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.

Yes / The first use of a dinuclear UIII/UIII complex in the activation of small molecules is reported. The octadentate Schiff-base pyrrole, anthracene-hinged ‘Pacman’ ligand LA combines two strongly reducing UIII centres and three borohydride ligands in [M(THF)4][{U(BH4)}2(m-BH4)(LA)(THF)2] 1-M, (M ¼ Li, Na, K). The two borohydride ligands bound to uranium outside the macrocyclic cleft are readily substituted by aryloxide ligands, resulting in a single, weakly-bound, encapsulated endo group 1 metal borohydride bridging the two UIII centres in [{U(OAr)}2(m-MBH4)(LA)(THF)2] 2-M (OAr ¼ OC6H2tBu3-2,4,6, M ¼ Na, K). X-ray crystallographic analysis shows that, for 2-K, in addition to the endo-BH4 ligand the potassium countercation is also incorporated into the cleft through h5-interactions with the pyrrolides instead of extraneous donor solvent. As such, 2-K has a significantly higher solubility in non-polar solvents and a wider U–U separation compared to the ‘ate’ complex 1. The cooperative reducing capability of the two UIII centres now enforced by the large and relatively flexible macrocycle is compared for the two complexes, recognising that the borohydrides can provide additional reducing capability, and that the aryloxide-capped 2-K is constrained to reactions within the cleft. The reaction between 1-Na and S8 affords an insoluble, presumably polymeric paramagnetic complex with bridging uranium sulfides, while that with CS2 results in oxidation of each UIII to the notably high UV oxidation state, forming the unusual trithiocarbonate (CS3)2 as a ligand in [{U(CS3)}2(m-k2:k2-CS3)(LA)] (4). The reaction between 2-K and S8 results in quantitative substitution of the endo-KBH4 by a bridging persulfido (S2)2 group and oxidation of each UIII to UIV, yielding [{U(OAr)}2(m-k2:k2-S2)(LA)] (5). The reaction of 2-K with CS2 affords a thermally unstable adduct which is tentatively assigned as containing a carbon disulfido (CS2)2 ligand bridging the two U centres (6a), but only the mono-bridged sulfido (S)2 complex [{U(OAr)}2(m-S (LA)] (6) is isolated. The persulfido complex (5) can also be synthesised from the mono-bridged sulfido complex (6) by the addition of another equivalent of sulfur. / EPSRC, European COST network