Iron-oriented ethylene oligomerization and polymerization: The Iron Age or a flash in the pan

Tianpengfei Xiao; Wenjuan Zhang; Jingjuan Lai; Wen-Hua Sun

doi:10.1016/j.crci.2011.02.004

Account/Revue

Iron-oriented ethylene oligomerization and polymerization: The Iron Age or a flash in the pan

Tianpengfei Xiao ¹ ; Wenjuan Zhang ¹ ; Jingjuan Lai ^1,² ; Wen-Hua Sun ¹

¹ Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
² Center of Analysis and Measurement, Shanxi Datong University, Datong 037009, China

Comptes Rendus. Chimie, Future of sciences, sciences for the future: Chemistry and its interfaces with biology and physics, Volume 14 (2011) no. 9, pp. 851-855.

Résumé

Iron complexes, especially bis(imino)pyridyliron dichlorides, had been extensively explored for their catalytic behaviour in ethylene oligomerization and polymerization. The fatal natures of late-transition metal pro-catalysts generally show that the catalytic activities are decreased for producing oligomers when the reaction temperatures are elevated. Iron complexes have recently been approved as useful pro-catalysts because such catalytic systems could be controlled for either oligomerization or polymerization, and catalytic activities remained high at the elevated temperature.

Métadonnées

Reçu le : 2010-12-07
Révisé le : 2011-02-07
Accepté le : 2011-02-09
Publié le : 2011-03-17

DOI : 10.1016/j.crci.2011.02.004

Mots-clés : Iron complex, Tridentate ligands, Ethylene oligomerization, Polymerization

Affiliations des auteurs :

Tianpengfei Xiao ¹ ; Wenjuan Zhang ¹ ; Jingjuan Lai ^{1, 2} ; Wen-Hua Sun ¹

¹ Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
² Center of Analysis and Measurement, Shanxi Datong University, Datong 037009, China

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Tianpengfei Xiao; Wenjuan Zhang; Jingjuan Lai; Wen-Hua Sun. Iron-oriented ethylene oligomerization and polymerization: The Iron Age or a flash in the pan. Comptes Rendus. Chimie, Future of sciences, sciences for the future: Chemistry and its interfaces with biology and physics, Volume 14 (2011) no. 9, pp. 851-855. doi : 10.1016/j.crci.2011.02.004. https://comptes-rendus.academie-sciences.fr/chimie/articles/10.1016/j.crci.2011.02.004/

Version originale du texte intégral

Le texte intégral ci-dessous peut contenir quelques erreurs de conversion par rapport à la version officielle de l'article publié.

1 Introduction

Iron is the most abundant transition metal on the Earth with the content of 5.1% after oxygen, silicon and aluminum, and one of the most inexpensive and environmentally friendly metals. In ancient Greek, ‘star’ and ‘iron’ are the same word because iron was firstly discovered in the aerolite. The first discovered bronze sword made in Shang Dynasty of China about 3300 years ago was unearthed in 1973 and proved the edge of the sword was made of the iron meteorite. Nowadays, iron is extensively utilized to produce steel, and chemists are kept in the dark regarding the influence and importance of using iron. Indeed, iron-promoted catalytic reactions have played important roles such as the ammonia synthesis [1–3] and cross couplings [4–8]. Considering additional coupling reactions, products of tremendous industrial importance result from the likes of olefin oligomerization and polymerization. In 1998, the emergence of iron pro-catalysts for ethylene polymerization spurred extensive investigations, and the number of papers mushroomed on iron complexes as pro-catalysts [9–13]. The iron pro-catalysts in ethylene reactivity was proclaimed as the “Iron Age”, however, it appears more likely “a flash in the pan” due to recently, there being only a few publications dealing with iron pro-catalysts. That is caused by more researchers focusing on understanding nature of iron pro-catalysts and few models of iron pro-catalysts have been extensively explored. Herein, the development of iron pro-catalysts in ethylene reactivity is discussed and their promising future in industrial applications is illustrated.

