Exploration into the displacement of Zn2+ by Ni2+, Cu2+, Cd2+, Co2+, and Fe2+ from within N-, S-, and O-chelated 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 the divalent metal salts in a methanol solution and yielded, in both cases, the hexa-coordinate M-1 '-Ac2  metal-exchanged product . The latter conditions imply an intact-ligand unwrapping process as the hexadentate N2S2O2 ligand is transferred from zinc to the exogenous metal. The former involves transfer of the pentadentate N2S2O ligand generating a penta-coordinate 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 hexadentate N2S2O2 ligand systems. The M-1 '-Ac2  complexes were characterized by ESI mass spectrometry, UV-Vis, FTIR, elemental analysis, and X-ray diffraction; and compared to the directly synthesized products. The kinetic rates and activation parameters for the transmetallation reaction are being investigated through UV-Vis monitoring.

Zinc/metal exchange and ligand cannibalism in N2S2O1,2 donor ligand sets: A bioinorganic approach to thiolate reactivity and coordination chemistry

245th National Meeting (2013)

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