Azamacrocyclic cobalt catalysts
Ten azamacrocyclic ligands were synthesised and characterised. The coordination chemistry of these ligands was evaluated by the study of their Ni(II), Cu(II) and Zn(II) complexes in the development of azamacrocyclic cobalt catalysts. Co(II) complexes of ligands L3 and L4 were evaluated as potential...
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University of Warwick
1991
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| Online Access: | https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316227 |
| Summary: | Ten azamacrocyclic ligands were synthesised and characterised. The coordination chemistry of these ligands was evaluated by the study of their Ni(II), Cu(II) and Zn(II) complexes in the development of azamacrocyclic cobalt catalysts. Co(II) complexes of ligands L3 and L4 were evaluated as potential auto-oxidation catalysts for aqueous gloss paint systems. These compounds act as catalysts, producing through dry paint films in a shorter time than commercially available catalysts. This surprising result could indicate the presence of a different drying mechanism for these complexes when compared to the commercial catalysts. Ligands L5 and L6 were designed to activate dioxygen when coordinated to Co(II). The X-ray crystal structure of [Zn(L5)](BF4)2 and n.O.e. experiments on [Zn(L6)](BF4)2 prove that the correct theoretical geometry is adopted by the ligands on coordination to metals. The Co(II) complexes of ligands L5 and L6 were not isolated as a result of their high reactivity towards dioxygen. The products obtained were the u-peroxo- bridged dimer species - a result of a bimolecular reaction. The Co(II) compounds were considered too reactive to be used as auto-oxidation catalysts. Azamacrocyclic organocobalt(III) complexes have been shown to act as photopolymerisation catalysts in the polymerisation of alkenes. In water a free radical mechanism occurs. In t.h.f. a metal centred polymerisation is proposed. Diode array gel permeation chromatography of polymeric solutions shows the presence of dimeric and trimeric species which could react to form high molecular weight species. A novel hydridocobalt(III) complex of L8 was prepared by reaction of hydrogen with [Co(L8)]2+. The presence of the Co-H bond was established by chemical means. A similar reaction was attempted for [Co(L7)](BF4)2 but the compound was unstable in solution, reductively eliminating H2-. |
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