The synthesis and study of bridging heterocyclic ligands
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis describes the synthesis and study of thirty four multidentate heterocyclic bridging ligands, twenty four of which are new compounds. A majority of these ligands incorporate a di-2-pyridyl coordination motif and are capable of chelation to a metal centre with the formation of a six-membered chelate ring, in contrast to the five-membered chelate rings formed by the majority of bridging ligands previously described in the literature. Four ligands were synthesised that represent the first examples of bridging heterocyclic ligands incorporating a radialene core. The ligands described in this thesis are divided into three sections: those prepared from dipyridylmethane precursors, ligands with a di-2-pyridylamine chelating motif, and tripodal ligands, which are capable of facial coordination to an octahedral metal atom. The coordination and metallosupramolecular chemistry of these ligands were investigated with several different metal atoms, predominantly silver(I), copper(II) and palladium(II). With the dipyridylmethyl ligands and the di-2-pyridylarnine-based ligands, both discrete and polymeric structures were obtained, including dinuclear complexes, [2+2] dimeric complexes, molecular polyhedra and one-dimensional coordination polymers. Some novel structures, including a hexanuclear silver cage with an encapsulated fluoride anion and a triply cyclopalladated compound, are described. The tripodal ligands showed a preference for forming discrete complexes with M2L and M2L2 compositions, which included a new type of helicate. Bis(2,2'-bipyridyl)ruthenium complexes of the di-2-pyridylmethane-based and di-2-pyridylamine-based ligands are described and structurally characterised. Despite forming dinuclear complexes in many cases with palladium and copper, all the multidentate di-2-pyridylmethane-based ligands were surprisingly resistant to chelating their intended number of ruthenium atoms. Visible absorption spectroscopy and cyclic voItammetry was used to probe the nature of the metal-ligand and metal-metal interactions in these complexes. In combination with NMR spectroscopy, mass spectrometry and elemental analysis, X-Ray crystallography was used to characterise many of the complexes and metallosupramolecular species produced. The crystal structures of five ligands and fifty one complexes are described.