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1. Ring-Opening Metathesis Polymerization of the Dewar Isomer of 1,2-Azaborinine, a B–N Isostere of Benzene

   https://doi.org/10.1021/acsmacrolett.3c00601  

   Lin, Huina; Yang, Xinyu; Liu, Shih-Yuan; Jäkle, Frieder (December 2023, ACS Macro Letters)

   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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2. Theoretical insight into the redox-switchable activity of group 4 metal complexes for the ring-opening polymerization of ε-caprolactone

   https://doi.org/10.1039/C9QI01466G  

   Xu, Xiaowei; Luo, Gen; Hou, Zhaomin; Diaconescu, Paula L.; Luo, Yi (February 2020, Inorganic Chemistry Frontiers)

   Redox-switchable polymerization has drawn increasing attention, in particular for the ring-opening polymerization (ROP) of biomass-derived monomers. However, an understanding of how the switch determines the observed changes is still limited. In this study, DFT calculations were employed to understand the redox-switchable ROP mechanism of ε-caprolactone catalyzed by group 4 metal complexes bearing [OSSO]-type ferrocene ligands. Our results suggest that two oxidized forms show higher reactivity because of the higher Lewis acidity of their catalytic metal centers in comparison with that of the corresponding reduced states. In one case, however, a lower activity of the oxidized species was observed that is likely due to the increased stability of the substrate-catalyst intermediate leading to a high activation barrier. In addition, other analogous metal complexes were computationally modelled by changing the metal center or modifying the ancillary ligand with different bridging-heteroatoms, and the results provide useful information on the development of new redox-switchable polymerization catalysts. 

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3. Chemical synthesis of perfectly isotactic and high melting bacterial poly(3-hydroxybutyrate) from bio-sourced racemic cyclic diolide

   https://doi.org/10.1038/s41467-018-04734-3  

   Tang, Xiaoyan; Chen, Eugene Y. -X. (June 2018, Nature Communications)

   Abstract Bacterial poly(3-hydroxybutyrate) (P3HB) is a perfectly isotactic, crystalline material possessing properties suitable for substituting petroleum plastics, but high costs and low volumes of its production are impractical for commodity applications. The chemical synthesis of P3HB via ring-opening polymerization (ROP) of racemicβ-butyrolactone has attracted intensive efforts since the 1960s, but not yet produced P3HB with high isotacticity and molecular weight. Here, we report a route utilizing racemic cyclic diolide (rac-DL) derived from bio-sourced succinate. With stereoselective racemic catalysts, the ROP ofrac-DL under ambient conditions produces rapidly P3HB with perfect isotacticity ([mm] > 99%), high melting temperature (T_m = 171 °C), and high molecular weight (M_n = 1.54 × 10⁵ g mol⁻¹,Đ = 1.01). With enantiomeric catalysts, kinetic resolution polymerizations ofrac-DL automatically stops at 50% conversion and yields enantiopure (R,R)-DL and (S,S)-DL with >99%e.e. and the corresponding poly[(S)-3HB] and poly[(R)-3HB] with highT_m = 175 °C. 

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4. Recent Strategies in Nickel-Catalyzed C–H Bond Functionalization for Nitrogen-Containing Heterocycles

   https://doi.org/10.3390/catal12101163  

   Yang, Ke; Li, Zhi; Hu, Qingyue; Elsaid, Mazen; Liu, Chong; Chen, Jun; Ge, Haibo (October 2022, Catalysts)

   N-heterocycles are ubiquitous in natural products, pharmaceuticals, organic materials, and numerous functional molecules. Among the current synthetic approaches, transition metal-catalyzed C–H functionalization has gained considerable attention in recent years due to its advantages of simplicity, high atomic economy, and the ready availability of starting materials. In the field of N-heterocycle synthesis via C–H functionalization, nickel has been recognized as one of the most important catalysts. In this review, we will introduce nickel-catalyzed intramolecular and intermolecular pathways for N-heterocycle synthesis from 2008 to 2021. 

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5. Reversible redox controlled acids for cationic ring-opening polymerization

   https://doi.org/10.1039/D1SC03011F  

   Supej, Michael J.; McLoughlin, Elizabeth A.; Hsu, Jesse H.; Fors, Brett P. (August 2021, Chemical Science)

   null (Ed.)

   Advancements in externally controlled polymerization methodologies have enabled the synthesis of novel polymeric structures and architectures, and they have been pivotal to the development of new photocontrolled lithographic and 3D printing technologies. In particular, the development of externally controlled ring-opening polymerization (ROP) methodologies is of great interest, as these methods provide access to novel biocompatible and biodegradable block polymer structures. Although ROPs mediated by photoacid generators have made significant contributions to the fields of lithography and microelectronics development, these methodologies rely upon catalysts with poor stability and thus poor temporal control. Herein, we report a class of ferrocene-derived acid catalysts whose acidity can be altered through reversible oxidation and reduction of the ferrocenyl moiety to chemically and electrochemically control the ROP of cyclic esters. 

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