The Synthesis Of Chiral Bis(Imidazoline) Pincer Palladium Complexes And Their Application In Asymmetric Hydrophosphination Reaction

In this thesis, studies on the synthesis and characterization of chiralbis(imidazoline) NCN pincer palladium(II) complexes were carried out. Applicationsof the obtained Pd(II) complexes in asymmetric hydrophosphination of enones werealso presented.1. Synthesis and characterization of chiral bis(imidazoline) NCN pincerpalladium complexes(a) The syhthesis of pincer Pd(II) chloride complexes via C-H activation method andcharacterizationThe chiral bis(imidazoline)benzenes1a-c were synthesized starting from5-nitroor5-tert-butyl isophthalic acid in three steps. Ligands1a-c and Pd(OAc)2wererefluxed in dry HOAc, then a solution of lithium chloride was added at roomtemperature, which led to the formation of the pincer palladium chloride complexes2a-c (Scheme1). The macrocyclic dinuclear Pd(II) complex3was directlysynthesized by ligand1c reacted with PdCl2in toluene (Scheme2). All of the newcompounds1a-b,2a-c and3were characterized by HRMS,1H NMR,13C NMR andelemental analysis. X-ray single-crystal diffraction further confirmed the molecularstructure of3. (b) The syhthesis of pincer Pd(II) bromide complexes via oxidative addition methodand characterizationAccording to the literature,2-bromo-1,3-dimethylbenzene was readily oxidizedto2-bromoisophthalic acid. Then, the chiral bis(imidazoline)benzenes4a-d weresynthesized from2-bromoisophthalic acid and chiral amino alcohols in three steps.Ligands4a-d reacted with Pd2(dba)3in dry toluene, which led to the formation ofpincer palladium bromide complexes5a-d (Scheme3). All of the new compounds4a-d and5a-d were characterized by HRMS,1H NMR,13C NMR and elementalanalysis. X-ray single-crystal diffraction further confirmed the molecular structure of5b. 2. Applications of the palladium complexes in asymmetric hydrophosphinationreaction.The obtained Pd(II) complexes were successfully applied to asymmetric reactionof enones with diphenylphosphine (Scheme4). The asymmetric hydrophosphinationwas investigated under the condition of5mol%pincer palladium bromide5a or5dcomplexes as catalyst, toluene as solvent, and KOAc as base at0oC or25oC for12h,providing optically active phosphine derivatives in enantioselectivities of up to94%ee.