Mechanisms of Ni-Catalysed C–O Functionalisation and Carboxylation Reactions

Understanding the mechanisms of catalytic transformations is extremely important as this allows chemists to improve reactions by, for example, reducing catalyst loading, preventing the formation of by-products, or obtaining fundamental knowledge about the structure and bonding of intermediates. The focus of this thesis lies with the recently developed transformations of Ni-catalysed C–O functionalisation and Ni-catalysed reductive coupling reactions. Although these reactions are facilitated by the favourable properties of Ni compared to Pd, the scope of possible mechanisms for a Ni-catalysed reaction is broader and less information is known about their mechanisms compared to Pd-catalysed transformations.

In this work, three mechanistic pictures for these Ni-catalysed transformations are presented. The first is a mechanistic study of the Ni-catalysed C–O silylation of aryl esters, where the first oxidative addition complexes of Ni and aryl esters with a monodentate phosphine are reported alongside the role of the fluoride-containing additives. The second is an investigation into a proposed intermediate in reductive coupling reactions – a rarely-isolated Ni(I)-alkyl complex. One example was isolated and characterised by EPR and X-ray crystallography. Significantly, its CO₂ insertion reactivity was also probed. The third project sheds light on the role of Zn as more than just a reductant in the Ni-catalysed carboxylation of arylsulfonium salts.