Influence of apical ligands on Cu-(C=C) interaction in Copper(I) halides (Cl-, Br-, I-) π-complexes with an 1,2,4-triazole allyl-derivative: Syntheses, crystal structures and NMR spectroscopy

New multifunctional 1,2,4-triazole based allyl-derivative as the ligand L (3-allylsulfanyl-4-allyl-5-phenyl-4H- 1,2,4-triazole) revealed an ability to form stable binuclear copper(I) pi-complexes. A series of related Cu(I) halides pi-complexes, [Cu-2(L)(2)X-2] (X = Cl, 1a; Br, 1b; I, 1c), [Cu-2(L)(2)I-2] 2 (1c'), [Cu-2(L)(2)(CuCl2)(2)] (2), [Cu-2(L)(2)Cu2Br4] (3) was obtained by alternating-current electrochemical synthesis, starting from acetonitrile solutions of the ligand L and CuX2 (in the case of 1a, 1b, 2, 3) or I-2 (1c, 1c'). This is the first notice of using iodine being reduced at copper electrodes under alternating current in the presence of a ligand for copper(I) iodide complexes synthesis. The crystal structures were determined by means of single crystal X-ray diffraction. The organic ligand acts as multidentate chelating sigma, pi-donor using triazole (tr) and eta(2)-allyl moieties, resulting in a formation of the dimeric {Cu2N4} core with a trigonal-pyramidal (2 N, C=C + X) environment of the Cu cation. Packing polymorphism was revealed for the iodine complex. In the case of 2 and 3 the Cu centers participate in a formation of both - metal-organic cations and copper(I) halide anions. In structure 3, the copper(I)-halide subunit is organized in the Cu-2(mu(2)-Br)(2)Br-2 cluster that links organometallic moieties leading to a 1D ladder fragment. High inertia of complexes in acetonitrile solutions enabled a comparative evaluation of a strength of the Cu(I)-(C=C) interaction by means of H-1 NMR spectra. NMR spectroscopic studies are consistent with the structural analysis. (C) 2017 Elsevier B.V. All rights reserved.