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The promotion of intramolecular cyclisations using various synthetic methodologies remains an area of considerable interest in organic chemistry. In this thesis, the potential for large, bulky groups ("steric buttresses") to promote intramolecular cyclisations by a combination of entropic and enthalpic factors is presented. For the purposes of this study both Diels-Alder and ene cyclisations have been studied. The use of steric buttresses to promote the ene cyclisation of a 1,7-diene under relatively mild conditions is described, with different buttressing groups attached, to enable comparison of their relative buttressing ability. In this series the thermal stability of the cyclic products was also investigated, thus allowing further conclusions to be drawn on the buttressing ability of the groups studied. The ene reaction of a range of 1,6-dienes to give substituted pyrrolidines was investigated. This has enabled comparisons to be made on the reactivity of the enophiles in question. More importantly, the relative buttressing ability of the buttresses studied has been assesseda, llowing their ability to both promote cyclisation and control selectivity to be classified. In addition our efforts to develop a viable synthetic route to kainic acid are discussed. The thermolysis of 1,6-dienes incorporating a hetero-enophile component was also the subject of study. The enophiles in this case ranged from carbonyl compounds to their imino and nitrile counterparts. Once again, this has enabled conclusions to be drawn on the reactivity of the enophiles involved. In addition, these studies have allowed us to better understand the suitability of steric buttressing as an aid to intramolecular cyclisations. Finally, in an effort to develop a chiral steric buttressing methodology, the use of ß-cyclodextrin ("macrocyclic steric buttressing") to promote an intramolecular Diels- Alder cyclisation is discussed. This study also resulted in the discovery of a remarkable solvent effect for an intramolecular, pericyclic reaction.

The work presented in this thesis is divided into three distinct chapters covering the chemistry high-nuclearity palladium cages, the many structures of Najera's catalyst compounds and the crystal structures of molecular tweezers and their compounds. The o-palladated, chloro-bridged dimers [Pd2-phenylpyridine(-H) -u-Cl]2 and [pdN,N-dimethylbenzylamine(-H)-Cl]2 react with cyanuric acid in the presence of base to afford closed, chiral cage-molecules in which 12 organo-Pd(11) centres, located in pairs at the vertices of an octohedron, are linked by four tetrahedally arranged cyanurator(3-) ligands.

The fields of anion recognition and anion transport are active areas of research within supramolecular chemistry. This project utilised choiic acid as an advanced starting material to produce a family of macrocyclic oligosteroids. The aim was to apply these novel materials to three separate supramolecular applications; firstly, to bind anions, secondly, to form pseudorotaxanes of DNA, and thirdly to effect the transport of anions across membrane bilayers.

The design, synthesis and crystallisation properties of molecular tectons that are capable of participating in the formation of 3D supramolecular architectures are outlined with two distinct aspects of research presented. A series of molecules which contain both hydrogen bond acceptor and donor sites is synthesised to test the scope of ligands to form porous supramolecular organic frameworks (SOFs). Two analogous tripodal tri carboxylate ligands which are able to form coordination complexes in both a convergent and a divergent mode of coordination are synthesised and their formation of complexes with a variety of metal salts is described.

Since the discovery that it is possible for single molecules to retain their magnetisation in the absence of a magnetic field, this area of research has been considered to be of immense interest research groups from around the world have been attempting to reproduce this phenomenon using a wide range of transition metals and different bridging ligands, each group utilising different synthetic routes in an attempt to produce large nuclearity clusters with large negative spin anisotropy.

