The use of rare and expensive noble metals in the chemical industry as organometallic catalysts has grown exponentially in the past few decades due to their high activity, selectivity and their ability to catalyze a wide range of reactions. With this growth in use has also come a proportional growth in concern as these toxic metals inevitably leach into the environment and their negative effects on public health and our ecosystems are becoming better understood. First-row transition metal catalysts provide both environmental and economic benefits as alternatives to these noble metals due to their lower toxicity and cheaper costs. The two-electron chemistry that makes the noble metals so attractive however, is more challenging to accomplish with first-row transition metals. Intelligently designing the ligand scaffold which surrounds the metal can mitigate or even eliminate some of the shortfalls of these first-row metals. Some key features that should be considered when designing a ligand are: 1) a strong chelating ability so the ligand can stay attached to the metal, 2) incorporation of strong donors to favour low-spin complexes, 3) inclusion of hemilabile groups to allow for substrate activation and metal stabilization throughout various oxidation states, 4) redox activity to be able to donate or accept electrons, and 5) inclusion of Lewis base functionalities which are able to assist the substrate activation. Ligands which incorporate these features are known as bifunctional ligands as they can accomplish more than one function in the catalytic cycle. Developing first-row transition metal complexes containing these ligands may enable these species to replicate the reactivity and selectivity generally associated with the precious metals. Being able to replace the noble metals used in industry with these catalysts would have tremendous environmental and economic benefits. The objective of this thesis is to advance the field of bifunctional catalysis by examining the behaviour of two sterically svelte, tridentate SNS ligands containing hard nitrogen and soft sulphur donors when bonded to cobalt. Previous work with iron provides a template of the ligand behaviour to which cobalt can be compared, allowing us to contrast the effects exerted by the different metals. After an introduction to bifunctional catalysis in Chapter 1, Chapter 2 describes the reactivity of the amido ligand, SMeNHSMe, with precursors ranging from Co(I) to Co(III), all of which yielded the 19e- pseudooctahedral cobalt(II) bis-amido complex, Co(SMeN-SMe)2 characterized by 1H NMR spectroscopy, single-crystal X-ray crystallography and cyclic voltammetry. Although this complex has a similar structure as the Fe analogue, the cobalt bis-amido complex did not exhibit the same hemilabile behaviour that allowed for simple ligand substitution of one of the thioether groups. Instead it reacted reversibly with 2,2’-bipyridine while 1,2-bis(dimethylphosphino)ethane (DMPE) and 2,6-dimethylphenyl isocyanide both triggered additional redox chemistry accompanied by the loss of protonated SMeNHSMe. In contrast, protonation gave the cobalt(II) amido-amine cation, [Co(SMeNSMe)(SMeNHSMe)](NTf2), which allowed for substitution of the protonated ligand by acetonitrile, triphenylphosphine and 2,2’-bipyridine based on 1H NMR evidence. The ability of Co(SMeNSMe)2 to act as a precatalyst for ammonia-borane dehydrogenation was also probed, revealing that it was unstable under these conditions. Addition of one equivalent of DMPE per cobalt, however, resulted in better activity with a preference for linear aminoborane oligomers using ammonia-borane and, surprisingly, to a change in selectivity to prefer cyclic products when moving to methylamine-borane. Chapter 3 delves into the chemistry of the thiolate ligand, SMeNHS, which formed a new 18e- cobalt(III) pseudooctahedral complex, Co(S-NC-)(SMe)(DEPE), from oxidative addition of the Caryl-SMe bond. Scaling up this reaction resulted instead in formation of an imine-coupled [Co(N2S2)]- anion which was characterized by 1H NMR/EPR spectroscopy, single-crystal X-ray diffraction, cyclic voltammetry and DFT studies. The latter revealed an interesting electronic structure with two electrons delocalized in the ligand, demonstrating the non-innocent nature of the N2S2 ligand. While the analogous iron complex proved to be an effective pre-catalyst for the hydroboration of aldehydes with selectivity against ketones, this behaviour was not observed with [Co(N2S2)]- which gave a slower rate and less selectivity. The knowledge acquired from this thesis work has advanced the field of bifunctional catalysis by extending the application of these two SNS ligands from iron to cobalt, revealing unpredictable differences in reactivity between the metals. By comparing the behaviour of these ligands with iron and cobalt, we gain a better understanding of the chemistry that is accessible by these ligands and the applications for which they may be used. This increased knowledge contributes to our long-term goal of replacing expensive and toxic noble metals with more benign first-row transition metals, improving the sustainability of the chemical industry.

