Application of cobalt complexes containing SNS ligands as catalysts for biomimetic paraffin activation.
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Date
2012
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Abstract
A series of SNS ligands have been successfully synthesised and characterised by IR, NMR and
MS. The ligands are divided into two groups and represented by the general formulae: 2,6-
bis(RSCH2)pyridine [R= methyl, ethyl, butyl, cyclohexyl, phenyl] and bis(RSCH2CH2)amine
[R= ethyl, butyl, decyl]. Cobalt complexes of the respective ligands with the general formulae
Co[2,6-bis(RSCH2)pyridine]Cl2 and Co[bis(RSCH2CH2)amine]Cl2 were synthesised and
characterised by IR, elemental analysis and X-ray crystallography (for selected complexes).
Thus, to investigate the electronic and steric effects of the ligand structure on the chemistry and
reactivity of the complexes, the substituents bonded to the two sulfur donor atoms were
sequentially varied and two different nitrogen sources were chosen. Crystal structures of Co[2,6-
bis(CH2SCH2)pyridine]Cl2 (Ia), Co[2,6-bis(CH2CH2SCH2) pyridine]Cl2 (IIa) and Co[2,6-
bis(CH2CH2CH2CH2SCH2)pyridine]Cl2 (IIIa) were obtained. It was found that complex Ia
exists as a molecular dimer linked through two chloride bridges resulting in an octahedral
geometry around each metal centre, while complexes IIa and IIIa are monomers exhibiting a
trigonal bypyrimidal geometry. The complexes were tested as catalysts for the activation of
paraffinic C−H bonds towards the formation of oxygenated products: octanol, octanone, octanal
and octanoic acid from the substrate n-octane. Gas chromatography was utilised to quantify the
products formed and also to calculate the conversion and selectivity of each catalyst system. The
catalytic testing revealed that the ketone products were the most dominant with selectivities of
ca. 90%. The catalyst that was the most active was Co[bis(CH2CH2SCH2CH2)amine]Cl2 (Ib)
with a total n-octane conversion of 23%.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2012.
Keywords
Cobalt compounds., Ligands (Biochemistry), Biomimetics., Theses--Chemistry.