Editorial

2 pages, 166 KiB

Open AccessEditorial

Catalysis in Plastics for the 21st Century

by Carl Redshaw and Gregory A. Solan

Catalysts 2022, 12(12), 1641; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12121641 - 14 Dec 2022

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For this Special Issue, which is part of the Organic and Polymer Chemistry Section, we would like to present the following editorial message [...] Full article

(This article belongs to the Special Issue Catalysis in Plastics for the 21st Century)

Research

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15 pages, 3230 KiB

Open AccessArticle

Transition Metal-Catalyzed and MAO-Assisted Olefin Polymerization; Cyclic Isomers of Sinn’s Dimer Are Excellent Ligands in Iron Complexes and Great Methylating Reagents

by Kaidi Yang and Rainer Glaser

Catalysts 2022, 12(3), 312; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12030312 - 09 Mar 2022

Cited by 3 | Viewed by 2266

Abstract

Methylaluminoxane (MAO) is the most commonly used co-catalyst for transition metal-catalyzed olefin polymerization, but the structures of MAO species and their catalytic functions remain topics of intensive study. We are interested in MAO-assisted polymerization with catalysts L(R₂)FeCl₂ (L = tridentate [...] Read more.

Methylaluminoxane (MAO) is the most commonly used co-catalyst for transition metal-catalyzed olefin polymerization, but the structures of MAO species and their catalytic functions remain topics of intensive study. We are interested in MAO-assisted polymerization with catalysts L(R₂)FeCl₂ (L = tridentate pyridine-2,6-diyldimethanimine; imine-R = Me, Ph). It is our hypothesis that the MAO species is not merely enabling Fe–Me bond formation but functions as an integral part of the active catalyst, a MAO adduct of the Fe-precatalyst [L(R₂)FeCl]⁺. In this paper, we explored the possible structures of acyclic and cyclic MAO species and their complexation with pre-catalysts [L(R₂)FeCl]⁺ using quantum chemical approaches (MP2 and DFT). We report absolute and relative oxophilicities associated with the Fe ← O(MAO) adduct formation and provide compelling evidence that oxygen of an acyclic MAO species (i.e., O(AlMe₂)₂, 4) cannot compete with the O-donor in cyclic MAO species (i.e., (MeAlO)₂, 7; MeAl(OAlMe₂)₂, cyclic 5). Significantly, our work demonstrates that intramolecular O → Al dative bonding results in cyclic isomers of MAO species (i.e., cyclic 5) with high oxophilicities. The stabilities of the [L(R₂)FeCl_ax(MAO)_eq]⁺ species demonstrate that 5 provides for the ligating benefits of the cyclic MAO species 4 without the thermodynamically costly elimination of TMA. Mechanistic implications are discussed for the involvement of such Fe–O–Al bridged catalyst in olefin polymerization. Full article

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10 pages, 2074 KiB

Open AccessFeature PaperArticle

Synthesis of Semicrystalline Long Chain Aliphatic Polyesters by ADMET Copolymerization of Dianhydro-D-glucityl bis(undec-10-enoate) with 1,9-Decadiene and Tandem Hydrogenation

by Mika Kojima, Mohamed Mehawed Abdellatif and Kotohiro Nomura

Catalysts 2021, 11(9), 1098; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11091098 - 12 Sep 2021

Cited by 9 | Viewed by 1950

Abstract

Acyclic diene metathesis (ADMET) copolymerization of dianhydro-D-glucityl bis(undec-10-enoate) (M1) with 1,9-decadiene (DCD) using ruthenium-carbene catalyst, RuCl₂(IMesH₂)(CH-2-OⁱPr-C₆H₄) [IMesH₂ = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene, HG2], afforded unsaturated polyesters (M_n = 9300–23,400) under [...] Read more.

