Deep Eutectic Solvents for Simple and Sustainable Organometallic Catalysis

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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. This project will take these observations further and develop novel catalytic reactions using DES as sustainable solvents under mild conditions, with no protection from atmospheric moisture or oxygen.