Imidazole Derivatives And Alkali Metal,alkaline-earth Metal Complexes For Ring-Opening Polymerization Of Lactides

Polylactides?PLA?,which has good biodegradability and biocompatibility,has attracted significant attention in biomedical and pharmaceutical applications.The ef-ficient synthesic method at present is the use of metal complex as catalyst?initiator?for the ring-opening polymerization?ROP?of lactides?LA?,but the removal of the residue heavy metal in the polymer during industrial production is quitely difficult,which limit the applicaton range of resultant polymers.The design and synthesis of low/non-toxicity organocatalysts and sodium,potassium,megnesium and calcium metal complexes has been the research hotspot for the ring-opening polymerization of cyclic esters.In this dissertation,we design and synthesis five imidazole derivates,sixteen low/non-toxicity alkali metal,alkaline-earth metal complexes bearing imidaz-ole derivatives,triphenol and bulky biphenol ligands.All of the catalysts have been fully characterized and the effects of different metal and different structure on the cat-alytic performance for the ROP of cyclic esters have been also investigated.The main contents in this dissertation were summarized as below:Chapter 1.A brief review of the mechanism for the ROP of lactides and the re-search progress of organocatalysts and metal complexes catalysts for the ROP of lac-tones.Chapter 2.Reaction of amino triacetic acid and o-phenylenediamine produced imidazole derivatives N,N,N-tris?2-benzimidazolyl-methyl?amine?NTB,L¹-H₃,1?with one step process and highly yield.Reaction of NTB with ethanol,benzyl alcohol,isopropanol and ethyl lactate?EL?produced adducts[?1·ROH?ROH]?2-5?,respec-tively.All of these adducts were characterized by ¹H and ¹³C NMR spectroscopic studies and X-ray diffraction determination as well as by elemental analysis.The mo-lecular structure of 2-5 revealed that 1 connected with two alcohol molecules through hydrogen bonds,indicating that they have similar structures.The polymerization ex-perimental results revealed that catalysts 1-5 have good activity toward ROP of L-lactide under melt conditions in the presence of different alcohols as initiators to produce PLAs with expected molecular weights and narrow molecular weight distri-butions.The catalytic performance of 2-5 is consistent with those of catalyst 1 and two equivalents of extra different alcohols under the same polymerization conditions for the ROP of L-LA.According to these experimental results and X-ray structures,the hydrogen bond activated mechanism is proposed.Chapter 3.Reaction of NTB with sodium ethoxide produced sodium homome-tallic complex[L₃¹Na₉?EtOH?₉]?6?.Reaction of four triphenol ligands L^2-5-H₃ with Na[N?SiMe₃?₂]in THF produced multinuclear sodium complexes[L₂^2-5Na₆?THF?₆]?7-10?.All of these complexes were characterized by ¹H and ¹³C NMR spectroscopic studies and X-ray diffraction determination as well as by elemental analysis.The mo-lecular structure of 6 consists of nine nuclears,with not completely same coordination environment of each sodium metal centers.The solid-state structures of 7-9 revealed that complexes 7-9 were similar hex-nuclear complexes with each four-coordinated sodium center.Three oxygen atoms of one ligand and three sodium atoms form a six-member ring,and these two rings staggered up and down through O-Na bonds to form a hexagonal prism structure.All of these complexes were efficient catalysts for the ROP of LA to give polylactides?PLAs?with the expected molecular weights and narrow molecular weight distributions.To achieve conversion up to 90%,the polyme-rization needed to react for 42 min catalyzed by complex 6 at 0?,but less than 6 min catalyzed by complexes 7-10 under the same polymerization conditions,producing PLA with expected molecular weight and narrow PDI.Chapter 4.Reaction of biphenol ligands L⁶-H₂ and Na[N?SiMe₃?₂]produced so-dium complexes 11-13.Reaction of sodium complex[Na?L⁷-H?]or potassium com-plex[K?L⁷-H?]bearing biphenol ligand with MgⁿBu₂ in THF produced sodium?pota-ssium?-magnesium heterometallic complexes 14-16,respectively.All of these com-plexes were characterized by ¹H and ¹³C NMR spectroscopic studies and X-ray dif-fraction determination as well as by elemental analysis.The solid-state structure of[?L⁶-H?Na?THF?₂]?11?revealed that 11 was mononuclear feature;[?L⁶-H?₂Na₂]?12?revealed a dinuclear feature;[L₄⁶Na₈]?13?revealed an octanuclear feature with three-coordinated and four-cooedinated sodium metal centers,and the neighboring phenyl rings via p-?interaction to stabilize the structure.The molecular structure of[L₂⁷Na₂Mg]?14?consisted of three heteronuclear with two four-coordinated sodium and one six-coordinated magnesium.The molecular structure of[L₂⁷K₂Mg₂??-OH?₂]?15?con-sisted of two five-coordinated K and two five-coordinated Mg.The molecular struc-ture of[?KL⁷?₂Mg₂??-OBn?₂]?16?was also tetranuclear,and the coordinated modes of K and Mg were different with those of 15.All of those complexes were efficient catalysts for the ROP of LA to give polylactides?PLAs?with the expected molecular weights and narrow molecular weight distributions.To achieve conversion up to 90%,the polymerization react for only 12min by using 11 at 0?.Futhermore,11 exhibited high heteroselectivity toward rac-LA polymerization?P_r=0.75?in toluene at 0?.By using 16 and increasing the ratio of monomer/catalyst,the reaction time was slightly shorten,speculating that the initiate rate was lower than the propagate rate,and the increase of the monomer amount could increase the initiate rate.Chapter 5.Reaction of bulky biphenol ligands L^6-7-H₂ and Ca[N?SiMe₃?₂]₂ in THF produced calcium complexes 17-19.Reaction of[Na?L⁷-H?]or[K?L⁷-H?]with half equiv.of Ca[N?SiMe₃?₂]₂ in THF to produce sodium?potassium?-calcium hetero-metallic complexes 20 and 21,respectively.All of these complexes were characterized by ¹H and ¹³C NMR spectroscopic studies and X-ray diffraction determination as well as by elemental analysis.The solid-state structure of[L₂⁶Ca₂?THF?₄]?17?revealed that complex 17 was binuclear with five-coordinated calcium centers.The molecular structure of[L⁷Ca?THF?₃]?18?revealed that complex 18 was mononuclear with a six-coordinated calcium center and the coordination geometry around the calcium center adopted a distorted octahedron.The molecular structure of[L₃⁷Ca₃?THF?₂]?19?illustrated an aggregation mode in the solid state with three five-coordinated calcium atoms.Complexes 18 and 19 were interchangeable in hexane and THF solvents.The molecular structures of[L₂⁷Na₂Ca]?20?and[L₂⁷K₂Ca]?21?consisted of two four-coordinated sodium?potassium?and one six-coordinated calcium,similiar with the molecular structure of 14.All of these complexes were efficient catalysts for the ROP of lactide in presence of initiator BnOH both in solution and under melt condition.The polymer molecular weight by using complex 19 as catalyst was high up to 103.8kg/mol.According to these experimental results and X-ray structures,the polymeriza-tion mechanism toward ROP of L-LA catalyzed by complex 19 included the process that the trinuclear complex would be separated into mononuclear species.