Synthesis, Characterization And Catalytic Behavior Towards The ROP Of The Cyclic Esters Of Lithium, Magnesium, Aluminum, Tin(Ⅱ) And Zinc Complexes Bearing Novel Iminophosphorane Ligands

Aliphatic polyesters such as poly(ε-caprolactone) (PCL), polylactide (PLA) and their copolymers have attracted increasing interest due to their biodegradable, biocompatible and permeable properties. An efficient way to synthesize the polyesters is the ring-opening polymerization of cyclic esters catalyzed by metal complexes. By careful selection of metal and ligands, reactions can be generated to form a desired polymer structure.The work presents in this dissertation focuses mostly on the design of ligands and the synthesis of different kinds of metal complexes. By using the basic iminophosphorane ligands combined with different kinds of metal centers, diverse catalysts that are active for the ring-opening polymerization ofε-caprolactone and lactide are synthesized. The main contents are summarized as the following:Chapter 1 describes the development of biodegradable aliphatic polyesters and an introduction of the polymerization mechanism of lactones/lactides, especially focuses on the latest development of the metal catalysts, including Al(III), Sn(II), Zn(II) and Mg(II) complexes, which fulfill the "Coordination-insertion" mechanism during the ring-opening polymerization of lactones/lactides.Chapter 2 introduces the classification of the iminophosphorane ligands and reports a new kind of iminophosphorane ligand (I) bearing a sidearm donor [o-RCHC₆H₄]PPh₂=N-SiMe₃]^- (R = H, SiMe₃). Synthesis, characterization and reactvities of lithium compounds bearing the lgand are explored. A dinuclear zinc complex [(o-CH(SiMe₃)C₆H₄)PPh₂=N-SiMe₃]₂Zn₂(μ-Cl)(μ-OSiMe₃), which contains the bridges of Zn-Cl-Zn and Zn-O-Zn, is also obtained. According to literature, the complex may be a potential catalyst for the ROP of cyclic esters.Chapter 3 presents our efforts in the synthesis of N,N-chelate organoaluminium (III) and organotin (II) complexes supported by diiminophosphorane ligand (II), the complexes including [Ph(ArCH₂)P(N^tBu)₂]AlMe₂ (Ar = Ph, 8-quinolyl), [Ph(ArCH₂)-P(N^rBu)₂]AlEt₂ (Ar=Ph, 8-quinolyl), [Ph(PhCH₂)P(N^tBu)₂]SnN(SiMe₃)₂ and [Ph(PhCH₂)P(N^tBu)₂]SnO-C₆H₄^tBu-4. In the presence of BzOH, these complexes can efficiently catalyze the ROP ofε-caprolactone, giving polymers with narrow polydispersities. Chapter 4 is about the synthesis of a series of zinc(II) and magnesium(II) complexes with structure III, including [ⁱPr₂(8-quinolyl-CH)P=N^tBu]ZnR (R = Ph, Me, Et,); [Ph₂(8-quinolyl-CH)P=N^tBu]ZnEt and [ⁱPr₂(8-quinolyl-CH)P=N^tBu]MgEt, and their catalytic behavior for the ROP of cyclic esters. The ring-opening polymerization ofε-CL catalyzed by the ethylzinc complex in the presence of benzyl alcohol behaves as a typical "living-polymerization" process. The homology magnesium complex exhibits very high catalytic activity. At -25℃in toluene and when [M]₀/[BzOH] equals 500, the conversion of the monomer to polymer can reach to 100 % in less than 1 min and the number average molecular weight of obtained polymer is about 300000 amu with PDI = 1.88. Interestingly, even without the addition of BzOH, the magnesium complex can still initiate the ring-opening polymerization ofε-caprolactone and D,L-lactide.