Computation Study On Cu(?)Catalyzed Ring-opening Of 2H-Azirines:Synthesized Of Mechanism Trisubstitute 1,2,3-triazole

Synthesis of trisubstituted triazole and the ring opening 2H-Azirines catalyzed by copper(I)has attracted considerable attention because it can occur at room temperature or low temperature.However,the mechanism of these two kinds of Cu(I)catalyzed reactions has not been clearly understood.In this thesis,we carried out density functional theoretical(DFT)calculation on thesynthesized mechanism of 1,4-substituted-5-enamine-1,2,3-triazole by azide,terminal alkyne and 2H-Azirines catalyzed by copper(I).Two reaction paths were proposed that double copper-nitrogen and "Interrupted" click reaction.Optimizing various possible intermediates and transition states involved in the whole reaction paths,we compared the reaction potential energies of the two paths.Through the analysis of bond order,charge,weak interaction,flexible force constant,bond degree,bonding critical point and ring-forming critical point for the reaction intermediates,it was concluded that the barrier was lower in the "Interrupted" click catalysis process involving double copper(I).The main results and key pointsare as follows:(1)The captured key intermediates of acetylene bis-copper and 1,4-substituted 5-bis-copper-1,2,3-triazole were optimized by B3LYP and M06-L density functional methods using different basis sets.The basis were chosen correctly,Lan12TZ+basis for Cu,6-31G*basis forthe active hydrogen atom of terminal acetylene and 6-3 1+G*basis for the other atomsby comparison the calculated bond parameters with the experimental data.The calculated structural parameters is in good agreement with the experimental valuesfor the non-metallic bonds and non-coordination bond lengthsby introducing dispersion force correction in the M06-L and B3LYP methods,further metaloordination bond lengths are closer to the experimental valuesat M06-L level.(2)The calculated "Interrupted" click reaction mechanism showed that the dicopper(I)activation barrier from the alkyne to copper alkynide was lower than that of mono-copper catalysis.On the one hand,the coordination of bis-copper with alkyne was stronger than that of single copper,which weakens the covalent interaction of terminal C-H.On the other hand,the determination step of the whole reaction was from 5-bis-copper(I)-1,2,3-triazole to 5-mono-copper(I)-1,2,3-triazole with a potential barrier of up to 19 kcal/mol.This also explained why there was no CuAAC product in the reaction.Moreover,the calculation further showed that the strongcoordination ligand could reduce the reaction barrier and compete with the dominate reaction pathway.(3)The calculated bimetallic copper(I)catalyzed mechanism showed that the potential barrier of bimetallic copper(I)catalyzed 2H-azirine to copper nitrenewas lower than that of mono-copper catalyzed process.AIM analysis showed that the ring opening of 2H-azirine became more difficult,because the stability of 2H-azirine three-membered ring was enhanced when the coordinatedby mono-copper(I),However,due to bimetallic copper(I)coordination,three membered ring of 2H-azirine became not stable.In the activation of C-H bond in terminal alkynes,copper nitrene is transformed from double copper to single copper.It was a strong Lewis base that can fix active hydrogen.We believed that this was another reason for the absence of CuAAC products in the reaction.It was a barrier less process for copper six-membered heterocyclic intermediate to 1,2,3-triazole porduct.The ring-opening 2H-azirine helped to reduce the barrier of 5-bis-copper-1,2,3-triazole to 5-mono-copper-1,2,3-triazole.