Facile Synthesis of Optically Active and Magnetic Nanoparticles Carrying Helical Poly(phenyl isocyanide) Arms and Their Application in Enantioselective Crystallization

In this paper, the facile synthesis of hybrid Fe3O4 magnetic nanoparticles carrying helical poly(phenyl isocyanide) (PPI) arms via both grafting from and grafting onto strategies is reported. First, alkyne-Pd(II) catalysts are anchored onto the surface of the Fe3O4 magnetic nanoparticle, which promote the polymerization of enantiopure phenyl isocyanide, affording the expected hybrid magnetic nanoparticle with Fe3O4 in core and helical PPI as arms. The nanoparticle also exhibits highly optical activity due to the excess of one-handed helicity of the PPI arms. Moreover, the hybrid magnetic nanoparticle can be alternatively synthesized via grafting onto strategy. A triethoxysilanyl-terminated single handed helical PPI bearing l-alanine ester pendants is prepared and grafted onto the surface of Fe3O4 nanoparticle. The generated hybrid magnetic nanoparticles show both magnetic character and optical activity. Taking advantage of these properties, they can be used in enantioselective crystallization of racemic threonine. The enantiomeric excess (ee) of the induced crystals is up to 93%. Moreover, the nanoparticles can be facilely recovered and recycle used for at least four times in enantioselective crystallization without significantly loss of its enantioselectivity.