稀土胺基双酚配合物的合成及催化性能研究
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摘要
本论文采用无水氯化稀土为原料,通过盐交换反应合成了一系列新型含双酚配体(胺基双酚与四氢席夫碱)的稀土配合物,得到了其中三种稀土配合物的单晶并通过X-射线单晶衍射确定了它们的晶体结构。详细研究了这些稀土配合物单组份催化ε-已内酯开环聚合的催化性能与聚合规律,制备得到了含有双酚配体端基的聚已内酯,直接验证了聚合机理；初步探索了上述稀土配合物与烷基铝组成的催化体系对异戊二烯聚合的催化性能。
合成了稀土胺基双酚配合物Ln(ONN'O) (Ln=Nd. Sm、Gd、Lu)以及稀土四氢席夫碱配合物Nd(SALAN),分别在正已烷或甲苯溶液中结晶得到了的配合物Sm(ONN'O)、Nd(ONN'O)与Nd(SALAN)的单晶,并进行X-射线单晶衍射确定其晶体结构。发现Sm(ONN'O)及Nd(ONN'O)两种配合物都是由μ-C1桥连的二聚体分子结构,且中心稀土原子都处于7配位状态；而Nd(SALAN)配合物的结构为由μ-Cl桥连的二聚体分子结构,中心稀土Nd原子处于6配位状态。
采用新型稀土胺基双酚配合物作为ε-已内酯(CL)开环聚合的单组分催化剂,比较了不同稀土元素、聚合溶剂及催化剂浓度对聚合的影响。结果表明,稀土钕的配合物Nd(ONN'O)的催化性能较佳,当[Nd]/[CL]为1：200和1：300在甲苯溶液中ε-CL开环聚合表现出一定的活性聚合的特征：PCL的分子量分布较窄；ln(M0/M)值与时间呈直线关系；PCL的分子量随着转化率的升高而线性升高。聚合过程存在一个很长的诱导期,这是由于Nd(ONN'O)分子在甲苯溶液中存在二聚体分子和单分子溶解平衡所导致的。
采用1H NMR、GPC等方法首次直接证明了含酚类配体的稀土配合物催化ε-CL开环聚合的聚合机理。以Nd(ONN'O)为催化剂,[Nd]/[CL]=1：20制备了低分子量PCL,用甲醇终止聚合反应。控制聚合物与甲醇的酯交换反应得到含有双酚配体端基与不含配体端基的聚合物P1和P2,结合GPC测定两者的分子量,直接证明了该开环聚合反应为Ln-O键断裂的配位-插入机理,而ε-CL以酰-氧键断裂的方式开环。
Lanthanide chloride complexes bearing amine-bis(phenolate) ligand Ln(ONN'O) (Ln= Nd, Sm, Gd and Lu) have been synthesized by metathesis reaction of anhydrous LnCl3 with amine-bis(phenolate) lithium salt in high yields. The complexes containing neodymium and samarium center were characterized, the single crystal X-ray crystallographic analysis shows these complexes are dimeric, consists of two seven-coordinate rare earth centers linked throughμ-Cl bridges. Neodymium chloride complex with tetradentate phenoxyamine (SALAN) ligand Nd(SALAN) was synthesized. Its single crystal X-ray crystallographic analysis shows this complex is also dimeric, consists of two six-coordinate neodymium centers linked throughμ-Cl bridges.
The ring-opening polymerization (ROP) ofε-caprolactone (CL) was successfully carried out by using these lanthanide complexes as single component catalysts and the influence of the reaction conditions on the monomer conversion, molecular weight and molecular weight distribution of the resultant polymers was investigated. The neodymium complex (Nd(ONN'O))exhibits highest catalytic activities and leads to controlled ROP of CL, preparing PCLs with controlled molecular weights and narrow molecular weight distributions. Under the [Nd]/[CL] molar ratio of 200 or 300, polymerized in toluene at 80℃, the polymerization rate was first-order with respect to the monomer concentration. A long induction period was observed in this system, which attributes to the dissolution equilibrium of dimer-monomer of complex in solution.