Acyclic diene metathesis (ADMET) copolymerization of dianhydro-D-glucityl bis(undec-10-enoate) (M1) with 1,9-decadiene (DCD) using ruthenium-carbene catalyst, RuCl₂(IMesH₂)(CH-2-OⁱPr-C₆H₄) [IMesH₂ = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene, HG2], afforded unsaturated polyesters (M_n = 9300–23,400) under the optimized conditions. Subsequent tandem hydrogenation (H₂ 1.0 MPa, 50 °C) with the addition of a small amount of Al₂O₃ resulted in the saturated polymers having a melting temperature of 71.7–107.6 °C, depending on the molar ratio of M1 and DCD. Full article

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15 pages, 2560 KiB

Open AccessArticle

Polymetallic Group 4 Complexes: Catalysts for the Ring Opening Polymerisation of rac-Lactide

by David T. Jenkins, Eszter Fazekas, Samuel B. H. Patterson, Georgina M. Rosair, Filipe Vilela and Ruaraidh D. McIntosh

Catalysts 2021, 11(5), 551; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11050551 - 27 Apr 2021

Cited by 8 | Viewed by 2734

Abstract

Five novel air- and moisture-stable polymetallic Ti and Zr amino acid-derived amine bis(phenolate) (ABP) complexes were synthesised and fully characterised, including X-ray crystallographic studies. The reaction of the ABP proligands with Ti or Zr alkoxides has resulted in the formation of polymetallic aggregates [...] Read more.

Five novel air- and moisture-stable polymetallic Ti and Zr amino acid-derived amine bis(phenolate) (ABP) complexes were synthesised and fully characterised, including X-ray crystallographic studies. The reaction of the ABP proligands with Ti or Zr alkoxides has resulted in the formation of polymetallic aggregates of different nuclearity. The steric bulk on the pendant arm of the ligand was found to play a critical role in establishing the nuclearity of the aggregated complex. Sterically, less-demanding groups, such as H or Me, facilitated the formation of tetrametallic Ti clusters, bridged by carboxylate groups, while increased steric bulk (^tBu) led to the formation of binuclear μ-oxo-bridged species. The isolated complexes were employed as catalysts for the ring opening polymerisation (ROP) of rac-lactide. Overall, the Ti catalysts were all active with the smaller, bimetallic Ti aggregates exhibiting relatively faster rates. A monometallic, bis(ABP) Zr complex was found to exert remarkable ROP activity, albeit with limited control over the tacticity and molecular weight distribution of the polymer. A further oxo-bridged Zr cluster was shown to display a previously unprecedented trimetallic structure and achieved a moderate rate in the ROP of rac-lactide. Full article

(This article belongs to the Special Issue Catalysis in Plastics for the 21st Century)

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9 pages, 1168 KiB

Open AccessArticle

Synthesis of Ethylene/1-Octene Copolymers with Ultrahigh Molecular Weights by Zr and Hf Complexes Bearing Bidentate NN Ligands with the Camphyl Linker

by Chunyu Feng, Qingqiang Gou, Shaofeng Liu, Rong Gao and Zhibo Li

Catalysts 2021, 11(2), 276; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11020276 - 18 Feb 2021

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Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) is a class of high-performance engineering plastics, exhibiting a unique set of properties and applications. Although many advances have been achieved in recent years, the synthesis of UHMWPE is still a great challenge. In this contribution, a series [...] Read more.

