The synthesis of new ‘reinforced’ O2N2- and O3N2-donor single macrocycles together with isomeric three-ring products is described. The new derivatives, which respectively incorporate intra- and inter-ring bridges between nitrogen donor atoms, were obtained on reaction of the parent membered macrocycles with 1,3-dibromopropane (or, in the case of the monomeric ‘reinforced’ rings, also 1,2-dibromoethane).
An investigation of the interaction of zinc(II), cadmium(II), silver(I) and lead(II) with a series of mixed-donor dibenzo-substituted macrocyclic ligands, incorporating O2N3-, O2N4-, O3N2-, O3N3-, O4N2- and O2N3S-donor sets, has been carried out. The log K values for the respective complexes in 95% methanol (I = 0·1; Et4NClO4, 25°C) have been determined potentiometrically. All ligands form 1 : 1 (metal/ligand) complexes with the above metal ions although in isolated cases species of type MLH2+ were also observed. An investigation of the effect of variation of ligand structure on the respective complex stabilities has been carried out and the results compared with those obtained previously for closely related mixed-donor macrocyclic systems. The binding of silver(I) and lead(II) to the 17- and 18-membered O3N2-ligand systems has been assessed in (CD3)2SO by means of 13C n.m.r. spin–lattice relaxation (T1) studies as well as by observation of the induced chemical shifts of particular ligand resonances on complex formation. Overall, the n.m.r. results correlate well with the observed thermodynamic stabilities of the individual complexes.
The syntheses of N-benzylated macrocyclic ligands incorporating O2N2-, O3N2- and O2N3-donor sets, and ring sizes from 15- to 18-membered, is described. The new derivatives were obtained by benzylation of the previously reported parent macrocycles with benzyl bromide in acetonitrile containing suspended sodium carbonate or bicarbonate. The X-ray structure determination of a tribenzylated product containing a 17-membered, O2N3-donor macrocyclic ring is described.