Development of a Graphene Oxide-Supported N-Heterocyclic Carbene Copper(I) Complex as a Heterogeneous Catalyst for the Selective N-Monoalkylation of Amines

Round 1

Reviewer 1 Report

This is a rather solid work on the catalytic alkylation of amines via GO-supported-NHCs. The work is broad in the sense that the authors report the preparation of the heterogeneous catalyst, a full characterization of this matrix, a proof of concept in terms of catalytic potential and then also exploratory work on the reaction mechanism. It certainly gives the impression of a complete piece of good chemistry. I detected two minor issues in the figures (highlighted in the attached pdf) and I have a single suggestion. At the end, in the proposal of a reaction mechanism, the authors ignore that they have discovered that this reaction requires "air" conditions (hence oxygen). So their proposal should be compatible with this observation, and in the present form it is not, the current proposal is a reaction that would operate under inert atmosphere. So, in which step is oxygen essential?

All in all I think this is a very good work and a rather nice manuscript that is easy to follow and to read, and I recommend its publication in Catalysts.

Author Response

Reviewer 1

This is a rather solid work on the catalytic alkylation of amines via GO-supported-NHCs. The work is broad in the sense that the authors report the preparation of the heterogeneous catalyst, a full characterization of this matrix, a proof of concept in terms of catalytic potential and then also exploratory work on the reaction mechanism. It certainly gives the impression of a complete piece of good chemistry. I detected two minor issues in the figures (highlighted in the attached pdf) and I have a single suggestion. At the end, in the proposal of a reaction mechanism, the authors ignore that they have discovered that this reaction requires "air" conditions (hence oxygen). So their proposal should be compatible with this observation, and in the present form it is not, the current proposal is a reaction that would operate under inert atmosphere. So, in which step is oxygen essential?

All in all I think this is a very good work and a rather nice manuscript that is easy to follow and to read, and I recommend its publication in Catalysts.

 Response: Thank you for appreciating our work. From the mechanistic discussion, we found that air is essential for the conversion of alcohol to aldehyde (Scheme 2, eq. vi).  Therefore, the oxidation of alcohol takes place in step 2 of Scheme 3. The same has been added in the text (line 257) and Scheme 3 of the revised manuscript.

Reviewer 2 Report

Dear Editor,

Thank you for giving me an opportunity to review the manuscript titled “Development of a graphene oxide-supported N-heterocyclic carbene copper(I) complex as a heterogeneous catalyst for selective N-monoalkylation of amines”. This manuscript focuses on preparing a new N-heterocyclic carbene (NHC) copper(I) complex supported on graphene oxide for selective N-monoalkylation of amines. The research falls into the scope of Catalysts. The manuscript can be accepted after a minor revision.

1.  Page 5, lines 97-100. The authors have carried out the FT-IR characterization for determining the coordination of NHC to copper. However,  it may be taken as an indirect evidence of this coordination, just as the authors mentioned. We hope that ⁶⁵Cu NMR might be employed to detect this coordination for obtaining a direct coordination evidence.

2. Page 9, lines 187-190. "A reaction in the absence of a base gave only 41% product yield (Table 2, entry 14). ... base also plays a vital role in product formation. " In view of the important role of bases, it is necessary to analyze and discuss the effects of bases on the reaction. However, there is little description on bases in the current manuscript.

Best regards,

                                                                        November 4, 2022

 

Author Response

Reviewer 2

Thank you for giving me an opportunity to review the manuscript titled “Development of a graphene oxide-supported N-heterocyclic carbene copper(I) complex as a heterogeneous catalyst for selective N-monoalkylation of amines”. This manuscript focuses on preparing a new N-heterocyclic carbene (NHC) copper(I) complex supported on graphene oxide for selective N-monoalkylation of amines. The research falls into the scope of Catalysts. The manuscript can be accepted after a minor revision.

1. Page 5, lines 97-100. The authors have carried out the FT-IR characterization for determining the coordination of NHC to copper. However,  itmay be taken as an indirect evidence of this coordination, just as the authors mentioned. We hope that ⁶⁵Cu NMR might be employed to detect this coordination for obtaining a direct coordination evidence.

Response 1: Thank you for your nice suggestion. However, the solid- state ⁶⁵Cu NMR facility is not available in our institute or at any other place nearby institutions. As a result, we are unable to record the ⁶⁵Cu solid-state NMR. We regret our limitations and appreciate the suggestion.

2. Page 9, lines 187-190. "A reaction in the absence of a base gave only 41% product yield (Table 2, entry 14). ... base also plays a vital role in product formation. " In view of the important role of bases, it is necessary to analyze and discuss the effects of bases on the reaction. However, there is little description on bases in the current manuscript.

Response 2: Thank you for your response. The effect of different bases in the reaction has now been discussed according to the optimization table in the revised manuscript, line 192-193.

