含NNO三牙Schiff-Base之鋅和鎂錯化合物的合成及結構鑑定: 乳酸交酯開環聚合反應的良好催化劑

Abstract

The objectives of the present investigations are (1) to study the electronic effect of the substituents affecting the activity of Schiff-base metal complexes on the polymerization rate of cyclic ester and (2) to synthesize block copolymers for use in drug delivery system. Although, extensive investigations on the Schiff-base metal type catalysts have been reported, studies on the steric and electronic effect of the substituents on imine carbon are rare. For this purpose, a series of zinc(II) and magnesium(II) complexes of the type [LZn(μ-OBn)]2 (1b-8b) and LMg(μ-OBn)]2 (1c-9c) supported on NNO-tridentate Schiff-base ligands have been synthesized. The reactions of diethyl zinc (ZnEt2) L1H-L8H yielded [(μ-L)ZnEt]2 (1a-8a), respectively. Further reaction of compounds 1a-8a with benzyl alcohol (BnOH) produced the corresponding compounds of [LZn(μ-OBn)]2 (1b-8b), respectively. The X-ray crystal structural studies reveal that all of these compounds 1a-8a are dimeric bridging through the phenolato oxygen atoms. However, compounds 1b-8b are dimeric character bridging through the benzylalkoxy oxygen atoms. The reactions of Mg(OBn)2 with one molar equivalent of related Schiff-base ligands (L1H-L9H) in toluene produce [LMg(μ-OBn)]2 (1c-9c) complexes. The X-ray crystal structural studies of compounds 2c, 3c, 5c, 7c, and 8c reveal that all of these compounds are penta-coordinated dimmers with the central magnesium atoms bridging by the oxygen atoms of benzyl alkoxides. All the complexes 1b-8b and 1c-9c proceeds rapidly with good molecular weight control, and yields polymers with a very narrow molecular weight distribution toward the ring-opening polymerization of L-lactide. Experimental results show that for complexes 1b-8b, the substituents on the imine carbon of the NNO-ligand affect the reactivity of zinc complexes dramatically. For the complexes 1c-9c, the reactivity is affected by the electronic effect of the substituents on the Schiff-base ligands. To synthesize block copolymers for use in drug delivery system, zinc complex [(MPTHQ)ZnEt]2 10 supported by bidentate sulfonamide ligand is designed. The reaction of 2-(2-methoxyphenyl)-3-tosyl-1,2,3,4-tetrahydroquinazoline (MPTHQ) (L10H) with ZnEt2 in toluene produced [(MPTHQ)ZnEt]2 10, and the X-ray crystal structural studies reveals that complex 10 is dinuclear bridging through the sulfoxide oxygen atoms and tetra-coordinated around the central metal atom. In the presence of benzyl alcohol, metal complex 10 gives rise to controll the ring-opening polymerization of lactide as shown by the linear relationship between the monomer-to-initiator ratio and the number-average molecular weight with low polydispersity indexes. In addition, block copolymers such as poly-(ethylene glycol) methyl ether-b-poly(L-lactide) (PEG-b-PLA) and poly(lactide)-b-tocopheryl polyethylene glycol succinate (PLA-TPGS) have also been prepared and characterized by NMR spectroscopy. Experimental results indicate that these block copolymers are potentially useful for drug delivery systems.