Catalysts For Polymerization Reactions Research Articles

Porous and Stable Zn-Series Metal–Organic Frameworks as Efficient Catalysts for Grafting Wood Nanofibers with Polycaprolactone via a Copolymerization Approach

A hydrothermal method was used to synthesize two highly stable Zn(II) metal-organic frameworks (MOFs), namely, [Zn2(L)2(HIPA)]n (1) and [Zn9(L)6(BTEC)3(H2O)4·6H2O]n (2) (HL = 3-amino-1H-1,2,4-triazole, H2HIPA = 5-hydroxyisophthalic acid, H4BTEC = benzene-1,2,4,5-tetracarboxylic acid). The physicochemical properties of 1 and 2 were characterized using a range of analytical techniques. The scanning electron microscopy images confirmed the stability of the MOFs under heating at 120 °C for 12 h. Following their preparation, the two MOFs were used as catalysts in the grafting of poly(ε-caprolactone) on wood nanofibers (WNFs) by means of a homogeneous ring-opening polymerization protocol in an ionic liquid. The grafting ratio achieved using catalyst 1 was higher than that achieved for catalyst 2, wherein a maximum of 92.43% was obtained using the former. Under comparable reaction conditions, the grafting ratio of 1 was found to be significantly higher than those achieved using 4-dimethylamino pyridine, Sn(Oct)2, and UiO-67 catalysts. In addition, fluorescence emission was detected from the residual catalysts present in the products. The calculated electrostatic potentials and average local ionization energies indicated that the grafting of ε-caprolactone on the WNFs follows a "coordination-insertion" mechanism. Overall, these two new and efficient MOF catalysts have the potential to replace highly toxic traditional catalysts in polymerization reactions. The grafted cellulose material with fluorescence emission may also be suitable for use in biomedical applications.

Synthesis and catalytic performance of banana cellulose nanofibres grafted with poly(ε-caprolactone) in a novel two-dimensional zinc(II) metal-organic framework

In this study, banana cellulose nanofibres (BNCFs) were prepared using waste banana stems. A novel two-dimensional (2D) Zn-MOF was synthesized using 5-(1-hydro-imidazolyl) isophthalic acid as the ligand. The results of the X-ray diffraction, thermogravimetry, and scanning electron microscopy analyses confirmed the stability of Zn-MOF. Thus, Zn-MOF was used to catalyze BNCFs grafted with poly(ε-caprolactone) (ε-CL) (BGCL) by homogeneous ring-opening polymerization in ionic liquid. The grafting ratio of the BGCL prepared by Zn-MOF reached 84.12 %, which was 10.03% higher than that catalyzed by 4-dimethylamino pyridine which was the state-of-the-art catalyst for this reaction. The banana cellulose nanofibres grafted with ε-CL reactions followed the coordination-insertion mechanism, which was confirmed by the theoretical calculations using the Materials Studio software. The cytotoxicity results indicated that BGCL was not only non-toxic to Hela cells but also promoted Hela cell growth within a certain concentration range. Therefore, this study demonstrated the promising potential of BGCL for biomedical applications, and the high efficiency, non-toxicity, and stability of Zn-MOF as the catalyst. Further, this will provide a theoretical basis for the application of MOFs as catalysts in polymerization reactions.

Metal-organic framework (MOF) materials as polymerization catalysts: a review and recent advances.

Synthetic polymers are ubiquitous across both the industrial and consumer segments of the world economy. Catalysts enable rapid, efficient, selective, and even stereoselective, formation of desired polymers from any of a host of candidate monomers. While numerous molecular catalysts have been shown to be effective for these reactions, separation of the catalysts from reaction products is typically difficult - a potentially problematic complication that suggests instead the use of heterogeneous catalysts. Many of the most effective heterogeneous catalysts, however, comprise supported collections of reaction centres that are decidedly nonuniform in their composition, siting, and activity. Nonuniformity complicates atomic-scale evaluation of the basis for catalytic activity and thus impedes scientific hypothesis-driven understanding and development of superior catalysts. In view of the fundamental desirability of structural and chemical uniformity at the meso, nano, and even atomic scale, crystallographically well-defined, high-porosity metal-organic frameworks (MOFs) have attracted attention as model catalysts and/or catalyst-supports for a wide variety of chemical transformations. In the realm of synthetic polymers, catalyst-functionalized MOFs have been studied for reactions ranging from coordination-mediated polymerization of ethylene to visible-light initiated radical polymerizations. Nevertheless, many polymerization reactions remain to be explored - and, no doubt, will be explored, given the remarkable structural and compositional diversity of attainable MOFs. Noteworthy emerging studies include work directed toward more sophisticated catalytic schemes such as polymer templating using MOF pore architectures and tandem copolymerizations using MOF-supported reaction centres. Finally, it is appropriate to recognize that MOFs themselves are synthetic polymers - albeit, uncoventional ones.

