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

Identifier:  TDX:3357

Handle: https://hdl.handle.net/20.500.11797/TDX3357

Authors:  Somerville, Rosemarie Janet

Abstract:
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. Whilst 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. Challenges in understanding mechanistic features include potentially unstable intermediates, a need for reliable kinetic data, and parsing the many mechanistic proposals that have been put forward. In this work, three mechanistic snapshots of these Ni-catalysed transformations are presented. The first is a broad 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. The second is an investigation into a proposed intermediate in reductive coupling reactions – a 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.