DFT Study On The Mechanisms Of Catalytic Alkynes Reactions Catalyzed By Copper, Gold And Silver Complexes

In the present paper, the density functional method (B3LYP functional) is employed to study the reaction mechanisms of direct amination of the synthesis of y,8-alkynyl-β-amino acid derivatives catalyzed by CuBr, and gold/silver-catalyzed cyclization of allenyne-1,6-diols, respectively. Factors that control the efficiency of catalysis are analyzed. The effects of the concentration of catalysts, their ligands on the mechanism and chemoselectivity have been examined, thereby these information for designing new type of catalysis reactions provide in theoretical level.1. DFT Study the Mechanism of the Synthesis of y,8-Alkynyl-β-amino Acid Derivatives Catalyzed by CuBrThe mechanism of the synthesis of y,δ-alkynyl-β-amino acid derivatives is investigated employing the density functional theory (the B3LYP functional is used), and three reaction pathways are suggested. The frequency analysis is performed for all the transition states, intermediates and products. The geometries of the important transition states are confirmed by the IRC scanning. In order to make clear the reaction mechanism, the charge distribution of all species and the electronic densities of the bond critical points (BCP) and the ring critical points (RCP) for the key bonds are calculated and discussed. Our results indicate that in the gas phase and the liquid phase, the rate-determining steps of the dominant pathways are the reaction between amine and alkynyl ester. The suggested mechanism can explain reasonably all experimental observations.2. Mechanism of Cyclization of Allenyne-1,6-diols Catalyzed by Gold and Silver Compounds:the Effects of Concentrations and Ligands of CatalystsBy means of the density functional theory (DFT) combined with the polarized continuum models, the cyclizations of allenyne-1,6-diols catalyzed by the gold and silver complexes are computed, the mechanisms of cyclization are suggested, and the effects of the concentration of catalysts, their ligands, and the solvent on the mechanisms are analysed in detail. As shown, the Au-catalyzed mechanism differs to the Ag-catalyzed mechanism. The most favorable reaction path for the Au-catalyzed mechanism gives the main product Px and that for the Ag-catalyzed mechanism leads to the main product Pz, which are in agreement with the experiment. All the reaction paths for the cyclization of allenyne-1,6-diols catalyzed by single AuCl3 complex have high energy barriers. Participation of two AuCl3 complexes in the catalyzed cyclization can make energy barriers for all the reaction paths be lowered remarkably. These results imply the close relationship between the concentration of catalysts and the chemoselectivity of products. The ligands, as a proton shuttle, can take part in the reaction and assist the transfer of proton, and further lower the reaction energy barriers and change the reaction routes. The choice of the ligands of catalysts may be important to the efficiency of catalysis. The effects of solvent on the gold-and silver-catalyzed mechanisms are remarkable and also quite different. The theoretically suggested mechanisms explain reasonably all the experimental observations.