Ligand design in general enables the formation of coordination compounds with multiple functionalities within a single framework. To date, two of the most widely studied ligands are 2,2′:6′,2′′-terpyridine (terpy) and acetylacetone (acac), whose tridentate and bidentate coordination pockets, respectively, enables the formation of metallic complexes with various geometries. The Brusso group had been incorporating imidoyl amidine (ImAm) ligands to build different materials such as organic radicals and fluorescent materials. In particular, the ligands N-2-pyridylimidoyl-2-pyridylamidine (Py2ImAm) and N-2-pyrimidylimidoyl-2-pyrimidylamidine (Pm2ImAm) were recently synthesized and have great appeal to build metallic complexes, as they poses two coordination sites similar to those in terpy and acac. The work presented herein represents the first studies involving the coordination of Py2ImAm and Pm2ImAm as discrete ligands. Our results demonstrate the versatility of these ligand frameworks, in which discrete mononuclear complexes, homometallic and heterometallic polynuclear complexes may be realized. Chapter one serves as a brief introduction to transition metal chemistry and has a comprehensive review of the coordination chemistry of the ImAm ligand framework. In chapter two, the selective coordination of first row transition metals into the bidentate or tridentate sites of Py2ImAm is explored. The formation of these mononuclear complexes is acid-base driven, where a weak acid induces coordination to the tridentate site and a weak base leads to coordination in the bidentate site. Coordination to both sides of Pm2ImAm with manganese or iron is explored in chapter three. The results show the formation of unusual tetranuclear complexes with the metal ions in both low spin and high spin configurations. Chapter four covers the coordination to cobalt, and the formation of polynuclear complexes with different geometries using Pm2ImAm. The magnetochemistry of these cobalt polynuclear complexes is also presented and reveal a single molecule magnet behaviour for one of the complexes. Finally, in chapter five, a one-pot synthesis of copper-manganese heterometallic complexes is presented. Overall, these imidoyl amidine ligands are able to build complexes with different geometries, different electronic configurations (i.e. low or high spin), and different metal ions. These results show a great versatility of ImAm ligands and suggest the future use of these ligands by other research groups.

The coordination- and organometallic chemistry of uranium complexes bearing the non-carbocyclic ancillary ligand XA2 (4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) has been developed as a major focus of this thesis. A number of air-sensitive actinide chloro complexes and alkyl derivatives featuring reactive An–C bonds were prepared, and investigated using a variety of structural and spectroscopic analytical techniques, including X-ray diffraction, NMR spectroscopy, elemental analysis, and electrochemical methods. The research described in this thesis serves to expand the currently underdeveloped, fundamental chemistry of actinide complexes supported by non-carbocyclic (i.e. non-cyclopentadienyl) ligands. For example, the use of the prototypical xanthene-based ligand XA2 has led to neutral dialkyl uranium(IV) complexes which a) react with alkyl anions to yield anionic trialkyl ‘ate’ complexes, b) C–H activate neutral pyridines to yield organouranium(IV) species featuring cyclometalated pyridine-based ligands, and c) react with Lewis acids to yield rare examples of cationic monoalkyl uranium(IV) complexes featuring coordinated arene ligands. By altering the nature of the arene solvent/ligand, latent catalytic ethylene polymerization behaviour has also been unlocked in cationic XA2 uranium and thorium complexes, and this development may offer industrial relevance. Additionally, new NON-donor ligand designs featuring bulky terphenyl-based substituents (the "XAT" ligand) as well as 1-adamantyl groups (the "XAd" ligand) have been developed; a family of crystallographically-characterized dipotassium XAT complexes have been prepared which feature unprecedented potassium–alkane interactions, and the XAd ligand has been employed for the development of new organometallic thorium chemistry. The developments described in this thesis contribute to an emerging field and delineate new reactivities and structural motifs, providing important steps forward in organoactinide chemistry. / Thesis / Doctor of Philosophy (PhD)