2 Bis(imino)pyridyliron derivatives

As a typical model in ethylene reactivity, the bis(imino)pyridyliron pro-catalysts have attracted much attention from both the academic and industrial areas [9–13]. The steric and electronic influences of the substituents in the ligands could affect the catalytic activity of their iron pro-catalysts, and the products could be verified; therefore many researches are concerned with the variation of imino aryl of 2,6-ortho substituents [14–18]. In general, higher catalytic activities were achieved by the iron complexes bearing bulky alkyl-substituents at the ortho-position or additional methyl group at the para-position of imino-aryl groups due to the positive steric effects and better solubility brought about by the substituents. The iron complexes ligated by bis(ketimino)pyridines are favorable for ethylene polymerization; however, iron complexes bearing bis(aldimino)pyridines prefer to produce lower molecular weight polyethylene waxes or oligomers. Meanwhile, investigations on the influence of electronic properties of the aryl group of bis(imino)pyridyliron complexes have been carried out, and the relationships between the complex structure and the activity have also been identified [19–22] (Fig. 1).

Fig. 1
Bis(imino)pyridyliron pro-catalysts.

To get first hand information about the catalytic behaviour of bis(imino)pyridyliron dichlorides, the modified nonsymmetrical and non-conjugated ligands were synthesized and used to form the iron derivatives (Fig. 2) [23]. Interestingly, three iron complexes with the same coordination framework showed different characteristic features in ethylene reactivity under the same reaction conditions: the catalytic performance by A was similar to observations by the more common bis(imino)pyridyliron pro-catalysts [14–16]; catalysis by B showed oligomerization only, but no activity was observed by C in Fig. 2. The observations indicated the significant effects of ligands on the catalytic behaviour. The causes come from the natures of the three ligands relying on the steric and electronic influences and electron-conjugation within the molecular system. The different catalytic behaviour of their iron complexes in ethylene reactivity indicated the power of homogeneous catalysis by complexes with many variations and interesting aspects.

Fig. 2
Our variation of bis(imino)pyridyliron dichlorides.

Further investigations have been divided into two targets: academically understanding the active species and catalytic mechanism, and some potential scale-up processes towards ethylene oligomerization and polymerization. Research has been conducted in investigating the actual oxidation state of the iron in the active species and the structure of the active species as well as the reaction mechanism of the polymerization process [24–44]; however, there were many debates on the actual oxidation state of iron in the catalytically active species [24–32]. Gibson suggested a trivalent Fe species formed by oxidation with methylalumiuminoxane [MAO] on the basis of Mössbauer and EPR studies [25]. This conclusion was further testified by the calculation results from Bruin's group and Cruz's group based on DFT calculation [41,42]. But the different view about active species was proposed by Talsi et al. [24,26,27], suggesting a paramagnetic Fe(II) alkyl complex bridging the aluminum co-catalyst as the active species illustrated by spectroscopic analysis. The commonly acceptable precursors are alkylated cationic Fe(II) alkyl derivative with a 14e intermediate, which was demonstrated by the recent achievement in Chirik's group [28,29] with isolating the dialkyliron intermediates. Moreover, Fe complexes could provide active species even upon treatment with Al or Zn alkyls [30], and the UV-vis spectra of the Fe pro-catalyst/TMA adducts show no significant changes for different Fe/Al ratios, suggesting similar species formed [33]. Though the iron hydride species could be identified at high Fe/Al ratio, a cationic monochloro-iron species could be identified at low Fe/Al ratio [34].

The study of the catalytic mechanism has been approached with experimental and theoretical techniques, focusing on the catalytic system of bis(imino)pyridyliron complexes. The computation simulations have been extensively done [38–44], including the initial full ab initio study [38] and the DFT and a combined DFT/MM (QM/MM) method [39,40]. The higher catalytic activities correlate with higher stabilities of the iron pro-catalysts at elevated temperatures. These calculation results were consistent with the experiment results. Recently, combined methods of structural, spectroscopic, and computational study were evaluated to understand the redox activity of the bis(imino)pyridyliron complexes by Chirik and coworkers [43,44]. The study indicated that the ferrous oxidation state was not transformed during treatment with MAO or other co-catalyst, and redox reactions are confined at the bis(imino)pyridine ligand.

The metal net charge correlation (MANCC) was employed in our study of the activities of bis(imino)pyridyl iron(II) pro-catalysts in ethylene oligomerization/polymerization [45]. The catalytic activity greatly relied on the electronic configuration of the ligands used, especially the net charge on the central metal atom, however, the catalytic activity did not monotonously vary with the net charge on the central metal.

3 2-(2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyliron derivatives

Besides the bis(imino)pyridine derivatives, much research on the 2,6-substituted-pyridines has attracted great attentions, and some successful derivatives of iron pro-catalysts are collected as the following in Fig. 3.

Fig. 3
Iron pro-catalysts based on 2,6-substituted-pyridines.

