Investigations on the Ethylene Polymerization with Bisarylimine Pyridine Iron (BIP) Catalysts

Round 1

Reviewer 1 Report

Here in this manuscript, the authors report interesting effect of large amounts of methyl aluminoxane on the bisarylimine pyridine iron catalyst. Although the output is not extraordinary exceptional, I think the paper will impact broad range of studies since the synthesis is strait forward and the concept " terminations of ethylene polymerization mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts and activated by large amounts of methyl aluminoxane" is clear. Nevertheless, I think some parts are missing for the paper at the current stage. The followings are my concerns and possible improvements.

Some more general references for late transition metal complexes as catalysts for ethylene polymerization are needed here, rather than few very specific works. Considerable progress means more than just a few papers from 1998. Many reviews and books have been written on the matter. Cite those. Please add some more recently references of Brookhart, Mecking, Nozaki, Coates, Long, Carrow here.

The productivity is not high, for most polymers the obtained molecular weight distribution is bimodal.

Please add necessary error bars in order to demonstrate the reproducibility of the method. (Figure 5b)

There is no information about the microstructure, like: number of branches per 1000 C, types of branches etc.

For some examples there are large differences between Mn (NMR) and Mn (SEC), it needs some comment.

Author Response

Dear Reviewer, we want to thank you for your time and the valuable comments to our manuscript. We have tried to process your remarks as close as we can. Please find below the changes that have made along your comments.

Comments and Suggestions for Authors

Here in this manuscript, the authors report interesting effect of large amounts of methyl aluminoxane on the bisarylimine pyridine iron catalyst. Although the output is not extraordinary exceptional, I think the paper will impact broad range of studies since the synthesis is strait forward and the concept " terminations of ethylene polymerization mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts and activated by large amounts of methyl aluminoxane" is clear. Nevertheless, I think some parts are missing for the paper at the current stage. The followings are my concerns and possible improvements.

Some more general references for late transition metal complexes as catalysts for ethylene polymerization are needed here, rather than few very specific works. Considerable progress means more than just a few papers from 1998. Many reviews and books have been written on the matter. Cite those. Please add some more recently references of Brookhart, Mecking, Nozaki, Coates, Long, Carrow here.

We now have included a broad range of new references (reviews and research papers) in the text. The introduction was shortened as well, following further comments of reviewers. This goes along with some reorganization of the text too. The new references are marked green in the manuscript.

Line 43: ref [14-19] were added.

14. Vaidya, T.; Klimovica, K.; LaPointe, A. M., Keresztes, I.; Lobkovsky, E. B.; Daugulis, O.; Coates, G. W. Secondary Alkene Insertion and Precision Chain-Walking: A New Route to Semicrystalline “Polyethylene” from α-Olefins by Combining Two Rare Catalytic Events, J. Am. Chem. Soc., 2014, 136 (20), 7213–7216.
15. Long, B. K.; Eagan, J. M.; Mulzer, M.; Coates, G. W. Semi‐Crystalline Polar Polyethylene: Ester‐Functionalized Linear Polyolefins Enabled by a Functional‐Group‐Tolerant, Cationic Nickel Catalyst. Angew. Chem. Int. Ed., 2016,  55(25), 7106-7110.
16. Tran, Q. H., Brookhart, M., & Daugulis, O. (2020). New Neutral Nickel and Palladium Sandwich Catalysts: Synthesis of Ultra-High Molecular Weight Polyethylene (UHMWPE) via Highly Controlled Polymerization and Mechanistic Studies of Chain Propagation., J. Am. Chem. Soc.,142(15), 7198-7206.
17. Chen, Z.; Leatherman, M. D.; Daugulis, O.; Brookhart, M. Nickel-Catalyzed Copolymerization of Ethylene and Vinyltrialkoxysilanes: Catalytic Production of Cross-linkable Polyethylene and Elucidation of the Chain-Growth Mechanism., J. Am. Chem. Soc.,2017, 139(44), 16013-16022.
18. Rhinehart, J. L.; Brown, L. A.; Long, B. K. A Robust Ni (II) α-Diimine Catalyst for High Temperature Ethylene Polymerization, J. Am. Chem Soc., 2013,  135(44), 16316-16319.
19. Carrow, B. P.; Nozaki, K. Transition-metal-catalyzed Functional Polyolefin Synthesis: Effecting Control Through Chelating Ancillary Ligand Design and Mechanistic Insights. Macromolecules, 2014,  47(8), 2541-2555.

