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The luminescent properties of transition metal complexes containing polypyridyl and cyclometalating ligands make them potential candidates for a range of applications; for example, as triplet-harvesting agents in organic light-emitting devices (OLEDs), owing to the potentially high quantum yields of triplet emission; in solar cells, converting light to electrical energy; and as sensors and probes in biological systems. The synthesis of a series of [M(NCN)(X^X^X)]’^n^+’ and [M(NCN)(X^X)C1](^n+) coordinated complexes (where M = Ir or Rh; X = heterocyclic N or cyclometalated aryl C; and n = 0-2) bearing pyridyl and pyrazolyl-based NCN-coordinating ligands (cyclometalating through the central phenyl ring) is reported, alongside their photophysical and electrochemical properties. Whilst luminescence was generally observed from the pyridyl-based iridium(III) complexes at ambient temperature, the charge-neutral Rh(III) complex [Rh(NCN)(NC)Cl] was the only complex amongst those containing a rhodium centre to be emissive under these conditions. Similarly, the pyrazolyl Ir(III) complexes exhibit lower luminescence intensities than their pyridyl analogues, owing to the poorer Ti-accepting ability of the pyrazole rings which results in a blue-shift in the emission profile and more ligand-based character. In addition to the synthesis of these complexes, a sequential cross-coupling - bromination - cross-coupling strategy has been developed for the linear stepwise expansion of an [Ir(NCN)(NNC)(^+) coordinated complex, incorporating a pendant bromophenyl group on the central pyridyl ring of the NNC ligand, via in situ palladium- catalysed Suzuki cross-coupling reactions with aryl boronic acids. This strategy has-been further extended to the controlled synthesis of linear multimetallic assemblies using boronic acid appended Ir(III) and Ru(II) complexes. A heterometallic trinuclear [Ir-ɸ-Ir- ɸ (_2)-Ru](^4+) assembly was prepared, where the phenylene bridges between the metal centres do not contribute to the excited state of the trimetallic system, and efficient energy-transfer occurs to the lower energy ruthenium terminus. The emissive and energy-channelling properties of such multimetallic assemblies can be tailored by the careful choice of the constituent "building blocks”.

In Chapter One, a background to the application of binucleating ligands in biomimetic chemistry sets the scene for a comprehensive discussion of homogeneous catalysis in the field. Chapter Two describes the strategies employed for the preparation of sterically encumbered multidentate oligopyridylimine ligands. In Chapters Three and Four, the new oligopyidylimine ligands prepared in Chapter Two are treated with divalent metal halides (iron, cobalt, nickel, zinc) and the resultant complexes fully characterised. Specifically, Chapter Three focuses on the reactivity of the potentially pentadentate ligands [bis(imino)terpyridine and imino-quaterpyridine] while Chapter Four concentrates on the resulting coordination chemistry of the potential tetra-, hexa- and hepta-dentate ligands [imino-terpyridine, bis(imino)quaterpyridine and bis(imino)quinquepyridine]. In both chapters, theoretical calculations (DFT) on pre-identified complexes are used in order to investigate the effect of the R substituent (H vs. Me) and metal centre on the coordination chemistry of the ligand. To conclude the synthetic work, the screening for polymerisation or oligomerisation of ethylene is systematically investigated with a selection of the new complexes. In Chapter Five, the synthesis of multidentate ligands featuring sterically encumbered imino-pyridine end-groups linked by phenyl-, thiophene- and phenolate-spacers is studied. The new (pro)ligands are fully characterised and their coordination chemistry with the same series of divalent metal halides is investigated. Furthermore, derivatisation of pre-identified bimetallic complexes is performed. Finally, a selection of the bimetallic compounds is screened as precatalysts for the oligomerisation and/or polymerisation of ethylene.

