Late Transition Metal Catalysts with Chelating Amines for Olefin Polymerization
Round 1
Reviewer 1 Report
Gao, Pei and co-authors has written this review titled ''Late Transition Metal Catalysts Chelating Amine Donors for 2 Olefins Polymerization''. The review presents a very nice complilation and discussion of the different N-chelating ligands for late transition metal based catalysts for olefin polymerization. The specfic combination of this type of chelating ligand with late transition metals as catalysts for olefin polymerization has not been reviewed before. The review is well written for the most parts and is mostly well organized. I would recommend this review for publication in Catalysts after minor revisions.
Following are my suggestion to be considered before final publication:
1) The title is somewhat confusing and it could be repharased as something like ''Chelating Amine coordinated Late Transition Metal Catalysts for Olefins Polymerization.''
2) a: In many places there are mistakes in English grammer, please revise carefully again. My suggestion is to check carefully for singular and plural nouns and their corresponding helping verbs. Also look out for other mistakes, for example line 116 was-->is, line 122 a-->an, line 126 high-->highly, and many more.
b: My suggestion for better flow of the review and general understanding, please follow simple rule of keeping all the facts like data, structural property like coordination environment in present tense and all the methods and process like synthesis and catalysis in past tense. Please consider this as my constructive criticism to improve the quality of your review.
3) The chemical formulas drawn in the schemes (possibly by ChemDraw) needs to be polished as the current form looks not so pleasent. Please try to keep the font same for all the scheme as figures and the relative bond angles and lengths reliable. This is just to make the review in a better shape.
4) In conclusion, combinations should be replaced by interactions in line 443 and 444.
5) This review chooses four metals with a set of ligands. The choice of metal seems unclear. Ni, Fe, Co are first row while Pd second row. Why Pd was added to this review and why not Ru and Rh. Please mention the rationale behind this selection in the introduction for clarity to the readers. If Ru and Rh are reviewed previously then mention it and cite.
6) The major portion of the review consist of Ni and Pd, presence Fe and Co is scarce. It would be worth to mention it in the conclusion that apart from making new [N, X] ligands (X is donor atom such as O, P, and S) containing amine, there are scopes for investigation of Fe and Co catalysts with N-chelating ligand in olefins polymerization. And in case this is not correct then mention the drawbacks of Fe and Co metals with the ligand systems of this review.
7) The statement in the conclusion (line 445 to 449) regarding the effect of different subsitituent on the ligand on the catalytic activity is not clear. There is no mention of any metal. Is this statement true for all four metal discussed in this review or for some selected metal(s)? This should be clearly explained in the conclusion as readers will get a clear understanding of the topic.
Author Response
1) The title is somewhat confusing and it could be repharased as something like ''Chelating Amine coordinated Late Transition Metal Catalysts for Olefins Polymerization.''
Response: The tile is changed to “Late Transition Metal Catalysts with Chelating Amines for Olefins Polymerization” accordingly.
2) a: In many places there are mistakes in English grammer, please revise carefully again. My suggestion is to check carefully for singular and plural nouns and their corresponding helping verbs. Also look out for other mistakes, for example line 116 was-->is, line 122 a-->an, line 126 high-->highly, and many more.
b: My suggestion for better flow of the review and general understanding, please follow simple rule of keeping all the facts like data, structural property like coordination environment in present tense and all the methods and process like synthesis and catalysis in past tense. Please consider this as my constructive criticism to improve the quality of your review.
Response: We check carefully throughout the text. We try our best to revise some spelling and grammar mistakes in the text. Thanks for your patience.
3) The chemical formulas drawn in the schemes (possibly by ChemDraw) needs to be polished as the current form looks not so pleasent. Please try to keep the font same for all the scheme as figures and the relative bond angles and lengths reliable. This is just to make the review in a better shape.
Response: We redraw all schemes and figures by ChemDraw, and we also try to keep the same font, bond angles and lengths for all the schemes and figures ASAP.
4) In conclusion, combinations should be replaced by interactions in line 443 and 444.
Response: In conclusion, “combinations” is replaced by “interactions”.
5) This review chooses four metals with a set of ligands. The choice of metal seems unclear. Ni, Fe, Co are first row while Pd second row. Why Pd was added to this review and why not Ru and Rh. Please mention the rationale behind this selection in the introduction for clarity to the readers. If Ru and Rh are reviewed previously then mention it and cite.
