19 Jul 2012

Ir-based Catalysis of Alkyl Halides: Scope, Mechanism, and Unexpected Reactivity Patterns

Literature Discussion

Submitted by Matt Hartings, American University

This literature review covers a paper by the Brookhart group in which they describe a very interesting catalytic route for reducing alkyl halides. The paper describes the catalytic mechanism in great detail and shows an unexpected trend in relative reactivities (Br > Cl > I and primary > secondary). One of the primary benefits for using this paper is that it can enable your students to rationalize a mechanism consistent with many different data sets.

Learning Goals: 

Students should be able to communicate, in simple terms, the chemical fundamentals from a detailed scientific publication.

Students should apply their understanding of organic chemistry to inform their understanding of organometallic reaction conditions.

Students should be able to analyze data to corroborate or justify the conclusions of the authors.

Students should, in their reading, advance their knowledge of techniques and analysis used from chemistry research.

Implementation Notes: 

Leading Questions

1) What is the actual catalytic mechanism discussed in the paper? How does it differ from the mechanism that you proposed at the end of the last class period?

2) The authors discuss a previously reported alternate system that uses silanes to reduce alkyl halides. What is the reference information for this paper? How do the trends in reactivity (Cl vs. Br vs I) from this referenced study differ from those in the Brookhart paper?

3) The authors use a term called the turnover number (TON) to describe catalytic activity? Without consulting your textbook or the internet, what is your perception of turnover number? What does it mean to have a single turnover in a catalytic cycle? Now, consulting your text or the internet: How does one calculate turn-over number (TON)? Try calculating the turnover number for one of the specific reactions mentioned in the article (for example conversion of 1-chloropentane to pentane. Note: I expect everyone to do a different sample, so don’t use the chloropentane example).

4) The authors use Schlenk techniques and J. Young NMR tubes in their experiments. Using a simple web search to inform your answer, briefly describe Schlenk techniques and why they are important in inorganic chemistry. Also, describe what a J. Young NMR tube is and how this is used in conjunction with Schlenk techniques.

5) What types of magnetic resonance experiments are used in this study? Assign all of the NMR spectra associated with one of the Ir complexes in the paper.

Time Required: 
50 minutes or less as needed
Evaluation Methods: 

Students are assessed, mainly, by in class participation and discussion.

For example:

At the beginning of the class discussion, we bring up the catalytic mechanisms proposed in the previous class. Focusing on the incorrect answers, and reminding the students that they didn't originally have all of the information necessary to know the right answer, we ask why the wrong mechanisms are wrong based on the experimental data.

Creative Commons License: 
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