Ultrahigh molecular weight polyethylene (UHMWPE) is a class of high-performance engineering plastics, exhibiting a unique set of properties and applications. Although many advances have been achieved in recent years, the synthesis of UHMWPE is still a great challenge. In this contribution, a series of zirconium and hafnium complexes, [2,6-(R¹)₂-4-R²-C₆H₂-N-C(camphyl)=C(camphyl)-N-2,6-(R¹)₂-4-R²-C₆H₂]MMe₂(THF) (1-Zr: R¹ = Me, R² = H, M = Zr; 2-Zr: R¹ = Me, R² = Me, M = Zr; 1-Hf: R¹ = Me, R² = H, M = Hf; 2-Hf: R¹ = Me, R² = Me, M = Hf), bearing bidentate NN ligands with the bulky camphyl backbone were synthesized by the stoichiometric reactions of α-diimine ligands with MMe₄ (M = Hf or Zr). All Zr and Hf metal complexes were analyzed using ¹H and ¹³C NMR spectroscopy, and the molecular structures of complexes 1-Zr and 1-Hf were determined by single-crystal X-ray diffraction, revealing that the original α-diimine ligand was selectively reduced into the ene-diamido form and generated an 1,3-diaza-2-metallocyclopentene ring in the metal complexes. Zr complexes 1-Zr and 2-Zr showed moderate activity (up to 388 kg(PE)·mol⁻¹(M)·h⁻¹), poor copolymerization ability, but unprecedented molecular weight capability toward ethylene/1-octene copolymerization. Therefore, copolymers with ultrahigh molecular weights (>600 or 337 × 10⁴ g∙mol⁻¹) were successfully synthesized by 1-Zr or 2-Zr, respectively, with the borate cocatalyst [Ph₃C][B(C₆F₅)₄]. Surprisingly, Hf complexes 1-Hf and 2-Hf showed negligible activity under otherwise identical conditions, revealing the great influence of metal centers on catalytic performances. Full article

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20 pages, 4823 KiB

Open AccessFeature PaperArticle

Comparison of the Reactivity and Structures for the Neutral and Cationic Bis(imino)pyridyl Iron and Cobalt Species by DFT Calculations

by Zilong Li, Yanping Ma and Wen-Hua Sun

Catalysts 2020, 10(12), 1396; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121396 - 30 Nov 2020

Cited by 8 | Viewed by 1922

Abstract

Density Functional Theory (DFT) method was adopted to investigate and compare the reaction mechanisms of ethylene polymerization catalyzed by neutral, cationic bis(imino)pyridyl (PDI) iron and cobalt derivatives. The electronic structure and the oxidation states of the metal center and the PDI ligand were [...] Read more.

Density Functional Theory (DFT) method was adopted to investigate and compare the reaction mechanisms of ethylene polymerization catalyzed by neutral, cationic bis(imino)pyridyl (PDI) iron and cobalt derivatives. The electronic structure and the oxidation states of the metal center and the PDI ligand were analyzed by taking spin states, natural bond orbital (NBO) charge distribution, etc. into consideration, revealing that the reactivity is closely related to the valence electron numbers instead of the charge numbers. The neutral Co(0) had the lowest reactivity as it possessed the most electrons. During the formation of the cationic Co(+)/Fe(+), one electron was mainly lost from PDI ligand rather than the metal center while the metal center maintained +II valence state through the process. Moreover, a special unsymmetrically bidentate N^N coordination manner was found to provide the deficient metal surroundings with 14e, which may initiate the reactivity of some unsymmetrical species with rich electrons. Finally, an anion [AlMe₄]⁻ participating process was proposed to explain the presence of the experimentally observed LCo(+)B(C₂H₄). A special intermediate, Co(+)B(C₂H₄) [AlMe₄]⁻ with Co in +I and absence of Co–C σ bond, was obtained. These calculation results may provide fundamental information for further understanding and designing the ethylene polymerization catalysts. Full article

(This article belongs to the Special Issue Catalysis in Plastics for the 21st Century)

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16 pages, 4706 KiB

Open AccessFeature PaperArticle

Adjusting Ortho-Cycloalkyl Ring Size in a Cycloheptyl-Fused N,N,N-Iron Catalyst as Means to Control Catalytic Activity and Polyethylene Properties

by Mingyang Han, Qiuyue Zhang, Ivan I. Oleynik, Hongyi Suo, Irina V. Oleynik, Gregory A. Solan, Yanping Ma, Tongling Liang and Wen-Hua Sun

