Macromolecular Helicity Induction on a Poly(phenylacetylene) with C₂-Symmetric Chiral [60]Fullerene-Bisadducts

Abstract

Three chiral N-methylfulleropyrrolidine bisadducts were prepared, isolated, and completely resolved into each enantiomer using a chiral HPLC column, which were then converted to the corresponding optically active, cationic C(60)-bisadducts to investigate if they could act as a macromolecular helicity inducer in a poly(phenylacetylene) bearing an anionic monoethyl phosphonate pendant (poly-1) in aqueous solution. Upon complexation with the chiral C(60)-bisadducts, only the trans-3 bisadduct exhibited the characteristic induced circular dichroism (ICD) in the UV-visible region of the polymer backbone in dimethyl sulfoxide-water mixtures due to the predominantly one-handed helix formation of poly-1, while the trans-2 and cis-3 bisadducts induced almost no apparent CD in the same region. These results indicate that the helicity induction on poly-1 is highly sensitive to the structure and geometry of the cationic C(60)-bisadducts with a different distance between the separated charges.

1H NMR Spectroscopic Studies of the Conformational Isomers of Pyrrolidinofullerenes

“…[19,20] Furthermore, when a cycloaddition reaction forms a bis-adduct with identical and symmetrical addends, some of the bis-adducts are chiral and racemic mixtures are often obtained. [21][22][23][24] In particular, trans-2, trans-3 and cis-3 adducts are mixtures of enantiomers due to their inherently chiral addition pattern. Although there have been studies of fullerene bis-adducts with two different substituents, only a few reports describe mixed bis-adducts bearing a cyclopropane and a pyrrolidine addend.…”

Buckyballs

“…Along with inherently chiral pristine fullerenes, optically active derivatives have been obtained by chiral induction from chiral starting reagents or after tedious and expensive HPLC separation from the racemic mixture [40]. The non-coordinating nature of fullerenes has hampered the use of asymmetric metal catalysis and, therefore, the employ of enantiopure fullerene derivatives has been limited to a few examples [42][43][44].…”

The transformation of chiral signals into macroscopic properties of materials using chirality-responsive polymers

“…Yashima and coworkers 58 have published a series of studies on the construction of chiral fullerene supramolecular assemblies through non-covalent complexation. In 2004, they reported that only specific structures and geometries of chiral C 60 -bisadducts could induce the formation of helical supramolecular assemblies.…”