The novel complexes [special characters omitted] and [special characters omitted] were prepared and characterized. Photoredox quantum yields for the formation of [special characters omitted] from the above compounds were measured on irradiation at 360 nm to be 0.065, 0.082, 0.0088 and 0.0040 respectively. With added thiocyanate a significant increase in ΦCo2+ occurred. This can be modeled in two ways; (i) scavenging of thiocyanate radical from an initial caged radical pair giving 6-25 ps estimates for the lifetime of the latter species; (ii) photolysis of a thiocyanate/complex ion pair, giving formation constants of 0.19, 0.09, 0.08 and 0.05 for the complexes [special characters omitted] and [special characters omitted] respectively. Subnanosecond laser flash photolysis studies showed evidence for the formation of [special characters omitted]. The effects of added electrolytes and of viscosity on the formation and decay of [special characters omitted] were also investigated. To help to distinguish between the above two mechanisms, the zero-charged novel complex [special characters omitted] (tacn = 1,4,7-triazacyclononane) was synthesized and characterized. It is thermally stable in aqueous/DMSO solution, but on irradiation at 360 nm undergoes parallel photosubstitution to form DMSO and aqua-substituted products with an overall quantum yield of 0.012. The product yields increase linearly with added thiocyanate. For a 1 M thiocyanate solution, the quantum yield for disappearance of the starting complex rose to 0.022 and a small redox yield of 0.0008 was found. Under these same conditions, ns laser flash photolysis at 355 nm revealed a transient absorption owing to [special characters omitted], which was produced with a quantum yield of 0.036. These results are interpreted in terms of scavenging of radical pair species by thiocyanate ion followed by back electron transfer to give a photosubstituted product, and a radical pair quantum yield of 0.29 and lifetime of 12 ps was derived. The emission of [special characters omitted] (where pop = μ-pyrophosphite-P,P’) can be quenched by the complexes [special characters omitted] (where X = [special characters omitted]) only in the presence of electrolytes. The salt effects have been studied using the salts MCl, M'Cl2, or [special characters omitted] (where M, M’ and R represent alkali, alkaline earth metals, and alkyl respectively, with n = 0-3), and [special characters omitted]. For 0.5 M cation concentration, second-order quenching rate constants kq lie in the range [special characters omitted]. For the different quencher complexes used, kq decreases in the order [special characters omitted]. The oxidative quenching products [special characters omitted] are observed, and their quantum yields are 0.083 and 0.027 respectively for the reaction of [special characters omitted] with [special characters omitted] and [special characters omitted] in 0.5 M KCl / pH2 solution. The quenching occurred by atom transfer (dominant) and electron transfer (minor) for quencher [special characters omitted] or [special characters omitted], while only electron transfer was observed for [special characters omitted] and [special characters omitted] quenchers. The quenching efficiency of the cobalt complexes increases with electrolyte concentration and specific cation effects are observed in the kq with the following trends Li+ < Na+ < K+ < Cs+: Mg2+ < Ca2+ < Sr2+ < Ba2+; NH4+ < MeNH3+ < Me2NH2+ < Me3NH+: Et3NH+ < Et2NH2+ < EtNH3+: n-PrNH3+ < EtNH3+ < MeNH3+. / Graduate

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Bibliography: pages 136-140. / This thesis set out to investigate the activity of various supported cobalt catalysts for high pressure propene oligomerization. This work was carried out as part of a larger research effort to upgrade light olefins to liquid fuels in the distillate range. The supports investigated included activated carbon, alumina, silica alumina, synthetic mica montmorillonite, zeolite Y and NH₄⁺-ZSM-5. A cobaltmolybdenum hydrodesulphurization catalyst was also tested. The synthesis procedures used in this work included double ammoniation (Co-C), incipient wetness impregnation (Co-C, alumina, NH₄⁺-ZSM-5), ion-exchange (NaY, NH₄⁺-ZSM-5), chemisorption (cobalt complex on activated carbon) and homogeneous deposition-precipitation (Co-Silica alumina).

