Studies On The Synthesis And Catalytic Activity Of Six-Membered N-heterocyclic Palladium Complexes

The organometallic chemistry of N-heterocyclic carbenes （NHCs） play very importantroles in the development of modern organic chemistry, especially organic synthesis. Most ofthe present research focus on the five-membered NHCs and their metal complexes, whilereports on six-, seven-, and other ring-expanded NHCs and corresponding metal complexesare quite rare. In this thesis, following research have been conducted based on the skeleton oftetrahydropyrimidine:â‘ Synthesis of the precursors of six-membered NHCsStarting from aromatic amine and3-bromopropylaminium bromide, through substitution,ring closure and bromination, et al reactions, a series of novel methylene-bridged3,4,5,6-tetrahydropyrimidinium salts were synthesized. The target product and some intermediates,total6, were characterized by ESI-MS,¹H NMR,¹³C NMR, IR and X-ray single crystaldiffraction technology.5are new compounds.â‘¡Synthesis of tetrahydropyrimidine palladium complexesHeating a mixture of methylene-bridged3,4,5,6-tetrahydropyrimidinium salts andPd（OAc）₂in DMSO at50oC leading to the formation of two new complexesdibromidobis（1-aryl-1,4,5,6-tetrahydropyrimidine）palladium（II） complexes4a and4b. Thestructure of the new complexes were characterized by ESI-MS, EA,¹H,¹³C NMR and X-raysingle crystal diffraction analysis. The results showed that the palladium atom is located on acrystallographic center of symmetry, the central Pd II atom is bonded to twotetrahydropyrimidine N atoms and two terminal Br atoms.â‘¢Suzuki cross-coupling reactions catalyzed by Palladium complexesUsing dibromidobis（1-aryl-1,4,5,6-tetrahydropyrimidine）palladium（II）（4a and4b） ascatalysts, the Suzuki-coupling of arylboronic acid with aryl halide were investigatedsystematicallyInitially, using the Suzuki-coupling of bromobenzene with phenylboronic acid catalyzedby4b as a model reaction. The best results were obtained with0.5mmol%catalyst loading,using tBuOK as a base in DMF/H2O （1.5/1.5, V/V）, reaching a satisfying yield.Designing orthogonal experiment to optimize the conditions. The results showed that when themole ratio of substrate is1.5:1, the amounts of the catalyst was0.5%of the substrate,1.5 time of amounts sodium tert-butoxide of the bromobenzene at100℃, the yield was above90%for1hUnder the optimized conditions, the catalytic activity of new palladium complexes4aand4b towards Suzuki cross-coupling of series aryl halides with phenylboronic acid and1-1-naphthylboronic acid were investigated. The results showed that the palladium complexesshowed high catalytic activity for the cross-coupling of series of phenylboronic acids and1-naphthylboronic acid with aryl halides （including phenyl iodide, aryl bromides and lowlyactive aryl chlorides）.