Functionalised azamacrocycles.

Abstract

Potential uses of functionalised azamacrocycles have been investigated. Nine new azamacrocyclic ligands have been synthesised and characterised, some containing redox active centres, and these are identified on the following page. In Chapter 2 a series of redox active macrocycles L1 , L2 and L3, incorporating ferrocene as the redox active centre have been synthesised, based on the parent macrocycle 1,4,8,11-tetraazacyclotetradecane (cyclam), and been investigated. Their potential as transition metal ion sensors has been studied. The ligand L1 shows irreversible electrochemistry in acetonitrile solution, with no reverse peak being observed in the cyclic voltammogram. However, on addition of Zn 2 + the system becomes reversible as shown by the reappearance of the reverse peak. The crystal structure of L2 reveals that the nitrogen atoms are not in suitable positions for chelation, in line with the observation that no metal complexes could be made of this macrocycle. The electrochemistry of L2 shows a single four electron cyclic voltammogram and there is no change on addition of transition metal ions. The ligand L3 does show a significant shift in the E½ value for the ferrocene/ferrocenium couple on addition of transition metal ions. In Chapter 3 studies of two macrocycles (L4 and L6) containing the redox active centre as part of the macrocyclic ring itself are described. In the case of L4 ferrocene was used, but owing to problems with the electrochemistry, it was not a good transition metal ion sensor. Metal complexes of this macrocycle were synthesised and are of the general formula [ML4](CH3 COO)2 .xH2O, {M = Zn2 + ,x = 2.5,Ni2 +,x = 4, Cu2 +,x = 3}. A more promising metal ion sensor was the cobalticenium macrocycle L6 and this shows very large shifts in the half wave potential, on the addition of transition metal ions like Zn2 + and Ni2 +. Problems with obtaining very pure samples at the moment hinder its useful application as a transition metal ion sensor. In Chapter 4, two pyrrolidinyl pendant arm triazamacrocycles are discussed L6 and L7, together with some of their transition metal complexes. Two crystal structures have been undertaken of the zinc(II) complexes of L6 and L7. A change in geometry from a trigonal bipyramid to a tetrahedron is brought about by an increase in length of the pendant arm in going from L6 to L7. In Chapter 5, a general route to N-alkylated macro cycles is described. Two new tetra-N-alkylated derivatives of cyclam (L8 and L9) have been synthesised, and their nickel(II) complexes studied. These metal complexes have been compared to the nickel(II) complexes of 1,4,8,11-tetramethyl, 1,4,8,11-tetraazacyclotetradecane (TMC). The complex [Ni(L8)]2 + was obtained as two isomers in nitromethane solution, these are tentatively assigned to the Trans-I and Trans-III conformations. The crystal structure of [Ni(L8)(NCS)2] is six co-ordinate and unusually the macrocycle adopts the Trans-I geometry. The nickel(II) complexes of L9 have the general formula [Ni(L9)(X)]2 + where X= DMSO or H2O. Only one isomer exists in solution as shown by 1 3 C n.m.r, and is assigned to the Trans-I conformation