Dft Study On The Mechanisms Of Synthesis Of Carbazoles Catalyzed By Gold And Platinum Complexes

In this paper, the reaction mechanisms of AuCl3-catalyzed cyclization of1-(indol-2-yl)-3-alkyn-l-ols and PtCl2-catalyzed1-(indol-2-yl)-2,3-allenols in toluene solvent have been computed employing density functional theory at the B3LYP method. The important factors affectting the reaction mechanism were studied in details, the factors include the role of the ligands of catalyst and H2O molecule produced in the reaction. The results we have obtained can afford the idea for design more effective transition metal catalyst.1. Mechanism of AuCl3-Catalyzed Cyclization of1-(Indol-2-yl)-3-alkyn-1-ols:A DFT StudyA computational study with the B3LYP functional was carried out to elucidate the mechanisms of AuCl3-and AgOTf-catalyzed cyclization of1-(indol-2-yl)-3-alkyn-l-ols. The theoretical studies suggested that the two main processes, cycloaddition and hydrogen-transfer, are included in all possible reaction pathways. Calculations revealed that AuCl3is more effective in catalytic ability than AgOTf to catalyze the cyclization of1-(indol-2-yl)-3-alkyn-l-ols into carbazole derivatives. More importantly, we found that the ligands of catalysts, Cl-and OTf, are critical in a stepwise proton-transport process involved in intramolecular nucleophilic addition because they act as a proton shuttle to lower activation free energy barrier of rate-determining step. The theoretical discovery of the role of ligands of catalysts in hydrogen shift process suggests that AuCl3-and AgOTf-catalyzed cyclization of1-(indol-2-yl)-3-alkyn-l-ols can be accelerated when ligands with the property of nucleophile are used. Our theoretical calculations reproduced the experimental results very well. The present study is expected to help ones understand other transition metal-catalyzed reactions and to give guidance for future design of new catalysts.2. Study on the Mechanism of PtCl2-Catalyzed Synthesis of Carbazoles Based on 1-(indol-2-yl)-2,3-allenolsThe mechanisms of PtCl2-catalyzed synthesis of carbazoles based on1-(indol-2-yl)-2,3-allenols were investigated using denstiy functional theory at the B3LYP level. Three plausible pathways that lead to the formation of carbazole derivatives were investigated and the optimal pathway was obtained. Calculations revealed that PtCl2is effective to catalyze the cyclization of1-(indol-2-yl)-2,3-allenols into carbazole derivatives. The ligand Cl" of catalyst and the H2O molecule produced in the reaction are improtant in the process of hydrogen shift. They can serve as proton shuttle to assisted H atom shift from the6-carbon atom to the oxygen atom of hydroxyl group and lower the energy barrier. The H2O molecule is more favorable. All these facts agree well with the experimental reports for the reaction.