Nickel containing metalloproteins have garnered much attention due to potential applications in the areas of drug discovery1 and clean energy2. A number of N2S2Ni model complexes have been synthesized in order to gain a better understanding of the active sites of some of these large proteins3; however, a vast majority of these N2S2Ni model complexes contain tetradentate ligand systems. Tetradentate ligand systems are often not as conformationally flexible as ligands with a lower denticity, and they tend to stabilize only square planer geometries. Exploring the nickel coordination of bidentate N,S ligands, such as l-cysteine ethylester (cysE), expands the data set of N2S2Ni coordination complexes and the use of these N2S2Ni complexes as ligands. Computational studies indicate that the trans-Ni(cysE)2 complex is slightly more stable than the cis-Ni(cysE)2 complex, but in order to form the trinuclear [Ni(Ni(cysE)2)2]2+ complex, a Ni2+ ion must bridge 2 cis-Ni(cysE)2 complexes. In addition N2S2Ni complexes using bidentate ligands are less stable than N2S2Ni with tetradentate ligands based on the chelate effect. By using Job’s Method of Continuous Variation and high resolution NMR studies (HSQC,ROESY, NOESY,TOCSY), the stability of the trinuclear [Ni(Ni(cysE)2)2]2+ in solution is addressed. Job’s method confirms the formation of the trinuclear nickel complex, and the high resolution NMR experiments provide evidence of additional structural isomers in solution. The synthesis of the trinuclear complex was also confirmed by mass spectrometry, UV-Vis, and elemental analysis. 1. Storr, T.; Thompson, K. H.; Orvig, C., Design of targeting ligands in medicinal inorganic chemistry. Chemical Society Reviews 2006, 35 (6), 534-544. 2. Kim, D.-H.; Kim, M.-S., Hydrogenases for biological hydrogen production. Bioresource Technology 2011, 102 (18), 8423-8431. 3. (a) Osterloh, F.; Saak, W.; Pohl, S., Unidentate and Bidentate Binding of Nickel(II) Complexes to an Fe4S4 Cluster via Bridging Thiolates:  Synthesis, Crystal Structures, and Electrochemical Properties of Model Compounds for the Active Sites of Nickel Containing CO Dehydrogenase/Acetyl-CoA Synthase. Journal of the American Chemical Society 1997, 119 (24), 5648-5656; (b) Darensbourg, M. Y.; Lyon, E. J.; Smee, J. J., The bio-organometallic chemistry of active site iron in hydrogenases. Coordination Chemistry Reviews 2000, 206–207 (0), 533-561.

Job’s method and high resolution NMR studies of trinuclear bis(bis(O-ethyl-L-cysteinato)2Ni)2Ni2+

249th National Meeting (2015)

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