Reactions of coordinated aminoacetato ligands on cobalt(III) : intramolecular alkylation and decarboxylation

Abstract

This thesis describes the synthesis and characterisation of a range of mixed ligand cobalt(III) complexes designed for the investigation of template alkylation reactions. These intramolecular reactions lead to the formation of complexes containing new macrocyclic and acyclic hexadentate ligands. One of the cobalt(IH) complexes contains a new pendant-arm macrocycle 1,4~bis(carboxymethyl)cyclam, 1,4-BCC. [Co(l,4-BCC)]+ undergoes a photochemically induced decarboxylation reaction to generate a complex which incorporates a o-bound alkyl carbon as part of the polydentate ligand. The isolation of 1,4-BCC-4HC1 through demetallation of [Co(l,4-BCC)]+ and the preparation of 1,4-BCC complexes of other transition metals are also described. Chapter One is a survey of the literature dealing with the preparation and coordination chemistry of cyclam (1,4,8,11-tetraazacyclotetradecane) and a range of related substituted tetraazamacrocycles based on the cyclam ligand framework. Chapter Two details the preparation of cobalt(III) complexes containing bidentate haloalkylamine and either amino acid or amine tetradentate ligands. The alkylation reactions of complexes containing A/A'-bis(carboxymethyl)ethylenediamine are described and the characterisation of the resulting products is reported. The products include a cobalt(III) complex of a polydentate ligand incorporating an aziridinyl moiety and a macrocyclic cobalt(III) complex, [Co(l,4-BCC)]+. Chapter Three provides an investigation of the photochemical decarboxylation reaction of [Co(l,4-BCC)]+. This leads to formation of a structurally interesting complex that contains an unusual three-membered chelate ring incorporating a coordinated alkyl carbon. The photochemical decarboxylation reactions of two related cobalt(III) macrocyclic complexes are also described. Chapter Four describes the preparation and characterisation of the cobalt(II) complex of 1,4-BCC and the isolation of 1,4-BCC-4HC1 through demetallation of [Co(l,4-BCC)]+. The synthesis and characterisation of copper(II) nickel (II), zinc(II) and chromium(III) complexes of 1,4-BCC are detailed.