Round 1

Reviewer 1 Report

This paper describes the Pd(II) Catalysts based on Monoanionic [N,O] Lig- 2 ands for Suzuki-Miyaura Cross-Coupling at Low Temperature. After reviewing it, I think it can be consider to publish if the following issues are solved:

1. For the introduction part, the recent achievements of this kind of Pd(II) Catalysts should be added and discussed in detail.

2. Could you provided more direct evidence like the NMR?

3. This kind of Pd(II) Catalysts should be measured by XPS.

4. Some relevant papers should be cited：Colloids and Surfaces A: Physicochemical and Engineering Aspects 646, 128962; Separation and Purification Technology 303 (2022) 122288

Author Response

1. For the introduction part, the recent achievements of this kind of Pd(II) Catalysts should be added and discussed in detail.

We thank the reviewer for their time taken to read the paper and provide a considered response. We agree regarding this point and have added some more up to date examples to address this.

2. Could you provided more direct evidence like the NMR?

The NMR characterisation of all species in this paper is included in the ESI and we have also included a link to further experimental data that is hosted by our university’s data repository. With regard to the catalytic experiments and nature of the active catalytic species, the catalyst is typically present in very low (relative) quantities. It is therefore not possible to directly observe the catalyst via NMR during the course of the reaction as the signals corresponding to it are typically overwhelmed by those of the substrate/product. We have run 31P NMR spectra but these were not informative in elucidating the mechanism any further.

3. This kind of Pd(II) Catalysts should be measured by XPS.

The catalyst we report here is characterised by a number of techniques including SCXRD. The bulk purity of the compounds was analysed using elemental analysis but unfortunately XPS is a technique that we do not have available to us.

4. Some relevant papers should be cited：Colloids and Surfaces A: Physicochemical and Engineering Aspects 646, 128962; Separation and Purification Technology 303 (2022) 122288

The first reference is for a paper titled ‘Plasmon-induced broad spectrum photocatalytic overall water splitting: Through non-noble bimetal nanoparticles hybrid with reduced graphene oxide’ and the second reference is for a paper titled ‘Construction of AgBr/BiOBr S-scheme heterojunction using ion exchange strategy for high-efficiency reduction of CO2 to CO under visible light’. Neither of these papers appear to be relevant to this work.

Reviewer 2 Report

This manuscript by McIntosh and Mansell describes the preparation and structure of a new palladium catalyst based on a [N,O] ligand. Then the behavior of this species in a Sukuki-Miyaura reaction has been explored. Although the catalyst is new and has been shown to be useful in a coupling reaction, the functionality tolerance of the catalyst has not been sufficiently investigated in my opinion. Therefore, the scope of the Suzuki-Miyaura reaction should be extended to the use of, for example, heterocyclic substrates, phenols or benzoic acid derivatives.

Author Response

We thank the reviewer for their time taken to read the paper and provide a considered response. We agree that a fuller investigation of activity is required, and we will be publishing details of this in future papers. The aim of this paper is to provide an initial report of our new catalytic system in line with the scope of this special edition. The exciting preliminary results reported here are intended to provide a proof-of-concept basis to the work and are not intended to be a comprehensive exploration of activity.

Reviewer 3 Report

The palladium promoted coupling reactions have been extensively investigated, and new palladium complexes and catalytic improvements have been achieved. Current system is using N,O-ligated system, and the work and results were well present and recommended its publication; however, it would be better for authors to have a comparative activity with the analogues with N,N-ligands, such as  a recent paper Applied Organometallic Chemistry, 2022, 36, 6474. Besides that, it would be recommended.  

Author Response

We thank the reviewer for their time taken to read the paper and provide a considered response. The suggestion is a good one and we have included a reference to the proposed work to allow the readers to make a comparison with these ligands.

