FLP Zintl Clusters for the Electrochemical Catalytic Reduction of Small Molecules

我们将利用Zintl离子的未开发的反应性，地球丰富的主族元素的polayanionic集群，以化学计量和催化方式影响小分子活化。偶联反应产生新的键，特别是C-C键，在合成化学中占据中心地位。为此，学术和工业化学家开发的Pd交叉偶联反应的丰富历史已经发展。然而，金属基催化剂的高操作成本和毒性激发了人们对可以代表这种反应性的主族系统的兴趣。也许主族催化剂中最多样化和最成功的例子是受挫的刘易斯对（FLP）。传统的FLP系统依赖于刘易斯酸性和刘易斯碱性位点来活化小分子，并且大多数同原子和杂原子键形成反应通过键极化机制进行。然而，这些键形成反应的范围仍然有限，并且与CO2的C-C键形成在该领域中仍然未被识别。在本项目中，一个新的家庭的FLP组成的集群能够多点激活将与电化学方法相结合，以促进成键化学。我们打算建立Zintl集群作为FLP化学的基本组成部分。初步研究的目标是[P7]3-，不仅是因为它的合成可及性，NMR手柄的存在，以及相对于第14族簇的更大稳定性，而且还因为膦作为已建立的FLP系统中的基本组分的广泛成功。一旦用酸性组分官能化，这些聚阴离子簇是通过FLP途径进行小分子活化的极好目标，因为它们具有必要的富电子和贫电子组分。考虑到这种接近性和经历氧化还原反应的倾向，这些系统将在小分子的电化学还原中进行评估，我们最雄心勃勃的目标是将CO2选择性还原为乙烷。将C1、环境毒素和工业副产品回收利用，使其成为燃烧时产生CO2的燃料那样的高附加值产品。本研究项目由梅塔和德赖夫两个研究小组共同进行，分为两个工作包。工作包1（主要由梅塔小组负责）：1.用刘易斯酸性组分2官能化第15族Zintl簇，即[P7]3-。在这些簇上的酸性和碱性中心之间进行插入化学，类似于FLP化学。特别感兴趣的小分子包括CO2，烯烃，羰基化合物，聚酰亚胺和异氰酸酯。博士项目呼叫20203。还原性耦合活化底物以形成新的键Work Package 2（主要基于Dryfe集团）：4.将FLP Zintl材料固定在合适的电极表面上，例如玻璃碳或边缘平面热解石墨5。通过还原预期的氧化偶联簇产物，以电化学方式关闭催化循环6。使用动力学分析方法，通过拟合电化学数据来确定和优化催化过程的速率。Zintl团簇吸引了学术界的想象力，因为它们是更大的非均相系统的分子模型。我们用[P7]3-开发的技术可以扩展到更大的聚磷化物，如[P11]3-，[P16]2-，[P21]3-，并最终告知与功能化赤磷的反应性。将CO2电化学/光化学转化为低附加值产品的策略被称为人工光合作用。

We will harness the untapped reactivity of Zintl ions, polayanionic clusters of earth abundant main-group elements, to affect small molecule activations in stoichiometric and catalytic fashions. Coupling reactions to yield new bonds, especially C-C bonds, occupy a central position in synthetic chemistry. To this end, a rich history of Pd cross-coupling reactions exploited by both academic and industrial chemists has developed. However, the high operational costs and toxicity of metal-based catalysts has spurred an interest in main-group systems that can represent this reactivity. Perhaps the most diverse and successful examples of main-group catalysts are frustrated Lewis pairs (FLPs). Traditional FLP systems rely on a Lewis acidic and a Lewis basic site to activate small molecules, and most homoatomic and heteroatomic bond formation reactions are accessed by bond polarisation mechanisms. However, the scope of these bond formation reactions remains limited and C-C bond formation with CO2 remains unidentified in the field. In this project, a new family of FLPs consisting of clusters capable of multi-site activation will be coupled with electrochemical methods to promote bond formation chemistries.We intend to establish Zintl clusters as the basic component in FLP chemistry. Preliminary investigations are targeted with [P7]3-, not only because of its synthetic accessibility, presence of an NMR handle, and greater stability relative to group 14 clusters, but also because of the wide-spread success of phosphines as the basic component in established FLP systems. Once functionalised with an acidic component, these polyanionic clusters are excellent targets for small molecule activation via a FLP pathway, as they feature both the necessary electron-rich and electron-poor components. With this proximity and the propensity to undergo redox reactions in mind, these systems will be assessed in the electrochemical reduction of small molecules, our most ambition target would be the selective reduction of CO2 to ethane. Recycling the C1 building-block, environmental toxin, and industrial by-product into value-added products reminiscent of the fuels from which CO2 is generated upon combustion.This research project will be collaboratively undertaken by the Mehta and Dryfe groups, and has been divided into two work packages.Work Package 1 (primarily based in the Mehta group):1. Functionalise the group 15 Zintl clusters, namely [P7]3-, with a Lewis acidic component2. Perform insertion chemistry between acidic and basic centres on these clusters akin to FLP chemistry. Small molecules of particular interest include CO2, olefins, carbonyls, carbodiimides, and isocyanates.PhD project call 20203. Reductively couple activated substrates to form new bondsWork Package 2 (primarily based in the Dryfe group):4. Immobilise FLP Zintl material on suitable electrode surfaces, e.g. glassy carbon or edge-plane pyrolytic graphite5. Electrochemically close catalytic cycles by reducing the expected oxidatively coupled cluster product6. Use kinetic analysis methods to determine, and optimise, rates of catalytic processes via fitting of electrochemical data.Zintl clusters capture the imagination of academics because they are molecular models for larger heterogenous systems. Technology we develop with [P7]3- can be expanded to larger polyphosphides, such as [P11]3-, [P16]2-, [P21]3-, and eventually inform reactivity possible with functionalised red phosphorus. The strategy of electrochemically / photochemically converting CO2 to reduced value-added products is referred to as artificial photosynthesis.