EVALUATION OF “Ru(0) AND Ru(II) NITROSYL PINCER COMPLEXES: STRUCTURE, REACTIVITY, AND CATALYTIC ACTIVITY,” BY FOGLER ET. AL.
1) Characterization of the compound
Complex 8 which is described as a Ruthenium complex with a bent nitrosyl ligand was characterized using three analytical techniques: Hydrogen NMR (1{H} NMR), X-ray Diffraction (DFT), and Infrared Spectroscopy (IR). The 1H NMR was used to verify the complex which gave a singlet signal at 56.6ppm, and its phosphine methylene ligand gave a signal at 3.27 ppm, these signals not only verify the presence of the types of hydrogen in the complex but also its Cs symmetry. The DFT analysis showed that the complex has its phosphine ligand to be positioned trans relative to the tertiary amine, an equatorial chloride, and a bent NO that is located cis relative to the pyridine-based ligand. It also confirmed the square pyramidal structure of the complex which is consistent with the computed bond lengths and bond angels of the complex. The angle of the two bonds connecting ruthenium, nitrogen and oxygen (R – N – O bond angle) was found to be 130.20. The IR analysis confirmed the NO stretch which strengthens the result of the DFT analysis on the RNO bond angle.
2) Importance of the complex
According to the research authors, the studied ruthenium pincer-type complexes have various applications in the industrial scale production of esters. Note that the ruthenium pincer-type complexes used in industrial scale usually contain a carbonyl ligand – carbonyl pincer type complexes. Nevertheless, the authors proposed to replace the carbonyl group with a nitrosyl group in order to increase the complexes’ catalytic activities. Accordingly, the said complexes, including complex 8, could be made to catalyze the conversion of alcohols to esters. They could also be made to catalyze the reverse process. They could also be used to catalyze diverse kinds of reactions aside from the aforementioned two. This other reactions include the synthesis of amides through the coupling of alcohols using primary amines, the synthesis of imines from amines and alcohols, which are usually followed by liberation of hydrogen gas. Depending on the type of ligand that they bond with the said ruthenium compounds could function as either electron donors or acceptors, which help facilitate redox reactions which are involved in the different syntheses aforementioned.
3) Are the arguments convincing or not?
In my opinion, the authors have presented convincing arguments that they have indeed synthesized and characterized complex 8. In characterizing transition metal complexes, there is nothing more effective than validating its structure as its structure will clearly show how the ligands are interacting with the transition metals orbitals, which in turn determine its structure. This was effectively done through the DFT analysis. The confirmation of the ligand’s presence was also essential for the verification process. Note that through the use of the three analytical method of analysis (IR, DFT, and H NMR), the authors were not only able to determine which or what ligand are interacting with the transition metal center, they were also able to show the nature of these interactions which through the structure of the resulting complex.
4) Brief Recap and Opinion on Publication
The article has shown the synthesis of 10 Ru-complexes. The complexes were verified using three analytical methods of analysis, which include: DFT, IR, and H NMR. These methods were able to show effectively the conformational structure of the complex as well as the types of ligands that bonded to it effectively. Although there may some uncertainties as to the mixture of isomers for complex 7 (7a and 7b) which was used to synthesize complex 8 which the authors argued to have both bent and linear RNO bond, I still think that the article is suited for publication, in that it presents convincing analytical evidences on the presence of the 10 complexes carefully and wisely choosing the analytical methods used for verifying them. Moreover, the doubts associated with the synthesis of the two isomers could become the next thing to be verified on future studies.
Reference
Fogler, E., Iron, M.A., Zhang, J., Ben-David, Y., Diskin−Posner, Y., Leitus, G., Shimon, L.J.W. and Milstein, W. Ru(0) and Ru(II) nitrosyl pincer complexes: structure, reactivity, and catalytic activity. Inorganic Chemistry. 2013. 52,1469−11479