Upon activation with MAO, both pro-catalysts D and E displayed moderate activities in ethylene polymerization, suggesting weaker interactions of the ligands, resulting in dissociation between iron and the ligands [46,47]. Pro-catalyst F performed high activity towards ethylene oligomerization with major products of 1-butene and 1-hexene as [48]. However, low activities towards ethylene polymerization was only observed by pro-catalyst G [49] due to the weak coordination. Meanwhile, pro-catalyst H showed low activity for ethylene polymerization and no activity for the copolymerization of ethylene with 1-hexene [50]. Moreover, pro-catalysts I and J initiated the ethylene oligomerization with high selectivity of α-olefins; however, the productivities were quite low [51].

Our attempts to use 2,6-bis(2-benzimidazole)pyridines [52] failed in the isolation of their iron complexes. And so a series of 2-(2-benzimidazolyl)-6-(1-(arylimino)ethyl) pyridines were synthesized and used in forming their iron complexes (Fig. 4) [53–55]. The pro-catalysts K showed high activity towards ethylene oligomerization with some amounts of polyethylene waxes, and indicated that their activities were in the order with R = H [55] > R = Me [53] > R = i-Pr [54] due to the electronic influence of the substituents.

Fig. 4
2-(2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyliron pro-catalysts.

4 2-iminophenathrolyliron derivatives

Inspired by the bis(imino)pyridyliron pro-catalysts, it was not difficult to image a model pro-catalyst as the 2-iminophenathrolyliron dichlorides (L, Fig. 5). However, there were no available substances used for the 2-acetylphenathrolyline. Instead, the 2,9-dimethyl-1,10-phenanthroline was commercially available; therefore a series of 2,9-bis(imino)-1,10-phenanthrolines and their iron complexes (M, Fig. 6) [56] were synthesized. Surprisingly, the iron complexes showed quite low activity towards ethylene polymerization, and it was believed that the additional imino group can coordinate with the iron center and occupy the space required for the ethylene. So there was no other choice, but to synthesize the iron pro-catalyst with the due model (L, Fig. 5).

Fig. 5
Designing 2-iminophenathrolyliron complexes.

Fig. 6
2,9-bis(imino)-1,10-phenanthrolyliron dichlorides.

Overcoming the difficulties encountered in synthesizing 2-acetyl1,10-phenanthroline, the 2-imino-1,10-phenanthrolines and their iron complexes (L, Fig. 5) were finally prepared. As expected, the pro-catalyst L showed very high activity up to 4.91 × 10⁷ g mol⁻¹ h⁻¹ for ethylene oligomerization with a high selectivity for α-olefins [57]. During the reviewing of that manuscript, the referees made comments questioning about products in the case with 9-substituted 2-imino-1,10-phenanthrolines. When the paper appeared [57,58], readers kindly gave us suggestions. Subsequently the iron complexes bearing 2-imino-9-phenyl-1,10-phenanthrolines (N, Fig. 7) were synthesized; however, they exhibited lower activities (2.69 × 10⁶ g mol⁻¹ h⁻¹) [59] in comparison with the model pro-catalyst L [57,58]. The presence of a phenyl group at the 9-position may hinder the coordination and insertion of ethylene.

Fig. 7
2-Imino-9-phenyl-1,10-phenanthrolyliron pro-catalysts.

5 Iron complexes bearing quinoline derivatives

Quinoline derivatives have high potential as ligands, however, complexes are limited to in nickel pro-catalysts [60–63] without successfully isolating their iron complexes. The tridentate ligands and their iron complexes, namely O and P have been synthesized (Fig. 8). The pro-catalyst O exhibited high activities towards ethylene oligomerization with dimers and trimers as products [64]. In comparison, the pro-catalyst P showed a rather unique property towards ethylene polymerization [65]: no activity was observed at low temperatures, but high activity was achieved at higher temperatures than 80 °C (at 100 °C). To the best of our knowledge, this is the first example of iron pro-catalysts that perform at high activity for ethylene polymerization at such high reaction temperatures (above 80 °C) without noticing oligomers.

Fig. 8
Iron pro-catalysts ligated by quinoline derivatives.

