My Notes
Categories
This set of questions was used to promote discussion within small groups (3 to 4 students) on how changing ligand properties can have dramatic effects on the product distributions in Pd-catalyzed cross coupling reactions. The questions are pretty difficult and not always straightforward, partly because they are derived from the primary literature and thus inherently "messy".
Prior to working through these problems, students would be expected to understand the basic steps in cross couplings such as Suzuki, Stille, Negishi, Kumada, Heck, etc. It will really help if they have seen some examples of how changes in ligand bulk, denticity, and/or electron richness can favor one reaction pathway over another.
NOTE: These could be used equally easily as problem set or exam questions!
| Attachment | Size |
|---|---|
| Cross coupling group exercise (for VIPEr).docx | 485.9 KB |
* Students should be able to recognize that catalytic chemical reactions often have many possible competitive pathways and come up with hypotheses about relevant mechanisms for a given set of reactions.
* Students should understand the effects that ligand properties (denticity, electron richness, steric bulk) have on cross coupling reactions and make predictions based on this understanding.
This activity was for an upper-level undergraduate organometallic chemistry class with about 20 students.
As mentioned above, I split students up into groups of 3 or 4. These questions sparked some nice discussions and really helped drive home some of the kinetics I was hoping for them to learn. I had groups volunteer to present answers, and that worked pretty well, although in the future I may just assign groups to go up to the board to draw out answers after they have had time to work on all the problems.
I have used some of these before as problems on an exam or problem set, and they work well for that purpose, too.
Evaluation
Student groups presented answers at the front of the room and were questioned by other groups who had worked on the same problems.
Generally the groups did well and arrived at some form of the correct answer, though the class discussion part was quite important, as some answers were incomplete or focused on less important aspects of the mechanism.
Having students draw competing reaction pathways with likely intermediates was VERY IMPORTANT.