Developments, Challenges, and Opportunities in Au(I)/Au(III) Redox Catalysis

Leveraging the intrinsic π-acidic character of gold complexes, gold has found widespread application in organic synthesis. Despite the extensive use of gold as a π-bond activator, its application in redox catalysis for achieving cross-coupling reactions has historically lagged behind. The primary obstacle in advancing gold redox catalysis is the inherent high redox potential of the Au(I)/Au(III) couple, arising from the pronounced relativistic effect. The instability of Au(III) complexes due to facile reduction to gold nanoparticles presents an additional challenge. Over the years, extensive efforts were made to overcome these limitations which led to the identification of several strategies to achieve gold redox catalysis. These strategies primarily rely on the use of external oxidants, photocatalyst/light, aryldiazonium salts, hemilabile ligands, electricity and dinuclear gold-complexes to facilitate Au(I)/Au(III) catalysis. Banking on these strategies, gold redox catalysis has emerged as a promising technique for various transformations such as cross-coupling reactions, C-H functionalization reactions and difunctionalization of C-C multiple bonds. Interestingly, the high electronegativity and π-acid character of gold complexes offer unique reactivities and selectivities compared to commonly used transition metals for cross-coupling reactions. Clearly, the field of Au(I)/Au(III) catalysis has significantly expanded the utility of gold in organic synthesis and its applications in biological and materials science. This review summarizes an up-to-date development in this field since its inception, with a particular emphasis on mechanistic aspects, while outlining the key opportunities and future directions.