Metal Amides Containing Chiral Center:Synthesis Characterization And Their Catalytic Activities

This dissertation focuses on synthesis, characterization of metal amides containing chiral center and their applications in the ROP of lactide. Including N-functionalized benzyl,η3-1-azaallyl, η3-1,3-diazaallyl, N, N (N, O)-bidentate ligands, and their corresponding transition metal complexes were successfully prepared. These complexes were characterized by1HNMR,3CNMR, elemental analysis and X-ray diffraction. The zinc, aluminum and magnesium organometallic complexes used as initiators for catalytic the ring-opening polymerization (ROP) of lactide were studied. The polylactide were structurally characterized by NMR and Gel Permeation Chromatography (GPC). Six main chapters are included in this dissertation:Chapter1:The research background and progress of this thesis were introduced:(1) The importance of metal amides is summarized;(2) The synthesis and development of1-azaallyl complexes have been briefly discussed;(3) Organometallic zinc, aluminium and magnesium complexes used as initiators for catalytic the ring-opening polymerization (ROP) of lactide were disclosed.Chapter2:Eight sterically hindered N-functionalized benzyl metal(II) complexes2and2a-2g were obtained (Scheme1and Scheme2). Each of the complexes was characterized by microanalysis, multinuclear NMR spectra at ambient temperature and X-ray single crystal study. Complex2a or2b would be the only sample for solvated-free homoleptic neutral benzylzinc or benzylcadmium compound, respectively. Both of complexes2a and2d exhibited moderate activity for the ring-opening polymerization of rac-lactide in toluene in the presence of benzyl alcohol at70℃. All the resulting polylactides are most predominantly heterotactic-rich by the methine region of the homonuclear decoupled1HNMR experiments.Chapter3:A series of η3-1-azaallyl and η3-1,3-diazaallyl ligands and their corresponding benzene-bridged asymmetric organometallic complexes of azaally3a-3j were prepared from the complexes2and2e, and characterized by NMR spectroscopy, element analysis and X-ray diffraction (see Scheme3and Scheme4). Chapter4:Some benzene-bridged di-anion ligands were prepared from o-tolualdehyde, phenyl methyl ketone or2-methylacetophenone with aniline,2,6-diisopropylaniline or α-phenylethylamine, respectively. And their corresponding benzene-bridged di-anion organometallic complexes were obtained (Scheme5and Scheme6). All the ligands and organometallic complexes were characterized by NMR spectroscopy, element analysis and X-ray diffraction. Scheme6Synthetic route to ligand complexes4b-4d Scheme7Synthetic route to complexes5a-5e Chapter5:The crystalline complexes5a-5k were synthesized from the reactions of the corresponding chiral ligands5-1,5-2,5-3,5-6or5-8with diethylzinc or trimethylaluminum, respectively (Scheme7, Scheme8and Scheme9). All of the complexes were well characterized by1H NMR,13C NMR spectroscopy, elemental analyses and single crystal X-ray crystallography. The catalytic behaviors of complexes5a-5d as initiators for the ring-opening polymerization (ROP) of rac-lactide were also investigated. In the presence of benzyl alcohol, complexes5a-5d are active initiators for the polymerization of rac-lactide leading to the isotactic-rich polylactides, which were determined by the methine region of the homonuclear decoupled1HNMR experiments (see Table1). Table1. Polymerization of rac-lactide catalyzed by chiral complexes5a-5ea Tolune; b The yields were calculated according to the mass of the polymer was precipitated by the addition of MeOH and was collected by filtration and dried; c Determined by gel-permeation chromatography, calibrated with polystyrene standards in tetrahydrofuran; dPm is the probability of meso linkages between monomer units and is determined from the methine region (5.30-5.00ppm) of the homonuclear decoupled1H NMR spectrum in CDCl3at25℃.Chapter6:The complexes6a-6c were synthesized by treatment of N,O-bidentate ligand6-1with diethylzinc or trimethylaluminum at25℃, respectively (Scheme10). All the organometallic complexes were characterized by NMR and X-ray diffraction analysis. Both of complexes6b and6c exhibited moderate activity for the ring-opening polymerization of rac-lactide in tetrahydrofuran in the presence of benzyl alcohol at25℃.