| Summary: | Green Chemistry aims to modify chemical processes so that they are more friendly to the environment. The 9th principle of Green Chemistry emphasises the use of catalytic reagents in chemical processes. One way in which ionic liquids can implement this principle is in two-phase catalytic processes. A major drawback of homogenous catalysis processes is associated with the separation of the catalyst from the products. This can be solved by the use of biphasic catalysis, in which the catalyst can be reused several times without any significant changes in its catalytic performance. However, it is vital to understand how catalysts interact with the solvents in a biphasic solvent system. On one hand, it is advantageous to use an ionic form of catalyst (e.g Cu2+) because this improves the retention of the catalyst in the ionic liquid. However, using charged ions affects their catalytic performance, because their coordination characteristics are changed. Many catalysts are transition metal complexes. Therefore, a solvatochromic transition metal is an ideal probe to study the behaviour of ionic liquid, specifically how do the non-coordinating anions in ionic liquids coordinate to metal centres? In this thesis, a set of solvatochromic copper complexes with different charges were synthesised and characterised. The monocationic complexes had the form [Cu(acac)(tmen)]X (acac = acetylacetonate, tmen = tetramethylethylenediamine) where X were Cl⁻, [NO3]⁻, [SCN]⁻, [OTf]⁻, [NTf2]⁻ and [PF6]⁻. The neutral complex was Cu(hfac)2 (hfac = hexafluoroacetonate). A set of non-functionalised ionic liquids and functionalised ionic liquids (FIL) containing hydroxyl, nitrile and ketone groups were also synthesised and characterised. The Kamlet-Taft multi parameter polarity scales were used to study the solvent-solute interactions of the ionic liquids by means of dipolarity/polarizability (π*), hydrogen bond donating ability (α) and hydrogen bond accepting ability (β). The UV-Vis absorption spectra of the complexes were measured in solid state, dichloroethane and ionic liquid solutions. Analysis of these spectra suggested all these weakly coordinating anions coordinate with the copper centre in a different manner depending on the How do Non-coordinating Anions in Ionic Liquids coordinate to Metal Centres coordinating ability of the anion and also the charge of the copper centre. The coordination mode and the order of binding strength for the individual anions were fully studied and analysed. The correlation between νmax and solvent donor number was investigated by measuring UV-vis spectra in a range of molecular solvents, and was used to predict the donor numbers of the ionic liquid solvents. The apparent donor number of ionic liquids was also predicted using the value from the spectra measured in ionic liquids. The effect of functionalised groups in ionic liquids on donor ability has also been investigated by comparing the results from non-functionalied and functionalised ionic liquids.
|
|---|