This thesis presents advancements in the chemistry of selenium-bearing pincer ligands with respect to their synthesis, metal association and reactivity in addition to the overall nature of selenium as a donor atom. The synthesis of a new disilylamido ligand HN(SiMe2CH2SePh)2 2.1 and its potassium salt 2.2 is reported. The attempted metal association of these species was unsuccessful with various transition metals. Multinuclear NMR data suggests coordination to silver(I), 2.3 and copper(I), 2.4 with dπ-dπ back donation from the metal to the selenium donors. It is suggested from this data that –SePh can potentially act as a π-acceptor ligand as well as a σ- donor with heavy d metals. Another explanation for the observed shielding is conformational restrictions introduced by chelation. The preparation of new selenium-bearing diarylamine compounds RN(C7H6SeMe)2 (R=H: 3.1; R= Me: 3.10; R= Boc 3.11) via aryllithium chemistry is reported. Unsuccessful attempts to synthesize the –SePh and –SetBu derivatives are described using: aryllithium chemistry, Buchwald-Hartwig Amination cross coupling and Pd-catalyzed C-Se cross coupling. When reacted with MCl2(COD) (M= Pd, Pt), compound 3.10 coordinates with PdII forming a bidentate complex 3.12, while 3.1 forms tridentate complexes with PdII and PtII. NMR spectroscopy suggests the formation of a silver(I) complex 3.1-Ag from 3.1 and AgOTf, but X-ray diffraction data is required to determine its coordination motif. The new ligands and complexes have been fully characterized by (1H, 13C, 77Se) NMR spectroscopy and X-ray crystal structures are reported for 3.10, 3.12, 3.3 and 3.4. The NMR spectrum of 3.1-Ag exhibits a similar effect as the complexes of disilylamido ligands with suggested potential dπ-dπ back donation from the metal to the selenium donors. The catalytic ability of the new complex 3.3 has been tested in the Suzuki-Miyaura cross coupling reaction without notable improvements to existing catalysts. The instability of reactive intermediates may contribute to the low conversions or the size of the methyl group may decrease nanoparticle formation, a suggested active species. / October 2016

This thesis involves the design and development of reagents for the recovery of base metals (specifically zinc, nickel and cobalt) in hydrometallurgical solvent extraction processes. The work aims to demonstrate how ligand design can affectively tune the strength and selectivity of extractants to achieve efficient recovery of the desired base metals. Chapter 1 reviews current solvent extraction processes used in extractive metallurgy, encompassing both the well established technologies developed for sulfate streams as well as those more recently explored for treating chloride streams. Also reviewed, is the nature of the chemical binding involved in the three key modes of extraction; namely cation transport, anion transport and metal salt transport. Chapter 2 summarises the methodologies that have been established during this research for the appropriate testing of these reagents. Chapter 3 deals exclusively with the processing of zinc sulfide ores with an aim to design reagents to achieve concentration and separation of zinc in chloride hydrometallurgical circuits. The amido functionalised reagents that are reported have a common structural feature with ligands that have been previously studied by the Tasker group (Ross J. Ellis Thesis, University of Edinburgh, 2009). A six membered chelate ring is formed by a protonated amino nitrogen atom and an amido oxygen atom in a sequence of the type R2HN+-CH2-NR-CO-R. This differs from those previously studied which have a sequence of the type R2HN+-CH2-CHR-CO-NR2. The pro-ligands (L) operate via an anion exchange mechanism (Equation 1) whereby two protonated ligands (LH+) coordinate to the outersphere of anionic zinc(II) or iron(III) chloridometalates from acid chloride solutions using both N-H and C-H hydrogen-bond donors. pH dependent solvent extraction experiments have concluded that this reagent series achieves zinc(II) loading with pH0.5 values that are competitive with the previous ligand series (Ross J. Ellis Thesis, University of Edinburgh, 2009). Chloride concentration dependent solvent extraction experiments have demonstrated that the reagents show an unusually good selectivity for ZnCl4 2- over chloride or FeCl4 - in equilibrium of the type; yLorg + yH+ +MClx y- ⇌ [(LH)yMClx](org) (1) The development of bidentate and tridentate pyrazolone-based pro-ligands for the extraction of nickel and cobalt from mixed metal sulfate streams is considered in Chapters 4 and 5. These reagents (LH) operate via metal cation transport, where an inner-sphere complex of nickel(II) or cobalt(II) is formed with the ligand (L-) see Equation 2. A combination of N, O and S donors has been incorporated into 1-phenyl-3-methyl-4- acylpyrazol-5-ones and their respective 4-acylpyrazolone oximes in order to tune the bidentate ligands (L-) for optimal coordination with nickel(II) or cobalt(II). Substituent effects have also been investigated, by synthesising a series of 1-(2-X-phenyl)-3-methyl-4- acylpyrazol-5-one oximes [X = Cl, H]. Substitution in the 3-position of the phenol group in phenolic oximes has been reported to increase extractant strength for copper by two orders of magnitude (Ross S. Forgan Thesis, University of Edinburgh, 2008). Similar improvements were not observed in this study. The nature of this effect has been attributed to buttressing of hydrogen-bonds, where the substituent forms a stabilising, bifurcated hydrogen-bond between the oximic hydrogen and the pyrazolonic oxygen. yLHorg + My+ ⇌ [(L)yM]org + yH+ (2) Tridentate analogues of the oxime reagents above have been prepared as imines derived from anilines contained o-O, S or N donor atoms. It was hoped that these would give high spin octahedral nickel(II) complexes in extraction processes. They proved to be weak extractants. Chapter 6 focuses of the development of bidentate pyrazolethiones for the selective extraction of cobalt from manganese in acidic sulfate streams. These reagents have been designed to favour coordination to metals in a tetrahedral geometry as shown by L. Emeleus and A. Smith for copper and zinc (Lucy Emeleus Thesis, University of Edinburgh 1999 and Andrew Smith Thesis, University of Edinburgh 2000).

