Cooperative Enantiomorphic-Site and Chain-End Chirality in Isoselective β‑Lactone Polymerization
- 1Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
- 2Scuola Superiore Meridionale, Largo San Marcellino, 80138 Naples, Italy
- 3Department of Chemical Sciences, University of Naples Federico II, Via Cintia, 80126 Naples, Italy
Abstract
Polymer properties are profoundly impacted by tacticity, necessitating an understanding of the origins of stereocontrol to make high-performance materials. Recently, we reported that controlled incorporation of stereoerrors into trans-poly(3-hydroxy-2-methylbutyrate) (trans-PHMB) through the isoselective polymerization of rac-trans-3,4-dimethylpropiolactone (trans-DMPL) using racemic “sandwich” (BDI)Zn alkoxide complexes (where BDI = β-diketiminate) enables tuning of mechanical properties to match those of low-density polyethylene. However, the mechanism of stereocontrol of these catalysts was not explored. Herein, we report a thorough experimental and computational investigation uncovering a distinct manifestation of cooperative enantiomorphic-site and chain-end control, which we describe as site-mediated asymmetric chain-end control, where catalyst (Δ and Λ) and chain-end chiralities (R,R or S,S) work synergistically to influence the reaction’s stereoselectivity and rate. Experimental and computational data converge remarkably well, revealing that a Δ-catalyst with an (R,R)-chain end (Δ-RR) is isoselective 90% of the time. In contrast, a Δ-catalyst with an (S,S)-chain end (Δ-SS) is unselective. Detailed Density Functional Theory (DFT) investigations suggest molecular-level rationale for this mechanism of stereocontrol, demonstrating that chain positioning, monomer distortion, and ligand interactions work in conjunction to foster isoselectivity. Finally, DFT and kinetic modeling reveal that when polymerizing rac-trans-DMPL, the populations of Δ-RR and Δ-SS are equal and the high overall isoselectivity (mm% = 71–73%; where mm% is the percent of triads with a meso configuration across both ester linkages) of the catalyst is attributed to Δ-RR being faster than Δ-SS.
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BibTeX
@article{young2026cooperative,
title = {{Cooperative Enantiomorphic-Site and Chain-End Chirality in Isoselective β‑Lactone Polymerization}},
author = {Morgan S. Young and Yolanda Rusconi and Ethan B. Flanagan and Samantha N. MacMillan and Claudio De Rosa and Anne M. LaPointe and Giovanni Talarico and Geoffrey W. Coates},
journal = {Journal of the American Chemical Society},
year = {2026},
month = oct,
doi = {10.1021/jacs.6c14172},
url = {https://doi.org/10.1021/jacs.6c14172},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Cooperative Enantiomorphic-Site and Chain-End Chirality in Isoselective β‑Lactone Polymerization
AU - Morgan S. Young
AU - Yolanda Rusconi
AU - Ethan B. Flanagan
AU - Samantha N. MacMillan
AU - Claudio De Rosa
AU - Anne M. LaPointe
AU - Giovanni Talarico
AU - Geoffrey W. Coates
PY - 2026
DA - 2026/10/22
JO - Journal of the American Chemical Society
DO - 10.1021/jacs.6c14172
UR - https://doi.org/10.1021/jacs.6c14172
AB - Polymer properties are profoundly impacted by tacticity, necessitating an understanding of the origins of stereocontrol to make high-performance materials. Recently, we reported that controlled incorporation of stereoerrors into trans-poly(3-hydroxy-2-methylbutyrate) (trans-PHMB) through the isoselective polymerization of rac-trans-3,4-dimethylpropiolactone (trans-DMPL) using racemic “sandwich” (BDI)Zn alkoxide complexes (where BDI = β-diketiminate) enables tuning of mechanical properties to match those of low-density polyethylene. However, the mechanism of stereocontrol of these catalysts was not explored. Herein, we report a thorough experimental and computational investigation uncovering a distinct manifestation of cooperative enantiomorphic-site and chain-end control, which we describe as site-mediated asymmetric chain-end control, where catalyst (Δ and Λ) and chain-end chiralities (R,R or S,S) work synergistically to influence the reaction’s stereoselectivity and rate. Experimental and computational data converge remarkably well, revealing that a Δ-catalyst with an (R,R)-chain end (Δ-RR) is isoselective 90% of the time. In contrast, a Δ-catalyst with an (S,S)-chain end (Δ-SS) is unselective. Detailed Density Functional Theory (DFT) investigations suggest molecular-level rationale for this mechanism of stereocontrol, demonstrating that chain positioning, monomer distortion, and ligand interactions work in conjunction to foster isoselectivity. Finally, DFT and kinetic modeling reveal that when polymerizing rac-trans-DMPL, the populations of Δ-RR and Δ-SS are equal and the high overall isoselectivity (mm% = 71–73%; where mm% is the percent of triads with a meso configuration across both ester linkages) of the catalyst is attributed to Δ-RR being faster than Δ-SS.
SN - 0002-7863
SN - 1520-5126
ER -