Highly Stereocontrolled Ring‐Opening Polymerization of Racemic Alkyl β‐Malolactonates Mediated by Yttrium [Amino‐alkoxy‐bis(phenolate)] Complexes. Issue 22 (15th April 2016)

• Record Type: Journal Article
• Authors: Jaffredo, Cédric G.; Chapurina, Yulia; Kirillov, Evgueni; Carpentier, Jean‐François; Guillaume, Sophie M.
• Is Part Of: Chemistry. Volume 22:Issue 22(2016)
• Page Start: 7629
• Page End: 7641
• Publication Date: 2016-04-15
• Subjects: density functional calculations -- lactones -- polymers -- ring-opening polymerization -- yttrium; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201600223
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Yttrium [amino‐alkoxy‐bis(phenolate)]amido complexes have been used for the ring‐opening polymerization (ROP) of racemic alkyl β‐malolactonates (4‐alkoxycarbonyl‐2‐oxetanones, rac ‐MLA R s) bearing an allyl (All), benzyl (Bz) or methyl (Me) lateral ester function. The nature of the ortho ‐substituent on the phenolate rings in the metal ancillary dictated the stereocontrol of the ROP, and consequently the syndiotactic enrichment of the resulting polyesters. ROP promoted by catalysts with halogen (Cl, Br)‐disubstituted ligands allowed the first reported synthesis of highly syndiotactic PMLA R s ( P r ≥ 0.95); conversely, catalysts bearing bulky alkyl and aryl ortho ‐substituted ligands proved largely ineffective. All polymers have been characterized by 1 H and 13 C{ 1 H} NMR spectroscopy, MALDI‐ToF mass spectrometry and DSC analyses. Statistical and thermal analyses enabled the rationalization of the chain‐end control mechanism. Whereas the stereocontrol of the polymerization obeyed a Markov first‐order (Mk1) model for the ROP of rac ‐MLA Bz and rac ‐MLA All, the ROP of rac ‐MLA Me led to a chain end‐control of Markov second‐order type (Mk2). DFT computations suggest that the high stereocontrol ability featured by catalysts bearing Cl‐ and Br‐substituted ligands does not likely originate from halogen bonding between the halogen substituent and the growing polyester chain. Abstract : Line them up ! Highly syndioselective yttrium catalysts based on halogenated ligand platforms for the ring‐opening polymerization of functional β‐lactones are presented (see figure; MLA=malolactonate, in which R is a allyl, benzyl, or methyl lateral ester function, PMLA=poly(β‐malolactonate)).