6 The critical problem and prospect

The discovery of 2,6-bis(arylimino)pyridylmetal (iron or cobalt) pro-catalysts marked a new era for late-transition metal pro-catalysts in ethylene reactivity, and the number of related papers has mushroomed. Regarding late-transition metal pro-catalysts, in general, deactivation occurs on producing polyethylenes with lower molecular weights (waxes or oligomers) on increasing reaction temperature. That is based on the concept of the same active species, which lead to more chain transfers and elimination at elevated reaction temperature, and it would be helpful to increase ethylene pressure. Though there were limited examples of 2,8-bis(imino)quinolyliron pro-catalysts, different active species would be highly likely with better activity at elevated reaction temperature [65]. A similar phenomenon was observed with cobalt pro-catalysts [66]. This provides a new strategy for targeting late-transition metal pro-catalysts, further investigation and results would not only be interesting in academic consideration but also potential applications in industry.

Acknowledgement

This work was supported by National Natural Science Foundation of China (No. 20874105) and MOST 863 program No. 2009AA033601. WHS is grateful to Prof. P. Braunstein for his kindly hosting the Trilateral Symposium between China, France and Germany.

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M. A. Mats’ko; N. V. Semikolenova; V. A. Zakharov New Ways of Controlling the Molecular Mass Characteristics and Distribution of Branches for Polyethylene Synthesized over Supported Catalysts Containing Fe(II) Bis(imino)pyridyl and Ni(II) Bis(imine) Complexes, Catalysis in Industry, Volume 15 (2023) no. 3, p. 267 | DOI:10.1134/s2070050423030066
Zheng Zuo; Mingyang Han; Yanping Ma; Gregory A. Solan; Xinquan Hu; Tongling Liang; Wen‐Hua Sun Fluorinated bis(arylimino)‐6,7‐dihydro‐5H‐quinoline‐cobalt polymerization catalysts: Electronic versus steric modulation in the formation of vinyl‐terminated linear PE waxes, Applied Organometallic Chemistry, Volume 36 (2022) no. 2 | DOI:10.1002/aoc.6500
Zheng Zuo; Qiuyue Zhang; Mingyang Han; Ming Liu; Yang Sun; Yanping Ma; Wen-Hua Sun 2-(Arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline Cobalt(II) Dichloride Polymerization Catalysts for Polyethylenes with Narrow Polydispersity, Catalysts, Volume 12 (2022) no. 10, p. 1119 | DOI:10.3390/catal12101119
M. A. Matsko; N. V. Semikolenova; V. A. Zakharov New Ways for Controlling the Molecular-Weight Characteristics and Branching Distribution in Polyethylene Obtained over Supported Catalysts Containing Bis(imino)pyridyl Complexes of Fe(II) and Bis(imine) Complexes of Ni(II), Kataliz v promyshlennosti, Volume 22 (2022) no. 5, p. 27 | DOI:10.18412/1816-0387-2022-5-27-39
Yuting Zheng; Shu Jiang; Ming Liu; Zhixin Yu; Yanping Ma; Gregory A. Solan; Wenjuan Zhang; Tongling Liang; Wen-Hua Sun High molecular weight PE elastomers through 4,4-difluorobenzhydryl substitution in symmetrical α-diimino-nickel ethylene polymerization catalysts, RSC Advances, Volume 12 (2022) no. 37, p. 24037 | DOI:10.1039/d2ra04321a
S. V. Zubkevich; V. A. Tuskaev; S. Ch. Gagieva; B. M. Bulychev Catalytic oligomerization and polymerization of ethylene with complexes of iron triad metals: influence of metal nature and new prospects, Russian Chemical Reviews, Volume 91 (2022) no. 3, p. RCR5021 | DOI:10.1070/rcr5021
