AbstractThis thesis explores redox gold catalysis: catalysis by gold whereby the gold centre alternates between the +1 and +3 oxidation states throughout the catalytic cycle. Following a brief general introduction, the second chapter describes the gold-catalysed oxyarylation of ethylene as a modular route to homobenzylic ethers. Using catalytic Ph3PAuCl, a variety of arylsilanes and alcohols undergo 1,2-addition to ethylene in the presence of an iodine(III) oxidant. A substrate scope demonstrated the compatibility of a variety of arylsilanes and alcohols in the protocol. Mechanistic investigations implicated the involvement of the ancillary phosphine throughout the catalytic cycle, in contrast to previous reports. Additionally, stoichiometric experiments suggest transmetalation of the arylsilane moiety occurs onto a gold(III) centre, prior to activation of ethylene towards alcohol attack and subsequent product forming reductive elimination.
The third chapter investigates the influence of the 2,2-bipyridine (bipy) ligand on the chemistry of gold, with an emphasis on the activation of gold(I) towards oxidative addition with aryl iodides. [(k2-bipy)Au(h2-C2H4)][NTf2] complexes were found to undergo reversible oxidative addition of a range of aryl iodides under mild conditions. The resulting gold(III) complexes [(k2-bipy)Au(aryl)I][NTf2] were found to undergo transmetalation with arylzinc chlorides and subsequent reductive elimination to give biaryl products. The overall process represents the first gold-mediated Negishi cross-coupling, albeit in a stoichiometric manner.
The fourth chapter explores the possibility of redox gold catalysis in the absence of an external oxidant. With the hypothesis that a phosphine ligand will better stabilise a gold centre throughout the catalytic cycle, a range of small bite-angle P,N-ligands were synthesised and coordinated to gold(I). Complexes supported by 8-quinolyl phosphine ligands were found to catalyse a Suzuki cross-coupling reaction. Of particular note is that the reaction proceeds in the absence of an external base, in contrast to standard palladium-catalysed Suzuki conditions.
|Date of Award
|23 Jan 2019
|Chris A Russell (Supervisor) & John Bower (Supervisor)