Fundamental Basis for Implementing Oxidant‐Free Au(I)/Au(III) Catalysis

Abstract

Oxidant-free Au(I)/Au(III) catalysis can still be regarded as a young and promising chemistry. Because the first examples of gold catalysis were limited to the activation and functionalization of π-CÀ C bonds and very little was known on fundamental organometallic transformations at gold, countless works during the past 15 years have been devoted to disclosing the elementary reactivity of gold and implementing it in catalysis. Remarkably, great emphasis on triggering oxidative addition at Au(I) has been placed, as the high redox potential of the Au(I)/ Au(III) pair disfavors this reaction. In fact, different strategies such as strain release, ligand design and photochemistry have been proven successful at allowing the bottleneck oxidative addition to occur. These approaches have led to the rational development of oxidant-free Au(I)/Au(III) redox catalysis, particularly catalytic cycles in cross-coupling transformations where oxidative addition is usually the entry point to the cycle. Herein, the background story, the development process, and relevant examples of oxidant-free gold-catalyzed cross-coupling reactions are reviewed.

Gold-Catalyzed Ascorbic Acid-Induced Arylative Carbocyclization of Alkynes with Aryldiazonium Tetrafluoroborates

“…In particular, we have been interested in processes where the diazonium salt is thermally or chemically activated . Initial reports on catalytic redox processes of Au­(I) with aryldiazonium salts required the use of a cocatalyst and light irradiation to promote the formation of Au­(III) species, but later studies manifested that, in some cases, just light, heat, or certain ligands and bases are enough to promote this process. , Recently, we evidenced that ascorbic acid, a natural reducing agent, is able to promote the oxidative addition of Au­(I) with aryldiazonium chlorides, and used this protocol for the arylation of N -methyl indoles . In that transformation, we needed to use a stoichiometric amount of gold because of the competitive formation of N -methylindoldiazo coupling derivatives.…”

Visible Light-Driven, Gold(I)-Catalyzed Preparation of Symmetrical (Hetero)biaryls by Homocoupling of Arylazo Sulfones

“… 37 The latter undergoes reductive elimination to release Ar–Ar while restoring the starting PPh 3 Au I L catalyst (path d). 38 The intermediacy of an aryl radical was ascertained by an experiment carried out in the presence of TEMPO (0.05 M), showing a significant lowering of the biphenyl yield (from 75% to 29% in the case of 2 ). As for the role of the cocatalyst, bis-pyridyl and phenanthryl ligands have been frequently adopted as beneficial additives in Au-mediated photo- and electrochemical coupling reactions.…”

Ligand-enabled oxidation of gold(i) complexes with o-quinones

“…Au( i )/Au( iii ) redox cycles also open new avenues in gold catalysis, and major achievements have been reported recently in cross-coupling and alkene difunctionalization reactions in particular. 1,7…”