
New methods for the preparation of extended structures are rightly highlighted as being of great importance to the UK. The EPSRC Grand Challenge 'Directed Assembly of Extended Structures with Targeted Properties' (referred to as the DA Grand Challenge) is championed by some of the UK's leading academic scientists. Interest from pharmaceutical companies in this initiative has been excellent, particularly based on the nucleation and crystallisation targets outlined in the Grand Challenge Documentation. Impact of the Grand Challenge Network on other areas is much less evident, although it is clear that the basic premise of the Challenge fits many other sectors. In this Established Career Proposal my vision is to demonstrate, through both transformative science and personal leadership, how the central tenets of the DA Grand Challenge Idea can be translated across disciplines. In particular I will focus on two areas, increasing the impact of the network in the chemicals sector, with a special emphasis on transformative new routes to heterogeneous zeolite catalysts (which strongly fits another EPSRC priority area), and novel multifunctionality in medical delivery agents. The proposed programme is firmly rooted in the EPSRC remit but is designed to be outward looking to maximise transdisciplinary impact cutting across to other important areas of science. The specific science proposed here focuses on nanoporous materials. Zeolites are one of the most important class of industrially applied catalysts we have. Manipulation of zeolites into hierarchical porous structures and ultra-thin layers has also risen to great prominence as a method of introducing new and beneficial features into zeolite catalysts. The journal Science rated this type of research as one of the ten most important current areas of current science, and so its importance is recognised internationally. Metal organic frameworks (MOFs) are some of the most exciting and fast-developing materials that have been prepared in the last decade or so. The great versatility of the chemistry of these solids leads to ultra-high porosity, extreme flexibility, post synthetic modification potential and many other interesting and conceivably useful attributes. Because of this wide ranging chemistry and function, potential applications of these solids range from gas storage, separation and delivery, catalysis, and sensing all the way to biology and medicine.
Reducing the energy requirements and steering reactions to desired products in key chemical processes involved in the production of fuels and energy carriers for a net-zero economy and for environmental clean-up are some of the most pressing demands for a future sustainable society. This challenge is intimately linked to efficient use of the most abundant energy source available to us, light. Light also provides us with the means to control reaction pathways, opening in turn further opportunities to define new routes to the next generation of pharmaceuticals. We propose to develop a comprehensive research programme in order to understand, and harness, the application of a unified approach for harvesting light energy and channelling it to achieve required chemical outputs, with reduced generation of unwanted or hazardous by-products, using the extraordinary properties of surface plasmons, charge-density waves excited in metallic nanostructures by light. These excitations enable efficient use of electromagnetic radiation over a broad wavelength range from the ultraviolet to the infrared, while at the same time passing this energy on to energetic charge carriers and lattice oscillations, hence providing an efficient pathway from light to excited electronic states of molecules adsorbed at surfaces as well as to local heat. This combination can induce chemical transformations with lower activation barriers for chemical reactions and open up new paradigms for controlling chemical reactions switchable with light. It is here the research fields of plasmonics and catalysis meet. Our team, consisting of key experts from the UK plasmonics and catalysis communities, will explore new research directions enabled by applying plasmonic advances to catalysis (plasmo-catalysis) in order to achieve impact on technologies which are of enormous importance for a future sustainable society. The combination of superior light harvesting and tuning of reaction dynamics that this new field offers will open up a wealth of new possibilities to tackle key challenges in catalysis. In a unified approach based on fundamental research on plasmo-catalytic nanomaterials and nanostructures, we will develop common design and methodology principles and apply them to chemical reactions important in clean fuel production, environmental monitoring and clean-up, as well as pharmaceuticals manufacture. We will establish new strategies for light-driven chemical reaction pathways amenable to industrial scale-up, while at the same time educating a new set of highly interdisciplinary researchers equipped with a key set of skills needed for the advancement of a future sustainable society.
