This review is based on a peer reviewed manuscript available at https://doi.org/10.1016/j.molliq.2017.05.081, and is intended to be an exercise in how to compose a post-publication review. Therefore, the comments here only reflect what I learned throughout Publons Academy as student, as well as what I feel can be constructive as a reader/researcher in the field of Catalysis and Inorganic Chemistry. There is no conflict of interest in the confection of this review, intended only for studying purposes.

This article adds in literature an outstanding opportunity to explore dithiocarbazate derivatives in catalysis, a missing content in the subject of catalytic coordinative compounds. I found especially relevant the results of the catalytic oxidation of cyclohexane for the iron complex found. This oxidative process in liquid phase is very difficult chemical reaction to achieve success in conversion and yield to KA-oil once the inertness of the substrate (an aliphatic hydrocarbon) offers a highly energetic obstacle to overcome, and the authors did a systematic analysis of the transition metal most suitable among most of the first row elements of this family. Such a type of study is scarce in literature, and helps to build the knowledge in the area. I did not detect any major flaws in any aspect whatsoever, and the observations I made in all sections of the manuscript was focused in looking for better understanding of what the authors would have intended, as well as possible missed opportunities for better describing the catalysts. The title of the article gives an informative remark in the content displayed in the abstract, being appropriate for its purpose. In the abstract, the aims, methods and most relevant catalytic conclusions of the study are clearly enounced, making the manuscript attractive for readers with interest in oxidation reactions. The authors remarked successfully, in a straightforward manner, the preparation of 6 different transition metal complexes with a dithiocarbazate-derived ligand (from 2,6-diacetylpyridine and S-benzyldithiocarbazate), employing metal precursors with 2+ oxidation state (namely copper, nickel, cobalt, iron, manganese and zinc), characterization of the materials (even the physicochemical analyses performed) and their potential as catalysts for liquid-phase cyclohexane oxidation with tert-butyl hydroperoxide (TBHP), easily preparing the reader in what will be presented ahead. As for the references, 30 of the 48 works (over 63%) employed for the insights and writing of the work are within a 10 year scope and mentions important and reliable journals of catalysis and coordination chemistry, what indicates both novelty of the work in the field (since it is a type of study on demand for dithiocarbazate derivatives) and careful selection of relevant works mainly in the area of preparation and application of metal complexes in oxidation reactions with industrial interest. The conclusions connects very well with the searched aims, opening positive perspectives for the field.

As for the introduction, the author gives clear information concerning preparation and importance of Schiff base compounds, general catalytic applications well dealt in literature for metal complexes from these ligands, and importance of the product of cyclohexane oxidation, the KA-oil (composed mainly of cyclohexanol and cyclohexanone), in an industrial manner. Even though at the end of this section there is a clear statement of the aims of the work, I felt the authors could have highlighted more information about the type of Schiff base investigated, and also mentioned that studies involving both preparation and catalytic usage of dithiocarbazate derivatives is scarce in literature, an added value for their manuscript and novelty within the current state-of-art (we must remark that article was published in 2017, and there are only a few articles so far dealing with the mentioned subject).

In the materials and methods, the preparation of the the pre-ligand (S-benzyldithiocarbazate) and the final Schiff base (2,6-diacetylpyridinebis(S-benzyldithiocarbazate)) are well detailed following classical procedures, and the techniques employed for the acquisition of characterization of the complexes, as well as the analytical methods from catalytic essays and estimations, are well described. What I would like to have seen mentioned were the design of the catalytic essays, like the type of reactor employed, whether or not a sample preparation was employed for the reaction mixtures previously of their analysis in gas chromatography, and details for sample preparation in ICP-OES. These are factors that greatly contributes for the quality of the results acquired since:

1. The reactor design can allow reproduction of the data as well as a notion for better understanding on how the aliquots were acquired for GC analysis;

2. The water present in the reaction mixture (both originated from the TBHP reactant and from the oxidation reaction) can affect the flame on FID detector, contributing for errors on the catalytic estimations of conversion and selectivity of the products, and the metal complex dissolved in the medium can diminish the performance of the column of the chromatographer. I believe an extraction step previous to the insertion of the sample in the GC analyzer and involving solvents with less polarity and solvating ability for the complexes, as well as a drying step afterwards would be good measures to avoid analytical problems in this subject;

3. The nitric acid concentration, dissolution and dilutions employed for attaining final solution for analysis in ICP-OES are sources for errors in analytical estimations as the one employed, and their mentioning can help to avoid other researchers dealing with this issue.