Jingjing Guo; Wenjuan Zhang; Ivan I. Oleynik; Gregory A. Solan; Irina V. Oleynik; Tongling Liang; Wen-Hua Sun Probing the effect ofortho-cycloalkyl ring size on activity and thermostability in cycloheptyl-fusedN,N,N-iron ethylene polymerization catalysts, Dalton Transactions, Volume 49 (2020) no. 1, p. 136 | DOI:10.1039/c9dt04325j
Shi-Fang Yuan; Zhe Fan; Yi Yan; Yanping Ma; Mingyang Han; Tongling Liang; Wen-Hua Sun Achieving polydispersive HDPE byN,N,N-Co precatalysts appended withN-2,4-bis(di(4-methoxyphenyl)methyl)-6-methylphenyl, RSC Advances, Volume 10 (2020) no. 71, p. 43400 | DOI:10.1039/d0ra09333e
Mingzhi Wang; Wei Wu; Xu Wang; Xing Huang; Yongning Nai; Xueying Wei; Guoliang Mao Research progress of iron-based catalysts for selective oligomerization of ethylene, RSC Advances, Volume 10 (2020) no. 71, p. 43640 | DOI:10.1039/d0ra07558b
Yohan Champouret; Obaid H. Hashmi; Marc Visseaux Discrete iron-based complexes: Applications in homogeneous coordination-insertion polymerization catalysis, Coordination Chemistry Reviews, Volume 390 (2019), p. 127 | DOI:10.1016/j.ccr.2019.03.015
Qiang Chen; Hongyi Suo; Wenjuan Zhang; Randi Zhang; Gregory A. Solan; Tongling Liang; Wen-Hua Sun 1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: exploring temperature and steric effects, Dalton Transactions, Volume 48 (2019) no. 23, p. 8264 | DOI:10.1039/c9dt01235d
Qiang Chen; Wenjuan Zhang; Gregory A. Solan; Randi Zhang; Liwei Guo; Xiang Hao; Wen-Hua Sun CH(phenol)-Bridged Bis(imino)pyridines as Compartmental Supports for Diiron Precatalysts for Ethylene Polymerization: Exploring Cooperative Effects on Performance, Organometallics, Volume 37 (2018) no. 21, p. 4002 | DOI:10.1021/acs.organomet.8b00602
Zheng Wang; Gregory A. Solan; Qaiser Mahmood; Qingbin Liu; Yanping Ma; Xiang Hao; Wen-Hua Sun Bis(imino)pyridines Incorporating Doubly Fused Eight-Membered Rings as Conformationally Flexible Supports for Cobalt Ethylene Polymerization Catalysts, Organometallics, Volume 37 (2018) no. 3, p. 380 | DOI:10.1021/acs.organomet.7b00809
Qaiser Mahmood; Jingjing Guo; Wenjuan Zhang; Yanping Ma; Tongling Liang; Wen-Hua Sun Concurrently Improving the Thermal Stability and Activity of Ferrous Precatalysts for the Production of Saturated/Unsaturated Polyethylene, Organometallics, Volume 37 (2018) no. 6, p. 957 | DOI:10.1021/acs.organomet.7b00909
Qaiser Mahmood; Wen-Hua Sun N , N -chelated nickel catalysts for highly branched polyolefin elastomers: a survey, Royal Society Open Science, Volume 5 (2018) no. 7, p. 180367 | DOI:10.1098/rsos.180367
Nayara T. do Prado; Ronny R. Ribeiro; Osvaldo L. Casagrande Vanadium(III) complexes containing phenoxy–imine–thiophene ligands: Synthesis, characterization and application to homo‐ and copolymerization of ethylene, Applied Organometallic Chemistry, Volume 31 (2017) no. 8 | DOI:10.1002/aoc.3678
Zheng Wang; Qingbin Liu; Gregory A. Solan; Wen-Hua Sun Recent advances in Ni-mediated ethylene chain growth: Nimine-donor ligand effects on catalytic activity, thermal stability and oligo-/polymer structure, Coordination Chemistry Reviews, Volume 350 (2017), p. 68 | DOI:10.1016/j.ccr.2017.06.003
Chuanbing Huang; Shizhen Du; Gregory A. Solan; Yang Sun; Wen-Hua Sun From polyethylene waxes to HDPE using an α,α′-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridyl-chromium(iii) chloride pre-catalyst in ethylene polymerisation, Dalton Transactions, Volume 46 (2017) no. 21, p. 6948 | DOI:10.1039/c7dt01077j
