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The successful polymerization of the Dewar isomer of an azaborinine heterocycle is reported. Controlled ring-opening metathesis polymerization was accomplished with Grubbs and Hoveya−Grubbs second generation catalysts (G2, HG2), as well as a Z-selective Ru catalyst (HGM2001). The structure of the polymers containing 4-membered B−N heterocycles was verified by GPC and multinuclear and 2D NMR. Differences in stereochemistry of polymers derived from G2/HG2 versus the Z-selective catalyst HGM2001 were substantiated by 2D NOESY, FT-IR, and Raman analyses. The incorporation of B−N heterocycles into these polymer structures is promising as a route to functional polymers that contain polar side groups.
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Contrasting Roles of Counterions in Anionic Ring-Opening Polymerization Mediated by Heterocycle Organocatalysts
A library of structurally related heterocycles containing N-H motifs are explored as ring-opening polymerization (ROP) pre-catalysts. Upon deprotonation of these heterocycles with appropriate bases, corresponding salts are formed, which catalyze the ROP of various lactones and cyclic carbonates, affording polymers with dispersity values ranging from 1.01 to 1.12. These catalysts exhibit a wide range of catalytic activities, spanning over seven orders of magnitude (>107), with their relative rates generally correlating to the pKa of the N-H group in the neutral heterocycle. Despite apparent structural and electronic similarities, these heterocycle catalysts display markedly different kinetic behaviors regarding the identity of different cations. Kinetic and NMR studies have revealed two distinct sets of mechanisms: small alkali metal cations such as Li+ and Na+ reduce the activity of imidazol(in)e derived catalysts due to their tendency to associate with the alkoxide chain-end, thus inhibiting its propagation; conversely, these cations form robust cation-π assemblies with indolocarbazole anions, simultaneously binding and activating monomer carbonyls towards the nucleophilic attack, resulting in a significant rate enhancement. This distinctive activation motif of the indolocarbazole sets it apart from other catalysts by utilizing cations as a potent handle for modulating polymerization reactivity. Coupled with its high availability, good solubility, high activity, moderate basicity, and high selectivity, the indolocarbazole heterocycle emerges as one of the most versatile organocatalysts for ring-opening polymerization.
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- Award ID(s):
- 2002933
- PAR ID:
- 10545574
- Publisher / Repository:
- ACS Catalysis
- Date Published:
- Journal Name:
- ACS Catalysis
- Volume:
- 13
- Issue:
- 24
- ISSN:
- 2155-5435
- Page Range / eLocation ID:
- 16097 to 16104
- Subject(s) / Keyword(s):
- Ring-opening polymerization, cation- π interaction, heterocycle, indolocarbazole, alkali metal, pKa, anionic polymerization
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acscatal.3c04772
