Center for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University , Hangzhou 310027, P. R. China.
Acc Chem Res. 2014 Apr 15;47(4):1199-207. doi: 10.1021/ar400265x. Epub 2014 Feb 6.
Metalloporphyrins are the active sites in monooxygenases that oxidize a variety of substrates efficiently and under mild conditions. Researchers have developed artificial metalloporphyrins, but these structures have had limited catalytic applications. Homogeneous artificial metalloporphyrins can undergo catalytic deactivation via suicidal self-oxidation, which lowers their catalytic activity and sustainability relative to their counterparts in Nature. Heme molecules in protein scaffolds can maintain high efficiency over numerous catalytic cycles. Therefore, we wondered if immobilizing metalloporphyrin moieties within porous metal-organic frameworks (MOFs) could stabilize these structures and facilitate the molecular recognition of substrates and produce highly efficient biomimetic catalysis. In this Account, we describe our research to develop multifunctional porphyrinic frameworks as highly efficient heterogeneous biomimetic catalysts. Our studies indicate that porous porphyrinic frameworks provide an excellent platform for mimicking the activity of biocatalysts and developing new heterogeneous catalysts that effect new chemical transformations under mild conditions. The porous structures and framework topologies of the porphyrinic frameworks depend on the configurations, coordination donors, and porphyrin metal ions of the metalloporphyrin moieties. To improve the activity of porous porphyrinic frameworks, we have developed a two-step synthesis that introduces the functional polyoxometalates (POMs) into POM-porphyrin hybrid materials. To tune the pore structures and the catalytic properties of porphyrinic frameworks, we have designed metalloporphyrin M-H8OCPP ligands with four m-benzenedicarboxylate moieties, and introduced the secondary auxiliary ligands. The porphyrin metal ions and the secondary functional moieties that are incorporated into porous metal-organic frameworks greatly influence the catalytic properties and activities of porphyrinic frameworks in different reactions, such as the oxidation of alkylbenzenes, olefins, and hexane and the photo-oxygenation of 1,5-dihydroxynaphthalene and sulfides. The porphyrin metal ions and the secondary auxiliary sites in the pores can work together synergistically to enhance the catalytic activities of porphyrinic frameworks. Compared with their homogeneous counterparts, the activities and stabilities of the heterogeneous porphyrinic frameworks are remarkable: the immobilization of metalloporphyrins onto the pore surfaces of MOFs not only prevents their suicidal self-oxidation but also allows them to activate inert substrate molecules, such as cyclohexane. Moreover, because the bulky molecules cannot easily access the active sites inside the pores of porphyrinic frameworks, these porous materials demonstrate interesting size-selective catalytic properties toward substrates.
金属卟啉是单加氧酶中的活性部位，能够在温和条件下高效氧化各种底物。研究人员已经开发出人工金属卟啉，但这些结构的催化应用有限。均相人工金属卟啉会通过自杀式自氧化而发生催化失活，从而降低其催化活性和可持续性，与自然界中的对应物相比更是如此。蛋白质支架中的血红素分子在多个催化循环中仍能保持高效。因此，我们想知道将金属卟啉部分固定在多孔金属-有机骨架（MOF）内是否可以稳定这些结构并促进底物的分子识别，从而产生高效的仿生催化。在本报告中，我们描述了我们的研究，以开发多功能卟啉框架作为高效的非均相仿生催化剂。我们的研究表明，多孔卟啉框架为模拟生物催化剂的活性和开发在温和条件下实现新化学转化的新型非均相催化剂提供了极好的平台。多孔卟啉框架的多孔结构和框架拓扑取决于金属卟啉部分的配位供体、构型和金属离子。为了提高多孔卟啉框架的活性，我们开发了一种两步合成方法，将功能多金属氧酸盐（POM）引入 POM-卟啉杂化材料中。为了调节多孔卟啉框架的孔结构和催化性能，我们设计了具有四个间苯二甲酸甲酯部分的金属卟啉 M-H8OCPP 配体，并引入了辅助配体。金属卟啉离子和引入多孔金属-有机骨架的次级功能部分极大地影响了不同反应中卟啉骨架的催化性能和活性，例如烷基苯、烯烃和己烷的氧化以及 1,5-二羟基萘和硫化物的光氧化。多孔金属-有机骨架中的金属卟啉离子和次级辅助位点可以协同作用，增强卟啉骨架的催化活性。与均相对应物相比，非均相卟啉骨架的活性和稳定性非常显著：将金属卟啉固定在 MOF 的孔表面上不仅可以防止其自杀式自氧化，还可以激活惰性底物分子，如环己烷。此外，由于大体积分子不易进入卟啉骨架孔内的活性位点，这些多孔材料对底物表现出有趣的尺寸选择性催化特性。
