Small-molecule activation at gold: synthesis and reactivity of cyclometalated Au(III) complexes

Abstract

The interest in organogold chemistry has increased rapidly during the last 20-30 years, and nowadays there are numerous research group across the world working with gold and its rich chemistry. Au(I) complexes have been more studied that Au(III) complexes, but lately, there has been an increased interest in Au(III) complexes and their reactivity as well. Gold is known for its ability to activate alkenes, alkynes, and other unsaturated species towards nucleophilic addition, and addition of nucleophiles to coordinated unsaturated species at gold are key steps in gold catalysis. In this thesis, the reactivity of Au(III) complex Au(OCOCF3)2(tpy) (2, tpy= 2-(p-tolyl)pyridine) towards a wide variety of small molecules was investigated. The nucleophilic addition of different oxygen-based nucleophiles to various alkenes at complex 2 furnishing β-functionalized Au(III) alkyl complexes is presented in Chapter 2. In Chapter 3, metallacycle construction at complex 2 was achieved upon reaction with ethylene, water, and acetonitrile. In Chapter 4, the catalytic transformation of acetylene into vinyl trifluoroacetate using complex 2 as a precatalyst is presented. The mechanism of the catalytic trifluoroacetoxylation was studied both experimentally and computationally. There are only a few examples of C(sp3)-H activation at Au(III), whereas C(sp2)-H activation is common at Au(III). In Chapter 5, the synthesis and characterization of a (N,C,C) Au(III) pincer complex via both C(sp2)-H and C(sp3)-H activation is presented. The (N,C,C) Au(III) pincer complex is found to outperform complex 2 as a catalyst for the acetylene trifluoroacetoxylation, because it is significantly more robust towards the conditions where catalysis takes place. Finally, in Chapter 6, the generation and characterization of Au(III) η1 and η3 allyl complexes is described. Transition metal η3 allyl complexes have been thoroughly studied, but there are no well-characterized Au(III) η3 allyl complexes reported in the literature.