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23 pages, 8630 KiB

Open AccessArticle

Finely-Tuned Bis(imino)pyridylcobalt Complexes Enhance Ethylene Polymerization: The Role of Bulky and Halogen Substituents

by Elizabeth Ogbe, Yanping Ma, Yizhou Wang, Jiahao Gao, Yang Sun and Wen-Hua Sun

Molecules 2025, 30(4), 859; https://doi.org/10.3390/molecules30040859 - 13 Feb 2025

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Abstract

The bis(imino)pyridylcobalt complexes have been finely tuned through using the aniline derivative bearing a meta-chloro substituent, besides its ortho- and para-di(4-fluorophenyl)methyl and ortho-methyl substituents for the series of 2-[1-(3-chloro-4,6-bis((di(4-fluorophenyl)methyl)-2-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylcobalt(II) chlorides (2,6-Me₂Ph, Co1; 2,6-Et₂Ph, Co2 [...] Read more.

The bis(imino)pyridylcobalt complexes have been finely tuned through using the aniline derivative bearing a meta-chloro substituent, besides its ortho- and para-di(4-fluorophenyl)methyl and ortho-methyl substituents for the series of 2-[1-(3-chloro-4,6-bis((di(4-fluorophenyl)methyl)-2-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylcobalt(II) chlorides (2,6-Me₂Ph, Co1; 2,6-Et₂Ph, Co2; 2,6-iPr₂Ph, Co3; 2,4,6-Me₃Ph, Co4; and 2,6-Et₂-4-MePh, Co5). The compounds were characterized using elemental analysis, ¹H/¹³C NMR, FT-IR spectroscopy, and the single-crystal X-ray diffraction used in confirming the molecular structures of Co1, Co2, Co4, and Co5. The newly synthesized precatalysts, maintaining steric influences with the addition of an electron-withdrawing meta-chloro group, achieved higher activities along with better thermal stability, and controlled molecular weights of polyethylenes obtained. Upon activation with either MAO or MMAO, all catalysts exhibited remarkable activity for ethylene polymerization, for example, 9.2 × 10⁶ g mol⁻¹ h⁻¹ by Co1 at 70 °C with 30 min and 18.0 × 10⁶ g mol⁻¹ h⁻¹ by Co4 with the first 5 min. Co4 demonstrated exceptionally thermal stability with the peak activity of 8.9 × 10⁶ g mol⁻¹ h⁻¹ at 70 °C and slightly decreased to 7.2 × 10⁶ g mol⁻¹ h⁻¹ at 80 °C, and even maintained an activity of 1.6 × 10⁶ g mol⁻¹ h⁻¹ at 100 °C. More importantly, all resultant polyethylenes were characterized as having vinyl-terminal and high-linear feature along with narrow dispersity; the molecular weights could be adapted in the ranges from 6.4 to 50.0 kg mol⁻¹. In comparison with previous cobalt analogs, the current system performed better thermal stability and polymerization efficiency. Therefore, such robust complex catalysts are potentially considered for the polyethylene industry. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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20 pages, 5000 KiB

Open AccessArticle

The Effect of Alkyl Substituents on the Formation and Structure of Homochiral (R*,R*)-[R₂Ga(µ-OCH(Me)CO₂R′)]₂ Species—Towards the Factors Controlling the Stereoselectivity of Dialkylgallium Alkoxides in the Ring-Opening Polymerization of rac-Lactide

by Magdalena Kaźmierczak, Łukasz Dobrzycki, Maciej Dranka and Paweł Horeglad

Molecules 2025, 30(1), 190; https://doi.org/10.3390/molecules30010190 - 6 Jan 2025

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Abstract

Building on our previous studies, which have demonstrated that homochiral propagating species—(R*,R*)-[Me₂Ga(µ-OCH(Me)CO₂R)]₂—were crucial for the heteroselectivity of [Me₂Ga(µ-OCH(Me)CO₂Me)]₂ in the ring-opening polymerization (ROP) of [...] Read more.

