Reaction mechanisms

3 Jan 2017
Description: 

This Guided Literature Discussion was assigned as a course project, and is the result of work originated by students Stefanie Barnett and Katelyn Yowell.  It is based on the article “Synthesis, Electrochemistry, and Reactivity of Half-Sandwich Ruthenium Complexes Bearing Metallocene-Based Bisphosphines”, Shaw, A.P.; Norton, J.R.; Bucella, D.; Sites, L.A.; Kleinbach, S.S.; Jarem, D.A.; Bocage, K.M.; Nataro, C. Organometallics 2009, 28, 3804-3814. It includes a Reading Guide that will direct students to specific sections of the paper emphasized in the discussion.  This article presents the study of an array of metallocene-based bisphosphine ligands.

Course Level: 
Corequisites: 
Learning Goals: 

After reading and discussing this article, a student should be able to…

-       Understand the nomenclature of metallocene-based bisphosphine ligands.

-       Apply the CBC electron-counting method in the presence of metallocene-based bisphosphine ligands, which may be in an oxidized form.

-       Appreciate the role of phosphine cone angles in organometallic synthesis.

-       Understand the effect of a ligand’s electron donor ability on a metal’s redox potential.

-       Appreciate how synthetic methods may emphasize either the kinetic or thermodynamic product.

-       Understand how 1H NMR can help differentiate dihydride/dihydrogen isomers.

29 Dec 2016

The Monsanto acetic acid process

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 one of early papers detailing the mechanism for the Monsanto acetic acid process (J. Am. Chem. Soc., 1976, 98, 846). In this communicaiton the identification of key intermediates in this process is carried out using infrared spectroscopy. While the paper is an easy read, there are lots of subtle points that can be brought out by asking the right questions which hopefully this LO does. Although we have plenty of excellent LOs asking students to identify the individual steps in the catalytic mechanism, this LO takes a slightly different approach and marches students through the mechanism.

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 rhodium compounds in this paper
  2. Describe the bonding interaction between a metal and a terminal carbonyl ligand
  3. Identify the various reactions taking place in the Monsanto acetic acid process
  4. Relate data from IR spectroscopy to the bonding interaction between a metal and a ligand and to the identification of intermediates in this process
Time Required: 
50 minutes or so
28 Dec 2016

Understanding the Mechanism of Grubbs-Catalyzed Olefin Metathesis

Submitted by Richard Lord, Grand Valley State University
Description: 

A literature discussion has been developed for two courses: (i) a more basic set of questions appropriate for a sophomore level course or, possibly, a one semester upper level course that does not spend much time on organometallics, and (ii) an in-depth, in- and out-of-class set of assignments appropriate for an organometallics unit or course. Both sets of questions explore the mechanism of olefin metathesis in first- and second-generation Grubbs catalysts using a variety of spectroscopic kinetic techniques that were presented in the paper Sanford, M. S.; Love, J. A.; Grubbs, R. H. J. Am. Chem. Soc. 2001, 123, 6543-6554 (doi: 10.1021/ja010624k).

Corequisites: 
Prerequisites: 
Subdiscipline: 
Learning Goals: 

A student should be able to do the following after completing this LO:

Identify and discuss the importance of an olefin metathesis reaction.

Distinguish between Fischer- and Schrock-type carbenes and count electrons in complexes featuring these ligands.

Predict Ia vs. Id mechanisms based on electron counting.

Discuss why 31P and 1H NMR, and UV-Vis, were appropriate spectroscopic techniques for measuring kinetics in these systems.

Explain how variations in the catalyst (halide, carbene substituent, phosphine substituent, phosphine vs. NHC, etc.) affect ligand exchange.

Describe why the second-generation catalysts outperform the first-generation catalysts based on olefin binding vs. phosphine loss (in contrast to the historical reasons for their design), and why trans- effect arguments do not apply to the Grubbs system.

