In the Classroom
A “Classic Papers” Approach to Teaching Undergraduate Organometallic Chemistry Andrew P. Duncan*† Department of Chemistry, Pomona College, Claremont, CA 91711; *
[email protected] Adam R. Johnson Department of Chemistry, Harvey Mudd College, Claremont, CA 91711
While organometallic chemistry has its roots in 19thand early 20th-century Europe with the works of Cadet, Grignard, Zeise, Frankland, and others (1), the renaissance of the discipline in the 1950s can be attributed largely to a single series of events: the serendipitous synthesis of ferrocene, (η5-C5H5)2Fe, by Kealy and Pauson (1951) (2) and, shortly thereafter, the elucidation of its unprecedented “sandwich” structure by Wilkinson and Woodward (3) and, independently, Fischer (4). In response to this achievement came a surge of research across the organic, inorganic, and physical disciplines, out of which emerged the paradigms of modern organometallic chemistry. Over the years, a number of papers have emerged as “classic” works in this field. Although there is no fixed definition of a classic work of chemical literature, the papers considered as such often spark major conceptual advances or illuminate significant, long-standing problems, and all possess elegant experimental design and execution (5). Given the traits common to these select papers, it seemed that many educational benefits could result from using them as both the primary textual resource and the unifying organizational theme for an undergraduate class in organometallic chemistry. Principal among these was the idea that students would be introduced to the central tenets of organometallic chemistry through studying some of the best work in the field in its original, published form. A more general goal of this approach was for the students to become comfortable and proficient in use of the primary literature as a main source of information, as will be expected of them in their future scientific undertakings. This goal is by no means novel: for years chemical educators have recognized the benefits of incorporating the primary literature into the classroom. Two reports describing literature-based courses in advanced organic chemistry were particularly influential in the design of our class (6, 7). We are unaware of any published work describing an organometallics course based on a series of noteworthy papers. Pedagogical Approach Having decided to base the organometallics class on a selection of classic papers, we reasoned that the advantages of this approach would be amplified by giving the students primary responsibility for researching, preparing, and presenting course material, with the faculty serving as “guides” or “facilitators” (8). The objectives of this strategy were to give the students a sense of responsibility for and ownership of † Current address: Department of Chemistry, Willamette University, Salem, OR 97301
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the class (9), as well as to afford them the chance to develop the skills involved in researching, preparing, and delivering informative presentations. Also, this format required that students not simply read a research paper, but identify, internalize, and organize its salient points so that they may be explained to others (10). Given the proven effectiveness of “student-directed” (9) approaches to chemical education, we felt confident that ceding control of the class period to the students would provide a richer, more dynamic experience for all involved. Breadth was an important consideration in selecting the classic papers around which the class was to be structured. Articles were selected to provide balance between synthetic, mechanistic, and structure–bonding studies of organometallic complexes across the transition series (see Table 1). Emphasis was also placed on applications: we included reports describing a transformation of industrial significance (the Monsanto acetic acid process) and organometallic reactions widely applied in organic synthesis (the Heck reaction and asymmetric olefin hydrogenation). Papers were vetted by the instructors to ensure an appropriate level of intellectual challenge without exceeding what could reasonably be expected of advanced undergraduates. Course Design The course was first offered in the spring term of 2005 as a “half course”, co-taught by the authors, with two, 50min meetings each week for slightly more than half the semester (21 meetings, total). The course enrollment was eight students, all of whom had completed a full year of organic chemistry. A minority of students had completed a course in inorganic chemistry prior to taking the class, with the balance of students either taking inorganic concurrently or not at all.
