Planar-to-Axial Chirality Transfer in the Polymerization of Phenylacetylenes.

Abstract

A pair of enantiomerically pure planar chiral phenylacetylenes, R- and S-2'-ethynyl-1,10-dioxa[10]-paracyclophane, were prepared and polymerized under the catalysis of Rh(nbd)BPh4 and MoCl5, respectively. The resultant polymers had high cis-structure contents and took dominant cis-transoid helical conformations with an excess screw sense as revealed by 1H NMR, Raman, polarimetry, circular dichroism spectroscopy, and computational simulation, manifesting the effective guidance of the planar chirality of monomers to the growth of the polymer main chains. The rigid ansa-structure of monomer unit made the helical structure of polymer backbone stable toward grinding and thermal treatments. The stereoselective interactions between these chiral polymers and the enantiomers of racemic ethynyl-1,10-dioxa[10]-paracyclophane and cobalt(III) acetylacetonate were observed. This work demonstrated the first planar-to-axial chirality transfer in the polymerization of acetylenes and offered a new strategy to prepare chiral materials based on optically active helical polymers.