Ring-Opening Polymerization of ε-Caprolactone by Using Aluminum Complexes Bearing Aryl Thioether Phenolates: Labile Thioether Chelation

In this study, aluminum complexes bearing ferrocene-based and arylthiomethylphenolate ligands were synthesized, and their catalytic activity for ε-caprolactone (CL) polymerization was investigated. The catalytic activity of the reduced form of Al complexes was higher than that of the oxidized form. The CL polymerization rate of the reduced form fcO₂AlMe (75 min, conversion = 100%) was higher than that of the oxidized form fc^oxO₂AlMe (4320 min, conversion = 45%), and the CL polymerization rate of fc(OAlMe₂)₂ (40 min, conversion = 100%) was higher than that of fc^ox(OAlMe₂)₂ (60 min, conversion = 97%). Electron deficiency substituents on phenolate decreased the catalytic activity of Al complexes bearing arylthiomethylphenolate ligands. Density functional theory calculations revealed that thioether coordination stabilized the transition state (TS1) and that the oxidized form fc^ox(OAlMe₂)₂ exhibited weaker thioether coordination and higher activation energy in TS1 compared with those of the reduced form fcO₂AlMe. In addition, our study determined that the thioether group is a suitable chelating group for Al catalysts in CL polymerization due to its labile nature.

Mechanistic Insight into the Ring-Opening Polymerization of ε-Caprolactone and L-Lactide Using Ketiminate-Ligated Aluminum Catalysts

The reactivity and the reaction conditions of the ring-opening polymerization of ε-caprolactone (ε-CL) and L-lactide (LA) initiated by aluminum ketiminate complexes have been shown differently. Herein, we account for the observation by studying the mechanisms on the basis of density functional theory (DFT) calculations. The calculations show that the ring-opening polymerization of ε-CL and LA are rate-determined by the benzoxide insertion and the C–O bond cleavage step, respectively. Theoretical computations suggest that the reaction temperature of L–LA polymerization should be higher than that of ε-CL one, in agreement with the experimental data. To provide a reasonable interpretation of the experimental results and to give an insight into the catalyst design, the influence of the electronic, steric, and thermal effects on the polymerization behaviors will be also discussed in this study.

Mechanistic Aspects of the Polymerization of Lactide Using a Highly Efficient Aluminum(III) Catalytic System

We report here a unique example of an in situ generated aluminum initiator stabilized by a C₂-symmetric salen ligand which shows a hitherto unknown high activity for the ROP of rac-lactide at room temperature. Using a simple and robust catalyst system, which is prepared from a salen complex and an onium salt, this convenient route employs readily available reagents that afford polylactide in good yields with narrow polydispersity indices, without the need for time-consuming and expensive processes that are typically required for catalyst preparation and purification. In line with the experimental evidence, DFT studies reveal that initiation and propagation proceed via an external alkoxide attack on the coordinated monomer.

Aluminum alkyl complexes: synthesis, structure, and application in ROP of cyclic esters

Aluminum alkyl complexes have very useful applications as catalysts or reagents in small molecule transformations and as cocatalysts in olefin polymerization. This short review focuses on some recent developments in the design, synthesis and structure of aluminum(iii) alkyl complexes supported by various ligands bearing nitrogen, oxygen, sulfur or phosphorus atoms, and their catalytic applications in the ring-opening polymerization (ROP) of cyclic esters. The coordination chemistry of the Al metal centre and the catalytic activity changes of the complexes caused by ligand modifications are also discussed.

Feasibility of novel (H3C)nX(SiH3)3−ncompounds (X = B, Al, Ga, In): structure, stability, reactivity, and Raman characterization from ab initio calculations

Stability of the (H₃C)_nX(SiH₃)_3−ncompounds.

Zr(iv) complexes containing salan-type ligands: synthesis, structural characterization and role as catalysts towards the polymerization of ε-caprolactone, rac-lactide, ethylene, homopolymerization and copolymerization of epoxides with CO2

Three new Zr(iv) complexes bearing salan-type diamine bis(phenolato) ligands were synthesized and their activities towards the ROP of ε-CL, rac-LA and homopolymerization, copolymerization and coupling of epoxides with CO₂ were investigated.