Chapter 1 provides an introduction to metalloenzymes that either feature active sites containing Ni-thiolate ligation or utilise phenoxyl radicals to perform their catalytic function, with a particular emphasis on the enzymatic active sites of Ni-containing superoxide dismutase (Ni SOD), [NiFe] hydrogenase and galactose oxidase. Studies concerning low molecular weight complexes of each active site are reviewed and their relevance with respect to enzyme function discussed. Details of the project outline conclude the chapter. Chapter 2 details the syntheses and characterisation of the [Zn(tsalen)] derived complexes [ZneBuLsC3N)], [ZneBuLsC2N)], [ZneBuLsNMe)], [ZneBuLlyl)], [Zn(IBuLsPy2)], [ZneBuLsPhl)], [Zn(IBuLslml)2], [ZneBuLsPy3)2], [Zn(LsC2N)], [Zn(LsNMe)], [Zn(Llyl)], [Zn(LsPy2)] and [Zn(LsPh1)], via Zn(II) templated Schiff- base condensation reactions using two thiosalicylaldehyde derived units and a range of primary amines. The syntheses of 2,4-di-tert-butyl-thiosalicylaldehyde from tert- butyl benzene and three functionalised 1,3-propyldiamines (2-(2-pyridylmethyl)-1,3- propanediamine, 2-(2-pyridylethyl)-I,3-propanediamine and 2-benzyl-I,3- propanediamine) are described. X-ray crystallographic studies demonstrate the successful integration of the additional N-donors into the backbone of the ligand framework at the N-imine position. The range of S2N2, S2N3 and S2N4 ligand sets are shown to adopt an array of coordination geometries about the Zn(II) metal centre providing scope for these ligands in tuning the electronic structures of their Ni- containing complexes. Chapter 3 describes the syntheses and X-ray crystallographic, electrochemical and spectroscopic studies of a series of Ni(II) Schiff-base dithiolate complexes, [Ni(IBuLsC3N)], [Ni(IBuLsc2N)], [NieBuLsNMe)], [NieBuLlyl)], [Ni(IBuLly2)], III [Ni(BuLlhl)], [Ni(BuLs1ml)2], [Ni(tBuLly3h]' [Ni(LsPyl)], [Ni(LsPY2)] and [Ni(LsPhl)] obtained via transmetallation from the analogous [Zn(BuLl)] and [Zn(LsR)] complexes described in Chapter 2. The effect that the additional pendant N-donors have upon the redox properties of the individual complexes are considered with respect to reproducing the structural, spectroscopic and functional properties of NiSOD. Particular attention is focussed on the redox properties of [Ni(BuLsPyl)], [Ni(tBuLsPy2)] and [Ni(BuLsPhl)], which together highlight a rare example of the ability of one N-donor group to assume the role of an endogenous donor upon oxidation. The proposed internal rearrangement of the Ni coordination sphere may encourage the formation of a predominantly metal-based SOMO following the oxidation process. Insight upon how this coordination chemistry relates to the chemistry of the active site of Ni SOD is discussed. Chapter 4 reports the electrochemical and spectroscopic characterisation of a range of binuclear [Ni(LsR)Fe(CO)3] and trinuclear [Ni(LsR){Fe(CO)3h] complexes (R = PhI, PyI and Me) synthesised via the reaction of [Ni(tsalen)]-type complexes, [Ni(LsR)], with Fe2(CO)9. X-ray crystallographic studies show that the complexes incorporate biologically relevant structural elements reminiscent of the active site of [NiFe] hydrogenase, including a binuclear Ni(1l2-S)Fe core featuring a ea. 2.9 A Ni- Fe separation. Chapter 5 details the preparation of a series of Zn(II), Ni(lI) and Cu(lI) Schiff-base diphenolate complexes utilising the two novel pentadentate pro-ligands, [H2tBuLo C3N] and [H2tBuLo NMe]. Cyclic voltammetric, spectroelectrochemical and EPR studies show the Zn(lI) and Cu(lI) complexes support two ligand-based oxidation processes, yielding kinetically inert species possessing phenoxyl radical character. Conversely, the paramagnetic Ni(lI) complexes, [Ni(BuLo NMe)] and IV [Ni(tBuLo C3N)], support both metal and ligand-based oxidation chemistry. The chapter concludes by discussing the relative stability of phenoxyl and phenylthiyl radical ligands by comparison with the redox properties of the analogous Schiff-base Zn(II)-dithiolate complexes described in Chapter 2.

