Studies on functionalised macrocyclic ligands

Tei, Lorenzo (2001) Studies on functionalised macrocyclic ligands. PhD thesis, University of Nottingham.

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Abstract

The work presented in this thesis hinges on three main topics: a) the coordination chemistry of symmetric and asymmetric derivatives of [9]aneN3 towards lanthanide ions; b) the transition metal co-ordination chemistry of nitrile and amino derivatives of [9]aneN3 and [15]aneN3O2; c) the use of macrocyclic ligands for the synthesis of polymeric Ag' complexes.

Chapter 3 describes the Ln"' complexes of the ligand obtained by Schiffbase condensation of 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane (L) with three molar equivalents of sodium pyruvate using the Ln0' ion as templating agent. The mononuclear complexes [Ln(La)] (Ln"' = Y10, Sm"', Gd"', Dy"', Eu", Yb"', La"') have been prepared and characterised, and in most cases the crystal structure has also been determined. NMR spectroscopic studies on the diamagnetic [Y(La)] and [La(La)] complexes and on paramagnetic [Yb(La)] and [Sm(La)] complexes have been carried out. Variable temperature 1H NMR behaviour of the [Y(La)] and [Yb(La)] complexes has also been investigated.

Hydrolysis experiments on the [La(La)] complex in D20 at neutral and acidic pH have been performed in order to determine the stability of such a complex in in vivo conditions. Moreover, lanthanide properties such as relaxivity of the Gd"' complex and Dysprosium Induced Shift (DIS) have been determined in order to obtain information either about the efficiency as contrast agent of the Gd"' complex and the number of water molecules bound to the metal centre. After the study on the nine co-ordinate complexes [Ln(La)] discussed in Chapter 3, Chapter 4 reports the Ln°1 complexes obtained by changing the ketone employed for the Schiff-base condensation with the triamine L. Two different acetylphosphonate monoesters have been used in order to form novel nine co-ordinate Ln"' complexes: the synthesis of [Ln(Lb)] (Ln"' = Y"', Gds", Yb"', La'y') and [Ln(Lc)] (Ln"' = Y"", Gd"', Eu") complexes has been achieved by Schiffbase condensation of the triamine (L) with methyl sodium acetyl phosphonate and methoxybenzyl sodium acetyl phosphonate, respectively, using the Ln01 ion as templating agent. These Ln"' complexes have been studied again by X-ray crystallography and NMR spectroscopy. Since the nine co-ordinate lanthanide complexes such as [Ln(Lb)] and [Ln(L`)] contain three chiral phosphorus centres, four possible diastereomers, each of them with two enantiomers, could be distinguished and NMR spectroscopic studies have been carried out in order to determine the four different diastereomers present in solution. As in Chapter 3, hydrolysis experiments on the Y" complexes with Lb and Lc and relaxivity ofthe Gd1° complexes have been determined.

The ligands discussed in Chapter 5 have been synthesised in order to provide a set of seven or eight donor atoms for the co-ordination of lanthanide ions, leaving one or two co-ordination sites available for the binding of water molecules. Therefore, 4,7-bis(2-aminoethyl)-1,4,7-triazacyclononane (L2), 1-(carboxymethyl)-4,7-bis(2-aminoethyl)-1,4,7-triazacyclononane (HL3) and 1-(2-hydroxyethyl)-4,7-bis(2-aminoethyl)-1,4,7-triazacyclononane (HL4) have been synthesised and then reacted with two equivalents of sodium pyruvate, methyl sodium acetyl phosphonate or methoxybenzyl sodium acetyl phosphonate using the Ln" ion as templating agent. A large number of lanthanide complexes with formulations [Ln(L2a)(CH3CO2)], [Ln(L2b)(CH3CO2)], [Ln(L2°)(CH3CO2)], [Ln(L3a)] [Ln(L3b)], [Ln(L4a)] and [Ln(L4b)] have been synthesised and characterised. The single crystal X-ray diffraction analysis of [Gd(L2a)(CH3CO2)]"CH30H, the 1H and 13C NMR spectra and the hydrolysis experiments on the V" complexes with L 2a, L2b, L2c, L3a, L3b, L 4a and L 4b are reported. Relaxivity of the Gd" complexes and Dysprosium Induced Shift on [Dy(L2a)(CH3CO2)], [Dy(L3a)] and [Dy(L4a)] have been determined.

