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The synthesis, reactivity and redox behaviour of tetraazaannulene transition metal complexes.

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posted on 2015-11-19, 08:45 authored by Andrew J. Grist
The introduction reviews the importance of macrocyclic complexes particularly tetraazaannulenes in biological systems such as in haem, chlorophyll, P450 enzyme and vitamin B12 as well as displaying the variety of chemistry apparent in the diversity of uses and applications in other research fields. In Chapter Two the dibenzo- and dipyridotetraazaannulene ligands are prepared and characterized. Many of these ligands are reported here for the first time. Two distinct types of dibenzotetraazaannulene ligands were studied. Those with a saddle shaped structure such as H2L1, H2L2 and H2L3 and those which are flat and y substituted H2L4 and H2L5. The potential of template and direct heating methods as alternatives to the synthetic routes already documented for the ligands was assessed in order to improve yields. Finally the transition metal complexes incorporating the various metal ions in oxidation states of +2, +3, +4 and +6 are synthesized. These complexes are characterized using a variety of techniques such as 1H nmr, infra red, UV-visible, mass(EI and FAB) and ESR spectroscopy. Copper, nickel and cobalt complexes of the y substituted flat ligands are prepared by utilizing an in situ method of synthesis instead of the preformed macrocycle method. This is also the case in the preparation of the family of y substituted oxovanadium(IV) complexes all of which are previously unreported. Oxotitanium(IV) complexes of the y substituted are reported here for the first time and titanium and vanadium complexes of the saddle shaped ligands are prepared with improved synthesis for TiCl2L1, TiOL1, TiO2L1 and VOL1 developed. Reactivity studies of the titanyl oxo moiety are undertaken leading to the isolation of amongst the first titanium imido complexes Ti(N-ptolyl)L1 and TiNPhL1. Attempts to react the oxo function with a Wittig reagent and carbonyl function are discussed. The reactivity of the vanadyl moiety is investigated and evidence for an imido vanadium species is accumulated using ESR spectroscopy which also provides information concerning the orientation of the unpaired electron in the VOL1 cationic and uncharged dimers. A number of synthetic routes are investigated for the production of manganese thiocyanato complexes and the solvatochromism of the system investigated in a range of solvents. Cyclic voltammetry studies of many of the ligands and complexes prepared are undertaken. Peripheral substitution on the benzenoid and diiminato framework and variation of the metal ion is shown to affect the form of the cyclic voltammogram and the values of the oxidation potentials.


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University of Leicester

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  • Doctoral

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  • PhD



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