Pateman, Andrew Glen; (1999) Copper catalysed aziridination reactions. Doctoral thesis (Ph.D.), University College London.

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Abstract

Numerous copper complexes of differing structural types, including a wide selection of poly(pyrazolyl)borate, dithiocarbamate and phosphine complexes, were synthesised and characterised. The structural and solution properties of these complexes are discussed. The ability of each of these complexes to catalyse the aziridination of styrene by Phl=NTos was assessed, the reactivities then being related to their structural and solution properties. A selected number of the more active complexes were assessed as catalysts for the aziridination of several different substrates. Nitrene sources other than Phl=NTos were also utilised, with TosNCINa being particularly effective. After a series of aziridinations using varying equivalents of substrate and quantities of catalyst, copper triphenylphosphine complexes were shown to be the most active catalysts yet employed. In contrast to the complexes [Cu(R2dtc)2]CIO4 (R=Me, Et), the copper (III) complexes [Cu(R2dtc)2][FeCl4] (R=Me, Et, Pyd) were found to be active catalysts. This activity is suggested to result from reduction by Cl- which is produced by reaction of [FeCl4]- with Phl=NTos. Asymmetric aziridination catalysed by novel ligand-metal combinations was also investigated. Complexes of the novel amido ligands TosNSC(NR2)S and TOSNSC(NR2)SNTOS, formed by step-wise insertion of NTos groups into metal sulfur bonds, were found to be by-products of aziridination reactions using dithiocarbamate complexes as catalysts. The crystal structures of [Cu(TosNSC(NMe2)SNTos)2], [Cu(TosNSC(NEt2)S)2], [Ni(TosNSC(NEt2)S)2] and [Co(TosNSC(NEt2)SNTos)2], as well as their reactivities and abilities as aziridination catalysts are discussed. The mechanism of copper catalysed aziridination was investigated and strong evidence for the active catalyst being a copper(I) species was obtained. Evidence for alkene precoordination was gathered and a case for the existence of a mononuclear catalytic site and for a concerted transfer of nitrene to substrate is discussed. A likely catalytic cycle is then proposed.

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