Line 46: new phrase added: The vast development can be taken from several recent reviews.[27-34] Ref. [27-34] added.

27. Gibson V. C.; Solan, G. A. Olefin Oligomerizations and Polymerizations Catalyzed by Iron and Cobalt Complexes Bearing Bis(imino)pyridine Ligands, In: Catalysis without Precious Metals, Bullock, M., eds., Wiley-VCH, Weinheim, Germany, 2010, 111-141.
28. Gibson, V. C.; Solan, G. A. Iron-Based and Cobalt-Based Olefin Polymerisation Catalysts. In: Metal Catalysts in Olefin Polymerization, Guan, Z., eds., Springer, Berlin, Heidelberg, 2009, 26, pp. 107-158.
29. Zhang, W.; Sun, W. H.;Redshaw, C. Tailoring Iron Complexes for Ethylene Oligomerization and/or Polymerization, Dalton Trans., 2013,  42(25), 8988-8997.
30. Bianchini, C.; Giambastiani, G.; Luconi, L.; Meli, A. Olefin Oligomerization, Homopolymerization and Copolymerization by Late Transition Metals Supported by (Imino) Pyridine Ligands, Coord. Chem. Rev., 2010,  254(5-6), 431-455.
31. Ma, J.; Feng, C.; Wang, S.; Zhao, K. Q.; Sun, W. H.; Redshaw, C.; Solan, G. A. Bi-and Tri-dentate Imino-Based Iron and Cobalt Pre-Catalysts for Ethylene Oligo-/Polymerization, Inorg. Chem. Front., 2014, 1(1), 14-34.
32. Britovsek, G. J.; Mastroianni, S.; Solan, G. A.; Baugh, S. P.; Redshaw, C.; Gibson, V. C.; Elsegood, M. R. Oligomerisation of Ethylene by Bis (Imino) Pyridyl Iron and Cobalt Complexes. Chem. A Eur. J., 2000, 6(12), 2221-2231.
33. Baier, M. C.; Zuideveld, M. A.; Mecking, S. Post‐Metallocenes, In: The Industrial Production of Polyolefins, Angew. Chem. Int. Ed., 2014, 53(37), 9722-9744.
34. Domski, G. J.; Rose, J. M.; Coates, G. W.; Bolig, A. D.; Brookhart, M. Living Alkene Polymerization: New Methods for the Precision Synthesis of Polyolefins, Prog. Polym. Sci., 2007, 32(1), 30-92.

Line 58: ref [39-44] were added.

39. Chen, Y.; Qian, C.; Sun, J. Fluoro-substituted 2,6-Bis (Imino) Pyridyl Iron and Cobalt Complexes: High-activity Ethylene Oligomerization Catalysts, Organometallics, 2003, 22(6), 1231-1236.
40. Kawakami, T.; Ito, S.; Nozaki, K. Iron-catalysed Homo-and Copolymerisation of Propylene: Steric Influence of Bis (imino) Pyridine Ligands, Dalton Trans., 2015, 44(47), 20745-20752.
41. Wang, Z.; Solan, G. A.; Zhang, W.; Sun, W.-H. Carbocyclic Fused N, N, N-Pincer Ligands as Ring-Strain Adjustable Supports for Iron and Cobalt Catalysts in Ethylene Oligo-/Polymerization, Coord. Chem. Rev. 2018, 363, 92−108.
42. Zhang, Q.; Zhang, R.; Han, M.; Yang, W.; Liang, T.; Sun, W. H. 4, 4′-Difluorobenzhydryl-modified Bis (imino)-pyridyliron (II) Chlorides as Thermally Stable Precatalysts for Strictly Linear Polyethylenes with Narrow Dispersities, Dalton Transactions, 2020. 49(22), 7384-7396.
43. Zhang, Y.; Wang, C.; Jian, Z. A Comprehensive Study on Highly Active Pentiptycenyl-substituted Bis (Imino) Pyridyl Iron (II) Mediated Ethylene Polymerization, Eur. Polym. J., 2020, 128, 109605.
44. Guo, L. H.; Gao, H. Y.; Zhang, L.; Zhu, F. M.; Wu, Q. An Unsymmetrical Iron (II) Bis (Imino) Pyridyl Catalyst for Ethylene Polymerization: Effect of a Bulky Ortho Substituent on the Thermostability and Molecular Weight of Polyethylene, Organometallics, 2010, 29(9), 2118-2125.

