Gold(I) Catalysis: Mechanistic Insights, Reactivity of Intermediates and its Applications

This thesis is dealing with a mechanistic study on the gold catalyzed reaction of o alkynylphenols with diazonium salts that can be controlled by light. It could be demonstrated, that the same starting materials can either undergo C C bond formation to form substituted benzofurans with N2 extrusion (blue LED irradiation) or C N bond formation to substituted azobenzofurans with N2 retention (no irradiation). Stoichiometric experiments demonstrate, that a common vinyl gold(I) intermediate for both catalytic cycles is involved, where essentially the same reaction conditions lead to different products simply by irradiation of light.
The formation of substituted benzofurans does not require an additional photo(redox) catalyst, which is in contrast to previous reported results. DFT calculations propose the formation of an Electron-Donor-Acceptor-Complex by the vinyl gold(I) complex and the diazonium salt at a low lying excitation state on the triplet surface leading to the desired products. This reactivity could be transferred to synthesize substituted benzodifurans which have a high quantum yield.
The reactivity of different substituted vinyl gold(I) complexes towards different substituted phenols was correlated in a Hammett plot, demonstrating that the protodeauration is dependent on the acidity of the proton source and the substitution pattern of the benzofuran unit.
Furthermore, different substituted azobenzofurans were probed towards their switching ability. The compounds were irradiated with blue LED to a photostationary state and the kinetics of the thermal relaxation was plotted against their Hammett parameters to form a so called V-shaped Hammett plot that indicates a change in switching mechanism depending on the substitution pattern of the azo unit.