Yanjun Chen; Shizhen Du; Chuanbing Huang; Gregory A. Solan; Xiang Hao; Wen‐Hua Sun Balancing high thermal stability with high activity in diaryliminoacenaphthene‐nickel(II) catalysts for ethylene polymerization, Journal of Polymer Science Part A: Polymer Chemistry, Volume 55 (2017) no. 12, p. 1971 | DOI:10.1002/pola.28562
Youfu Zhang; Hongyi Suo; Fang Huang; Tongling Liang; Xinquan Hu; Wen‐Hua Sun Thermo‐stable 2‐(arylimino)benzylidene‐9‐arylimino‐5,6,7,8‐tetrahydro cyclohepta[b]pyridyliron(II) precatalysts toward ethylene polymerization and highly linear polyethylenes, Journal of Polymer Science Part A: Polymer Chemistry, Volume 55 (2017) no. 5, p. 830 | DOI:10.1002/pola.28433
Daisuke Takeuchi; Yuriko Chiba; Shigenaga Takano; Hideo Kurihara; Minoru Kobayashi; Kohtaro Osakada Ethylene polymerization catalyzed by dinickel complexes with a double-decker structure, Polymer Chemistry, Volume 8 (2017) no. 34, p. 5112 | DOI:10.1039/c7py00333a
Fang Huang; Wenjuan Zhang; Erlin Yue; Tongling Liang; Xinquan Hu; Wen-Hua Sun Controlling the molecular weights of polyethylene waxes using the highly active precatalysts of 2-(1-aryliminoethyl)-9-arylimino-5,6,7,8-tetrahydrocycloheptapyridylcobalt chlorides: synthesis, characterization, and catalytic behavior, Dalton Transactions, Volume 45 (2016) no. 2, p. 657 | DOI:10.1039/c5dt03779d
Shizhen Du; Wenjuan Zhang; Erlin Yue; Fang Huang; Tongling Liang; Wen‐Hua Sun α,α′‐Bis(arylimino)‐2,3:5,6‐bis(pentamethylene)pyridylcobalt Chlorides: Synthesis, Characterization, and Ethylene Polymerization Behavior, European Journal of Inorganic Chemistry, Volume 2016 (2016) no. 11, p. 1748 | DOI:10.1002/ejic.201600098
Fang Huang; Wenjuan Zhang; Yang Sun; Xinquan Hu; Gregory A. Solan; Wen-Hua Sun Thermally stable and highly active cobalt precatalysts for vinyl-polyethylenes with narrow polydispersities: integrating fused-ring and imino-carbon protection into ligand design, New Journal of Chemistry, Volume 40 (2016) no. 9, p. 8012 | DOI:10.1039/c6nj01867j
Shizhen Du; Xinxin Wang; Wenjuan Zhang; Zygmunt Flisak; Yang Sun; Wen-Hua Sun A practical ethylene polymerization for vinyl-polyethylenes: synthesis, characterization and catalytic behavior of α,α′-bisimino-2,3:5,6-bis(pentamethylene)pyridyliron chlorides, Polymer Chemistry, Volume 7 (2016) no. 25, p. 4188 | DOI:10.1039/c6py00745g
Shizhen Du; Qifeng Xing; Zygmunt Flisak; Erlin Yue; Yang Sun; Wen-Hua Sun Ethylene polymerization by the thermally unique 1-[2-(bis(4-fluoro phenyl)methyl)-4,6-dimethylphenylimino]-2-aryliminoacenaphthylnickel precursors, Dalton Transactions, Volume 44 (2015) no. 27, p. 12282 | DOI:10.1039/c5dt00052a
Eike B. Bauer Iron Catalysis: Historic Overview and Current Trends, Iron Catalysis II, Volume 50 (2015), p. 1 | DOI:10.1007/3418_2015_107
Shizhen Du; Shaoliang Kong; Qisong Shi; Jing Mao; Cunyue Guo; Jianjun Yi; Tongling Liang; Wen-Hua Sun Enhancing the Activity and Thermal Stability of Nickel Complex Precatalysts Using 1-[2,6-Bis(bis(4-fluorophenyl)methyl)-4-methyl phenylimino]-2-aryliminoacenaphthylene Derivatives, Organometallics, Volume 34 (2015) no. 3, p. 582 | DOI:10.1021/om500943u
Junjun Ba; Shizhen Du; Erlin Yue; Xinquan Hu; Zygmunt Flisak; Wen-Hua Sun Constrained formation of 2-(1-(arylimino)ethyl)-7-arylimino-6,6-dimethylcyclopentapyridines and their cobalt(ii) chloride complexes: synthesis, characterization and ethylene polymerization, RSC Advances, Volume 5 (2015) no. 41, p. 32720 | DOI:10.1039/c5ra04722f
Adrien Boudier; Pierre-Alain R. Breuil; Lionel Magna; Hélène Olivier-Bourbigou; Pierre Braunstein Ethylene oligomerization using iron complexes: beyond the discovery of bis(imino)pyridine ligands, Chemical Communications, Volume 50 (2014) no. 12, p. 1398 | DOI:10.1039/c3cc47834c
