Green‐Light‐Driven Reductive Elimination of Chlorine from a Carbene‐Xanthylium Gold(III) Complex

Abstract

With the discovery of late transition metal platforms that support clean photoreductive halogen eliminations, we now describe an indazol-3-ylidene gold trichloride complex ([7] + ) decorated at the 4-position by a xanthylium unit. This orange complex features a low energy band in the visible part of the spectrum, assigned to the charge transfer excitation of the indazol-3ylidene/xanthylium donor/acceptor dyad. Green-light irradiation of this complex in the presence of a chlorine trap elicits the clean photoelimination of chlorine radicals, producing the corresponding gold(I) complex. This visible-light-induced photoreduction is very efficient, reaching quantum yields close to 10 %. A neutral analog of [7] + featuring an anthryl group rather than a xanthylium unit proved to be perfectly photostable, supporting the importance of the xanthylium-based photoredox unit present in [7] + .

Synthetic Application of Bismuth LMCT Photocatalysis in Radical Coupling Reactions

“…The reason for inactivity is probably that a higher oxidation state (III) was not achieved by oxidation with oxygen. Remarkable is the LMCT activity of gold across multiple reaction conditions . We did not further investigate this observation but hope that the reactivity and synthetic use of these complexes will be further investigated in a different context.…”

Placing gold on a π+-surface: ligand design and impact on reactivity

“…This situation is reminiscent of that occurring in previously reported gold( i ) complexes such as [ 4 xant ] + and [ 4 acr ] + , featuring an intramolecularly installed xanthylium or acridinium unit (Scheme 1). 12–14 In the case of [ 3 acr ] + , the gold-bound chloride anion of this complex forms a short contact with a hydrogen atom of the N -methyl group, indicating a hydrogen bonding interaction.…”

Ligand-Enabled Oxidative Fluorination of Gold(I) and Light-Induced Aryl–F Coupling at Gold(III)

“…Now that several ways have been developed to efficiently promote Au­(I) to Au­(III) oxidation, ,,, the situation is somewhat reversed and the limiting step may be reductive elimination . The results obtained with complexes 1e,f­(- trans ) suggest that light-induced reductive elimination holds much potential to achieve challenging coupling reactions at gold and might even enable new ones …”