Precipitation of calcium sulfates has been investigated on modified cellulose interfaces and in situ. Spin-coated cellulose thin films were used as model substrates to investigate the crystallization of calcium sulfate dihydrate (gypsum) under industrially relevant conditions using highly concentrated dispersions of calcium sulfate hemihydrate (bassanite). The films were pre-treated in aqueous solutions of calcium, magnesium or iron ions, where regeneration in a solution of Ca 2 + promoted gypsum crystallization on the polysaccharide substrate in the presence of bassanite or in control solutions comprising supersaturated calcium sulfate. Cellulose-bassanite hybrid thin films were also applied as crystallization substrates for gypsum from a dispersion of bassanite. Hybrid thin films were prepared by adding bassanite into a mixture of dissolved polymeric cellulose and nmethyl- morpholine-n-oxide (NMMO) before regeneration of the cellulose structure. The bassanite aggregates acted as crystal growth sites for gypsum, which promoted the crystal growth of gypsum on the hybrid thin film substrate. In situ characterisation of the precipitation of gypsum on the cellulose interface with Raman spectroscopy and X-ray diffraction showed the crystallization to proceed via a bassanite intermediate phase in a solution of calcium and sulfate ions. The existence of the otherwise thermodynamically unstable phase was attributed to the stabilizing effect of dissolved polymeric cellulose and dehydrated NMMO. Precipitation of calcium sulfates in situ produced nanoparticulate amorphous calcium sulfate within a cellulose polymer network. The composite material was prepared by adding aqueous solutions of calcium and sulfate ions into NMMO prior to the dissolution of cellulose, where the hydration of NMMO controlled the transformation of amorphous calcium sulfate to crystalline gypsum.

This work is conducted on nanocrystalline nickel using a range of novel techniques in order to investigate the thermal stability of the microstructure and the mechanical properties of subsequent microstructures. Work is focused on two sources of nanocrystalline nickel produced via electrodeposition with varying levels of impurity sulphur. Impurity sulphur alters the thermal stability of the material; a low sulphur system is stable up to a temperature of 400°C and then coarsens normally to produce a micro-polycrystalline structure, a high sulphur material coarsens at 300°C and the coarsening quickly stagnates leaving a stable microstructure of rv550nm grains. Above 485°C, the high sulphur material is observed to undergo abnormal growth of large planar faceted grains. Observation of the growth post heat treatment via standard electron microscopy techniques gave statistical data complemented by in-situ heat treatment scanning electron microscopy and high temperature resistivity measurement tests to elucidate the stages of growth. A range of macro and micro scale tests were undertaken to investigate the physical properties of the materials; from Vickers hardness and four point bend, to novel in-situ micro-cantilever bend tests. The effect of the increased grain size from heat treatment leads to a reduction in the hardness and yield strength of the materials and in the case of the high sulphur material, segregation of the impurity to the grain boundary led to a ductile to brittle transition.

This thesis describes the synthesis, characterisation and reactions of intramolecular Frustrated Lewis Pairs (FLPs) based on zirconium (IV) complexes bearing nitrogen donor ligands.

