This study concerns the development of a frequency response (FR) reactor capable of investigating heterogeneous catalytic systems under realistic operating conditions. Diffuse Reflectance Infrared Fourier Transform Spectrometry (DRIFTS) and mass spectrometry (MS) have been used together to follow the effects of modulation of the adsorbent/reactant gas composition as elevated temperatures and atmospheric pressure. Initial assessment of the performance of the reactor involved studies of the diffusion of propane though silicalite-1 using MS detection. A mathematical model has been developed to describe the diffusion of the propane, yielding diffusion and adsorption coefficients from the FR data. Investigations using the integrated DRIFTS/MS reactor have been made on the catalytic oxidation of CO over a 2% Rh/Al₂O₃ catalyst supplied by Johnson Matthey. The catalyst was studied at different temperatures and in both a 'pre-reduced' and 'as received' state. Conventional studies involving CO uptake, temperature programming and desorption measurements showed that adsorbed species observed on the catalyst surface are in good agreement with the literature. Dicarbonyls, linear CO on both metallic and oxidised Rh sites, carbonates and bridging CO were all observed. Transient studies in the form of concentration modulation experiments were performed and showed the major active surface species to be linearly adsorbed CO on oxidised Rh sites (v_CO= 2105 cm^-1) on a catalyst surface otherwise dominated by unreactive CO adsorbed predominantly as the geminal dicarbonyl species. Full frequency response experiments were conducted over a narrower range of experimental conditions, but allowed calculation of surface residence times and activation energies for reaction of the surface Rh⁺CO species and desorption of CO₂.

Studies have been made of the kinetics of the hydrogenation of mixtures containing 2% of acetylene in ethylene on an alumina supported palladium catalyst in a static system. Information has been obtained about the nature of the selectivity of the reaction of acetylene. Detailed analyses of the kinetics have been made as the ratio of the pressures of acetylene to ethylene decreases and subsequently as the remaining hydrogen is used up. The poisoning action of carbon monoxide, which selectively inhibits the hydrogenation of ethylene, has also been studied. Tracer studies using carbon 13 labelled acetylene, light ethylene and hydrogen with analysis by combined gas chromatography-mass spectrometry, have shown unambiguously that ethane produced from the hydrogenation of a mixture of acetylene in ethylene comes predominantly from the ethylene. The reaction between acetylene, ethylene and deuterium gives a greater understanding of the surface processes involved and produces ethane which is mainly ethane-dt. It is postulated that two types of site exist on the surface, type X which hydrogenates both acetylene and ethylene and on which acetylene is adsorbed - 2200 times more strongly than ethylene at 293° K and type Y which is easily poisoned by carbon monoxide and can hydrogenate ethylene even in the presence of acetylene. The hydrogenation of acetylene has also been investigated in a spinning-basket reactor. The rate of disappearance of acetylene was found to be controlled by pore diffusion at low acetylene concentrations and was independent of acetylene at high acetylene pressures. In the non-diffusion-controlled region the reaction of acetylene was first order in hydrogen and the rate of ethane formation was independent of both the acetylene and ethylene pressures. This latter observation is consistent with the presence of two types of site. The nature of the C, products has been shown to be dependent on the packing of adsorbed acetylene molecules and on the availability of surface hydrogen. The analysis of a heavy involatile product is also reported.