Abstract Chapter one introduces this thesis with a brief overview of macrocyclic chemistry and provides examples of macrocyclic complexes as well as briefly discussing the applications of macrocyclic complexes, the macrocyclic effect and the co-ordination chemistry of sulfur-based macro cyclic transition metal complexes. The concepts of paramagnetism and Jahn- Teller distortion are approached with respect to the target metal oxidation states Ni(III), Pt(III) and Pd(III). The overall aim of the work presented in this thesis is also stated. Chapter two continues from the concept of paramagnetism briefly discussed in chapter one and describes the technique of EPR spectroscopy and the energy terms associated with the EPR spin Hamiltonian such as the electron Zeeman interaction (g) and the hyperfine and superhyperfine coupling parameters (A, a). The limitation of this technique is discussed in terms of observed hyperfine splitting and the technique of ENDOR spectroscopy is introduced. Chapter three describes the chemistry of Ni(III) macrocyclic complexes and a brief history of 61Ni EPR spectroscopic studies. The Ni(II) complexes [Ni([9]aneNS2-CH3)2]2+ ([9]aneNS2-CH3 = N-methyl-l-aza-4, 7 -dithiacyclononane), 1 2-bis-(1-aza-4 7- , , dithiacyclononylethane), [Ni([9]aneS3)2]2+ ([9]aneS3 = 1,4,7 -trithiacyclononane) and I-phenyl-l-phospha-4,7- dithiacyclononane) have been prepared and can be chemically oxidized to gave the formal Ni(III) products [Ni([9]aneS3)2]3+, [Ni(bis[9]aneNS2-C2H4)]3+ and [Ni([9]aneNS2-CH3)2]3+ and [Ni([9]aneS2P-C6Hs)2]3+ which have been characterized by multi-frequency EPR spectroscopy. The multi-frequency X-, L-, S-, K- and Q- [Ni([9]aneS3)2]3+ and their 86.2% 61Ni-enriched analogues as both fluid and frozen 11 Abstract solutions were simulated. Treatment of the spm Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6%, 42.8% and 37.2% Ni 3dz' character m and [Ni([9]aneS3)2]3+ respectively, consistent with DFT calculations and reflecting delocalization of charge onto the S-thioether centres. EPR spectra for C8Ni([9]aneS3)2]3+ and [61,S8Ni([9]aneS3)2]3+ are consistent with a dynamic Jahn- Teller distortion in this compound. In contrast to [Ni([9]aneNS2-CH3)2]3+, [Ni(bis[9]aneNS2-C2H4)]3+ and [Ni([9]aneS3)2]3+, DFT calculations on [Ni([9]aneS2P-C6Hs)2]3+ reveal that the SOMO for this complex has 30.9% Ni 3dxy character. Chapter four details the chemistry of Pt(III) and that of Pt(II) macrocyclic complexes. The Pt(II) complexes [Pt([9]aneS3)2]2+ ([9]aneS3 1,4,7- trithiacyclononane), [Pt([18]aneS6)]2+ ([18]aneS6 1,4,7,1 0, 13, 16- hexathiacyclooctadecane) and [Pt([ 1 0]aneS3)2f+ ([ 1 0]aneS3 1,4,7- trithiacyclodecane) have been synthesised. The electrochemical two electron oxidation of [Pt([9]aneS3)2]2+ to [Pt([9]aneS3)2t+ in MeCN [0.2 M NBli4PF6, vs. Fe + IFc, N2, chemically reversible at 243 K] proceeds via an unusually stable [Pt([9]aneS3)2]3+ intermediate [E« = +0.37 V vs. Fc+IFc, ~E = 142 mY, A = 396 nm (5700)]. Single crystals of [Pt([9]aneS3)2](PF6kMeCN were grown from a solution following a limited one electron electrochemical oxidation of the parent Pt(II) complex [Pt([9]aneS3)2]2+. [Pt([9]aneS3)2](PF6)3.MeCN possesses a distorted octahedral geometry consistent with a J ahn- Teller distorted low-spin 5d7 Pt(III) centre. Multi-frequency EPR spectroscopy of chemically-generated [Pt([9]aneS3)2]3+ in HCI04 at Q-, X-, S- and L-band show that [Pt([9]aneS3)2]3+ undergoes a dynamic Jahn-Teller distortion in solution which was minimised at 80 K to reveal rhombic parameters. Treatment of the Spin Hamiltonian reveals that the Pt Sd» orbital iii Abstract contribution to the SOMO of this Pt(III) species, supported by DFT calculations is :S 30.4% and reflecting the non-innocence of the thioether crown macrocyc1e. In addition to this, DFT calculations identify significant spin density on four protons pendant to the macrocyc1ic backbone. The couplings associated with these protons were confirmed by S- and X-band EPR spectroscopy and studied further by double resonance methods to reveal that these protons interact with the Pt 5dz2 