Inclusion of chirality in the copper(II) 12-metallacrown-4 framework and the construction of two-dimensional networks

Metallacrowns are metallamacrocyclic analogs of crown ethers that contain an (-M-N-O-) repeat unit {lcub}M = transition metal ion{rcub} in place of the (-C-C-O-) repeat typically found in organic crowns. Previous work with α-aminohydroximate ligands showed that the inclusion of resolved, chiral ligands can results in facial differentiation in 15-Metallacrown-5 complexes. This thesis explores methods of derivatizing β-aminohydroximate ligands to incorporate resolved, organic chirality into copper(II) 12-Metallacrown-4 species. Synthesis of β-phenylalanine involves condensation of benzaldehyde with malonic acid in the presence of ammonium acetate. This is resolved by selective crystallization of the resolved tartrate salt of the β-amine. Introduction of chirality to the α-position involves protection of the parent β-amino acid to a perhydropyrimidin-4-one which can then be selectively alkylated at the α-position. Synthesis of the copper metallacrown is accomplished by combining 5 equivalents of copper salt with 4 equivalents of ligand in methanol or water in an open container resulting in 30–80% yield of crystalline product. {lcub}Cu(II)[12-MC _{Cu(II)N(β-pheHA)}-4]{rcub}2+ is structurally similar to tetraphenylporphyrin (TPP), and although the metallacrown is 25–30% larger, it contains five metal ions and four resolved chiral centers in comparison to the mononuclear, achiral TPP. Addition of a methyl group in {lcub}Cu(II)[12-MC _{Cu(II)N(α-Me-β-Ph-β-alaHA)}-41]{rcub}2+ does not significantly alter the structure of the metallacrown; however, the resulting 12-Metallacrown-4 dimerizes though axial interactions between copper(II) ions of one metallacrown and oxygen atoms within the other metallacrown (Average Cu-O distance = 2.9Å). Bridging also occurs through sulfate anions coordinating to the exterior faces of the metallacrown dimer to form columns of alternating face-to-face interactions and anion bridges through the solid. Inclusion of copper benzoate paddlewheel dimers (Cu₂Bz₄) and nitrate anions in the synthesis of {lcub}Cu(II)[12-MC_{Cu(II)N(β-pheHA)}-4]{rcub}2+ leads to nitrate anion bridging in one dimension and (Cu₂Bz₄) bridging in a second, approximately orthogonal, dimension via coordination to peripheral ligand oxygen atoms. These linkages generate a 2-dimensional layered material. Channels (∼8 × 10Å) exist between the layers containing solvent, and bound nitrate and benzoic acid guests. Use of resolved, chiral ligand in these syntheses results in noncentrosymmetric solids (Space group = P1) that may lead to future use in the areas of selective recognition or catalysis.