Building on our previous studies, which have demonstrated that homochiral propagating species—(R*,R*)-[Me₂Ga(µ-OCH(Me)CO₂R)]₂—were crucial for the heteroselectivity of [Me₂Ga(µ-OCH(Me)CO₂Me)]₂ in the ring-opening polymerization (ROP) of racemic lactide (rac-LA), we have investigated the effect of alkyl groups on the structure and catalytic properties of dialkylgallium alkoxides in the ROP of rac-LA. Therefore, we have isolated and characterized the rac-[R₂Ga(µ-OCH(Me)CO₂Me]₂ (R = Et (1), ⁱPr (2) and rac-[R₂Ga(µ-OCH(Me)C₅H₄N]₂ (R = Et (3), ⁱPr (4)) complexes, to demonstrate the effect of alkyl groups on the chiral recognition induced the formation of the respective homochiaral species—(R*,R*)-[R₂Ga(µ-OCH(Me)CO₂Me)]₂ and (R*,R*)-[R₂Ga(µ-OCH(Me)C₅H₄N]₂. Moreover, we have investigated the structure of (S,S)-[R₂Ga(µ-OCH(Me)CO₂Me]₂ (R = Et ((S,S)-1, R = ⁱPr ((S,S)-2,) and their catalytic activity in the ROP of rac-LA. With an increase in the bulkiness of alkyl substituents on gallium the following can be observed: (a) the tendency for the formation of homochiral complexes decreased, (b) the symmetry of homochiral (S,S)-[R₂Ga(µ-OCH(Me)CO₂Me]₂ (M = Me, Et (S,S)-1), ⁱPr (S,S)-2) changed, and both have resulted in (c) lower or no heteroselectivtity across these complexes in the ROP of rac-LA. Importantly, the results have confirmed the crucial role of the chiral-induced formation of homochiral asymmetric dimers on the heteroselectivity of dialkylgallium alkoxides in the ROP of rac-LA. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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12 pages, 3914 KiB

Open AccessArticle

Synthesis of Branched Cyclo-Olefin Copolymers Using Neutral α-Sulfonate-β-Diimine Nickel Catalyst

by Donghui Li, Lixia Pei, Wenbo Du, Xieyi Xiao, Heng Gao, Handou Zheng and Haiyang Gao

Molecules 2025, 30(1), 157; https://doi.org/10.3390/molecules30010157 - 3 Jan 2025

Cited by 2 | Viewed by 728

Abstract

The homopolymerization of norbornene and the copolymerization of norbornene and ethylene were carried out using the neutral α-sulfonate-β-diimine nickel catalyst SD-Ni. The neutral α-sulfonate-β-diimine catalyst is highly active in the homopolymerization of norbornene, producing vinyl-addition polynorbornene [...] Read more.

The homopolymerization of norbornene and the copolymerization of norbornene and ethylene were carried out using the neutral α-sulfonate-β-diimine nickel catalyst SD-Ni. The neutral α-sulfonate-β-diimine catalyst is highly active in the homopolymerization of norbornene, producing vinyl-addition polynorbornene (PNB) with a high molecular weight. The copolymerization of norbornene (NB) and ethylene (E) using the catalyst SD-Ni was also investigated. The α-sulfonate-β-diimine catalyst SD-Ni shows distinctive catalytic copolymerization properties to produce high-molecular-weight E-NB copolymers with low norbornene incorporation. Importantly, microstructure analyses confirm that the resultant E-NB copolymers are branched cyclo-olefin copolymers (COCs) with branched polyethylene units. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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16 pages, 4292 KiB

Open AccessArticle

Reactions of an Anionic Gallylene with Azobenzene or Azide Compounds Through C(sp²)–H and C(sp³)–H Activation

by Jinfeng Sun, Fangfeng Chen, Juan Liu, Yihu Zhang, Dongyu He, Vladimir A. Dodonov and Yanxia Zhao

Molecules 2024, 29(21), 5021; https://doi.org/10.3390/molecules29215021 - 24 Oct 2024

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Abstract

The activation of inert C–H bonds remains a challenge in current chemistry. Here, we report the excellent reactivity of the anionic gallylene species [LGa:][Na(THF)₃] (L = [(2,6-iPr₂C₆H₃)NC(CH₃)]₂²⁻, 1 [...] Read more.

