Some insights into the gold-catalysed A 3 -coupling reaction

Abstract

Abstract.A series of cyclometallated and functionalised NHC gold(I) and gold(III) complexes, many of which feature chiral ligands, and their application to A 3 -coupling reactions is presented. Gold(III) complexes were found to be particularly effective catalysts for the coupling in a range of solvents, however no asymmetric induction was obtained when using chiral gold complexes and the rate of product formation was found to be similar even when using different ligand systems. In-situ NMR analysis of these reactions indicates that decomposition of the catalyst occurs during the course of the reaction while TEM studies revealed the presence of gold nanoparticles in crude reaction mixtures. Taken together these data suggest that the gold nanoparticales, rather than the intact gold complexes, could be the catalytically active species, and if so this may have significant implications for other gold-catalysed systems.Dedicated to Dr. Mark Whiteley (an outstanding colleague) on his retirement from the School of Chemistry, University of Manchester.

The Synthesis of Group 10 and 11 Metal Complexes of 3,6,9‐Trithia‐1‐(2,6)‐pyridinacyclodecaphane and Their Use in A3‐Coupling Reactions

“…Given the beneficial effects that we[7a] and others[11e], [11g] have noted in the promotion of A 3 ‐reactions when using focused microwave radiation as a heating source we turned our attention to this mode of activation in the present study. After some experimentation we noted that much reduced reaction times (30 min instead of 16 h) and catalyst loadings (typically 2 mol‐%) can be utilised to good effect when irradiating these reactions (to an internal temperature of 150 °C) in a focused microwave reactor.…”

“…The complexes 3a , 4a and 4b have been characterised by single‐crystal X‐ray crystallography where it has been shown that, in the case of 3a and 4a , the ligand binds to Ag + in both endo ‐ and exo ‐modes generating one‐dimensional co‐ordination polymers , . A 3 ‐reactions proceed efficiently in either toluene or aqueous media when conducted in the presence of these complexes; A 3 ‐coupling reactions conducted in a focused microwave[11e], [11g], [7b], reactor have a beneficial effect both on reaction rate and catalyst loading. Further optimisation of these A 3 ‐reactions is currently under investigation.…”

“…The A 3 ‐reaction has been the subject of intense scrutiny in recent years especially in connection with the development of more active catalysts[3b], [3c] or in the development of enantioselective variants. [3h] Metal salts and their complexes including iron, indium, iridium, zinc, nickel, cobalt, rhodium, gold, silver, copper and bimetallic systems such as RuCl 3 /CuBr have been found to catalyse A 3 ‐coupling reactions although it may be argued that the development of catalysts based upon the more abundant coinage metals would be preferable. In addition, concerns arising from the use of heavy metals in chemical processes and the drive to recycle expensive catalysts has resulted in the development of heterogeneous protocols for such reactions .…”

Heterocyclic thiolates and phosphine ligands in copper‐catalyzed synthesis of propargylamines in water

“…Efficient catalysts based on N‐heterocyclic carbene complexes of coinage metals have been developed during past few years. [ 28–37 ] Copper‐based catalysts because of natural abundance of copper metal and high reactivity have also attracted great attention. [ 38 ]…”

Immobilized Gold Nanoparticles Prepared from Gold(III)-Containing Ionic Liquids on Silica: Application to the Sustainable Synthesis of Propargylamines

“…Homogeneous catalysts based on a large number of transition metal ions have been used for the A 3 coupling reaction, including Cu [ 8 , 9 , 10 , 11 , 12 ], Ag [ 13 , 14 , 15 , 16 ], Cu/Ru bimetallic systems [ 17 , 18 ], Zn [ 19 , 20 , 21 ], Fe [ 22 , 23 ], In [ 24 , 25 ], Ir [ 26 , 27 ], Hg [ 28 ], Ni [ 29 ], Rh [ 30 ], Mn [ 31 ], Co [ 32 ], Bi [ 33 ], and Cd [ 34 ]. Over the past few years, increasing attention has been paid to the catalytic performance of Au in promoting the A 3 coupling reaction, including Au(I) and Au(III) salts and organic Au complexes [ 35 , 36 , 37 , 38 ]. Despite cationic Au species showing very high catalytic activity, their rapid reduction under alkyne activation conditions is an important drawback [ 39 , 40 , 41 ].…”