Structure of the Course The course was divided roughly into thirds. The first third was a series of seven lectures, given by the faculty, covering basic organometallic principles. Topics included a brief history of the field, oxidation state and electron counting formalisms, construction of qualitative molecular orbital diagrams, and basic principles of organometallic reactivity. Explicit coverage of this material was deemed necessary because of the variability in inorganic chemistry preparation within the class (6). This section culminated in a take-home, midterm exam. The second third of the class involved presentation and discussion of classic papers by individual students. Students were assigned papers randomly and were responsible for com-
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piling and distributing to the class a short bibliography (3–4 papers, including the classic) one week prior to their presentation date. Each student’s presentation was one class-period long, with no format restrictions imposed (lecture vs discussion, power point vs “chalk talk”, etc.). Students were also asked to generate a question based on their classic paper that would be suitable for use on the final exam. The final third of the class consisted of another series of student presentations covering several important areas of the field. Given the demonstrated benefits of cooperative and team learning experiences in chemistry (11), we decided that these presentations would be researched and delivered by groups of two or three students over two class periods. Groups chose a topic from a selection compiled by the faculty (List 1) and gave their presentation in a more formal, seminarstyle format.
Assessment Strategies Grades for the course were based on performance on the midterm and final exams, as well as through evaluations of individual and group oral presentations. Primary evaluations of
List 1. Faculty-Suggested Topics for Group Presentations 1. Palladium-Catalyzed Reactions: Cross-Couplings and Allylic Alkylations 2. Small Molecule Activation: N2 fixation, Alkane Functionalization, and Compounds of Noble Gas Elements 3. Ziegler–Natta Polymerization: The Development of Metal-Catalyzed Poly-␣-Olefin Synthesis 4. Olefin Metathesis: Catalysts, Mechanisms, and Applications in Synthesis 5. Metal-Catalyzed Hydroamination: Reactions of Amines with Unsaturated Hydrocarbons
presentations were done by the faculty; however, students were also asked to submit written evaluations of their peers’ presentations. This served both to encourage students to reflect out-
Table 1. Some Classic Papers Selected for Individual Presentations, Categorized by Concept Article Citations of Papers Used in the Course
Concepts Emphasized Mechanism elucidation
1.
Noack, K.; Calderazzo, F. Carbon Monoxide Insertion Reactions V. The Carbonylation of Methylmanganese Pentacarbonyl with 13CO. J. Organomet. Chem. 1967, 10, 101.
2.
Heck, R. F.; Nolley, J. P., Jr. Palladium-Catalyzed Vinylic Hydrogen Substitution with Aryl, Benzyl, and Styryl Halides. J. Org. Chem. 1972, 37, 2320.
3.
Adams, R. D.; Cotton, F. A. On the Pathway of Bridge-Terminal Ligand Exchange in Some Binuclear Metal Carbonyls. Bis(pentahapto cyclopentadienyldicarbonyliron) and Its Di(methyl isocyanide) Derivative and Bis(pentahapto cyclopentadienylcarbonylnitrosylmanganese) J. Am. Chem. Soc. 1973, 95, 6589.
Mechanism elucidation
4.
Schrock, R. R. An “Alkylcarbene” Complex of Tantalum by Intramolecular ␣-Hydrogen Abstraction. J. Am. Chem. Soc. 1974, 96, 6796.
Structural characterization; Bonding theory
5.
Chan, A. S. C.; Pluth, J. J.; Halpern, J. Identification of the Enantioselective Step in the Asymmetric Catalytic Hydrogenation of a Prochiral Olefin. J. Am. Chem. Soc. 1980, 102, 5952.
6.
Forster, D. On the Mechanism of a Rhodium–Complex-Catalyzed Carbonylation of Methanol to Acetic Acid. J. Am. Chem. Soc. 1976, 98, 846.
7.
Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J.; Wasserman, H. J. Characterization of the First Examples of Isolable Molecular Hydrogen Complexes, M(CO)3(PR3)2(H2) (M = Mo, W; R = Cy, i-Pr). Evidence for a Side-on Bonded H2 Ligand. J. Am. Chem. Soc. 1984, 106, 451.
8.
Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.; Santasiero, B. D.; Schaefer, W. P.; Bercaw, J. E. “ Bond Metathesis” for C–H Bonds of Hydrocarbons and Sc–R (R = H, alkyl, aryl) Bonds of Permethylscandocene Derivatives. Evidence for Noninvolvement of the System in Electrophilic Activation of Aromatic and Vinylic C–H Bonds. J. Am. Chem. Soc. 1987, 109, 203.
Novel reactivity; Mechanism elucidation
9.
