Ene addition reactions involving jojoba bean oil (a wax ester), sunflower oil (a triglyceride) and the synthetic fluids polyisobutene and polyalphaolefin have been investigated. Several enophiles have been employed, including azo compounds [diethyl azodicarboxylate (DEAD), 4-phenyl-1-1,2,4-triazoline-3,5-dione (PTAD) and 4-methyl-1,2,4-triazoline-3,5-dione (MTAD)], a sulfinyl compound [<I>N</I>-sulfinyl-<I>p</I>-toluenesulfonamide (TosNSO)] and formaldehyde. In order to investigate the scope of these reactions, and to gain spectral information for use in the analysis of more complex product mixtures, model alkenes were studied. For this purpose, methyl oleate, methyl elaidate and oleyl acetate were chosen, as were the symmetrical simple alkenes 3-hexene and 5-decene, and a series of terminal alkenes. In each case, identification and characterisation of addition products was achieved principally by NMR (<SUP>I</SUP>H and <SUP>13</SUP>C) and FAB mass spectroscopy. Addition of the azo enophiles to jojoba oil and the mono-ene models resulted, in most cases, in the formation of adducts containing an alkene double bond with exclusively <I>trans</I> configuration. The exception to this was the addition of DEAD to 1-alkenes which resulted in adducts with <I>ca.</I> 20% of <I>cis</I> units. Where the lipid ene components were unsymmetrically substituted, the products were formed as 1:1 mixtures of regioisomers, as determined by high field <SUP>13</SUP>C NMR spectroscopy. Kinetic measurements were made on the relative reactivities towards PTAD of methyl oleate, methyl elaidate, jojoba and <I>trans</I>-jojoba by two methods: using UV-visible spectroscopy to follow the consumption of the enophiles and secondly, by monitoring the relative rates of disappearance of lipid components by capillary gas chromatography. These measurements confirmed the visual observation that <I>cis</I> ene components reacted more quickly with PTAD than those with <I>trans</I> geometry. On reaction of the azo compounds with methyl linoleate, three major adduct types were isolated: non-conjugated dienes, conjugated dienes and diadducts resulting from a tandem ene/Diel-Alder cycloaddition. The ratio of these three adduct types was found to vary depending on the enophile. With the triazolines the non-conjugated dienes and tandem diadducts predominated while, conversely, for DEAD the conjugated dienes were the major products.

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This thesis describes a range of investigations undertaken with the aim of increasing insight into alkene dimerization systems formed via reaction of WCI(_6) and an aniline. Chapter 1 introduces alkene dimerization systems based on reaction of WCI(_6) with an amine and an Et(_x)AICI(_2-x) co-initiator. As imido complexes are postulated to form in situ in such WCI(_6) -based dimerization systems, the imido chemistry of group VI has briefly been reviewed. Finally the aims of this work are outlined. Chapter 2 outlines a comparative investigation, examining the capacity of a range of discrete molybdenum and tungsten imido pre-catalysts to initiate ethylene dimerization. This has enabled for the first time direct comparison as to the relative activities of each type of imido complex. With the aim of establishing the nature of the initiator complex formed in situ, a range of discrete imido complexes were reacted with the co-initiators EtAICI(_2) and Et(_3)AI(_2)CI(_3) in the absence of any alkenes. Furthermore, the relative capacities of EtAICI(_2), Et(_3)AI(_2)CI(_3) and EtMgCI to activate mono(imido) complexes for propylene and ethylene dimerization were assessed. Lastly, WCI(_6) was reacted with an aniline using similar conditions to those employed in the preparation of WCI(_6)-based initiator solutions. Chapter 3 outlines the reactions of discrete bis(imido) chloride complexes with Me(_x)AICI(_3-x) reagents. This study was undertaken with the aim of clarifying the mode by which bis(imido) complexes are activated for ethylene dimerization by the co- initiator EtAICI(_2). During this investigation a new class of complexes, with the general formula M(N{Ar}AIMe(_(x-1))CI(_(3-x)){μ-CI})(NAr)Me(_2) (M = Mo or W) were discovered. These dimethyl compounds result from coordination of a Me(_x)AICI(_3-x) (x ≥ 1) fragment to an imido ligand. Furthermore, the reactivity of these new complexes with both Lewis bases and Lewis acids was examined. Finally, a number of ethylene dimerization systems were identified based on bis(imido) complexes. Chapter 4 examines the reactivity of discrete mono(imido) chloride complexes with Me(_x)AICI(_3-x) reagents. It was determined that in contrast to the bis(imido) complexes examined in Chapter 3, coordination of Me(_x)AICI(_3-x) groups to mono(imido) ligands was disfavoured. Instead, a range of adducts were formed via coordination of Me(_x)AICI(_3-x) fragments to tungsten chloride ligands. Next, attention turned to assessing the capacity of Me(_x)AICI(_3-x) reagents to activate mono(imido) complexes for ethylene dimerization. All the experimental details and supporting information and data for this thesis are presented in Chapter 5. In Chapter 6 further possible investigations are outlined.

Two recent investigations have shown that an x-chlorine substituent increases S(_N)1 reactivity, but analysis of the trends in E(_A) and (_Δ)S* values in each case, shows that serious discrepancies exist between them. In view of this it was considered that the role of an x-chlorine substituent was still uncertain and it was decided to look into the matter further. Towards this end, the solvolyses of benzyl chloride, benzal chloride, benzotrichloride, diphenylmethyl chloride and diphenylmethylene chloride have been examined in various solvents, over as wide a range of temperatures as possible, consistent with accurate results, it being considered that the mechanism of solvolysis was S(_N)1 in all cases, with the possible exception of benzyl chloride. Analysis of the E(_A) and ΔS* values for the solvolyses of these compounds shows, in the first place, that the sol volysis of benzyl chloride is not straight forward S(_N)1. Its mechanism of solvolysis is discussed in chapter VII where it is concluded that it proceeds by a single, predominantly S(_N)2 mechanism. Further analysis of the E(_A) and ΔS* values (and in some cases AC*(_p) values) of the other compounds, in chapter VI, indicates that the primary role of an x-chlorine substituent in S(_N)1 reactions is electron release, although, as a second order effect it appears to cause an increase in the extent of solvation of the transition state. The disturbing effects in the hydrolysis of diphenyl methylene chloride in aqueous acetone are analysed in part II where it is shown that they can be quantitatively explained, over a wide range of experimental conditions, on the basis of the mass law and ionic strength effects, proposed by Hughes and Ingold, in S(_N)1 reactions. The exceptionally large mass law effect for diphenyl methylene chloride is ascribed to powerful electron release by the x-chlorine atom, so confirming the conclusions reached in part I.

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