Reaction mechanisms

27 Mar 2017

Nanomaterials for Carbon Dioxide Reduction

Submitted by Anne Bentley, Lewis & Clark College
Evaluation Methods: 

The problems presented here represented half the points on the final exam – I have included point totals to give an idea of the weight assigned to each problem.

Evaluation Results: 

Twelve students were enrolled in my course in the fall 2016. The average overall score for these problems was 78%.

For problem 1b, I calculated the oxidation numbers using the familiar general chemistry method of assigning oxygen as –2 and hydrogen as +1. Students recently coming through organic may have some other way to do it, and you may need to provide directions for your students about your preferred method.  I think I could have worded part (c) better to try to emphasize the redox processes involved. I wanted them to think of combustion, but I think they needed to be specifically prompted, such as "Give an example of the combustion processes that generate CO2 and trace the oxidation state of carbon through the reaction." Overall my students scored 86% on problem 1.

The second problem (about another method that could be used to measure d-spacing) was fairly hit or miss.  Five students got full credit, six students got 3 points, and one got zero. Eleven out of twelve did answer part (a) correctly.  I realized as I made this LO that the article says the carbon-based material doesn’t diffract X-rays, but doesn’t actually directly explain whether or not the Cu nanoparticles diffracted X-rays, so you may need to adjust the question to be technically accurate.

Question three (re: surfactants in nanoparticle synthesis) referred back to knowledge from earlier in the course. The overall score was 61%.

Question 4 (define and describe electrodes) was fairly straightforward, and students scored 85%.

Question 5 caused some confusion, as some students missed that I was looking for “carbon-containing” products only. I didn’t count off for that mistake, but it made the problem harder for students who included hydrogen in each box.  Overall, students did very well on this problem (89% correct).

Question 6 – again, not too much trouble here (84% correct).

Question 7 – I was surprised that students didn’t do better on this question, as I thought that water reduction was mentioned often in the article.  Only three (of 12) students scored 5 points on this problem, and the average score was 53%.  This was probably my favorite question, as it foreshadows electrochemistry topics I cover in my inorganic course.

Description: 

This literature discussion is based on an article describing the use of copper nanoparticles on an N-doped textured graphene material to carry out the highly selective reduction of CO2 to ethanol (Yang Song et al., “High-Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle / N-Doped Graphene Electrode” ChemistrySelect 2016, 1, 6055-6061.  DOI: 10.1002/slct.201601169). The article provides a good introduction to the concepts of electrochemical reduction, selectivity and recycling of fossil fuels. The literature discussion assignment shared here was used as half of the final exam in a half-credit nanomaterials chemistry course, but could be adapted for use as a take-home or in-class assignment.

Corequisites: 
Course Level: 
Learning Goals: 

After reading this paper and working through the problems, a student will be able to:

  • assign oxidation states to carbon and trace the oxidation and reduction of carbon through fossil fuel combustion and CO2 conversion
  • describe the role of control experiments in studying the CO2 conversion presented in the article
  • define the word “selective” in the context of this research
  • use the proposed mechanism to explain why the electrode studied produces ethanol in such a high proportion
  • identify the primary reaction competing with CO2 reduction for available electrons
Implementation Notes: 

These questions comprised half of the final exam for my half-credit nanomaterials chemistry course in the fall of 2016.  I gave the article to the students one week ahead of time. They were encouraged to read the article, make any small notes they liked, and meet with me in office hours with questions. At the final exam they were allowed to use their copy of the article, but they were also required to hand in their copy with their exam so that I could make sure they hadn't written lots of extraneous information on the exam copy.

The nanomaterials course features near-weekly homework assignments centered around articles from the literature. Because I used this article at the end of the course, students were already familiar with nanomaterials synthesis and characterization techniques. Thus, some of the questions I asked relied on previous knowledge. 

Please feel free to adapt these questions and add some of your own. Leave comments describing any new questions you’ve added.

Time Required: 
one hour
1 Mar 2017

Reactivity and Bonding of Complexes with Metal-Metal Bonds

Submitted by S. Chantal E. Stieber, Cal Poly Pomona
Evaluation Methods: 

Evaluation was conducted by the instructor walking around the classroom and addressing individual problems students had.

