the thiol-end adsorption under visible light condition.Especially when removing the second hydrogen atom, the activation energy reduced by31.04kcal/mol. It is clear that visible light contributed to removing of hydrogen atom and lighting helpthe catalytic effect. The chemical reaction mechanism in two conditions, N and S atomic adsorptionof aniline or only N atomic adsorption on silver clusters, had been studied. The activation energy of moving the second hydrogen atom are both increased with dark reaction and visible light. It isindicated that the thiol-end S atomic had little contribution to catalysis. Under visible lightcondition, the activation energy of rate-determining step is37.08kcal/mol. So the coupling reactioncould take place under the thermodynamics.The catalytic coupling reaction mechanism of4-dimethylaminobenzenethiol (4-DMABT)adsorption on silver cluster (Ag5) had been explored. It is similar that the key of the counterpartreaction was the dissociation of on amino. Under dark reaction and visible light condition, Theactivation energy of moving two methyls with two-end adsorption, N and S atomic simultaneousadsorption, both were very high, which are57.95、63.88kcal/mol respectively. So the reaction wasdifficult to take place. The activation energy of moving the second methyl with visible light washigher, by5.93kcal/mol, than the counterpart with dark reaction, which indicates that the visiblelight didn’t play a catalytic role. Under dark reaction condition, the activation energy of moving thefirst methyl with N and S atomic simultaneous adsorption on silver clusters was a bit higher thanthe counterpart with only N atomic adsorption on silver clusters. In the same condition, however,the activation energy of moving the second methyl was reduced by20.66kcal/mol. It is indicatedthat thiol-end adsorption help catalytic effect and the goal response was a two-end concertedcatalysis process. But under visible light condition, silver clusters two-end concerted catalysis wasnot obvious.