The molecular and supramolecular chemistry of the rhenium-selenium cluster core: Synthesis and structural studies of stereospecific materials

Abstract

The subject of this dissertation is the development of synthetic methods to allow the employment of the hexanuclear octahedral [Re₆(μ₃-Se)₈]²⁺ cluster core as both a structural component in host materials and as a novel photoactive Lewis acid catalyst. The first chapter describes the first method, cluster condensation, and its application in the preparation in a series of cluster-supported molecular squares. The squares, of the general formula cyclo-[Re₆(μ₃-Se)₈(PR₃)₄(L)]₄(SbF₆)₈ (R=Et, Ph; L=4,4'-dipyndyl derivative), use the cis-coordination mode of the starting material cis-[Re₆(μ₃-Se)₈(PEt ₃)₄(MeCN)₂](SbF₆)₂ as the sole structure directing component. The reaction is shown to be useful for small cyclic species and discrete molecules which feature more elaborate ligands. Based on the limitations of the cluster condensation reaction, a different approach to cluster linkage formation is developed in Chapters two and three. In the interest of continuing the expression of cluster stereochemistry in assemblies larger than the squares, these chapters introduce monocluster complexes featuring secondary functionality placed at the ends of pyridyl based ligands. These secondary functions are moieties capable of hydrogen bonding and metal ion coordination. Chapter three describes a range of hydrogen bound polymers and the use of cluster stereochemistry to dictate their dimension and shape. Chapter four elaborates a series of clusters linked by coordination to secondary metal ions forming porous and nonporous coordination polymers. The rational use of cis-[Re₆(μ₃-Se)₈(PPh₃)₄(4,4'dipyridyl)₂](SbF₆)₂ as a shape directing ligand results in the creation a chain of fused squares and a related zig-zag polymer which can also be created by direct conversion of the square chain structure. Chapter five describes the design of a novel photoactivated Lewis acid catalyst for the preparation of imino esters based on the activated nitrile of [Re₆(μ₃-Se)₈(PEt₃)₅(MeCN)](SbF₆)₂. The synthesis and subsequent photolysis of two imino ester complexes is recounted. Chapter six summarizes the dissertation and proposes some future experiments.