Aldehydes are important intermediates for the preparation of a large variety of fine- and bulk-chemicals. Applications of these compounds are found in the pharmaceutical industry, aroma and flavour industry, and in the production of agrochemicals and detergents. Many of these products are currently prepared via stoichiometric reactions which often results in large amounts of chemical waste. There is an increasing demand for new production methods based on mild and selective reactions with a very high atom efficiency , thus reducing the chemical waste problem. The rhodium catalysed hydroformylation of alkenes is an example of such a mild and clean process for the production of high-quality aldehydes, using only CO and H2 as reagents and therefore producing no waste products at all.In this project we will develop a new generally applicable catalyst system capable of converting both internal alkenes and conjugated dienes into high value-added aldehydes and / or esters. Atom economic and clean hydroformylation technology of butadiene to the intermediate 1,6-hexanedial would create a major contribution to the sustainable production of polyamides. Many industries and academic researchers, however, have studied the rhodium-catalyzed hydroformylation of butadiene, but generally the reported selectivity for the desired product 1,6-hexanedial is very low. This is caused by the formation of deleterious Rh allyl and enolate complexes, which can be suppressed by simultaneous activation of both alkene functions using properly designed bimetallic catalysts.Therefore, we will develop well-defined tetraphosphine ligand systems for the formation of bimetallic complexes capable of activating otherwise unreactive substrates by mutual interactions with functional groups by both metals. Starting point will be a successful class of bidentate ligands, already developed by the PI, which will be modified in such a way that they can be bridged straightforwardly by condensation with diacids. The resulting tetraphosphines will provide novel bimetallic complexes that will be applied in the hydroformylation of conjugated dienes. In a later stage the novel ligands systems will be explored in different reactions like palladium catalyzed alkoxycarbonylation of dienes. The exact ligand structures can be optimized by subtle changes in steric, electronic and bite-angle properties. In another approach we will aim at coupling of two different ligand backbones which opens the possibility of the formation of heterobimetallic complexes. Differences in the structure of the ligand backbone will have impact on the complexation constants of different transition metals. It is anticipated that this can be employed to influence the preferential coordination of one transition metal over another. It will be investigated if this will lead to the selective formation of heterobimetallic complexes based on rhodium and palladium without interference of homometallic binuclear compounds. We will explore the use of these rhodium palladium heterobimetallic complexes as catalyst for one-pot hydroformylation / methoxycarbonylation of dienes. The formation of these alpha,omega-aldehyde esters via a two-step process has been investigated intensively by DSM/DuPont.The design of the new chiral catalysts will be supported by fundamental spectroscopic (including kinetic) studies of the catalytic species present under actual reaction conditions. HP-NMR will be used to study the structure of the bimetallic complexes under static conditions. The effect of the metal-metal distance on the interaction with bifunctional substrates will be investigated. HP-IR will be used to study these complexes under actual catalytic conditions.
The quest for more highly selective, cleaner and more efficient catalysts e.g for olefin trimerisation or tetramerisation remains a high priority for the chemical industry. Achieving these targets demands a detailed understanding of the catalytic cycle(s) and the nature of the active species. Characterisation of the individual stages in a homogeneous catalytic cycle is not easily achieved since the active species are likely to be highly reactive and often very transient, making their crystallographic characterisation highly unlikely. Furthermore, for the paramagnetic e.g. Cr-based catalysts NMR spectroscopy is not informative. Under this project we will develop and use a unique freeze-quench cell to allow the transient and active species to be trapped at various selected stages through the cycle, allowing in situ spectroscopic analysis by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy techniques. We will prepare and characterise a series of related metal complexes based on Cr, Mo and Sc in the presence of a selected set of N-, S-, N/S- and N/P-donor ligands, including complexes of the industrially important NH(CH2CH2Sdecyl)2 and iPrN(PPh2)2. Using a range of techniques (UV-visible, EPR, 45Sc NMR spectroscopy), in conjunction with XAFS and XANES data using the set-up described above, we will probe in detail the oxidation state and structures at various stages through the activation and catalysis to provide a much more detailed understanding of the mechanisms at work. We also expect to demonstrate the potential of the new rapid (millisecond) freeze-quench XAFS/XANES approach much more widely to provide key information regarding other homogeneous catalysis systems.
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