Revisiting the Influence of Silver in Cationic Gold Catalysis: A Practical Guide

Abstract

An excess amount of silver salt to generate cationic gold from a gold catalyst precursor such as L-Au-Cl almost always has adverse effects on the reactivity of the cationic gold catalyst. A preformed L-Au(+)X(-) complex, generated by sonication followed by centrifugation, increases the reactivity in a gold catalyzed reaction. The adverse silver effect might be caused by the interaction of silver salts with gold intermediates.

Expedient Syntheses of Neutral and Cationic Au(I)–NHC Complexes

“…1 The exploration of gold(I)-NHC chemistry in particular has gained increased attention mainly due to the ever-growing development of NHC (NHC = N-heterocyclic carbene) ligand design and tunability ( Problematically, silver salts were shown to persist as impurities and interfere with catalytic reactions through the formation of silver-stabilized intermediates (e.g. gemdimetallated complexes) 6 or catalytically active acids. 7 Furthermore, avoiding the use of light-and moisture sensitive silver salts is highly desirable in an effort to decrease cost and to simplify handling.…”

Synthesis of α‐Fluoroketones by Insertion of HF into a Gold Carbene

“…The low reactivity of the Et 3 N‐HF system may be due to high basicity of Et 3 N . Previously, we found that excess amounts of silver activators are harmful to gold‐catalyzed reactions, and preformed cationic gold catalysts usually have the best efficiency . Indeed, the preformed gold catalyst JohnPhos‐Au‐NTf 2 gave a faster reaction, and we could even reduce the gold catalyst loading to 0.5 mol %, although longer reaction time was needed (entry 15).…”

Divergent Regio‐ and Stereoselective Gold‐catalyzed Synthesis of α‐Fluorosulfones and β‐Fluorovinylsulfones from Alkynylsulfones

“…Buchwald type ligands gave slightly better results, and, among them, JohnPhos gave the best chemical yield (Table , entry 6). Recently, we had demonstrated that excess amounts of silver almost always had a deleterious effect on the reactivity of gold catalysts, and that a preformed gold catalyst (e.g., L ‐Au‐NTf 2 ) rendered better results. Indeed, a preformed JohnPhos‐Au‐NTf 2 catalyst gave a good result in our reaction (Table , entry 8).…”