Chi-Tien Chen

A series of six benzamidinate‐oxazolinate complexes of Ca ²⁺ , Mg ²⁺ , and Zn ²⁺ were synthesized and fully characterized by NMR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. Their catalytic performances in the ring‐opening polymerization (ROP) of lactide and ε‐caprolactone were systematically investigated. These complexes exhibit distinct reactivities following the order Ca ²⁺ > Mg ²⁺ > Zn ²⁺ , which correlates with the ionic radius and coordination flexibility of the metal centers. Structural analyses reveal that variations in the M‐N coordination environment indirectly regulate M‐O interactions and, consequently, metal–monomer binding strength. The more flexible coordination sphere of Ca ²⁺ weakens M‐O bonding, thereby facilitating monomer insertion and enhancing polymerization efficiency. In contrast, Mg ²⁺ forms stronger M‐O interactions and displays reduced reactivity, while Zn ²⁺ , constrained by a more rigid coordination geometry, exhibits the lowest catalytic activity. Kinetic studies demonstrate the first‐order dependence on monomer concentration, and spectroscopic evidence supports a monomer‐activation mechanism. Overall, this work establishes clear structure–activity relationships linking coordination dynamics to catalytic performance and provides useful design principles for developing efficient divalent metal catalysts for sustainable cyclic ester polymerization.

Treatment of two classes of oxazolinyl‐indolate ligand precursors with an equivalent trimethylaluminum reagent afforded four corresponding aluminum dimethyl complexes. Intramolecular functional groups were employed to switch coordination behaviors, resulting in the formation of two classes of five‐ or six‐membered aluminum metallocyclic complexes. The screening of the prepared aluminum complexes, mediated by 9‐anthracenemethanol as the initiating reagent in the ring‐opening polymerization of ε‐caprolactone, showed significant activities at room temperature. The aluminum compound ligated by 2‐(1H‐indol‐2‐yl)‐4,4‐dimethyl‐4,5‐dihydrooxazole possessed a suitable chelated ring size, and its intrinsic electronic properties maintained higher activity.

Seven asymmetric zinc benzamidinate complexes featuring or lacking side-arm functionalities were synthesized. Using equimolar zinc reagent produced distinct dinuclear motifs [(C₆H₅-C = NC₆H₅)ZnEt]₂ (R = tBu, 1; (CH₂)₂OMe, 2; (CH₂)₂NMe₂, 3). Half the zinc reagent yielded dinuclear [(C₆H₅-C = NC₆H₅)₂Zn]₂ (R = tBu, 4) or mononuclear zinc bis(chelate) complexes (R = (CH₂)₂OMe, 5; (CH₂)₂NMe₂, 6; CH₂Py, 7). Molecular structures of 1–4 and 7 were determined via single-crystal X-ray diffraction. Altering benzamidinate substituents modifies both coordination modes and catalytic activities in ring-opening polymerization of L-lactide. Specifically, complex 7 exhibits enhanced catalytic activity at 25 °C using 100 equivalents of L-lactide with a turnover frequency of 1820 h⁻¹.

A family of aluminium complexes supported by mono-anionic indolyl-phenolate ligands are described. Reactions of indolyl-phenolate based ligand precursors, IndHPh^ROH, with 1.0 or 0.5 equivalents of AlMe₂Cl in toluene afforded aluminium indolyl-phenolate complexes 1–4 and aluminium bis-indolyl-phenolate complexes 5–8 respectively. The molecular structure is reported for 5. Based on the NMR spectroscopic and X-ray crystallographic studies, a 1,3-hydrogen shift could happen from nitrogen to carbon on the five-membered ring of the indolyl group upon reacting with aluminium reagents. These novel aluminium complexes demonstrate catalytic activities toward the ring-opening polymerization of cyclic esters in the presence of alcohol.

In this study, a series of N-heterocyclic indolyl ligand precursors 2-Py-Py-IndH, 2-Py-Pz-IndH, 2-Py-7-Py-IndH, 2-Py-7-Pz-IndH, and 2-Ox-7-Py-IndH (L¹H-L⁵H) were prepared. The treatment of ligand precursors with 1 equivalent of palladium acetate affords palladium complexes 1–5. All ligand precursors and palladium complexes were characterized by NMR spectroscopy and elemental analysis. The molecular structures of complexes 3 and 5 were determined by single crystal X-ray diffraction techniques. The application of those palladium complexes 1–5 to the Suzuki reaction with aryl halide substrates was examined.

This paper describes a new mutual transformation mode occurred between two aluminium complexes, L¹(AlMe₂)₂·AlMe₃and (L¹AlMe)₂, which were generated upon different solvents and bearing the oxazoline‐amido‐phenolate ligand. Density functional theory (DFT) studies support plausible mechanisms. Their catalytic studies were investigated towards ring opening polymerization of ε‐caprolactone andl‐lactide with the benzyl alcohol as the initiating reagent.

This paper describes the effect of solvent‐induced synthetic routes of aluminium pendant oxazoline‐amido‐phenolate complexes. Treatment of ligand precursor L with AlMe₃ in a 1:1 ratio in diethyl ether yielded the four‐coordinated complex (LAlMe)₂. Reaction of ligand precursor L with AlMe₃ in a 1:2 ratio in hexane generated the four‐coordinated complex L(AlMe₂)₂. A novel transformation mode occurred from L(AlMe₂)₂ to (LAlMe)₂ when using diethyl ether or tetrahydrofuran as solvent. A density functional theory computational study also supports a plausible mechanism. All results were supported by spectroscopic data and in agreement with single‐crystal X‐ray diffraction structural analysis.

(NPyC₂OMe)₈Zn₁₀Et₄(μ⁴-O)₄ (1) has been synthesized in situ by hydrolysis of ZnEt₂ in a one pot process and it was proved by applying X-ray structure analysis that the organozinc anilido-pyridinate moiety encapsulated the zinc oxide cluster, which demonstrated one self-assembled coordinate mode “Zn₁₀O₄”. Moreover, the catalytic activity was investigated and good activity for L-lactide and ε-caprolactone ring opening polymerization was observed with both living and controllable properties.