Polymer of Intrinsic Microporosity Induces Host-Guest Substrate Selectivity in Heterogeneous 4-Benzoyloxy-TEMPO-Catalysed Alcohol Oxidations
Polymer of Intrinsic Microporosity Induces Host-Guest Substrate Selectivity in Heterogeneous 4-Benzoyloxy-TEMPO-Catalysed Alcohol Oxidations
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DOI：
10.1007/s12678-015-0284-8
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发表时间：
2016-01-01
期刊：
影响因子：
3.1
通讯作者：
Marken, Frank
中科院分区：
文献类型：
--
作者：
Ahn, Sunyhik D.;Kolodziej, Adam;Marken, Frank
自由基4-苯甲酰氧基-2，2，6，6-四甲基哌啶-1-氧基（4 B-TEMPO）当固定在电极表面并浸入碳酸盐缓冲水溶液中时作为伯醇氧化的电催化剂是活性的。为了改进催化过程，基于（i）直径为2-12 μ m的碳微粒以增强电荷传输和（ii）具有固有微孔性的聚合物（此处为BET表面积为1027 m（2）g（-1）的PIM-EA-TB）开发了复合膜电极。后者充当嵌入式自由基催化剂的高度刚性分子框架，同时接近水相和底物。所得到的伯醇的氧化的机制被示出为随着底物浓度的增加而在反应顺序上从第一切换到第零，这与在聚合物层-电极界面处具有电荷竞争性扩散的动力学限制过程一致（这里是Albery-Hillman符号中的“LEk”情况）。反应性优化和筛选更广泛的伯醇结合DFT的相对反应性相关性揭示了底物疏水性作为一个重要因素，提高催化电流。提出PIM-EA-TB主体基质来控制底物分配，从而控制催化剂反应性和选择性。
The free radical 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4B-TEMPO) is active as an electrocatalyst for primary alcohol oxidations when immobilised at an electrode surface and immersed into an aqueous carbonate buffer solution. In order to improve the catalytic process, a composite film electrode is developed based on (i) carbon microparticles of 2-12 mu m diameter to enhance charge transport and (ii) a polymer of intrinsic microporosity (here PIM-EA-TB with a BET surface area of 1027 m(2) g(-1)). The latter acts as a highly rigid molecular framework for the embedded free radical catalyst with simultaneous access to aqueous phase and substrate. The resulting mechanism for the oxidation of primary alcohols is shown to switch in reaction order from first to zeroth with increasing substrate concentration consistent with a kinetically limited process with competing diffusion of charge at the polymer layer-electrode interface (here the "LEk" case in Albery-Hillman notation). Reactivity optimisation and screening for a wider range of primary alcohols in conjunction with DFT-based relative reactivity correlation reveals substrate hydrophobicity as an important factor for enhancing catalytic currents. The PIM-EA-TB host matrix is proposed to control substrate partitioning and thereby catalyst reactivity and selectivity.