The activation of inert C–H bonds remains a challenge in current chemistry. Here, we report the excellent reactivity of the anionic gallylene species [LGa:][Na(THF)₃] (L = [(2,6-iPr₂C₆H₃)NC(CH₃)]₂²⁻, 1) that allows the selective activation one ortho sp² C–H bond of several azobenzene and azide derivatives at ambient temperature, with the transfer of the hydrogen atom to one of the nitrogen atoms. The process leads to the formation of the aryl amido products [LGa-κ²N,C-PhNN(H)(p-R-C₆H₃)][Na(solvent)₃] (2, R = H solvent = DME (1,2-Dimethoxyethane); 3, R = –OMe, solvent = DME; 4, R = –NMe₂ solvent = THF), [LGa-κ²N,C-(m-CH₃-C₆H₄)NN(H)(m-CH₃-C₆H₃)][Na(15-C-5)₂] (5) with new Ga–C and Ga–N bonds. Moreover, 1 is also effective for the C–H activation of two azides RN₃ (R = 2,4,6-Me₃C₆H₂ or 2,6-iPr₂C₆H₃), resulting in the formation of gallium amides [LGa(NH-2-(CH₂)-4,6-Me₂C₆H₂)][Na(15-C-5)₂] (6) and [LGa(NH-2,6-iPr₂C₆H₃)₂][Na(THF)₅] (7) through intra- or intermolecular sp³ C–H amination. Significantly, these reactions occur for the highly challenging activation of inert C(sp²)–H and C(sp³)–H bonds, thus demonstrating the excellent reactivity of the Ga(I) species 1. The products 2–7 were characterized by X-ray crystallography, ¹H and ¹³C NMR, UV–vis spectroscopy, and density functional theory (DFT) calculations. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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11 pages, 2025 KiB

Open AccessArticle

Ethylene/Styrene Copolymerization by (Me₃SiC₅H₄)TiCl₂(O-2,6-ⁱPr₂-4-RC₆H₂) (R = H, SiEt₃)-MAO Catalysts: Effect of SiMe₃ Group on Cp for Efficient Styrene Incorporation

by Tiantian Huang, Taiga Fujioka, Daisuke Shimoyama and Kotohiro Nomura

Molecules 2024, 29(18), 4473; https://doi.org/10.3390/molecules29184473 - 20 Sep 2024

Cited by 1 | Viewed by 1078

Abstract

The synthesis and structural analysis of (Me₃SiC₅H₄)TiCl₂(OAr) [OAr = O-2,6-ⁱPr₂-4-RC₆H₂; R = H, SiEt₃] revealed that it exhibits higher catalytic activities than (^tBuC [...] Read more.

The synthesis and structural analysis of (Me₃SiC₅H₄)TiCl₂(OAr) [OAr = O-2,6-ⁱPr₂-4-RC₆H₂; R = H, SiEt₃] revealed that it exhibits higher catalytic activities than (^tBuC₅H₄)TiCl₂(OAr), Cp*TiCl₂(OAr), with efficient comonomer incorporation in ethylene/styrene copolymerization in the presence of a methylaluminoxane (MAO) cocatalyst. The catalytic activity in the copolymerization increased upon increasing the charged styrene concentration along with the increase in the styrene content in the copolymers, whereas the activities of other catalysts showed the opposite trend. (Me₃SiC₅H₄)TiCl₂(O-2,6-ⁱPr₂C₆H₃) displayed the most suitable catalyst performance in terms of its activity and styrene incorporation, affording amorphous copolymers with styrene contents higher than 50 mol% (up to 63.6 mol%) and with random styrene incorporation confirmed by ¹³C-NMR spectra. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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18 pages, 2994 KiB

