Iron-Catalysed Oxygenation with O2

氧化被用于催化生产超过一半的商业化学品，是仅次于聚合的最重要的工业反应之一。毫不奇怪，美国能源部将有机化学品的选择性氧化确定为影响未来化学工业的最重要的研究领域。然而，它仍然是“最有改进潜力的反应之一”，这主要是因为在绝大多数氧化反应中遇到的选择性低，以及化学计量比、有毒和危险的氧化剂的广泛使用，如CrO_3、H_2S_2O_8、PHIO、HNO_3。使用催化剂和环境友好的氧化剂无疑是解决这些问题的最现实的方法。在这方面，由于铁和氧气的丰富、低成本和无害的性质，发展铁催化好氧氧化是最有吸引力的。然而，尽管含铁金属酶能够在温和的条件下选择性地氧化各种底物，但已知的人造铁催化剂很少能够有效地、选择性地催化有氧氧化。我们最近发现了一类新型的含吡啶联咪唑啉(双吡啶)配体的铁配合物，它允许醚和烯烃的高度化学选择性氧化。在这一成功的基础上，该项目寻求开发下一代更活跃的铁催化剂，用于更具挑战性的底物的选择性氧化。特别是，我们将集中在两个反应，木质素的解聚和脂肪族C=C双键的裂解，在有氧条件下。这些反应在性质上有很大的不同，因此可以证明铁催化剂的广泛范围，具有基本的和商业意义。木质素是唯一由芳香族单元组成的天然聚合物，可用于生产多种平台芳香族化合物。然而，这需要首先解聚木素醚键。考虑到实现这一目标的任何可能过程的巨大规模，理想情况下，使用的催化剂应该以廉价金属(如铁)为基础。烯烃氧化裂解为羰基是一种广泛使用的转化方法。然而，臭氧最常用于工业操作，这伴随着众所周知的安全问题，如爆炸性、特殊设备的成本和产生的大量废物。因此，开发替代臭氧的催化方法具有很强的诱因。铁基催化剂尤其令人感兴趣，它不仅考虑到铁的环境效益，还考虑到铁加氧酶以极高的选择性将烯烃氧化为羰基化合物的能力。对于这两种反应，已知的能够利用O2作为氧化剂的铁催化剂很少。铁-吡啶双核苷配合物有望在应对这些挑战方面带来阶段性变化。这种新型催化剂还将在其他反应中得到应用。醚键是自然界和人造化学品中最普遍的键之一，从药品和农用化学品到家用产品，再到木质素和煤炭。因此，使用新的催化剂和O2，含有醚键的化合物可以转化为高附加值的产品，污染塑料、农用化学品和洗涤剂可能会在空气中降解。为了进一步证明铁催化剂的价值，将与一家中小企业合作，通过芳烃的酰化反应生产具有直接商业利益的化合物。

Being used in the catalytic production of more than half of all the commercial chemicals, oxidation is one of the most significant industrial reactions, second only to polymerisation. Not surprisingly, the U.S. Department of Energy identified selective oxidation of organic chemicals to be the most important research area to impact the future chemical industry. However, it remains "one of the reactions with the greatest potential for improvement", primarily because of the low selectivity encountered in the vast majority of oxidation reactions and the widespread use of stoichiometric, toxic and hazardous oxidants, such as CrO3, H2S2O8, PhIO, HNO3. Using catalysts and environmentally benign oxidants is undoubtedly the most realistic way to address these issues. In this regard, developing iron-catalysed aerobic oxidation is most appealing, due to the unrivalled advantage of abundance, low cost and benign nature of Fe and O2. However, although iron-containing metalloenzymes are capable of selectively oxidizing various substrates with O2 under mild conditions, few man-made iron catalysts are known that can catalyse efficient, selective aerobic oxidation.We recently uncovered a novel class of well-defined iron complexes bearing pyridine bisimidazoline (PyBisulidine) ligands, which allow for highly chemoselective oxygenation of ethers and olefins. Building on this success, this project seeks to develop the next generation of more active iron catalysts for selective oxygenation of more challenging substrates. In particular, we will concentrate on two reactions, depolymerisation of lignin and cleavage of aliphatic C=C double bonds, under aerobic conditions. These reactions, which are vastly different in nature and can thus demonstrate the wide scope of the iron catalysts, are of both fundamental and commercial significance. Lignin is the only natural polymers made of aromatic units and could be used to produce a wide range of platform aromatic compounds. However, this requires the depolymerisation of the lignin ether linkage in the first place. Considering the huge scale of any possible processes toward this end, the catalyst to be used should ideally be based on a cheap metal such as iron. Oxidative cleavage of alkenes into carbonyls is a widely used transformation. However, ozone is most often used in industrial operations, and this comes with the well-known safety issues of explosivity, the cost of special equipment, and the large amount of waste generated. Thus, there has been a strong incentive to develop catalytic methods to replace ozone. Iron-based catalysts are particularly interesting, considering not only the environmental benefit of iron but also the ability of iron oxygenases to oxidize olefins to carbonyl compounds with exquisite selectivity. For both of these reactions, few iron catalysts are known that can make use of O2 as oxidant. The Fe-PyBisulidine complexes are expected to bring about a step change in addressing these challenges. The new catalysts will find applications in other reactions as well. The ether linkage is one of the most ubiquitous bonds found in nature and manmade chemicals, ranging from pharmaceuticals and agrochemicals through household products to lignin and coal. Thus, using the new catalysts and O2, compounds containing an ether bond may be transferred into highly value-added products, and polluting plastics, agrochemicals and detergents may be degraded in air. To further demonstrate the value of the iron catalyst, collaboration with a SME to produce, via acylation of arenes, compounds of direct business interest will be implemented.