Redox Noninnocent Copper(I) Complex Where Metal Is a Spectator and Ligand Is an Actor in the Glaser Coupling Reaction of Alkynes
Swati Rani, kamal kamal, Muskan Muskan, Avtar Changotra, Subhas Samanta
Abstract
An extended trisazo dipyridyl ligand, L, and its copper(I) complex, [ 1 ] +, were synthesized and fully characterized. Complex [ 1 ] + has five coordination geometry satisfied by ligand L . L has a low-lying π* orbital; thus, [ 1 ] + showed very facile multiple ligand-based redox events. Moreover, due to the strong π-acceptor nature of L, the Cu(II)/Cu(I) redox potential of [ 1 ] + was anodic (0.62 V). The redox events of both L and [ 1 ] + were characterized using various spectroscopic studies and density functional theory (DFT) calculations. Taking advantage of the multiple facile ligand-based reductions in [ 1 ] +, the Glaser coupling reaction of terminal alkynes was explored. Various kinds of alkynes were found to be effective when using [ 1 ] + as a precatalyst. The mechanism of the reaction was investigated thoroughly by several controlled experiments, isolation, and characterization of the intermediates using various spectroscopic studies as well as by single-crystal X-ray structure determination. These studies showed that the L in [ 1 ] + acted not only in the electron transfer events but also as a locus for binding the substrate, breaking and forming bonds, and, finally, releasing the product. Thus, here, the metal mainly acted as a spectator and ligand L acted as an actor.