The synthesis, characterization, and reactivity properties of a mononuclear Ni(II) cis-beta-keto-enolate complex, [(6-Ph2TPA)Ni(PhC(O)C(OH)C(O)Ph)]ClO4 (1) (6-Ph2TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine) are reported. Complex 1 was characterized by X-ray crystallography, elemental analysis, 1H NMR, and electronic absorption and infrared spectroscopy. Treatment of 1 with 1 equiv of Me4NOH.5H2O in the presence of O2 results in oxidative carbon-carbon bond cleavage and the formation of a new Ni(II) dicarboxylate complex, [(6-Ph2TPA)Ni(O2CPh)2(H2O)] (2). Complex 2 has been characterized by X-ray crystallography, 1H NMR, UV-vis, IR, and elemental analysis. Use of 18O2 in the reaction of 1 to produce 2 results in the incorporation of one 18O atom per carboxylate ligand in the majority of the sample. Production of CO in the oxidative conversion of 1 to 2 was detected using the palladium chloride method. This is the first functional model system of relevance to acireductone dioxygenase (ARD), a novel Ni(II)-containing enzyme that catalyzes a reaction that is a shunt out of the methionine salvage pathway in K. pneumoniae.