Burger, P.; Bergman, R. G. Facile Intermolecular Activation of C–H Bonds in Methane and Other Hydrocarbons and Si–H Bonds in Silanes with the Ir(III) Complex Cp*(PMe3)Ir(CH3)(OTf). J. Am. Chem. Soc. 1993, 115, 10462.
Novel reactivity
10.
Sanford, M. S.; Love, J. A.; Grubbs, R. H. Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts. J. Am. Chem. Soc. 2001, 123, 6543.
Novel reactivity; Mechanism elucidation
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Mechanism elucidation; Metal-mediated synthesis Mechanism elucidation; Metal-mediated synthesis; Industrial chemistry Structural characterization; Bonding theory
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In the Classroom
Table 2. Comparison of Treatment Group and Control Group Student Responses to a Class Sur vey Treatment Group Responses a (N ⫽ 6)
Survey Question
Control Group Responsesb (N ⫽ 6)
1.
How well did you understand this paper, including both major concepts and specific results?
4.0 ± 0.6
2.4 ± 1.1
2.
How well could you present this paper to a class at the next meeting? (a 15–30 min. presentation)
3.8 ± 1.2
1.8 ± 1.1
3.
If you needed a deeper understanding of the information presented in the paper, how confident are you in your abilities to find this information?
4.8 ± 0.4
2.8 ± 1.7
4.
How comfortable are you working in a group to put together a scientific presentation?
4.8 ± 0.4
3.3 ± 1.2
a b
Students responded using a Likert-type scale with a number range of 1–5 (1 5 “not at all”; 5 5 “well”). See note 2 for composition of this group.
side of class on what had been covered and to gauge the efficacy of the presentations in conveying the substance of the papers. Both the midterm and final were given in a free-response, takehome format, with students having one week to complete the assignments. Both exams drew heavily from the primary literature, with the final based largely on questions written by the students themselves. Students were permitted to use whatever resources (class notes, textbooks, journals) they needed to complete the exams, as long as all sources used were cited appropriately. The rationale for this approach was that it most closely represents the type of open-source problem solving that will be required of students after graduation. As the semester progressed, we observed that the quality of presentations increased and in-class discussion generally became more sophisticated. Interestingly, several students commented that even the weaker presentations were effective, as the class was compelled to take a more active role in helping the presenter work through difficult concepts. Also noteworthy was the substantial improvement in overall performance on the final exam (mean score: 91%) as compared to the midterm (mean score: 74%), both exams being of similar difficulty. Answers to the free-response questions on the final were on the whole both more thoroughly researched and more carefully reasoned. Taken together, these observations suggest that the student-led presentations and discussions were indeed effective in both communicating material and instilling a sense of responsibility in the students for the overall quality of the course. Evaluation Efforts In order to further assess the overall success of the course in meeting the learning objectives established for the students, a short, anonymous, literature-based exercise was distributed with the final exam. This consisted of a short paper from the journal Organometallics (12) accompanied by a series of questions. Students were asked to spend about five minutes studying the article and to then respond to the questions using a Likert-type scale with a number range of 1–5 (1 ⫽ “not at all”; 5 ⫽ “well”). The questions and student response mean values for students in the course and a control group2 of students are reported in Table 2.
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Overall, we found the results of the survey encouraging. Although the small enrollment in the course precludes a detailed statistical analysis of the numerical responses, students who took the class responded to the survey with systematically higher scores than the control group. Particularly pleasing is the fact that students who participated in the class rated very highly their confidence in using the literature to obtain more in-depth information (question 3). Altogether, these data argue that the students have achieved a significant level of comfort with both the chemical literature and some important themes in organometallic chemistry. Although students at the Claremont Colleges are generally of high caliber,3 we feel that an organometallics course of this type could be successful at many institutions. The intrinsic flexibility in the course model, in terms of selection of papers and extent of instructor intervention, allow the course to be taught at a level appropriate for any group of advanced undergraduate majors. Revising the Course Having observed some success in our first attempt at teaching an organometallics class in this format, we continue to apply and improve the model. One of the authors is again currently teaching the course with some modifications that are briefly described below. First, the class now meets for seventy-five minutes, once per week for the entire semester. This has proven to be advantageous, as it gives students more time to study and contemplate the reading assignments between classes and allows more time for discussion in-class. Also, students are now required to generate two questions or comments about the classic paper assigned for a given week (6, 7). These are e-mailed both to the student responsible for presentation of that paper and to the instructor two days before the class meeting. This tactic has markedly raised the level of student preparation for class as compared to the first offering of the course. Finally, a number of problem-solving and group discussion activities are now incorporated into the introductory instructor-led portion of the course. Gratifyingly, this “templating” strategy has been highly effective, with the majority of presenting students now including active-learning activities in the class periods for which they are responsible.
