Role of Electronic and Steric Effects on Ruthenium Catalysts with Bulky NHC Ligands and Relationship with the Z-Selectivity in Olefin Metathesis

Round 1

Reviewer 1 Report

Article under revision is devoted to the study of the influence of ruthenium complexes ligand environment on the selectivity in cross-metathesis (CM) reaction by DFT method, as well as a detailed study of CM mechanism. For calculation, the authors chose six model Hoveyda-Grubbs-type complexes with asymmetric NHC ligands, which were synthesized and characterized by the research group of Prof. Grubbs in the period from 2012 to 2019. These complexes also contain nitro- or pivalate functional groups as anionic ligands. The authors put forward a theory about the combined influence of the electronic effects of anionic ligands and the steric effects of bulky substituents (Dipp and Dipep) in NHC ligands. The importance of theoretical approaches to the contemplation of a CM reaction mechanism, especially in the field of Z-selective catalysis was emphasized in the final part of the paper. The data obtained may be useful for the development of new stereospecific catalysts for olefin metathesis.

This referee has no principal objections; however, several comments should be voiced.

1.     The introduction is excessively voluminous (more than 3 pages) and filled with a lot of redundant information. The authors are advised to shorten the introduction by removing well-known facts (for example, lines 83-87) and unnecessary historical information. We believe that the introduction should take no more than 1-2 pages.

2.     Scheme a in Fig. 1 is confusing. The upper and lower parts should be combined, since in the most part of cross-metathesis reactions both cis and trans isomers are formed, it is also preferable to mark the catalyst (cat.) above the arrows.

3.     The second sentence, line 66. For clarity, a scheme of the acrylamide-olefin cross-metathesis reaction should be given.

4.     In its present form, Figs 2, 3, 4 are in low resolution; especially this reduces the quality of perception of information in Fig. 4. In addition, the source from which Fig. 4 was taken is not indicated; there is no unambiguous information in the text.

5.     The last three paragraphs of the introduction (lines 101-148) are in a different font.

6.     In Figs 5 and 6 it is worthwhile to show the structures of transition states from Fig. 4.

7.     Line 490 duo must be a typo.

The experimental part raises no questions in terms of the methodology and correctness of obtained results of DFT calculations. Nevertheless, the somewhat vague term that the authors apply to the Hoveyda-Grubbs-type (in this work Keitz-Grubbs) ruthenium catalysts raises questions. In our opinion, it is not correct to call complexes studied in detail more than 5 years ago «novel». Indeed, the catalysts chosen by the authors have not been studied in this way, to the best of our knowledge. On the other hand, it is worth emphasizing the importance of such studies for a comprehensive understanding of catalytic processes.

The above-mentioned shortcomings do not detract from the importance of the work made, and we are recommending this draft for publication in the Catalysts after a minor revision.

 

Author Response

Thank you so much for the comments and suggestion that helped to improved the manuscript. The answer are in the attached file .

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled "Role of electronic and steric effects into novel Ruthenium catalysts with bulky NHC ligands and relationship with the Z-selectivity in olefin metathesis" describes the use of density functional calculations to explore the reaction mechanism and understand the energetic contributions to the rate-determining step, emphasizing the differences that occur when 2,6-diisopropylphenyl (Dipp) and 2,6-diisopentylphenyl (Dipep) are used. The manuscript is well-written, and the results are important for the scientific community, especially for researchers working with this class of catalysts. However, I believe the authors could give greater prominence to the novelty of their work compared to others reported in the literature. 

Author Response

Thank you so much for the comments and suggestion that helped to improved the manuscript. The answer are in the attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Katherine Paredes-Gil and Valentina Diaz-González have studied the effect of the bulky substituents on nitrogen atoms of NHC ligands of cyclometalated ruthenium complexes, stabilized with nitrate and pivalate as counterion. They are interested to rationalize the effects that induce the Z-selectivity in the cross-metathesis reaction. The authors have investigated through density functional calculations steric and electronic effect in the limiting stage on the ethane cross-metathesis reaction mechanism. In my opinion, the manuscript describes in depth the effects that play a crucial role for the determination of the geometry of the products. The paper is well written and the result were reported in clear mode, however,some aspects require to be improve and need the attention from the authors:

1.       From line 101 to line 148, the font of the manuscript is different between the original font used for the Catalyst (Palatino Linotype);

 

2.      Some lines are not used, I suggest removing the unused lines to improve the pagination ( e.g. Lines from 177 to 191, etc);

Author Response

Thank you so much for the comments and suggestion that helped to improved the manuscript. The answer are in the attached file.

Author Response File: Author Response.pdf