Evaluation Results: 

From classroom observations, most students were able to properly count electrons and oxidation states for the metals in the complexes and rationalize the ligand coordination modes. Here, the main source of confusion was how to account for the Z-type Co-Zr interaction. The MO diagrams generated the most discussion and were the most difficult part for students (as was expected). The reactivity was also initially conceptually difficult for students, but once they realized how to treat the M-M bonded system, students were able to apply fundamental organometallic reactions to the system. Many students forgot what they had learned about magnetic moments in the previous quarter, but figured it out and were excited to apply knowledge from the previous course. 

Description: 

This problem set was designed to be an in-class activity for students to practice applying their knowledge of metal-metal bonding (as discussed in the previous lecture) to recently published complexes in the literature. In this activity, complexes from four papers by Christine M. Thomas and coworkers are examined to give students practice in electron counting (CBC method), drawing molecular orbitals, and fundamental organometallic reactions.

Corequisites: 
Course Level: 
Learning Goals: 

Following the activity, a student should be able to:

·      Determine electron counts and oxidation states of complexes with M-M bonds using CBC electron counting method

·      Draw molecular orbital diagrams for M-M bonds

·      Determine M-M bond order

·      Propose mechanisms for reactions at M-M centers

·      Apply fundamental inorganic chemistry to reports in the literature

Implementation Notes: 

This was implemented in the second quarter of advanced inorganic chemistry (4th year level) before the second midterm as an in-class group activity. The worksheet generated a lot of interest from the students and generated good discussions in a class of 23 students. In the previous lecture, we discussed basic metal-metal bonding, including drawing MO diagrams and determining bond order for homobimetallic complexes. This worksheet was a reasonable extension, requiring students to apply this knowledge to more complicated systems.

Time Required: 
65 min
21 Feb 2017
Evaluation Methods: 

Graded problems students turned in.

Informal evaluation during discussion.

Evaluation Results: 

Graded assignments: mean of 84, std dev of 12, so a fairly broad range of understandings

Informal: Students really enjoyed getting to evaluate published work critically and were quite engaged in discussions, which helped to bring some of the students who didn't understand the paper as well up to speed.  After the paper, students have felt much more comfortable questioning what is stated in papers, particularly if little or no support is given.

I will definitely use this again!  Unfortunate to find a paper with several important oversights in the literature, but it is a good learning opportunity.

Description: 

This LO is a problem-set-style literature discussion that leads students through a critical analysis of an interesting but flawed paper from the recent chemical literature.  Students use the questions to help them work through the paper prior to class, providing plenty of raw material for an in-class discussion about various aspects of the work from a mechanistic organometallic perspective.  The questions help students critically analyze substrate tables, spectroscopic data, and computational results from DFT.

Corequisites: 
Course Level: 
Learning Goals: 
  • Students will be able to pull out important mechanistic information from substrate tables in an organometallic paper
  • Students will be able to use knowledge of organometallic mechanisms and organic chemistry to rationalize findings in a catalysis paper
  • Students will be able to use knowledge of spectroscopy, particularly NMR, to understand structure and bonding arguments in an organometallic paper
  • Students will critically analyze a paper and learn to feel comfortable questioning assertions by authors, including the major findings of a paper
Implementation Notes: 

I had students prepare answers to these questions ahead of class and bring the answers with them.  To add incentive, I collected them as a homework assignment (though I graded some of the harder ones fairly leniently).  The questions helped prepare them for a class discussion of the paper, which I led with a few slides containing information from the paper and some other useful tidbits (I am happy to send those to you if you like, just contact me).

Time Required: 
1-2 hours student prep (reading paper); 45 minutes in class discussion
27 Jan 2017

Iron Catalysts for Lactide Polymerization

Submitted by Anthony L. Fernandez, Merrimack College
Evaluation Methods: 

This LO will be used to facilitate an in-class discussion of polymers and polymerization catalysts (in general) within the context of the article. Student responses will not be graded, but this LO will be evaluated by the quality of the discussion and how well it guides the students to the main points of the article.

Evaluation Results: 

This LO has not been used yet, but will be used in the Fall 2017 semester. Evaluation results will be posted after it has been used in class.

Description: 

This set of questions is intended to guide students through an excellent article by Jeff Byers and co-workers that describes the use of bis(imino)pyridine iron bis(alkoxide) complexes as catalysts for the polymerization of lactide. This set of questions is appropriate for a second-semester sophomore/first-semester junior level course in inorganic chemistry. The research described in the article ties together concepts of organometallic synthesis and characterization, catalysis, mechanistic studies, and polymer chemistry.

Given the recently revised ACS certification guidelines, this LO might be useful to faculty looking to incorporate polymer chemistry concepts into the inorganic curriculum.

