Oxidant-free oxidative gold catalysis: the new paradigm in cross-coupling reactions

Abstract

The construction of C-C and C-X (X = hetero atom) bonds is the core aspect for the assembly of molecules. In this regard, late transition-metal-catalyzed cross-coupling reactions have retained their dominance for decades. Lately, gold catalysts have been emerging as a reliable contender for such transformations owing to the recent findings that reveal gold's potential beyond carbophilic π-Lewis acid. The newfound ability of gold to undergo redox transformations under certain circumstances has allowed us to explore gold catalysts as a viable alternative to other late transition-metals for efficient construction of cross-coupled products. This feature article critically presents an overview of all the redox neutral cross-coupling reactions enabled by gold catalysis, which we believe would stimulate further research activities in this promising area.

Ascorbic Acid as an Aryl Radical Inducer in the Gold‐Mediated Arylation of Indoles with Aryldiazonium Chlorides

“…In the latter case, diazonium salts have been the electrophiles of preference. [4] In initial reports on the use of diazonium salts, the Au I oxidation proceeded via at wo single-electron oxidation mechanism, mediated by ap hotocatalyst under irradiation. More recently, alternative protocolst hat avoid the use of ap hotocatalyst have been developed.…”

Oxidative Addition of Alkenyl and Alkynyl Iodides to a AuI Complex

“…Bourissou, Amgoune, and co‐workers and our group have shown that Au I systems modified with appropriate ligands are effective for hitherto unknown Ar−X (X=I, Br) oxidative additions . In addition to these thermal pathways, significant progress has also been made in oxidative addition at gold using photochemically activated routes . In part, such oxidative addition steps are challenging because of the high energy barrier associated with the Au I /Au III redox couple ( E red °: Au III/I =1.41 V vs. Pd II/0 =0.92 V) .…”

“…[2][3][4] In addition to these thermal pathways, significant progress has also been made in oxidative addition at gold using photochemically activated routes. [5,6] In part, such oxidative addition steps are challenging [7] because of the high energy barrier associated with the Au I /Au III redox couple (E red 8: Au III/I = 1.41 V vs. Pd II/0 = 0.92 V). [8] Catalysts that can overcome this are significant because they dispense with the highly reactive external [9] or internal [10] oxidants typically required in Aumediated cross-couplings.…”

Light‐Induced Mechanistic Divergence in Gold(I) Catalysis: Revisiting the Reactivity of Diazonium Salts

“…If the reaction is carried out in the absence of a light source, the N 2 ‐unit from the diazonium salt is retained and azobenzofurans are formed in moderate to high yields. Stoichiometric experiments demonstrate that these products are accessible from the same vinyl Au I intermediate and lead us to propose that the often suggested photochemical oxidative addition–––– either occurs after the formation of a vinyl Au I species or may even not involve oxidation state changes.…”