Response: In this review, we focus on late transition metal olefins polymerization catalysts with chelating amines. Herein, the olefins coordination polymerization is the addition polymerization of vinyl olefins and the ring-opening-metathesis polymerization of cycloolefins is not included. The Ru and Rh based catalysts are good candidates for ring-opening-metathesis polymerization of cycloolefins, but they are not excellent olefins polymerization catalysts. To the best of our knowledge, there is no report on Ru and Rh based olefins polymerization catalysts with amine ligands. In the text, we explain the choice of metal.
Although few Ru and Rh based catalysts are reported to be active for olefins polymerization, there is no report on the Ru and Rh based olefins polymerization catalysts with amine ligands up to date.
6) The major portion of the review consist of Ni and Pd, presence Fe and Co is scarce. It would be worth to mention it in the conclusion that apart from making new [N, X] ligands (X is donor atom such as O, P, and S) containing amine, there are scopes for investigation of Fe and Co catalysts with N-chelating ligand in olefins polymerization. And in case this is not correct then mention the drawbacks of Fe and Co metals with the ligand systems of this review.
Response: In conclusion, we supply the outlook on Fe and Co based olefins polymerization catalysts. Besides, Fe and Co based olefins polymerization catalysts with chelating amines are worth to further develop.
7) The statement in the conclusion (line 445 to 449) regarding the effect of different subsitituent on the ligand on the catalytic activity is not clear. There is no mention of any metal. Is this statement true for all four metal discussed in this review or for some selected metal(s)? This should be clearly explained in the conclusion as readers will get a clear understanding of the topic.
Response: Generally, this statement is true for all four metal catalysts. In conclusion, we clearly explain this statement in the conclusion.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The publication of this review will be a useful contribution for the scientists working in this catalysis area, some minor corrections and additions should be made before issuing. I have marked some mistakes and add some comments with my suggestions
Current references have been used, good scheme reactions, etc.
I suggest its publication
Comments for author File: Comments.pdf
Author Response
(1) I think could be better to replace "Ziegler-Natta" by coordination, since in industry every time more polyolefins are produced with other kind of coordination catalysts like metallocenes, CGC, besides Ziegler-Natta
Response: "Ziegler-Natta" is changed to “coordination”.
(2) Previous to this paragraph rapidly explain how or why this 5c catalyst polymerize in a living fashion, related to the structure of the catalysts or to the polymerization conditions?
Response: The structure of the catalysts is shown in Scheme 2, and the polymerization conditions (-20 °C, Al(MAO)/Ni = 200) are supplied in the text.
(3) Is this 9A? or 7a? Figure or compound
Response: 9A is corrected to 11A.
(4) Figure 13 is a Fe Complex, not Ni
Response: Ni is corrected to Fe.
(5) But here why the electron-rich ligand enhance ethylene polymerization activities? What effect has the electron-rich ligand in the stability of the catalytic system? Maybe? Explain a little bit in the text please
Response: We make an explanation that the introduction of electron-donating groups makes catalyst more stable.
(6) In Table 1 put the head name of the first column
Response: “Ni” is put the head name of the first column.
(7) Improved with respect the last results of the complexes of Table 1? Or compared with which?
Response: These polymerization results are compared between the bulky amine-pyridine nickel catalyst and the imine-pyridine nickel analogue. In the text, we clearly state this point.
The bulky amine-pyridine nickel catalyst (13 in Figure 9) showed higher activity and produced higher molecular weight PE than the imine-pyridine nickel analogue.
(8) Should be Scheme 8?
Response: Figure 8 is corrected to Scheme 8
(9) I suggest here to add (NE)
Response: “N-E” is added.
(10) I suggest to considere some information about Fe, compared with other late transition metals studied (Ni, Pd) cocerning its activity with other monomers, like dienes.
Response: There is no literature report on dienes polymerization using amine-pyridine Ni/Pd catalysts. In the text, ethylene polymerizations are compared.
In addition, amine-pyridine iron catalysts should be inactive for ethylene polymerization, which is contrast to amine-pyridine nickel catalysts.
(11) substitute dicholopalladium for dichloropalladium
Response: This typo-error is corrected.
Reviewer 3 Report
This manuscript reports on late transition metal (Ni, Pd, Fe, and Co) catalysts chelating amine donors for olefins polymerization. The information provided by the authors is very interesting and relevant. The conclusions seem sound.
But I would like to note that, in my opinion, the review lacks information about the nature of catalytically active centres that are formed during the interaction of the late transition metal (Ni, Pd, Fe, and Co) complexes with nitrogen containing ligands and cocatalysts (MAO, MMAO, or Et2AlCl). Such information is important since the nature of the catalytically active centers determines the activity, productivity, selectivity of multicomponent systems, as well as the nature of the target products.
Do the authors believe that hydride complexes of transition metals possess catalytic activity? Or they consider that structures of a different nature exert such activity?