Supramolecular cage complexes are of great interest, not only for their structural elegance, but also for their applications. Chapter 1 describes a collection of the many types of cage complexes based on three-dimensional polyhedral shapes and the host-guest chemistry that some cages complexes, enabled by their central cavities, are able to exhibit as they encapsulate small molecules. This thesis contains a number of studies, starting with an investigation into the host-guest chemistry of the tetrahedral cage complex [M4(Lbip)6⊃(BF4)](BF4)7 [where M = Co(II) or Cd(II)]. Anion exchange is able to take place in these complexes, replacing tetrafluoroborate counterions for 1-naphthyl sulfonate or tetraphenylborate molecules. This is summarised in Chapter 2. Chapter 3 details three experiments that look into the stability and the self-assembly process of tetrahedral cage complexes in solution. Two experiments involve the use of electrospray mass spectrometry, one to monitor the exchange of ligands between two tetrahedral cages, and the other to monitor the exchange of metal(II) ions between two isostructural cages. The third study follows the self-assembly of a tetrahedral cage by employing UV/vis spectroscopic titrations and uses equilibrium-restricted factor analysis to model the additive factors in the data as definite chemical species. Chapters 4 and 6 describe new ligands and modifications to ligands by altering the pyrazolyl-pyridine binding units. It has been discovered that using pyrazine in place of pyridine (Chapter 4) on the ligands has a dramatic effect on the construction of the final product. The encapsulation of neutral molecules by the cubic cage complex [Co8(L1,5-nap)12](BF4)16 is investigated in Chapter 5 and it has been discovered that coumarin binds to the internal cavity of the cage. The paramagnetic Co(II) metal centres cause the signals of the cage protons in the 1H NMR spectrum to be spread over a wide range (± 100 ppm). This makes it easy to see the guest signals and to identify any changes due to host-guest binding.

Le modèle de potentiels effectifs d'interactions interatomiques (champ de forces) pour la modélisation d'oxydes a été développé avec l'utilisation de calculs ab initio basés sur la théorie de la fonctionnelle de la densité. Le champ de forces décrit l'énergie potentielle totale du système par la somme de l'énergie électrostatique, celle de dispersion, et l'énergie d'interactions à courte portée. L'énergie électrostatique a été décrite par le modèle d'équilibration des tranferts de charge (SQE) basé sur l'approche d'égalisation du potentiel chimique (CPE). Le calcul de coefficients de dispersion, qui déterminent les interactions de dispersion, a été réalisé avec l'utilisation de fonctions Wannier maximalement localisées (MLWF). Dans les oxydes la position des centres des MLWF près d'atomes permet de calculer les coefficients de dispersion pour chaque atome. Les calculs de ces coefficients ont montré que leur valeur dépend du nombre d'atomes et du rayon de la première sphère de coordination. Le développement de potentiels d'interactions à courte portée a été réalisé avec l'utilisation de la méthode "force-matching", ce qui a permis de choisir la forme analytique des potentiels. Les paramètres des composants du champ de force ont été obtenus sur la base de calculs de chimie quantique de systèmes isolés et périodiques de structures de silicates. Les paramètres du modèle SQE on été calibrés en utilisant le potentiel électrostatique comme la grandeur de référence. Le champ de forces complet a été testé par simulation de polymorphes cristallins de la silice par la méthode de la dynamique moléculaire. Les résultats des calculs ont permis de choisir le meilleur modèle. Le champ de forces sélectionné reproduit bien les caractéristiques structurelles de α-quartz et α-cristobalite. Le calcul de spectres vibrationnels des systèmes montre que le champ de forces sous-estime les constantes de forces Si-O, ce qui conduit à un déplacement de spectres vibrationnels vers les basses fréquences par rapport aux spectres expérimentaux. Des voies visant l'amélioration de la performance du champ de forces sont proposées. / The effective interatomic potential model (force field) for the atomistic modeling of oxide materials was developed with the extensive use of ab initio density functional calculations. The force field represents the total potential energy of system as a sum of the long-range electrostatic, dispersion, and short-range energy contributions. The long-range energy electrostatic energy was described with the use of split-charge equilibration (SQE) model based on the chemical potential equalization (CPE) approach. The electrostatic potential was used as the reference quantity for the calibration of parameters of the SQE model. The computation of dispersion coefficients, which determine the magnitude of the dispersion interactions, was carried out with the use of maximally localized Wannier functions (MLWF). The position of MLWF centers close to the nuclei in oxides permits the computation of the dispersion coefficients in an atom-wise manner. The values of the dispersion coefficients were found to be affected by the coordination number and the radius of the first coordination sphere of atom. The short-range (SR) interaction potentials were designed with the use of force-matching method, which has allowed a judicious choice of the functional form of the SR potentials. The parametrization of the force field components was performed on the basis of extensive quantum-chemical calculations of isolated and periodic silicate systems. The complete force field was tested in the molecular dynamics simulations of crystalline silica polymorphs. Results of the calculations allowed to choose the best model. The selected force field well reproduces structural characteristics of the α-quartz and α-cristobalite polymorphs. The calculation of the vibrational spectra of the systems has shown that the model underestimates the Si-O force constants that leads to a downward shift of the vibrational spectra in comparison with the experimental data. A number of ways aimed at improving the force field's performance are suggested.

