FLP Zintl Clusters for the Electrochemical Catalytic Reduction of Small Molecules

我们将利用锌离子（富含地球主族元素的聚阴离子簇）未开发的反应性，以化学计量学和催化方式影响小分子的活化。偶联反应生成新键，特别是碳-碳键，在合成化学中占据中心地位。为此，学术界和工业化学家开发了丰富的钯交叉偶联反应历史。然而，金属基催化剂的高操作成本和毒性激发了人们对能够代表这种反应性的主群系统的兴趣。也许最多样化和最成功的主基团催化剂的例子是受挫路易斯对（FLPs）。传统的FLP系统依靠刘易斯酸性和刘易斯碱性位点来激活小分子，大多数同原子和杂原子的键形成反应都是通过键极化机制来实现的。然而，这些成键反应的范围仍然有限，与二氧化碳形成的C-C键在该领域仍未被识别。在这个项目中，一个新的FLPs家族由能够多位点激活的簇组成，将与电化学方法相结合，以促进化学键的形成。我们打算建立Zintl簇作为FLP化学的基本组分。初步研究的目标是[P7]3-，不仅因为它的合成可及性，核磁共振手柄的存在，以及相对于14族簇更大的稳定性，而且还因为磷化氢作为已建立的FLP系统的基本成分的广泛成功。一旦用酸性成分功能化，这些多阴离子簇通过FLP途径成为小分子活化的绝佳目标，因为它们具有必要的富电子和贫电子成分。考虑到这种接近性和发生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将是选择性地将二氧化碳还原为乙烷。将C1积木、环境毒素和工业副产品回收为增值产品，让人想起燃烧时产生二氧化碳的燃料。该研究项目将由Mehta和Dryfe小组共同承担，并分为两个工作包。工作包1（主要基于Mehta组）：用路易斯酸性成分功能化15个Zintl团簇，即[P7]3-。在这些簇的酸性中心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二氧化碳、烯烃、羰基、碳二亚胺和异氰酸酯。博士项目征集20203。还原偶联活化底物形成新的键工作包2（主要基于Dryfe组）：4。将FLP Zintl材料固定在合适的电极表面，如玻碳或边缘平面热解石墨5。通过减少预期的氧化偶联簇产物实现电化学闭合催化循环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簇吸引了学者们的想象力，因为它们是更大的异质系统的分子模型。我们用[P7]3-开发的技术可以扩展到更大的多磷酸盐，如[P11]3-， [P16]2-, [P21]3-，并最终确定功能化红磷的反应性。电化学/光化学将二氧化碳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.