As for the data collected and the discussion, the presentation of the results and their significance are well intertwined, especially the physicochemical data, FTIR and NMR results concerning the ligand and its complexes to prove complexation, and even the catalytic performance. Nonetheless, I believe there are some aspects that would need a careful look before the assumptions made by the authors could be taken, and possibly opportunities missed for better describing the systems synthesized or for better unraveling the catalytic output:

1. The authors described the molecular formula of the synthesized complexes concluding in them being dimeric only based on CHNS elemental analysis and ICP-OES results (Table 1), which I believe is a hasty assumption. Even though the copper(II) dithiocarbazate complex synthesized has already been described crystallographically by Mirza and coworkers in 2014 as being a helical dimer with pentacoordinate centers (see Dimeric nickel(II) and copper(II) complexes of the pentadentate N3S2 chelating agents derived from S-alkyl/aryl esters of dithiocarbazic acid, Polyhedron. 81 (2014) 723–727), and there is evidence for a similar type of coordination mode for a nickel (II) analog in the latter, such conclusion cannot be extended for the other complexes once such a characteristic can also be dependent of metal precursors and ligand substituents once these polydentate systems can afford many types of packing topologies (see Condensed, solution and gas phase behaviour of mono- and dinuclear 2,6-diacetylpyridine (dap) hydrazone copper complexes probed by X-ray, mass spectrometry and theoretical calculations, Dalt. Trans. 42 (2013) 11497–11506; and Syntheses, structural diversity and thermal behavior of first row transition metal complexes containing potential multidentate ligands based on 2,6-diacetylpyridine and benzyl carbazate, Polyhedron. 141 (2018) 5–16). Hence, the elemental analysis data by themselves can only give a notion of the molar prportion between metal and ligand, which is 1:1 in all cases. Since there is a noticeable variation of the metal percentage accounted from ICP-OES, I would say that the best mode for accounting the molecular formula would be associating such results with other techniques, like mass spectrometry for understanding the solution behavior of the compounds, and many spectroscopic and microanalytic analysis like EPR and thermogravimetry, if it were available for the authors;

2. From what was said previously, other data available in the study, if combined with the elemental analysis, could give better understanding in the molecular formula, like the electronic spectra and the magnetic susceptibility results (Tables 2 and 3), since the wavelength and amount of d-d transitions alongside with the effective magnetic moment, hints coordination geometry and number of unpaired electrons, respectively. Also, there was a poor description of the d-d transitions of each complex, which could have been used at the very least to attest if the oxidation state of these systems is really 2+ once some of the transition elements studied can surprisingly alternate to higher states upon complexation (such as cobalt and iron, for example. See S-allyl-3-(2-pyridyl-methylene)dithiocarbazate ligand and its manganese(II), cobalt(III) and nickel(II) complexes, Inorganica Chim. Acta. 371 (2011) 36–41). Hence, these might have been missed opportunities in better describing the catalysts with what the authors had in hands;

3. The catalytic analysis made for all solids is displayed in a understandable manner, but I found confusing the mention of “Selectivity” twice throughout Figures 8 to 11. Since in the materials and methods section, as well as some of the catalytic discussion and conclusions, mentions the idea of “Yield” being calculated in this work, could the term for “Selectivity” in every part A of those Figures mean “yield for KA-oil” (i.e. mixture of cyclohexanol and cyclohexanone)? The captions of the Figures as well does not help the reader to better understand this;

4. Once it is a known fact that cyclohexyl hydroperoxide can have a certain stability and persist even after the reaction is over, the authors could have tested the addition of an excess of solid triphenylphosphine in mixture aliquots before doing GC measurements once the latter can reduce the mentioned hydroperoxide formed to cyclohexanol, changing the product distribution of the reaction (see New oxidovanadium(IV) complexes with 2,2′-bipyridine and 1,10-phenathroline ligands: Synthesis, structure and high catalytic activity in oxidations of alkanes and alcohols with peroxides, Catalysts. 9 (2019) 217 for more details in the Shul’pin method). I think this is an important aspect to be considered once any method for product recovery from liquid phase reaction mixtures is essential in industrial applications, where monetary interests is a guding reason for these environmentally friendly processes to be considered as substitutes for the standard processes known;

5. The comparision of reaction yields and temperatures between literature accounts and the iron complex made in Table 7 could be more atractive if including the amount of catalyst, molar ratio between cyclohexane and oxidant, oxidant type and especially the use of additives. Every catalyst is unique once it has different optimal catalytic outcomes on depending on the reaction conditios investigated, an for the oxidation of cyclohexane in liquid phase systems is very well known for having the nedd of initiators to begin the radical mechanism proposed by the authors, such as acetic acid (used even as solvent in some cases) or TEMPO. Hence, once the catalytic conditions explored in the study avoids the need of such special reactants, and have mild experimental parameters, a more complete comparative table could have been an added value for the work of the authors.

Overall, I found this study inspiring for readers who are in the beginning of their training in the subject of oxidation processes applied for the investigation of catalytic potential of inorganic compounds. I believe the authors have contributed positively to the field with sound experiments and a well-designed discussion, opening more possibilities that they can even imagine. Fine tuning of the results compiled, as well as better literature substantiation would be more proper to highlight the importance of the conclusions of the study, and future research in the topic might use the ideas within the manuscript as guidelines to enhance the knowledge in catalysis.