8,8′-Dichloro-2,2,2′,2′-tetraethyl-4,4′-bibenzo[1,3,6,2]dioxazastannocinylidene

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript describes the synthesis and characterisation of a 1D 1D-coordination polymer from the reaction of glyoxal-bis(2-hydroxy-5-chlorophenyl)imine with diethyltin dichloride, in the presence of a base (Et₃N) in DMSO. Characterisation of the product unequivocally established the structure and composition of the product.  Above-all, the rigorous single-crystal X-ray diffraction analysis contributed to identifyinf the species. For this reason, the manuscript can be reconsidered foe publication in Molbank one the following issues have been addressed:

 

Scheme 2 and its description are a little confusing. An intermediate product is included in the scheme. However, while reasonable, there is no evidence for formation of this product and its inclusion is speculative. It is also unnecessary as this intermediate is later included in scheme 3 as a hypothesis for the mechanism. The arrow above the first step appears to include all the synthesis steps performed, so it should lead directly to the final product. For this reason, it is not clear what conditions lead from the intermediate to the final product. The text seems to suggest that the addition of methanol leads to the precipitation of the final product but this is included above the first arrow, while circle is shown above the second arrow, the meaning of which is not clear to me. The text also describes the formation of a microcrystalline, nearly insoluble dark violet product. Although I realise that this is unrelated to scheme 3, inclusion of the intermediate in the Figure might cause confusion in this regard. I believe that the intermediate should be removed from the scheme.

 

I also have some issues with scheme 3. First, it is entirely speculative. The description is a possible rationalisation of the final product obtained but no mechanistic evidence is offered. For this reason, I believe that the scheme should be moved to the supporting information. Second, is it correct to describe the third step as an aldol condensation? Water is not eliminated as a condensation product and aldehyde alpha hydrogens do not appear to be involved. From a stoichiometric point-of-view, this step is an addition reaction. Finally, I find the numbers 0.5 to be confusing and inconsistent with the figures. Thus, in the last step, a whole aminophenol molecule is eliminated from the “half-dimeric” species (or 2 from the fully dimeric specie). I don’t believe that the 0.5 coefficients are necessary or helpful.

Author Response

Comment 1: Scheme 2 and its description are a little confusing. An intermediate product is included in the scheme. However, while reasonable, there is no evidence for formation of this product and its inclusion is speculative. It is also unnecessary as this intermediate is later included in scheme 3 as a hypothesis for the mechanism. The arrow above the first step appears to include all the synthesis steps performed, so it should lead directly to the final product. For this reason, it is not clear what conditions lead from the intermediate to the final product. The text seems to suggest that the addition of methanol leads to the precipitation of the final product but this is included above the first arrow, while circle is shown above the second arrow, the meaning of which is not clear to me. The text also describes the formation of a microcrystalline, nearly insoluble dark violet product. Although I realise that this is unrelated to scheme 3, inclusion of the intermediate in the Figure might cause confusion in this regard. I believe that the intermediate should be removed from the scheme.

Response 1: We agree with this comment. We have excluded the intermediate product from Scheme 2.

Comment 2: I also have some issues with scheme 3. First, it is entirely speculative. The description is a possible rationalisation of the final product obtained but no mechanistic evidence is offered. For this reason, I believe that the scheme should be moved to the supporting information. Second, is it correct to describe the third step as an aldol condensation? Water is not eliminated as a condensation product and aldehyde alpha hydrogens do not appear to be involved. From a stoichiometric point-of-view, this step is an addition reaction. Finally, I find the numbers 0.5 to be confusing and inconsistent with the figures. Thus, in the last step, a whole aminophenol molecule is eliminated from the “half-dimeric” species (or 2 from the fully dimeric specie). I don’t believe that the 0.5 coefficients are necessary or helpful.

Response 2: We agree with this comment. We have moved Scheme 3 to the Supplementary information. We agree that the term "aldol condensation" is not appropriate in this case. The process described is an analog of benzoin condensation. Here, we consider condensation in a broader sense: a chemical reaction in which two or more molecules combine to form a larger molecule, typically with the release of a small molecule. According to our proposed mechanism, this condensation results in the formation of the L' ligand and the release of aminophenol. We have removed the detailed discussion of the proposed transformation mechanism for ligand L from the article text. To maintain stoichiometry, we have retained the coefficients in the provided Scheme of the proposed transformation process.

Reviewer 2 Report

Comments and Suggestions for Authors

Review of: 8,8'-Dichloro-2,2,2',2'-tetraethyl-4,4'-bibenzo[1,3,6,2]dioxa-2-zastannocinylidene

The authors report the interesting reactivity of a dimeric imine–phenolic complex that, upon addition of a tin reagent and base, forms an inorganic coordination polymer held together by intramolecular dative interactions. To my knowledge, this complex is novel and merits publication after revision. Below are several comments and suggestions to improve the quality of the manuscript.

Introduction

• The authors should consider moving Scheme 1 into the Introduction so that readers can easily associate the compound’s name with its structure.

