Chiral(Phosphine)-(Imidazoline)PCN Pincer Palladium(Ⅱ) Complexes:Synthesis And Catalytic Studies In Asymmetric Hydrophosphination

Pincer metal complexes have been noticed by more and more researchers because of their unique terdentate coordination structure and excellent catalytic activity since Moulton and Shaw first reported the synthesis in 1976.The metals in pincer metal complexes are generally late-transition metals,and relatively more studied metals are Pd,Ni,Rh,Ir,Ru,Pt,and so on.Among them,pincer palladium compounds have been studied most,mainly because palladium exhibits good catalytic performance in various catalytic reactions.Among the pincer palladium complexes,the non-symmetrical chiral pincer Pd catalysts have been far less studied.In particular,researches on those unsymmetrical pincer catalysts with high performance are still rather limited.Compared with the symmetric chiral pincer palladium complexes,unsymmetric chiral pincer palladium complexes have different electron donors on both sides.Due to the large difference in the coordination of different electron donors,it is likely to specifically change the electron cloud distribution around the central palladium atom.Therefore,the pincer palladium complexes may have some special reaction properties or improve their catalytic activity and enantioselective in catalytic reactions.In our previous work,we have successfully prepared a variety of unsymmetric pincer palladium complexes and applied them to catalyze various reactions.In addition,we also synthesized chiral(phosphine)-(imidazoline)PCN pincer palladium complexes and initially applied them to catalyze asymmetric hydrophosphination,but the catalytic results were not satisfactory.Based on the previous work of our group,a series of novel chiral(phosphine)-(imidazoline)PCN pincer palladium compounds were synthesized and explored their catalytic performance in asymmetric hydrophosphination of pyridine functionalized ketene and diphenylphosphine.1、Based on the previous work of our group,twelve chiral(phosphine)(imidazoline)PCN pincer palladium complexes were synthesized by two novel synthesis routes.Seven of them are new complexes.In order to further determine their structures,three of them were characterized by X-ray single crystal diffraction.2、The properties of chiral(phosphine)-(imidazoline)PCN pincer palladium complexes in asymmetric hydrophosphination of 2-alkenoylpyridines and diphenylphosphine were investigated.the addition of diphenylphosphine to(E)-2-(3phenylacryloyl)pyridine was chosen as a model reaction.After a series of optimization conditions,the optimized conditions are 5 mol%of catalytic dosage,10 mol%of KOAc as the base,acetone as the solvent,for 12 hours at room temperature.3、Under optimized conditions,different substituted 2-alkenoylpyridines and diphenylphosphine to evaluate the scope of the system,and the highest yield of the catalytic product was more than 99%and ee was 87%.