Synthesis of Thiophene-Fused Siloles through Rhodium-Catalyzed Trans-Bis-Silylation
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The authors reported a Rhodium-catalyzed reactions of 3-ethynyl-2-pentamethyldisilanylthiophene derivatives and synthesized several thiophene-fused siloles. Similar reactions have been developed by this group using pryidine ring (Molecules 2023, 28(8), 3284) . Therefore, the novelty is not enough.
Some minor issues are needed to be desolved
(1) Nuclear magnetic frequency should be specified including 1H, 13C, etc.
(2) The authors should try more transition metal catalysts to screen the conditions.
(3) The detailed structures of catalysts should be applied in main text with chemdraw soft.
Author Response
We thank the reviewer for their comments.
- Nuclear magnetic frequency should be specified including 1H, 13C, etc.
We have specified the nuclear magnetic resonance frequencies.　
On line 53, we added “[1H NMR (400 MHz), 13C NMR (100.6 Hz), 29Si NMR (79.5 MHz)]”.
- The authors should try more transition metal catalysts to screen the conditions.
We have tried Pd, Pt, and Ru complex catalysts for these reactions, but so far, synthesis of the silole derivatives has not been successful. In the future, I would like to explore various other metal complexes.
(3) The detailed structures of catalysts should be applied in main text with chemdraw soft.)
We have included the catalyst structure in Scheme 2.
Reviewer 2 Report
Comments and Suggestions for Authors
The authors described a rhodium-catalzyed reaction of 3-(ethynyl)-2-(1,1,2,2,2-pentame- thyldisilanyl)thiophene derivatives (1) to give thiophene-fused silole 6,6-dimethyl-4-(trimethylsilyl)-6H-silolo[2,3-454 b]thiophene derivatives. This paper reports a new method for the synthesis of thiophene-fused siloles. However, the examples are limited and the yield is low. Thus, the scope and yield are recommended to update through further condition screenings.
Comments on the Quality of English Language
Minor editing of English language required.
Author Response
We thank the reviewer for their comments.
(The authors described a rhodium-catalzyed reaction of 3-(ethynyl)-2-(1,1,2,2,2-pentame- thyldisilanyl)thiophene derivatives (1) to give thiophene-fused silole 6,6-dimethyl-4-(trimethylsilyl)-6H-silolo[2,3-454 b]thiophene derivatives. This paper reports a new method for the synthesis of thiophene-fused siloles. However, the examples are limited and the yield is low. Thus, the scope and yield are recommended to update through further condition screenings.)
We thank the reviewer for their comments.
We have explored various conditions for these reactions, but currently, the conditions outlined in this paper are optimal. In the future, we aim to further investigate in order to improve the yields.
(Minor editing of English language required.)
This paper has implemented English language editing in Editage (www.editage.jp).
Reviewer 3 Report
Comments and Suggestions for Authors
The present manuscript describes several novel and useful transformations for the synthesis of fused-thiophene bis-siloles. Convenient entry into the key substrates can be accomplished by a Sonogashira compound from a common iodothiophene. The Rh-catalyzed cyclization en route to the titled class of compounds was successful on several substrates, but not other compounds (due to hindrance or functional group incompatability). I appreciated that the authors include these negative results to better clarify the scope of this method.
The introduction is well written and thoroughly cites related synthetic methods and applications of these types of silylated heterocycles. The discussion of synthetic results are easy to follow, but I recommend adding the percent yields within all reaction schemes. The biggest improvement I suggest are related to the experimental and supplemental information:
1 - The general phrase "hydroloysis" is mentioned numerous times in the experimental (lines 73, 87, 103, 120, 135, 143, 157, 166, 180, 197-198, 210, 221. 233, 244, 258, 271, 284, 299, 314, 330). But this is too vague, as a hydrolysis could occur under neutral, acidic, or basic conditions and might confuse somebody outside of this lab attempting to replicate the procedure. Please include more specific experimental details for the hydrolysis steps (or, alternatively, provide one General Method for hydrolysis).
2 - In the supplemental information, the 1H spectra are difficult to read do to slightly blurry images and lack of zoomed-in regions (i.e., you cannot tell what the splitting patterns of most peaks are). I recommend improving the quality of these spectra since they are of key compounds for the paper.
Author Response
We thank the reviewer for their comments.
Comments:
(The introduction is well written and thoroughly cites related synthetic methods and applications of these types of silylated heterocycles. The discussion of synthetic results are easy to follow, but I recommend adding the percent yields within all reaction schemes. The biggest improvement I suggest are related to the experimental and supplemental information.)
