Zinc/Nickel exchange and ligand cannibalism in N2S2O1,2 donor ligand sets

Abstract

To explore the displacement of Zn²⁺ by Ni²⁺ from within N-, S-, and O-chelate ligands, (N-(3-thiabutyl)-N′-(3-thiapentaneoate)-1,4-diazacycloheptane)zinc(II), Zn-1′-Ac, and 1,4-diazacycloheptane-1,4-diylbis(3-thiapentanoato) zinc(II), Zn-1′-Ac₂, were reacted with Ni(BF₄)₂ in a methanol solution and were found to yield, in both cases, the bright blue, hexa-coordinate Ni-1′-Ac₂ metal-exchanged product. The latter conditions imply an intact-ligand unwrapping process as the hexadentate N₂S₂O₂ ligand is transferred from zinc to nickel. The former involves transfer of the pentadentate N₂S₂O ligand generating a green, penta-coordinate nickel intermediate which engages in CH₂CO₂ fragment scavenging from a second zinc unit. This conclusion is supported by the observed analogous reformulation of the stable Zn-1′-Ac complex into Zn-1′-Ac₂ and the dithiolato [Zn-1′]₂ dimer. To our knowledge, this is a rare (possibly the first) example of cannibalism reported in such ligand systems. The M-1′-Ac₂ complexes were characterized by X-ray diffraction and compared to the directly synthesized products.