Katherine O. Puffer, Brandon S. Portela, Alexis J. Olson-Gwin, Katherine A. Chism, Sylwia Dworakowska, Ethan J. Crace, Robert S. Paton, Garret M. Miyake
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引用次数: 0
摘要
随着 N,N-二芳基二氢吩嗪有机光氧化催化剂（PCs）的开发，甲基丙烯酸甲酯（MMA）单体的有机催化原子转移自由基聚合（O-ATPR）成为具有低分散性（Đ < 1.30）和接近统一引发剂效率（I* ∼ 100%）的聚合物以及小分子合成的大量实例。在这项工作中，我们研究了烷基、芳基和杂原子基团的核取代（CS）对单线激发态还原电位（ES1°*）的影响。我们观察到，高还原 ES1°* 部分是 CS PC 中以局部激发（LE）为主的杂化局部和电荷转移（HLCT）激发态的结果，而这种激发态受到核心取代基身份的影响。此外，与之前研究中报道的完全 LE PC 相比，具有 LE 主导 HLCT 特性的 PC 在 O-ATRP 中保持了相对氧化的 PC 自由基阳离子氧化电位（E1/2）。例如，噻吩酚核取代（杂原子 CS，HetCS）PC 显示出最负的 ES1°*（-2.07 V vs SCE）、更多的 LE 特性（斯托克斯偏移 = 124 nm），并具有氧化性 PC 自由基阳离子（E1/2 = 0.30 V vs SCE）。CS PC 的性能得到了改善，包括 ES1°* 更负，在 MMA 的 O-ATRP 中表现最佳，其中 HetCS PC 在 DMAc（Đ = 1.08，I* = 89%）和 EtOAc（Đ = 1.06，I* = 97%）中的控制效果最好。此外，研究还发现 HetCS PC 能够介导丙烯酸正丁酯（n-BA）的受控聚合（Đ = 1.24，I* = 97%），而在没有辅助失活策略的情况下，这种聚合在 O-ATRP 中仍然具有挑战性。研究发现，芳基 CS 多氯联苯在百万分之 1 的多氯联苯浓度下具有适度的控制能力，这表明低多氯联苯负载具有促进作用（Đ = 1.33，I* = 69%）。这项研究观察到的激发态特性、ES1°* 和聚合控制之间的关系为提高吩嗪多氯联苯在光氧化催化中的效用奠定了基础。
Influence of Dihydrophenazine Photoredox Catalyst Excited State Character and Reduction Potentials on Control in Organocatalyzed Atom Transfer Radical Polymerization
The development of N,N-diaryl dihydrophenazine organic photoredox catalysts (PCs) has enabled numerous examples of organocatalyzed atom transfer radical polymerization (O-ATRP) of methyl methacrylate (MMA) monomer to polymers with low dispersity (Đ < 1.30) and near-unity initiator efficiency (I* ∼ 100%), as well as small molecule synthesis. In this work, we investigate the influence of core substitution (CS) by alkyl, aryl, and heteroatom groups on singlet excited state reduction potential (ES1°*). We observe that a highly reducing ES1°* is in part a result of a locally excited (LE)-dominated hybridized local and charge transfer (HLCT) excited state in CS PCs, which is influenced by the identity of the core substituent. Additionally, the PCs that possess a LE-dominated HLCT character maintain a relatively oxidizing PC radical cation oxidation potential (E1/2) for deactivation in O-ATRP compared to fully LE PCs reported in prior work. For example, a thiophenol core substituted (heteroatom CS, HetCS) PC shows the most negative ES1°* (−2.07 V vs SCE), more LE character (Stokes shift = 124 nm), and has an oxidizing PC radical cation (E1/2 = 0.30 V vs SCE). The CS PCs with improved properties, including more negative ES1°*, perform best in O-ATRP of MMA with the HetCS PC showing the best control in both DMAc (Đ = 1.08, I* = 89%) and EtOAc (Đ = 1.06, I* = 97%). Additionally, the HetCS PC was found to mediate the controlled polymerization of n-butyl acrylate (n-BA) (Đ = 1.24, I* = 97%), which has remained challenging in O-ATRP without supplemental deactivation strategies. An aryl CS PC was found to have moderate control as low as 1 ppm PC, indicating facilitation of low PC loadings (Đ = 1.33, I* = 69%). The relationship between excited state character, ES1°*, and polymerization control observed in this work provides a foundation for increasing the utility of phenazine PCs across photoredox catalysis.
期刊介绍：
ACS Catalysis is an esteemed journal that publishes original research in the fields of heterogeneous catalysis, molecular catalysis, and biocatalysis. It offers broad coverage across diverse areas such as life sciences, organometallics and synthesis, photochemistry and electrochemistry, drug discovery and synthesis, materials science, environmental protection, polymer discovery and synthesis, and energy and fuels.
The scope of the journal is to showcase innovative work in various aspects of catalysis. This includes new reactions and novel synthetic approaches utilizing known catalysts, the discovery or modification of new catalysts, elucidation of catalytic mechanisms through cutting-edge investigations, practical enhancements of existing processes, as well as conceptual advances in the field. Contributions to ACS Catalysis can encompass both experimental and theoretical research focused on catalytic molecules, macromolecules, and materials that exhibit catalytic turnover.
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