Dinuclear Pentacoordinated Organoyttrium Biphenolates as Initiators for the Synthesis of High-Molecular Weight Isotactic Poly(2-vinylpyridine)

Dinuclear
organoyttrium biphenolato complexes have been synthesized for the
first time starting from Y­(CH2SiMe3)3(THF)2 and readily available biphenols with bulky substituents
at the 3,3′-positions. XRD analysis revealed that these complexes
are formed as homochiral dimers even though racemic biphenols were
employed. Such dinuclear penta-coordinated yttrium complexes were
evaluated as initiators in the polymerization of 2-vinylpyridine (2-VP).
High activity and excellent isotacticity (mm > 99%) were observed.
DSC analysis of poly­(2-VP) showed a Tm = 221 °C, which is the highest value reported to date. Attempts
to improve the low initiation efficiency of the present system were
made by co-use with several organo-main-group metal reagents. Specifically,
good molecular weight control within the high Mn region was achieved by the addition of Et3Al (Al/Y
= 10).

首次从Y-(CH2SiMe3)3(THF)2和易得的具有3,3'-位位阻基团的二苯酚出发，合成了双核有机铒二苯酚配位复合物。X射线衍射分析显示，尽管使用了外消旋二苯酚，这些复合物仍以同手性二聚体的形式形成。作为2-乙烯基吡啶（2-VP）聚合反应的引发剂，这种五配位双核钇复合物得到了评估，结果显示出高活性及优异的顺式立构性（mm > 99%）。聚（2-VP）的热重分析显示其熔点Tm为221°C，是目前报道的最高值。为改善现有体系较低的引发效率，尝试与多种有机主族金属试剂协同使用。特别是，通过添加Et3Al（Al/Y = 10），在高Mn区域实现了良好的分子量控制。