Early Transition Metal Catalysis for Olefin–Polar Monomer Copolymerization

Introducing polar functional groups into widely used polyolefins can enhance polymer surface, rheological, mixing, and other properties, potentially upgrading polyolefins for advanced, value-added applications. The metal catalyst-mediated copolymerization of non-polar olefins with polar comonomers represents the seemingly most straightforward, atom- and energy-efficient approach for synthesizing polar functionalized polyolefins. However, electrophilic early transition metal (groups 3 and 4)-catalyzed processes which have achieved remarkable success in conventional olefin polymerizations, encounter severe limitations here, largely associated with the Lewis basicity of the polar co-monomers. In recent years, however, new catalytic systems have been developed and successful strategies have emerged. In this Minireview, we summarize the recent progress in early transition metal polymerization catalyst development, categorized by the catalytic metal complex and polar comonomer identity. Furthermore, we discuss advances in the mechanistic understanding of these polymerizations, focusing on critical challenges and strategies that mitigate them.     

Synthesis and Catalytic Application of Homo-bimetallic Metallocene Complexes as Ethylene Polymerization Catalysts

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Polymerization of ε-Caprolactone and its Copolymerization with γ-Butyrolactone using Metal Complexes

Solution polymerization of ε-caprolactone (ε-CL) was performed using four different initiators namely: tin(II) octanoate (Sn(Oct)₂)/ethanolamine, aluminium Schiff's base complex-HAPENAlOⁱPr, lithium diisopropyl amide (LDA) and aluminium isopropoxide. The reaction conditions varied with the initiator used. LDA gave rise to the most rapid polymerization with the highest amount of cyclic species as detected by ¹³C NMR. However, no cyclic species were detected when HAPENAlOⁱPr was used as initiator. The tin(II) octanoate/ethanolamine system lead to an α,ω-dihydroxy-polycaprolactone (PCL). The copolymerization of ε-CL was then performed with the hard to oligomerize γ-butyrolactone using the four initiators. GPC (Gel Permeation Chromatography) analyses showed the formation of copolymers. The highest incorporation of polybutyrolactone (PBL) in the copolymer was obtained using HAPENAlOⁱPr as evidenced by ¹H NMR. ¹³C NMR indicated the presence of pseudoperiodic random copolymers with short blocks of PCL whose block length varied with initiator used. The longest and shortest block length were obtained using Sn(Oct)₂ and HAPENAlOⁱPr respectively as calculated from ¹³C NMR. The reactivity ratios were determined using the Finemann-Ross method at low conversion with HAPENAlOⁱPr as initiator. The values obtained, r_CL = 19.4 and r_BL = 0.11, confirmed the presence of long blocks of CL units in the copolymer.     

Cobalt–Pincer Complexes in Catalysis

Non-noble metal catalysts based on pincer type compounds are of special interest for organometallic chemistry and organic synthesis. Next to iron and manganese, currently cobalt–pincer type complexes are successfully applied in various catalytic reactions. In this review the recent progress in (de)hydrogenation, transfer hydrogenation, hydroboration and hydrosilylation as well as dehydrogenative coupling reactions using cobalt–pincer complexes is summarised.     

Catalysis of Carbon–Gas Reactions

The characteristic features on the catalysis of carbon–gas reactions has been studied by combining various techniques such as transient kinetics, temperature-programmed desorption and others. Some of recent achievements are presented to comprehend the state of the art. Many industrial processes associated with catalytic carbon–gas reactions are then discussed in relation to the fundamental chemistry of catalysis.     

Homogeneous Reforming of Aqueous Ethylene Glycol to Glycolic Acid and Pure Hydrogen Catalyzed by Pincer-Ruthenium Complexes Capable of Metal–Ligand Cooperation

Glycolic acid is a useful and important α-hydroxy acid that has broad applications. Herein, the homogeneous ruthenium catalyzed reforming of aqueous ethylene glycol to generate glycolic acid as well as pure hydrogen gas, without concomitant CO₂ emission, is reported. This approach provides a clean and sustainable direction to glycolic acid and hydrogen, based on inexpensive, readily available, and renewable ethylene glycol using 0.5 mol % of catalyst. In-depth mechanistic experimental and computational studies highlight key aspects of the PNNH-ligand framework involved in this transformation.     

