Browsing by Subject "vanadyl"
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Item Development of Metallodithiolates as a New Class of Versatile Ligands to Transition Metals(2013-12-09) Pinder, TiffanyMetallodithiolate 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 N_(2)S_(2) 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 NiN_(2)S_(2) moieties were used to synthesize propeller-type nickel-gold complexes within a group of [Ni(N_(2)S_(2))_(x)Au_(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(N_(2)S_(2))_(x)Au_(y)] complexes as compared to the NiN_(2)S_(2) precursors. The incorporation of the paramagnetic vanadyl ion, [V?O]^(2+), in N_(2)S_(2) motifs has been studied in our laboratory. Previous studies of M(N_(2)S_(2)) complexes where M is Ni^(2+), ZnCl^(+), and Fe(NO) with the W(CO)_(x) 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?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 (?-I)_(2)[Fe(NO)_(2)]_(2) dimer (in the {Fe(NO)_(2)}^(9) form) was achieved with two metalloligands, Ni(bme-daco) and (V?O)bme-daco, and also N-heterocyclic carbene, IMes. Using infrared spectroscopy, the ?(NO) stretching frequencies of the LFe(NO)_(2)I (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)_(2)I complexes show a more accessible {Fe(NO)_(2)}^(9/10) couple for stronger donors. Electron paramagnetic resonance (EPR) measurements of the LFe(NO)_(2)I complexes demonstrate super-hyperfine coupling of the ^(127)I to the unpaired electron on iron, and complex equilibria that indicates dissociation of the metallodithiolate ligand from the dinitrosyl iron unit.Item Studies in Bioinorganic Chemistry: Synthesis and Reactivity of Nickel and Vanadyl NxSy Complexes(2011-08-08) Jenkins, Roxanne MichelleAs inspired by the coordination environment of nickel in NikR and NiSOD, imidazole ligands were incorporated into N2SNiII square planar complexes in order to investigate the electronic and structural features of NiII species containing both imidazole and thiolate ligation. Rare examples of nickel complexes containing such ligand sets in continuous tetradentate (N2N'S) and discontinuous (N2S---N') coordination were synthesized and characterized. A significant finding in these studies is that the plane of the imidazole ligand is oriented perpendicular to the N2SNi plane. Further investigations addressed the orientational preference and stereodynamic nature of flat monodentate ligands (L = imidazoles, pyridine and an N-heterocyclic carbene) bound to planar N2SNi moieties. The solid state molecular structures of planar [N2SNiL]n+ complexes accessed through bridge-splitting reactions of dimeric, thiolate-S bridged [N2SNi]2 complexes, reveal that the plane of the added monodentate ligand orients largely orthogonal to the N2SNiL square plane. Variable temperature 1H NMR characterization of dynamic processes and ground state isomeric ratios of imidazole complexes in their stopped exchange limiting spectra, readily correlate with DFT-guided interpretation of Ni-L rotational activation barriers. Full DFT characterization relates the orientation mainly to steric hindrance derived both from ligand and binding pocket. In the case of the imidazole ligands a minor electronic contribution derives from intramolecular electrostatic interactions (imidazole C-2 C-H[superscript delta]+- - S[superscript delta]- interaction). Our group has firmly established the versatility of the (bme-daco)2-, (bme-dach)2-, and (ema)[left arrow]- ligands to accommodate a number of metals (M = Ni, Zn, Cu, and Fe ), and have demonstrated reactivity of such N2S2M complexes occurs predominately at the S-thiolate sites. As vanadium is of interest for its biological, pharmacological and spectroscopic/analytical probe abilities, vanadyl analogues were explored as mimics of possible chelates formed from Cys-X-Cys binding sites in vivo. The structural and electronic changes from the incorporation of V=O2+ in such dianionic and tetraanionic N2S2 binding pockets is investigated and compared to Ni2+ and Zn2+ in similar N2S2 environments. The nucleophilicity of the S-thiolate in these systems is explored with alkylating agents and W(CO)x. Furthermore, the vanadyl interaction with the CGC peptide, the biological analogue of the tetraanionic N2S2 ligand, was produced and characterized by EPR; its W(CO)x adducts were indentified by ?(CO) infrared spectroscopy.