Studies on the Organometallic Reactivity of Gold(III)
- Author(s): Wolf, William James
- Advisor(s): Toste, F. Dean
- et al.
The work contained in thesis represents our efforts towards a fundamental understanding of gold in the context of redox cycling. The use of late transition metals in catalysis typically relies on two or more readily accessible oxidation states for bond breaking and bond forming events. However, the heaviest coinage metal does not enjoy such a wealth of reactivity and has been comparatively unexplored.
Chapter 1 summarizes the research by our group and others in advancing the concept of redox active gold catalysis. Two strategies that differ on the use sacrificial oxidants to affect catalysis are described, as well as our efforts to improve on the performance of bimetallic gold catalysts through a ligand design approach. A brief survey of fundamental reactivity of Au(I) towards oxidative addition is also presented, to provide context for our studies as described in the subsequent chapters.
Chapter 2 describes our studies on the C(sp2)–C(sp2) reductive elimination of biaryls from Au(III). Low temperature NMR studies revealed and characterized an unexpectedly rapid process that is mechanistically distinct from previous studies on C(sp3)–C(sp3) reductive elimination from Au(III). In addition, our preliminary efforts towards the development of a gold-catalyzed biaryl cross-coupling were informed by these studies on reductive elimination.
Chapter 3 focuses on our investigations of a photochemical oxidative addition of CF3I to Au(I) complexes. This type of transformation was initially described for the oxidation of phosphine-supported Au(I) alkyl complexes; however the use of phosphine-supported Au(I) aryl complexes allows for the isolation and characterization of organometallic Au(III) complexes containing the –CF3 moiety. These complexes are also capable of C(sp2)–CF3 bond forming reductive elimination upon halide abstraction at low temperature and represent a unique class of compound in this regard.
Chapter 4 builds on the results from chapter 3 and focuses on the effects of halide ligands on the C(sp2)–CF3 reductive elimination from Au(III) at elevated temperature. A series of Au(III) complexes containing each member of the halide family (I, Br, Cl, and F) were prepared and the effects of these ancillary ligands on the selectivity of C(sp2)–CF3 vs. C(sp2)–X (X = halide) elimination from Au(III) were characterized. The selectivity can be tuned by choice of halide ligand, and this phenomenon is attributed to increasing Au–X bond strengths which correlate with an increase in selectivity for C(sp2)–CF3 elimination.