Optically Active Conjugated Polymer from Solvent Chirality Transfer Polymerization in Monoterpenes

Abstract

Disubstituted acetylene monomers [1,2-diphenylacetylenes (DPAs: DPA-pC1, DPA-mC1, DPA-pC8); 1-phenyl-2-hexylacetylene (PHA-pC1)] are tested for asymmetric polymerization in chiral monoterpenes used as solvents and compared with the corresponding monosubstituted acetylene monomer [1-phenylacetylene (PA-pC1)]. DPA-pC1 containing a trimethylsilyl group in the para-position of the phenyl ring produces an optically active polymer with a large Cotton effect, despite the absence of a stereogenic center. The polymer sample obtained by polymerization in 87% ee (-)-α-pinene shows the strongest CD signal (gCD value at 385 nm: ∼3.2 × 10⁻³). The Cotton bands of the polymers obtained in (-)- and (+)-α-pinenes show the opposite sign in the CD signals. Theoretical calculations show that only the cis-cisoid model adopts a helical conformation. A time-correlated single photon counting experiment shows that the emission of the chiral polymer originates from a virtually single excited species with a 98% component fraction. This polymer solution does not show any significant decrease in gCD value over a wide temperature range of 20 to 80 °C. No noticeable decrease in the gCD value is detected when the polymer solution is kept at relatively low temperatures for a prolonged period (35 d). In contrast, the other polymers show no CD signal.

Synthesis of Optically Active Poly(diphenylacetylene)s Using Polymer Reactions and an Evaluation of Their Chiral Recognition Abilities as Chiral Stationary Phases for HPLC

“…for HPLC because of their preferred-handed helical conformation [17][18][19][20][21][22][23][24][25][26]. However, very few optically active poly(diphenylacetylene)s have been prepared to date, which has limited research towards evaluating the scope and efficiency of the chiral recognition abilities of these materials [27][28][29][30][31][32][33][34][35]. We recently reported the first example of an optically active poly(diphenylacetylene)-based CSP for HPLC [36].…”

Asymmetric polymerisation of substituted phenylacetylene using chiral Rh(2,5-norbornadiene)(L-proline) catalyst

“…The chiral polymerisation solvent can result in greater benefits in HSSP in relation to other chiral media. Kim recently discovered that certain achiral di-substituted acetylene monomers could produce optically active polymers with ordinary achiral transition metal catalysts in chiral monoterpene solvents (Kim et al, 2013 was lower than when using the [Rh(cod)Cl] 2 /(R)-PEA catalytic system. When using the [Rh(cod)Cl] 2 /(R)-PEA catalytic system (Table 1), the yield and M r of the polymers were lower than with [Rh(nbd)Cl] 2 /(R)-PEA.…”

Chiral Recognition Ability of an Optically Active Poly(diphenylacetylene) as a Chiral Stationary Phase for HPLC

“…8,9 Until now, optically active poly(diphenylacetylene)s have been prepared by the polymerization of optically active monomers, 813 the introduction of optically active groups into the pendants through a macromolecular reaction, 14 or by solvent chirality transfer. 15,16 These polymers are considered to form a preferred-handed helical conformation in solution because they show characteristic Cotton effects at wavelengths >330 nm, attributed to the absorption of the polyene backbone. However, the number of optically active poly(diphenylacetylene)s bearing polar functional groups reported so far is very limited.…”