This thesis describes work on short-lived gaseous intermediates in organosilicon chemistry. The first part of this thesis discusses experiments carried out to verify the existence of the intermediate species dimethylsilanone, Me2SiO, containing a silicon-oxygen double bond, while the second part discusses the kinetics of the thermal decomposition of three chloromethyldisilanes to give silylenes and some of the insertion reactions of these silylenes. Three types of experiment were undertaken to verify the existence of dimethylsilanone. Using octamethylcyclotetra-siloxane, (Me2SiO)4, as a thermal source of Me2SiO, co-pyrolyses of (Me2SiO)4 with alkenes and dienes were carried out to observe any formation of cyclic adducts between the hydrocarbons and the intermediate, Me2SiO. Pyrolyses of (Me2SiO)4 with chloromono-silanes were also carried out to determine whether the intermediate, Me2SiO, would insert into the silicon-chlorine bond or bonds in the chloromonosilanes, to give linear chloromethylsiloxanes. The formation of cyclic adducts and insertion products would provide good evidence for the independent existence of Me2SiO. Finally, co-pyrolyses of (Me2SiO)4 with another cyclic siloxane, (MePhSiO)3, were undertaken to determine whether cyclic siloxanes containing both Me2SiO and MePhSiO units would be formed. Again formation of these 'mixed' siloxanes would provide further evidence for the existence of Me2SiO. In the work on silylenes, in the second part of this thesis, the thermal decomposition of three chloro-disilanes was studied and the Arrhenius parameters determined in each case. The three chlorodisilanes were : pentamethyl- chlorodisilane, Me5Si2Cl; 1,1,2,2-tetrachloro-l,2-dimethyl- disilane, Me2Si2Cl4; and 1,1,2-trime thyl-1,2 ,2-trichlorodisilane, Me3Si2Cl3. Some of the insertion reactions of the silylenes generated were also studied, especially insertion into the silicon-hydrogen and silicon-chlorine bonds.

This thesis describes work conducted using a linear time-of-flight (TOF) mass spectrometer concerning the gas phase reactivity of atomic and small molecular doubly charged positive ions (dications) with neutral species at low collision energies (below 20 eV). The process of analysis by which measured ion intensities gathered using this instrument are converted into reaction cross-sections is completely redeveloped, permitting for the first time the cross-sections of all ionic products of bimolecular reactions to be derived. The new methodology calculates reaction cross-sections in arbitrary units furthermore the absolute size of these arbitrary units depends only on the absolute value of the number density distribution of the neutral reactant and thus is independent of collision energy and changes from one collision system to another only due to differences in the effusive properties of the neutral reactant. While a number of collision systems have been observed, three were selected for more rigorous study: SF2+ + Ar, Cl2+ + CO and HC12+ + CO, and these are reported herein. The first and second of these collisions are particularly novel because their chemistry includes reaction channels that produce a doubly charged product 2"1" 2"F containing new chemical bonds (ArS and CC1 respectively). This class of dication- neutral reaction is highly unusual and only a very limited number of examples have been reported previously. The chemistry of HC1 with CO, while bearing similarities to that of Cl2+, also exhibits proton transfer (to form HCO+) that occurs with a branching ratio similar to electron transfer. The new procedure of analysis is applied to each system, allowing calculation of the reaction cross-sections for all charged products and is demonstrated to perform suitably well. The mechanism of electron transfer in dication-neutral systems is well understood, and computational calculations are conducted to complement the experimental results, but consideration of energetics also allows the observation of bond-forming products to be rationalized. The development of a more satisfactory means of extracting reaction cross- sections from experimental measurements, while an achievement, has highlighted a number of shortcomings in the present experimental design and a number of suggestions have also been made for a future upgrade of the experiment that would facilitate simpler analysis as well as improved resolution and flexibility.

