Composites Of Conducting Polymers: Polyacetylene - Polypyrrole

Pyrrole can be electrochemically polymerised onto polyacetylene anodes. The morphology of the resulting conducting composites depends on the initial doping state (e.g. conductivity) of the polyacetylene. The air and water stability of the conducting composites is excellent compared to doped polyacetylene. Both components conduct the current.     

Diastereo‐ and Enantioselective Iridium Catalyzed Carbonyl (α‐Cyclopropyl)allylation via Transfer Hydrogenation

The first examples of diastereo‐ and enantioselective carbonyl α‐(cyclopropyl)allylation are reported. Under the conditions of iridium catalyzed transfer hydrogenation using the chiral precatalyst (R)‐Ir‐ I modified by SEGPHOS, carbonyl α‐(cyclopropyl)allylation may be achieved with equal facility from alcohol or aldehyde oxidation levels. This methodology provides a conduit to hitherto inaccessible inaccessible enantiomerically enriched cyclopropane‐containing architectures.     

C‐Propargylation Overrides O‐Propargylation in Reactions of Propargyl Chloride with Primary Alcohols: Rhodium‐Catalyzed Transfer Hydrogenation

The canonical S_N2 behavior displayed by alcohols and activated alkyl halides in basic media (O‐alkylation) is superseded by a pathway leading to carbinol C‐alkylation under the conditions of rhodium‐catalyzed transfer hydrogenation. Racemic and asymmetric propargylations are described.     

Hierarchic Supramolecular Interactions within Assemblies in Solution and in the Crystal of 2,3,6,7‐Tetrasubstituted 5,5′‐(Anthracene‐9,10‐diyl)bis[pyrimidin‐2‐amines]

The title compounds 6 and 7 were synthesized in good yield (Schemes 1 and 2), and their mode of assembly was studied both in solution, for the tetrakis(decyloxy) derivative 6 , and in the crystal, for the tetramethoxy analogue 7 . The pyrimidin‐2‐amine moieties of 6 and 7 can engage in three different supramolecular interactions: i) metal ligation via one of the pyrimidine N‐atoms, ii) cooperative double H‐bonding via the NH₂ group, and iii) π–π‐stacking interactions. In solution, coordination of the central Zn‐atom within the soluble porphyrinatozinc complex 19 leads to significant changes in the NMR and absorption spectra of 6 . In the absence of metal ligation, the next strongest interaction is H‐bonding which can operate in nonpolar or moderately polar solvents. In these cases, however, no stacking interaction or inclusion compounds could be put into evidence in the case of 6 by absorption, fluorescence, or NMR spectroscopies. The π‐stacking interactions were only observed in the crystal of 7 in conjunction with double H‐bonding. Slightly disordered DMSO molecules are also H‐bonded to the NH₂ groups of 7 , perturbing the expected packing. The present study illustrates some of the challenges inherent to directing hierarchical assembly processes in the solid state.     

Duplex molecular strands based on the 3,6-diaminopyridazine hydrogen bonding motif: amplifying small-molecule self-assembly preferences through preorganization and iterative arrangement of binding residues

Structural parameters obtained through single-crystal X-ray diffraction analysis of the one-dimensional H-bonding motif expressed by 3,6-diaminopyridazine are applied to the design of related monomeric, dimeric, and trimeric duplex molecular strands. The mode of assembly and the interstrand affinity of the oligomers are established in solution by (1)H NMR dilution experiments, isothermal titration calorimetry (ITC), and vapor pressure osmometry. Single-crystal X-ray crystallographic analysis of the dimeric diaminopyridazine 2a corroborates the intended duplex mode of assembly. Binding free energy per unimer (-DeltaG degrees /n) increases upon extension from monomer to dimer to trimer, signifying a positive cooperative effect. Micromolar binding affinity (K(d) = 1.25 +/- 0.1 microM) was determined for the duplex trimer by ITC in 1,2-dichloroethane at 20 degrees C. These data provide further insight into the structural and interactional features of synthetic duplex oligomers required for high-affinity, high-specificity binding and define new recognition elements for use in nanoscale assembly.