Gold Catalysis: The Benefits of N and N,O Ligands

Abstract

Dedicated to Professor Johann Mulzer on the occasion of his 60th birthdayThe catalysis of organic reactions by gold compounds has been recently shown to be a powerful tool in synthesis. [1, 2] When gold(i) compounds are used as precatalysts, ligands such as phosphanes [3][4][5][6][7][8] or phosphites [9] can be applied. The gold(iii) precatalysts are mainly simple halides; [2] other examples include one thioether-containing, [10] one phosphite-containing, [9] and organogold(iii) [11] compounds. For the gold-catalyzed phenol synthesis, [12] AuCl 3 usually delivers good results with simple substrates, but with more complicated ones a significant loss of activity is observed. At lower temperature, kinetic studies with our most simple testsubstrate 1 (see Scheme 1) showed that the problem with regard to the loss of activity occurs even with as much as 5 mol % of catalyst ( Figure 1). With small amounts of catalyst, the conversion remains incomplete.We have now tested several gold(i) and gold(iii) complexes with different ligands as catalysts for this reaction. Gold(i) complexes showed low selectivity and led to several side products. Satisfactory results in terms of activity, long-term stability and product-selectivity were obtained only with gold(iii) complexes with pyridine derivatives, some of which contained chelating oxygen functionalities. The most interesting complexes were precatalysts 3-6.[13] The complexes did not suffer deactivation, as shown in Figure 2 for 3-the activity even holds in a second catalytic run. Unlike with AuCl 3 , a mechanistically interesting induction period was observed for 3-6, clearly proving that here the complexes are precatalysts. This is also the reason for the higher activity in the second run, since the catalytically active species is already present and does not have to be formed in a slow reaction.With as little as 0.07 mol % of 3 a complete conversion could be achieved; this corresponds to 1180 instead of the usual 20-50 turnovers. The complexes 4-6 are also highly stable catalysts; a comparison of their activity is depicted in Figure 3: the acceptor-substituted pyridine carboxylate 5 is the most reactive one, followed by the unsubstituted 4 and the donor-substituted 6. Nevertheless, the initial activity of 3, 4, and 6 is lower than that of AuCl 3 . In part, this problem can be solved by switching to dichloromethane/acetonitrile mixtures or even pure dichloromethane (as shown for 3 in Figure 4). In

Novel cycloaurated gold(III) complexes and their effects on styrene polymerization

“…When gold complexes added to the reaction media s-PS was formed ( Fig. 2; Table 1; run nos., [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] After these results were evaluated, series of experiments were conducted at room temperature with different solvents and results. Bulk polymerization was carried out at different catalyst concentrations but conversion did not pass 25% yield.…”

“…The 1.72-2.43 ppm are methyne hydrogen signals and chemical shifts between 0.97 and 1.76 ppm are methylene hydrogen signals in polystyrene [21]. Figure 3 shows the comparison 13 C-NMR spectrums of polystyrene in CDCl 3 solution with catalyst and without catalyst. All spectrums were analyzed in terms of triads.…”

“…Applications of organogold chemistry have been explored by Hashmi [2][3][4]. Organic derivatives of both Au(I) and (III) ions were reported in the review and in more recent papers [5][6][7][8][9][10][11][12][13].…”

Metal (Au, Ag and Cu) NPs in Ionic Liquid: Potential Catalytic System for Organic Reactions

“…However, low solubility of reactants, incompatibility of certain intermediate or competition between the desired reactants and hydrolysis restrict the use of water as a common solvent to carry out organic reaction, although many reactions have been studied in water using different catalyst. The use of IL, easily synthesized, non-volatile for various reactions is reclaiming its importance due to pressing environmental, economic and safety concerns [16][17][18][19][20][21][22][23][24][25][26][27][28].…”

C–C coupling reactions using a gold(iii) phosphorus complex confined within metal–organic framework fibers in aqueous solution

“…[1][2][3][4][5] Among the reported metals used in catalysis, gold is the most stable catalyst, and it has been widely studied because of its catalytic properties, which can be leveraged for various uses, such as in the Sonogashira, [6][7][8] Suzuki-Miyaura,…”