Earth Abundant Metals for Simple Coupling Reactions

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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.