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Ce travail est motivé par l’utilisation dans de nombreux dispositifs électrochimiques des mélanges de liquides ioniques (LIs) à base du cation 1-butyl-3-méthylimidazolium (C4mim+) couplés à des anions perfluorés (BF4−, PF6−, TFO−, TFSI−), avec d’autre part des solvants aprotiques polaires tels que l'acétonitrile (AN), la γ-butyrolactone (γ-BL), le carbonate de propylène (PC). Nous avons réalisé des simulations de dynamique moléculaire afin de caractériser la structure locale de ces mélanges. Les variations de la structure microscopique en fonction de la composition du mélange ont été calculées via l’utilisation d’un arsenal de fonctions statistiques avancées, basé sur la structure locale. Celle-ci est largement déterminée par la distribution radiale et orientationelle des plus proches voisins à un ion ou une molécule de référence. Dans un premier temps, la structure locale dans les LIs purs et dans les solvants moléculaires a été analysée. Pour l'ensemble des LIs, il a été établi que les interactions de liaison H de type C-H···X impliquant les atomes d’hydrogène H2,4,5 du cycle imidazolium et les atomes électronégatifs de l’anion sont faibles et peuvent être classés dans l’ordre suivant TFO-, BF4-, PF6-, TFSI-. Pour le solvant pur, nos résultats montrent que les interactions dipôle-dipôle jouent un rôle important dans la structure locale des solvants étudiés, alors que les interactions liaison H dans le PC et le γ-BL sont faibles.Les résultats montrent que dans tous les mélanges LI/solvant moléculaire étudiés, la distribution de l'anion autour du cation n'est pas fortement affectée lorsque la fraction molaire du LI, xIL, varie entre 0,3 et 1,0. Mais pour les valeurs de xIL inférieures à 0,3 les interactions entre cation et anion sont fortement diminuées. Ces résultats corroborent les données publiées sur le comportement du déplacement chimique du proton H² en fonction de xIL. Nos résultats soulignent aussi l'importance des interactions anion-solvant dans la description de la structure locale des mélanges LI/solvant moléculaire. / Mixtures of imidazolium ionic liquids (ILs) with perfluorinated anions and dipolar aprotic solvent are promising candidates for electrolytic components used in different electrochemical applications. Current state of technologies requires detailed information on the influence of the mixture composition on the physical and chemical properties of the mixture. This thesis presents a molecular dynamics simulation analysis of the local structure organization of the mixtures of 1-butyl-3-methylimidazolium (C4mim+) ILs with perfluorinated anions (BF4‒, PF6‒, TFO‒, TFSI‒) and dipolar aprotic solvents such as acetonitrile (AN), γ-butyrolactone (GBL) and propylene carbonate (PC). As a first step, the local structure in the neat ILs and molecular solvents has been analyzed. For the set of ILs it was established that H-bonding interactions at the H2 site is strongly enhanced compared to the H4-5 sites in the case of asymmetric and/or strongly basic anions like TFO− or TFSI−. The cation-cation contacts via the aggregation of the butyl chains is much stronger and less anion-dependent than the π+-π+ stacking of the imidazolium rings. For the pure solvent our results show that although the dominant dipole-dipole orientation between a reference molecule and first neighbor is the antiparallel one, while for the subsequent neighbors the antiparallel orientation is gradually weakened in favor of the parallel one. More distant neighbors tend to be parallel to the reference molecule. A deep analysis of the local structure made it possible to identify the presence of weak hydrogen bonds in the selected dipolar solvents. For the mixtures of imidazolium-based ILs the results show that in all the studied IL/molecular solvent mixtures, the distribution of the anion around the cation is not drastically affected in the range of xIL between 1.0 and 0.3 and for further decrease of xIL noticeable changes in the distance characteristics describing the cation and anion hydrogen bonding interactions, occur. These changes are associated with the expected weakening of the cation and anion interactions. These results are in good agreement with the behavior of the 2H chemical shift as a function of xIL. Furthermore, our results point out to the importance of the anion-solvent interactions in describing the local structure in these mixtures.