Study On Photocatalytic Synthesis Of Amines By Oxygen Vacancy Rich Tungsten Oxide

Amines and their derivatives are the most basic and important nitrogenous organic compounds,which are widely used in pharmaceutical,natural products,fine chemicals and other fields.N-alkylation of amines with alcohols and hydroamination of alkynes and amines are green,efficient and atom-economical methods for selective synthesis of amines.In this paper,based on tungsten oxide with abundant reserves,adjustable composition,high chemical stability and good electrical conductivity,a tungsten oxide with controllable concentration of oxygen vacancy was constructed by introducing oxygen vacancy into tungsten oxide.On the one hand,the light absorption capacity of tungsten oxide was improved to make use of the light energy.On the other hand,the surface oxygen vacancy enhanced the adsorption and activation of the substrates on the surface of catalys.A mild and efficient photocatalytic N-alkylation of amines with alcohols was achieved over tungsten oxide with controlled oxygen vacancy concentration.Based on above studies,Cu ions were supported on tungsten oxide with abundant oxygen vacancies,which can be applied to the highly efficient photocatalytic hydroamination of alkynes and amines.The tungsten oxide with oxygen vacancies not only can improve the light utilization of the catalyst via its excellent light absorption capacity,but can limit and stabilize the Cu ions and adjust the electronic environment of Cu center to ensure the stability of the catalyst in the reaction process.The mechanisms of photocatalytic N-alkylation of amine with alcohol and hydroamination of alkynes and amine have been studied to further undestand the structure-activity relationship.The main contents were shown as follows:（1）The tungsten oxide with controllable concentration of oxygen vacancies was constructed for the photocatalytic N-alkylation of amines with alcohols under inert atmosphere and mild conditions without alkali additive.The oxygen vacancies in WO_xas the light absorption and alcohols activation sites ensure the high activity and selectivity of the photocatalytic N-alkylation of amines with alcohols.The photocatalytic N-alkylation of amines with alcohols on WO_x was carried out through the borrowing hydrogen mechanism.（2）Cu/WO_x catalyst was prepared by supporting Cu ions on tungsten oxide with abundant oxygen vacancies.The photocatalytic hydroamination of alkynes and amines was successfully achieved by using Cu/WO_x catalyst in an inert atmosphere and under mild conditions without additives.The oxygen vacancies in WO_x support can improve the light utilization of the catalyst and realize the limitation and stability of Cu ions and the regulation of the electronic environment of Cu center,which can ensure the efficiency and stability of the catalyst in the reaction process.Electron transfer between support and Cu provides the key active site Cu⁺for photocatalytic hydroamination.The mechanism studies show that light can promote the adsorption of alkynes on the surface of catalyst and the coordination of alkynes with the Cu center.