Design, synthesis and evaluation of novel, metal complexing agents

Hagemann, Justin Philip (1997) Design, synthesis and evaluation of novel, metal complexing agents. PhD thesis, Rhodes University.

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Abstract

Various chelating ligands have been designed and synthesised; these include amino-ainide ligands, tetraacetic acid systems and sulfur-containing amide ligands. Difficulties in the synthesis and purification ofthe amino-amide ligands were largely overcome, permitting the mono acylation of ethylenediamine and the synthesis ofbis(2-aminoethyl)-2-benzylpropanediamide. Novel tetraacetic acid ligands, based on the propanediamide backbone and targeted as EDTA analogues, were obtained from their methyl and benzyl esters; but the instability ofthe tetraacids prevented their full characterisation. Bidentate, tridentate and tetradentate sulfur-containing monoamide ligands, based on the orthothio acetanilide moiety, were designed to specifically chelate platinum and palladium in the presence of base metals. In their synthesis, thiocyanation was used to introduce the orth-thio group on para-substituted anilines, and further functionalisation was achieved via appropriate protection of nucleophilic sulfur moieties. A range of tetradentate, sulfur-containing diamide ligands was also synthesised by reacting substituted 2-mercaptoacetanilides with 1,2- dibromoethane. Novel ligands were characterised by spectroscopic ¹H and ¹³C NMR; IR and M S) techniques and elemental (combustion and high resolution MS) analysis. Computer modelling and ¹H NMR chemical shift data have been used to explore the conformational preferences of the sulfur-containing acetanilide ligands. The macrocyclic ligands and systems with ortho-methylthio substituents appear to exhibit the greatest degree of coplanarity ofthe aromatic and amide functions. Solvent extraction studies revealed that the sulfur-containing amide ligands selectively extracted palladium(II) from platinum(II), copper(II}, nickel(II} and cobalt(II}. Even though the palladium(II} was extracted from an acidic medium, certain monoamide ligands were able to complex palladium(II) through their sulfur and deprotonated amide nitrogen donors, a trithia mono amide ligand being observed to displace all the .chloride ligands on palladium to form a monomeric tetracoordinate complex. The diamide'ligands, however, appeared to favour extraction ofpalladium(II) by coordination through their sulfur donors, forming 5-membered sulfur-sulfur chelates. In basic media (pH 8-9), selected sulfur-containing mO!l9apride and diamide ligands have been shown to complex platinum(II) and palladium(II) through their sulfur and deprotonated amide nitrogen donors. At neutral pH, a dimercapto mono amide ligand has been shown to complex platinum from cisplatin with partial expulsion of the ammine ligands, while a macro cyclic trithia mono amide ligand has been observed to complex platinum from tetrachloroplatinate with concomitant deprotonation of the amide nitrogen. Where possible, the complexes were characterised by infrared and ¹H NMR spectroscopy and have also been studied using the computer modelling soft-ware programmes, Momec® and Hyperchem®.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Ligands, Metal complexes, Novel
Subjects:Q Science > QD Chemistry
Divisions:Faculty > Faculty of Science > Chemistry
Supervisors:Kaye, Perry
ID Code:3232
Deposited By: Mrs Carol Perold
Deposited On:29 Aug 2012 06:31
Last Modified:29 Aug 2012 06:31
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