Development of Titanium Dioxide-Supported Pd Catalysts for Ligand-Free Suzuki–Miyaura Coupling of Aryl Chlorides
Round 1
Reviewer 1 Report
The manuscript submitted by Sajiki and coll. reports the synthesis of palladium-supported catalyts for Suzuki–Miyaura cross-coupling. The present work is an interesting contribution to the discovery of new and efficient catalysts for C-C bonds formation.
Remarks and comments:
- The authors must investigate the homogeneous or heterogeneous nature of the palladium active species.
- Information about differences between the nine Pd-TiO2 materials must be added in order to better understanding why material D is a efficient precatalyst.
- Lines 198-207: Analytic instruments not used in the experimental part must be remove.
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- . Time and optimisation of the catalytic conditions are missing. The PEPPSI complex is extremely efficient ([Pd] 1 mol % at room temperature) the authors must based their manuscript on the latter catalyst and not on the in situ catalytic system made by mixing a palladium source and four equivalents of phosphonium.
The work has to be completed; I thus recommend this manuscript to be published in Molecules with minor revision.
Author Response
Dear Reviewer 1,
We greatly appreciate your time and thoughtful and constructive comments. We have revised the manuscript by your comments.
I have attached a point-by-point response to your comments as a PDF file.
The revised and newly added portions are highlighted in green on the manuscript. The removed parts in the original manuscript are underlined.
Furthermore, the English corrections of this manuscript were reviewed by Editage Co., which develops an English corrections business.
Sincerely yours,
Hironao Sajiki
Author Response File: 
Author Response.pdf
Reviewer 2 Report
A novel heterogeneous catalyst (Pd supported in TiO2) has been prepared and used for the Suzuki-Miyaura reaction of aryl chlorides and bromides with aryl boronic acids. Electron poor aryl chlorides can be used, but as usual electron rich aryls require the use of bromides to achieve the coupling. Characterization of the catalyst is effected by XPS spectroscopy. Even if the catalyst is easily recovered by simple filtration, it experiences a high loss of activity and it cannot be reused. The paper is well written and referenced. The Supporting Information is also adequate.
I endorse publication since I have only minor questions or remarks:
a) In lines 177-180, the authors attribute the loss of catalyst efficiency after the reaction to "degradation of the specific surface", but electron microscopy images of the catalyst surface are missing. I suggest that studies by AFM could give support to this hypothesis.
b) The authors should also check if after the standard workup (chromatographic purification) the coupling products are contaminated with Pd
Author Response
Dear Reviewer 2,
We greatly appreciate your time and thoughtful and constructive comments. We have revised the manuscript by your comments.
I have attached a point-by-point response to your comments as a PDF file.
The revised and newly added portions are highlighted in green on the manuscript. The removed parts in the original manuscript are underlined.
Furthermore, the English corrections of this manuscript were reviewed by Editage Co., which develops an English corrections business.
Sincerely yours,
Hironao Sajiki
Author Response File: Author Response.pdf
Reviewer 3 Report
The Authors report the preparation of anatase-, rutile- and brookite-type TiO2-supported Pd catalyst by simple impregnation process without reduction or by reduction with NH2-NH2, NaBH4 or H2. The catalytic activity of prepared catalyst has been evaluated in the Suzuki-Miyaura coupling reaction of 4’-chloroacetophenone and phenylboronic acid.
The catalytic activity of TiO2-supported Pd catalyst obtained by reduction is very low, while the catalyst obtained by simple impregnation show higher activity. The best result were obtain with anatase- type Cat D obtained by impregnation in MeCN and Brookite-type Cat I obtained by impregnation in Ethyl acetate. The Authors suggest that the catalytic activity is related to the crystal form of TiO2 but the result obtained with Cat A-C suggest that it strongly depend also on Pd oxidation state. In fact when the CAT D is recovered and reused the catalytic efficiency decreases due to the increase in Pd (0) content.
I suggest to determine the Pd(II)/Pd(0) ratio also for the catalyst E-I since the different supports and solvents could provide a different Pd(II)/Pd(0) ratio.
I suggest : 1.To determine the content of Pd(II)/Pd(0) for the cat E-I to establish if the catalytic activity is related to the crystal form of TiO2 or to Pd oxidation state. 2. Since Cat I shows the same conversion of Cat D, to perform the reaction with Cat I at 1000 rpm. 3. To determine the Pd content in the reaction product and reaction medium to exclude the releasing of Pd from the support.
In the panorama of catalysts known today for the Suzuki-Miyaura reaction ( Ref 13-33 and 34-42 for TiO2-supported Pd catalysts), this catalyst does not add anything new, moreover the catalyst is used in high quantities (5 mol%) and it is not reusable.