The work described in this thesis is primarily focused on the synthesis and characterisation of two-coordinate zerovalent palladium complexes bearing an N-heterocyclic carbene ligand. These complexes have been assessed as pre-catalysts for coupling reactions in particular ami nation reactions involving the generation of a C-N bond. Chapter 1 presents the synthesis of complexes r, r bearing the ligand [CNCBu)(CH)2NCBu)]. An alternative synthesis for [Pd{CNCBu)(CH)2NCBu)h] 1 is reported involving reaction of [{Pd(T)3-C4H7)Clhl with sodium dimethyl malonate and carbene. Reaction of 1 with iodobenzene led to formation of a Pd(II) speCies, r , [Pd{CNCBu)(CHhNCBu)h(C6Hs)I] 2. An intermediate in the synthesis of 1, r [Pd(T)3-C4H7){CNCBu)(CHhNCBu)h(C6Hs)C] 3, has been isolated and fully characterised. Two r , mixed carbene phosphine complexes, [Pd{CNCBu)(CHhNCBu)}{P(o-tolylh}] 4 and r , [Pd{CNCBu)(CHhNCBu)} {PCY3} 1 S, have also been synthesised. Complexes 1,4 and S have been assessed as a pre-catalysts for ami nation couplings with limited success. Chapter 3 presents the r , synthesis of two complexes bearing the ligand [CN(Me)(CMe)2N(Me)]. Metal vapour synthesis was r , used to synthesise [Pd{CN(Me)(CMehN(Me)h] 6 and the diiodide complex r , [Pd{CN(Me)(CMehN(Me)hI2] 7 was also prepared. Complexes 6 and 7 were shown to have no activity as pre-catalysts in amination couplings. Chapter 4 presents the synthesis of complexes r· ~. bearing the ligand [CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'PrrC6H3)]. The methodology used to synthesise r. ~. 1 was applied to the synthesis of [Pd{CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'PrrC6H3)h] 8. Substitution of a phosphine ligand In [Pd {P(o-tolylh hl by carbene led to formation of r. ~. [Pd{CN(2,6-'PrrC6H3)(CH2hN(2,6-'PrrC6H3)}{P(o-tolyl)3}] 9. Complexes 8 and 9 were successfully employed as pre-catalysts for amination couplings. 4-Chlorotoluene was shown to couple to a variety of primary and secondary amines including cyclic, acyclic and aryl substituted as well as an imine. The same proceedure was also used to couple chloropyridines with morpho line Reactions were typically conducted with 2 mol% pre-catalyst and KOtBu base in dioxane at 100 °C and were found to be complete after 0.5-5 h. The isolated yields of product obtained were typically r· ~. above 95%. Reaction of 1 with [CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'Pr2-C6H3)] led to formation of r \ r. ~. [Pd{CN(,Bu)(CH)2N(,Bu)} {CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'Pr2-C6H3)}] 10. Complex 10 was found to be less active as a pre-catalyst for amination couplings than either 8 or 9. A copper carbene r. ~. complex [Cu {CN(2,6-'Pr2-C6H3)(CH2)2N(2,6-'Pr2-C6H3)} I] 11 was also synthesised and shown to facilitate the coupling of 4-iodotoluene with morpholine to give the coupled product in a 38% yield. Chapter 5 presents the results of some ligand substitution reactions. Complexes 1 and 8 were reacted with phosphines to give mixed carbene phosphine complexes 4, S and 9. The results obtained showed that phosphines can displace carbenes despite the strength of metal carbene bonds

Zeolite ZSM-5 is a standard material in the petrochemical industry used as a catalyst in oil refining processes. Its shape selectivity toward parasubstituted aromatics has been very valuable in the processing of BTX (benzene, toluene, xylene). The adsorption of aromatic molecules inside the zeolite ZSM-5 presents also some unusual adsorption isotherms which has generated a great body of experimental and theoretical articles with only partial agreements. It is believed that the source of these discrepancies originates from the main characteristic of this system, a tight fit situation between the diameter of the aromatic ring and the size of the zeolite pore. The aim of this thesis is to achieve a consistent explanation between the experimental data measurements and the theoretical models. The determination of some adsorption values such as the Henry coefficient or the isosteric heat of adsorption by data interpolations or calculation from theoretical simulation is the numerical criterion to check this consistency. It is also the prerequisite to validate the parameters used to carry out the Monte Carlo simulation of such system. This work studies the limits of this epistemological approach. We start from a review of the different standard interpolation models and a discussion of the relevance of the Henry and isosteric heat values calculated. We continue with the investigation of the limits of a Monte Carlo simulation; from the difficulties to assess a heterogeneous set of Force Field simulation parameters, to the study of new bias Monte Carlo algorithms used to carry out an efficient simulation.