 

 

Implementation Notes: 

Two of us ran portions of these (they were not complete) in Fall 2016. Both of us noted that students were confused by the NHC representation in the manuscript because the authors assume that the reader knows there is no H on the carbene carbon, yet one would predict a H there based on the line structure formalism.

It is important to point out to students that the work here represents only the first 1-2 steps of the overall mechanism of olefin metathesis. There is a question in both the basic and advanced exercises that has students analyze the metallacyclobutane intermediate, but this species is formed later in the mechanism than any of the work presented here.

Time Required: 
~1 class period
28 Dec 2016

Virtual Issue of Organometallics

Submitted by Chip Nataro, Lafayette College

You can find the virtual issue with our editorial and all of the papers here.

Subdiscipline: 
Prerequisites: 
Corequisites: 
Course Level: 
27 Dec 2016

Energetics and mechanisms of reductive elimination from Pt(IV)

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

This LO was used in class to help a student guide a discussion of the paper. We did not cover all of the LO in a 75 minute class period, as we let the discussion take us where it wanted to.

A better way to ensure student preparation would be to collect the questions at the beginning (or end, if they wanted to use their notes in class) of class to ensure that they had really studied the paper.

Evaluation Results: 

I used this LO as a guided reading handout and did not collect the answers so I do not have any assessment data at this time.

My students found this paper to be highly readable and very clear. It is dense, with a lot of information presented, but once the students dove in, we were able to discuss it at a high level.

Description: 

This literature discussion is based on a paper by Karen Goldberg (J. Am. Chem. Soc., 1995, 117, 6889-6896). In this early paper by Goldberg, she studied the reductive elimination of ethane and methyl iodide from dppePtMe3I. The paper is well written, and approachable for undergraduates. It shows a real, interesting application of thermodynamic and kinetic methods to the study of a problem in mechanistic chemistry. The experimental details are complete, and this paper would serve as a good review of kinetics, thermodynamics, and organometallic reaction mechanisms. 


This LO presents a series of guided reading questions that help a student approach some of the material presented in the paper in a more thorough way. It asks students to derive equations and understand how experimental data can be combined into a reaction coordinate free energy diagram. The LO is suitable for junior or senior undergraduates in an organometallics course or unit within an inorganic course.

An update and correction was made to the LO in April 2018. Questions 7 and 8 in the learning object have students address the point of the differing M-C and M-I bonds. For the purposes of understanding what was written at the time, the questions are still valid, but the conclusions drawn in the paper about M-X bond strengths are not. For more information, see the "faculty only" file entitled "Goldberg Update 201804."

Course Level: 
Learning Goals: 

upon completing this LO students should be able to

1. demonstrate where thermodynamic parameters come from in a reaction coordinate free energy diagram

2. derive complex rate equations using the steady state approximation

3. describe the principle of microscopic reversibility

4. gain a deeper appreciation for the experimental methods (thermodynamic and kinetic) used in mechanistic chemistry

Subdiscipline: 
Implementation Notes: 

I used this LO as a guided reading handout for a senior-level organometallics class. The questions and the paper were provided to the students a week in advance and the in-class activity was a student-led discussion of the paper.

Time Required: 
one 50-75 minute class period
15 Dec 2016
Evaluation Methods: 

I had the students prepare for the discussion before class by reading the entire article. Students then answered the guiding questions in small groups during a class period.

I graded this assignment based upon class participation. All 33 students participated in the discussion. 

Evaluation Results: 

The average grade on this assignment was an A. Students very much enjoyed reading an article from the literature and connecting it to topics we discussed in class. This article opened up our discussion on catalysis and mechanisms. The article nicely describes the rational design of experiments to probe and catalytic reaction. 

Good paper to introduce kinetics and mechanistic studies.

Description: 

Reading and understanding a journal article is a critical skill to obtain as a student. After college, many students will pursue careers in which learning occurs exclusively from the literature. Students  will read a full paper from the journal Inorganic Chemistry and answer guiding questions pertaining to the article. There will be an in class discussion about the article to introduce which is used to introduce the topic of catalysis. This assignment breaks down the article through a series of questions that helps students to navigate a journal article.