Shigenaga Takano; Yuji Takeuchi; Daisuke Takeuchi; Kohtaro Osakada Selective Formation of Ethyl- and/or Propyl-branched Oligoethylene Using Double-decker-type Dinuclear Fe Complexes as the Catalyst, Chemistry Letters, Volume 43 (2014) no. 4, p. 465 | DOI:10.1246/cl.131065
Fang Huang; Qifeng Xing; Tongling Liang; Zygmunt Flisak; Bin Ye; Xinquan Hu; Wenhong Yang; Wen-Hua Sun 2-(1-Aryliminoethyl)-9-arylimino-5,6,7,8-tetrahydrocycloheptapyridyl iron(ii) dichloride: synthesis, characterization, and the highly active and tunable active species in ethylene polymerization, Dalton Trans., Volume 43 (2014) no. 44, p. 16818 | DOI:10.1039/c4dt02102a
Jing Ma; Chun Feng; Shaoli Wang; Ke-Qing Zhao; Wen-Hua Sun; Carl Redshaw; Gregory A. Solan Bi- and tri-dentate imino-based iron and cobalt pre-catalysts for ethylene oligo-/polymerization, Inorg. Chem. Front., Volume 1 (2014) no. 1, p. 14 | DOI:10.1039/c3qi00028a
Qing Yan; Zelin Sun; Wenjuan Zhang; Kotohiro Nomura; Wen‐Hua Sun Vanadyl Di(5‐t‐butyl‐2‐(aryliminomethyl)quinolin‐8‐olate): Synthesis, Characterization, and Ethylene (Co‐)Polymerization, Macromolecular Chemistry and Physics, Volume 215 (2014) no. 18, p. 1744 | DOI:10.1002/macp.201400199
Wenjuan Zhang; Shaoli Wang; Shizhen Du; Cun‐Yue Guo; Xiang Hao; Wen‐Hua Sun 2‐(1‐(2,4‐Bis((di(4‐fluorophenyl)methyl)‐6‐methylphenylimino)ethyl)‐6‐(1‐(arylimino)ethyl)pyridylmetal (iron or cobalt) Complexes: Synthesis, Characterization, and Ethylene Polymerization Behavior, Macromolecular Chemistry and Physics, Volume 215 (2014) no. 18, p. 1797 | DOI:10.1002/macp.201400140
Daisuke Takeuchi; Shigenaga Takano; Yuji Takeuchi; Kohtaro Osakada Ethylene Polymerization at High Temperatures Catalyzed by Double-Decker-Type Dinuclear Iron and Cobalt Complexes: Dimer Effect on Stability of the Catalyst and Polydispersity of the Product, Organometallics, Volume 33 (2014) no. 19, p. 5316 | DOI:10.1021/om500629a
Rong Gao; Wen-Hua Sun; Carl Redshaw Nickel complex pre-catalysts in ethylene polymerization: new approaches to elastomeric materials, Catalysis Science Technology, Volume 3 (2013) no. 5, p. 1172 | DOI:10.1039/c3cy20691b
Wenjuan Zhang; Wen-Hua Sun; Carl Redshaw Tailoring iron complexes for ethylene oligomerization and/or polymerization, Dalton Trans., Volume 42 (2013) no. 25, p. 8988 | DOI:10.1039/c2dt32337k
Shaoli Wang; Baixiang Li; Tongling Liang; Carl Redshaw; Yuesheng Li; Wen-Hua Sun Synthesis, characterization and catalytic behavior toward ethylene of 2-[1-(4,6-dimethyl-2-benzhydrylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylmetal (iron or cobalt) chlorides, Dalton Transactions, Volume 42 (2013) no. 25, p. 9188 | DOI:10.1039/c3dt00011g
Minkyu Yang; Eunhee Kim; Jong Hwa Jeong; Kil Sik Min; Hyosun Lee Synthesis, structure, and magnetic properties of the halide-bridged dimeric complex [(bpmaL1)Fe(μ-Cl)Cl]2, Inorganica Chimica Acta, Volume 394 (2013), p. 501 | DOI:10.1016/j.ica.2012.09.010
Shaoli Wang; Weizhen Zhao; Xiang Hao; Baixiang Li; Carl Redshaw; Yuesheng Li; Wen-Hua Sun 2-(1-2,6-Bis[bis(4-fluorophenyl)methyl]-4-methylphenyliminoethyl)-6-[1-(arylimino)ethyl]pyridylcobalt dichlorides: Synthesis, characterization and ethylene polymerization behavior, Journal of Organometallic Chemistry, Volume 731 (2013), p. 78 | DOI:10.1016/j.jorganchem.2013.02.016
Wen-Hua Sun Novel Polyethylenes via Late Transition Metal Complex Pre-catalysts, Polyolefins: 50 years after Ziegler and Natta II, Volume 258 (2013), p. 163 | DOI:10.1007/12_2013_212
