H-bond directed self-assembly of oligomeric molecular strands and hydrogen mediated rhodium-catalyzed reductive cyclization of 1,6-enynes

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dc.contributor.advisorKrische, Michael J.en
dc.creatorGong, Heguien
dc.date.accessioned2008-08-28T22:24:01Zen
dc.date.available2008-08-28T22:24:01Zen
dc.date.issued2005en
dc.descriptiontexten
dc.description.abstractKey structural and interactional features of the components for hydrogen bond mediated self-assembly are reviewed, with emphasis on the assembly of synthetic oligomers to form duplexes and tubular structures, as well as related applications in the design of functional materials. A strategy for the preparation of molecular strands that self-assemble through the action of interstrand H-bonds to form duplex superstructures is described. Specifically, duplex oligomers based on the 3,6-diaminopyridazine hydrogen-bonding motif were designed and prepared. The mode of assembly and the thermodynamic parameters of duplex aggregation are established by X-ray crystallographic analysis, 1 H NMR dilution experiments, isothermal titration calorimetry (ITC) and vapor pressure osmometry (VPO). ITC analysis indicates a strong positive cooperative effect upon strand extension from monomer to trimer. In addition, studies toward the design of molecular strands that assemble to form tubular structures are described. Here, alkyl chains decorated with aminopyrazolone moieties were examined. In the solid state, aminopyrazolones aggregate to form either linear H-bonded tapes or discrete cyclic tetramers, as established by single crystal X-ray diffraction analysis. Evidence for cyclic aggregation in solution, though not conclusive, led us to investigate bis(aminopyrazolone) systems, whereby the energy bias between the linear and cyclic aggregation modes could potentially be magnified to favor the latter. However, single crystal X-ray diffraction analysis of S,S-dihexylpropyl bis(aminopyrazolone) reveals a double H-bonded tape. The mode of assembly in solution for the bis(aminopyrazolone) could not be established unambiguously. Finally, the use of elemental hydrogen as a terminal reductant in the rhodiumcatalyzed enantioselective reductive cyclization of 1,6-enynes is described. Whereas 1,6- enynes containing 1,2-substituted alkenes fail to provide reductive cyclization products due to competitive cycloisomerization, related alkenes in the form of conjugated enones afford reductive cyclization products in good to excellent yield and enantioselection.
dc.description.departmentChemistry and Biochemistryen
dc.description.departmentChemistryen
dc.format.mediumelectronicen
dc.identifierb6073131xen
dc.identifier.oclc67233340en
dc.identifier.urihttp://hdl.handle.net/2152/1925en
dc.language.isoengen
dc.rightsCopyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en
dc.subject.lcshHydrogen bondingen
dc.subject.lcshOligomersen
dc.titleH-bond directed self-assembly of oligomeric molecular strands and hydrogen mediated rhodium-catalyzed reductive cyclization of 1,6-enynesen
dc.type.genreThesisen

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