Reviewer 4 Report

Comments

on the manuscript «Preformed Pd(II) Catalysts based on Monoanionic [N,O] Ligands for Suzuki-Miyaura Cross-Coupling at Low Temperature»

The paper deals with an important subject - the development of effective and environmental-friendly catalyst for Suzuki-Miyaura reaction. The results reported are of interest to the readers of Catalysts. Therefore, the paper can be recommended for publication after all points stated below will be revised.

Major remarks:

1.                When the types of catalytic systems for Suzuki-Miyaura reactions presented in literature are discussed in Introduction, the authors refer to the examples dealing with aryl chlorides conversion. However, the majority of experiments performed in the paper includes 4-bromoacetophenone. There are several examples in literature for ligand-free Pd catalytic systems converting aryl bromides under mild conditions, i.e., Maegawa, T., Kitamura, Y., Sako, S., Udzu, T., Sakurai, A., Tanaka, A., Kobayashi, Y., Endo, K., Bora, U., Kurita, T., Kozaki, A., Monguchi, Y., & Sajiki, H. (2007). Chem. Eur. J., 13(20), 5937–5943. https://doi.org/10.1002/chem.200601795. It should be cited appropriately.

2.                When the authors discuss the results of initial optimization studies (Table 1) at p. 5, they state that “carrying the reaction out in air was not detrimental to the yield ”, while the conversion was higher than for the reaction under N₂. Can the authors propose based on their data or on those of literature, how it can realize when readily oxidized phosphine ligands were presented in the catalyst 3?

3.                For Table 2 the authors state “The choice of base has been seen to have an important effect on the rate of reaction, with the base playing various roles within the catalytic cycle.¹¹” The role of base in Suzuki-Miyaura catalytic systems was elucidated in three papers Amatore, C., Jutand, A., & le Duc, G. (2011). Chem. Eur. J., 17(8), 2492–2503. https://doi.org/10.1002/chem.201001911; Carrow, B. P., & Hartwig, J. F. (2011). J. Am. Chem. Soc., 133(7), 2116–2119. https://doi.org/10.1021/ja1108326; Schmidt, A. F., Kurokhtina, A. A., & Larina, E. V. (2011). Russ. J. Gen. Chem., 81(7), 1573–1574. https://doi.org/10.1134/S1070363211070334. They should be cited here with appropriate comments.

4.                There are disagreements between the data presented in Tables 1-3. The same experiments have different yields in different Tables. The reaction under r.t. with K₂CO₃ as base and MeOH as solvent has 85% yield in Table 1 and 81% yield in Table 2. For the reaction with Na₂CO₃ as base and MeOH as solvent the yield is 82% in Table 2 and 80% in Table 3.

5.                For solvent scope, it is stated that “the addition of water was beneficial for an improved conversion, possibly due to the increased solubility of the reagents. There is a balance with the number of equivalents of water though, as by decreasing the proportion of water to 25% (entry 26), a further increase in conversion is seen to 97%.” The water-alcohol mixture was previously used in the papers of Schmidt et al. and Maegawa et al. mentioned above. Here, they should also be referred to.

6.                When Table 4 and Figure 3 are discussed, it is pointed that “The rate of conversion over time was investigated through the use of an NMR scale reaction and monitored using the addition of mesitylene to act as an internal standard with MeOD as the solvent (ESI!).” It is unclear why internal standard was applied here if it was not needed earlier for the evaluation of NMR conversion and TON through comparative integration of the starting material at 2.44 ppm and the product at 2.50 ppm. If two signals in starting material and converted mixture were compared, no standard was needed because the conversion degree was directly obtained thus. An exclamation mark in parentheses (ESI!) is unclear also.

7.                Can the authors propose based on their data or on those of literature, can phosphine ligands presented in the catalyst 3 remain stable in an aqueous medium?

Minor remarks:

1                   At p. 3 after Scheme 1 there are unreadable symbols “4+-*+3”. What does it mean?

2                   At p. 7 the statement presents “This graph shows that no induction period was observed, with a fast rate of reaction occurring from the start of the experiment (Table 4)”. In my opinion, it would be more correct to say “the fastest”, because at the reaction beginning the highest value of the reaction rate was observed.

