Helix-Sense-Selective and Enantiomer-Selective Living Polymerization of Phenyl Isocyanide Induced by Reusable Chiral Lactide Using Achiral Palladium Initiator

Abstract

Polymerization of phenyl isocyanide using achiral Pd­(II) initiator with the presence of chiral l- or d-lactide (l-LA or d-LA) as additive was found to proceed in helix-sense-selective manner. The polymerization of achiral phenyl isocyanide, 4-isocyanobenzoyl-2-aminoisobutyric acid decyl ester (1) by this method produced optically active helical poly-1 m(L), whose chirality was solely come from the helical conformation without containing of any other chiral atoms. The added chiral LA can be facilely recovered and reused in the helix-sense-selective polymerizations without significantly loss of its chiral induction, and the chiral economy of the polymerization is high. When enantiomerically pure phenyl isocyanide bearing an R- or S-alanine pendent with a long n-decyl chain (1r or 1s) were polymerized by this method, the polymerization was found to proceed in a highly enantiomer-selective manner with one of the enantiomers preferentially polymerized over the antipode by a factor of 3.6. Single-handed helical polyisocyanides can be achieved when the chirality of the monomer was appropriately matched with the added LA.

Grafting polymerization of single‐handed helical poly(phenyl isocyanide)s on graphene oxide and their application in enantioselective separation

“…In the previous work, we have developed a series of air‐stable but effective alkyne‐Pd(II) complexes that can prepare well‐defined poly(phenyl isocyanide)s with living/controlled features. This polymerization method could synthesize poly(phenyl isocyanide)s with controlled single‐handed helical sense using chiral monomers or adding chiral additives from achiral monomers . On the basis of the facile modification of this type of Pd(II) initiator, we explored to incorporate it onto GO nanosheets and grow single‐handed helical poly(phenyl isocyanide)s chains from GO surface.…”

“…In previous studies, we developed a series of novel alkyne‐palladium(II) complexes which could promote the polymerization of various isocyanides in a living/controlled fashion, affording well‐defined polyisocyanides in high yields with controlled molecular weight ( M n s), narrow molecular weight distribution ( M w / M n s), and high stereoregularity . Using this family of versatile catalysts, a number of polyisocyanides with single‐handed helical sense can be facilely prepared . Despite a variety of chiral composite materials bearing helical polymers have been reported, the examples of chiral polymer grafting onto GO nanosheets are still very limited .…”

Recent Advances in Palladium-Catalyzed Isocyanide Insertions

“…Nickel-catalyzed polymerization of isocyanides to helical polyimines is extensively reported in literature [11,12]. Recently, significant advances have been made in using palladium catalysis for similar transformations to polyimines [13][14][15][16][17][18]. Due to the nature of this transformation, affording polymeric structures rather than small molecules, these examples will not be treated in this review.…”

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

“…Synthetic helical polymers have been used in chiral recognition, enantiomer separation, and asymmetric catalysis, among others. In this context, polyisocyanides are one of the most studied helical polymers owing to their stable helical conformation and wide applications . Polyisocyanides have been fabricated into block copolymers, grafting polymers, and star polymers, which brought out a series of new functional chiral materials .…”