The aim of this thesis was the experimental investigation of fundamental, gas phase, bimolecular chemical processes, using laser methods for the state-selective preparation of reagents and for the state-specific detection of nascent products. An apparatus was developed which allowed the state-specific spectroscopic detection of gas phase molecules by either laser-induced fluorescence (LIF) or resonance-enhanced-multiphoton-ionisation (REMPI). The apparatus incorporates time-of-flight (TOF) mass discrimination of ions produced in the REMPI process. A spectroscopic investigation was performed to establish whether LIF or REMPI was the optimum detection method for the OH radical. Our preliminary conclusion was that LIF remained the optimum method for the detection of OH. The dynamics of elementary O(<SUP>3</SUP>P) atoms + saturated hydrocarbon reactions have been investigated experimentally. Reaction was initiated by pulsed laser photolysis of NO<SUB>2</SUB> precursor molecules to produce reactive O(<SUP>3</SUP>P) atoms with a characteristic distribution of recoil velocities. These atoms collide and react with saturated hydrocarbon molecules chosen to contain representative primary, secondary and tertiary C-H bonds, respectively. The nascent OH(X<SUP>2</SUP>II) product was detected in a state-specific fashion by LIF. The partitioning of the available energy among vibrational, rotational and fine-structure states of the products has been determined. The (2+1) REMPI spectroscopy of HC1 was investigated to determine which transitions would be suitable for the measurement of ground state rovibrational populations of nascent HC1 produced in a chemical process. Certain vibronic bands of the <I>V</I><SUP>1</SUP>Σ<SUP>+</SUP> → <I>X</I><SUP>1</SUP>Σ<SUP>+</SUP> transition were found to be sufficiently unperturbed to be suitable candidates for population studies.

The initial aim of this thesis was to apply and extend the chemistry of pyrrolizin-3-one ring systems to the synthesis of naturally occurring pyrrolizidine alkaloids. The methods of synthesis of unsubstituted-, 1-monosubstituted-, 7-monosubstituted- and 1,7-disubstituted pyrrolizidin-3-ones have been reviewed. Many pyrrolizin-3-ones have been synthesised by Flash Vacuum Pyrolysis (FVP) of propenoate ester derivatives or Meldrum's acid derivatives. A new synthetic route to pyrrolizin-3-ones substituted at the 1-position by electron-withdrawing groups has been developed by FVP of Wittig condensation products from pyrrol-2-ylglyoxylic acid derivatives. Unexpectedly 1-methoxycarbonylpyrrolizin-3-one spontaneously dimerises at room temperature within two days, in contrast to all other pyrrolizin-3-ones which are known to be stable. The dimerisation is thought to take place <I>via</I> a captodative diradical intermediate. Hydrogenation of 1- and 7-monosubstituted pyrrolizin-3-ones proceeds smoothly to give the perhydro system with very high diastereoselectivity after optimisation, in particular from the 7-monosubstituted pyrrolizin-3-ones. The level of selectivity attained is greatly dependent on experimental conditions, namely catalysts and solvents. Hydrogenation of 1,2-dihydro-1, 7-disubstituted pyrrolizin-3-ones is more complex due to addition steric interactions but some degree of diastereoselectivity is nevertheless observed. Reduction of the pyrrolizidin-3-one systems thus obtained allowed the synthesis of the pyrrolizidines heliotridane, isoretronecanol (both by two complementary routes) and retronecanol. Cycloaddition reactions of 1- and 2-monosubstituted pyrrolizin-3-ones with isobenzofuran have been studied. High selectivity for the <I>endo</I> products has been observed for pyrrolizin-3-one itself and the 1-methoxycarbonyl derivative, possibly due to a stabilisation of the transition state by favourable secondary orbital interactions. The methodology was then applied to the synthesis for the natural product pyrrolam A in three steps from pyrrolizin-3-one by a Diels Alder - hydrogenation - retro Diels Alder sequence. The rate of ring opening of a variety of monosubstituted pyrrolizin-3-one by reaction with sodium methoxide was followed by Stopped Flow kinetics. The rate was found to be greatly dependent on the nature of substituents and to a less extent on their position. The results have been applied to the synthesis of <I>cis</I>-urocanic acid in two steps from methyl (<I>E</I>)-3-(imidazol-4-yl)propenoate. Finally extension of the chemistry of pyrrolizin-3-ones has been briefly investigated, in particular reactions with organolithium derivatives and thiophenol, oxidation and reduction reactions and photochemical dimerisation.

