Square planar Ni(II) thiosemicarbazone complexes as functional models for carbon monoxide dehydrogenase

Two Ni(II) complexes, [Ni(dmoTSCH)Cl] (1) and [Ni(dmoPhTSCH)Cl] (2) of the tridentate thiosemicarbazone ligands diacetylmonooxime thiosemicarbazone (dmoTSCH(2)) and diacetylmonooxime (4-phenyl)thiosemicarbazone (dmoPhTSCH(2)) have been synthesized. X-ray crystal structure of [Ni(dmoTSCPhTSCH)Cl] (2) indicates that the Ni(II) assumes a square planar geometry in the complexes, with the ligand coordinated in a monoanionic N,N,S donor mode and the fourth coordination position of Ni(II) is occupied by a chloride ion. Cyclic and differential pulse voltammetric experiments suggest that the Ni(II) complexes can undergo a two electron reduction at about -1.0V. It is shown that the Ni(II) complexes in DMF or DMSO solutions can mimic CO-dehydrogenase activity by oxidizing CO to CO2 in presence of a base like NaOAc and a sacrificial electron acceptor like methyl viologen and the colour of the resultant MV center dot+ can be used to monitor the reaction.