Chelating tris(amidate) ligands: versatile scaffolds for nickel(II)

The synthesis and characterization of nickel complexes supported by a family of open-chain, tetradentate, tris(amidate) ligands, [N(o-PhNC(O)R)₃]³⁻ ([L^R]³⁻ where R = ⁱPr, ^tBu, and Ph) is described. The complexes [Ni(L^iPr)]⁻, [Ni(L^tBu)]⁻, and [Ni(L^Ph)(CH₃CN)]⁻ have been characterized by solution-state spectroscopic methods and single crystal X-ray diffraction. Each ligand gives rise to a different primary coordination sphere about the nickel centre. These studies indicate that the ligands' acyl substituents can be used to regulate the coordination mode of the amidate donors to nickel and the coordination number of the nickel centres. In addition, the ability of these complexes to bind cyanide has been explored. These experiments demonstrate that only one of these complexes, [Ni(L^iPr)]⁻, is able to irreversibly bind cyanide and can be used to assemble [Et₄N]₃[Ni(L^iPr)(μ₂-CN)Co(L^iPr)], a cyanide bridged, heterobimetallic complex. The synthesis and characterization of the cyanide containing complexes, including magnetic susceptibility studies, are described.