Open AccessArticle

Intensive Cycloalkyl-Fused Pyridines for Aminopyridyl–Zinc–Heteroimidazoles Achieving High Efficiency toward the Ring-Opening Polymerization of Lactides

by Yun Wang, Wenjuan Zhang, Pengjiang Zhu, Wei You, Xiaopan Xue, Rui Wang, Yanping Ma and Wen-Hua Sun

Molecules 2024, 29(17), 4150; https://doi.org/10.3390/molecules29174150 - 31 Aug 2024

Viewed by 1321

Abstract

The model precatalyst sp³- and sp²-N dinitrogen-coordinated zinc–heteroimidazole has been used as an efficient catalyst for the ring-opening polymerization of cyclic esters. Subsequent to our exceptional active 5,6,7-trihydroquinolin-8-amine-zinc catalysts for the ring-opening polymerization (ROP) of ε-caprolactone, various pyridine-fused [...] Read more.

The model precatalyst sp³- and sp²-N dinitrogen-coordinated zinc–heteroimidazole has been used as an efficient catalyst for the ring-opening polymerization of cyclic esters. Subsequent to our exceptional active 5,6,7-trihydroquinolin-8-amine-zinc catalysts for the ring-opening polymerization (ROP) of ε-caprolactone, various pyridine-fused cycloalkanones (ring size from five to eight) are developed for the correspondent fused amine–pyridine derivatives and their zinc–heteroimidazole chloride complexes Zn1–Zn8 (LZnCl₂) bearing N-diphenylphosphinoethyl pendants. Activated with two equivalents of LiN(SiMe₃)₂, the title zinc complexes efficiently promote the ROP of L-lactide (L-LA) in situ; among them, Zn4/2Li(NSiMe₃)₂ catalyzed 500 equivalent L-LA at 80 °C with 92% conversion in 5 min (TOF: 5520 h⁻¹). Under the same conditions, the catalytic efficiency for the ROP of rac-LA by Zn1–Zn8/2Li(NSiMe₃)₂ was slightly lower than that for L-LA (highest TOF: 4440 h⁻¹). In both cases, cyclooctyl-fused pyridyl–zinc complexes exhibited higher activity than others, while the cycloheptyl-fused zinc complexes showed the lowest activity. The microstructure analysis of the polymers showed they possessed a linear structure capped with CH₃O as major and cyclic structure as minor. In this work, all the ligands and zinc complexes were well characterized by ¹H/¹³C/³¹P NMR, FT-IR spectroscopy as well as elemental analysis. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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13 pages, 3670 KiB

Open AccessArticle

Influence of Polytetrafluoroethylene Content, Compaction Pressure, and Annealing Treatment on the Magnetic Properties of Iron-Based Soft Magnetic Composites

by Mei Song, Fan Luo, Yajing Shang and Zhongxia Duan

Molecules 2024, 29(17), 4019; https://doi.org/10.3390/molecules29174019 - 25 Aug 2024

Cited by 1 | Viewed by 1047

Abstract

To improve the magnetic properties of iron-based soft magnetic composites (SMCs), polytetrafluoroethylene (PTFE) with excellent heat resistance, electrical insulation, and extremely high electrical resistivity was chosen as an insulating coating material for the preparation of iron-based SMCs. The effects of PTFE content, compaction [...] Read more.