Catalysts 2020, 10(9), 1002; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10091002 - 02 Sep 2020

Cited by 18 | Viewed by 2135

Abstract

Five examples of bis(arylimino)tetrahydrocyclohepta[b]pyridine dichloroiron(II) complex, [2-{(Ar)N=CMe}-9-{N(Ar)}C₁₀H₁₀N]FeCl₂ (Ar = 2-(C₅H₉)-4,6-(CHPh₂)₂C₆H₂Fe1, 2-(C₆H₁₁)-4,6-(CHPh₂)₂C₆H₂Fe2 [...] Read more.

Five examples of bis(arylimino)tetrahydrocyclohepta[b]pyridine dichloroiron(II) complex, [2-{(Ar)N=CMe}-9-{N(Ar)}C₁₀H₁₀N]FeCl₂ (Ar = 2-(C₅H₉)-4,6-(CHPh₂)₂C₆H₂Fe1, 2-(C₆H₁₁)-4,6-(CHPh₂)₂C₆H₂Fe2, 2-(C₈H₁₅)-4,6-(CHPh₂)₂C₆H₂Fe3, 2-(C₁₂H₂₃)-4,6-(CHPh₂)₂C₆H₂Fe4, and 2,6-(C₅H₉)2-4-(CHPh₂)C₆H₂Fe5), incorporating ortho-pairings based on either benzhydryl/cycloalkyl (ring sizes ranging from 5 to 12) or cyclopentyl/cyclopentyl groups, have been prepared in reasonable yield by employing a simple one-pot template strategy. Each complex was characterized by FT-IR spectroscopy, elemental analysis, and for Fe3 and Fe5 by single crystal X-ray diffraction; pseudo-square pyramidal geometries are a feature of their coordination spheres. On treatment of Fe1–Fe5 with modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), a range in catalytic activities for ethylene polymerization were observed with benzhydryl/cyclopentyl-containing Fe1/MMAO achieving the maximum level of 15.3 × 10⁶ g PE mol⁻¹ (Fe) h⁻¹ at an operating temperature of 70 °C. As a key trend, the activity was found to drop as the ortho-cycloalkyl ring size increased: Fe1_C5H9/CHPh2~Fe5_C5H9/C5H9 > Fe2_C6H11/CHPh2 > Fe3_C8H15/CHPh2 > Fe4_C12H23/CHPh2. Furthermore, strictly linear polyethylenes (T_m > 126 °C) were formed with molecular weights again dependent on the ortho-cycloalkyl ring size (up to 55.6 kg mol⁻¹ for Fe1/MAO); narrow dispersities were a characteristic of all the polymers (M_w/M_n range: 2.3–4.7), highlighting the well-controlled nature of these polymerizations. Full article

(This article belongs to the Special Issue Catalysis in Plastics for the 21st Century)

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Review

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49 pages, 10500 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Synthesis of Biodegradable Polymers: A Review on the Use of Schiff-Base Metal Complexes as Catalysts for the Ring Opening Polymerization (ROP) of Cyclic Esters

by Orlando Santoro, Xin Zhang and Carl Redshaw

Catalysts 2020, 10(7), 800; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10070800 - 18 Jul 2020

Cited by 75 | Viewed by 7419

Abstract

This review describes the recent advances (from 2008 onwards) in the use of Schiff-base metal complexes as catalysts for the ring opening polymerization (ROP) of cyclic esters. The synthesis and structure of the metal complexes, as well as all aspects concerning the polymerization [...] Read more.

This review describes the recent advances (from 2008 onwards) in the use of Schiff-base metal complexes as catalysts for the ring opening polymerization (ROP) of cyclic esters. The synthesis and structure of the metal complexes, as well as all aspects concerning the polymerization process and the characteristics of the polymers formed, will be discussed. Full article

(This article belongs to the Special Issue Catalysis in Plastics for the 21st Century)

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