Nickel complexes with “click”-derived pyridyl-triazoleligands: weak intermolecular interactions and catalytic ethylene oligomerisation

Abstract

The ligands 1-(cyclohexyl)-4-(2-pyridyl)-1,2,3-triazole (1), 1-(2,6-diisopropylphenyl)-4-(2-pyridyl)-1,2,3-triazole (2), 1-(4-butoxyphenyl)-4-(2-pyridyl)-1,2,3-triazole (3) and 1-(methyl)-4-(2-pyridyl)-1,2,3-triazole (4) were synthesized by the Cu(I) catalyzed “Click” reaction between 2-pyridylacetylene and the corresponding azides. The ligands were then reacted with NiBr₂·3H₂O to generate the complexes (1)₂NiBr₂ (1a), (2)₂NiBr₂ (2a), (3)₂NiBr₂ (3a) and (4)₂NiBr₂ (4a). Structural characterization of 1a confirmed the mononuclear and distorted octahedral environment around the Ni(II) center, with the pyridyl-triazole ligands coordinating in a bis-chelating fashion. Bond length analysis inside the 1,2,3-triazole ring shows a short NN double bond that is flanked by two longer C–N and N–N bonds pointing to the existence of “azo” character in the ring. The highly polar five-membered 1,2,3-triazole ring makes its C–H bond acidic, and these bonds participate in an extended weak intermolecular C–H⋯Br interactions with the Br-groups of neighboring molecules, resulting in a 3-D network. The nickel complexes with these “Click” ligands were tested as pre-catalysts for ethylene oligomerization, and the complexes showed moderate activity in that reaction with good selectivity towards C4 oligomers.