Jozef Hodyl PhD Thesis - Theses - Flinders University

co-workers in their investigations relating to neutral oxygen donors as regulators ofselectivity for Pb(II) ions. 100 Kimura et al. 125 utilised (S)-styrene oxide to attach abenzyl alcohol pendant arm to cyclen. This mono-N substituted cyclen derivativewas then complexed with zinc(II) to yield a model biocatalyst for cleavage ofphosphodiester bonds. 125 In an investigation of full cavity development by tetra-Nsubstitutionwith benzyl alcohol pendant arms, Whitbread et al., found through abinitio modelling work that the phenyl groups of a ligand formed in this way wouldjuxtapose to give a shallow cavity. 99, 100, 126 However, although these studies of thiscomplex showed its suitability as a potential receptor, exploration of guest inclusionwith 25 was not pursued due to the low yields (ca. 40%) obtained when producing96, 126the ligand.In 1999 Smith synthesised 26, which has come to be known, within theWainwright group, as one of the first generation metal-ion activated aromatic anionreceptors. 90, 93-97 It is possible to alter the size of the cavity within these receptors incorrespondence with the ionic radius of the coordinating metal. 126, 127 Thus the Pb(II)complexes appear to have slightly larger cavities than the Cd(II) complexes. Thesestudies by Smith proved to be the advent of investigation into receptor complexes ofthis class. They operate with considerable efficacy by including aromatic anions,such as phenolates, sulfonates and benzoates and, aromatic amino acids.Smith obtained crystal structures for many of the inclusion complexes formedwith his first generation receptor, 26, two of which are shown in Figures 1.10 and1.11. These crystal structures reveal the mode of bonding between the aromaticanionic guest species and the first generation receptor as primarily being hydrogenbonding between the guest oxoanion and the host pendant hydroxy groups. Althoughπ-π interactions between the host aromatic rings and that of the guest are not22