My Notes
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This LO was inspired by a talk that Megan Fieser gave at the 2024 Organometallic Chemistry Gordon Research Conference. It was an excellent talk with some really interesting chemistry. Wanting something with practical application for my class focused on organometallic chemistry, I looked at one of her 'older' papers and found this really interesting rhodium catalyst. In the main paper for this LO (Mater. Horiz. 2023, 10, 2047), the catalytic dechlorination of poly(vinyl chloride) (PVC) using a rhodium pincer complex is described. This process requires a source of "H-" and several different sources were examined. The dechlorination process is fairly efficient, leading to a material that is pretty much polyethylene. As PVC is a highly used material that is not easily recycled, this process could be an effective way to convert used PVC into a useful material. Reading this paper took me on a bit of a deep dive into several other papers which show up in the LO. I will likely keep my student reading limited to the main paper but will include links to all of the papers that appear in this LO. This LO has not been used as a traditional literature discussion that I would use. Instead, I used it as the final exam in my senior level inorganic course in the fall of 2024. Moving forward, I will likely be using it as a more traditional literature discussion in my class. Both versions of this learning object are included. Note that the final exam was 'comprehensive' and so there are some questions added to the exam that are related to the papers, but perhaps not somewhere I would want to go during an in-class discussion.
During the course of the fall 2024 semester, I decided to use this as my final exam in my senior level inorganic class. This was untested as an in-class discussion and modifications were made to make it a more appropriate cumulative final. While I think the NMR and group theory questions are decent questions, they are somewhat tangential to the point of the paper and I would certainly not include them as part of a regular in-class discussion. As such, I have included both versions of this LO, the one I would consider a more classic literature discussion and the version I gave as an exam.
| Attachment | Size |
|---|---|
| The learning object | 23.77 KB |
| The learning object as an exam | 45.41 KB |
| DOI links for all papers | 13.39 KB |
Students will
- Gain a better appreciation for the problems associated with poly(vinyl chloride) (PVC) and its recycling
- Use the Covalent Bond Classification method to classify and count electrons in several rhodium species including an examination of the variable coordination modes of a pincer ligand
- Interpret experimental data to draw conclusions about catalytic efficiency
- Interpret experimental data to draw conclusions about a polymeric material
- Examine a proposed mechanism for this reaction
Some of the questions will be assigned prior to class, most likely the 'big picture' questions that ask about the techniques used and the problems with recycling PVC.
For fun, I decided to use this as my final in my senior inorganic class in the fall of 2024 prior to publication. There were come modifications including a little bit more review material as well as removing some of the questions that might require an outside source. Students were given the paper 1 week prior to the exam and allowed to have a 'clean' copy of the paper during the exam time. They had three hours, but most were done in 2-2.5 hrs.
Evaluation
The class had 9 students. In general, the students did fairly well.
All of the students received full credit for questions 1, 2, 3, 16 and 21.
Question 4: One student earned 6 points because they did not really address the complications of the styrene component of the co-polymer. One student earned 5 points for not quite having the structure of styrene correct and not really addressing the complications of the styrene in the co-polymer. Two students earned four points for not being close on the structure of styrene and not really addressing the complications of the styrene in the co-polymer.
Question 5: One student earned 6 points for doing everything right but having the wrong number of electrons on rhodium to start with.
Question 6: Two students earned 6 points for doing everything right but having the wrong number of electrons on rhodium to start with. One student earned 4 points for misassigning the phosphines as X type ligands and either keeping the O coordinated or making the COD ligand eta-2.
Question 7: A total of 5 students earned 4 points, two for having Inequivalent P atoms, two for coupling to an H atom and one seeing a singlet with cis- P atoms, so no coupling. Two students earned 2 points for having equivalent P atoms coupling.
Question 8: Two students earned 6 points, one for putting H atoms where the C-O bonds should be or for not quite getting the relativie intensities correct. One student got 5 points for failure to discuss the relative intensities.
Question 9: Two students earned 6 points, one for attempting to use a combination of full molecule motions and select vibrations, the other for not using group theory.
Question 10: One student earned 6 points for getting an 18 electron count with O bonding. Three students earned 4 points for miscounting the bridge and O, making the P atoms X type, or making one P atom X and included O.
Question 11: One student earned 6 points for having the wrong number of electrons coming from Rh.
Question 12: Three students earned 6 points, two for different bonding of Xanthphos as L3 vs LX2 and one for "folded" vs "unfolded" ligand.
Question 13: One student earned 6 points for not addressing the formation of other R groups. One student earned 4 points for ignoring the unsaturation in the backbone.
Question 14: Two students earned 11 points for calling a step decarboxylation and not beta-hydride elimination.
Question 15: One student earned 7 points for not accounting for the loss of an L type ligand to do associative. Four students earned 6 points, two for changing the P from L to X to do associative and two for having either associative or dissociative and then some completely unrelated mechanism. One student earned 2 points for having some thoughts about the importance of electron counts, but had the wrong mechanisms. One student earned zero points for an answer that was unrelated to the question.
Question 17: Two students earned 8 points for not describing the different sources of H.
Question 18: Three students earned 6 points, two for not describing the composition of the different polymers and one for not discussing the different H sources.
Question 19: One student earned 4 points for not mentioning the phase transition.
Question 20: One student earned 6 points for not discussing the similarities.