Synthesis And Properties Of Helical Poly(Phenylacetylene)s Bearing L-Proline Derivatives Pendents

In this work, a series of helical poly(phenylacetylene)s bearing L-proline derivatives were synthesized and their chiroptical properties investigated. Furthermore,the asymmetric catalytic performance as chiral catalyst and anion recognition ability as chemosensor for one polymer among the synthetic poly(phenylacetylene) derivatives were discussed.The phenylacetylene monomer with Fmoc-L-hydroxyproline group (PAA-Fmoc-Pro-OH)was synthesized via Sonogashira coupling reaction, off-protecting group TMS and amidation reaction. Then two phenylacetylene monomers with Fmoc groups were synthesized via the reaction between benzoyl chloride or 2-naphthoyl chloride and the active hydroxyl of PAA-Fmoc-Pro-OH. And three novel phenylacetylene monomers with free secondary amino groups were obtained through removing Fmoc groups using morphine. The phenylacetylene monomers with Fmoc groups were polymerized in DMF using a rhodium complex as the catalyst to yield three poly(phenylacetylene) derivatives. And the poly(phenylacetylene) derivatives with free secondary amino groups were synthesized via deprotection reaction. The structure of monomers and polymers were characterized by 1H NMR, IR and GPC. The results showed that the main chain of all the polymers possessed cis-transoid configuration.The main-chain helical conformations of the poly(phenylacetylene) derivatives were confirmed through the analyses of circular dichroism (CD) and polarimeter, and the polymers exhibited various helical conformations in different solvents. Based on above, the main-chain helicity could be manipulated by temperature and solvent composition (good solvent/good solvent system, non-solvent/good solvent system or non-solvent/non-solvent system). And the analyses of 1H NMR, IR and CD showed that the helical conformation was mainly stabilized by the steric repulsion between the side chains and the intramolecular hydrogen bonding might play a crucial role on the secondary structure of PPAA-Fmoc-Pro-OH, PPAA-Pro-OH, PPAA-Pro-BC and PPAA-Pro-2NC. Moreover, CD spectra of PPAA-Fmoc-Pro-BC in THF/toluene demonstrated that aggregation of chiral polymers into chiral superstructures could induce the change in chiroptical properties of conjugated systems.The monomer PAA-Pro-OH and polymer PPAA-Pro-OH were used as chiral catalysts for asymmetric Aldol reaction between cyclohexanone and p-nitrobenzaldehyde, and the ee values of the product obtained by reaction catalyzed by PPAA-Pro-OH were low compared with those obtained by PAA-Pro-OH in single solvent. The possible reason for this result is the presence of intramolecular interaction between the side chains, which may disturb the efficient coordination to the substrates. But the polymer exhibited excellent catalytic abilities in mixed solvent systems such as THF/H2O, DMF/H2O, DMAC/H2O and NMP/H2O. On the other hand,a unique enhancement of the enantioselectivity was observed for PPAA-Pro-OH in THF/H2O,and thus affording a higher enantioselectivity compared to the corresponding monomer and non-helical polymer, which was resulted from the synergistic effect of the helical chirality.Meanwhile,polymer PPAA-Pro-OH as anion receptor showed high selectivity for F- and OH-with strong basicity as judged from UV-vis spectrophotometric titrations.