Helix-Sense-Selective Polymerization of 35-bis(hydroxymethyl)phenylacetylene Rigidly Bearing Galvinoxyl Residues and Their Chiroptical Properties

摘要

Four kinds of newly synthesized achiral phenylacetylenes bearing a phenylhydrogalvinoxyl residue at 4-position were polymerized by using a chiral rhodium catalyst system, [Rh(nbd)B(C H ) ] or [Rh(nbd)Cl] catalysts in the presence of chiral ( )-(+)- or ( )-(–)-1-phenylethylamine (( )- or ( )-PEA) cocatalysts. Poly( -HGDHPA) and poly( -HGTHPA) in THF showed Cotton signals at the absorption regions of the main chain and hydrogalvinoxyl in the circular dichroism (CD) spectra. It indicated that excess of one-handed helical polyacetylene backbone was induced by helix-sense-selective polymerization (HSSP) under the asymmetric conditions despite the achiral monomer, and the hydrogalvinoxyl moieties were also arranged to form one-handed helical structure. However, there was no Cotton effect for poly( -HGDHPA) and poly( -HGTHPA) because the intramolecular hydrogen bonding did not act well to stabilize the helical conformation. The hydrogalvinoxyl units of poly( -HGDHPA) and poly( -HGTHPA) were converted to the corresponding galvinoxyl radicals after treatment with PbO . In the CD spectra of the polyradicals, the Cotton effects decreased depending on their static stability of helical conformation, suggesting that reversal conformation of the polymer chain arose.