11 Jan 2009

Bonding and Electronic Structure of a 14-electron W(II) bound to 4-electron pi-donors

Literature Discussion

Submitted by Hilary Eppley, DePauw University
Categories
Description: 
This paper is a meaty communication that covers novel bonding of 4 e- π-donors to a 14-electron species. Requires students to apply their knowledge of electron counting and organometallic bonding to ligands that are acting in novel ways.  This also includes exercises dealing with chemical information and general questions that require students to put the science in context. 
AttachmentSize
Microsoft Office document icon Fourelectrondonor.doc43 KB
Learning Goals: 

Understanding

  • Students can explain the electron count in an organometallic π-complex
  • Students can explain the molecular orbitals involved in 4 e- π bonding to alkynes and nitriles
  • Connect electron count to molecular orbital picture

 Application to new situations

  • Students can apply their knowledge of organometallic chemistry to explain the structure and bonding in 4 e- complexes of imines, ketones, and aldehydes (using bond lengths etc.)

Broader Perspectives of Science

  • Connect the science in the paper to the larger picture, broader interests
  • Students locate additional information about articles' authors
  • Place work within context of a larger body of work
Implementation Notes: 
This would be appropriate to cover after discussing electron counting and simple π bonding and backbonding in organometallic complexes, possibly as a capstone experience for the organometallic section of a course. The number of questions could easily be winnowed down significantly--the current version includes questions about synthesis, chemical information skills (Cambridge Structural Database, SciFinder Scholar), and general questions about the importance of the science.
Time Required: 
1-2 50 min class periods depending on how many of the questions you want to discuss in class.
Evaluation
Evaluation Methods: 
I graded on the basis of class participation but you could also collect problem sets and grade them individually. With a paper with so many subtleties, I might be tempted to have them submit their answers and then give them a chance to revise them after the in-class discussion.
Evaluation Results: 
The students generally did a good job of discussing this paper--the subtleties of the delta backbonding were difficult for them to visualize. It would be helpful to bring orbital models with you to show these interactions in 3-D.
Creative Commons License: 
Creative Commons Licence

Comments

Dear VIPEr community,

This learning object (LO) is an excellent model for writing LO's.

  1. It has clear and measurable learning goals.
  2. There is feedback about what students find difficult or what misconceptions they might have (Evaluation Results).
  3. There are suggestions for alternate ways to teach the object (under Implementation Notes and Evaluation Methods).
  4. It is short and concise.

It would be helpful to have an answer guide. To protect the privacy of the answers, the LO author could post it in the "Problem Set" section of VIPEr.

We would also like to see authors include, when possible, more specific information about their assessment results. This might include, for example, the average, range, and standard deviation of the scores for one class and comments on where students typically lost points.

Great job!

My Inorganic II students and I discussed this paper yesterday. Overall, I thought we had a pretty good discussion. We spent a fair amount of time talking about orbital overlap and the bonding in the molecule.One thing that surprised me is that my students thought this wasthe most challenging paper that we discussed this semester.

It took me a while to be able visualize the bonding in the complex well. I found the pictures on alkyne bonding in the Organometallics HyperText - in conjunction with my molecular model kit - to be incredibly helpful. http://www.ilpi.com/organomet/alkyne.html

Next year, I will be more explicit about the bonding questions. I will probably define a coordinate system for my students and ask directly which d-orbitals are interacting with which nitrile (triple bond) orbitals and is the bonding interaction a sigma, pi, or delta type interaction. I think that would have helped guide the students to make the paper a bit easier. 

 

I have now used this lit discussion twice in my upper level Organometallics class (all seniors). The discussion easily filled the 50 min period both times. Its a great paper because of the discussion of bonding, electron counting, and orbital diagrams- all topic which the student have learned in the previous Inorganic course.

My students were interested in the practical aspects of preparing such complexes and asked about the use of Schlenk glassware and even what  makes acetone "neat".

At the end of the discussion I discussed the follow-up paper which shows that the nitrile can be converted to an imine via reaction with an eletrophile followed by a nucleophile.

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