Tuning ligand electronics and peripheral substitution on cobalt salen complexes: structure and polymerisation activity
Tuning ligand electronics and peripheral substitution on cobalt salen complexes: structure and polymerisation activity
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DOI：
10.1039/c3dt51846a
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发表时间：
2014-01-01
影响因子：
4
通讯作者：
Shaver, Michael P.
中科院分区：
文献类型：
--
作者：
Chiang, Linus;Allan, Laura E. N.;Shaver, Michael P.
本文制备了一系列钴salen配合物，其中salen代表N2O2双希夫碱双酚酸酯框架，并对其进行了表征和研究，用于可逆终止有机金属介导的自由基聚合（RT-OMRP）。salen配体含有环己烷二亚胺桥和系统改变的对取代苯氧基，作为一种方法来研究配体对复杂结构和反应性的电子影响。用单晶x射线衍射、循环伏安法、x射线光电子能谱、电子顺磁共振能谱和计算方法对配合物进行了表征。结构研究都支持一种可定制的金属中心反应性，这种反应性是由salen配体的给电子能力改变的。本文报道了苯乙烯、甲基丙烯酸甲酯和醋酸乙烯的RT-OMRP，结果表明钴-碳键强度随配体取代而变化。竞争性的-氢萃取提供了长链烯烃端聚合物链和良好控制的醋酸乙烯聚合，与退化转移OMRP的低温缔合交换机制形成对比。
A series of cobalt salen complexes, where salen represents an N2O2 bis-Schiff-base bis-phenolate framework, are prepared, characterised and investigated for reversible-termination organometallic mediated radical polymerisation (RT-OMRP). The salen ligands contain a cyclohexane diimine bridge and systematically altered para-substituted phenoxide moieties as a method to examine the electronic impact of the ligand on complex structure and reactivity. The complexes are characterised by single crystal X-ray diffraction, cyclic voltammetry, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and computational methods. Structural studies all support a tailorable metal centre reactivity altered by the electron-donating ability of the salen ligand. RT-OMRP of styrene, methyl methacrylate and vinyl acetate is reported and suggests that cobalt-carbon bond strength varies with the ligand substitution. Competing beta-hydrogen abstraction affords long-chain olefin-terminated polymer chains and well controlled vinyl acetate polymerisations, contrasting with the lower temperature associative exchange mechanism of degenerative transfer OMRP.