Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization
Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization
复制标题
光引导无催化剂格氏光聚合中的单体配位
DOI：
10.1021/jacs.1c09595
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发表时间：
2021
影响因子：
15
通讯作者：
Kalow, Julia A.
中科院分区：
文献类型：
--
作者：
Woods, Eliot F.;Berl, Alexandra J.;Kantt, Leanna P.;Eckdahl, Christopher T.;Wasielewski, Michael R.;Haines, Brandon E.;Kalow, Julia A.
π共轭聚合物可以作为柔性和轻质电子器件的有源层，传统上是通过过渡金属介导的高温缩聚合成的。我们最近报道了一种缺电子的杂芳基格氏单体的光聚合反应，使无催化剂合成n型π共轭聚合物成为可能。在此，我们描述了对这种光聚合机理的实验和计算研究。原位和猝灭后的光谱研究表明，传播链是带有卤化物端基的自由基阴离子。对模型低聚物的密度泛函计算表明，这是一种镁模板SRN1型偶联，其中格氏单体与自由基阴离子链配位避免了自由基sp2的形成，并允许以非常低的势垒形成C-C键。我们发现光在反应中发挥了不寻常的作用，光激发自由基阴离子链将电子密度转移到末端，从而使单体能够有效结合。
π-Conjugated polymers can serve as active layers in flexible and lightweight electronics and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein, we describe an experimental and computational investigation into the mechanism of this photopolymerization. Spectroscopic studies performed in situ and after quenching reveal that the propagating chain is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated SRN1-type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp2radicals and allows C–C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus enabling productive monomer binding.