Long relegated to the background by the pre-eminence of magnesium-based, stoichiometric Grignard reagents, a distinct chemistry of the heavier alkaline earth metals, calcium, strontium and barium, is only now starting to emerge. As similarities have been drawn between the large, electropositive, redox-inert and d0 alkaline earth Ae2+ dications and the Ln3+ cations of the lanthanide series, a growing group 2-mediated catalytic chemistry has developed over the last decade, including polymerisation reactions, heterofunctionalisation reactions of multiple bonds and some rare examples of dehydrocoupling reactions. Among these catalytic reactions the magnesium- and calcium-catalysed intramolecular hydroamination of aminoalkenes has attracted particular interest. Mechanistic studies have demonstrated many parallels with the lanthanide-mediated catalytic cycle based upon successive σ-bond metathesis and insertion steps. In the first part of this thesis, further investigations into the hydroamination/cyclisation reaction have demonstrated the prominent role of the charge density of the catalytic group 2 cation (M = Mg, Ca, Sr, Ba), the beneficial influence of stabilising spectator ligands, and the importance of the choice of the reactive co-ligand for efficient catalyst initiation. Kinetic analyses of reactions monitored by NMR spectroscopy have given new insight into activation energies, entropic effects, substrate and product inhibition, and kinetic isotope effects, leading to a review of the previously suggested lanthanide-mimetic mechanism. In a second part, this study seeks to address two of the main challenges posed by the intramolecular hydroamination reaction in particular, and heavier alkaline earth-catalysed reactions in general: (i) The need to design new monoanionic spectator ligands capable of stabilising heteroleptic heavier alkaline earth complexes and preventing deleterious Schlenk-type ligand redistribution processes in solution; (ii) The stabilisation of highly reactive heteroleptic group 2 alkyl functionalities for fast, irreversible catalyst initiation and novel reactivity.

La preparación de nuevos ligandos quirales P-OP (fosfina-fosfinitos y fosfina-fosfitos), fácilmente preparados con una estrategia sintética en dos etapas desde una aproximación covalente, es descrita en la presente Tesis Doctoral. El mejor catalizador de la serie ha demostrado tener propiedades catalíticas excelentes en la hidrogenación asimétrica catalizada por rodio de una amplia variedad de olefinas funcionalizadas. El resultado excelente y el diseño modular de los ligandos sintetizados hacen éstos muy atractivos para futuras aplicaciones.La presente Tesis Doctoral describe también la preparación de nuevos ligandos quirales que pueden comportarse como catalizadores supramoleculares inspirados en el mecanismo de regulación alostérica de los enzimas. / A library of enantiomerically pure P-OP ligands (phosphine-phoshinites and phosphine-phosphites) straightforwardly available in two synthetic steps from enantiopure Sharpless epoxy ethers is reported in the present PhD. Thesis. The "lead" catalyst of the series has proven to have outstanding catalytic properties in the rhodium-catalysed asymmetric hydrogenation of a wide variety of functionalised alkenes. Their excellent performance and modular design makes them attractive for future applications.This PhD. Thesis also reports the development of a practical route to chiral diphosphine ligands with supramolecular motifs, with potential for allosteric modulation, which we prepared for future catalytic studies.