Chapter 6 describes the co-ordination chemistry of symmetric and asymmetric derivatives of [9]aneN3 towards transition metal ions. The two ligands tris(cyanomethyl)- and tris(2-cyanoethyl)-1,4,7-triazacyciononane (L' and L5, respectively) form peculiar complexes with Cull: using Cu(BF4)2.4H20 in MeOH at 65°C, the methanolysis of two nitriles with formation of imino-ether groups have produced square-based pyramidal Cull complexes. However, from the reaction of L5 with CuC12.2H2O in CH3CN at room temperature, the distorted square-based pyramidal Cull complex [Cu(L5)C12] with the nitrite pendant arms left uncoordinated has been formed. Cull and Zn" complexes with 1-(2-aminoethyl)-1,4,7-triazacyclononane (L7), Mn", Nil', Cull and Zn" complexes with L2, Mn", Cull and Zn" complexes with 1,4,7-tris(3-aminopropyl)-1,4,7 triazacyclononane (L) and Mn" and Zn" complexes with HL3 and HL4 have been prepared and characterised, and in most cases the crystal structure has also been determined. Furthermore, the EPR spectra of the Cull complexes and the 13C NMR spectroscopic data for the Zn" complexes are reported.

Synthesis, solution studies and structural characterisation of complexes with [15]aneN302 derivatives are the topics of Chapter 7. The two ligands 1,4,7-tris(cyanomethyl)-1,4,7-triaza-10,13-dioxacyclopentadecane (L8) and 1,4,7-tris(2-aminoethyl)-1,4,7-triaza-10,13-dioxacyclopentadecane (L9) have been synthesised and their co-ordination chemistry towards transition and posttransition metal ions (Cull, Zn°, Cd" and Pbll) has been studied. Most of the complexes have been structurally characterised and they all show interesting structures: the pendant nitrile arms of L8 are not involved in co-ordination of the metal except for the Pbl' crystal structure and with L9 only larger metal ions such as Cd" and Pbll are bound to all the donor atoms of the ligand. The protonation equilibria of the two ligands and the formation of the Cu", Zn", Cd" and Pb" complexes with L8 and L9 have been studied by means of potentiometric measurements. The protonation constants of the ligands and the stability constants of the complexes are reported and compared to other ligands with similar macrocyclic framework and donor atoms. In order to further investigate the structural features of the complexes in solution, 'H NMR spectra of diamagnetic complexes have also been recorded at various temperatures.

In Chapter 8, the nitrite pendant arm derivatives L', L5, L8 and L1° have been used as building blocks for the synthesis of extended inorganic architectures by reaction with Ag'. The complexes {[Ag(L')]PF6},,,, {[Ag(L')]BF4}oo, {[Ag(L8)]BF4}. and [Ag(L10)]PF202 have been prepared and structurally characterised. Analogously to other complexes of the same type prepared in the Schröder group, these compounds show nuclearity and dimensionality strictly dependent upon the number and length of the nitrite functionalised pendant arms present in the ligand: these act as linkers between different metal centres. Ag' complexes of [9]aneN3 and [15]aneN302 derivatives bearing three 7-methylquinoline pendant arms have also been prepared and characterised. The crystal structure of the Ag' complex with 1,4,7-tris(7-methylquinolyl)-1,4,7-triaza-10,13-dioxacyclopentadecane (L12) shows theformation of a dimer {[Ag2.5(L12)(PF202)2.5"CH3CN]2w}i th one Ag' co-ordinated linearly by two heterocyclic N-donors and bridging the two units.

Item Type:Thesis (PhD)
Supervisors:Schroder, M.
Faculties/Schools:UK Campuses > Faculty of Science > School of Chemistry
ID Code:2386
Deposited By:Mrs Olga Lashkova
Deposited On:22 Dec 2011 15:20
Last Modified:22 Dec 2011 15:22

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