Reviewer 3 Report

In this paper, the authors synthesized a novel N-heterocyclic carbene (NHC) copper (I) complex supported on graphene oxide (GO NHC Cu). The catalytic activity of the supported complex is explored in the N-alkylation of anilines with alcohols under solvent-free and aerobic conditions to afford the monoalkylated products in good to excellent yields. The air stability, selectivity, recyclability of the catalyst, and high yield of the products under solvent-free conditions are some of the salient features of the reported methodology. I believe that publication of the manuscript may be considered only after the following issues have been resolved.

 

1.      The author mentioned the air stability of synthetic samples in the abstract. What data support is there in the article? Whether the aging test under air environment has been conducted.

2.      Scheme 1 suggests that the author delete it, which does not play a significant role in the introduction.

3.      The introduction can be improved. The articles related to the some applications of graphene  materials should be added such as Sensors 2022, 22, 6483; ACS Sustain. Chem. Eng. 2015, 3, 1677–1685; RSC Adv. 2022, 12, 7821–7829; Talanta 2015, 134, 435–442.

4.      The text information in some figures is not clear enough, and the author needs to readjust it, such as Figure 2, 3,

5.      Please check the grammar and spelling mistakes of the whole manuscript.

Author Response

Reviewer 3

In this paper, the authors synthesized a novel N-heterocyclic carbene (NHC) copper (I) complex supported on graphene oxide (GO NHC Cu). The catalytic activity of the supported complex is explored in the N-alkylation of anilines with alcohols under solvent-free and aerobic conditions to afford the monoalkylated products in good to excellent yields. The air stability, selectivity, recyclability of the catalyst, and high yield of the products under solvent-free conditions are some of the salient features of the reported methodology. I believe that publication of the manuscript may be considered only after the following issues have been resolved.

 

1. The author mentioned the air stability of synthetic samples in the abstract. What data support is there in the article? Whether the aging test under air environment has been conducted.

Response 1: Thank you for your response. All organic transformations were carried out in air and the catalyst could be  recycled up to five consecutive cycles with insignificant loss in its catalytic activity. The FT-IR spectra (Figure S5) and FESEM image (Figure S6) of the spent catalyst after the fifth cycle shows no discernable change in the characteristic peaks of FT-IR and the surface morphology. All these observations supports the air stability of the catalyst.

2. Scheme 1 suggests that the author delete it, which does not play a significant role in the introduction.

Response 2: As suggested by the reviewer Scheme 1 has been removed from the revised manuscript.

3. The introduction can be improved. The articles related to the some applications of graphene  materials should be added such as Sensors 2022, 22, 6483; ACS Sustain. Chem. Eng. 2015, 3, 1677–1685; RSC Adv. 2022, 12, 7821–7829; Talanta 2015, 134, 435–442.

Response 3: As desired, all the suggested references have been added. Please see references 38-41 in the revised manuscript.

38. Cheng, Z.; Liao, J.; He, B.; Zhang, F.; Zhang, F.; Huang, X.; Zhou, L. One-Step Fabrication of Graphene Oxide Enhanced Magnetic Composite Gel for Highly Efficient Dye Adsorption and Catalysis. ACS Sustain Chem Eng 2015, 3, 1677–1685, doi:10.1021/acssuschemeng.5b00383.
39. Shangguan, Q.; Chen, Z.; Yang, H.; Cheng, S.; Yang, W.; Yi, Z.; Wu, X.; Wang, S.; Yi, Y.; Wu, P. Design of Ultra-Narrow Band Graphene Refractive Index Sensor. Sensors 2022, 22, 6483, doi:10.3390/S22176483.
40. Chen, H.; Chen, Z.; Yang, H.; Wen, L.; Yi, Z.; Zhou, Z.; Dai, B.; Zhang, J.; Wu, X.; Wu, P. Multi-Mode Surface Plasmon Resonance Absorber Based on Dart-Type Single-Layer Graphene. RSC Adv 2022, 12, 7821–7829, doi:10.1039/D2RA00611A.
41. Zhang, Z.; Cai, R.; Long, F.; Wang, J. Development and Application of Tetrabromobisphenol A Imprinted Electrochemical Sensor Based on Graphene/Carbon Nanotubes Three-Dimensional Nanocomposites Modified Carbon Electrode. Talanta 2015, 134, 435–442, doi:10.1016/J.TALANTA.2014.11.040.

 

4. The text information in some figures is not clear enough, and the author needs to readjust it, such as Figure 2, 3,

Response 4: As per your suggestion we have improved the resolution of Figure 2 and 3, page 5 and 6, in the revised manuscript.

5. Please check the grammar and spelling mistakes of the whole manuscript.

Response 5: As per your suggestion we have rechecked the grammar and spelling in the whole manuscript.

Round 2

Reviewer 3 Report

Accept in present form.