We thank the reviewer for their comments.
We have specified the yields of compounds in the Scheme 1-3.
1 - The general phrase "hydroloysis" is mentioned numerous times in the experimental (lines 73, 87, 103, 120, 135, 143, 157, 166, 180, 197-198, 210, 221. 233, 244, 258, 271, 284, 299, 314, 330). But this is too vague, as a hydrolysis could occur under neutral, acidic, or basic conditions and might confuse somebody outside of this lab attempting to replicate the procedure. Please include more specific experimental details for the hydrolysis steps (or, alternatively, provide one General Method for hydrolysis).
We changed “hydroloysis” to “distilled water was added to the mixture”.(line 75, 90, 106, 123, 138, 146, 160, 169, 183, 200, 213, 224, 236, 247, 261, 273, 287, 302, 317, 333)
2 - In the supplemental information, the 1H spectra are difficult to read do to slightly blurry images and lack of zoomed-in regions (i.e., you cannot tell what the splitting patterns of most peaks are). I recommend improving the quality of these spectra since they are of key compounds for the paper.)
In the supplemental information, we have included enlarged views of the aromatic region for 1H NMR of 3-iodo-2-(1,1,2,2,2-pentamethyldisilanyl)thiophene, compounds 1a-1c and compounds 2a-2c.
Reviewer 4 Report
Comments and Suggestions for Authors
Dr. Naka and coworkers reported rhodium-catalyzed trans-bis-silylation to access thiophene-fused siloles. Furthermore, DFT calculation was present to elucidate the reaction pathway. The results sounds clear. However, the substrate scope seems a little bit narrow, and only aryl substituented alkyne could undergo rhodium-catalyzed bis-siylation. Maybe more optimization experiments were required to extend the reaction generality.
Author Response
Comments:
(Dr. Naka and coworkers reported rhodium-catalyzed trans-bis-silylation to access thiophene-fused siloles. Furthermore, DFT calculation was present to elucidate the reaction pathway. The results sounds clear. However, the substrate scope seems a little bit narrow, and only aryl substituented alkyne could undergo rhodium-catalyzed bis-siylation. Maybe more optimization experiments were required to extend the reaction generality.)
Thank you for the comments. Moving forward, we aim to explore reaction conditions from various perspectives, including the selection of metal complexes, to further enhance our understanding.
Reviewer 5 Report
Comments and Suggestions for Authors
In the manuscript, 3-ethynyl-2-pentamethyldisilanylthiophene derivatives reacted at 100 oC in the presence of a rhodium complex catalyst, yielding thiophene-fused siloles through intramolecular trans-bis-silylation. To understand the reaction, the mechanism was investigated using Density Functional Theory (DFT) calculations. All products were fully analyzed. The manuscript can be considered for publication after revision.
Comments
1. For Scheme 4, the Si-Si bond in TS0 should be dash line. The C-Rh bond in TS2 should be dash line.
2. Coordinates of all calculated structures should be provided in SI.
Author Response
We thank the reviewer for their comments.
Comments:
(In the manuscript, 3-ethynyl-2-pentamethyldisilanylthiophene derivatives reacted at 100°C in the presence of a rhodium complex catalyst, yielding thiophene-fused siloles through intramolecular trans-bis-silylation. To understand the reaction, the mechanism was investigated using Density Functional Theory (DFT) calculations. All products were fully analyzed. The manuscript can be considered for publication after revision.)
Comments
- For Scheme 4, the Si-Si bond in TS0 should be dash line. The C-Rh bond in TS2 should be dash line.
Thank you for their comments. We have represented the Si-Si bond in TS0 and the C-Rh bond in TS3 as dashed lines.
- Coordinates of all calculated structures should be provided in SI.
Coordinates of all optimized structures were included in Supplementary Materials.
Reviewer 6 Report
Comments and Suggestions for Authors
The authors have done a fantastic experimental work to prepare the thiophene-fused siloles starting from 3-ethynyl-2-pentamethyldisilanylthiophene derivatives obtained by themselves via rhodium-catalyzed reactions. They also proposed a catalytic mechanism leading to 6,6-dimethyl-4-(trimethylsilyl)-6H-silolo[2,3-b]thiophene derivatives (2), which was modeled by means of DFT calculations.
The manuscript deserves to be published in the journal after minor revisions.
Since the journal is a general journal for publishing applied research, perceiving the names of organic substances without having detailed pictures in front of the reader's eyes is very difficult. Therefore, it is necessary to make a table containing pictures with the names of organic and organometallic compounds using IUPAC names.
In the experimental part a detailed description of the hydrolysis process, where it was carried out, should be added. Why IR spectra were not presented?
