Journal of the American Chemical Society, Vol.120, No.46, 11880-11893, 1998
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 H-1 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.
Keywords:NICKEL-CATALYZED POLYMERIZATION, SELECTIVE POLYMERIZATION;ENANTIOSELECTIVE CYCLOPOLYMERIZATION, ALTERNATINGCOPOLYMERIZATION, ACHIRAL ISOCYANIDES, CARBON-MONOXIDE, MAIN-CHAIN, COMPLEXES, POLYMERS, CHIRALITY