| Abstract: | Metallodithiolate ligands play an important role in providing the appropriate electronic environment for the catalytic function of various metalloenzymes; acetyl coA synthase serves as paradigm. Using tetradentate N₂S₂ ligands to bind transition metals, a library of well-characterized synthetic analogues has been established. These metal-bound cis-dithiolates, display a wide range of reactivity, including S-based metallation, oxygenation, and alkylation. Sulfur's affinity for gold(I) is well known and typically follows Pearson's HSAB theory. With this in mind, the NiN₂S₂ moieties were used to synthesize propeller-type nickel-gold complexes within a group of [Ni((N₂S₂)[subscript x]-Au[subscript y]] ( x = 1 or 2; y = 1, 2, or 4) complexes.The solid-state molecular structures of these square planar cis-dithiolate nickel complexes to which gold(I) is bound contain within them classical aurophilic interactions. Electrochemical studies reveal a positive shift in the Ni (II/I) couple for the [Ni(N₂S₂) [subscript x]Au[subscript y]] complexes as compared to the NiN₂S₂ precursors. The incorporation of the paramagnetic vanadyl ion, [V[triple bar]O]²⁺⁺, in N₂S₂ motifs has been studied in our laboratory. Previous studies of M(N₂S₂) complexes where M is Ni²⁺, ZnCl⁺, and Fe(NO) with the W(CO)[subscriptx] reporter unit have been explored to determine the donor ability of these metallodithiolate ligands. According to their response or binding to a tungsten carbonyl unit, we have found that the sulfurs of the dianionic [(V[triple bar]O)(ema)]²⁻ are activated as nuclephilies. To further investigate the donor ability of the neutral vanadyl-bound thiolate sulfurs, the oxidized {Fe(NO)₂}⁹ unit was used. Cleavage of the (μ-I)₂[Fe(NO₂]₂ dimer (in the {Fe(NO₂}⁹ form) was achieved with two metalloligands, Ni(bme-daco) and (V[triple bar]O)bme-daco, and also N-heterocyclic carbene, IMes. Using infrared spectroscopy, the ν(NO) stretching frequencies of the LFe(NO)₂I (L = Ni(bme-daco), (V=O)bme-daco, and IMes) complexes were used to report the donor ability of the ligands. Cyclic voltammetry for the LFe(NO)₂I complexes show a more accessible {Fe(NO)₂}⁹⁽¹⁰ couple for stronger donors. Electron paramagnetic resonance (EPR) measurements of the LFe(NO)₂I complexes demonstrate super-hyperfine coupling of the ¹²⁷I to the unpaired electron on iron, and complex equilibria that indicates dissociation of the metallodithiolate ligand from the dinitrosyl iron unit. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151904 |
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