Asymmetric Synthesis of Helical Poly(quinoxaline-2,3-diyl)s by Palladium-Mediated Polymerization of 1,2-Diisocyanobenzenes:  Effective Control of the Screw-Sense by a Binaphthyl Group at the Chain-End

Aromatizing polymerization of 1,2-diisocyanobenzene derivatives was mediated by optically active organopalladium(II) complexes bearing 1,1‘-binaphth-2-yl groups to give optically active poly(quinoxaline-2,3-diyl)s with varying screw-sense selectivities, which crucially depended upon the substituents on the binaphthyl groups. The most effective catalyst, which has 7‘-methoxy-1,1‘-binaphthyl group, induced the formation of a single screw-sense. Isolation and structural analyses (single-crystal X-ray diffraction and 1 H NMR spectroscopy) of intermediary [oligo(quinoxalinyl)]palladium complexes revealed that the screw-sense selection in the polymerization may be decisively governed by the diastereomeric ratios of the (terquinoxalinyl)palladium(II) complex intermediate.