 

Results and Discussion

• The following sentence could be improved:
  “A procedure described in reference [6] was tested for the synthesis of the tin complex based on LH₂,.”
  There is an unnecessary comma after LH₂. Consider revising to:
  “A tin complex was prepared by literature methods using LH₂ (ref. 6).”
• The sentence “nearly insoluble dark violet product that could not be identified exactly” needs clarification. What is meant by “exactly”? The authors should specify which analytical methods were used to characterize this complex.
• The statement “involving not only ring opening in the initial benzoxazine form but also subsequent hydrolysis and condensation” requires supporting evidence. What data indicate a condensation process has occurred?
• The terms “Cl…Cl intercontacts” and “Sn–O_–OPhN bond lengths” are unclear and should be more clearly explained or corrected.
• The authors should compare the reported bond lengths with those of related compounds and provide appropriate literature references.
• The proposed mechanism is speculative and lacks experimental support. Unless mechanistic studies are added, this section should be removed or substantially reduced.
• The UV–Vis spectrum should include labeled λ_max values.

Experimental Section

• The authors should include melting point data for all isolated solids.
• It would be valuable to provide mass spectrometry data for the complex.
• Some C-level alerts in the CIF report should be addressed before publication.
• The correct abbreviation for milliliter is mL, not ml.

 

Overall Assessment

The work presents a potentially new tin-containing coordination polymer with interesting bonding features. However, the manuscript requires improved clarity, additional data, and minor corrections before it can be recommended for publication.

 

Author Response

Comment 1. Introduction

The authors should consider moving Scheme 1 into the Introduction so that readers can easily associate the compound’s name with its structure.

Response 1: Thank you for the comment. Scheme 1 would be better placed at the beginning of the Results and Discussion section.

 

Comment 2: Results and Discussion

The following sentence could be improved:

“A procedure described in reference [6] was tested for the synthesis of the tin complex based on LH₂,.”

There is an unnecessary comma after LH₂. Consider revising to:

“A tin complex was prepared by literature methods using LH₂ (ref. 6).

Response 2: Thank you for pointing that out. The unnecessary comma was deleted. It was not possible to synthesize tin complex 1 using the method described in the literature [6]. We tested this method and found it to be unsuitable. To obtain complex 1, a base (Et₃N) was added to the reaction mixture, and the reaction was carried out in DMSO.

 

Comment 3: The sentence “nearly insoluble dark violet product that could not be identified exactly” needs clarification. What is meant by “exactly”? The authors should specify which analytical methods were used to characterize this complex.

Response 3: Thank you for the comment. This product could not be unambiguously identified due to its very low solubility. We have removed the word "exactly" from the manuscript. The product was characterized by IR spectroscopy and elemental analysis; however, relying solely on these techniques does not allow for definitive conclusions about its structure to be drawn. We have included its description in the article to demonstrate why it was necessary to alter the synthesis conditions, specifically by switching the solvent from methanol to DMSO.

 

Comment 4: Results and Discussion

The statement “involving not only ring opening in the initial benzoxazine form but also subsequent hydrolysis and condensation” requires supporting evidence. What data indicate a condensation process has occurred?

Response 4: Thank you for the comment. Here, we consider condensation in a broader sense: a chemical reaction in which two or more molecules combine to form a larger molecule, typically with the release of a small molecule. According to our proposed mechanism, this condensation results in the formation of the L' ligand and the release of aminophenol. Thus, the large ligand L' molecule is formed from small fragments of the initial ligand L.

 

Comment 5: Results and Discussion

The terms “Cl…Cl intercontacts” and “Sn–O_–OPhN bond lengths” are unclear and should be more clearly explained or corrected.

Response 5: We agree with this comment. The corresponding explanations have been added to the manuscript text.

 

Comment 6: Results and Discussion

The authors should compare the reported bond lengths with those of related compounds and provide appropriate literature references.

Response 6: Thank you for the comment. The relevant literature references have been provided in the manuscript.

 

Comment 7: Results and Discussion

The proposed mechanism is speculative and lacks experimental support. Unless mechanistic studies are added, this section should be removed or substantially reduced.

Response 7: We agree with this comment. The mechanism shown is proposed. This Scheme has been moved to the Supplementary Materials, and the related discussion has been significantly shortened in the main text of the article.

 

Comment 8: Results and Discussion

The UV–Vis spectrum should include labeled λ_max values.

Response 8: Thank you for pointing that out. Figure 3 has been corrected, and the λmax values have been included.

 

Comment 9: Supplementary Materials:

The authors should include melting point data for all isolated solids. It would be valuable to provide mass spectrometry data for the complex.

Response 9: Thank you for the comment. Complex 1 is a coordination polymer. It is impossible to determine its melting point; it decomposes at temperatures above 200 °C. Analysis by mass spectrometry is not feasible for this compound for the same reasons.

 

Comment 10: Supplementary Materials:

Some C-level alerts in the CIF report should be addressed before publication.

Response 10: Thank you for the comment. Unlike B-level, C-level alerts in the CIF do not require explanation.

 

Comment 11: Supplementary Materials:

The correct abbreviation for milliliter is mL, not ml.

Response 11: Thank you for pointing that out. We completely agree. The corresponding corrections have been made in the text of the article.