Abstract

We report that 1-(2-picolyl)-1,2,3-triazole (click triazole) forms stable complexes with transition-metal ions in which the coordination involves the triazole N2 nitrogen atom and the pendant 2-picolyl group. This is exemplified by model compound 1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole (L-x) and its complexes with transition-metal ions of Pt-II, Pd-II, Cu-II, Ru-II, and Ag-I. The coordination was investigated experimentally and theoretically. Ligand L-x easily reacted at room temperature with cis-[PtCl2(DMSO)(2)], [Pd(CH3CN)(4)](BF4)(2), CuCl2, [RuCl(mu-Cl)(eta(6)-p-cymene)](2), and AgNO3 to give stable chelates [PtCl2Lx] (1), [Pd(L-x)(2)](BF4)(2) (2), [CuCl2(L-x)(2)] (3), [RuCl(eta(6)-p-cymene)L-x]OTf (4), and [Ag-2(L-x)(2)(NO3)(2)] (5), respectively, in 60-98% yield. The structures of 1-5 were unambiguously confirmed by NMR spectroscopy and single-crystal X-ray diffraction analysis. Density functional theory calculations were carried out in order to theoretically investigate the stabilization factors in 1-5. A comparison of the chelating properties of ligand L-x was made with structurally similar and isomeric 1-(2-aminoethyl)-substituted 1,2,3-triazole (L-y) and 4-(2-aminoethyl)-substituted 1,2,3-triazole (L-z). The complexation affinity of L-x was attributed to pi-back-donation from the metal to the pendant pyridine side arm, whereas the stability of the complexes involving L-y and L-z mainly originates from efficient pi-back-donation to the triazole ring.