Connecting Main-Group Metals (Al, Ga, In) and Tungsten(0) Carbonyls via the N2S2 Metallo-Ligand Strategy
Round 1
Reviewer 1 Report
In this paper, the authors described the synthesis and characterization of three new main-group metal (Al(III), Ga(III), and In(III)) complexes having tetradentate N2S2 ligand (bismercaptoethanediazacycloheptane). The reactions of these complexes with transition-metal (Ni(II) and W(0)) complexes were also investigated. Although the authors have already reported NiN2S2 complexes, the properties of MN2S2 complexes (M = main-group metals) has remained largely unexplored. Thus, this referee considers that these results are of interest to the readers of Inorganics. However, the following points should be addressed.
1) The structures of complexes A, B, and C (Figures 3 and 5) are different from the solid state structures described in Figure 4 (the ethylene unit is located syn to the axial X ligand (X = Me, Cl)). Are complexes A, B, and C fluxional in solution to interconvert between syn and anti isomers? Please comment it on the text.
2) How did the authors confirm the formation of mononuclear Ni(II) complex with N2S2 ligand (Figure 5)? Please add the yield and the compound characterization data for this complex on the text.
3) In Figure 5, please comment the stability of complexes A, B, and C (especially, Al(III) complex A) in alcoholic solvent on the text. Are there possibility that complexes A, B, and C react with MeOH to generate free N2S2 ligand, prior to the reaction with Ni(II) complex? Ni(II) displacement studies should be further performed in non-alcoholic solvent.
4) Color information for the lines should be added to Figure 7 as described in Figure 6(a).
5) Is ClInW(CO)5 also converted into ClInW(CO)4 under UV light?
6) In the Materials and Methods section, NMR signal assignment of new compounds (XMN2S2) should be performed.
7) For new compounds, elemental analysis data or HRMS data should be reported.
Author Response
In this paper, the authors described the synthesis and characterization of three new main- group metal (Al(III), Ga(III), and In(III)) complexes having tetradentate N2S2 ligand (bismercaptoethanediazacycloheptane). The reactions of these complexes with transition- metal (Ni(II) and W(0)) complexes were also investigated. Although the authors have already reported NiN2S2 complexes, the properties of MN2S2 complexes (M = main-group metals) has remained largely unexplored. Thus, this referee considers that these results are of interest to the readers of Inorganics. However, the following points should be addressed.
Response: We thank the reviewer for the careful review and comments.
1) The structures of complexes A, B, and C (Figures 3 and 5) are different from the solid state structures described in Figure 4 (the ethylene unit is located syn to the axial X ligand (X = Me, Cl)). Are complexes A, B, and C fluxional in solution to interconvert between syn and anti isomers? Please comment it on the text.
Response: Thanks for pointing out this. We fixed the chem draw in Figures 3 and 5.
Regarding this comment we have added two sentences following Figure 4, p. 4.
“In all cases of A, B, and C, the 2-carbon linker within the diazacycloheptane ring is on the same side as the MIII-X bond vector. This means that the MN2C3 cyclohexane-type ring in the chair configuration is oriented “underneath” the N2S2 base of the square pyramidal X-MN2S2 structure. We have seen no evidence of fluxionality in solution.”
Precisely why this structural type is so persistent is not known to us. We see no evidence of fluxional behavior.
2) How did the authors confirm the formation of mononuclear Ni(II) complex with N2S2 ligand (Figure 5)? Please add the yield and the compound characterization data for this complex on the text.
Response: We confirmed the formation of NiN2S2 by Mass Spectrometry (Figure S12) and also by XRD of the maroon crystal obtained from this reaction. We have added the yield and changed our description as follows (page 4, last paragraph):
“Addition of NiCl2 or Ni(BF4)2 to XMIIIN2S2 complexes resulted in formation of NiN2S2 with MIII replacement by NiII, concomitant with an color change from colorless to dark maroon, Figure 5, the resulting maroon product gave a yield of 75-80% and confirmed as our reported NiN2S2 complex by Mass Spectra (Figure S12) and X-ray structure.”
