Efficient Oxidative Alkyne Homocoupling Catalyzed by a Monomeric Dicopper‐Substituted Silicotungstate

Abstract

It goes on the dicopper core! A monomeric γ‐Keggin silicotungstate with a dicopper core that is bridged by two μ‐1,1‐azido ligands catalyzes oxidative alkyne homocoupling reactions whereby various kinds of aromatic and aliphatic alkynes are selectively converted into the corresponding diynes (see picture).

Copper-Impregnated Magnetite as a Heterogeneous Catalyst for the Homocoupling of Terminal Alkynes

“…The reaction fails in absence of base (entry 12). The effect of the base in the reaction was also studied using different amines (entries [13][14][15] and similar yields were obtained in only 4 hours with primary amines. However the corresponding amides were obtained as byproducts.…”

“…Heterogeneous catalysts were designed to perform this transformation with an easy method for removal, recovering and recycling the catalysts. Although, there are several examples of insoluble copper derivatives able to perform the Glaser-Hay reaction, 9 the most used strategy has been supporting copper salts on different inert oxides such as hydrotalcite, 10 alumina, 11 zeolite, 12 titania, 13 a silicotungstate complex, 14 molecular sieves 15 and mesoporous silica. 16 However, there are still some drawbacks that should be improved, such as the high metal catalyst loading required, 9-16 the high temperatures used, 12,13a,14,15 the use of non-environmentally benign solvents, 9b,10b,c,12,13a,14-16 the need of oxygen pressure 10a,b,13a,14,15 and the recyclability of the catalyst in some cases.…”

“…The presence of a steric hindrance at the aromatic decreased the yield (entry 6). Finally, the reaction could also be performed using the less reactive aliphatic alkynes and the expected products 2 were obtained in all the tested cases (entries [10][11][12][13][14], albeit with slightly lower yields. Encouraged by the success obtained in the homocoupling of terminal alkynes, the hydration reaction of 1,3-diynes to afford the corresponding 2,5-disubstituted furans was examined, which is catalyzed by different copper salts.…”

An Efficient Copper-mediated 1,3-Dipolar Cycloaddition of Pyrazolidinone-based Dipoles to Terminal Alkynes to Produce N,N-Bicyclic Pyrazolidinone Derivatives

“…5 The dicopper core plays an important role for the click reaction: Initially, the alkyne homocoupling efficiently proceeds via the Cu(II)alkynyl intermediate {Cu 2 (®-C¸CR) 2 }, followed by the formation of the corresponding diyne (as a co-product) and truly active Cu(I) species. 6 This means that an alkyne itself can act as an efficient reducing reagent to generate the catalytically active Cu(I) species in situ and no additional reducing reagents are necessary in the case of "dicopper complexes".…”

“…6 An alkyne 2a (100 equivalents) was added to a chloroform solution of [Cu(®-OH)(tmen)] 2 Cl 2 (1.7 mM), and the resulting solution was heated to 60°C for 30 min under Ar atmosphere. Then, the UVvis spectrum was measured.…”