Fundamentals and applications of co-crystal methodologies: reactivity, structure determination, and mechanochemistry

1 This thesis describes applications in co-crystal reactivity, structure determination, and mechanochemical preparation. We also investigate the solution-phase reactivities of products derived from a template-directed synthesis. Specifically, we described the acid treatment of an achiral molecular ladder of C2h symmetry composed of five edge-sharing cyclobutane rings, or a [5]-ladderane, that results in cisto transisomerization and/or oxidation of end pyridyl groups. Solution NMR spectroscopy and quantum chemical calculations support the isomerization to generate two diastereomers; namely, an achiral and a unique chiral ladderane. The NMR data, however, could not lead to unambiguous configurational assignments of the two isomers. Single-crystal X-ray diffraction was employed to determine each configuration. One isomer readily crystallized as a pure form and X-ray diffraction revealed the molecule as being achiral based on Ci symmetry. The second isomer resisted crystallization under a variety of conditions. Consequently, a strategy based on a co-crystallization was developed to generate single crystals of the second isomer. Co-crystallization of the isomer with a carboxylic acid readily afforded single crystals that confirmed a chiral ladderane based on C2 symmetry. We also demonstrate how the stereochemistry can be retained upon treatment with acid. It will be shown how a monocyclobutane can be used as a model system when investigating the reactivity of the [5]-ladderane. While investigating the reactivity of a diene diacid we determined that a bicyclobutyl that bears six carboxylic acid groups results from a trimerization of the solid in pure form in the solid state. Powder X-ray diffraction and a co-crystallization are used to solve the structure of the diene and elucidate the stereochemistry of the bicyclobutyl, respectively. Having established the reactivity of the diene diacid we used hydrogenbond-acceptor (HBA) templates to assemble the diacid in the solid state in a photoactive solid for an intermolecular [2 + 2] photocycloaddition as well as a photostable solid. 2 To enhance strategies to generate stereocontrolled products derived from reactive co-crystals mechanochemical methods were applied to eliminate or reduce the solvent used to prepare the co-crystal solids. In particular, we show how supermolecules with olefins organized by hydrogen-bond donor and acceptor templates that react in the solid state rapidly form co-crystals via solvent-free and liquid-assisted grinding. Abstract Approved: ________________________________________ Thesis SupervisorApproved: ________________________________________ Thesis Supervisor ________________________________________ Title and Department _________________________________________