A part of the review is devoted to the authors own works, which are of course interesting from a fundamental point of view, and also contribute to the development of several branches of modern chemistry of transition metal complexes and catalysis. It would be intriguing to know how the authors plan to develop this topic in the future.
Author Response
This manuscript reports on late transition metal (Ni, Pd, Fe, and Co) catalysts chelating amine donors for olefins polymerization. The information provided by the authors is very interesting and relevant. The conclusions seem sound.
(1) But I would like to note that, in my opinion, the review lacks information about the nature of catalytically active centres that are formed during the interaction of the late transition metal (Ni, Pd, Fe, and Co) complexes with nitrogen containing ligands and cocatalysts (MAO, MMAO, or Et2AlCl). Such information is important since the nature of the catalytically active centers determines the activity, productivity, selectivity of multicomponent systems, as well as the nature of the target products.
Response: We supply information about the nature of catalytically active centres using amine-pyridine nickel catalyst as a sample.
A crucial question, the nature of active species of amine-pyridine nickel/MAO system for ethylene polymerization, needs to answer. It is reported that the amine group (C−(R)NH) can be deprotonated to produce the amide (C−(R)N-) group, and the amide−metal combination arrangement also generally occurs. Therefore, the “true” active species is whether cation pyridine-amine nickel ([Py−CNRH]Ni+R,) or neutral pyridine-amide nickel ([Py−CNR]NiR) when a hydrogen on the amine group is removed by the cocatalyst MAO. Comparisons of ethylene polymerizations using amide-pyridine nickel/MAO and amine-pyridine nickel/MAO support the “true” active species is the cation pyridine-amine nickel ([Py-CNRH]Ni+P) because bulky steric hindrance may prohibit the deprotonation of the amine group.
(2) Do the authors believe that hydride complexes of transition metals possess catalytic activity? Or they consider that structures of a different nature exert such activity?
Response: In previous comments on our papers, reviewers had same questions on the nature of metal active species for olefins polymerization. Possibly, there is the reaction between amine group and cocatalysts (MAO, MMAO, or Et2AlCl). We have previously proved that true metal active species is cationic amine-imine ligated nickel. Especially, cationic amine-imine palladium can directly catalyze (co)polymerization of ethylene without any cocatalysts, which reflecting amine-imine palladium is true active species.
(3) A part of the review is devoted to the authors own works, which are of course interesting from a fundamental point of view, and also contribute to the development of several branches of modern chemistry of transition metal complexes and catalysis. It would be intriguing to know how the authors plan to develop this topic in the future.
Response: Thanks for your nice comment. From a fundamental point of view, we will study systematically nickel and palladium-based olefins polymerization catalysts with α-diimine, amine-imine, amido-imine, and α-diamine ligands, and will disclose the effects of the different nitrogen donor. Besides, the electronic effect of the amine moiety on olefins polymerization will be also studied because of the lack of investigation.
Author Response File: Author Response.pdf
Reviewer 4 Report
The authors present late transition metal (Ni, Pd, Fe, and Co) catalysts chelating amine donors for olefin polymerization. The review is well structured and organized, and easy to read. The main ideas and concepts are undoubtedly logically structured and focused on the topic. The schemes are clear, well presented, and are helping the reader to follow the point. I would suggest adding the possible mechanistic elucidations and pathways explaining the activity of the presented catalysts since it would enrich the presented review. Further, I suggest commenting on and comparing catalytic parameters' activity and selectivity for the presented catalysts.
For the above-mentioned reasons, I suggest minor revision.
Author Response
The authors present late transition metal (Ni, Pd, Fe, and Co) catalysts chelating amine donors for olefin polymerization. The review is well structured and organized, and easy to read. The main ideas and concepts are undoubtedly logically structured and focused on the topic. The schemes are clear, well presented, and are helping the reader to follow the point. I would suggest adding the possible mechanistic elucidations and pathways explaining the activity of the presented catalysts since it would enrich the presented review. Further, I suggest commenting on and comparing catalytic parameters' activity and selectivity for the presented catalysts. For the above-mentioned reasons, I suggest minor revision.
Response: According to reviewer’s suggestion, we supply the information about the nature of catalytically active centres. Besides, we also supply chain walking mechanism of amine-imine Ni-catalyzed ethylene polymerization (Scheme 2) and the reaction path of copolymerization of ethylene and MA using amine-imine palladium catalyst (Scheme 8). Besides, Different enchainment pathways in 1-hexene polymerization using amine-imine nickel catalysts 5c and 6c have been shown in Scheme 6.
Author Response File: Author Response.pdf
