Solvents play a fundamental role in synthesis. Unfortunately, many commonly used volatile organic solvents (VOS) are harmful to humans and/or the environment. Some halogenated and polar aprotic solvents such as dimethylformamide, N-Methyl-2-pyrrolidone and 1,2-dichloroethane are already categorised as “substances of very high concern” under REACH. However, suitable alternatives are challenging to find. The search for environmentally benign solvents is currently a hot topic in sustainable chemistry.
Recently, deep-eutectic solvents (DES) have emerged as novel reaction media. DES are related to ionic liquids (ILs) and are usually composed predominantly of ions. They are often formed by combination of a quaternary ammonium salt (e.g. choline chloride, ChCl) with a metal salt (e.g. ZnCl2) or hydrogen-bond donor (e.g. urea) to form eutectic mixtures. They have low vapour pressures, good thermal stabilities and are able to dissolve a range of solutes. However, in contrast to many ILs, they are cheap, non-toxic, biodegradable and have relatively short synthetic routes from potentially renewable feedstocks. As such, they have many desirable characteristics as sustainable alternatives to VOS.
It has been shown that using DES as solvents allows reactions involving highly reactive organometallic reagents (e.g. Grignard or alkyllithium reagents) to take place even in the presence of water. This is very surprising, as these conditions would rapidly degrade the organometallic in conventional solvents. Our own recent work has pushed the boundaries of what is possible in this area and has allowed highly selective catalysis with reactive organozinc reagents in DES. This project will build on this success to develop catalytic hydrogenation reactions using DES as sustainable solvents under mild conditions, with no protection from atmospheric moisture or oxygen. An important part of this project will be to understand catalyst speciation and reaction mechanisms in these systems using advanced NMR spectroscopic methods in combination with hyperpolarisation.
1) To prepare and characterise a range of DES
2) To explore the speciation and reactivity of organometallic catalysts within DES
3) To develop catalytic protocols for hydrogenation, under mild reaction conditions, in DES
4) To probe the catalytic mechanisms in DES
The synthesis of DES is generally very simple, often involving combination of off-the-shelf starting materials. However, where necessary bespoke DES will be prepared, which will involve the synthesis of salts or hydrogen-bond donors with specific functionality and/or with isotopic labelling (e.g. deuteration). We will test the success of DES as media for hydrogenation reactions. Initially, studies will focus on neutral systems like RhCl(PPh3)3 and charged complexes like [Ir(COD)(PCy3)(pyridine)][BF4]. We will probe the mechanisms of these reactions looking for evidence of reactive hydride containing intermediates that will be readily detectable by NMR. Other important characterisation methods will include, IR, UV/Vis, MS. Catalytic reactions will be monitored using GC and GC/MS.
DES have been known for some time, but their application as solvents for organometallic catalysis is limited, particularly when compared to conventional solvents. The ability to perform catalysis under mild and convenient conditions, in more sustainable solvents, is very timely and will contribute to the move towards more sustainable industrial chemical processes.
This project will offer a wide range of training and will provide a student with varied and versatile skills. Training will be given in the synthesis of organic and organometallic compounds, including the use of Schlenk techniques. Training will be provided in advanced multinuclear NMR spectroscopy and hyperpolarisation techniques, IR, UV/Vis, MS etc. The project will allow the student to develop good skills in analytical chemistry, in particular GC and GC/MS. There is scope for interested students to learn to use computational methods, such as DFT, to support the experimental work. All Chemistry research students have access to our innovative Doctoral Training in Chemistry (iDTC): cohort-based training to support the development of scientific, transferable and employability skills: https://www.york.ac.uk/chemistry/postgraduate/cdts/
The Department of Chemistry holds an Athena SWAN Gold Award and is committed to supporting equality and diversity for all staff and students. The Department strives to provide a working environment which allows all staff and students to contribute fully, to flourish, and to excel: https://www.york.ac.uk/chemistry/ed/.
For more information about the project, click on the supervisor's name above to email the supervisor. For more information about the application process or funding, please click on email institution
This PhD will formally start on 1 October 2022. Induction activities may start a few days earlier.
To apply for this project, submit an online PhD in Chemistry application: https://www.york.ac.uk/study/postgraduate/courses/apply?course=DRPCHESCHE3
You should hold or expect to achieve the equivalent of at least a UK upper second class degree in Chemistry or a related subject. Please check the entry requirements for your country: https://www.york.ac.uk/study/international/your-country/