The mechanisms of a range of cross-coupling reactions catalysed by cheaper metal catalysts have been investigated in detail using a combination of spectroscopic techniques and computational modelling. For iron-catalysed Negishi cross-coupling reactions supported by phosphine ligands, it is shown that the iron(II) pre-catalysts are reduced in situ to iron(I), which is found to be the only kinetically relevant oxidation state. The characterisation of a range of relevant low-spin iron(l) phosphine complexes has allowed the study of the mechanism in significantly greater detail than before via direct detection of in situ formed iron(I) intermediates using EPR and UV-Vis spectroscopy. Through the study of reaction kinetics, an Eyring analysis and detailed computational modelling, it has been possible to determine the most likely mechanism for the oxidative addition of the electrophile during cross-coupling. The importance of spin-state changes has been demonstrated through computational modelling; only the involvement of high-spin intermediates, arising from the lowspin ground state, can permit the observed rates. iron-catalysed cross-coupling reactions using amine ligands or ligand-free conditions have been shown to behave in a very different manner to those employing phosphine ligands, with a further clear distinction between systems using aryl- and alkyl-based nucleophiles. The use of alkyl nucleophiles containing β-hydrogen atoms leads to immediate decomposition of iron intermediates, whilst the use of β-hydrogen-free alkyl nucleophiles give thermally stable homoleptic 'ate' complexes including [FeBn₃] and [FeBn₄]. Two classes of intermediates are formed simultaneously from aryl based nucleophiles; a thermally stable iron(I) complex proposed as [Fe(ɳ⁶-(4,4'-bitoly)4-tolyl)₂], and thermally labile homoleptic iron(II) 'ate' complexes including [Fe(4-tolyl)₃] and [Fe(4-tolyl)₄]². Crucially, the identity of the metal in the nucleophile is central to the observed reactivity. Computational modelling has been used to investigate the mechanism of transmetallation and aryl transfer in mixtures of boronic acids, diethylzinc and benzyl halides to form diarylmethanes. It is proposed that transmetallation between boron and zinc occurs by direct alkyl and aryl transfer via boron-zinc zwitterionic-like intermediates. The calculated distribution of organoboron and zinc intermediates based on this mechanism in a range of solvents is in good agreement with existing experimental results. A number of potential mechanisms have been considered, using computational modelling, in the coupling of benzyl bromide with mixtures of diethylzinc and aryl boronic acids.

The field of "Frustrated Lewis Pairs" (FLPs), originally associated with the main group, has changed the manner in which the reactivity of small molecules is considered. The aim of the research described in this thesis was to develop the role of transition metals within the field of FLPs. Chapter 1 is a general introduction to the reactivity of small molecules, comparing FLPs and transition metals, focusing on drawing parallels between repOlted transition metal chemistry and FLPs. Chapter 2 describes the limits of phosphine-zirconium FLP systems. Firstly modification of the phosphine within an tethered (intramolecular) system was carried out, comparing the previously reported alkylphosphines with arylphosphines. It was found that the reduced bulk of the arylphosphines resulted in adduct formation between zirconium and phosphorus, this reduced the reactivity when the ancillary ligands on zirconium were Cp* and totally precluded reactivity when the ligands were Cpo Secondly a series of intermolecular phosphine-zirconium systems were investigated for FLP reactivity in an attempt to realise less synthetically demanding systems. Cationic alkoxyzirconocenes were combined with tertiary phosphines and trialled for FLP reactivity; removal of the linker leads to side reactions that prevented the FLP chemistry. In Chapter 3 the concept of taking a transition metal system reported for cooperative action on dihydrogen and applying it as a general frustrated Lewis pair for reaction with a range of small molecules is described. Previously it has been reported that a platinum(II) centre combined with an amine could heterolytically cleave dihydrogen and the same system has been trialled as a general FLP; although directly analogous chemistry is not observed, reactions with carbon dioxide and phenyl acetylene have been shown to occur. Chapter 4 is a description of the coordination chemistry of complexes of the type [Pt(CO)n(diphos)] (n = 1 or 2) where diphos is a xylenyl or tolyl backboned ligand with tert-butyl phosphorus substituents. X-ray diffraction and variable temperature NMR experiments have been carried out to gain better understanding of the supporting xylenyl and tolyl diphos ligands. Under an atmosphere of CO dicarbonyl complexes were observed and found to be in equilibrium with the monocarbonyls. Reaction of the complexes with hydrogen resulted in a mixture of products including the dihydridoplatinum complex. Reaction with ethene led to displacement of the carbonyl ligands. The platinum(O) complexes are shown to be basic by reaction with a Bmnsted acid. In Chapter 5 the chemistry of [Pt(CO)(diphos)] as a base for FLP-type chemistry is reported and discussed. Specifically the platinum(O) complex is combined with B(C6F5)3 and reacted with hydrogen, ethene and carbon dioxide; the products produced show the platinum(O) centre and B(C6F5)3 have acted in a cooperative manner with the small molecule .

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