Highly Syndiotactic or Isotactic Polyhydroxyalkanoates by Ligand‐Controlled Yttrium‐Catalyzed Stereoselective Ring‐Opening Polymerization of Functional Racemic β‐Lactones

Abstract

Reported herein is the first stereoselective controlled ROP of a specific family of racemic functional β-lactones, namely 4-alkoxymethylene-β-propiolactones (BPL s). This process is catalyzed by an yttrium complex stabilized by a nonchiral tetradentate amino alkoxy bisphenolate ligand {ONOO } , which features both a good activity and a high degree of control over the molar masses of the resulting functional poly(3-hydroxyalkanoate)s. A simple modification of the R' substituents in ortho and para position on the ligand platform allows for a complete reversal from virtually pure syndioselectivity (P up to 0.91 with R'=cumyl) to very high isoselectivity (P up to 0.93 with R'=Cl), as supported by DFT insights. This is the first example of a highly isoselective ROP of a racemic chiral β-lactone.

Yttrium‐Mediated Ring‐Opening Copolymerization of Oppositely Configurated 4‐Alkoxymethylene‐β‐Propiolactones: Effective Access to Highly Alternated Isotactic Functional PHAs

“…Herein we report on the preparation and characterization of new PHA copolymers from a class of functional β‐lactones just recently released in ROP, 4‐alkoxymethylene‐β‐propiolactones (BPL OR s) . The alkoxymethylene moiety in this class of β‐lactones induces quite different interactions with the Y{ONXO R′,R′′ } catalysts, in particular with halogenated complexes Y{ONXO hal,hal } (hal=F, Cl, Br) in which hal⋅⋅⋅HHCOR attractive contacts apparently enforce a unique isotactic stereocontrol .…”

“…The Y{ONOO cum }/ i PrOH system (Scheme ) that combines high activities and syndiotacticities in the ROP of rac ‐BPL OR s was herein explored to promote the ROCOP of equimolar mixtures of two oppositely configurated 4‐alkoxymethylene‐β‐propiolactones bearing different substituents, ( R )‐BPL OR1 and ( S )‐BPL OR2 (Scheme ). These experiments aimed at probing, beyond the anticipated control of classical parameters of the ROP (molar mass values and dispersity, terminal functionalities), the stereocontrol of the catalyst and the targeted alternation of the enchainment of the two monomers.…”

“…Herein we report on the preparation and characterization of new PHA copolymers from a class of functional β‐lactones just recently released in ROP, 4‐alkoxymethylene‐β‐propiolactones (BPL OR s) . The alkoxymethylene moiety in this class of β‐lactones induces quite different interactions with the Y{ONXO R′,R′′ } catalysts, in particular with halogenated complexes Y{ONXO hal,hal } (hal=F, Cl, Br) in which hal⋅⋅⋅HHCOR attractive contacts apparently enforce a unique isotactic stereocontrol . The functionalities borne by the monomers (OR=OBn, OSiR 3 , OAllyl) used in this study have been selected for the potential post‐polymerization functionalization of the resulting copolymers (debenzylation, desilylation, hydrogenation, etc.…”

Evaluation of Band-Selective HSQC and HMBC: Methodological Validation on the Cyclosporin Cyclic Peptide and Application for Poly(3-hydroxyalkanoate)s Stereoregularity Determination

“…As previously reported, the stereoselective ROP of rac-BPL OAll by diamino-bis(phenolate) yttrium catalyst provides different microstructures of PHB OAll depending on the ortho-substituent group on the ligand [21] (Scheme 1), as assessed by 13 C{ 1 H} analysis.…”

“…The PHB OR samples used for tacticity determination were synthesized according to the reported literature [21].…”