Poly(carbyne)s via reductive C1 polymerization

Synthesis of Optically Active Helical Polycarbenes through Helix-Sense-Selective Polymerization Strategy and Their Application in Chiral Separation

In this work, helical polycarbenes with optical activity were designed and facilely synthesized through the helix-sense-selective polymerization (HSSP) of the diazoacetate monomer with a dimethylbenzyl ester pendant catalyzed by π-allylPdCl with chiral phosphine ligands at room temperature. The polymerization was carried out in a living and controlled style, and a range of helical polycarbenes with the desired number-average molecular weights and narrow molecular weight distributions were obtained. Circular dichroism and UV-vis analyses revealed that these polycarbenes exhibited a stable helical conformation with a preferred handedness, and their helical directions were dependent on the chirality of the chiral phosphine ligands. Further studies showed that the helical conformation of the obtained polycarbenes was from the polymeric backbone rather than the intermolecular aggregation in the solutions. Moreover, the prepared, optically active, helical polycarbenes possessed excellent enantioselective crystallization ability for threonine racemates. The enantiomeric excess (e.e.) of the induced crystals could be up to 83% via utilizing the prepared helical polycarbenes as a chiral separation agent.

A Versatile Method for the End-Functionalization of Polycarbenes

End-functionalization is an effective strategy for constructing functional materials. A method for chain-end functionalization of helical polycarbenes is herein developed that relied on Sonogashira coupling reaction. In this work, a family of helical polycarbenes with controlled molecular mass (M_n ) and low polydispersity (M_w /M_n ) is readily prepared using Pd(II) and the Wei-Phos ligand as initiator. The Pd(II) complex is confirmed to remain at the chain end of polycarbene. Subsequently, a series of terminal alkyne derivatives with interesting functional groups, including the F atom, aldehyde, or anthracene groups, are synthesized. They could be installed at the chain end of polycarbene through Sonogashira coupling reaction catalyzed by the Pd(II) complex at the chain end. Moreover, a couple of hybrid block copolymers are easily obtained by installing terminal alkynes modified by another type of polymer. The structures of the isolated polymers are confirmed by ¹ H nuclear magnetic resonance (¹ H NMR), ¹⁹ F nuclear magnetic resonance (¹⁹ F NMR), ³¹ P nuclear magnetic resonance (³¹ P NMR), and Fourier transform infrared spectroscopy (FT-IR), respectively. The self-assembly properties of the hybrid block copolymers are also investigated by atomic force spectroscopy analysis. By the hereby developed method, various functional groups can be introduced at the chain end of helical polycarbenes for constructing functional polymer materials, moreover, the transition metal residues at the end of polymer chains can be easily removed.