Alkali and Alkaline Earth Metal Complexes as Versatile Catalysts for Ring-Opening Polymerization of Cyclic Esters

Crafting sustainable solutions: architecting biodegradable copolymers through controlled ring-opening copolymerization

Polylactic acid (PLA) is a biodegradable and biocompatible polymer with versatile applications in packaging and medicine. It is derived from lactic acid and thus represents an eco-friendly option sourced from renewable raw materials. Despite its advantages, PLA exhibits few drawbacks, such as brittleness and relatively high melting and glass transition temperatures. However, these limitations can be addressed through copolymerization with other monomers like ε-caprolactone (ε-CL), resulting in a composite material with improved physical properties. This paper comprehensively reviews achievements in PLA-PCL copolymerization using organometallic catalysts, discussing scientific findings and various copolymer architectures obtained, including random or block configurations. It also demonstrates various sustainable catalysts for achieving the required microstructure under mild reaction conditions without the aid of any external initiator.

Enzymatic synthesis of pyridine heterocyclic compounds and their thermal stability

An efficient method was discovered for catalyzing the esterification under air using Novozym 435 to obtain pyridine esters. The following conditions were found to be optimal: 60 mg of Novozyme 435, 5.0 mL of n-hexane, a molar ratio of 2:1 for nicotinic acids (0.4 mmol) to alcohols (0.2 mmol), 0.25 g of molecular sieve 3A, a revolution speed of 150 rpm, a reaction temperature of 50 °C, and reaction time of 48 h. Under nine cycles of Novozym 435, the 80 % yield was consistently obtained. Optimum conditions were used to synthesize 23 pyridine esters, including five novel compounds. Among them, gas chromatography-mass spectrometry-olfactometry (GC-MS-O) showed phenethyl nicotinate (3g), (E)-hex-4-en-1-yl nicotinate (3m), and octyl nicotinate (3n) possessed strong aromas. Thermogravimetric analysis (TG) revealed that the compounds 3g, 3m and 3n exhibited stability at the specified temperature. This finding provides theoretical support for adding pyridine esters fragrance to high-temperature processed food.

Tunable zinc benzamidinate complexes: coordination modes and catalytic activity in the ring-opening polymerization of L-lactide

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.

Grignard reagents as deprotonation agents for oxazoline-amido-phenolate ligands: structural and catalytic implications with the role of halogen ions

In this study, various halogen-substituted Grignard reagents were assessed as deprotonating agents for the oxazoline-amido-phenolate ligand, leading to the formation of magnesium complexes. The newly synthesized complexes with halogen substituents displayed three distinct coordinative modes, all extensively characterized through crystallographic methods. The introduction of halogen substituents induced changes in the Lewis acid properties of the complexes, thereby impacting their structural attributes and catalytic behavior during the initiation and propagation of ring polymerization of cyclic esters.

Role of Bis(phosphinimino)methanides as Universal Ligands in the Coordination Sphere of Metals across the Periodic Table

The coordination chemistry of bis(phosphinimino)methanide ligands is widespread and accompanies a large number of metal ions in the periodic table ranging from lithium to neptunium. This unique class of ligand systems show copious coordination chemistry with the main-group, transition, rare-earth, and actinide metals and are considered to be among the most attractive ligand systems to researchers. The bis(phosphinimino)methanide metal complexes offer an extensive range of applications in various fields and have been demonstrated as one of the universal ligand systems to stabilize the metal ions in not only their usual but also their unusual oxidation states. The main-group and transition metal chemistry using bis(phosphinimino)methanides as ligands was last updated almost a decade ago. In this review, we provide a comprehensive overview of various state-of-the-art bis(phosphinimino)methanide-supported metal complexes by dealing with their synthesis, characterization, reactivity, and catalytic studies which were not included in the last critical reviews.

Lithium anthraquinoids as catalysts in the ROP of lactide and caprolactone into cyclic polymers

New lithium anthraquinoids 2b–d active in the synthesis of cyclic PLA and cyclic PCL have been synthesized and fully characterized.

Three-Dimensional Printing Strategies for Irregularly Shaped Cartilage Tissue Engineering: Current State and Challenges

Although there have been remarkable advances in cartilage tissue engineering, construction of irregularly shaped cartilage, including auricular, nasal, tracheal, and meniscus cartilages, remains challenging because of the difficulty in reproducing its precise structure and specific function. Among the advanced fabrication methods, three-dimensional (3D) printing technology offers great potential for achieving shape imitation and bionic performance in cartilage tissue engineering. This review discusses requirements for 3D printing of various irregularly shaped cartilage tissues, as well as selection of appropriate printing materials and seed cells. Current advances in 3D printing of irregularly shaped cartilage are also highlighted. Finally, developments in various types of cartilage tissue are described. This review is intended to provide guidance for future research in tissue engineering of irregularly shaped cartilage.

Highly efficient Ti-catalyst for deoxygenative reduction of esters at ambient conditions: experimental and mechanistic insights from DFT Study

In this paper, we report the synthesis of dianionic amidophosphineborane–supported titanium chloride [{Ph2P(BH3)N}2C6H4}TiCl2] (1) and TiIV alkyl complex [{Ph2P(BH3)N}2C6H4}Ti(CH2SiMe3)2] (2) using salt metathesis reaction. The TiIV complex 1 was obtained...

Highly Active Homoleptic Zinc and Magnesium Complexes Supported by Constrained Reduced Schiff Base Ligands for the Ring-Opening Polymerization of Lactide

New homoleptic zinc and magnesium complexes containing constrained reduced Schiff base ligands based on substituted 7-hydroxy-1-indanone were successfully synthesized and used as a catalyst for the polymerization of lactide. The ligands contain a side arm having different basicity because dimethylamino, pyridyl, and furfuryl groups are shown to greatly affect the polymerization rates. The homoleptic zinc complex containing constrained reduced Schiff base ligands and a dimethylamino side arm was highly active, giving a 92% conversion of l-lactide in 3 min using [LA]:[Zn]:[BnOH] = 500:1:2 at room temperature. The polymerization is pseudo-first-order dependent on the LA concentration. Well-controlled and living behavior of the zinc complex was observed and demonstrated in the preparation of stereodiblock and triblock copolymers of l-, d-, and rac-lactide in a one-pot sequential synthesis with a predictable block length, block sequence, and narrow dispersity rapidly in 10 min. Stereocomplex formation was observed for PLA made sequentially from 100 l-LA, 100 rac-LA, and 100 d-LA having a high T_m of up to 220 °C.