Gold catalysis with less fuss

In an advance that simplifies gold redox catalysis, a research team led by A. Stephen K. Hashmi of Heidelberg University, in Germany, has discovered a means for carrying out visible-light-mediated reactions without the need for an auxiliary oxidant or a ruthenium or iridium photosensitizer. The additional reagents are typically needed to promote oxidation of gold(I) to gold(III) as part of the catalytic cycle. The Hashmi group determined that a phosphine gold(I) chloride catalyst can function as its own photosensitizer when irradiated with visible light. When paired with an aryldiazonium salt, the gold(I) species is oxidized to a gold(III) species that can complete the difunctionalization of alkynes to make α-aryl ketones (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201511487). What’s more, by using a P,N-bidentate ligand, the researchers were able to isolate and obtain the X-ray crystal structure of the gold(III) species (shown above). Chemists have debated whether gold(III) intermediates are involved given gold’s high oxidation potential. The Heidelberg group’s effort provides the first direct evidence to satisfy that curiosity, and further studies show that the group’s approach is a general method for generating arylgold(III) complexes (Chem. Commun. 2016, DOI: 10.1039/c6cc02199a).