 

Corequisites: 
Learning Goals: 

After completing this exercise, students should be able to:

  • Define basic terms used to describe polymerization reactions;

  • Differentiate between living polymerizations and other types of polymerization reactions;

  • Describe why the polymerization of lactic acid is important;

  • Explain how the bis(imino)pyridyl iron complex catalyzes the polymerization reaction;

  • Contrast characteristics of NMR spectra for paramagnetic complexes to those of typical diamagnetic complexes;

  • Explain how the evidence presented in the article supports the suggested mechanism;

  • Describe how the oxidation state of the iron center is critical for catalytic activity.

Implementation Notes: 

This set of questions is intended to help students extract important and useful material from this excellent article. About a week before class, students will be provided with the article and this set of questions so that they have sufficient time to read the article and answer the questions. When the students arrive in class on the designated day, the instructor should lead the discussion of the paper and have the students share and discuss their answers to ensure that each answer is correct and complete.

Time Required: 
1 hour or more
27 Jan 2017
Evaluation Methods: 

Since this assignment has not been implemented, I am still determining the evaluation method. I plan to grade on accuracy of the answers and class participation. I will be most interested in making sure the students can see the big picture with the chemistry and also apply the materials we cover in class on NMR, CBC and electron counting, and catalysis. 

Evaluation Results: 

not applicable. will update when this has been implemented :) 

Description: 

This is a literature assignment for a junior/senior level course. Guiding questions are provided to assist students with reading the article so that they see the value and importance of developing catalysts for polymerization reactions. This assignment is based upon the article 

Redox-Controlled Polymerization of Lactide Catalyzed by Bis(imino)pyridine Iron Bis(alkoxide) Complexes

Ashley B. Biernesser, Bo Li, and Jeffery A. Byers

Journal of the American Chemical Society 2013 135 (44), 16553-16560

DOI: http://dx/doi/org/10.1021/ja407920d

 

This paper includes topics related to sustainable polymers and catalysts. This is an excellent article that ties in the concepts of organometallic synthesis and characterization,catalysis, mechanistic studies and polymer chemistry. An LO for faculty looking to incorporate polymer chemistry into the inorganic curriculum, in light of the ACS standards for certification. 
 
 
Prerequisites: 
Corequisites: 
Course Level: 
Learning Goals: 

After completing this exercise, students should be able to:

  • Define basic terms used to describe polymerization reactions;

  • Differentiate between living polymerizations and other types of polymerization reactions;

  • Describe why the polymerization of lactic acid is important;

  • Explain how the bis(imino)pyridyl iron complex catalyzes the polymerization reaction;

  • Contrast characteristics of NMR spectra for paramagnetic complexes to those of typical diamagnetic complexes;

  • Explain how the evidence presented in the article supports the suggested mechanism;

  • Describe how the oxidation state of the iron center is critical for catalytic activity.
Implementation Notes: 

I plan to implement this during my junior/senior level inorganic course this semester. I will assign the questions and article to the students before lecture. The students will work in groups of about 4 to answer the questions before coming to class. We then will have an active discussion about the article and the questions. I will use this to help the students to start to build guiding questions for an article they are interested in studying more. 

 

Time Required: 
1 hour
25 Jan 2017

Synthesis and reactivity of palladium and platinum carbenes

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This paper was presented late in the fall semester and as such I was unable to use it in class. I look forward to using it in the fall.

Description: 

The literature discussion is based on a paper (Organometallics ASAP) in which the synthesis and reactivity of a palladium and platinum carbene compound. The palladium and platinum compounds exhibit some interesting differences that show up throughout the paper. There is a lot of detail in the experimental section so this paper seems longer than it actually is for the purposes of having students read it. The authors do a good job of going through the rationale of the work that was done and students should be able to follow along. There is a large amount of spectroscopic data in the paper and a nice presentation of coupling to spin 1/2 nuclei that is less than 100% naturally abundant.

Subdiscipline: 
Corequisites: 
Prerequisites: 
Course Level: 
Learning Goals: 

Upon completing this LO students should be able to 

  1. Use the CBC method to count electrons in the compounds in this paper
  2. Describe the bonding in carbene compounds presented in this paper
  3. Present a rationale for the differences in the reactivity of related palladium and platinum compounds
  4. Formulate reaction mechanisms for the compounds in this paper
  5. Explain 195Pt satellites
Implementation Notes: 

Students should read the paper before coming to class. Although there are a lot of questions in the LO, if the students have done a good job reading the paper I would anticipate that they can get through them all. Certainly some of the questions can be left out, or perhaps only provide the students with a few of them before class, in particular the students should be able to do electron counts before class.