Lines 67-68, 82-85, 86-87,90-91, 102-103, 106-110, 116-121, 134-137, 146-154, 159-160, 186-188 and 195-198 were removed (lines are referring to the actual manuscript, with complete markup of changes).

Lines 96-101 were transferred to lines 77-82.

The productivity is not high, for most polymers the obtained molecular weight distribution is bimodal.

The productivity as the product of average activity and time is actually not so bad. The activities of 1-4 are lying between 20 – 65 t/mol Fe bar h which is also a typical range. It may be noticed that most of the experiments are conducted at high aluminum concentrations leading to lower maximum activities (equation 1) but easily controllable and constant reaction rates.

The bimodal distributions were also reported earlier. It arises on account of the various rates and modes of chain terminations. The extended data of this study suggest that the (reaction time dependent) rate of the chain shuttling in relation to the ethylene insertion and the beta-hydrogen transfer are underlying the observations.

Please add necessary error bars in order to demonstrate the reproducibility of the method. (Figure 5b)

Error bars were added to Figure 5b and 6. The confidence intervals of the measurements of the kinetic study is included in Table S1 in the supplements.

There is no information about the microstructure, like: number of branches per 1000 C, types of branches etc.

The obtained products are highly linear polyethylenes, no branches were detected in NMR spectra. This is a typical result for the used catalysts 1-5.

Adding Line 380: The products obtained are highly linear with no branches detected in NMR spectra.

For some examples there are large differences between Mn (NMR) and Mn (SEC), it needs some comment.

Lines 395-401 were added.

The molecular masses are as planned in the lower range. The masses were obtained from endgroup analyses in the proton NMR spectra and by SEC (Table 4). The values are mostly close to each other, however, both methods have a limited accuracy and differences occur. These originate from the inherent errors in determining the integral values of small signals of sparingly soluble compounds in NMR spectra. In addition, the linearity of the log M – elution volume dependency, especially at low molecular weights, peak selection and the validity of the Kuhn-Mark-Houwink-Sakurada equation for obtaining absolute masses in SEC determinations gives some spread.

Reviewer 2 Report

The topic regarding "kinetics and terminations" is always interesting and worthily investigated. The manuscript presents some new observations, which is worthily for readers to know. However, the introduction and decriptions are too long for readers to realize the results and their obersations. It would be depended on authors, but better to focus the iron catalytic achievements and their new observation. Therefore my suggestions are followings:

1  Authors would be better to catach the progress of iron complex catalysts instead of the various topics of historic polyolefin, though it is good to illustrate the historic background, but the detail review Coord. Chem. Rev., 2018, 363, 92-108, new article Dalton Trans., 2020, 49, 7384 – 7396 and etc. recommended. At least, the differences would be considered to heterogeneous and homogeneous catalysis, ethylene polymerization would be not necessarily considered isotactic property in the polymerization. 

2 Authors enphasized many general decisive views, but some were truly wrong. For example, "Generally, more bulky aryl (imine) substituents lead to lower activities but higher molecular weights than the less bulky analogues", which was partly right.

3 Regarding the correlations of catalytic performance with using catalysts, there are more complex issues depending reaction time on the initial stages. Probably authors should carefully ponder over them.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript deals with the polymerization of ethylene with five tridentate Fe(II) pre-catalysts incorporating bulky substituted arylimine moieties. Although polymerization tests using these Fe(II) complexes, as well as reaction kinetics of the chain propagation in ethylene polymerization are well done, my concern is that this manuscript seems to more or less duplicate previous studies in refs. 4, 14,16, 17, 21, and 109 using the same complexes 1-5. In my opinion, therefore, this manuscript does not justify acceptance in a journal such as Catalysts.

1. The introduction is well organized, but the details of the general reaction mechanism in the coordinative polymerization and alkylaluminum compounds are quite insistent as in a textbook, Thus, the introduction should be shortened to become more concise.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors improved their manuscript however I would suggest some more recently references at least from last year.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript was revised with considering my comments, and could be recommended for publication.

Author Response

No additional task were open.

Reviewer 3 Report

All my concerns have been addressed in the revised version, and I was able to really understand the author’s concept and the background in this research. However, it seems to me that the introduction is still long and lacking incoherence. Therefore, I request that the introduction be shortened and edited again.

Author Response

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Author Response File: Author Response.pdf