Carboxylation And Semihydrogenation Of Alkynes With Carbon Dioxide

Carbon dioxide(CO₂)is a major greenhouse gas and a rich C1 resource.Converting CO₂ into alkyne acid by carboxylation reaction of alkynes is an effective way to utilize CO₂.In addition,the synthesis of alkenes by semihydrogenation of alkynes also plays an important role in organic synthesis.Therefore,it is of great theoretical significance and practical value to develop efficient carboxylation and semi-hydrogenation of alkynes.This paper focuses on the utilization of alkynes and CO₂.On the one hand,CO₂was used as C1 resource and carboxylated directly with terminal alkyne to achieve the conversion of CO₂into alkyne acid.On the other hand,On the other hand,an example of indirect utilization of CO₂ was developed for the preparation of alkenes through CO₂promoted semihydrogenation of alkynes.The specific contents are as follows:An efficient method for the synthesis of alkyne acid via carboxylation reaction between terminal alkyne and CO₂ in the absence of any catalyst was studied.The effect of the reaction parameters including the kinds and the amount of base,the solvent and the reaction temperature on the reaction were investigated.With Cs₂CO₃ as the base and DMSO as the solvent,the reaction can proceed smoothly at 1 atm of CO₂ pressure.The products could be obtained in 80%yields after 6 h.Increasing the reaction time,the yield of alkyne acid can be increased to more than 97%.The reaction has many advantages,such as good functional group compatibility and wide substrate applicability,high yields and easy scalability.By using hydrothermal method octahedral MIL-101 with uniform size and regular morphology was synthesized,and then Pd@MIL-101 was prepared by double solvent method and hydrogen reduction with MIL-101as the catalyst support.Moreover,an amorphous Pd@MIL-101-NH₂ material was synthesized by using amino-modified ligand.Then,the catalytic activity of Pd@MIL-101 and Pd@MIL-101-NH₂nanomaterial in CO₂-promoted semihydrogenation of alkynes was investigated.The results show that Pd@MIL-101-NH₂ nanomaterial can catalyze the semihydrogenation of alkynes efficiently and give the alkene products in good yields and high selectivity under CO₂-promoted conditions,and the reaction has wide substrate applicability and good functional groups adaptability.In addition,the nanomaterial Pd@MIL-101-NH₂could be recycled and reused for four times without any significant loss of activity.No obvious structural change was observed after the reaction by analysis of TEM,indicating the Pd@MIL-101-NH₂ nanomaterial exhibits good stablity in CO₂promoted semihydrogenation of alkynes.