To improve the magnetic properties of iron-based soft magnetic composites (SMCs), polytetrafluoroethylene (PTFE) with excellent heat resistance, electrical insulation, and extremely high electrical resistivity was chosen as an insulating coating material for the preparation of iron-based SMCs. The effects of PTFE content, compaction pressure, and annealing treatment on the magnetic properties of Fe/PTFE SMCs were investigated in detail. The results demonstrate that the PTFE insulating layer is successfully coated on the surface of iron powders, which effectively reduces the core loss, increases the resistivity, and improves the frequency stability and the quality factor. Under the combined effect of optimal PTFE content, compaction pressure, and annealing treatment, the iron-based SMCs exhibit a high effective permeability of 56, high saturation magnetization of 192.9 emu/g, and low total core losses of 355 mW/cm³ and 1705 mW/cm³ at 50 kHz for B_m = 50 mT and 100 mT. This work provides a novel insulating coating layer that optimizes magnetic properties and is advantageous for the development of iron-based SMCs. In addition, it also provides a comprehensive understanding of the relationship between process parameters and magnetic properties, which is of great guiding significance for scientific research and industrial production. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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Review

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25 pages, 8015 KiB

Open AccessReview

Metal Complexes of Bispidine Derivatives: Achievements and Prospects for the Future

by Altynay B. Kaldybayeva, Valentina K. Yu, Feyyaz Durap, Murat Aydemir and Khaidar S. Tassibekov

Molecules 2025, 30(5), 1138; https://doi.org/10.3390/molecules30051138 - 3 Mar 2025

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Abstract

Multidentate bispidine ligands, including tetra-, penta-, hexa-, hepta-, and octadentate variants, exhibit strong coordination tendencies due to their intrinsic rigidity, significant reorganization potential, and ability to efficiently encapsulate metal ions. These structural attributes profoundly influence the thermodynamic stability, metal ion selectivity, redox behavior, [...] Read more.

Multidentate bispidine ligands, including tetra-, penta-, hexa-, hepta-, and octadentate variants, exhibit strong coordination tendencies due to their intrinsic rigidity, significant reorganization potential, and ability to efficiently encapsulate metal ions. These structural attributes profoundly influence the thermodynamic stability, metal ion selectivity, redox behavior, and spin-state configuration of the resulting complexes. Metal ions, in turn, serve as highly suitable candidates for coordination due to their remarkable kinetic inertness, rapid complex formation kinetics, and low redox potential. This review focuses on ligands incorporating the bispidine core (3,7-diazabicyclo[3.3.1]nonane) and provides an overview of advancements in the synthesis of metal complexes involving p-, d-, and f-block elements. Furthermore, the rationale behind the growing interest in bispidine-based complexes for applications in radiopharmaceuticals, medicinal chemistry, and organic synthesis is explored, particularly in the context of their potential for diagnostic and catalytic drug development. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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12 pages, 1727 KiB

Open AccessReview

Recent Advancements in the Synthesis of Functional Polyolefins by Non-Bridged Half-Titanocenes

by Yanjun Chen and Haiqian Dong

Molecules 2025, 30(1), 39; https://doi.org/10.3390/molecules30010039 - 26 Dec 2024

Viewed by 809

Abstract

Polyolefins are used widely due to their benefits such as being lightweight, chemical inertness, low cost, tunable properties, and easy processability. However, their nonpolar nature significantly limits their high-end applications. The non-bridged half-titanocenes exhibit remarkable catalytic activities with good comonomer incorporations in the [...] Read more.

Polyolefins are used widely due to their benefits such as being lightweight, chemical inertness, low cost, tunable properties, and easy processability. However, their nonpolar nature significantly limits their high-end applications. The non-bridged half-titanocenes exhibit remarkable catalytic activities with good comonomer incorporations in the olefin polymerization. The synthesis of functional polyolefins has attracted more and more attention recently. The non-bridged half-titanocenes have been used in the preparation of functional polyolefins, in particular the functional olefin copolymers. Herein, the recent advancements in the synthesis of functional polyolefins by non-bridged half-titanocenes were reviewed. The functional polyolefins have been synthesized by direct copolymerization of olefin with functional comonomers using half-titanocenes as precatalysts. In addition, polyolefins containing reactive groups could be synthesized by the olefin (co)polymerization using half-titanocenes as precatalysts. The functional polyolefins were synthesized successfully by the post-functionalization of polyolefin containing reactive groups. Full article

(This article belongs to the Special Issue Organometallic Compounds: Design, Synthesis and Application)

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