The paper can be considered if it is useful to explain how the type of support acts on the Pd oxidation state and therefore on the catalytic activity.
Author Response
Dear Reviewer 3,
We greatly appreciate your time and thoughtful and constructive comments. We have revised the manuscript by your comments.
I have attached a point-by-point response to your comments as a PDF file.
The revised and newly added portions are highlighted in green on the manuscript. The removed parts in the original manuscript are underlined.
Furthermore, the English corrections of this manuscript were reviewed by Editage Co., which develops an English corrections business.
Sincerely yours,
Hironao Sajiki
Author Response File: Author Response.pdf
Reviewer 4 Report
This work presents Development of Titanium Dioxide-Supported Pd Catalysts for Ligand-Free Suzuki–Miyaura Coupling of Aryl Chlorides. Developing durable recoverable catalysts is an important issue for both academic research areas and industries. This manuscript is recommended to be published after including and addressing the below listed comments with major corrections.
- The authors should eliminate the current grammatical and punctuation mark errors and also confirm the correct scientific English. Make sure to avoid or insert commas on the right positions. Make sure to use the definite and indefinite articles on the right positions.
- The authors should write the complete terms of all abbreviations (including the instruments) before the first use in the abstract and main manuscript.
- The authors should clearly explain the innovation and importance of their work on the introduction of the manuscript. They should justify the value of the work and compare their work with previously similar published papers. They should develop the heterogeneous advantage and applications. The introduction section is very short and needs to be elaborated.
- The advantages of the heterogeneous catalysts should be highlighted in the revised manuscript. The relevant references should be cited.
- The authors should work on the scientific English of the manuscript and elaborate it.
- The authors should explore the recyclability of the prepared catalyst and include the result in the revised manuscript. The recycling results are not discussed in detail and highlighted on the manuscript. The authors must clearly explain the recycling results on the revised manuscript with proper caption.
- The Pd amount (mol%) used in each reaction should be analyzed by ICP or AA and reported in the revised manuscript.
- The authors should cite important references related to heterogeneous catalysts, reusability of the catalysts, supported catalysts and Palladium catalysts. The below reference should be cited on the revised manuscript:
Res. Chem. Intermed., 2018, 44, 1617–1626.
Catalysts, 2015, 5, 534–560.
Res. Chem. Intermediat., 2019, 45, 599–611.
Green Chem., 2018, 20, 3809-3817.
Bulletin of the Korean Chemical Society, 2013, 34 (5), 1477-1480.
Energy Environ. Focus 2015, 4 (1), 18-23.
Chem. Commun. 2013, 49 (42), 4779-4781.
Applied Catalysis A: General 2014, 476, 133-139
- The authors are strongly suggested to include the TEM image of their prepared catalyst to present the size of the nanoparticles, as the Pd precursor can be reduced in nanoparticles which their relevant size has effect on the catalytic reactions.
Author Response
Dear Reviewer 4,
We greatly appreciate your time and thoughtful and constructive comments. We have revised the manuscript by your comments.
I have attached a point-by-point response to your comments as a PDF file.
The revised and newly added portions are highlighted in green on the manuscript. The removed parts in the original manuscript are underlined.
Furthermore, the English corrections of this manuscript were reviewed by Editage Co., which develops an English corrections business.
Sincerely yours,
Hironao Sajiki
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The work has been significantly improved and can be accepted for publication.
Only two small observations:
Row 232 and 242: “the degradation of catalytic activity” should be “the decreasing of catalytic activity”
The Pd content in the product should be determined before silica gel column chromatography purification.
Author Response
We greatly appreciate your time and thoughtful and constructive comments. We have revised the manuscript by your comments.
The newly revised and added portions are highlighted in yellow. The removed parts in the original manuscript are underlined.
Thank you very much foryour kind suggestion.
Row 232 and 242 (234 and 244 for the revised manuscript): " the degradation of the catalytic activity " was replaced with "the decreasing of catalytic activity".
The Pd content in the product should be determined before silica gel column chromatography purification: Contamination of Pd in the isolated product is a problem to be avoided in both pharmaceuticals and liquid crystal materials for safety and performance maintenance.
It has been clear that there was no Pd elution in the filtrate after the reaction in which the product was fully dissolved. That is, Pd is not contained at all in the reaction solution.
Therefore, it was expressed focusing on the contamination of Pd in the isolated product as a final confirmation.
Reviewer 4 Report
The authors have revised manuscript properly. The manuscript can be accepted for publication after approve of the editor.Author Response
We greatly appreciate your time and thoughtful and constructive comments.
The manuscript was again carefully corrected according to the editor's comments.
Thank you very much for your kind suggestion.
