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Title: Transition metal complexes containing phenylthiolate and phenolate ligands
Author: Franks, Mark A.
ISNI:       0000 0004 2747 5006
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2011
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Chapter 1 provides an introduction to metalloenzymes that either feature active sites containing Ni-thiolate ligation or utilise phenoxyl radicals to perform their catalytic function, with a particular emphasis on the enzymatic active sites of Ni-containing superoxide dismutase (Ni SOD), [NiFe] hydrogenase and galactose oxidase. Studies concerning low molecular weight complexes of each active site are reviewed and their relevance with respect to enzyme function discussed. Details of the project outline conclude the chapter. Chapter 2 details the syntheses and characterisation of the [Zn(tsalen)] derived complexes [ZneBuLsC3N)], [ZneBuLsC2N)], [ZneBuLsNMe)], [ZneBuLlyl)], [Zn(IBuLsPy2)], [ZneBuLsPhl)], [Zn(IBuLslml)2], [ZneBuLsPy3)2], [Zn(LsC2N)], [Zn(LsNMe)], [Zn(Llyl)], [Zn(LsPy2)] and [Zn(LsPh1)], via Zn(II) templated Schiff- base condensation reactions using two thiosalicylaldehyde derived units and a range of primary amines. The syntheses of 2,4-di-tert-butyl-thiosalicylaldehyde from tert- butyl benzene and three functionalised 1,3-propyldiamines (2-(2-pyridylmethyl)-1,3- propanediamine, 2-(2-pyridylethyl)-I,3-propanediamine and 2-benzyl-I,3- propanediamine) are described. X-ray crystallographic studies demonstrate the successful integration of the additional N-donors into the backbone of the ligand framework at the N-imine position. The range of S2N2, S2N3 and S2N4 ligand sets are shown to adopt an array of coordination geometries about the Zn(II) metal centre providing scope for these ligands in tuning the electronic structures of their Ni- containing complexes. Chapter 3 describes the syntheses and X-ray crystallographic, electrochemical and spectroscopic studies of a series of Ni(II) Schiff-base dithiolate complexes, [Ni(IBuLsC3N)], [Ni(IBuLsc2N)], [NieBuLsNMe)], [NieBuLlyl)], [Ni(IBuLly2)], III [Ni(BuLlhl)], [Ni(BuLs1ml)2], [Ni(tBuLly3h]' [Ni(LsPyl)], [Ni(LsPY2)] and [Ni(LsPhl)] obtained via transmetallation from the analogous [Zn(BuLl)] and [Zn(LsR)] complexes described in Chapter 2. The effect that the additional pendant N-donors have upon the redox properties of the individual complexes are considered with respect to reproducing the structural, spectroscopic and functional properties of NiSOD. Particular attention is focussed on the redox properties of [Ni(BuLsPyl)], [Ni(tBuLsPy2)] and [Ni(BuLsPhl)], which together highlight a rare example of the ability of one N-donor group to assume the role of an endogenous donor upon oxidation. The proposed internal rearrangement of the Ni coordination sphere may encourage the formation of a predominantly metal-based SOMO following the oxidation process. Insight upon how this coordination chemistry relates to the chemistry of the active site of Ni SOD is discussed. Chapter 4 reports the electrochemical and spectroscopic characterisation of a range of binuclear [Ni(LsR)Fe(CO)3] and trinuclear [Ni(LsR){Fe(CO)3h] complexes (R = PhI, PyI and Me) synthesised via the reaction of [Ni(tsalen)]-type complexes, [Ni(LsR)], with Fe2(CO)9. X-ray crystallographic studies show that the complexes incorporate biologically relevant structural elements reminiscent of the active site of [NiFe] hydrogenase, including a binuclear Ni(1l2-S)Fe core featuring a ea. 2.9 A Ni- Fe separation. Chapter 5 details the preparation of a series of Zn(II), Ni(lI) and Cu(lI) Schiff-base diphenolate complexes utilising the two novel pentadentate pro-ligands, [H2tBuLo C3N] and [H2tBuLo NMe]. Cyclic voltammetric, spectroelectrochemical and EPR studies show the Zn(lI) and Cu(lI) complexes support two ligand-based oxidation processes, yielding kinetically inert species possessing phenoxyl radical character. Conversely, the paramagnetic Ni(lI) complexes, [Ni(BuLo NMe)] and IV [Ni(tBuLo C3N)], support both metal and ligand-based oxidation chemistry. The chapter concludes by discussing the relative stability of phenoxyl and phenylthiyl radical ligands by comparison with the redox properties of the analogous Schiff-base Zn(II)-dithiolate complexes described in Chapter 2.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available