Twelve mono and dinucleating dipicolylamine(dpa)-based ligands have been designed and synthesized to investigate the catalytic activity of their corresponding zinc complexes toward the hydrolysis of phosphodiester bonds of RNA model substrates. The identity and stoichiometry of the metal complexes in solution were evaluated by potentiometric pH titrations, in water and/or in the binary solvent mixture DMSO:H₂O (67%:33%), for four potentially dinucleating dpa-based ligands: <i>N,N,N’,N’-</i>tetrakis[(2-pyridyl)methyl]-2,6-diamino-<i>p</i>-nitrophenol (LOH), <i>N,N,N’,N’-</i>tetrakis[(6-amino-2-pyridyl)methyl]-2-hydroxy-1,3-diaminopropane (LOH’), 1,3-Bis[bis(pyridine-2-ylmethyl)amino]-propan-2-ol (L¹OH) and <i>N,N,N’,N’­</i>-tetrakis[(6-amino-2-pyridyl)methyl]-2,6-diamino-<i>p</i>-nitrophenol (L¹OH’). Results showed that all ligands in the presence of Zn(II) are able to form mononuclear and dinuclear complexes but their stability is strongly affected by the presence of the amino groups in the dipicolylamine core and dependent on the nature of the bridging unit (phenol or alcohol group). In general, the ligand L¹OH’ forms the less stable zinc complexes and mainly mononuclear species, whereas LOH’ forms the most stable dinuclear complexes. The introduction of hydrogen bonding functionalities also affects the basicity of the ligands, which is enhanced, and decreases the p<i>K</i>_a of a zinc-bound water molecule by ca. two p<i>K</i>_a units. The catalytic efficiency of metal complexes of the ligands with four amino hydrogen bonding groups (L¹OH’ and LOH’) has been tested on small RNA models and the mechanism of catalysis was investigated with the help of inhibition, Solvent Kinetic Isotope Effect (SKIE) and computational studies. The cleavage rate of HPNPP, an activated RNA model, as well as the more stable substrate UpU, is accelerated of a million fold over the uncatalyzed reaction in water, at 25°C and neutral pH. Geometry optimisations and SKIE suggest a general base catalysis with proton transfer. The catalytic ability of dinickel(II), dicobalt(II), dicopper(II) and dicadmium(II) complexes of the ligand LOH’ was also investigated and found to follow the order: Ni(II) &gt;&gt; Co(II) &gt; Cd(II) &gt;&gt; Cu(II). The X-Ray crystal structure of the complex [Zn₂(LOH’)] with 4-nitrophenol phosphate reveals that the phosphodiester dianion binds the complex by bridging the two Zn(II) atoms and hydrogen bonding the four amino groups. These interactions are responsible for the enhanced reactivity of the most active dinuclear zinc catalyst for phosphodiesters hydrolysis reported to date.

Resin plugs were developed back in 1999 as a convenient form of resin handling. In this modular cylindrical format, resin beads are embedded in an inert, porous polymer matrix. In this study, the physical and chemical characteristics of resin plugs were evaluated under a variety of reaction conditions, looking at their physical integrity, their chemical utility and reaction uniformity throughout the plugs. Investigations using Raman microscopy showed uniform beads distribution. Plugs were subjected to microwave chemistry and it was demonstrated that temperatures had to be carefully controlled to maintain their physical shape. A number of plugs-supported Pd catalysts were prepared: phosphine ligand-bound Pd, anchored palladacycle and cross-linked resin plugs-entrapped Pd. Their activity was assessed in Suzuki, Sonogashira and Heck cross-couplings and ranged from moderate to excellent. The latter displayed the best properties (activity, recyclability, low leaching), while reaction times could be reduced from days to minutes through the use of microwave irradiation. 3-phase tests revealed that the catalysts were truly heterogeneous when supported on the m-XL-Pd plugs. Peptides were synthesised on plugs with great efficiency and purity by either continuous flow or use of microwave irradiation.