It is very unfortunate that the authors did not cite doi in the reference list. This could have made the review process easier and faster.
Full review text (with pictures of the organic chemical compounds) is presented in attached pdf file.
Comments for author File: 
Comments.pdf
Author Response
We thank the reviewer for their comments.
Comments:
(The manuscript deserves to be published in the journal after minor revisions.)
Since the journal is a general journal for publishing applied research, perceiving the names of organic substances without having detailed pictures in front of the reader's eyes is very difficult. Therefore, it is necessary to make a table containing pictures with the names of organic and organometallic compounds using IUPAC names.)
We added the structure of 8-(2-substituted-1,1,2,2-tetramethyldisilanyl)quinoline (TMDQ) on line 38.
(In the experimental part a detailed description of the hydrolysis process, where it was carried out, should be added.)
Thank you for their comments. We changed “hydroloysis” to “distilled water was added to the mixture”.
(Why IR spectra were not presented?)
We consider the compound's structure determination to be sufficient based on 1H, 13C, and 29Si NMR data, as well as high-resolution mass spectrometry.
(It is very unfortunate that the authors did not cite doi in the reference list. This could have made the review process easier and faster.)
In the reference list, we have included the DOI.
Reviewer 7 Report
Comments and Suggestions for Authors
This manuscript presented a Rh(I)-catalyzed trans-bis-silylation methodology for the preparation of thiophene-fused siloles, which are expected to be employable as molecular electronic devices, and the DFT validation for the Rh(I)-catalysis. The topic and the synthetic work looked to me extremely interesting, and the authors did a good job in both the above aspects. On the other hand, as a computational chemist, I found some aspect of the DFT mechanistic study that must be revised.
1) The reaction between 1 and (Rh(nbd)Cl)2 is operated in toluene (at reflux) and is finally worked out by adding water. The computational investigation of this process was instead carried on in the gas phase. Why the authors did not include solvation in their DFT calculations? The energy and free energy of all structures should be recalculated by using implicit solvation.
2) The employed level of theory sounds strange to me. If I understood correctly, the authors applied the LANL2DZ pseudo-pot. corrected (double-zeta) to Rh and the 6-311G(d) basis set (triple-zeta) to the other atoms.
In this basis scheme, we miss the f-polarization on the Rh center and the p-polarization on the hydrogen atoms. May be I am wrong, but I guess this level of theory may have incorrectly described the approach of the metal fragment on the ethynyl group, indeed the optimized structure of IM-1 presents no evidence of eta2-coordination (the Rh-C(ethynyl) distances of 4.74 and 4.28 are too long).
I think the optimization (and freq) calculations should have been done with the LANL2DZ plus f-polarization (Rh) and the 6-31+G(d,p) (all other atoms) basis, while single points at higher level of theory could have been done to estimate the electronic energies of the minimized structures.
3) The authors chose to scale the calculated energy or free energy profiles by the energy of 1 plus the half of the (Rh(nbd)Cl)2 energy. While this is not necessary because the dissociation of the dimeric complex can be assumed as matter of fact in a reflux process, the authors' assumption to estimate energy cost for the decomposition is totally incorrect. The authors can thus choose if either simply rescaling all profiles to the energy/free energy of 1+Rh(nbd)Cl or calculating the decomposition energy as the reaction energy for the process (Rh(nbd)Cl)2--->2Rh(nbd)Cl.
4) The calculated energy and free energy barriers are too high to be representative of a catalytic process. The authors reported that the reaction of 1 with (Rh(nbd)Cl)2 are worked out in 1 h, so I expected energy barriers lower than 20 kcal/mol. The authors must comment this computational outcome in the narrative.
5) The computational studies' section present no description of the optimized geometries but, by looking at supporting information, it seems to me that some of the species sketched on the Scheme 4 were not confirmed by calculations. For example, the calculated structure of IM-1 showed no eta2-coordination of the ethynyl group. I suggest the authors to describe the optimized geometries of the species intercepted along the process and to compare these structures with those hypothesized in the Scheme 4.
6) If possible, the optimized geometries of all calculated species should be reported in XYZ files available as electronic supporting material. In alternative, the atomic Cartesian coordinates should be added to the SI file.
Comments on the Quality of English Language
Good
Author Response
We thank the reviewer for their comments.
We upload the response as a Word file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
The revised manuscript can be accepted in current form.
Reviewer 2 Report
Comments and Suggestions for Authors
Accept in present form
Reviewer 5 Report
Comments and Suggestions for Authors
Authors responsed all comments satisfactorily.