3) In Figure 5, please comment the stability of complexes A, B, and C (especially, Al(III) complex A) in alcoholic solvent on the text. Are there possibility that complexes A, B, and C react with MeOH to generate free N2S2 ligand, prior to the reaction with Ni(II) complex? Ni(II) displacement studies should be further performed in non-alcoholic solvent.
Response: We confirmed the stability of complexes A, B and C in solution as listed in Fig.5. After stirring in MeOH for overnight, there is no degradation; thus we exclude the possibility that complexes A, B, C react with MeOH before Ni(II). We also did the reaction of Ni(II) displacement studies in MeCN for all complexes, the same product NiN2S2 was formed. To make this point clear, we added a sentence to the caption of Figure 5:
“Figure 5. Reactions of XMN2S2 with NiII salts and with (diphos)NiCl2. * Pure MeOH, or MeCN, or a mixture of MeOH/MeCN (1:1) resulted in the same products.”
4) Color information for the lines should be added to Figure 7 as described in Figure 6(a). 5) Is ClInW(CO)5 also converted into ClInW(CO)4 under UV light?
Response: Color information is added to Figure 7 caption, as follows:
“Figure 7. Reactions of ClGaN2S2•W(CO)5 and ClGaN2S2•W(CO)4: under UV light, the ClGaN2S2•W(CO)5 converted to ClGaN2S2•W(CO)4 and bubbling CO(g) to ClGaW(CO)4 resulted in formation of ClGaW(CO)5. Green line is for ClGaN2S2•W(CO)5 and orange line is for ClGaN2S2•W(CO)4..”
ClInW(CO)5 also converted into ClInW(CO)4 under UV light. We have added a sentence to describe this on p.6 :
“Similar to the ClGa N2S2•W(CO)5 complex, the ClInN2S2•W(CO)5 converted into ClInN2S2•W(CO)4 under light, giving ? (CO): 2007 (w), 1929 (m), 1894(m), 1850(m) cm-1, see Figure S17.”
6) In the Materials and Methods section, NMR signal assignment of new compounds (XMN2S2) should be performed.
Response: Thanks for the point and we added the assignments after each new compound, p.7:
“MeAlN2S2:…. δ (ppm) = 4.98 (s, 8H, N2S2) 2.63(q, 2H, N2S2), 2.61(q, 8H, N2S2), 1.70(q, 2H, N2S2), 0.10(s, 1H, Me)
ClGaN2S2:…δ (ppm) = 5.75(s, 8H, N2S2), 3.62(s, 4H, N2S2), 2.84(s, 2H, N2S2), 2.17(q, 2H, N2S2), 1.27(q, 2H, N2S2).
ClInN2S2:…δ (ppm) = 5.75(s, 8H, N2S2), 3.62(s, 4H, N2S2), 2.84(s, 2H, N2S2), 2.17(q, 2H, N2S2), 1.27(q, 2H, N2S2).”
7) For new compounds, elemental analysis data or HRMS data should be reported.
Response: HRMS data is given, please see p.8, “3.1 Synthesis of XMN2S2”, as follows:
“MeAlN2S2: …High Resolution +ESI-Mass: [M+H]+ (C10H22AlN2S2) Calculated 261.1040 (Most Abundant Isotopic Mass) Found: 261.1033, detailed isotope abundance is shown in SI, Figure S4.
ClGaN2S2:… High Resolution +ESI-Mass: [M-Cl]+(C9H18GaN2S2) Calculated 287.0162; Found: 287.0157(Most Abundant Isotopic Mass), detailed isotope abundance is shown in SI, Figure S5.
ClInN2S2: …High Resolution +ESI-Mass: [M-Cl]+(C9H18InN2S2) Calculated 332.9945; Found: 332.9939(Most Abundant Isotopic Mass), detailed isotope abundance is shown in SI, Figure S6. ”
Reviewer 2 Report
Manuscript presents three new XMN2S2 complexes and two reactions with them. This study extends main group coordination chemistry.