orbital through an orbital through-bond interaction. A comparative multi-frequency EPR spectroscopic study was undertaken on the chemically-generated complexes [Pt([18]aneS6)]3+ and [Pt([10]aneS3)2]3+ in 70% HCl04. Interpretation of the spin Hamiltonian parameters reveals that the Pt 5dz> orbital contributions to the SOMOs of these Pt(III) species are :S23.8%. Pt(III) solid state structures were unobtainable for [Pt([18]aneS6)]3+ and [Pt([10]aneS3)2]3+, but attempts to isolate [Pt([l 0]aneS3)2]3+ led to the isolation of the octahedral Pt(IV) complex [Pt([l 0]aneS3)2] (Cl04k(H30)2 [Pt- S = 2.3610(11), 2.3552(10), 2.3792(11) A]. Chapter five begins with a discussion of Pd(III) chemistry and the chemistry of Pd(II) with macrocyc1ic ligands. The Pd(II) complexes [Pd([9]aneS3)2]2+ ([9]aneS3 = 1,4,7-trithiacyc1ononane) and [Pd([18]aneS6)f+ ([18]aneS6 = 1,4,7,10,13,16- hexathiacyc1ooctadecane) have been prepared and can be chemically oxidized to gave the formal Pd(III) products [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+, which have been characterized by X-ray crystallography and multifrequency EPR spectroscopy. The single of crystal X-ray structures distorted octahedral stereochemistries for the Pd centres with Pd-S distances of [2.3692, 2.3695(8), 2.5356(9) A] and [2.3454(5), 2.3490(6), 2.5474(6) A] respectively, consistent with the Jahn- Teller distorted geometry expected for d7 Pd(III) complexes. Further to the chemical oxidation, [Pd([9]aneS3)2](PF6)2 shows a iv Abstract one-electron oxidation process in MeCN [0.2 M NBll4PF6, 293 K] at Ey, = +0.57 V vs. F c + IF c assigned to a formal Pd(III)/Pd(II) couple. Multi-frequency EPR spectra of [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+ as both fluid (X-band) and frozen (Q-, X-, S- and L-band) solutions were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 21.8% and 25% Pd character in [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+ respectively, consistent with DFT calculations and reflecting the significant electronic charge distributed over the S-thioether centres. Both [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+ exhibit a clear five line superhyperfine splitting in the g== region in the EPR spectra. Double resonance spectroscopic measurements supported by DFT calculations have shown that four protons pendant to the macrocyclic backbone give rise to this feature through a through-bond interaction with the Pd 4dz2orbital. Chapter six concludes this thesis with a discussion on the overall conclusions to the work on the transition metal macrocyclic complexes presented in this thesis. v

The transition metal-catalysed N-arylation of cyanate salts represents an atom-economical approach to the synthesis of aryl isocyanates and isocyanate derivatives, which are commonly produced using hazardous reagents such as phosgene or azides. This thesis describes the development of copper and nickel-catalysed methodologies for the cross-coupling of aryl halides to commercially available cyanate salts, where reactions performed in the presence of various nucleophiles provide access to a wide range of useful products through intermolecular or intramolecular trapping. Firstly, an effective copper-catalysed system was developed using ligand screening and extensive optimisation work, allowing for the synthesis of aromatic carbamates, ureas and various heterocyclic compounds from aryl iodides. Though no isocyanates were isolated or detected during these experiments, this approach provided a novel, efficient method for the synthesis of these compounds. The 'reaction conditions were also used in the synthesis of commercial drug molecule Sorafenib, providing phosgene-free access to this valuable product. A nickel-catalysed variant was also developed, allowing for the synthesis of aromatic carbamates and ureas from inexpensive aryl bromides and chlorides, though issues of poor reproducibility meant that the reaction was of limited synthetic value. In the process of these investigations, a novel arylnickel(Il) cyanate complex was synthesised and its reactivity investigated.

