The self-assembly of two-dimensional molecular systems is of significant interest, offering an insight into the fundamental interactions which drive the formation of complex supramolecular structures. A careful choice of the molecular 'building blocks' for such self-assembled systems potentially allows the design and production of nanoscale architectures with pre-determined geometries and specific chemical functionalities. Within this thesis the two-dimensional structures formed by the self-assembly of complex organic molecules, deposited on an Au(111) surface held in an ultrahigh vacuum (URV) environment, are studied using a combination of scanning tunnelling microscopy (STM), photoelectron spectroscopy (PES), molecular dynamics (MD), and density functional theory (DFT) techniques. A UHV electrospray deposition (URV-ESD) technique is employed to facilitate the introduction of thermally labile molecules into the URV environment. Bi-molecular networks, formed from perylene tetracarboxylic diimide (PTCDI) and melamine, have previously been observed to assemble on the Au(111) surface. Several more complex phases are reported here, as characterised by S'I'M, with the balance between isotropic and anisotropic interactions giving rise to a variety of structures. Chemical functionality may be added to these networks by incorporating functionalised derivatives of PTCDI. Alternative structures produced by altering the shape of the molecular 'building blocks' are also discussed. The URV-ESD technique is demonstrated here to be compatible with the deposition of the fullerene C60,the single molecule magnet Mn12012(02CCR3h6(H20)4 (Mn12(acetate)16), and porphyrin based oligomers (P4 and P6) and polymers (Pn). The URV-ESD of C60on the clean AU(ll1) surface, and on a surface prepatterned with a PTCDI/melamine network, results in similar structures to those previously observed to be produced by sublimation. Mn12(acetate)16 and the porphyrin oligomers and polymers represent complex molecules which are thermally labile and possess, respectively, novel magnetic and electronic properties. Mn12(acetate) 16is observed to form filamentary aggregates due to the anisotropic nature of the molecule-molecule and molecule-substrate interactions, while P4, P6 and Pn form highly ordered close-packed domains driven by the interdigitation of the alkyl chains attached to the porphyrin cores. The findings presented within this thesis demonstrate that self-assembled molecular structures can be understood in terms of intermolecular interactions, and that for systems containing complex molecules the molecule-molecule interaction potential can lead to the formation of novel structures.

CHAPTER 1: A background to the techniques of matrix isolation, liquid xenon solution and flash photolysis with fast IR detection is presented. The application of infrared spectroscopy in structural studies of metal carbonyl compounds is also discussed. Chapter 2: Photolysis of((nu5-C5R5)Pt(CO))2 (R=H, Me) in frozen gas matrices results in production of ((nu5-C5R5)Pt2(mu-CO)). 13CO enrichment and polarised photochemistry show that the photoproduct contains a single symmetrically bridging CO group. Photolysis of (CpNi(mu-CO))2 in frozen gas matrices results in formation of CP2Ni2(CO) with a terminal CO ligand. The stability these dinuclear photoproducts in room temperature solution has been investigated using fast TRIR spectroscopy. Photolysis in CO matrices leads to M-M bond cleavage and reaction with CO to give Pt(CO)4 or Ni(CO)4 as the final product. CHAPTER 3: Photolysis of Os2(CO)9 or OS2(CO)8- - (mu-nu1, nu1-C2H4) in frozen gas matrices leads to formation of Os2(CO)8, which has only terminal CO groups. The thermal and photochemical reactivity of Os2(CO)a towards CO, N2 and C2H4 is investigated. Photolysis using plane polarised light provides confirmation of the C2v structure of Os2(CO)9, and gives evidence favouring a D2h structure for Os2(CO)8. Prolonged UV photolysis of Os2(CO)9 in CO matrices leads to cleavage of the Os-Os bond and production of Os(CO)5. CHAPTER 4: The mechanism of the photochemical deoligomerisation of FpSiMe2SiMe3 is investigated using a variety of techniques. The reaction is shown to proceed via two photochemical steps. Primary CO-loss is followed by intramolecular trapping to give a silyl(silylene) intermediate. The second step involves expulsion of an SiMe2 fragment and coordination of a ligand. L. to give CpFe(CO)(L)SiMe3 (L = CO, PPh3,C2H4 or N2). CHAPTER 5: A study of the photochemistry of Fp-disilyl complexes containing beta-silyl hydrogens implies beta-H transfer from Si to Fe as the dominant process following photodissociation of CO. The product, a metalladisilacyclopropane or nu2-disilene complex, is implicated as an intermediate in the photochemical formation of FpH in this system. CHAPTER 6: The experimental techniques and spectrometers used in this research are described. along with a discussion of the theory and advantages of FTIR spectroscopy.