Time Required: 
50 minutes or so
23 Jan 2017

Reactivity of a platinum benzyne compound

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point.

Description: 

The literature discussion is based on a paper by Gagné (Organometallics 2015, 34, 2707).  In this work, the in situ generation of benzyne is examined. The benzyne coordinates to a platinum center with a tridentate (pincer) phosphine ligand and a methyl group. This provides an opportunity to discuss the characterization of compounds that have NMR active nuclei that are not 100% naturally abundant. Protonation of the benzyne compound results in the formation of toluene. Different mechanisms are considered.

Prerequisites: 
Course Level: 
Corequisites: 
Learning Goals: 

Upon completing this LO students should be able to 

  1. Describe what benzyne is and how it is formed
  2. Explain the coordination of benzyne (and therefore all alkynes) as L type donors to a metal center
  3. Use the CBC method to count electrons in all of the compounds and intermediates in this study
  4. Rationalize reaction pathways using electron counting techniques
  5. Explain 195Pt satellites
Subdiscipline: 
Time Required: 
50 minutes or so
19 Jan 2017

Nucleophilic attack at an iridium arene

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point.

Description: 

This literature discussion is based on a paper describing the nucelophilic attack on a coordinated arene (Organometallics, 2015, 34, 4626). The basic goal is to devise a catalytic method for converting an alkene into a phenol. While the authors do not accomplish that goal, they do manage to present a series of steps that would be the basis for a catalytic cycle. The compounds are relatively straightforward, and while there are some additional reactions that might be a little complicated for students, they should be able to get through the main parts of the short paper.

Prerequisites: 
Course Level: 
Corequisites: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Use the CBC method to count electrons in the iridium compounds in this paper
  2. Describe the bonding interaction between a metal and an arene
  3. Discuss nucleophilic attack on a coordinated arene
  4. Rationalize the point of attack on a substituted arene
Time Required: 
50 minutes or so
17 Jan 2017

Reactions of Cp*2Zr(2,3-dimethylbutadiene)

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point. I anticipate having students read the paper prior to coming to class to answer these questions in a group.

Description: 

This literature discussion is based on a paper detailing the structure and reactivity of the title compound (Organometallics, 201635, 3163). The 2,3-dimethylbutadiene ligand is a bit misleading as these typically bond as X type ligands to early transition metals. Students will get a lot of pracitce counting electrons, in particular considering the different ways the 2,3-dimethylbutadiene ligand might be thought of in terms of bonding. These will then be compared to X-ray data to help the students arrive at the proper binding mode. The reactivity of these compounds with carbon monoxide and isonitriles (isocyanides) is examined. Students should be given the paper to read before coming to class for discussion. I use the CBC method of electron counting and that is reflected in the questions on electron counting. Students are taught this at the beginning of a senior level course that is primarily focused on organometallic chemistry.

Prerequisites: 
Course Level: 
Corequisites: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Use the CBC method to count electrons in the zirconium compounds in this paper
  2. Describe the bonding interaction between a metal and a Cp* ligand
  3. Describe the bonding of a 2,3-dimethylbutadiene ligand to zirconium based on the available X-ray data
  4. Classify the reactions of CO and isonitriles with the complexes by reaction type
Time Required: 
50 minutes or so
13 Jan 2017

Ruthenium catalyzed transfer hydrogenation

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point.

Description: 

This literature discussion is based on a paper detailing catalytic transfer hydrogenation of various unsaturated organic molecules (Organometallics, 2016, 35, 943). In this paper, two ruthenium compounds with N-heterocyclic carbene (NHC) ligands are examined as catalytic precursors for transfer hydrogenation. This LO walks students through the paper, but it does so in a slightly different order than the paper presents the material. In parcticular, the proposed catalytic mechanism appears very late in the paper, but very early in the LO.

Course Level: 
Prerequisites: 
Corequisites: 
Subdiscipline: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Use the CBC method to count electrons in the ruthenium compounds in this paper
  2. Describe the bonding interactions in a N-heterocyclic carbene (NHC) ligand
  3. Describe catalytic transfer hydrogenation and identify the reactions taking place in the proposed mechanism
  4. Examine a series of catalytic results and rationalize observed trends
Time Required: 
50 minutes or so

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