The synthesis and characterization by X-ray crystallography of the complexes [Ir(cod)(py)(L)]PF6 (L = IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (2); L = IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (3); L = ICy, 1,3-bis(cyclohexyl)imidazol-2-ylidene (4)) are reported. Complexes 2−4 have been employed as catalysts for transfer hydrogenation reactions from 2-propanol to a number of unsaturated substrates and their activity compared with that of the related cationic iridium(I) species [Ir(cod)(py)(SIMes)]PF6 (1), [Ir(cod)(py)(PCy3)]PF6 (5), and complexes formed in situ from [Ir(cod)(py)2]PF6 and diazabutadienes (RNCHCHNR, DAB-R; R = cyclohexyl, DAB-Cy; R = 2,4,6-trimethylphenyl, DAB-Mes; R = adamantyl, DAB-Ad; R = 2,4,6-trimethoxyphenyl, DAB-trimethoxyphenyl). All complexes tested were found to be active catalysts for transfer hydrogenation of ketones, with complex 4 displaying the highest activity. Complex 4 also exhibits moderate activity toward simple olefins and an aromatic nitro co...

Cationic iridium complexes bearing imidazol-2-ylidene ligands as transfer hydrogenation catalysts

This thesis describes the use of SABRE as a hyperpolarisation technique in NMR spectroscopy. Hyperpolarisation is a technique to increase the observed signal during NMR and MRI experiments. The primary aim of this research project was to develop SABRE towards a specific application – either for the study of reaction mechanisms around a metal centre or for medical imaging.

In this dissertation the use SABRE hyperpolarisation on a number new of substrates, both organic and inorganic, is described. The pyridine derivatives, 3-aminopyridine, (4-phenyl)pyridine, 3-hydroxypyridine, 4-hydroxypyridine, 3-methoxypyridine, 4-methoxypyridine and 2-fluoro-3hydroxypyridine, have been shown to undergo SABRE polarisation for the first time. Two ferrocene derivatives, ferroceneacetonitrile and (4-pyridyl)ferrocene, have been polarised as has [tris(bipyrazyl)ruthenium(II)]2+. This is the first time that SABRE hyperpolarisation of a substrate containing a metal centre has been reported. 

Chapters 4 and 5 detail the effects of pH on SABRE hyperpolarisation with a view to applying SABRE hyperpolarised substrates as pH probes for MRI imaging. The results of this study suggest that tracking the chemical shift of a carbon environment within a substrate will be a viable method for applying SABRE to the production of a hyperpolarised pH probe. The addition of acetic acid to the sample inhibited SABRE polarisation of 3-hydroxypyridine. The addition of caesium carbonate also reduced the SABRE polarisation of 3-hydroxypyridine, in contrast it increased the SABRE polarisation of 4-hydroxypyridine. The dissociation rate constant for both of these substrates increased in the samples containing caesium carbonate when compared to the native samples. SABRE polarisation of 3-methoxypyridine and 4-methoxypyridine was hindered by the addition of caesium carbonate and deuteration of these substrates proceeded much more rapidly in the presence of the base. These effects were seen for both proton and carbon resonances. Additionally, the tertiary carbon resonances of 3-hydroxypyridine and 4-hydroxypyridine were shown to change by 4 ppm across the pH ranges tested. This result has the potential to be further developed into a pH sensitive, SABRE hyperpolarised, probe for medical application.

Harnessing high sensitivity NMR for organic and inorganic substrates

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Harnessing high sensitivity NMR for organic and inorganic substrates