Sequence-controlled ethylene/styrene copolymerization catalyzed by scandium complex
Sequence-controlled ethylene/styrene copolymerization catalyzed by scandium complex
复制标题
钪络合物催化顺序控制乙烯/苯乙烯共聚
作者：
Bo Liu;Lingfang wang;Chunji Wu;Dongmei Cui
稀土金属络合物可以催化乙烯/苯乙烯的共聚反应，得到具有较长间规聚苯乙烯序列的共聚物。在这里，通过调控钪前驱体的电子和空间性质，实现了顺序可控的乙烯/苯乙烯共聚。当使用(2，4，5，6-ME4-4H-环戊二烯[b]硫代苯基)Sc(CH2SiMe3)2-(2，4，5，6-ME4-4H-环戊二烯)Sc(CH2SiMe3)2时，得到了具有较长间规聚苯乙烯序列的共聚物。配合物1(1·THF)的四氢呋喃(THF)加合物由于金属中心周围的空间效应增加，生成的共聚物具有较短的聚苯乙烯序列。吡啶加合物1·Py和1·PyF5完全是惰性的。在相同条件下，络合物2((2，5-dimethyl-3-phenyl-4-H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2)，是1的类似物，将苯乙烯分散地加入到共聚物中形成“伪随机”微结构。(Flu-CH2-Py)Sc(CH2SiMe3)2是一种体积大、电子给体较少的限制几何构型配体，它能以活泼的方式催化共聚反应，得到主要含有交替的乙烯/苯乙烯序列的共聚物，并观察到快速可逆链转移反应生成烷基铝。阐述了钪前驱体的结构和电子因素，如配体的空间膨胀性和路易斯碱在活性金属中心的掺入，对所得共聚物的催化活性和序列分布的影响。
Rare earth metal-based complexes can catalyze ethylene/styrene copolymerization to give copolymers with long syndiotactic polystyrene sequences. Here, sequence-controlled ethylene/styrene copolymerization was achieved by regulating the electronic and steric properties of scandium precursors. When a thiophene-fused cyclopentadienyl scandium complex 1, (2,4,5,6-Me4-4H-cyclopenta[b]thiophenyl) Sc(CH2SiMe3)2, was used, a copolymer with long syndiotactic polystyrene sequences was obtained. The tetrahydrofuran (THF) adduct of complex 1 (1·THF) showed lower activity to give a copolymer with short polystyrene sequences owing to an increase in the steric effects around the metal center. The pyridine adducts 1·Py and 1·PyF5 were totally inert. Under the same conditions, complex 2 ((2,5-dimethyl-3-phenyl-4-H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2), an analog of 1, incorporated styrene discretely into the copolymer to form a “pseudo random” microstructure. Complex 3 bearing a bulky and less electrondonating constrained-geometry configuration ligand ((Flu-CH2–Py)Sc(CH2SiMe3)2) could catalyze copolymerization in a livingness manner to afford copolymers containing mainly the alternating ethylene/styrene sequence, where a fast and reversible chain-transfer reaction to aluminum alkyl was observed. The influences of structural and electronic factors of the scandium precursors, such as the steric bulkiness of a ligand and incorporation of a Lewis base to the active metal center, on the catalytic activity and sequence distribution of the resulting copolymers were elucidated.