Review Reports

Round 1

Reviewer 1 Report

The manuscript by Klein Gebbink and coworkers describe investigation of Re-catalyzed deoxydehydration reaction of diols. This is an important concept in an attempt to produce useful feed stock chemical from biomass type materials, which consists largely of carbohydrates. Although this system is far from any practical utility as it produces stoichiometric amount of hard-to-treat phosphine-oxide by product, I find this study important. It is excellent mechanistic investigation of reaction mechanism and possible catalytically active species. Authors isolated two new Re-complexes and characterized them by X-ray crystallographic analysis. In-depth mechanistic study (kinetic, MS and IR spectroscopy of number of Re-complexes) provided invaluable information about reaction mechanism, even though it was not possible to ascertain the nature of catalytically active species. I fully support acceptance of this manuscript by Catalysts with only two minor suggestions.

1) Can authors comment on the use of stoichiometric reductant used in this process in terms of other possibilities and also briefly discussing advantages and disadvantages of PPh3?

2) Some additional experimental details might be present directly in the manuscript, perhaps description of a typical deoxydehydration reaction.

 

Author Response

 

1）Can authors comment on the use of stoichiometric reductant used in this process in terms of other possibilities and also briefly discussing advantages and disadvantages of PPh3?

In this study we have primarily focused on the question on the use of a rhenium-dioxo moiety in DODH catalysis and haven’t focused on optimizing the reaction conditions, for example testing different reductants. More elaborate discussions on the use of different reductants, including the use of PPh₃, can be found in references 5, 19, 23, and 25. 

2) Some additional experimental details might be present directly in the manuscript, perhaps description of a typical deoxydehydration reaction.

The general procedure was described in electronic supporting information, which is another separate document.

Reviewer 2 Report

The manuscript „N-Donor Ligand Supported “ReO2+”: A Pre-Catalyst: 3 for the Deoxydehydration of Diols and Polyols “ explains mechanistic aspects of using rhenia-based homogeneous catalysts for up-grading of biomass originated feed. Due to the fact that this type of research foresee utilization of heterogeneous type catalysts that are unavoidable in real full-scale bio-refinery, the reviewer has tried to arise a few suggestions that could be answered by the author before publishing. Therefore, minor revisions were suggested. Concerns are the following:

 

1. Line 32: With respect of link between homogeneous and solid catalyst solution of oxygen removal from biomass derived feed, a new reference could be inserted on “deoxygenation” reaction, for example: Reaction Kinetics, Mechanisms and Catalysis 2019, 127(2), pp. 887-902 (https://doi.org/10.1007/s11144-019-01620-x).
2. Lines 89, 129, 176, 279, and 409: The number 3. should be avoided in the headings. The sections start at 2.
3. Lines 446 and 457: The headings should start 3. and 4., respectively, instead of 4. And 5.
4. Line 469: Please check grammar “… a species that is also …”
5. Lines 300 and 303: Please consider whether the conjunction “plus” is better than “and”.
6. The author could add info about apparatus: Presumably, reflux under back condenser was used to avoid evaporation of resultant olefins from reaction mixtures heated at 180 degree C. Section 2.2. or section 3. should provide convenient place to do it.
7. The authors deliver to a reader fundamental understanding of catalysis of deoxydehydration reaction. The selectivity was 100 percent. However, the reductants such as triphenylphosphine or 3-penthanol seem costly for large scale refining. The authors may consider discussing how to replace them in model bio-refinery. Would it be possibly to use hydrogen (finally)? Would other sources of secondary alcohols, possibly originated also from biomass derived feed, be convenient?

To sum up, the manuscript is well written. The reviewer should be happy if the above mentioned suggestions of minor importance would increase the quality of the manuscript, which is, in any case, actual and comprehensive.

Author Response

1. Line 32: With respect of link between homogeneous and solid catalyst solution of oxygen removal from biomass derived feed, a new reference could be inserted on “deoxygenation” reaction, for example: Reaction Kinetics, Mechanisms and Catalysis 2019, 127(2), pp. 887-902 (https://doi.org/10.1007/s11144-019-01620-x).

 

This reference has been added in line 32 as reference 6, also in line 506.

 

2. Lines 89, 129, 176, 279, and 409: The number 3. should be avoided in the headings. The sections start at 2.

 

All these sub-titles have been modified.

 

3. Lines 446 and 457: The headings should start 3. and 4., respectively, instead of 4. And 5.

These two titles have been modified.

 

4. Line 469: Please check grammar “… a species that is also …”

 

Grammar checked; no change needed.

 

5. Lines 300 and 303: Please consider whether the conjunction “plus” is better than “and”.

 

The word “and” is replaced by “plus”.

 

6. The author could add info about apparatus: Presumably, reflux under back condenser was used to avoid evaporation of resultant olefins from reaction mixtures heated at 180 degree C. Section 2.2. or section 3. should provide convenient place to do it.

 

Catalysis was performed in thick-walled glass pressure tubes (Ace) fitted with a Teflon screw-cap. The general procedure was described in detail in the electronic supporting information.

 

7. The authors deliver to a reader fundamental understanding of catalysis of deoxydehydration reaction. The selectivity was 100 percent. However, the reductants such as triphenylphosphine or 3-penthanol seem costly for large scale refining. The authors may consider discussing how to replace them in model bio-refinery. Would it be possibly to use hydrogen (finally)? Would other sources of secondary alcohols, possibly originated also from biomass derived feed, be convenient?

 

H₂ could be a very attractive reductant for deoxydehydration. In this work we haven’t yet test H₂ as reductant. The main purpose of this work is to investigate the use of rhenium-dioxo complexes in DODH catalysis. Also see answer to comments of first reviewer.