The application of supercritical C0₂(scC0₂) as a solvent for the synthesis of fine and bulk chemicals has been well documented; however its application as a solvent for the synthesis of pharmaceuticals is yet to be exploited fully. To address this issue, two synthetically important reactions have been investigated in scC0₂; chemoselective N-debenzylation and diastereoselective hydrogenation. Chapter 3 details the study of catalytic N-debenzylation in the presence of sensitive functional groups (COMe and Cl). It has been shown that selective N-debenzylation in the presence of a carbonyl (COMe) is difficult to achieve due to the high operating temperatures that are required to facilitate continuous flow debenzylation. N-debenzylation in the presence of chloro- substituents was also investigated. Dechlorination can be a major problem during this reaction however several different strategies were developed to suppress dechlorination including: (i) the correct selection of catalyst support; (ii) selective poisoning of a Pd catalyst; (iii) the addition of acids, such as H₂S0₄ to the reactant stream; (iv) the use of an aprotic co-solvent, such as THF. Chapter 4 covers progress made on the diastereoselective hydrogenation of the pharmaceutical intermediate, rac-sertraline imine. It has been shown that the hydrogenation reaction can be performed with excellent levels of chemo- and diastereoselectivity (cis:trans ratio of 97:3, 0.7 % by-product formation) by performing the reaction as a continuous flow process in the presence of scC0₂ All details of the apparatus, experimental and synthetic procedures are reported in Chapter 2.

Intramolecular vibrational energy redistribution (IVR) is a commonly-observed phenomenon whereby vibrational energy can be transferred between different parts of a polyatomic molecule. This process has profound implications for the understanding of chemical reactivity. In this work, IVR is studied in the S1 electronic state of toluene using time-resolved and frequency-resolved techniques. Both experiments are based upon laser photoelectron spectroscopy in the collision-free environment of a molecular beam. The time-resolved experiments employ laser pulses of ~1 ps duration and ~15 cm^-1 bandwidth. In a pump-probe scheme, the molecule is first excited to a chosen superposition of vibrational states in the S1 manifold and then ionised by a second photon. The photoelectrons produced by the probe laser pulse are detected using velocity map imaging in order to obtain a vibrationally resolved photoelectron spectrum. Changes in the spectrum as a function of time give a direct view of the evolution of the vibrational state. The use of a two-colour ionisation scheme substantially improves the resolution compared with previous work. High resolution zero kinetic energy (ZEKE) photoelectron spectra have also been obtained for the first time from excited vibrational levels in the S1 electronic state of toluene. These experiments employed laser pulses of ~5 ns duration and ~0.3 cm^-1 bandwidth, allowing the excitation of individual S1 vibrational levels rather than a superposition. The nanosecond and picosecond experiments therefore give complementary information. A Fermi resonance at ~460 cm^-1 above the S1 origin in toluene is shown to be more complicated than previously thought, and provides the first demonstration of the use of time-resolved photoelectron spectroscopy to gain quantitative measurements of vibrational coupling matrix elements. Lifetimes of dissipative IVR have been determined following the preparation of high-frequency vibrations, and at intermediate energies several "doorway states" which mediate the IVR mechanism have been identified for the first time.

The performance of X-ray spectroscopy techniques has been advanced by recent reviving in X-ray sources. These techniques that involve the excitation of core electrons can provide an atom specific probe of electronic structure and provide powerful analytical tools that are used in many fields of research. Theoretical calculations can often play an important role in the analysis and interpretation of experimental spectra. In this thesis, I report a recent developments in quantum chemical calculations of X-ray absorption spectra, focusing on the use of time-dependent density functional theory to study core excitations. The practical application of these calculations is illustrated with examples drawn from surface science,and the application of these methods to study X-ray emission spectroscopy is also explored.

