Active-Site-Accessible, Porphyrinic Metal−Organic Framework Materials

On account of their structural similarity to cofactors found in many metallo-enzymes, metalloporphyrins are obvious potential building blocks for catalytically active, metal−organic framework (MOF) materials. While numerous porphyrin-based MOFs have already been described, versions featuring highly accessible active sites and permanent microporosity are remarkably scarce. Indeed, of the more than 70 previously reported porphyrinic MOFs, only one has been shown to be both permanently microporous and contain internally accessible active sites for chemical catalysis. Attempts to generalize the design approach used in this single successful case have failed. Reported here, however, is the synthesis of an extended family of MOFs that directly incorporate a variety of metalloporphyrins (specifically Al3+, Zn2+, Pd2+, Mn3+, and Fe3+ complexes). These robust porphyrinic materials (RPMs) feature large channels and readily accessible active sites. As an illustrative example, one of the manganese-containing RPMs is shown to be catalytically competent for the oxidation of alkenes and alkanes.

鉴于金属卟啉（metalloporphyrins）的结构与诸多金属酶中的辅因子高度相似，其无疑是制备具有催化活性的金属有机框架（metal−organic framework, MOF）材料的理想构筑基元。尽管已有众多基于卟啉的金属有机框架被报道，但兼具高度可及活性位点与永久微孔结构的同类材料却极为稀缺。事实上，在已公开报道的70余种卟啉基金属有机框架中，仅有一款被证实同时具备永久微孔结构，且拥有可供化学催化使用的内部可及活性位点。此前学界试图推广该单一成功案例所采用的设计策略，均以失败告终。然而本文报道了一类可直接嵌入多种金属卟啉（具体为Al³+、Zn²+、Pd²+、Mn³+及Fe³+配合物）的拓展型金属有机框架家族的合成工作。这类稳定卟啉基材料（robust porphyrinic materials, RPMs）具有大尺寸孔道与易于访问的活性位点。作为示例，其中一款含锰的RPM被证实可高效催化烯烃与烷烃的氧化反应。