N-heterocyclic Carbene-Pd(Ⅱ) Complexes:Systhesis And Their Application In C-N Cross-coupling

In the last two decades,N-heterocyclic carbene-Pd(Ⅱ)complexes have been developed rapidly.Due to their excellent catalytic activity,perfect NHC/Pd ratio and high stability,many scientists have been attracted to the investigations of this field.In this article,a series of novel NHC-Pd(Ⅱ)complexes have been reported.Carboxyl group was introduced to the ortho-position of the ancillary ligand,which replaced one of the chlorine atoms coordinated with the palladium center in the normal complexes,giving a new coordination model.In addition,their catalytic activity has been tested by the Buchwald-Hartwig amination of aryl chlorides,and based on these results,the structure-activity relationship was also fully discussed.The introduction of the carboxyl group has at least two advantages: first,the presence of the carboxyl group may increase the catalytic activity of the complexes;second,it may probably stabilize the NHC-Pd(0)active species in the catalytic cycle,thus prolongs the catalyst’s lifetime and enhances their efficiency.By introducing the carboxyl group to the ancillary ligand will enhance the catalysts’ efficiency,and will give new strategy for the development of NHC-Pd(Ⅱ)complexes with higher catalytic activity.