Reactions of metal complexes with Lewis bases and their utilisation in the selective filtration of smoke
This thesis is concerned with internal redox reactions of metal complexes and the application of such reactions in the selective filtration of tobacco smoke. The reactions of Fe(II), Fe(III) and Cu(II) quinoneoximic complexes and of some other complexes of these metals with Lewis bases (e.g. Ph3P and py) have been investigated. From the results obtained and from a critical consideration of analogous reactions reported in the literature the behaviour of metal chelates towards Lewis bases has been assessed. It has been established that the reaction between a metal chelate and a Lewis base may lead to: (i) Adduct formation, (ii) condensation and (iii) to an internal redox reaction, M(chel)n LB[over arrow] M(chel)n-1(LB)x + chel* The latter is favoured when the metal in M(chel)n has a stable lower oxidation state, by Lewis bases capable of E[eta]—bonding and by chelating ligands exerting a strong ligand field. The type of behaviour shown by chel* has been considered. The dissociated radical may: (i) Abstract a hydrogen atom to give the protonated ligand, (ii) dimerise, (iii) undergo coupling or degradation. A detailed investigation of the reactions of Fe(l-nqo)3 and Fe(2-nqo)3 with Ph3P (including kinetic studies) showed that these complexes undergo internal redox reactions to give iron(II) complexes and products arising from the deoxygenation of the nqo* radical. Mechanisms for these resctions have been proposed. The behaviour of quinoneoximic complexes of iron towards the Lewis base CO has been examined both directly and indirectly by studying the behaviour of nqoH towards Fe(CO)5 or Fe(CO)5/PhNH2. Fe(CO)5 and 1-nqoH or 2-nqoH afforded complexes of the type Fe(nqo)2, without formation of CO adducts or deoxygenation products. In the presence of PhNH2 complexes of type Fe(nqo)2 and Fe(nqo-A)2 resulted, where nqo-A is a species arising from the coupling of the nqo ligand with PhNH2. Both systems also afforded various organic products. On the basis of Mossbauer and other techniques oligomeric structures have been suggested for the complexes Fe(nqo)2 and Fe(nqo-A)2. Whereas CO did not react with Fe(nqo)2 or Fe(nqo)2.2py, it reacted with Fe(nqo)3, possibly via an internal redox process. For Fe(2-nqo)3 products arising from a deoxygenated ligand and a complex tentatively formulated as the nitrene species, Fe(2-nq)2, were isolated. The reactivity of the Fe(nqo), complexes towards CO has been successfully utilised in the selective filtration of tobacco smoke. Both Fe(1-nqo)3, and Fe(2-nqo)3 were shown to be capable of significantly reducing the level of CO in tobacco smoke under smoking conditions when supported on suitable filters. Reduction of the levels of other Lewis bases in tobacco smoke, e.g. nicotine and furfural, was observed. The complexes Fe(nqo)2, Fe(nqo)2.2py and Fe(nqo)3 reacted readily with NO to give complicated mixtures, but their effectiveness in removing NO from tobacco smoke has not been unambiguously established.
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