Cross-coupling, which relies on the use of transition metals, is among the most utilized chemical means of establishing carbon-carbon or carbon-heteteroatom bonds between appropriately functionalized sp, sp2, or sp3 centres. However, most cross-coupling reactions rely on the use of palladium to synthesize valuable synthetic targets. This is problematic for the chemical industry as palladium is limited in supply and expensive. Chemists have therefore sought to replace palladium with first-row transition metals (e.g., iron, cobalt and nickel) and recent reports on cobalt and nickel catalyzed cross-coupling reactions indicate that these metals can be used in this capacity. Unfortunately, protocols developed (so far) for these metals are unsuitable for the synthesis of targets with base-sensitive functional groups as they involve strongly basic reaction conditions. Research in this thesis aims to develop both cobalt and nickel pre-formed catalysts that will display high catalytic activity in mildly basic reaction conditions. Current methodologies for cobalt and nickel cross-coupling reactions use either phosphine ligands or NHC ligands of moderate steric bulk (IMes or IPr). Recent advancements in the development of Pd-PEPPSI catalysts have demonstrated that both pre-forming the catalyst and using larger NHC ligands (IPent, IPentCl, or IHept) are required for high catalytic activity in weakly basic conditions. Thus, it was hypothesized that the development of pre-formed cobalt and nickel NHC complexes analogous to their Pd counterparts would improve reactivity in Negishi, Suzuki-Miyaura, and Buchwald-Hartwig amination cross-coupling reactions. Co(IPent)Cl2(Pyr), Co(IPentCl)Cl2(Pyr), and Co2IPr2(OAc)4 were prepared, identified by X-ray crystallography, and evaluated in preliminary Negishi cross-coupling reactions. These complexes were found to be ineffective, but Co2IPr2(OAc)4 was found to be effective for Suzuki-Miyaura cross-coupling. A base screen was performed to enable the use of weak bases, however, the reaction only worked by pre-forming the boronate with n-BuLi, rendering the reaction conditions intolerant of base-sensitive functional groups. [Ni(IPr)]2(µ-Cl)2 , Ni(IPr)Cl(allyl), and Ni(IPent)Cl(allyl) complexes were synthesized and evaluated in Buchwald-Hartwig aminations. Several bases were examined for these reactions but only sodium tert-butoxide was found to be effective. The presence of TEMPO and BHT in these transformations proved deleterious suggesting the involvement of radical intermediates. Finally, stoichiometric reactions were performed to isolate intermediates in the catalytic cycle, supporting the formation of nickel(0).

The instability constant of a substance shows the tendency of a substance to dissociate into simple ions. The stability of the substance can be related to stabilities of other substances through the instability constant. Schubert gives a method for the determination of the instability constant which involves measurements of the adsorption of a radiotracer cation on a cation exchange resin. Two different types of resin were employed in this research. It was found that with a resin containing carboxylic acid exchange groups the adsorption of the cobaltous ion changed rapidly with pH but with a resin containing nuclear sulfonic acid as the exchange group, the adsorption of the cobaltous ion changed very little with pH. The presence of an exchange resin in an equilibrium presents the problem of activity of the resin. Boyd's approach to the activity of the resin using the law of mass action was applied to the resin and cations used in this research. The data obtained in this research supported Boyd's approach to the activity of resins. The activity coefficients of the ions in solution were calculated using the Debye Huckel theory. Measurements of actual activity coefficients were not taken. Schubert's method was applied to two complex ions of cobalt using cobalt-60 as a tracer. The pK of the instability constants of the cobaltous citrate and cobaltous oxalate complex ions were determined to be 6.39 and 4.61 respectively. Hydrolysis of the complexing anion into an inactive form changed the pK of the instability constant of the oxalate complex ion 1.5 per cent and the citrate complex ion 7.8 per cent. Precautions were taken at all times during this research to avoid the dangers of radiation to personnel and equipment.

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