Part 1 of this thesis describes the continued development of a new method for the synthesis of olefins from sulfur reagents and carbonyl compounds. The proposed catalytic olefination investigated the reaction of sulfur ylides or sulfines with carbonyl compounds to produce the corresponding alkene, catalysed by a transition metal oxo complex. A variety of literature trioxo rhenium and molybdenum di-oxo and oxo-imido complexes were reacted with dimethylsulfoxonium methylide and generally led to degradation. The reaction of diphenylsulfonium benzylide with the rhenium and molybdenum oxo complexes gave no reaction or led to degradation. Diphenylsulfine was also reacted with the metal-oxo complexes and produced benzophenone and degradation of the metal oxo complex. Part 2 of this thesis describes the investigation into the novel complex MoO(NtBu)(2,6-R2C6H3O)2py [where R = iPr (72a) or Me (72b)], which was developed in the Anderson group, as an epoxidation catalyst. The initial epoxidation conditions were optimised for trans-stilbene. The optimised conditions were used to epoxidise a variety of alkenes. The catalyst 72 is effective at epoxidation of electron rich alkenes, will selectively epoxidise allylic alcohols and does not epoxidise electron deficient alkenes. The rate of epoxidation of cis-stilbene using catalyst 72a and 72b were compared and showed that 72b had a faster rate of epoxidation than 72a. The rate of reaction for catalyst 72b was also compared with MoO2(2,6-Me2C6H3O)2py2 98 for the epoxidation of cis-stilbene and found to be similar, indicating that the catalytically active species may be common to both. Part 3 of this thesis describes an investigation into the synthesis of (-)-dysibetaine using the aza-[2,3]-Wittig rearrangement-cyclisation protocol. The initial retrosynthesis led to a -lactone enolate 57 in the aza-[2,3]-Wittig rearrangement cyclisation. However the desired cyclised product 58 was not obtained and instead ring opening of the -lactone to the acrylic acid 80 was observed. A revised route used a phenyldimethylsilyl amino acid 106 as a masked hydroxyl group to mimic a serine amino acid that would not undergo -elimination. The aza-[2,3]-Wittig precursor 109 was prepared and subjected to the standard aza-[2,3]-Wittig rearrangement-cyclisation protocol and the desired cyclised product 110 was obtained in 43% yield. This product contained the correct dysibetaine skeleton and would require functional group transformations to complete the synthesis.

The 3s, 3d and 4s Rydberg states of nitric oxide (NO), bound to a rare gas (Rg) atom in a van der Waals complex (NO-Rg), are probed using resonance-enhanced multiphoton ionisation, in order to investigate the effect of electronic excitation on these complexes. The spectroscopy is interpreted in terms of interactions between the Rydberg electron, the nitric oxide (NO+) core and the Rg atoms. Larger NO-Rgx clusters are investigated offering the prospect of bridging the spectroscopic gap between van der Waals dimers and the bulk. The spectroscopy is determined by an NO+-Rg2 moiety and formation of the Rydberg state provokes a dynamic response from the Rgx cluster, similar to that observed in matrix studies. High-resolution zero electron kinetic energy spectroscopy is employed to derive vibrational frequencies of the para-fluorotoluene cation and assignments for previously unidentified (or in some cases, erroneously assigned) features have been presented. The first electronically-excited state of para-fluorotoluene (pFT), where a pFT chromophore is bound to several pFT molecules in a van der Waals cluster, has been studied. The effects of laser power and the internal temperature of the clusters on the fragmentation are considered. A model potential analysis is carried out to determine whether binding in metal cation/rare gas (M+-Rg) complexes is physical (due to electrostatic, dispersion and induction interactions), or whether a chemical component (classical covalent interactions) must be considered. For alkali metal (Alk+)/Rg complexes, the model potential successfully describes the binding (the interaction is purely physical). For Au+-Rg, the model potential analysis reveals the emergence of a chemical component to the interaction, which becomes more significant as Rg gets larger.

The work presented in this thesis was carried out with the ultimate aim of learning about the photoionization dynamics of polyatomic molecules. This is a complex problem; in order to obtain sufficient experimental data to shed light on the dynamics careful measurement of photoelectron angular distributions (PADs) is required. Ideally these measurements are rotationally-resolved, and the angular distributions measured correspond to the formation of the molecular ion in a single rotational state. The ionization event, in the dipole approximation, can be completely described by the dipole matrix elements. If sufficient experimental data to determine the radial components of the matrix elements and associated phases, the dynamical parameters, can be obtained the photoionization experiment may be said to be complete. Analysis of such experiments requires that the initial state of the molecular system is also known, to this end resonance-enhanced multi-photon ionization (REMPI) schemes can be used in order to populate a single quantum state prior to ionization. The experiments presented here follow this methodology, with various REMPI schemes used to prepare (pump) and ionize (probe) the molecule under study, and the velocity-map imaging (VMI) technique used to (simultaneously) record the photoelectron spectra and angular distributions. Two molecules have been studied experimentally, acetylene (C2H2) and ammonia (NH3). In both cases dynamical parameters pertaining to the formation of specific states (vibronic or vibrational) of the molecular ion have been determined from experimental data. Additionally, in the ammonia work, rotationally-resolved photoelectron images were obtained.

