The oxidative Glaser–Hay coupling of two terminal alkynes to furnish a butadiyne is a key reaction for acetylenic scaffolding. Although the reaction is performed under rather simple conditions [CuCl/TMEDA/O2 (air)], the mechanism is still under debate. Herein we present detailed studies on the scope of this reaction by using both 13C NMR and UV/Vis spectroscopic methods. The former method was used to study the kinetics of the coupling of aryl‐substituted alkynes as the aryl carbon resonances of the reactants and products have similar NOEs and relaxation times. The reaction was found to be zero‐order with respect to the terminal alkyne reactant under standard preparative conditions. Moreover, as the reaction proceeded, a clear change to slower reaction kinetics was observed, but it was still apparently zero‐order. The onset of this change was found to depend on the catalyst loading. This unfavorable change in reaction profile could be avoided by adding molecular sieves to the reaction mixture, thereby removing the water that is accumulated from the air and produced in the reaction in which dioxygen acts as the oxidizing agent. Not unexpectedly, the stirring rate, and hence uptake of air (O2), was found to have a significant effect on the rate of the reaction: The percentage of alkyne remaining after a certain time decreased linearly with the rate of stirring. On the basis of systematic studies, the optimized conditions for the coupling reaction using CuCl/TMEDA as the catalyst system are presented. Finally, we investigated the effect of different ligands and found that piperidine can also be conveniently employed as a ligand, albeit monodentate, in accord with related studies.

A series of dinuclear gold σ,π-propyne acetylide complexes were prepared and tested for their catalytic ability in dual gold catalysis that was based on the reaction of an electrophilic π-complex of gold with a gold acetylide. The air-stable and storable catalysts can be isolated as silver-free catalysts in their activated form. These dual catalysts allow a fast initiation phase for the dual catalytic cycles without the need for additional additives for acetylide formation. Because propyne serves as a throw-away ligand, no traces of the precatalyst are generated. Based on the fast initiation process, side products are minimized and reaction rates are higher for these catalysts. A series of test reactions were used to demonstrate the general applicability of these catalysts. Lower catalyst loadings, faster reaction rates, and better selectivity, combined with the practicability of these catalysts, make them ideal catalysts for dual gold catalysis.

A wide range of gold-catalyzed reactions based on a dual activation mechanism has recently been reported in the literature. Herein, we present a computational investigation of the mechanism for the formation of dibenzopentalenes from 1-ethynyl-2-(phenylethynyl)benzene. Transition states have been found, which substantiate the dual activation mechanism previously published and furthermore point towards a continuous presence of two gold moieties throughout the mechanistic cycle, an observation of high importance for all reactions in the field of dual activation. The initial activation of the diyne has been shown to proceed via an intermolecular transfer of a cationic gold catalyst from the thermodynamically preferred geminal-σ,π-acetylide complex to the active non-geminal analogue. Furthermore, the regioselectivity of a 5-endo versus a 6-endo cyclization has been addressed, and the 5-endo cyclization was found to be most favorable both thermodynamically and with regard to the activation barrier.

Seven different NHC gold­(I) phenolate complexes were synthesized. Structural data, including X-ray crystal structure analyses, could be obtained for each of them. An investigation by computational chemistry, including NBO analysis, indicates three-center–four-electron hyperbonds among the carbene carbon, the gold atom, and the oxygen atom of the phenolate with an approximate 60:40 distribution of the bonding interaction in favor of the carbene–gold bond. The new class of complexes shows only moderate catalytic activity.

The reaction of a platinum acetylide derived from a 1,2‐dialkynylarene with a phosphanegold(I) species delivered a σ‐platinum‐π‐gold coordination to the same triple bond of the organic substrate. Cyclopentadienyl‐di(phosphanyl)ruthenium(II) acetylides of the same substrate type gave vinylgold(I)‐vinylideneruthenium(II) complexes in similar reactions. A switch to the corresponding cyclopentadienyl‐di(carbonyl)ruthenium(II) species with a phenyl group on the second alkyne provided vinylruthenium(II) complexes in which the ruthenium was still bound to the same carbon as in the starting material, with a tert‐butyl group on the second alkyne vinylruthenium(II) complexes in which the ruthenium has migrated to another carbon, were obtained. This reactivity mimics the initial steps suggested for dual gold catalysis with these substrates and thus for the first time experimentally confirms the organometallic reactivity patterns proposed for the single steps.magnified image