Solvent Effect on the Sergeants-and-Soldiers Effect Leading to Bidirectional Induction of Single-Handed Helical Sense of Poly(quinoxaline-2,3-diyl)s Copolymers in Aromatic Solvents.

Random poly(quinoxaline-2,3-diyl) copolymers, containing chiral ()-3-octyloxymethyl and achiral propoxymethyl side chain units, experience an abnormal sergeants-and-soldiers effect, that is, they adopt, depending on the chiral monomer mole fraction, either - or -helical conformations in anisole (PhOCH) and benzotrifluoride (PhCF). In benzene (PhH) and toluene (PhCH), these copolymers exclusively adopt an -helical conformation, regardless of the chiral monomer mole fraction. For a co-300mer, with a 40% mole fraction of chiral units, the selective induction of an -helix (>99%) was observed in PhH, while in PhCF, a -helical conformation was induced selectively (>99%). This helix inversion of the polymer backbone is thus able to control the chirality of a chiral polymer ligand in aromatic solvents. The incorporation of a small amount of coordinating PPh groups into the copolymer resulted in a chiral macromolecular ligand, which allowed the enantioselective synthesis of both enantiomeric products in an asymmetric Suzuki-Miyaura coupling reaction (-product: 91% ee in PhH; -product: 95% ee in PhCF) from a single catalyst.