Earth Abundant Metals for Simple Coupling Reactions

可持续化学过程的未来取决于催化剂的安全供应。由于大多数催化剂依赖于稀有、昂贵和有毒的铂族金属(PGM)，因此开发替代品的动力越来越大。这些元素，特别是主族金属，传统上一直被忽视；人们认为，与普遍存在的后过渡金属相比，它们几乎没有什么用处。现在很明显，情况并非如此，地球上丰富的金属，如铝和钛(它们是地球上第三和第九丰富的元素)拥有丰富的催化化学，等待开发。在这个项目中，我将准备一系列用于小分子催化的离散均相体系，串联过程，并研究最有希望的体系随后的多相化为二氧化硅。两个选定的例子(但不限于)包括氢胺化/还原和氢膦酰化。氢胺化是在C-C不饱和键上直接加成N-H键，提供了一种原子有效的策略来制备含氮底物。目前，这些限制在较窄的底物范围内，这与可用催化剂的选择(或缺乏)有关。在本项目的这一部分中，我们将评估底物范围(包括分子间和分子内氢胺)与一系列基于Salalen、Salan、尿酸盐、胍酸盐或三氮杂化物的钛(IV)和锆(IV)络合物。这将允许探索一系列的空间/电子效应，以确定structure-activity-relationships.Hydrophosphonylation是一个膦酰基和一个氢原子在C-C不饱和键上的直接加成。这使得能够生产光学活性的羟基和氨基膦酸，这是制药工业的一类重要化合物。在这个项目中，我将基于上述氢氨化反应中的类似配体，制备一系列对这种转化具有活性的铝配合物。一旦成功地开发出均相催化剂，这些催化剂将被拴在用于多相催化的二氧化硅上，以期评估该体系的可回收性，并与均相情况下的选择性进行比较。配基将使用文学策略简单地连接起来。最后，我们还将研究在同一锅中进行多个转化的并发串联催化。为此，我们需要匹配催化剂的稳定性，并对反应动力学有深入的了解。

The future of sustainable chemical processes is dependent on a secure supply of catalysts. Since most catalysts rely on platinum group metals (PGMs), which are rare, expensive, and toxic, there is an increasing impetus to develop alternatives. These elements, especially main-group metals, have traditionally been overlooked; it has been assumed that they have little utility compared to the ubiquitous late-transition metals. It is now apparent that this is not the case, and Earth abundant metals such as Al and Ti (which are the 3rd and 9th most abundant elements on Earth) have a wealth of catalytic chemistry that is waiting to be exploited. In this project, I will prepare a range of discrete homogeneous systems for small molecular catalysis, tandem processes and investigate the subsequent heterogenisation of the most promising systems to silica. Two selected (although not limited) examples include hydroamination/reduction and hydrophosphonylation.Hydroamination is the direct addition of an N-H bond across a C-C unsaturated bond providing an atom efficient strategy to prepare nitrogen containing substrates. Currently, these are limited to a narrow substrate scope which are related to the choices (or lack) of available catalysts. In this part of the project we will assess the substrate scope (both inter and intramolecular hydroaminations) with a range of Ti(IV) and Zr(IV) complexes based on salalen, salan, ureates, guanidinates or triazinides. These will allow a range of steric/electronic effects to be probed to ascertain structure-activity-relationships.Hydrophosphonylation is the direct addition of a phosphonyl group and a hydrogen atom across a C-C unsaturated bond. This enables the production of optically active -hydroxy and -amino phosphonic acids, an important class of compounds for the pharmaceutical industry. In this project I will prepare a series of Al complexes that are active for this transformation, based on similar ligands mentioned above in hydroamination.Once successful homogeneous catalysts have been developed, these will be tethered to SiO2 for heterogeneous catalysis, with a view to assess the recyclability of the system and compare the selectivity to the homogeneous case. The ligands will be simply attached using literature strategies. Finally, we will also investigate concurrent tandem catalysis to perform more than one transformation in the same pot. For this we will need to match the stability of the catalysts and have an in-depth understanding of the reaction kinetics.