Catalytic Silylation of Aryl C-H Bonds with Earth Abundant Metal Catalysts

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Silylation of organic molecules remains a potent challenge in the field of synthetic chemistry, still requiring lengthy synthetic pathways involving wasteful, intensive stages. Despite silyl-containing molecules having unique interactions with receptor proteins in the body, causing different pharmacochemical activities compared to a carbon analogue, this issue remains a fundamental roadblock in their application. In addition, catalysts for silylation reactions have historically been dominated by platinum-group metal-centred complexes such as those based on iridium and rhodium. These metals are significantly more expensive and also generally more toxic than their more earth abundant counterparts. A number of other issues plague silylation chemistry currently. Hydrogen scavengers, such as alkenes are added to reaction mixtures in super stoichiometric quantities to drive the thermodynamic equilibrium of the reaction forwards. Directing groups are often needed for silylation reactions to progress and can be sensitive to the silane being used, the production of which uses wasteful, toxic reagents. Finally, to form the active catalytic species, stoichiometric or even super stoichiometric oxidants are needed to generate the active catalyst. As a result, the continued development of new catalysts and condition sets which combat these issues and allow access to different substrates is of paramount importance. The aim will be to develop iron and manganese containing complexes with -accepting ligands and test their efficacy as homogeneous catalysts for the silylation of anisole as a standard to optimise the catalysts. Once the catalysts have been optimised for this aromatic, we will investigate functional group tolerance and selectivity, and will extend the methodology to different substrates, ranging from heteroaromatics (pyridine, pyrrole, furan, thiophene and indole) whilst also testing aromatics with weaker directing groups such as acetylbenzene with the aim of advancing eventually towards aromatics with weaker or no directing groups. From there, investigation on how the silane affects the reaction, such as whether is primary, secondary, or tertiary can be conducted. Throughout, kinetics and mechanistic studies will be conducted to elucidate mechanistic pathways of reaction. Based on these outcomes, calculations at a DFT level of theory may then be undertaken to compute activation barriers and provide further mechanistic insight.