3                   At p. 8 the mercury test is meant “In order to test for the formation of Pd(0) nanoparticles, a mercury drop test was carried out. This showed a decrease in NMR conversion from 97% to an average of 40%, leaving the role of nanoparticles as a possibility. In order to test for the formation of Pd(0) nanoparticles, a mercury drop test was carried out”. Firstly, the conditions of the test procedure should be specified. Also, the attention should be paid to the limitations of the test applying catalyst poisoning arisen from fast interconversions of various active and inactive Pd forms in the Suzuki-Miyaura reaction (see Schmidt, A. F., & Kurokhtina, A. A. (2012). Kinet. Catal. 53, 6, pp. 714–730. https://doi.org/10.1134/S0023158412060109).

8.                At p. 9 there is the text “compound 3.12 was trialled for catalytic activity”. However, there is no such compound in the paper. Only the catalyst 3 is. The same is fair for compound 4 at p. 10: “compound  4 shows good catalytic activity.” and “catalyst 4 was capable of cross-coupling 4-chloroacetophenone”.

Author Response

Major remarks:

1. When the types of catalytic systems for Suzuki-Miyaura reactions presented in literature are discussed in Introduction, the authors refer to the examples dealing with aryl chlorides conversion. However, the majority of experiments performed in the paper includes 4-bromoacetophenone. There are several examples in literature for ligand-free Pd catalytic systems converting aryl bromides under mild conditions, i.e., Maegawa, T., Kitamura, Y., Sako, S., Udzu, T., Sakurai, A., Tanaka, A., Kobayashi, Y., Endo, K., Bora, U., Kurita, T., Kozaki, A., Monguchi, Y., & Sajiki, H. (2007).  Eur. J., 13(20), 5937–5943. https://doi.org/10.1002/chem.200601795. It should be cited appropriately.

We thank the reviewer for their time taken to read the paper and provide a considered response. The suggestion is a good one and we have included the suggested references.

2. When the authors discuss the results of initial optimization studies (Table 1) at p. 5, they state that “carrying the reaction out in air was not detrimental to the yield ”, while the conversion was higher than for the reaction under N₂. Can the authors propose based on their data or on those of literature, how it can realize when readily oxidized phosphine ligands were presented in the catalyst 3?

We believe our complex is air stable. The compound was prepared and stored for use over a period of months and showed no signs of degradation over this timescale. The reported conversion was indeed higher but the values are also within the range of experimental error. We do not propose that the conditions are optimised, but merely state that the presence of air seems to not have a significant effect on the activity. PPh3 is the only phosphine ligand we used. It is known to be relatively air tolerant. However, it is anticipated that PPh3 needs to dissociate as part of the catalytic cycle. It is possible that the formation of OPPh3 (once PPh3 has dissociated) stops reassociation of the coligand and therefore helps the catalysis. However, more work would be required to deduce this for certain.

3. For Table 2 the authors state “The choice of base has been seen to have an important effect on the rate of reaction, with the base playing various roles within the catalytic cycle.¹¹” The role of base in Suzuki-Miyaura catalytic systems was elucidated in three papers Amatore, C., Jutand, A., & le Duc, G. (2011).  Eur. J., 17(8), 2492–2503. https://doi.org/10.1002/chem.201001911; Carrow, B. P., & Hartwig, J. F. (2011). J. Am. Chem. Soc., 133(7), 2116–2119. https://doi.org/10.1021/ja1108326; Schmidt, A. F., Kurokhtina, A. A., & Larina, E. V. (2011). Russ. J. Gen. Chem., 81(7), 1573–1574. https://doi.org/10.1134/S1070363211070334. They should be cited here with appropriate comments.

We thank the reviewer for drawing these papers to our attention, we have included reference to them and amended the section in question.