Over all, the study is well designed and presented. There is one minor issue with ESI-MS:
1. Experimental details are missing: instrument name, solution, concentration, and ESI-MS parameters (for example: resolution).
2. It is unknown whether the MS instrument used is of high or low resolution. If high resolution MS is used, authors should be able to extend decimal places of [M+H]+ to 4 instead of 2, and specify the presented mass as monoisotopic mass or most abundant isotopic mass. Theoretical masses of two complexes are listed below for reference.
[ClGaN2S2C9H18 + H]+
# m/z abundance
1 322.992850 92.541
2 323.996167 11.376
3 324.991677 100.000
4 325.995251 12.092
5 326.988974 28.756
6 327.992363 3.329
7 328.984819 2.178
8 329.988175 0.217
Reported in this manuscript: 322.99 (Monoisotopic Mass)
[ClInN2S2C9H18 + H]+
# m/z abundance
1 366.971330 4.400
2 367.974685 0.541
3 368.971092 100.000
4 369.974439 12.283
5 370.968159 41.078
6 371.971524 4.833
7 372.964000 3.345
8 373.967348 0.334
Reported in this manuscript: 368.97 (Most Abundant Isotopic Mass)
3. Full chemical formula should accompany with the ESI-MS result of each compound.
Author Response
Manuscript presents three new XMN2S2 complexes and two reactions with them. This study extends main group coordination chemistry.
Response: Thanks for the reviewer’s comments.
Over all, the study is well designed and presented. There is one minor issue with ESI-MS:
Experimental details are missing: instrument name, solution, concentration, and ESI-MS parameters (for example: resolution).Response: Thanks for the suggestion, we have added the description of the ESI-MS on p. 7, as follows:
“Both High Resolution and Low Resolution Mass spectrometry (Thermo fisher Q Exactive Mass Spectrometer, ESI-MS) were performed in the Laboratory for Biological Mass Spectrometry at Texas A&M University.”
The solution for XMN2S2 is MeCN/MeOH, for ClMN2S2W(CO)x is THF, for NiN2S2 and Ni(dipos)NiN2S2 is MeOH. Selections of solvents are dependent on compounds’ solubilities. These solvent usages were described in the captions of Figure S4-12, in Supporting Information. About the concentration, however, our Mass spectroscopist lab personell diluted the compounds and directly injected into the instrument, thus we do not know the exact concentration for each compound.
It is unknown whether the MS instrument used is of high or low resolution. If high resolution MS is used, authors should be able to extend decimal places of [M+H]+ to 4
1
instead of 2, and specify the presented mass as monoisotopic mass or most abundant isotopic mass. Theoretical masses of two complexes are listed below for reference.
[ClGaN2S2C9H18 + H]+ # m/z abundance
1 322.992850 92.541
2 323.996167 11.376
3 324.991677 100.000 4 325.995251 12.092 5 326.988974 28.756 6 327.992363 3.329
7 328.984819 2.178
8 329.988175 0.217
Reported in this manuscript: 322.99 (Monoisotopic Mass)
[ClInN2S2C9H18 + H]+ # m/z abundance
1 366.971330 4.400
2 367.974685 0.541
3 368.971092 100.000 4 369.974439 12.283 5 370.968159 41.078 6 371.971524 4.833
7 372.964000 3.345
8 373.967348 0.334
Reported in this manuscript: 368.97 (Most Abundant Isotopic Mass)
Response: Both High and Low resolution mass spectrometer have been used in this study. All details are in SI, Figure S4-12.
We also modified the related descriptions p.8, “3.1 Synthesis of XMN2S2”, as follows:
“MeAlN2S2: …High Resolution +ESI-Mass: [M+H]+ (C10H22AlN2S2) Calculated 261.1040 (Most Abundant Isotopic Mass) Found: 261.1033, detailed isotope abundance is shown in SI, Figure S4.
ClGaN2S2:… High Resolution +ESI-Mass: [M-Cl]+(C9H18GaN2S2) Calculated 287.0162; Found: 287.0157(Most Abundant Isotopic Mass), detailed isotope abundance is shown in SI, Figure S5.
