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

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)BPh 4 and MoCl 5 , respectively. The resultant polymers had high cis -structure contents and took dominant cis - transoid helical conformations with an excess screw sense as revealed by 1 H 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.