Qifeng Xing; Tong Zhao; Yusen Qiao; Lin Wang; Carl Redshaw; Wen-Hua Sun Synthesis, characterization and ethylene polymerization behavior of binuclear iron complexes bearing N,N′-bis(1-(6-(1-(arylimino)ethyl) pyridin-2-yl)ethylidene)benzidines, RSC Advances, Volume 3 (2013) no. 48, p. 26184 | DOI:10.1039/c3ra42631a
Simon A. Cotton Iron, ruthenium and osmium, Annual Reports Section "A" (Inorganic Chemistry), Volume 108 (2012), p. 186 | DOI:10.1039/c2ic90010f
Wen-Hua Sun; Shaoliang Kong; Wenbin Chai; Takeshi Shiono; Carl Redshaw; Xinquan Hu; Cunyue Guo; Xiang Hao 2-(1-(Arylimino)ethyl)-8-arylimino-5,6,7-trihydroquinolylcobalt dichloride: Synthesis and polyethylene wax formation, Applied Catalysis A: General, Volume 447-448 (2012), p. 67 | DOI:10.1016/j.apcata.2012.09.011
Wen-Hua Sun; Shengju Song; Baixiang Li; Carl Redshaw; Xiang Hao; Yue-Sheng Li; Fosong Wang Ethylene polymerization by 2-iminopyridylnickel halide complexes: synthesis, characterization and catalytic influence of the benzhydryl group, Dalton Transactions, Volume 41 (2012) no. 39, p. 11999 | DOI:10.1039/c2dt30989k
David Schweinfurth; Cheng-Yong Su; Shi-Chao Wei; Pierre Braunstein; Biprajit Sarkar Nickel complexes with “click”-derived pyridyl-triazole ligands: weak intermolecular interactions and catalytic ethylene oligomerisation, Dalton Transactions, Volume 41 (2012) no. 41, p. 12984 | DOI:10.1039/c2dt31805a
Jingjuan Lai; Xiaohua Hou; Yongwen Liu; Carl Redshaw; Wen-Hua Sun 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylnickel(II) halides: Synthesis, characterization and ethylene oligomerization behavior, Journal of Organometallic Chemistry, Volume 702 (2012), p. 52 | DOI:10.1016/j.jorganchem.2011.12.031
Fan He; Weizhen Zhao; Xiao-Ping Cao; Tongling Liang; Carl Redshaw; Wen-Hua Sun 2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-aryliminoethyl]pyridyl cobalt dichlorides: Synthesis, characterization and ethylene polymerization behavior, Journal of Organometallic Chemistry, Volume 713 (2012), p. 209 | DOI:10.1016/j.jorganchem.2012.05.020
Wen‐Hua Sun; Weizhen Zhao; Jiangang Yu; Wenjuan Zhang; Xiang Hao; Carl Redshaw Enhancing the Activity and Thermal Stability of Iron Precatalysts Using 2‐(1‐2,6‐bis[bis(4‐fluorophenyl)methyl]‐4‐methylphenyliminoethyl)‐6‐[1‐(arylimino)ethyl]pyridines, Macromolecular Chemistry and Physics, Volume 213 (2012) no. 12, p. 1266 | DOI:10.1002/macp.201200051
Wenjuan Zhang; Wenbin Chai; Wen-Hua Sun; Xinquan Hu; Carl Redshaw; Xiang Hao 2-(1-(Arylimino)ethyl)-8-arylimino-5,6,7-trihydroquinoline Iron(II) Chloride Complexes: Synthesis, Characterization, and Ethylene Polymerization Behavior, Organometallics, Volume 31 (2012) no. 14, p. 5039 | DOI:10.1021/om300388m
Weizhen Zhao; Jiangang Yu; Shengju Song; Wenhong Yang; Hao Liu; Xiang Hao; Carl Redshaw; Wen-Hua Sun Controlling the ethylene polymerization parameters in iron pre-catalysts of the type 2-[1-(2,4-dibenzhydryl-6-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl] pyridyliron dichloride, Polymer, Volume 53 (2012) no. 1, p. 130 | DOI:10.1016/j.polymer.2011.11.024
Shengju Song; Weizhen Zhao; Lin Wang; Carl Redshaw; Fosong Wang; Wen-Hua Sun Synthesis, characterization and catalytic behavior toward ethylene of cobalt(II) and iron(II) complexes bearing 2-(1-aryliminoethylidene)quinolines, Journal of Organometallic Chemistry, Volume 696 (2011) no. 18, p. 3029 | DOI:10.1016/j.jorganchem.2011.06.003

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