My Notes
Categories
This Literature Discussion considers the synthesis of the first carbene-bismuthinidene complex by Gilliard and coworkers in 2019. This molecule serves as an illustration of different bonding models, as it can be described by multiple resonance structures invoking fully covalent, zwitterionic, and coordinate/dative bonding forms. Students analyze these resonance structures and their geometrical implications, then compare to the experimental structural evidence to come to a conclusion about which bonding model(s) best describe this molecule!
A handout with reading discussion questions and a pre-discussion worksheet is provided (with answer key in Faculty-Only files).
| Attachment | Size |
|---|---|
| BiCAAC Coord Bonding with MG Metals.docx | 23.88 KB |
After completing this Literature Discussion, students should be able to:
- Describe the features of the reported carbene-bismuthinidene and how carbene molecules can act as ligands toward metal atoms
- Sketch Lewis structures and different resonance forms for organo-main group molecules
- Predict hybridization and VSEPR geometry for atoms in molecules based on Lewis structures
- Describe the features of covalent, ionic, and coordinate/dative bonding models
- Use structural evidence to choose a model that best explains the bonding in an unusual molecule
I used this as a full-class (75-minute) Literature Discussion activity in my upper-level Inorganic Chemistry course in Spring 2024. The students were assigned to read the paper and complete the Pre-Discussion Worksheet ahead of class for participation credit. Then, during class, we went through the discussion questions and wove in a review of the worksheet exercises as we discussed the various reagents and resonance structures of the product.
This was the first Literature Discussion (of 3) that I assigned in my course, and I introduced it at the end of our first major unit in which we reviewed aspects of the covalent and ionic bonding models from General Chemistry (including Lewis structures, VSEPR, and hybridization) and introduced the coordinate/dative bonding model to describe metal-ligand complexes. This activity served as a review of all of those concepts while also being a relatively short and accessible first introduction to a chemical research article.
This paper also serves as a great example of how real research in synthetic chemistry goes, as it presents multiple attempts at the synthesis of this molecule, including failures and what was learned from them! This provides an opportunity to talk about the grit that it takes to be able to create something that is a "first" in science. I gushed pretty hard to my class about how gutsy this work was, between using super-toxic beryllium reagents and celebrating 10% isolated yields just to show they could do it. The fact that this paper showcases the achievement of a chemist of color is even more icing on this cake.
Evaluation
Student learning was evaluated through completion of the Pre-Discussion Worksheet and participation in the in-class discussion. Additionally, concepts such as Lewis structures and VSEPR geometry were tested on future exams, and a carbene molecule was featured on a final exam problem.
Most students completed the Pre-Discussion Worksheet with little difficulty. Lewis structures, hybridization, and VSEPR geometry were concepts familiar from General Chemistry, so with a little brushing up these exercises were very doable. Having them work through sketching the Lewis structures and assigning hybridization and geometry was helpful to illustrate what is special about carbenes (formally electron-deficient at carbon, violating the octet rule) and how they form metal-ligand bonds (sigma donating via the lone pair, pi accepting via the "empty" unhybridized p orbital at C).
There were a few disengaged students who did not do the preparatory work and were consequently not able to participate fully in the discussion. However, among students who prepared, the discussion was lively and well-received. They were able to identify important points from the text about the synthetic methods and structural evidence provided for the bonding model in the molecule. The connection between the bonding model and the predicted/reported geometrical features (e.g. bond lengths and angles) was difficult for students to make, so they had to be guided through the logic there. The students were able to appreciate the hard work that went into doing this chemistry and how the researchers went through multiple attempts to make this molecule!
Students tended to do well on the follow-up exam questions on Lewis structures and VSEPR geometry, although they struggled with the carbene question on the final exam. This difficulty, however, stemmed less from a lack of understanding of what a carbene was and more from the specific concepts assessed by that question (constructing an MO diagram based on group theory, a topic that was covered later in the course than this Literature Discussion).