Macrocycles as platforms for mono-and dinuclear calcium chemistry

Abstract

This thesis presents the design and structure of a number of Schiff-base pyrrole macrocycles, their use in the formation of mono- and dinuclear calcium complexes, and reactions with various alkali- and transition metals to form mixed-metal clusters. Chapter One introduces the range of Schiff-base macrocycles with tuneable properties for various synthetic applications. Previously reported complexes of various s-, d- and f-block metals in these macrocyclic frameworks are also discussed. Research into calcium chemistry is reviewed, both in catalysis of synthetic organic processes, and in synthetic modelling of reaction clusters found in protein structures. Chapter Two details the synthesis of three monometallic calcium complexes utilising Schiff base macrocycles H4LEt and H4LA, and dipyrrin ligand HLD. Reactions of Ca(THF)2(H2LEt) with transition metal halides and amines is outlined, leading to the formation of M2(LEt) (M = Fe, Co, Cu). Deprotonation of Ca(THF)2(H2LEt) with alkali metal amines forms calcium-alkali metal complexes; further reactivity of these with transition metal halides demonstrates unusual stoichiometry in the synthesis of mixed-metal clusters. Some of these complexes were assessed for catalytic activity in the hydroamination of isocyanates. Chapter Three describes the synthesis and characterisation of bimetallic calcium complexes of the ligands H4LEt, H4LA and H4LS5. Reactions of Ca2(THF)2(μ- THF)(LEt) with a range of small molecules - including H2O, LiOH and KOH - is outlined. In particular, reactivity of Ca2(THF)2(μ-THF)(LEt) with NaOH yielded calcium-alkali metal clusters Ca2(THF)2(μ-OH)(Na{THF}2)(LEt) and Ca2(THF)2(μ- OH)2(Na{THF})2(LEt), which displayed alternate wedged and bowl-shaped conformations of the macrocycle ligand. Further homobimetallic complex syntheses of M2(LEt) (M = Sn, Mn, Sr) are also outlined for comparison to calcium complexes. Chapter Four presents a summary of the work presented in this thesis, and Chapter Five outlines the full experimental procedures and analytical data for all described complexes.