Single Component Iron Catalysts for Atom Transfer and Organometallic Mediated Radical Polymerizations: Mechanistic Studies and Reaction Scope

Tetradentate amine–bis­(phenolate)­iron­(III) halide complexes containing chloro substituents on the aromatic ring are extremely efficient catalysts for controlled radical polymerization. Molecular weights are in good agreement with theoretical values, and dispersities are as low as 1.07 for substituted styrenes and methyl methacrylate polymerizations. Kinetic data reveal activity for styrene polymerization among the fastest reported to date, with the excellent control shown to be electronic rather than steric in origin. Mechanistic studies implicate a multimechanism system with cooperation between atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP). The in situ reduction of the Fe­(III) complex with ascorbic acid or tin octanoate allows polymerizations to be initiated by both 1-phenylethyl chloride (1-PECl, ATRP regime) and azobis­(isobutyronitrile) (AIBN, OMRP regime) to isolate the mechanism of control and offer unique initiation pathways.

四齿胺-双(酚氧基)铁(III)卤化物配合物（芳环上带有氯取代基）是可控自由基聚合的高效催化剂。该体系中聚合产物的分子量与理论值吻合度极佳，取代苯乙烯与甲基丙烯酸甲酯聚合的分散度最低可达1.07。动力学数据表明，该催化剂用于苯乙烯聚合时的活性处于迄今已报道的最快水平之一，其优异的可控性源于电子效应而非空间位阻效应。机理研究显示该体系属于多机理协同体系，结合了原子转移自由基聚合（atom transfer radical polymerization, ATRP）与有机金属介导自由基聚合（organometallic mediated radical polymerization, OMRP）两种作用机制。通过抗坏血酸或辛酸锡对Fe(III)配合物进行原位还原，可分别以1-氯-1-苯乙烷（1-PECl，ATRP路径）和偶氮二异丁腈（AIBN，OMRP路径）引发聚合，从而得以单独解析其可控聚合机理，并提供了独特的引发路径。