2‑Methoxyethylamino-bis(phenolate)yttrium Catalysts for the Synthesis of Highly Isotactic Poly(2-vinylpyridine) by Rare-Earth Metal-Mediated Group Transfer Polymerization

Highly isotactic poly­(2-vinylpyridine) (P2VP) was synthesized by the group transfer polymerization of the prochiral 2-vinylpyridine (2VP) with 2-methoxyethylamino­bis­(phenolate)yttrium complexes. Isotacticities of up to <i>P</i>_<i>m</i> = 0.92, narrow molecular weight distributions, and high molecular weights were achieved by steric modifications of the variable bisphenolate ligand structure. The resulting polymer samples were characterized by thermoanalysis (DSC, TGA), GPC, and ¹³C NMR. The origin of the isotactic microstructure was attributed to an enantiomorphic site control mechanism based on ¹³C NMR mechanistic studies and allowed new insights into ¹³C pentad assignments

Electron-Deficient β‑Diiminato-Zinc-Ethyl Complexes: Synthesis, Structure, and Reactivity in Ring-Opening Polymerization of Lactones

A series of β-diiminato zinc­(II) complexes bearing two electron-withdrawing trifluoromethyl groups in the pentane ligand backbone were successfully isolated ((BDI^CF₃-I)H = [CH­(CCF₃N­C₆H₄-2,6-CH­(CH₃)₂)₂]; (BDI^CF₃-II)H = [CH­(CCF₃N­C₆H₄-2,6-C₂H₅)₂], and (BDI^CF₃-III)H = [CH­(CCF₃N­C₆H₄-2,6-CH₃)₂]). The solid-state structures illustrate differences in the ligation of the Zn atom compared to a literature known BDI-ZnEt complex. All catalysts show good activities in the ring-opening polymerization of the cyclic ester (<i>rac</i>)-β-butyrolactone (BL), whereas only BDI^CF₃-II-ZnEt and BDI^CF₃-III-ZnEt are active initiators for the polymerization of (<i>rac</i>)-lactide (LA)