Students will look copper complexes which catalyze atom transfer radical addition (ATRA) under sustainable means. 

The citation is Inorganic Chemistry 2012, 51, 11917-11929. 

Corequisites: 
Course Level: 
Prerequisites: 
Learning Goals: 
Students should be able to:
  1. Read a full journal article pertaining to organometallic chemistry
  2. Critically think about the chemical literature
  3. Read about and understand organometallic mechanistic and kinetic studies
  4. Determine that structural and electronic ligand modification influences the reactivity of catalysts
  5. Describe spectroscopic methods used to obtain rate constants
  6. Distinugish between coordinating and non-coordinating anions and effects on catalysis
  7. Define inner and outer spehere electron transfer and relate this to the proposed reaction mechanism
  8. Explain the mechanistic studies done to probe the lability of the TPMA ligand
Implementation Notes: 

I conducted this with a class of senior and junior chemistry majors and it went very well! This is a very long article so you could break this up into more basic topic and then more challenging ones.

Some of these questions could also be used on an exam. 

The questions are doable as students in the course actually helped develop these questions. I broke the article up into sections and assigned each section to a group of 4 students who were required to develop at least two questions per section. I then helped form the questions with the students. This model worked well and may be of interest to other people in the community.

But this assignment can be delivered as is - as a literature assignment with the focus on electron transfer, catalysis, mechanistic studies, and kinetics.

Time Required: 
50 minutes to 1 hour
2 Dec 2016

Methane activation by a tungsten allyl

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. However, I will likely use it as the basis for my final. As a discussion I would envision collecting the answers to the questions that the students come up with jointly in class. I would also envision some component of their grade being based on participation. 

Evaluation Results: 

None currently

Description: 

The literature discussion is based on a paper by Legzdins (Organometallics, 2017, 36, 26). In this work, the C-H activation of methane by a [Cp*W(NO)(allyl)(alkyl)] compound is described. The paper is extremely well written and approachable for undergraduates, although the initial length and large quantity of experimental data might be a bit intimidating at first. The problem of using methane is a signifiant real world problem and as such should provide an interesting context to talk about this paper. The bonding of NO and allyl ligands is discussed as are a number of reactions in the process of converting methane to a larger ketone. These include C-H activation at a d0 compound (so it is not oxidative addition), CO insertion and an internal nucleohilic attack. Electron counting is an important component of this exercise. There is a large amount of spectroscopic data in the paper, but this LO only briefly examines the relationship between IR vibrations and electron density at the metal center and coupling to spin 1/2 nuclei that are less than 100% naturally abundant.

Course Level: 
Prerequisites: 
Corequisites: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Describe why the activation of methane is a significant problem that needs to be addressed
  2. Use the CBC method to count electrons in the tungsten compounds in this paper
  3. Describe the bonding in compounds with linear NO and η3-allyl ligands
  4. Outline the steps for the C-H activation of methane by this tungsten complex including a description as to why the C-H activation is not an oxidative addition
  5. Explain 183W 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, question 1 is about the big picture problem of methane transportation, and would likely be good for the students to do some research into this area before talking about the paper in class.

Time Required: 
50 minutes or so
1 Jul 2016

Introduction to Atom Economy and the Hydroamination Reaction

Submitted by Eugene Chong, University of Michigan
Description: 

This 5 slides about introduces the term "atom economy" as a means for undergraduates to start thinking about the efficiency of synthetic reactions. While this term may not be the best measure of the overall process of a reaction (as it ignores other factors such as solvents and materials used in purification), it provides a nice introduction to a concept on green chemistry. An example of an atom economic reaction, hydroamination, is briefly highlighted as it is an important ongoing research area. Notes for the instructor are included in the slides.

