[Silver(I)(Pyridine-Containing Ligand)] Complexes As Unusual Catalysts for A³-Coupling Reactions

Abstract

Two original macrocyclic silver(I)(pyridine-containing ligand) complexes [Ag(I)(Pc-L)] were synthesized and characterized. Their ability to catalyze the coupling among aldehydes, terminal alkynes and amines (A(3)-coupling) was demonstrated. The reaction could be performed under conventional as well as dielectric heating. The catalysts were effective in both cases, but dielectric heating allowed a lower catalyst loading and reduced ratio among reaction partners in shorter reaction times. The reaction scope was broad, including aryl/alkyl aldehydes, aryl/alkyl acetylenes and secondary aliphatic amines. Some unprecedented propargylamines have been prepared. The new catalytic system was also tested with more challenging coupling partners such as aniline and ketones.

Organometallic Reactivity of [Silver(I)­(Pyridine‐Containing Ligand)] Complexes Relevant to Catalysis

“…Silver complexes 2 were easily obtained as white crystals in yields up to 91 % by precipitation, concentrating the solvent, and adding nhexane. Complexes 2a 1-3 and 2c 1,2 have been already described, [17,18] and experimental details for all others complexes can be found in the Experimental Section and in the Supporting Information. All the obtained silver complexes 2 have been fully characterized by 1 H and 13 C NMR spectroscopy, ESI-MS, and IR and UV/Vis spectroscopy.…”

“…Concerning the catalytic applications we previously reported for these compounds, [17,18] the interactions with alkynes are those of greatest interest. We found that 2c 1 reacted with a terminal alkyne, such as phenylacetylene, to give silver phenylacetylide 4 and the protonated ligand 3, which partially precipitated as the tetrafluoroborate salt.…”

“…[18] We have reported here their rich coordination chemistry with special emphasis on their behavior with reagents commonly employed in the above-mentioned reactions. Both the π-philic (alkyne coordination) and the σ-philic (alcohol and nitrile coordination) nature of silver(I) has been clearly demonstrated.…”

“…The ligands 1a-e [12][13][14] and the silver(I) complexes 2a 1-3 and 2c 1,2 were synthesized as previously reported. [17,18] General Procedure for the Synthesis of Silver Complexes 2b,d,e: The silver salt and all silver-containing solutions were kept in the dark until the final isolation of the product. Ligand 1 was dissolved in 1,2-dichloroethane (≈ 2 ϫ 10 -2 m), the silver salt (weighed under a nitrogen atmosphere) was added, and the mixture was stirred for 1 h, then filtered to remove any traces of unreacted solid.…”

“…[17] The same silver(I) catalysts have shown a good catalytic activity in the microwaveenhanced synthesis of propargylamines starting from aldehydes, terminal alkynes, and amines (A 3 -coupling). [18] The great advantage of the [Ag I (Pc-L)] complexes with respect to simple silver salts, is their enhanced stability and the ease of handling. In fact, they can be stored indefinitely in open air/light conditions at room temperature without any appreciable decomposition.…”