This project develops the chemistry of Group 1 dihydropyridines, a class of compound previously largely confined to lithium. A synthetic approach to sodium and potassium derivatives has been optimised via metathesis, the new compounds have been thoroughly characterised and the catalytic ability of the family has been assessed.Firstly, the previously reported lithium dihydropyridine (LiDHP) proved a valuable precursor to access five new s-block dihydropyridines that have been isolated and characterised by X-ray crystallography and NMR spectroscopy. The isomerisations of the 1,2- to the 1,4- isomeric forms have been monitored by NMR spectroscopy.Thermal studies on the non-solvated derivatives were performed and related to their ability to release metal hydride. Their proficiency to act as metal hydride surrogates was confirmed in reactions reducing benzophenone. Secondly, the first catalytic role of LiDHPs was established in the successful catalysed dehydrogenative cyclisation of diamine boranes. It was found that the LiDHP catalyst could compete with a ruthenium catalyst to prepare desired 1,3,2-borolidines. A three-step mechanism has been suggested, (deprotonation, β-hydride elimination and intramolecular hydrogen loss) supported by crystallographically characterised intermediates and extensive NMR studies. Formed in situ, the borolidines were further functionalised to more synthetically useful phenylborane derivatives.The LiDHP was next subjected to a further catalytic screening for hydroboration of carbonyls. This also proved successful for preparing boronate esters, from a range of aldehydes and ketones with pinacolborane.The reaction was thought to proceed akin to that reported in the literature, namely a hydrometallation followed by a metathesis step. However, an acceptor-donor adduct of pyridine and pinacolborane, characterised by X-ray crystallography, provided insight to a potential alternative pathway in the catalytic cycle.Finally, expanding on the monometallic dihydropyridines, six new heterobimetallic dihydropyridine complexes, Li/Al, K/Al and K/Zn, have been synthesised andcrystallographically characterised. Their structural assembly is contrasted with similar literature complexes.
|Date of Award||20 Sep 2017|
- University Of Strathclyde
|Sponsors||EPSRC (Engineering and Physical Sciences Research Council)|
|Supervisor||Robert Mulvey (Supervisor) & Charles O'Hara (Supervisor)|