Potential applications of optically active helical polymers that mimic the structures of enzymes, involve enantioselective catalysis and adsorbents [1, 2, 5]. The one-handed helical polymethacrylates prepared by the helix-sense selective polymerization of TrMA and its analog 5 (Section 11.2.1) exhibit excellent chiral recognition abilities when coated on a macroporous silica gel and used as chiral stationary phases (CSPs) in HPLC [121, 122]. These packing materials can resolve a wide range of racemic compounds including chiral drugs and stereochemically
interesting molecules, and are commercialized . The typical chromatogram for the separation of 2,20-dihydroxy-1,10-binaphthyl and some chiral molecules resolved on PTrMA are shown in Fig. 11.20 [5, 121, 122]. A stereoregular helical poly(phenylacetylene) (31) can also be used as a CSP for HPLC, which resolved several enantiomers including Troger's base and stilbene oxide . However, a stereoirregular poly(phenylacetylene) with an identical chemical structure as 28, prepared by a different synthetic route showed poor chiral recognition, clearly indicating that the one-handed helical conformation induced by a stereoregular polymer backbone with chiral pendant groups is indispensable for effective chiral recognition. Other helical polyacetylenes such as 27 have been used as enantiose-lective permeable membranes for separating amino acids and chiral alcohols .
Reggelin et al. took advantage of the versatility of helical polymethacrylates developed by Okamoto and reported the first successful catalytic asymmetric C-C bond forming reaction using the helical polymers as a chiral polymeric ligand. The polymethacrylates were prepared by the helix-sense selective anionic polymerization or copolymerization with TrMA , producing an isotactic, fully one-handed helical polymer and copolymer with a large optical rotation. Complexed with palladium, the resulting monodentate (87)  and bidentate (88)  palladium catalysts promoted the asymmetric allylic alkylation reaction (Scheme 11.8) resulting in the substitution product with ca. 30 and 40-60% ee, respectively. Reggelin et al. further applied this strategy to a dynamic helical polyisocya-nate. The copolymer composed of a chiral isocyanate and an achiral isocyanate bearing a phosphine pendant (60:40, mol/mol) (89) , although its helical sense excess was not perfect, showed a low, but apparent catalytic enantioselective
activity in an asymmetric hydrogenation reaction when complexed with a rhodium catalyst, thus producing a hydrogenated product with 14.5% ee. These static and dynamic helical polymers lacking any other elements of chirality except for helicity are a promising new class of ligands for asymmetric catalysis.
A large number of other chiral polymeric ligands have been synthesized from chiral small molecules such as 1,10-bi-2-naphthol (BINOL) and 2,20-bis(diphenylphosphino)-1,10-binaphthyl (BINAP). Some of them may have a helical structure and serve as ligands in various enantioselective transformations .
As previously described, the most important and unique feature of dynamic helical polymers is a remarkable amplification of chirality, which may be utilized to construct a novel helical polymer with the desired pendant group in a one-handed helical array along the polymer backbone. In fact, the copolymerization of an achiral phenylacetylene bearing a fullerene pendant with a small amount of an optically active phenylacetylene yielded a helical copolymer with an excess of one helical-sense in which the pendant C6o groups adopt a predominant screw-sense along the polymer backbone (Scheme 11.9) , because the copolymer exhibited an ICD in the achiral fullerene chromophore region as well as in the polymer backbone region. In a complementary approach, an enantiomerically pure cati-onic C60-bisadduct (90) induced a predominantly one-handed helix in a dynamically racemic poly(phenylacetylene) (37b) with the opposite negative charges in DMSO-water mixtures through noncovalent bonding interactions, which further results in a helical array of the C60-bisadducts with a predominant screw-sense along the polymer chain .
Optically active helical polymers often show chiral LC phases due to their rigid rodlike backbones. Such liquid crystalline helical polymers combined with a specific property of inversion of the helicity regulated by external stimuli will offer switchable chiral materials suitable for data storage, optical devices and use in other fields involving chiral nanotechnology .
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