ClInN2S2: …High Resolution +ESI-Mass: [M-Cl]+(C9H18InN2S2) Calculated 332.9945; Found: 332.9939(Most Abundant Isotopic Mass), detailed isotope abundance is shown in SI, Figure S6. ”
The detailed experimental and calculated isotope abundances are shown in SI, Figure S4-12.
Full chemical formula should accompany with the ESI-MS result of each compound.
Response: We added to each compound. This information can be found on p.8.
Reviewer 3 Report
The manuscript reports on isolation and structural characterization of metal complexes with tetradentate ligand containing N2S2 structural motif. The article however suffers from a number of shortcomings.
In the abstract (lines 10 – 12) - The authors state that “ Well-oriented N2S2 binding sites are ideal for d8 transition metals with square planar preferences, especially NiII, but also as a square pyramidal base for those metals with pentacoordinate preferences…” - Please extend this interesting thread in the main text and provide the appropriate reference citations.
In the introduction section ( line 62) – The author state that “There is novelty and potential for applications of the N2S2 platform for the main group metals.”, however the manuscript lacks evidence for any potential practical application of the complexes obtained. This is the major issue which significantly decreases the overall scientific soundness of the paper. Therefore, an additional set of experiments evidencing the practical applicability (e.g catalytic or any other activity) of the compounds is strongly recommended.
In the materials and methods section – A more detailed information regarding the MS equipments should be added. In particular, the conditions for mass spectrometry experiments should be given in greater detail. Please specify whether the MS or LC-MS instrument was used. If the chromatography was involved, then please provide the information on column, solvents, and gradients used. Similar, more detailed information regarding the NMR analysis of the complexes should be provided. The respective NMr spectra should be added into the supplementary materials.
Concluding, I recommend the major revision of this manuscript.
Author Response
The manuscript reports on isolation and structural characterization of metal complexes with tetradentate ligand containing N2S2 structural motif. The article however suffers from a number of shortcomings.
In the abstract (lines 10 – 12) - The authors state that “ Well-oriented N2S2 binding sites are ideal for d8 transition metals with square planar preferences, especially NiII, but also as a square pyramidal base for those metals with pentacoordinate preferences...” - Please extend this interesting thread in the main text and provide the appropriate reference citations.
Response: This statement describes synthetic, structural and bonding results from our labs over the past 20+ years, as well as from others as described in reference (Denny, J. A.; Darensbourg, M. Y. Metallodithiolates as Ligands in Coordination, Bioinorganic, and Organometallic Chemistry. Rev. 2015, 115, 5248-5273.)In the introduction section ( line 62) – The author state that “There is novelty and potential for applications of the N2S2 platform for the main group metals.”, however the manuscript lacks evidence for any potential practical application of the complexes obtained. This is the major issue which significantly decreases the overall scientific soundness of the paper. Therefore, an additional set of experiments evidencing the practical applicability (e.g catalytic or any other activity) of the compounds is strongly recommended.
Response: We have preliminary data on the use of the MeAlN2S2 complex as a catalyst precursor in the copolymerization of CO2 and epoxides. However this study is too preliminary to describe in the manuscript.
In the materials and methods section – A more detailed information regarding the MS equipments should be added. In particular, the conditions for mass spectrometry experiments should be given in greater detail. Please specify whether the MS or LC-MS instrument was used. If the chromatography was involved, then please provide the information on column, solvents, and gradients used. Similar, more detailed information regarding the NMR analysis of the complexes should be provided. The respective NMr spectra should be added into the supplementary materials.
Response: This question is related to reviewer 2’s question 1 &2.
We used MS, not LC-MS. We have added more detail about MS equipment on p.7, as follows “Both High Resolution and Low Resolution Mass spectrometry (Thermo fisher Q Exactive Mass Spectrometer, ESI-MS) were performed in the Laboratory for Biological Mass Spectrometry at Texas A&M University.” The other details (resolution of MS, solvent, isotope abundances and full spectra) can be seen in Supporting Information (PDF), Figure S4-12.