Corequisites: 
Subdiscipline: 
Learning Goals: 

Students should be able to:

- define atom economy and use it to assess the efficiency of a reaction

- explain the hydroamination reaction and the strategies involved to facilitate the reaction with a metal catalyst

- describe the bonding of metal-imido bonds and metal-pi-C=C bonds

 

Implementation Notes: 

Calculation of atom economy or drawing of molecular orbitals of the bonds involved could be a useful classroom activity. The mechanisms presented are selected examples that have been simplified, and one should keep in mind that other mechanisms exist, as well as other metals.

30 Jun 2016
Evaluation Methods: 

Some or all of the student answers may be collected for grading. One or more of the application questions may be used as a quiz/exam question. Instructor should also observe the students as they work and determine whether they are understanding the important points as they progress through the activity; be prepared to step in to assist.

Evaluation Results: 

This activity has not yet been used in the classroom.

Description: 

Based on the literature reference, this activity allows students to discover inner-sphere and outer-sphere catalytic hydrogenation mechanisms then apply their knowledge to hydroborylation. This is a guided-inquiry in-class activity that students can complete in small groups or individually with instructor support. 

Learning Goals: 

The student will be able to...

1.      Compare and contrast mechanisms for inner- and outer-sphere catalytic hydrogenation.

2.      Predict behavior of more polar and less polar substrates.

3.      Compare H2 to E-H as a substrate.

4.      Compare hydrogenation to hydroborylation with respect to mechanisms.

Corequisites: 
Subdiscipline: 
Course Level: 
Equipment needs: 

None.

Topics Covered: 
Implementation Notes: 

This activity is intended to be used in class by small groups of students. They may or may not have previously read the JACS paper on which it is based, but they should have some understanding of: organic chemistry, metal atom oxidation states, coordination numbers, basic types of organometallic reactions (oxidative addition/reductive elimination). If the activity requires more time than the class period, or by instructor choice, one or more of the final application questions can be assigned as homework/used as exam questions.

Note that all ligands in the catalytic cycles are assumed to be "L" type.

Time Required: 
50-100 minutes
30 Jun 2016
Evaluation Methods: 

Students should be assessed based on participation if there is no written portion to hand in.

Evaluation Results: 

This is a new learning object created at the 2016 Summer VIPEr Workshop and has not yet been implemented.  Results will be added by the creators after use in a class.  Please feel free to share your results.

 

Description: 

The article “Synthesis and Reactivity of Oxorhenium(V) Methyl, Benzyl, and Phenyl Complexes with CO; Implications for a Unique Mechanism for Migratory Insertion,” Robbins, LK; Lilly, CP; Smeltz, JL; Boyle, PD; Ison, EA;, Organometallics 2015, 34, 3152-3158 is an interesting read for students studying reaction mechanisms of organometallic complexes.  The reading guide directs students to the sections of the paper that support the question posed in the Discussion Questions document. 

Corequisites: 
Course Level: 
Learning Goals: 

After reading and discussing this paper, students will be able to explain the mechanisms of migratory insertion reactions of CO and explain the evidence supporting a new mechanism of direct insertion.  In addition students will be better prepared to read and appreciate original research articles without a reading guide.

 

A student should be able to

 

1. identify and state the goals and findings of the paper in their own words

2. explain the various methods/techniques used to probe the mechanism, describe what was measured, and explain how the observations support the conclusions presented.

3. apply the CBC method for electron counting of the Re complexes in this paper

4. describe the bonding in metal oxo compounds and explain trans influence

5. understand kinetic parameters such as the reaction rate equation and the reaction order

6. analyze 1H NMR spectra

7. interpret thermodynamic parameters and how they apply to the reaction mechanism

Implementation Notes: 

The reading guide covers the first part of the paper only.  The DFT studies are not included nor are the synthetic details. We suggest giving the reading guide to the students with the original manuscript and allowing two days or longer for the students to read and digest.  Then, in small groups, or as a class discussion, ask students to answer the questions in the Literature Discussion document.

 

Time Required: 
at least 1 class period

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