Designing Heteroatom-Codoped Iron Metal–Organic Framework for Promotional Photoreduction of Carbon Dioxide to Ethylene

Rational engineering active sites and vantage defects of catalysts are promising but grand challenging task to enhance photoreduction CO₂ to high value-added C2 products. In this study, we designed an N,S-codoped Fe-based MIL-88B catalyst with well-defined bipyramidal hexagonal prism morphology via a facile and effective process, which was synthesized by addition of appropriate 1,2-benzisothiazolin-3-one (BIT) and acetic acid to the reaction solution. Under simulated solar irradiation, the designed catalyst exhibits high C₂H₄ evolution yield of 17.7 μmol g⁻¹⋅h, which has been rarely achieved in photocatalytic CO₂ reduction process. The synergistic effect of Fe-N coordinated sites and reasonable defects in the N,S-codoped photocatalyst can accelerate the migration of photogenerated carriers, resulting in high electron density, and this in turn helps to facilitate the formation and dimerization of C−C coupling intermediates for C₂H₄ effectively.     

Cleavage of Nucleotides by Lanthanide Metal Complexes

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Synthesis and Characterization of Two Extended High-dimensional Architectures Formed by Transition Metal–Glycine Complexes

Under the same experimental condition, changing the kinds of the transition metal (TM) of the reaction, we gained two new compounds: Na₃[Cu(Gly)₂][Cr(OH)₆Mo₆O₁₈]·13H₂O 1, and NaCo₂(gly)₆ClO₄ 2. Compound 1 exhibits an unusual three-dimensional (3D) network constructed from [Cr(OH)₆Mo₆O₁₈]³⁻ building blocks, trinuclear Na⁺ ions and [Cu(gly)₂] coordination complexes as linkers, representing the first example of a 3D extended framework based on Anderson type polyanions and amino acid molecules. Compound 2 consists of an unusual 3D network grafted with Na[Co(gly)₃]₆ complexes. Moreover, compound 2 contains left-handed and right-handed helical chains. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Aggregation and Tunable Color Emission Behaviors of l-Glutamine-Derived Platinum(II) Bipyridine Complexes by Hydrogen-Bonding, π–π Stacking and Metal–Metal Interactions

A n l -glutamine-derived functional group was introduced to the bis(arylalkynyl)platinum(II) bipyridine complexes 1 – 4 . The emission could be switched between the ³MLCT excited state and the triplet excimeric state through solvent or temperature changes, which is attributed to the formation and disruption of hydrogen-bonding, π–π stacking, and metal–metal interactions. Different architectures with various morphologies, such as honeycomb nanostructures and nanospheres, were formed upon solvent variations, and these changes were accompanied by ¹H NMR and distinct emission changes. Additionally, yellow and red emissive metallogels were formed at room temperature due to the different aggregation behaviors introduced by the substituent groups on bipyridine. The thermoresponsive metallogel showed emission behavior with tunable colors by controlling the temperature. The negative Gibbs free-energy change (ΔG) and the large association constant for excimer formation have suggested that the molecules undergo aggregation through hydrogen-bonding, π–π, and metal–metal interactions, resulting in triplet excimeric emission.     

Ethylene Oligomerization Catalyzed by Nickel(II) Diimine Complexes

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Ethylene Oligomerization Catalyzed by Nickel（Ⅱ） Diimine Complexes

Ethylene oligomerization has been investigated by using catalyst systems composed of nickel(II) diimine complexes (diimine = N, N′‐o‐phenylene bis (salicylideneaminato), N, N′‐o‐phenylenebisbenzal, N, N′‐ethylenebisbenzal) and ethylaluminoxane (EAO). The main products in toluene and at 110–200 °C were olefins with low carbon numbers (C₄—C₁₀). Effects of reaction temperature, Al/Ni molar ratio and reaction period on both the catalytic activity and product distribution were explored. The activity of 1.84 × 10⁵ g of oligomer/(mol_NI · h), with 87.4% of selectivity to C₄—C₁₀ olefins, was attained at 200 °C in the reaction when a catalyst composed of NiCl₂ (PhCH = o‐NC₆H₄N = CHPh) and EAO was used.     