For the purpose of investigating the mechanism, a ROP of CL using Nd(ONN'O) with a 1:20 initiator to monomer molar ratio was carried out, and the polymerization was terminated by adding methanol. By controlling the transesterification reaction between aryl ester end group (ArOOC) and methanol, the oligomer ofε-caprolactone with or without phenol end group from ligand could be obtained. 1H NMR end group analyses and GPC determination demonstrate the coordination-insertion mechanism of ROP of CL catalyzed by amine-bis(phenolate) based rare-earth metal complexes directly.
合成了稀土胺基双酚配合物Ln(ONN'O) (Ln=Nd. Sm、Gd、Lu)以及稀土四氢席夫碱配合物Nd(SALAN),分别在正已烷或甲苯溶液中结晶得到了的配合物Sm(ONN'O)、Nd(ONN'O)与Nd(SALAN)的单晶,并进行X-射线单晶衍射确定其晶体结构。发现Sm(ONN'O)及Nd(ONN'O)两种配合物都是由μ-C1桥连的二聚体分子结构,且中心稀土原子都处于7配位状态；而Nd(SALAN)配合物的结构为由μ-Cl桥连的二聚体分子结构,中心稀土Nd原子处于6配位状态。
采用新型稀土胺基双酚配合物作为ε-已内酯(CL)开环聚合的单组分催化剂,比较了不同稀土元素、聚合溶剂及催化剂浓度对聚合的影响。结果表明,稀土钕的配合物Nd(ONN'O)的催化性能较佳,当[Nd]/[CL]为1：200和1：300在甲苯溶液中ε-CL开环聚合表现出一定的活性聚合的特征：PCL的分子量分布较窄；ln(M0/M)值与时间呈直线关系；PCL的分子量随着转化率的升高而线性升高。聚合过程存在一个很长的诱导期,这是由于Nd(ONN'O)分子在甲苯溶液中存在二聚体分子和单分子溶解平衡所导致的。
采用1H NMR、GPC等方法首次直接证明了含酚类配体的稀土配合物催化ε-CL开环聚合的聚合机理。以Nd(ONN'O)为催化剂,[Nd]/[CL]=1：20制备了低分子量PCL,用甲醇终止聚合反应。控制聚合物与甲醇的酯交换反应得到含有双酚配体端基与不含配体端基的聚合物P1和P2,结合GPC测定两者的分子量,直接证明了该开环聚合反应为Ln-O键断裂的配位-插入机理,而ε-CL以酰-氧键断裂的方式开环。
Lanthanide chloride complexes bearing amine-bis(phenolate) ligand Ln(ONN'O) (Ln= Nd, Sm, Gd and Lu) have been synthesized by metathesis reaction of anhydrous LnCl3 with amine-bis(phenolate) lithium salt in high yields. The complexes containing neodymium and samarium center were characterized, the single crystal X-ray crystallographic analysis shows these complexes are dimeric, consists of two seven-coordinate rare earth centers linked throughμ-Cl bridges. Neodymium chloride complex with tetradentate phenoxyamine (SALAN) ligand Nd(SALAN) was synthesized. Its single crystal X-ray crystallographic analysis shows this complex is also dimeric, consists of two six-coordinate neodymium centers linked throughμ-Cl bridges.
The ring-opening polymerization (ROP) ofε-caprolactone (CL) was successfully carried out by using these lanthanide complexes as single component catalysts and the influence of the reaction conditions on the monomer conversion, molecular weight and molecular weight distribution of the resultant polymers was investigated. The neodymium complex (Nd(ONN'O))exhibits highest catalytic activities and leads to controlled ROP of CL, preparing PCLs with controlled molecular weights and narrow molecular weight distributions. Under the [Nd]/[CL] molar ratio of 200 or 300, polymerized in toluene at 80℃, the polymerization rate was first-order with respect to the monomer concentration. A long induction period was observed in this system, which attributes to the dissolution equilibrium of dimer-monomer of complex in solution.
For the purpose of investigating the mechanism, a ROP of CL using Nd(ONN'O) with a 1:20 initiator to monomer molar ratio was carried out, and the polymerization was terminated by adding methanol. By controlling the transesterification reaction between aryl ester end group (ArOOC) and methanol, the oligomer ofε-caprolactone with or without phenol end group from ligand could be obtained. 1H NMR end group analyses and GPC determination demonstrate the coordination-insertion mechanism of ROP of CL catalyzed by amine-bis(phenolate) based rare-earth metal complexes directly.
引文
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