Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
Dalton Trans. 2014 Mar 21;43(11):4295-304. doi: 10.1039/c3dt51846a.
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 β-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.
一系列钴席夫碱配合物被制备、表征，并用于可逆终止有机金属介导自由基聚合（RT-OMRP）的研究。席夫碱配体含有环己二亚胺桥和系统改变的对位取代的酚氧基部分，作为一种研究配体对配合物结构和反应性的电子影响的方法。这些配合物通过单晶 X 射线衍射、循环伏安法、X 射线光电子能谱、电子顺磁共振波谱和计算方法进行了表征。结构研究均支持可调节的金属中心反应性，这是由席夫碱配体的给电子能力决定的。苯乙烯、甲基丙烯酸甲酯和醋酸乙烯酯的 RT-OMRP 被报道，并表明钴-碳键的强度随配体取代而变化。竞争的β-氢原子夺取提供长链烯烃端基聚合物链和良好控制的醋酸乙烯酯聚合，与较低温度的缔合交换机制的退化转移 OMRP 形成对比。
