Earth Abundant Metals for Simple Coupling Reactions
Lead Research Organisation:
University of Bath
Department Name: Chemistry
Abstract
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.
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.
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509589/1 | 01/10/2016 | 30/09/2021 | |||
| 1939886 | Studentship | EP/N509589/1 | 01/10/2017 | 30/09/2021 | Oliver DRISCOLL |
| Description | Sustainability in chemical processes is critical to address issues with global population, energy and material demands increasing. This is dependent on a secure supply of catalysts for these processes. Most catalysts used in processes currently rely on expensive, toxic and rare metals (Platinum group metals) and therefore there has been impetus to explore Earth abundant metals for example, iron. There has been a resurgence in the use of iron as a catalysts due to its high abundance (4th most abundant element in the Earth's crust), low toxicity, low cost (both at commercial and industrial scale) and potential air-stability. Two emerging 'green' areas / reactions which has seen a resurgence of iron catalysis is the ring-opening polymerization (ROP) of rac-lactide to form poly(lactic acid) (PLA) and the catalytic coupling of epoxides with CO2 (a small coupling reaction with two molecules) to form cyclic organic carbonates (COCs). For both reactions, there are only a limited number of iron examples reported. Cyclic organic carbonates (COCs) are in high demand for a range of applications used in chemistry research, industry and everyday applications such as high boiling polar aprotic solvents, lithium-ion battery electrolytes (in batteries), anti-foam additives and plasticisers. Using the new, novel iron catalysts synthesized in this work, COCs can be selectively produced using renewable, non-toxic, abundant, cheap CO2 and epoxide. This is desirable as CO2 can be obtained as a 'waste material'. Poly(lactic acid) (PLA) is a sustainable, renewable, biodegradable and biocompatible alternative plastic compared to those derived from crude oil. PLA can be used in food packaging, drug delivery systems and biomedical applications. PLA is formed via the 'Ring-opening Polymerisation (ROP)' of lactide and industrially is made using tin. Few issues arise from the use of tin such as potential toxicity issues and selectivity / control of the properties of the PLA plastic. Examples of Fe-mediated ROP in the literature are less prevalent despite the numerous benefits associated again with iron. Using the new, novel iron compounds / complexes synthesized from the this work, we were able to apply these to the ROP of PLA effectively and control the properties of the PLA successfully. |
| Exploitation Route | In terms of taking the research forward, there is lots more that can be done in this work / funding by exploring other sustainable metals (not just iron) and moving to other 'green' sustainable reactions. In terms of what can be put to use for others, the work we have carried out has been published in papers and therefore other people in academia can put to use the ideas and systems we have developed to help with their future research into these applications. There is hope that in the future, more efficient and effective catalysts / systems will be developed by using research generated in the area for non-academic use / industry to replace the use of more toxic metals. Therefore sharing knowledge / publishing is crucial. |
| Sectors | Agriculture, Food and Drink,Chemicals,Electronics,Energy,Environment,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology |