Selective small molecule activation towards sustainable chemical synthesis

发展新的可持续过程是现代化学的一个重要目标。化学工业目前采用的大多数大规模反应消耗不可再生资源，并需要基于金属的催化剂，而金属往往稀缺、昂贵且有毒。这对于由烃基聚合物（如聚乙烯）制成的塑料来说尤其如此。这些都是从石化产品中生产出来的，因此它们的生产需要持续开采地球上有限的化石燃料供应，并推动气候变化。这些塑料也是不可生物降解的，由于它们在海洋和其他自然栖息地的积累，导致了有充分记录的环境问题。因此，利用可再生资源生产可生物降解的聚合物是至关重要的。一种有希望的解决方案是使用内酯和丙交酯等分子，它们被称为环酯，是通过发酵玉米和甜菜等可再生生物质产生的。这些分子是环状的，但它们的环状结构可以被含有带电金属离子的催化剂激活。这使得反应性的碳-氧键被打破，打开环形成一个短的线性链，然后可以通过在它们之间形成新的碳-氧键与其他链连接，形成一个长聚合物链。金属催化剂加速反应，并在循环结束时再生，使其有可能被循环利用。开发能够在低温下控制聚合物合成的新型催化剂是关键。使用金属碳基催化剂是一种行之有效的方法，可以激活小分子，如内酯和丙交酯，并使其转化为有用的产品。考虑到可持续性，任何新的催化剂都有利于含有丰富、廉价和无毒的金属。这些可持续性标准被所谓的碱土金属所满足，它们占据了元素周期表的第二列（第2组），使它们成为有吸引力的可持续性催化剂的候选者。特别是，重族2元素锶和钡作为催化剂具有未开发的潜力，值得进一步研究。其他潜在的候选者是元素钐、铕和镱——像锶和钡一样，这些重元素体积大，而且相对于其他重金属也丰富且无毒。该项目属于EPSRC物理科学研究领域，将在奥黑尔集团进行。其最初的目标将是开发含有锶和钡的新型催化剂，在后期阶段还将研究含有钐、铕和镱的配合物。通过与麦迪团队的合作，计算方法将被引入到项目中。目的是发展这些催化剂的结构-功能关系。将研究这些配合物与内酯和丙交酯的反应性，以确定哪种金属最有效地催化生产生物可降解聚合物。

The development of new sustainable processes is a crucial goal of modern chemistry. Most large-scale reactions currently employed by the chemical industry consume non-renewable resources and require catalysts based on metals which are often scarce, expensive and toxic. This is especially true for plastics made from hydrocarbon-based polymers such as polyethylene. These are produced from petrochemicals and so their production requires the continued extraction of the earth's limited supply of fossil fuels and drives climate change. These plastics are also non-biodegradable, resulting in well documented environmental issues caused by their accumulation in the ocean and other natural habitats.As such the production of biodegradable polymers from renewable resources is of paramount importance. One promising solution is the use of molecules such as lactones and lactide, which are known as cyclic esters and are produced by fermenting renewable biomass such as corn and sugar beets. These molecules are cyclic, but their ring-shaped structures can be activated by a catalyst containing a charged metal ion. This enables a reactive carbon-oxygen bond to be broken, opening up the ring to form a short linear chain, which can then be linked with others to form a long polymer chain by forming new carbon-oxygen bonds between them. The metal catalyst speeds up the reaction and is regenerated at the end of the cycle, potentially enabling it to be recycled.The development of new catalysts that enable the controlled synthesis of polymers at low temperatures is key. The use of metal-carbon based catalysts is a well-established method for activating small molecules such as lactones and lactide and enabling their transformation into useful products. With sustainability in mind, it is beneficial for any new catalysts to contain metals which are abundant, cheap and non-toxic. These sustainability criteria are satisfied by the so-called alkaline earth metals that occupy the second column of the periodic table (group 2), making them attractive candidates for use as sustainable catalysts. In particular, the heavy group 2 elements strontium and barium hold untapped potential as catalysts and are worthy of further investigation. Other potential candidates are the elements samarium, europium and ytterbium - like strontium and barium these heavy elements are large in size, while also being abundant and non-toxic relative to other heavy metals. This project falls within the EPSRC Physical Sciences research area and will take place in the O'Hare group. Its initial aims will be to develop novel catalysts containing strontium and barium, at a later stage complexes containing samarium, europium and ytterbium will also be investigated. Computational methods will be brought into the project via a collaboration with the McGrady group. The objective will be to develop structure-function relationships for these catalysts. The reactivity of these complexes with lactones and lactide will be investigated to determine which metal most effectively catalyses the production of biodegradable polymers.