|dc.description.abstract||Key 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.||