Light in Gold Catalysis

Abstract

Within the wide family of gold-catalyzed reactions, gold photocatalysis intrinsically features unique elementary steps. When gold catalysis meets photocatalysis, a valence change of the gold center can easily be achieved via electron transfer and radical addition, avoiding the use of stoichiometric sacrificial external oxidants. The excellent compatibility of radicals with gold catalysts opens the door to a series of important organic transformations, including redox-neutral C–C and C–X coupling, C–H activation, and formal radical–radical cross-coupling. The photocatalysis with gold complexes nicely complements the existing photoredox catalysis strategies and also opens a new avenue for gold chemistry. This review covers the achieved transformations for both mononuclear gold­(I) catalysts (with and without a photosensitizer) and dinuclear gold­(I) photocatalysts. Various fascinating methodologies, their value for organic chemists, and the current mechanistic understanding are discussed. The most recent examples also demonstrate the feasibility of both, mononuclear and dinuclear gold­(I) complexes to participate in excited state energy transfer (EnT), rather than electron transfer. The rare applications of gold­(III) photocatalysts, both homogeneous and heterogeneous, are also summarized.

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C−H Bond Functionalization

“…As opposed to the majority of d-block metal catalysis, the high redox potential of the Au(I)/Au(III) redox couple (E o = 1.41 V) in general requires the use of powerful oxidation conditions and thus permits most Au(I)-catalyzed transformations to progress without necessitating the exclusion of air. [48][49][50][51][52][53] With respect to gold catalysis, an extensive collection of Au(I)-and Au(III)-complexes with diverse auxiliary ligands is either commercially available or accessible by easy to perform benchtop chemistry. [54][55][56][57] In practice, the most convenient gold complexes would be of the type either [AuLL']X or [AuLX], where L' is a weak coordinated neutral ligand and X is an anionic ligand.…”

“…With an electronic configuration of [Xe]4f 14 5d 10 6 s 1 for the metallic Au 0 atom, gold catalysts mostly exist in +1 (5d 10 ) and +3 (5d 8 ) valent states. As opposed to the majority of d‐block metal catalysis, the high redox potential of the Au(I)/Au(III) redox couple (E o =1.41 V) in general requires the use of powerful oxidation conditions and thus permits most Au(I)‐catalyzed transformations to progress without necessitating the exclusion of air [48–53] …”

Reactant-Induced Photoactivation of a Gold-Catalyzed Csp2-Csp Cross-Coupling Leading to Indoles

“…[a]* [a] Sorbonne Université, CNRS, Institut Parisien de Chimie Moléculaire, 4 Place Jussieu, CC 229, F-75252 Paris Cedex 05 France sequences have resulted but the question to know how those actually work is still pending, notably because some of these reactions proceed in photocatalyst-free conditions. 20,21,22 Recently, we have reported a new reactivity paradigm by providing the first example of an energy transfer promoted oxidative addition at gold(I). 23,24 Upon visible-light irradiation, an iridium photocatalyst triggers via triplet sensitization the oxidative addition of an alkynyliodide onto a vinylgold(I) intermediate to deliver Csp 2 -Csp coupling products after reductive elimination.…”

Cycloisomerization of π‐Coupled Heteroatom Nucleophiles by Gold Catalysis: En Route to Regiochemically Defined Heterocycles

“…Looking from a historical perspective, the field of gold catalysis went mostly unnoticed for a period of time, obviously for its high‐price and chemical inertness [24–30] . Yet, the last two decades saw the boom of gold catalysis through major breakthroughs, [31–41] thanks to the understanding of fundamental concepts like frontier orbitals, π‐acidity, relativistic effects and redox behaviour [42–52] . In particular, the unique ability of gold catalysts to activate C−C multiple bonds like alkynes, alkenes and allenes has paved the way for the discovery of numerous hitherto unknown organic reactions [53–55] .…”