The work presented in this Thesis describes the modular design and spectroscopic study of polynuclear systems based on ruthenium (II) and rhenium (I) complexes. A combination of UV/vis, luminescence and TRIR spectroscopies, electrochemistry, spectroelectrochemistry and conformational analysis have been employed to understand the electronic structure of the ground and excited states of these compounds. Chapter I gives an introductory background to this Thesis. An overview of transition metal photophysics and excited states, and the typical spectroscopic and electrochemical techniques used in their study is presented. Previous studies of the ground and excited state properties of the complexes [Ru(bpy)3]2+ and [ReCl(CO)3bpy)] which are used as supramolecular building blocks in this Thesis are presented and a number of relevant studies of supramolecular systems are described. Chapter 2 contains a study extending the known family of [Ru(CN)4(NN)]2- complexes and describes their unique advantages over [Ru(bpy)3]2+. The results obtained are discussed alongside previous studies. This completes the introduction of the molecular building blocks used in Chapters 3 and 4. Chapter 3 details a study of through-space PEnT in bimetallic systems constructed from the complexes introduced in Chapters I and 2, bridged by a saturated alkyl linker between bpy ligands on either metal. This Chapter demonstrates the solvent-switchable nature of the direction and gradient of PEnT, using ps-TRIR spectroscopy to directly probe these processes in real time. Chapter 4 describes a study of bimetallic systems bridged by conjugated the ligand 2,2'- bipyrimidine. Monometallic, homobimetallic and heterobimetallic systems are studied and questions arising from limitations of previous studies are addressed. In particular ps-TRIR spectroscopy gives new insight into the numerous ultrafast processes occurring. Chapter 5 summarises the achievements of this Thesis and suggests promising directions for extending this work in the future. Chapter 6 describes the experimental and theoretical techniques used in this Thesis.

This thesis presents electronic structure calculations on problems related to the bonding in inorganic coordination compounds and clusters. A wide range of molecules with the ability to exist in different structural forms or electronic states has been selected and density functional theory is systematically applied in order to gain detailed insight into their characteristics and reactivity at the electronic level. First, we address the question of redox non-innocent behaviour of bipyridine in a series of 1st row transition metal complexes. Complexes of the type [M(2,2'-bipyridine)(mes)₂]⁰ (M = Cr, Mn, Fe, Co, Ni; mes = 2,4,6-Me₃C6H₂) and their one-electron reduced forms have been explored. The results clearly show that the anions are best described as complexes of the monoanionic bipyridine radical (S_bpy = 1/2), giving a rationale for the observed structural changes within the ligand. Likewise, we have identified dianionic bipyridine in both the complexes [Zn2(4,4'-bpy)(mes)₄]²⁻ and [Fe(2,2'-bpy)₂]²⁻. In no case have we found evidence for significant metal-to-ligand backbonding. The subject of redox-noninnocence is further revisited in a comparative study of the two complexes [M(o-Clpap)₃] (M = Cr, Mo; o-Clpap = 2-[(2-chloro-phenyl)azo]-pyridine), and their associated electron transfer series. The results indicate that all electron transfer processes are primarily ligand-based, although in the case of the Mo analogue these are coupled to substantial electron density changes at the metal. The ability of pap to form radical anions finds a contrasting case in the di- nuclear Rh complex [Rh₂(μ-p-Clpap)₂ (cod)Cl₂], where the two ligand bridges act as acceptors of strong dπ∗ backbonding from a formally Rh^–I centre. We then direct our attention to the endohedral Zintl clusters [Fe@Ge₁₀]³⁻ and [Mn@Pb₁₂]³⁻, which reveal peculiar topologies. We have probed the electronic factors that influence their geometric preferences, and propose a model based on the shift of electron density from the endo- hedral metal to the cage to account for the observed geometries. Subsequently, we reassess the electronic structure of the xenophilic clusters Mn₂(thf)₄(Fe(CO)₄)₂ and [Mn(Mn(thf)₂)₃(Mn(CO)₄)₃]^–. We conclude that these are best viewed as exchange coupled Mn^II centres bridged by closed- shell carbonylate fragments. In the closing chapter the reduction of NO₂^– to NO by the complex [Cu(tct)(NO₂)]⁺ (tct = cis,cis-1,3,5-tris(cinnamylideneamino)cyclohexane) is studied, a process that mimics the enzyme-catalysed reaction. Two viable pathways for the reaction have been traced and key inter-mediates identified. Both direct release of NO or via decomposition of a Cu-NO complex are kinetically and thermodynamically feasible.