Characterization and Photophysical Properties of a Luminescent Aluminum Hydride Complex Supported by a β-Diketiminate Ligand

Aluminum hydrides are versatile compounds utilized as reducing agents, precursors of aluminum complexes, and as catalysts for polymerization reactions. However, their photophysical properties have been overlooked, although several luminescent aluminum complexes have been utilized conventionally for emitting layers in modern light-emitting devices. Herein, we report the synthesis and photophysical properties of a luminescent β-diketiminate dihydride complex through the reaction between lithium aluminum hydride and the corresponding ligand. The obtained compound exhibits crystallization-induced emission (CIE) properties at room temperature and long-lifetime phosphorescence at 80 K. Our experimental and theoretical investigations suggest that low-energy molecular vibration could play an important role in the realization of the CIE property.

Molecular structures of a series of substituted bis(η5-cyclopentadienyl)titanium dihalides CpR2TiX2 [X = F, Cl, Br and I; R = CHPh2, CH(p-Tol)2 and adamantyl

Metallocene dihalides and derivatives thereof are of great interest as precursors for catalysts in polymerization reactions, as antitumor agents and, due to their increased stability, as suitable starting materials in salt metathesis reactions and the generation of metallocene fragments. We report the synthesis and structural characterization of a series of eleven substituted bis(η5-cyclopentadienyl)titanium dihalides, namely bis[η5-1-(diphenylmethyl)cyclopentadienyl]difluoridotitanium(IV), [Ti(C18H15)2F2], bis{η5-1-[bis(4-methylphenyl)methyl]cyclopentadienyl}difluoridotitanium(IV), [Ti(C20H19)2F2], and bis{η5-1-[bis(adamantan-2-yl)methyl]cyclopentadienyl}difluoridotitanium(IV), [Ti(C15H19)2F2], together with the bromide and iodide analogues, and the chloride analogues of the diphenylmethyl and adamantyl complexes. These eleven complexes were prepared by the reaction of the corresponding bis(η5:η1-pentafulvene)titanium complexes with different hydrogen halides (Cl, Br and I). The titanocene fluorides become available via chloride-fluoride exchange reactions.

Nucleophilicity of Alkyl Zirconocene and Titanocene Precatalysts, and Kinetics of Activation by Carbenium Ions and by B(C6 F5 )3.

Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6 F5 )3 were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal-carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal-alkyl bond cleavage (M=Zr, Ti) were studied and structure-reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis.

Synthesis and structural characterization of titanium and zirconium complexes containing half-salen ligands as catalysts for polymerization reactions

Ti(iv) and Zr(iv) complexes of tridentate half-salen ligands were synthesized for the polymerization of lactide and ε-CL, homopolymerization, copolymerization and coupling of epoxides with CO2. All the complexes were found to be effective catalysts for different polymerization reactions.

Group 4 alkoxide complexes containing [NNO]-type scaffold: synthesis, structural characterization and polymerization studies

A series of new dinuclear group 4 complexes containing [NNO]-type ligands are utilized as catalysts for polymerization reactions.

Metallocene Complexes of Group 4 Elements in the Polymerization of Monoolefins

Abstract Metallocene compounds are becoming an important class of catalyst for the synthesis of organic molecules and polymers [1–6]. These complexes also have good potential to act as catalysts or catalyst precursors for a number of organic reactions [2]. The discovery of Group 4 metallocene-alumoxane systems [7–10] as catalysts for polymerization reactions has opened up a new frontier in the area of organometallic chemistry and polymer synthesis [11–18]. Metallocene systems are comprised of 1) bicomponents consisting of a metallocene and an alumoxane and 2) a single component such as [Cp2MR]+[B(C6F5)4]−. The polymerization of monoolefins by metallocenes in comparison to conventional Ziegler-Natta systems [19–25] offers a versatile possibility to polymer synthesis [26]. The broader flexibility of electronic and steric variations in the cyclopentadienyl (Cp) type ligands allows greater maneuvering in the design of catalyst systems. Such modifications govern the polyinsertion reaction leading to regio- and...