Poly(quinoxaline-2,3-diyl) copolymers bearing various "sergeant" chiral units with common "soldier" achiral units have been synthesized to investigate the efficiency of screw-sense induction and its dependence on the nature of the solvents. Optically active 2-alkoxymethyl side chains located at the 6- and 7-positions of the quinoxaline ring induced a single-handed helical conformation more efficiently than 3-methylpentyl or 2-methylbutoxy chiral side chains. Among the 2-alkoxymethyl side chains, those bearing higher 2-alkoxy groups induced a single-handed screw sense more efficiently. For instance, a monomer unit bearing (R)-2-octyloxymethyl groups stabilized the P-helix by 1.01 kJ/mol, whereas the monomer bearing (S)-2-butoxymethyl groups stabilized the M-helix by 0.59 kJ/mol. The effect of the position of the sergeant units in the polymer main chain on the screw-sense induction was also investigated using copolymers in which the positions of the sergeant units were carefully controlled by their synthesis via living polymerization. Chiral units placed sparsely could induce single-handed helical structure efficiently. Chiral units bearing 2-alkoxymethyl, 3-methylpentyl, and 2-methylbutoxy groups showed solvent-dependent helix inversion in CHCl3 and 1,1,2-trichloroethane. No helix inversion was observed in those solvents with chiral units bearing 2-butoxy or (2-methylbutoxy)methyl side chains. The 40-mer of the (R)-2-octyloxymethyl units showed P-helical structures in THF, t-BuOMe, and c-C5H11OMe, toluene, pyridine, Et3N, 1-BuOH, CHCl3, CH2Cl2, 1,4-dichlorobutane, 1,1,-dichloroethane, and 1,1,1-trichloroethane, whereas M-helical structures were induced in 1-BuCN, 1-PrCN, 1,2-dichloroethane, 1,3-dichloropropane, and 2-BuOH.

The poly(quinoxaline-2,3-diyl)-based helically chiral phosphine ligands PQXphos exhibited high enantioselectivities up to 97% ee in palladium-catalyzed desymmetrization of meso-1,2-dialkylsubstituted-3-methylenecyclopropanes through silaborative cleavage of the C-C bond. The observed enantioselectivities were higher than those obtained with 2-diarylphosphino-1,1'-binaphthyl in our original report. Remarkable rate enhancement was also observed with a series of PQXphos in comparison with the corresponding low-molecular weight ligands.

Single-handed PQXphos, i.e., helical poly(quinoxaline-2,3-diyl)s bearing diarylphosphino pendant groups, served as remarkable chiral ligands in palladium-catalyzed asymmetric hydrosilylation of styrenes and asymmetric biaryl synthesis by Suzuki–Miyaura coupling, affording up to 98 % enantiomeric excess (e.e.) in both reactions. A palladium complex of high-molecular-weight variant (1000mer) of PQXphos could be reused eight times by virtue of the formation of an insoluble polymer complex. PQXphos underwent solvent-dependent inversion of the helical sense, enabling production of either of two enantiomeric products using a single PQXphos.

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Post-polymerization CH activation of poly(quinoxaline-2,3-diyl)-based helically chiral phosphine ligands (PQXphos) with palladium(II) acetate afforded chiral phosphapalladacycles quantitatively. In situ generated palladacycles exhibited enantioselectivities up to 94 % ee in the palladium-catalyzed asymmetric ring-opening arylation of 1,4-epoxy-1,4-dihydronaphthalenes with arylboronic acids.