DC meta investigated a large number of reaction systems based around the transition metal ruthenium (Ru). We had previously established a number of novel catalysis systems in the area of C-H activation, which operated at high temperature. For this project, we concentrated on bringing the C-H activation into the room temperature regime through the agency of visible light. We were successful in our objective for one main catalysis system that occupied the majority of the research activity - Ru-ortho arylation of arenes. This transformation proceeds under mild conditions, in good yields and is very easy to handle. A wide scope of aryl halides were compatible under standard conditions, producing C-H arylated products that are typically accessed at high temperatures. A thorough scoping of the reaction, along with preliminary mechanistic studies, formed the basis for a paper communicated to the peer-reviewed literature in 2020 in the journal Chemical Science.
Encouraged by the success of arylation, we turned our attention to other underexplored radical precursors that could grow the system to encompass different building blocks. For this purpose, we synthesised a number of N-Hydroxysuccinimide esters, which are widely being used in photoredox catalysis, and tested them out under the standard conditions. This was largely unsuccessful, despite extensive screening of bases, solvents and the wavelength of light, we tried as well to carry out the reaction at different temperatures, switched to a more powerful and widely applied iridium catalysts with various ligands. Extending this idea to other potential precursors for C-H functionalization gave similar results. Despite our persistent attempts to optimize the conditions, we observed either starting materials or traces of products.
Finally, the project examined another approach to arylation using the Smiles rearrangement, a classic organic chemistry transformation that the Greaney laboratory has worked on extensively. The Fellow recorded a number of promising preliminary results for the sulfonate class of starting materials, which will form the basis of future work in the host laboratory.
The project concluded slightly early, after 21 months out of 24, owing to the Fellow securing a permanent research position elsewhere.
