Stereoselective photoredox ring-opening polymerization of O-carboxyanhydrides

Abstract

Biodegradable polyesters with various tacticities have been synthesized by means of stereoselective ring-opening polymerization of racemic lactide and β-lactones but with limited side-chain groups. However, stereoselective synthesis of functional polyesters remains challenging from O-carboxyanhydrides that have abundant pendant side-chain functional groups. Herein we report a powerful strategy to synthesize stereoblock polyesters by stereoselective ring-opening polymerization of racemic O-carboxyanhydrides with the use of photoredox Ni/Ir catalysts and a selected Zn complex with an achiral ligand. The obtained stereoblock copolymers are highly isotactic with high molecular weights ( > 70 kDa) and narrow molecular weight distributions (Mw/Mn < 1.1), and they display distinct melting temperatures that are similar to their stereocomplex counterparts. Furthermore, in one-pot photoredox copolymerization of two different O-carboxyanhydrides, the use of such Zn complex mediates kinetic resolution of the comonomers during enchainment and shows a chirality preference that allows for the synthesis of gradient copolymers.

Recent Advances in Metal‐Mediated Stereoselective Ring‐Opening Polymerization of Functional Cyclic Esters towards Well‐Defined Poly(hydroxy acid)s: From Stereoselectivity to Sequence‐Control

“…In 2018, Xie and Tong disclosed another powerful strategy to stereoselectively ring‐open polymerize racemic OCA R s . Using a catalytic system made of photoredox [Ni]/[Ir] catalysts coupled with a Zn complex supported by an achiral diaminophenolate ligand—a catalytic system previously elaborated for the non‐epimerizing ROP of enantiopure OCAs—, they synthesized stereoblock PAHAs that are highly isotactic ( P m =0.88–0.97), show high molar mass ( M n >70,000 g mol −1 ) and very low dispersities ( Ð M <1.06) (Scheme ) . The {NNO R }ZnEt complex is converted upon addition of an alcohol (BnOH) into a Zn‐alkoxide species, that is the ROP active species which operates by coordination–insertion.…”

“…Using their isoselective {NNO t Bu }ZnEt/BnOH/Ni/Ir system for the ROP of rac ‐OCA R s, Xie and Tong investigated the ROP of mixtures of enantiomerically pure but different OCA R s (Scheme ) . Comonomers with opposite chirality are required for accessing copolymers with a distinctive, namely gradient, microstructure.…”

“… Access to gradient poly(α‐hydroxyalkanoate)s (PAHA R1R2 s) from the ROP of mixtures of various pairs of enantiomers of O ‐carboxyanhydrides (OCA R1,R2 s) with the {NNO t Bu }ZnEt/BnOH/Ni/Ir system (see Scheme ) …”

Diastereoisomer‐Induced Morphology Tunable Self‐Assembled Organic Microcrystals of Conjugated Molecules for Ultraviolet Laser

“…As a hot topic in the domain of material science, organic stereochemistry focuses on precisely controlling the self‐assembly behavior and macroscopic property of organic materials by tuning molecular stereoisomerism, which is an original driving force to promote rapid development of nano‐photonics, generating medicines, biological probes, and other artificial materials. [ 1–4 ] In general, stereoisomerism is a fundamental concept to screen molecules which are composed of the same atoms in the same sequence of bonds but with different spatial and geometric arrangements of atoms, and has a profound influence on the chemical and physical properties of materials. [ 2 ] Therefore, the stereoisomerism‐tuning strategy is a smart method to control the intermolecular interaction, molecular self‐assembly, and ordered hierarchical structure.…”

Metal-supported and -assisted stereoselective cooperative photoredox catalysis

“…The application ranges from natural product chemistry, [3][4][5][6][7] drug development and crop protection agents 8 to materials sciences (e.g., for polymers). [9][10][11][12][13] A particular feature of the last few years has been the development of visible light photoredox catalysis. [14][15][16][17][18][19] In the last 100 years of preparative photochemistry (from the key discoveries of Paternò 20 and Ciamician 21 ), novel approaches have been used to address various issues.…”