Divergent Gold Catalysis: Unlocking Molecular Diversity through Catalyst Control

Abstract

The catalyst-directed divergent synthesis, commonly termed as “divergent catalysis”, has emerged as a promising technique as it allows chartering of structurally distinct products from common substrates simply by modulating the catalyst system. In this regard, gold complexes emerged as powerful catalysts as they offer unique reactivity profiles as compared to various other transition metal catalysts, primarily due to their salient electronic and geometrical features. Owing to the tunable soft π-acidic nature, gold catalysts not only evolved as superior contenders for catalyzing the reactions of alkynes, alkenes, and allenes but also, more intriguingly, have been found to provide divergent reaction pathways over other π-acid catalysts such as Ag, Pt, Pd, Rh, Cu, In, Sc, Hg, Zn, etc. The recent past has witnessed a renaissance in such examples wherein, by choosing gold catalysts over other transition metal catalysts or by fine-tuning the ligands, counteranions or oxidation states of the gold catalyst itself, a complete reactivity switch was observed. However, reviews documenting such examples are sporadic; as a result, most of the reports of this kind remained scattered in the literature, thereby hampering further development of this burgeoning field. By conceptualizing the idea of “Divergent Gold Catalysis (DGC)”, this review aims to consolidate all such reports and provide a unified approach necessary to pave the way for further advancement of this exciting area. Based on the factors governing the divergence in product formation, an explicit classification of DGC has been provided. To gain a fundamental understanding of the divergence in observed reactivities and selectivities, the review is accompanied by mechanistic insights at appropriate places.

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

“…[68][69][70][71][72][73] Hence, fine-tuning factors such as valence state, counterion and auxiliary ligand in homoge-neous gold catalysis is imperative in controlling the selectivity of product formation. [74] We note primarily three parameters potentially influencing the electronic properties: the oxidative state of the metal, the charge and the stereoelectronic interactions between the ligands and the metal center. Concerning the electronic parameter, σ-donation, π-donation as well as π-accepting properties of the ligand must be taken into account.…”

“…Indeed, a catalyst could be considered as a complicated combination of different parameters influencing the bonding characteristic of the complex, resulting in different properties and reactivities [68–73] . Hence, fine‐tuning factors such as valence state, counterion and auxiliary ligand in homogeneous gold catalysis is imperative in controlling the selectivity of product formation [74] . We note primarily three parameters potentially influencing the electronic properties: the oxidative state of the metal, the charge and the stereoelectronic interactions between the ligands and the metal center.…”

Synthesis of 4-Substituted-1,2-Dihydroquinolines by Means of Gold-Catalyzed Intramolecular Hydroarylation Reaction of N-Ethoxycarbonyl-N-Propargylanilines

“…With regard to the regiochemical outcome, the meta -substituted derivatives 1k – n mainly underwent the para -position cyclization to give the corresponding 1,2-dihydroquinolines 2k – n in the presence of JohnPhosAu(CH 3 CN)SbF 6 (catalyst A ). Fine tuning factors such as valency state, counterion, and auxiliary ligand in homogeneous gold catalysis is imperative in controlling the product divergence [ 28 ]. Indeed, for compounds 1k – l, the para -position cyclization was revealed to be enhanced in the presence of catalyst A′ bearing NTf 2 as counterion (catalyst A′ , entries 2 and 6).…”

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] .…”