Insights into the Mechanism of Gold(I) Oxidation with Aryldiazonium Salts

Abstract

In the last decade, aryldiazoniums alts have attracted interest as coupling partnersi nc ross-couplingr eactions mediated by gold. Initially,t he presence of ap hotocatalyst and al ight sourcew as neededt oa chieve gold oxidation with these electrophiles.H owever, recently,i th as been shown that in some instances just heating, light irradiation, or the addition of certain bases and/or nucleophiles is enough. In this review,t he transformations developed so far using aryldiazonium salts as electrophiles are summarized with special emphasis on mechanistic studies.T he information gained by different authors, indicatest hat the specific steps of gold oxidation with aryldiazonium salts depends upon the activation mode of the diazonium salt.

Light in Gold Catalysis

“…The proposed mechanism was in accordance to the previously described sequences containing a nucleophilic addition of electrophilic arylgold(III) species (55) to the terminal alkyne. However, quantum yield measurement by chemical actinometry gave a value of 3.6.…”

“…However, quantum yield measurement by chemical actinometry gave a value of 3.6. Thus, an innovative second SET process between the arylgold(II) intermediate (54) with another equivalent of diazonium salt delivering arylgold(III) species (55) and an aryl radical was proposed to occur (dashed arrows). The authors stated that this process would mainly contribute to the formation of gold(III) intermediate.…”

“…As will be thoroughly discussed in this review, the initial and majority of applications of mononuclear gold(I) complexes in photoredox catalysis applied a photosensitizer (such as Ru(bpy) 3 Cl 2 ) and aryldiazonium salts (or aryl iodonium salts) to achieve the oxidation of the gold catalyst. 50,55 Subsequently, Hashmi and co-workers revealed that the presence of a photosensitizer is redundant. The sole use of a gold catalyst was capable of undergoing the redox cycle for a series of coupling reactions, complementing the classical Pd-catalyzed transformations.…”

“…Photochemical conversions involving gold catalysis have added a synthetically new reactivity pattern in this research area. − The approach of combining gold catalysis with photoredox catalysis addressed the barrier of the Au­(I)/Au­(III) cycle by circumventing the previously described harsh reaction conditions. As will be thoroughly discussed in this review, the initial and majority of applications of mononuclear gold­(I) complexes in photoredox catalysis applied a photosensitizer (such as Ru­(bpy) 3 Cl 2 ) and aryldiazonium salts (or aryl iodonium salts) to achieve the oxidation of the gold catalyst. , Subsequently, Hashmi and co-workers revealed that the presence of a photosensitizer is redundant. The sole use of a gold catalyst was capable of undergoing the redox cycle for a series of coupling reactions, complementing the classical Pd-catalyzed transformations.…”

Switchable Divergent Synthesis in Gold-Catalyzed Difunctionalizations of o-Alkynylbenzenesulfonamides with Aryldiazonium Salts

“…Gold-catalyzed nucleophilic addition/cross-coupling cascade reactions have been developed in recent years involving strong oxidants, diazonium salts (photoredox pathway involving two single-electron oxidation processes), etc. − Diazonium salts − were identified as both oxidants and coupling partners in the latter gold-catalyzed processes under thermal , or photochemical conditions. − Deep mechanistic studies − have been conducted, and this type of gold-catalyzed photoredox reactions − represents a fundamental tool to increase the molecular complexity.…”