Cooperative Carbon Dioxide Adsorption in Alcoholamine- and Alkoxyalkylamine-Functionalized Metal–Organic Frameworks

A series of structurally diverse alcoholamine- and alkoxyalkylamine-functionalized variants of the metal–organic framework Mg₂(dobpdc) are shown to adsorb CO₂ selectively via cooperative chain-forming mechanisms. Solid-state NMR spectra and optimized structures obtained from van der Waals-corrected density functional theory calculations indicate that the adsorption profiles can be attributed to the formation of carbamic acid or ammonium carbamate chains that are stabilized by hydrogen bonding interactions within the framework pores. These findings significantly expand the scope of chemical functionalities that can be utilized to design cooperative CO₂ adsorbents, providing further means of optimizing these powerful materials for energy-efficient CO₂ separations.     

β-Diketiminato Rare-Earth Metal Complexes: The Influence of Monoatomic Substituents in the N-aryl Moieties on Structures and Properties

Treatment of β-diketiminate ligands bearing different N-aryl monoatomic substituents [HL^H = (C₆H₅)N = C(Me)CH=C(Me)NH(C₆H₅), HL^F = (2,6-F₂C₆H₃)N=C(Me)CH=C(Me)NH(2,6-F₂C₆H₃), and HL^Cl = (2,6-Cl₂C₆H₃)N=C(Me)CH=C(Me)NH(2,6-Cl₂C₆H₃)] with Ln(CH₂SiMe₃)₃(THF)₂ (Ln = Y and Lu) afforded a variety of β-diketiminato rare-earth metal complexes depending on substituents, namely, phenyl ring C–H bond activated complexes (L')(L^H)Lu(THF) ( 1b , L' = (C₆H₄)N = C(Me)CH=C(Me)N(C₆H₅)), six-coordinate homoleptic complexes (L^H)₃Ln [Ln = Y ( 1aa ), Lu ( 1bb )], five-coordinate monoalkyl complexes (L^F)₂Ln(CH₂SiMe₃) [Ln = Y ( 2a ), Lu ( 2b )], and four-coordinate dialkyl complexes (L^Cl)Ln(CH₂SiMe₃)₂ [Ln = Y ( 3a ), Lu ( 3b )]. All these complexes were characterized with NMR spectroscopy, and lutetium complexes 1b , 1bb and 3b were structurally validated by single-crystal X-ray diffraction analysis. Moreover, dialkyl complexes 3 promoted the polymerization of 2-vinylpyridine (2-VP) to produce atactic poly(2-vinylpyridine) (P2VP) with quantitative yield. On activation with an equimolar amount of [Ph₃C][B(C₆F₅)₄], complexes 3 afforded highly isotactic P2VP with an mm value up to 94 %. Both ¹H NMR spectrum and MALDI-TOF mass analysis of an oligomer indicate that the polymerization was initiated by coordination insertion of 2-VP into the Y-CH₂SiMe₃ bond.     

Heterogeneous Copolymerization of Ethylene and α-olefins Using Aluminohydride-Zirconocene/SiO2/MAO by High-Throughput Screening

Copolymerizations of ethylene and α-olefins (1-hexene and 1-octene) using a supported catalyst derived from the activation of a zirconocene aluminohydride complex with PMAO and MMAO are reported. The supported (nBu-Cp₂ZrH₃AlH₂)/SiO₂/MAO system was evaluated by high-throughput techniques, in order to find approaches to the optimal copolymerization conditions. The polymerization reactions were carried out in a parallel polymerization reactors system (PPR) by Symyx Technologies, Inc. The screening of the activity of the supported system and the molecular weight (MW) of the polymers and copolymers obtained in the PPR, allowed us to optimize copolymerization conditions, like hydrogen (H₂) addition to control MW and molecular weight distribution (MWD), polymerization temperature, cocatalyst ratio, and solvent type. The copolymerization reactions were scaled-up in order to validate the performance of the catalytic system at higher polymerization scales, according to the results obtained in the combinatorial phase. The scaled-up copolymerizations of ethylene with 1-hexene and 1-octene, showed high activities and MW, and low comonomer incorporation (from 0.3 to 1.3 mol-%, determined by ¹³C NMR). However, the crystallinity (X_c), thermal properties (T_c and T_m) and densities of the polyethylenes obtained with the supported (nBu-Cp₂ZrH₃AlH₂)/SiO₂/MAO system, were significantly modified, approaching those of metallocene linear low-density polyethylenes (mLLDPE).     

