Stereoselective Ring-Opening Polymerization of rac-Lactides Catalyzed by Aluminum Hemi-Salen Complexes

Understanding catalytic synergy in dinuclear polymerization catalysts for sustainable polymers

Understanding the chemistry underpinning intermetallic synergy and the discovery of generally applicable structure-performances relationships are major challenges in catalysis. Additionally, high-performance catalysts using earth-abundant, non-toxic and inexpensive elements must be prioritised. Here, a series of heterodinuclear catalysts of the form Co(III)M(I/II), where M(I/II) = Na(I), K(I), Ca(II), Sr(II), Ba(II) are evaluated for three different polymerizations, by assessment of rate constants, turn over frequencies, polymer selectivity and control. This allows for comparisons of performances both within and between catalysts containing Group I and II metals for CO2/propene oxide ring-opening copolymerization (ROCOP), propene oxide/phthalic anhydride ROCOP and lactide ring-opening polymerization (ROP). The data reveal new structure-performance correlations that apply across all the different polymerizations: catalysts featuring s-block metals of lower Lewis acidity show higher rates and selectivity. The epoxide/heterocumulene ROCOPs both show exponential activity increases (vs. Lewis acidity, measured by the pKa of [M(OH2)m]n+), whilst the lactide ROP activity and CO2/epoxide selectivity show linear increases. Such clear structure-activity/selectivity correlations are very unusual, yet are fully rationalised by the polymerization mechanisms and the chemistry of the catalytic intermediates. The general applicability across three different polymerizations is significant for future exploitation of catalytic synergy and provides a framework to improve other catalysts.

New GSH-responsive amphiphilic zinc(II) phthalocyanine micelles as efficient drug carriers for combinatorial cancer therapy

Combination therapies for the treatment of cancer have attracted wide attention. The poor selectivity and biocompatibility of photosensitizers (PS) limit the use of combination therapies in chemotherapy and photodynamic therapy (PDT) for cancer. In this work, the Gender PS (mPEG-[Formula: see text]-PLA-S-S-ZnPC), asymmetric zinc(II) phthalocyanine (ZnPC) and mono-methoxy oxygen-based polyethylene glycol-polylactic acid (mPEG-b-PLA) were designed and synthesized for PDT through disulfide bond (-S-S-). The amphipathic PS could be self-assembled into a micelle in aqueous solution, and paclitaxel (PTX) was encapsulated in the core of the micelle for chemotherapy (PTX/mPEG-[Formula: see text]-PLA-S-S-ZnPc). The PTX/mPEG-[Formula: see text]-PLA-S-S-ZnPc micelle was spherical with a uniform diameter of about 184 nm. At the first 48 h, the release behaviors of ZnPC and PTX at 10 mmol / L GSH were 30% and 75.2%, respectively. These results suggested that GSH-responsive PTX/mPEG-[Formula: see text]-PLA-S-S-ZnPc micelle was an active ingredient in combination therapies for cancer.

l- and rac-lactide polymerisation using scandium and aluminium permethylindenyl complexes

Scandium and aluminium constrained geometry permethylindenyl complexes are reported and their lactide polymerisation study discussed.

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.

Preparation of star-shaped functionalized polylactides by metal porphyrin complexes as both catalysts and cocatalysts

Several aluminum porphyrin complexes as catalysts and a copper porphyrin complex as a cocatalyst were prepared. These complexes were characterized by 1H NMR and elemental analysis. These complexes are used for L-lactide polymerization. The kinetic data of the polymerization using complex 2 as catalyst revealed that the polymeric rates were first-ordered in both the monomer and catalyst. There is a linear relationship between lactide conversion and the number-averaged molecular weight of PLA.

Al(Salen) Metal Complexes in Stereoselective Catalysis

Salen ligands are a class of Schiff bases simply obtained through condensation of two molecules of a hydroxyl-substituted aryl aldehyde with an achiral or chiral diamine. The prototype salen, or N,N'-bis(salicylidene)ethylenediamine has a long history, as it was first reported in 1889, and immediately, some of its metal complexes were also described. Now, the salen ligands are a class of N,N,O,O tetradentate Schiff bases capable of coordinating many metal ions. The geometry and the stereogenic group inserted in the diamine backbone or aryl aldehyde backbone have been utilized in the past to efficiently transmit chiral information in a variety of different reactions. In this review we will summarize the important and recent achievements obtained in stereocontrolled reactions in which Al(salen) metal complexes are employed. Several other reviews devoted to the general applications and synthesis of chromium and other metal salens have already been published.

Synthesis of biodegradable and biorenewable polylactides initiated by aluminum complexes bearing m-xylylenediamine derivatives via the ring-opening polymerization of lactides

Aluminum complexes derived from m-xylylenediamine were synthesized and investigated as initiators for l-lactide and rac-lactide polymerization.

Crown ether complexes of potassium quinolin-8-olates: synthesis, characterization and catalysis toward the ring-opening polymerization of rac-lactide

Crown ether complexes of potassium quinolin-8-olates were synthesized and demonstrated to catalyze the stereoselective polymerization of rac-lactide.

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.

Synthesis and characterization of rare-earth metal complexes supported by a new pentadentate Schiff base and their application in heteroselective polymerization of rac-lactide

Both rare-earth metal salen aryloxides and amides can efficiently initiate the ring-opening polymerization of rac-lactide to give heterotactic-rich polylactides.

Ring-opening polymerization of lactide using chiral salen aluminum complexes as initiators: high productivity and stereoselectivity

Chiral salen aluminum complexes have been synthesized and investigated as initiators for l-lactide and rac-lactide polymerization.

Stereoselective ring-opening polymerization of rac-lactides catalyzed by titanium complexes containing N,N-bidentate phenanthrene derivatives

Titanium complexes bearing N,N-bidentate diamido derived from Schiff bases were investigated as catalysts for lactide polymerization.

Synergistic effect of PLA–PBAT–PLA tri-block copolymers with two molecular weights as compatibilizers on the mechanical and rheological properties of PLA/PBAT blends

Systematic study on the synergistic effects of different molecular-weight PLA–PBAT–PLA tri-block copolymers on the mechanical and rheological properties of PLA/PBAT blends.

Ring-opening polymerization of rac-lactide mediated by tetrametallic lithium and sodium diamino-bis(phenolate) complexes

Sodium complex contains interesting intramolecular η⁶-arene interaction and shows excellent catalytic behaviour for polymerization of lactide.

Metal-size influence in iso-selective lactide polymerization

Iso-selective initiators for the ring-opening polymerization (ROP) of rac-lactide are rare outside of Group 13. We describe the first examples of highly iso-selective lutetium initiators. The phosphasalen lutetium ethoxide complex shows excellent iso-selectivity, with a P(i) value of 0.81-0.84 at 298 K, excellent rates, and high degrees of polymerization control. Conversely, the corresponding La derivative exhibits moderate heteroselectivity (P(s)=0.74, 298 K). Thus, the choice of metal center is shown to be crucial in determining the level and mode of stereocontrol. The relative order of rates for the series of complexes is inversely related to metallic covalent radius: that is, La>Y>Lu.