The full NMR spectra are in Supporting Information (PDF), Figure S1-3.
Concluding, I recommend the major revision of this manuscript.
Reviewer 4 Report
There are only x-ray structure data in Supplementary Materials
Author should be provide the spectroscopy information of [NiN2S2Ni(diphos)Cl] anion.
Page 3 line 96: “the best N2S2 planes” should be corrected to “the basal N2S2 planes”.
Page 3 figure 4: The value of M –N2 for complex B is 2.090, which is different from the other two complexes.
Page 5 line 127: “THF•W(CO)5,” should be corrected to “W(CO)5(THF)”.
Pages 5, 6 GaClW(CO)5 should be corrected to ClGaN2S2W(CO)5.
InClW(CO)5 should be corrected to ClInN2S2W(CO)5.
ClGaN2S2•W(CO)5 should be corrected to ClGaN2S2W(CO)5.
ClGaN2S2•W(CO)4 should be corrected to ClGaN2S2W(CO)4.
There are some typos in Ref. 5, 12, 22, and 23.
Comments for author File: 
Comments.pdf
Author Response
There are only x-ray structure data in Supplementary Materials
Response: We do not know what happened when the reviewer opened this file, as a pdf of Supporting Information was uploaded.
Author should be provide the spectroscopy information of [NiN2S2Ni(diphos)Cl] anion.
Response: It is in the Supporting Information PDF, on p. S13, Figure S11.
Page 3 line 96: “the best N2S2 planes” should be corrected to “the basal N2S2 planes”.
Response: “best” is what we mean. We used the crystal program Mercury to calculate the best N2S2 planes. In the Figure S18 (p. S24 in S.I.), we noted all the deviations of N and S atoms to the calculated plane.
Page 3 figure 4: The value of M –N2 for complex B is 2.090, which is different from the other two complexes.
Response: As from Al to Ga and In, the size of the atom is bigger. It is very reasonable that the M-N2 increased.
Page 5 line 127: “THF•W(CO)5,” should be corrected to “W(CO)5(THF)”. Pages 5, 6 GaClW(CO)5 should be corrected to ClGaN2S2W(CO)5. InClW(CO)5 should be corrected to ClInN2S2W(CO)5.
ClGaN2S2•W(CO)5 should be corrected to ClGaN2S2W(CO)5. ClGaN2S2•W(CO)4 should be corrected to ClGaN2S2W(CO)4.
Response: Thanks for pointing out these and we corrected them, please see p. 5 and p.6.
There are some typos in Ref. 5, 12, 22, and 23.
Response: We corrected the typo in ref 22. “Darensbourg D. J.; Kump, R. L. A Convenient Synthesis of cis-Mo(CO)4L2 Derivatives (L = Group 5A Ligand) and a Qualitative Study of Their Thermal Reactivity toward Ligand Dissociation. Inorg. Chem. 1978, 17, 2680-2682.
But we did not see typos in other references. Perhaps the editorial staff will find these as we go to press.
Round 2
Reviewer 1 Report
The authors have carefully addressed all the issues pointed out by this referee and revised their manuscript. I would like to recommend that this paper is accepted for publication in Inorganics.
Author Response
Thanks for your reviewing.
Reviewer 3 Report
Most issues which weakened the quality of the previous version were properly addressed in the revised manuscript.
On the other hand, the statement (line 62) regarding the novelty and potential practical applications for the complexes isolated is still insufficient and may mislead the reader. I strongly recommend a better clarification of this sentence or addition another few. Please state clearly whether there are any practical applications of similar compounds reported to date and if so please add the appropriate reference citations. Otherwise, please clarify the aim and potential practical application for these compounds.
Therefore, a minor revision of this manuscript is strongly recommended.
Author Response
To my knowledge there are no practical applications that reviewer 3 is asking for.Please simply remove the offending sentence , line 63. There is absolutely no need for it to be in the manuscript. So, please remove “ There is novelty and potential for applications of the N2S2 platform for the main group metals. “. That sentence is redundant with the prior paragraph. I don’t know how it got in the manuscript. I hope there are no further issues.
