Novel Multidentate Phosphine and Phosphinite Ligands for Catalytic and Imaging Applications

Lead Research Organisation: Imperial College London
Department Name: Dept of Chemistry

Abstract

Phosphines, phosphinites and phosphites are ubiquitous ligands in inorganic chemistry. They are widely used to chelate a host of transition metals, stabilise oxidation states and generate catalytic species. This project will investigate synthesis of a range of new multidentate phosphine and phosphinite ligands that have potential applications in catalysis and for medical imaging. Recently our group has developed a range of multidentate phosphine complexes that have found to be effective catalysts for the hydrogenation of biomass derived acids, such as levulinic acid, to higher value chemicals like 1,3-pentanediol and 2-methylTHF. This project will build on this initial work and examine the effect new chelating ligands will have on the catalytic hydrogenation of a range of other biomass derived substrates. Additionally, such multidentate chelating ligands are known to form highly stable chelates with relevant imaging and therapy radioistopes of metals such as 99mTc, 188Re, 68Ga and 64Cu, hence applications of such ligands in this field will also be investigated.
Objectives:
- design and synthesis of a new class of multidentate phosphine and phosphinite ligands that will enable the formation of stable tri and tetradentate complexes
- systematic study of the coordination chemistry of these ligands with a range of transition metal ions such as Ru, Re and Cu
- application of complexes for catalytic hydrogenation reactions, specifically for the conversion of biomass derived carboxylic acids
- application of ligands for the complexation of ligands with relevant metal radioisotopes for imaging applications
Work-Plan:
Ligand synthesis: A novel approach using phosphonium chloride salts to generate tridentate phosphine ligands has been used to good effect within our group. An analogous route will be attempted for the synthesis of new phosphinite and phosphite ligands.
Complex synthesis: reaction of ligands with a range of appropriate transition metal precursor salts will be investigated. The structures and stabilities of the complexes formed will be investigated by NMR, X-ray diffraction, mass spectrometry etc. in particular we will look at Ru for the formation of catalysts and Re complexes as a model for studying Tc chelates
Applications: using our in-house high pressure hydrogenation reactor newly generated catalysts will be screened for a range of acid to alcohol transformations. In collaboration with colleagues at King's College London we will investigate the formation of novel chelates with radioactive 99mTc, 68Ga and 188Re.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 30/09/2021
1828966 Studentship EP/N509486/1 01/10/2016 31/10/2020 Samuel John Page
 
Description To minimise the use of fossil fuels to generate fuels and chemicals, many scientists are researching the use of biomass (i.e. plants and trees) as a more sustainable chemical feedstock. The conversion of biomass feedstocks into valuable fuels and chemicals requires catalysts. Often these are based upon a transition metal, connected to a chemical framework which modifies its properties.
Levulinic acid is a chemical feedstock which is derived from cellulose. The hydrogenation of levulinic acid produces useful products; primarily gamma-valerolactone which can be used as a green solvent, fuel additive or fine chemical intermediate. Hydrogenation of levulinic acid into gamma-valerolactone typically uses high-pressures of hydrogen gas, which can be dangerous, expensive or complicated to use. Often, the catalysts used are based on expensive metals, or use complicated chemical frameworks, called ligands.
This work has trialled a novel series of metal catalysts, primarily based on palladium, ruthenium and iridium metals. The ligand framework used is straight-forward to prepare compared to many systems reported in the literature. It also has great structural versatility and can be readily modified. For the conversion of levulinic acid into gamma-valerolactone, transfer hydrogenation conditions have been used. These use an alternative hydrogen donor source, in place of hydrogen gas. This makes the reactions easier and safer to operate. With the catalysts trialled, moderate conversions have been achieved. The substituents of the ligand have a major effect on the activity of the catalyst. A drawback of the catalysts is their insolubility in water. Water is considered to promote the efficacy of the reactions. There are strategies to enable water solubility of the catalyst, but these must be finely tuned to maintain the activity of the catalyst. Although the catalysts trialled are not highly active under transfer hydrogenation conditions, the ease of their syntheses, and structural versatility, makes them promising candidates for future work. Interesting coordination chemistry of both phosphine and phosphine oxide ligands with transition metals have been encountered, widening the knowledge of phosphorus coordination chemistry with row 1 and row 2 transition metals.
Exploitation Route The hydrogenation reactions performed in this work have been using a small scale. It would be interesting to investigate the reaction efficacy on larger scales. A wide number of biogenic acids could be trialled, in addition to levulinic acid. Given the potential for modifying the structure of both the ligands and catalysts used, a wider scope of substituents could be trialled, and the effect that this has on both catalyst activity and solubility could be investigated. The reactions could be trialled under high-pressure hydrogenation, or continuous flow conditions.
Sectors Agriculture, Food and Drink,Chemicals,Energy,Environment,Healthcare,Pharmaceuticals and Medical Biotechnology

 
Description Collaboration between Professor Zhao of Tsinghua University and Dr Miller of Imperial College London 
Organisation Tsinghua University China
Country China 
Sector Academic/University 
PI Contribution During summer 2018, I spent 1 month at Tsinghua University, Chemical Engineering department, in the research group of Professor Xuebing Zhao. This was a chance for me to learn about their research, contribute to practical work in the lab, and to input chemistry knowledge into their research. Since the placement, meetings have taken place between the two research groups to identify potential areas for collaboration.
Collaborator Contribution Our partners hosted me in their laboratories in summer 2018. Since then, we have collaborated on a research paper, published early 2020. Meetings/presentations have taken place to identify areas for future collaboration.
Impact Chemistry, Chemical Engineering. Journal paper: Y Bai, SJ Page, J Zhang, D Liu, X Zhao, Kinetic modelling of acid-catalyzed liquid-phase dehydration of bio-based 2,3-butanediol considering a newly identified by-product and an updated reaction network (Chemical Engineering Journal, 2020, 389, 124451)
Start Year 2018
 
Description Article entered for Imperial College Graduate School 4Cs Science Communication writing competition (May 2019) 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact I entered the Imperial College Graduate School 4Cs Science Communication writing competition in May 2019. My article was titled "Biomass: A renewable resource to meet society's needs?". The aim was to communicate my research to a non-specialist audience - other students who are not necessarily familiar with chemistry/my field of research. My article was shortlisted in the competition.
Year(s) Of Engagement Activity 2019
 
Description Article written for Catalyst magazine (STEM Learning) 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Catalyst magazine is published three times a year by STEM Learning, for school pupils and their teachers. Articles were written for 2 of the 2019 editions: "From waste biomass to valuable chemicals", Catalyst magazine Edition 35 (Sept 2019, p18-19) and "From oil to plastic - and back to oil?", Catalyst magazine Edition 34 cover story (April 2019, p18-19). These are intended to convey current areas of scientific research in a manner which is engaging for school pupils, and can be used by teachers in lessons to expand upon the curriculum. The editors of the magazine responded positively to my articles, stating that they were well-written for the intended audience.
Year(s) Of Engagement Activity 2019