Mass analysed ion kinetic energy (MIKE) spectra following collisions have been recorded using a double focusing mass spectrometer with 5 kV acceleration voltage. Metal complexes studied were formed by pick-up of metal atoms in mixed argon/solvent clusters made by supersonic expansion. DFT calculations were used to rationalise experimental data. Complexes of the form MLn+ where M = Mg, Ca, Mn, Cu, and Zn while L = NH3, CO2, benzene, pyridine, acetonitrile, and acetone have been collided with O2 and MgLn+ also with CO2, N2O, acetonitrile, and benzene. Complexes with few ligands are the most prone to oxidation due to their high speed which facilitates electron transfer. Calculated electron affinities, Mulliken populations, and natural bond orbitals of collision gases were used to rationalise electron transfer trends. Collision gases trap electrons more efficiently if they have π-bonds or adjacent electronegative atoms. Metal complex and molecular dications were collided with H2 and O2 to determine the stability of their reduced products. No systematic differences were found between collisions with the two gases at the collision energies examined. The fate of monocations formed in collision depends on their relaxation energy and the dissociation energy of relaxed monocations. LZ theory was unable to explain MIKE spectra. Metal complexes MLn+ and MLn2+ were collided with O2 to determine the propensity to form MXLn-m+ where M = Mg, Ca, Mn, Cu, and Zn while L = CH3X with X = F and Cl. Reactivity is determined by the IE of MLn+ which decrease with increasing n. Dications due to their high dissociation energy are much more likely to react as they can have enough internal energy to overcome potential barriers.

This Thesis investigates immobilised metal- and biocatalysts for continuous reactions in scC02. Chemical transformations with high atom economy and low E-factor (amount of waste per kg of product) are highly desired in the green chemical viewpoint. One of the approaches to decrease the production of waste is the use of catalysis (possibly highly selective). Another approach is the use of a 'green' reaction medium as a substitute for traditional solvents that can reduce the production of harmful solvent waste. How this Thesis encompasses by these topics is discussed in Chapter 1. The details of the apparatus, experimental and analytical equipment and procedures are reported in Chapter 2. The field of asymmetric catalytic hydrogenation is a currently important and expanding field of research. In Chapters 3 and 4, the continuous asymmetric hydrogenation of dimethyl itaconate is covered. High enantioselectivity (ees up to 83 %) was obtained in the continuous asymmetric hydrogenation of dimethyl itaconate catalysed by supported homogeneous chiral Rh catalysts on alumina in SCC02 (Chapter 3). This is one of the first examples of the use of chiral catalyst in a continuous flow system without the need for the addition of the chiral modifier. The continuous asymmetric hydrogenation of dimethyl itaconate was also examined with chiral Rh catalysts immobilised in ionic liquids in a biphasic system ionic liquid/scC02 (Chapter 4). High enantioselectivity was achieved in the continuous flow system: ees up to 76 %. Chapter 5 describes the kinetic resolution of secondary alcohols catalysed by immobilised Candida antarctica lipase B (Cal B) in a continuous flow scC02 system. The continuous kinetic resolution of a-tetralol with Cal B immobilised in the form of Cross-Linked Enzyme Aggregate (CLEA) gave excellent enantioselectivity (eeR to 99 %). Different acyl donors (vinyl acetate, phenyl acetate and p-nitrophenyl acetate) were investigated, and were shown to influence the enantioselectivity of the reaction. In Chapter 6, a two step catalytic cascade reaction is described in a continuous flow scC02 system: hydrogenation of acetophenone with a Pd catalyst (Pd Type 31) followed by the kinetic resolution of the product with Cal B CLEA. The series reaction gave good results even when un-optimised: • Step 1 (hydrogenation of acetophenone): conversion up to 91 % • Step 2 (kinetic resolution of (R/S)-l-phenylethanol): conversion of (R)-l-phenylethanol up to 22 %, enantioselectivity (R) > 99 %. Chapter 7 details the preparation of cholesterol oxidase CLEA and combi-CLEA of cholesterol oxidase and catalase, and their application for the continuous oxidation of cholesterol in scC02 with 'in-flow' cholesterol extraction. CLEA were successfully prepared with high retained activity: • Individual cholesterol oxidase CLEA: cholesterol oxidase activity up to 99 % (relative to native), • Combi-CLEA: cholesterol oxidase activity up to 99 % (relative to native), catalase activity up to 53 % (relative to native). Unfortunately, the activity of the CLEA in the continuous oxidation was low, however, the findings of this work will aid in improving the performance of the continuous catalytic oxidation of cholesterol in the future. The possible future directions of this research are presented in Chapter 8.