Bioisosterism is a field that is widely applied to biological molecules, including drugs and agrochemicals. Bioisosterism is the replacement of an active fragment in a molecule with another fragment similar in activity. The replacement is designed to alter the behavior of the molecule in its target environment. In previous work a bioisostere database called the Quantum Isostere Database (QID) was built out of descriptors derived from the theory of Quantum Chemical Topology (QCT). The current work aims to expand the existing QID to include ring fragments. A series of rings were characterised by QCT properties taken from the ring. It was found that four features of a ring each independently have a systematic effect on the ring’s properties. In other words, each of the characteristics of a ring can be changed and have the same effect on the ring’s properties irrespective of the other ring features. The rings were also characterised using the three QCT properties taken from a point within the ring. The three properties established a space where rings were positioned based on their respective three properties. The positions of the rings showed that the space was able to discern between ring types, and that the features of a ring could be predicted if only its three properties were known. To improve the QID the alignment method and scoring were tested. The alignment procedure is unable to correctly align collinear fragments. Therefore, a principal axis alignment procedure was successfully employed to align collinear fragments. For terminal fragments an alternative alignment procedure was proposed to account for the increased rotational freedom. A global axis system meant that the direction dependent properties for all fragments were expressed in this new axis system. This idea was extended further and it was found that the geometry of a molecule was imprinted in the electrostatics when they were expressed in the global axis system. Finally, a pKa prediction method which correlates a single ab initio bond length was tested against two data sets (enols and guanidines). The method relies on subsets to form, where molecules within a subset share a chemical or structural commonality. These subsets were able to distinguish between the five tautomeric forms for the guanidines and different conformations for the enols. All predictions were within 1.0 pKa units of experimental values.

The current project examined the ability of a novel series of guandine and amidine-containing nicotine analogs to interact with several native and recombinantlyexpressed mammalian neuronal nicotinic-acetylcholine receptor (nAChR) subtypes. Rational drug design methods and parallel organic synthesis was used to generate a library of guanidine-containing nicotine (NIC) analogs (AH compounds). A smaller series of amidine-containing nicotine analogs (JC compounds) were also synthesized. In total, >150 compounds were examined. Compounds were first assayed for affinity in a high-throughput [3H]epibatidine radioligand-binding screen. Lead compounds were evaluated in subtype-selective binding experiments to probe for affinity at the α4β2* and α7* neuronal nAChRs. Several compounds were identified which possess affinity and selectivity for the α4β2* subtype [AH-132 (Ki=27nm) and JC-3-9 (Ki=11nM)]. Schild analysis of binding suggests a complex one-site binding interaction at the desensitized high-affinity nAChR. Whole-cell functional fluorescence (FLIPR) assays revealed mixed subtype pharmacology. AH-compounds were identified which act as activators and inhibitors at nAChR subtypes, while lead JC-compounds were found which possess full agonist activity at α4β2* and α3β4* subtypes. Compounds were identified as partial agonists, full agonists and inhibitors of multiple nAChR subtypes. Several SAR-based, ligand-receptor pharmacophore models were developed to guide future ligand design. Second-generation lead compounds were identified.

For the purpose of incorporating indoles into organometallic complexes for catalysis, as well as in the generation of new heterocyclic systems, various reactions have been carried out at C2, C6 and C7 of the indole system. In order to achieve this, 3-substituted 4,6-dimethoxyindoles and 6-hydroxy- 4-methoxyindoles were necessary as starting materials. Consequently, a lithium-bromide-templated one-pot procedure for the synthesis of some 3-substituted 4,6-dimethoxyindoles and a selective demethylation procedure for 3-substituted 6-hydroxy-4-methoxyindoles were developed. Various kinds of novel methylene-bridged bi-, tri-, and tetradentate pyridyl-indole ligands were synthesised via Vilsmeier-Haack, Friedel-Crafts or electrophilic addition reactions on the indole heterocycle. However, their metal complexing properties were generally weak and variable. Nevertheless, some of the tridentate pyridylindole ligands showed strong anion binding to halides, whereas a remarkable ligand transformation occurred with a bidentate 2-pyridylindole ligand and zinc(II), giving a substituted indolo[2,3-c]pyrrolo-[3,2,1-ij]quinoline system. Two new types of tetradentate Schiff base ligands were prepared from 2-formyl-indoles and 7-formyl-6-hydroxyindoles, and diamines. These preformed ligands were reacted with first- and second-row transition metals to give neutral metal complexes. Novel heterocyclic systems such as 4H-pyrrolo[3,2,1-ij]quinolines, 3H-pyrrolo-[1,2-a]indoles, and 1H-furo[2,3-g]indoles were synthesised from 2-formyl-, 7-formyl-, and 6-hydroxyindoles, utilising mainly intra-molecular Wittig reactions, Claisen-Schmidt condensations or acid- and base-catalysed cyclisations. A common feature of the prepared 4H-pyrrolo[3,2,1-ij]quinolines and 3H-pyrrolo-[1,2-a]indoles was their intense fluorescent character, which was examined as well.