30 Jun 2016

Zones of Catalysis: Only the Metal? A literature Discussion of Outer-Sphere Hydroboration

Literature Discussion

Submitted by Santiago Toledo , St. Edward's University
Categories
Description: 

This literature activity is designed to introduce students to the concept of outer-sphere hydroboration catalytic reactions. It can be used after hydrogenation and hydroboration reactions have been introduced in class (typically covered in organic chemistry). Additionally, this activity allows students to apply their understanding of redox chemistry, acid base chemistry, and physical techniques to characterize products and elucidate reactions mechanisms.

The LO is built around a paper by the Szymczak group (JACS, 2015, 137, 12808-12814) where they describe the role of ligand design and its ability to be modified via acid-base reactions to change the reactivity of a hydroboration catalyst.

The LO has a modular design and can be taught in its entirety or in pieces. It also contains links to related LOs that can serve to reinforce, or introduce, concepts covered in this activity.

Learning Goals: 

After completing this assignment students will be able to…

Lower-order thinking

  • Recognize the key features of a hydroboration outer-sphere catalytic mechanism
  • Define turnover frequency and explain how turnover frequency represents catalyst effectiveness
  • Label the nucleophile and electrophile in different hydroboration species
  • Explain the key features of a hydroboration outer-sphere catalytic mechanism
  • Describe how redox-potential affects the nucleophilicity of metal-hydride complexes
  • Describe how spectroscopy is used to help elucidate reaction mechanisms
  • Summarize key points from an article in the primary literature

Higher-order thinking

  • Elucidate how (de)protonation of the catalysts modulates their nucleophilicity
  • Write and revise a hypothesis
  • Compare and contrast hydroboration of nitriles using NaBH4 (stoichiometric) and an outer-sphere hydroboration catalyst
  • Generalize how (de)protonation of metal complexes modulates their nucleophilicity
  • Infer how the secondary coordination of metal complexes can alter reactivity
  • Optional: Apply symmetry rules to assign the point group of compounds
  • Optional: Connect spectroscopic experimental evidence to the symmetry of compounds
Implementation Notes: 

Note to the instrucutor: This activity has not been tried in class before. We look forward to hearing input from anyone who implements this LO.

Before reading the article students will generate their initial hypothesis as an exercise to test their initial understanding purely on theoretical background from the course (2016 Szymczak LitDiscussion-Handout). Students will then read the paper and during the next class period they will work in groups of 2 or 3 students to answer the questions about the paper (2016 Szymczak LitDiscussion).

This activity is intended to be modular; each section is divided according to themes. If an instructor wants to do the whole activity it is possible but each module can be taught independently. The hypothesis generation and revision prompts are also something that instructors might choose to leave out depending on the needs of the class.

The faculty member will alternate between periods of monitoring the students’ progress and having the class report out their findings.

Time Required: 
One class period
Evaluation
Evaluation Methods: 

Informally faculty will walk around the room evaluate and assist with the challenges students face as they go through the activity.

Every group of students will submit one set of answers that will be graded for accuracy. Some questions are lower-level and intended to help students identify key ideas and relevant data from the paper. These questions could be worth fewer points while more complex quesitons could be worth more points.

We envision that faculty members will not have a challenging grading load since the discussion will happen during class and most answers will generated during class discussion.

Evaluation Results: 

We have not yet tested this activity in the class.

Creative Commons License: 
Creative Commons Licence

Comments

I used this LO in my senior-level discussion-based organometallics course in Fall 2016. Although I did not collect student responses, I gave the students the reading guide to help them prepare for class. This allowed the discussion to be aimed/developed in a non-random way. In future years, I would recommend assigning it as preclass homework, letting students use their notes during class, and then collecting it after the discussion, to give something to grade or evaluate student performance.

 

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