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This literature discussion is based on a short paper describing a series of Group VI metal carbonyl compounds that have pincer ligands (Organometallics, 2016, 35, 229). While the paper is relatively straightforward, there are many subtle points that can be brought out by asking the right questions which hopefully this LO does. Some of the questions the students should be able to answer directly from the paper. I feel it is important that they do this. However, these questions nicely set up further questions that require the students to go beyond what is covered in the paper. In addition to the synthesis, there are many questions related to the spectroscopic characterization of these compounds. And of course, it wouldn't be one of my LOs if students weren't being asked to count electrons and do group theory.
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| Questions for students | 21.98 KB |
Upon completing this LO students should be able to
- Use the CBC method to count electrons in the tungsten compounds in this paper
- Describe the bonding interaction between a metal and a terminal carbonyl ligand
- Explain how NMR can be used to characterize these compounds including a discussion of 183W satellites
- Relate data from IR spectroscopy to the bonding interaction between a metal and a ligand and describe how the IR data can provide information about the electron donor ability of related ligands
- Recognize that some observed trends just do not have good explanations
This might be a bit on the long side, you could certainly omit some of the questions or have the students work on it outside of class.
Evaluation
This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point.
Comments
Hi Chip - I'm thinking of adapting this LO as a lab replacement in this current period of isolation. Have you used this LO with your class? Do you have any feedback/common student errors to share?
Thanks!
Yes I have used it in class. I should mention this was in a senior level class pretty much focused on organometallics. My students struggled a bit with the 183W satellites so if I were going to cut anything it would likely be that. Overall it could make a nice lab replacement because there is some wonderful data that they have to interpret. It might be challenging depending on how much you have talked about carbonyls. I kind of beat them over the head with it so my students seemed to pick up on it fairly quickly. They liked the paper overall so I say give it a go and let us know how it works.
I did end up using this as a virtual lab this spring, and I think it worked pretty well. I did not use the questions on the tungsten NMR, as you suggested. I did add a few new questions in order to highlight some additional information, provide some foundational knowledge on carbonyls, dig deeper into relevant extensions in the literature, etc.
2 out of the 3 students got themselves completely twisted around with thinking that a decrease in the frequency of the carbonyl stretch meant that there was a decrease in backbonding instead of an increase in backbonding. Even though there were explicit questions about the frequency of organic carbonyls and inorganic carbonyls. This greatly impacted their ability to correctly rank the different ligands in terms of their donor ability, etc.
The students did seem to engage well with the paper and the material, and it was not above their level of comprehension, even working mostly independently.
If you would like to see my modified version of this LO, let me know!
I used this literature discussion in Fall 2022 and cut out many of the questions (in particular the NMR questions). This was used towards the end of the semester, after a number of other literature discussions, and this was one of the tougher articles/questions we did.