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Title: The synthesis and characterisation of some thiadiazolium rings and related heterocycles
Author: Bacon, C. E.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2010
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This thesis focuses on new synthetic routes to five-membered heterocycles. Chapter 1 reviews five-membered sulphur/nitrogen ring systems with an emphasis on the magnetic and electronic properties of 1,2,3,5-dithiadiazolyl (DTDA) and 1,3,2-dithiazolyl (DTA) radical. Chapter 2 describes a new route to DTDA ring systems which were unobtainable using previous synthetic methodologies; lithium/halogen exchange, treatment with Me3SiN=C=NSiMe3 and subsequent condensation with SC12 followed by a 1e- reduction afforded the 1,2,3-5-dithiadiazolyl radical. The 1-naphthyl, 2-naphthyl and sterically-demanding mesityl derivatives were each characterised using EPR spectroscopy and X-ray diffraction. Whilst 1-naphthyl and 2-naphthyl derivatives dimerise in the solid state, the mesityl derivative remains monomeric in the solid state. Chapter 3 describes the synthesis and characterisation of a new class of thiadiazolylium (TDA) cations via intramolecular co-ordination of S by a 2’-pyridyl substituent in R(py)C=NSC1 (R = py, Ph, C4H3S, pyCO). The nature of the bonding between the pyridyl N atom and S was probed via solution NMR, solid state X-ray diffraction and DFT studies. These studies reveal a synergic interaction between the strength of S-N and S-Cl bonding and subsequent metathesis for less co-ordinating anions leads to further S-N bond strengthening. The methodology was successfully extended to the isoelectronic selenium derivatives. Structural studies reveal stronger Se-Cl covalency and weaker Se-N bonding than their sulphur analogues. Attempts to coordinate these new heterocycles to CuI led to metal-promoted decomposition and isolation of CuII complexes of dipyridylketone (py2CO) and [(py)2C(OEt)(O)]-. Chapter 4 exploits the synthetic methodology outlined in Chapter 3 to form other main group heterocycles; derivatives with BEet2, C(py)(Ph) and C(py)2 in place of sulphur were synthesised.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available