Synthesis and application of novel homochiral imidazolium salts
Alhashimy, Nameer (2004) Synthesis and application of novel homochiral imidazolium salts. PhD thesis, Dublin City University.
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Imidazolium salts derived from azolium systems have diverse applications in a wide range o f areas within chemistry and biology. Of particular interest is the application o f imidazolium salts as potential anion and small molecule receptors. Recent work has demonstrated the potential o f arranging imidazolium salts around a benzene scaffold. These new tripodal receptors demonstrated excellent selectivities and strong binding constants for halide anions. We believed that this work could be further developed to expand the range of binding capabilities for this new class of tripodal receptor. The objectives o f this research was to prepare a new series o f enantioselective homochiral tripodal receptors using a benzene ring scaffold.
Herein we report the synthesis of l,3,5-tris[N-((-)-cis-myrtanylimidazolium) methyl]2,4,6,-trimethylbenzene tri(hexafluorophosphate) (156a), l,3,5-tris[((R)-3-methyl-2-butylimidazolium)methyl]2,4,5-trimethylbenzene tri(hexafluoroosphate) (156b), l,3,5-tris[((S)-l-(2-phenyl)ethylimidazolium)methyl]2,4,6-trimethylbenzene tri(hexafluorophosphate) (156c), l,3,5-tris[((S)-l-(2-Naphthyl) ethylimidazolium)methyl]2,4,6-trimethylbenzene tri(hexafluorophosphate) (156d).
All receptors were completely characterised. These new receptors were fully investigated for both anion recognition and as enantioselective anion receptors. It was found by 1U NMR studies that these new chiral receptors can selectively bind chloride and bromide with high binding constants. Further 1H NMR studies revealed that receptor (156a) is able to enantioselectively discriminate between the enantiomers of sodium 2-aminopropionate salts.
These new homochiral imidazolium receptors were also converted to their respective silver carbenes and their potential as ligands in the catalysis of 1,4 conjugate addition reactions was explored. It was found that the carbene derivatives of these tripodal receptors were inefficient as ligands, perhaps due to the small size o f the receptor cavities. All o f the homochiral receptors that were prepared were investigated for possible biological activity against P. aeruginosa and C. albicans.
Also reported is the preparation o f a new l,3-7V-heterocyclic silver carbene complex which was studied as a potential ligand for 1,4 conjugate additions. This ligand was also successfully converted to its palladium complex and was explored as a potential catalyst in the Heck reaction.
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