4. There are disagreements between the data presented in Tables 1-3. The same experiments have different yields in different Tables. The reaction under r.t. with K₂CO₃as base and MeOH as solvent has 85% yield in Table 1 and 81% yield in Table 2. For the reaction with Na₂CO₃ as base and MeOH as solvent the yield is 82% in Table 2 and 80% in Table 3.

These slightly differing numbers represent variation due to experimental error. The conditions are the same but these were not the same experiment.

5. For solvent scope, it is stated that “the addition of water was beneficial for an improved conversion, possibly due to the increased solubility of the reagents. There is a balance with the number of equivalents of water though, as by decreasing the proportion of water to 25% (entry 26), a further increase in conversion is seen to 97%.” The water-alcohol mixture was previously used in the papers of Schmidt et al. and Maegawa et al. mentioned above. Here, they should also be referred to.

We have included reference to the suggested articles

6. When Table 4 and Figure 3 are discussed, it is pointed that “The rate of conversion over time was investigated through the use of an NMR scale reaction and monitored using the addition of mesitylene to act as an internal standard with MeOD as the solvent (ESI!).” It is unclear why internal standard was applied here if it was not needed earlier for the evaluation of NMR conversion and TON through comparative integration of the starting material at 2.44 ppm and the product at 2.50 ppm. If two signals in starting material and converted mixture were compared, no standard was needed because the conversion degree was directly obtained thus.An exclamation mark in parentheses (ESI!) is unclear also.

We utilised an internal standard here to ensure that our assumed conversion of starting material to product was correct. This assumption was proven to be correct as after one hour, 81% yield was observed (80 - 82% seen in previous experiments). The typographical error has been removed.

7. Can the authors propose based on their data or on those of literature, can phosphine ligands presented in the catalyst 3remain stable in an aqueous medium?

From our experimental data the catalysts are clearly stable in aqueous media over the timeframe of the reaction but we would require further investigations to establish how long they remained active for.  The only phosphine ligand we used was PPh3 which is known to be relatively tolerant to air.

Minor remarks:

• At p. 3 after Scheme 1 there are unreadable symbols “4+-*+3”. What does it mean?

This appears to be a typographical error which we have now corrected.

• At p. 7 the statement presents “This graph shows that no induction period was observed, with a fast rate of reaction occurring from the start of the experiment (Table 4)”. In my opinion, it would be more correct to say “the fastest”, because at the reaction beginning the highest value of the reaction rate was observed.

We have made the suggested change.

• At p. 8 the mercury test is meant “In order to test for the formation of Pd(0) nanoparticles, a mercury drop test was carried out. This showed a decrease in NMR conversion from 97% to an average of 40%, leaving the role of nanoparticles as a possibility. In order to test for the formation of Pd(0) nanoparticles, a mercury drop test was carried out”. Firstly, the conditions of the test procedure should be specified. Also, the attention should be paid to the limitations of the test applying catalyst poisoning arisen from fast interconversions of various active and inactive Pd forms in the Suzuki-Miyaura reaction (see Schmidt, A. F., & Kurokhtina, A. A. (2012). Catal. 53, 6, pp. 714–730. https://doi.org/10.1134/S0023158412060109).

The reviewer is correct to point out the limitations of the mercury drop test and the somewhat inconclusive results it produced support this. We have amended the text to reflect the suggested changes, including the reference above and a reference to the method used

At p. 9 there is the text “compound 3.12 was trialled for catalytic activity”. However, there is no such compound in the paper. Only the catalyst 3 is. The same is fair for compound 4 at p. 10: “compound  4 shows good catalytic activity.” and “catalyst 4 was capable of cross-coupling 4-chloroacetophenone”.

These appear to be a typographical errors which we have now corrected.

Round 2

Reviewer 1 Report

accept

Reviewer 2 Report

Changes made by the authors suggested by all the referees have improved the manuscript. Therefore I consider that the manuscript in its current form meets the criteria to be pubished in Catalysts as an article

Reviewer 4 Report

I am satisfied with the corrections/additions made. The article can be published in presented form