Polymer–Metal Complexes Obtained by Radiation‐Induced Grafting Process onto Polyester Fabrics

Abstract

This paper reports the preparation of chelating copolymers via grafting of acrylic acid, and/or acrylamide onto polyester microfiber (PETMF) fabrics using a γ‐radiation technique. The effect of monomer concentration on the grafting process at irradiation dose 20?kGy was studied. The prepared graft chains (PETMF‐g‐AA), (PETMF‐g‐AAm), and (PETMF‐g‐PAAc/PAAm) acted as chelating sites for some selected transition metal ions. The effect of grafting on mechanical properties of PETMF and its copolymer–metal complexes was investigated. The prepared chelating copolymers and their metal complexes were characterized using x‐ray (energy dispersive x‐ray, EDX), differential scanning calorimeter (DSC), color parameters, and electrical conductivity measurements. The possibility of practical uses for such prepared graft copolymer–metal complexes was discussed and determined. The observed results showed that the electrical conductivity of the grafted copolymers and their metal complexes are thermally activated. Moreover, the degree of grafting enhanced the conductivity values of the grafted and non‐complexed copolymer up to three orders of magnitude, on the other hand, the conductivity of the copolymer–metal complexes slightly increased.     

Polar Isotactic and Syndiotactic Polypropylenes by Organozirconium-Catalyzed Masking-Reagent-Free Propylene and Amino–Olefin Copolymerization

Polar functionalized isotactic and syndiotactic polypropylenes (PPs) are synthesized by direct, masking-reagent-free propylene and amino–olefin (AO, CH₂=CH(CH₂)_xNⁿPr₂, x=2, 3, 6) copolymerizations using the activated precatalysts rac-[Me₂Si(indenyl)₂]ZrMe₂ and [Me₂C(Cp)(fluorenyl)]ZrMe₂, respectively. Polymerization activities at 25 °C are as high as 4208 and 535 kg/(mol h atm) with AO incorporation up to 4.0 mol % and 1.6 mol %, respectively. Remarkably, introducing the amino-olefin comonomers significantly enhances stereoselection for both isotactic (mmmm: 59.5 %→91.0 %) and syndiotactic (rrrr: 66.3 %→81.3 %) products.     

A Novel Carbon Nanotube-Supported NiP Amorphous Alloy Catalyst and Its Hydrogenation Activity

A carbon nanotube-supported NiP amorphous catalyst (NiP/CNT) was prepared by induced reduction. Benzene hydrogenation was used as a probe reaction for the study of catalytic activity. The effects of the support on the activity and thermal stability of the supported catalyst were discussed based on various characterizations, including XRD, TEM, ICP, XPS, H2-TPD, and DTA. In comparison with the NiP amorphous alloy, the benzene conversion on NiP/CNT catalyst was lower, but the specific activity of NiP/CNT was higher, which is attributed to the dispersion produced by the support, an electron-donating effect, and the hydrogen-storage ability of CNT. The NiP/CNT thermal stability was improved because of the dispersion and electronic effects and the good heat-conduction ability of the CNT support.     

Continuous Flow Synthesis of Metal–NHC Complexes**

The use of weak bases and mild conditions is currently the most sustainable and attractive synthetic approach for the preparation of late-transition metal complexes, some of which are widely used in catalysis, medicinal chemistry and materials science. Herein, the use of cuprate, aurate or palladate species for a continuous flow preparation of Cu^I, Au^I and Pd^II-NHC complexes is reported. All reactions examined proceed under extremely mild conditions and make use of technical grade acetone as solvent. The scalability of the process was exemplified in a multigram-scale synthesis of [Cu(IPr)Cl].     

Carbon–Phosphorus Coupling from C^N Cyclometalated AuIII Complexes

With the aim of exploiting new organometallic species for cross-coupling reactions, we report here on the Au^III-mediated C_aryl−P bond formation occurring upon reaction of C^N cyclometalated Au^III complexes with phosphines. The [Au(C^N)Cl₂] complex 1 featuring the bidentate 2-benzoylpyridine (C^CON) scaffold was found to react with PTA (1,3,5-triaza-7-phosphaadamantane) under mild conditions, including in water, to afford the corresponding phosphonium 5 through C−P reductive elimination. A mechanism is proposed for the title reaction based on in situ ³¹P{¹H} NMR and HR-ESI-MS analyses combined with DFT calculations. The C−P coupling has been generalized to other C^N cyclometalated Au^III complexes and other tertiary phosphines. Overall, this work provides new insights into the reactivity of cyclometalated Au^III compounds and establishes initial structure–activity relationships to develop Au^III-mediated C−P cross-coupling reactions.