An Industrial Perspective on Counter Anions in Gold Catalysis: On Alternative Counter Anions

Abstract

A comparison of versatile counter anions was investigated by means of a variety of well‐known test reactions representing the key reactivity patterns of homogeneous gold catalysis, the catalytic activity was monitored by GC and 1H NMR. As previously reported, the counter anion influence is usually more pronounced than the corresponding ligand effect. Due to this, the study is focused on the investigation of counter anions so far not included from investigation of homogeneous gold‐catalyzed reactions. The examinations using so far neglected counter anions (BArF4)−, [B(C6F5)4]−, [Al(OC(CF3)3)4]− and [B(C6F5)3(OAcF)]− showed surpassing or at least similar catalytic activities as the commonly used counter anions. The expanded use of counter anions can occupy an important role in future concerning catalyst optimization in gold catalysis.magnified image

Gold‐Catalyzed Cross‐Coupling Reactions: An Overview of Design Strategies, Mechanistic Studies, and Applications

“…[53][54][55][56] Compared with the advances in heterogeneous goldc atalysis, the field of homogeneous gold catalysis startedt og row only in the first decade of the 21st century.O ver the past two decades, homogeneousg old catalysis has emerged as an eminent synthetic methodology.T he progress in the syntheses and applications of Au catalysts, related reaction mechanisms, and the future prospects of traditional Au I -catalyzed reactions have been reviewed by the groups of Hashmi, [57][58][59][60][61][62] Fürstner, [63,64] To ste, [65] Echavarren, [66][67][68] and others. [92,93,102,[94][95][96][97][98][99][100][101] Some reactions are best catalyzed when multiple Au centers are available to activate the reactants and/or intermediates. Being ah eavy atom with a5 d 10 6s 1 electronic configuration, the relativistic effects strongly affect the dynamics of the valence electrons of Au.…”

“…Hashmi and others have reviewed the applications of Au in the total synthesis of natural products and complex target molecules . Recent studies have also focused on the cooperative catalysis of Au with other metal/nonmetal catalysts for accelerating selective organic transformations . Some reactions are best catalyzed when multiple Au centers are available to activate the reactants and/or intermediates .…”

Gold‐Catalyzed One‐Pot Synthesis of 1,3‐Disubstituted Allenes from Benzaldehydes and Terminal Alkynes

“…[12] Indeed, we herein report the first gold(I)catalyzed Crabbé-like reaction, applicable to the syn-thesis of a wide range of 1,3-disubstituted allenes using as little as 2.5 mol% of catalyst, mild conditions, open flask techniques and commercially available starting materials, such as morpholine, benzaldehyde derivatives and terminal alkynes (Scheme 2c). After that, two different counter ions [13] were tested in combination with the common IPr gold(I) species: The nitrilestabilized preactivated [IPrAu(NCCH 3 )]SbF 6 catalyst (entry 4) only delivered a poor yield of propargylic amine 4 a, however, to our delight, the stronger coordinating counter ion of IPrAuNTf 2 (entry 6), successfully yielded the allene 5 a. Just as expected, similar conditions to Che's, using Au(III) species, such as AuBr 3 (entry 1) and KAuCl 4 .…”

“…H 2 O (entry 2), promoted the formation of the A 3 -coupling product 4 a, but with no formation of the desired allene 5 a. After that, two different counter ions [13] were tested in combination with the common IPr gold(I) species: The nitrilestabilized preactivated [IPrAu(NCCH 3 )]SbF 6 catalyst (entry 4) only delivered a poor yield of propargylic amine 4 a, however, to our delight, the stronger coordinating counter ion of IPrAuNTf 2 (entry 6), successfully yielded the allene 5 a. As a next step, different solvents were also tested (entries [7][8][9][10][11][12].…”

Synthesis of pyrazolopyrimidines in mild conditions by gold nanoparticles supported on magnetic ionic gelation in aqueous solution

“…Gold catalysis is a rapidly developing topic in both academic [ 34–38 ] and industrial research, [ 39,40 ] with significant advances having been made within the last decade. Au‐catalyzed heterocyclizations/C–C bond formations, [ 41 ] reactions involving carbine intermediates, [ 42 ] alkyne hydration reactions, [ 43–45 ] and oxidation reactions [ 46–48 ] have all been the subject of intense research.…”