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This has, in turn, raised the amount and level of discussion noticeably. In summary, we have found that a primarily studentdirected undergraduate course in organometallic chemistry based on classic literature is an effective introduction to this sub-discipline. Students benefit from extensive interaction with the primary literature and develop the skills necessary to organize and give an informative presentation. An additional benefit to this approach is its inherent flexibility: criteria for designating a paper as a “classic” are clearly subjective, thus the instructor has significant latitude in choosing the concepts emphasized in the class. Also, papers can be added and removed from semester to semester without disrupting the overall structure of the course, allowing the course to evolve along with the field and with student or instructor interests. Notes 1. Sections of Spessard and Miessler’s text were occasionally used as ancillary references, typically for general information relating to class material. 2. The control group consisted of students (rising juniors and seniors) doing summer research at Pomona College and Harvey Mudd College. None of the control group had taken a course in organometallics at the time of the survey. 3. Pomona College median SAT scores: Verbal, 730; Math, 730. In the Fall 2005 entering class, 88% were in the top 10% of their high school classes. Harvey Mudd College median SAT scores: Verbal, 700; Math, 750. Roughly 90% of Harvey Mudd students were ranked in the top 10% of their high school classes. Information gathered from both schools’ Web sites: http://www.pomona.edu; http://www.hmc.edu (accessed Dec 2006).
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Literature Cited 1. (a) Crabtree, R. L. The Organometallic Chemistry of the Transition Metals, 3rd ed.; Wiley Interscience: New York, 2001. (b) Elschenbroich, C.; Salzer, A. Organometallics: A Concise Introduction, 2nd ed.; VCH: New York, 1992. (c) Spessard, G. O.; Miessler, G. L. Organometallic Chemistry, 1st ed.; Prentice Hall: Upper Saddle River, NJ, 1997. 2. Kealy, T. J.; Pauson, P. L. Nature 1951, 168, 1039–1040. 3. Wilkinson, G.; Rosenblum, M.; Whiting, M. C.; Woodward, R. B. J. Am. Chem. Soc. 1952, 74, 2125–2126. 4. Fischer, E. O.; Pfab, W. Z. Naturforsch. B 1952, 7, 377–379. 5. A fascinating Web site collecting many “classic” works in all areas of chemistry (mostly older works, as compared to those used in our class) may be found at Classic Chemistry Compiled by Carmen Giunta: http://web.lemoyne.edu/~giunta/ index.html (accessed Dec 2006). 6. French, L. G. J. Chem. Educ. 1992, 69, 287–289. 7. Fikes, L. E. J. Chem. Educ. 1989, 66, 920–921. 8. Black, K. A. J. Chem. Educ. 1993, 70, 140–144. 9. Katz, M. J. Chem. Educ. 1996, 73, 440–445. 10. There is empirical evidence that “high ability” students, such as may be found in an upper-level chemistry course, derive substantial benefit from explaining (i.e., teaching) concepts to others: Peterson, P. L.; Janicki, T. C. J. Educ. Psychol. 1979, 71, 677–687. 11. (a) Dinan, F. J.; Frydrychowski, V. A. J. Chem. Educ. 1995, 72, 429. (b) Paulson, D. R. J. Chem. Educ. 1999, 76, 1136. (c) Kogut, L. S. J. Chem. Educ. 1997, 74, 720–722. 12. Vogt, M.; Pons, V.; Heinekey, D. M. Organometallics, 2005, 24, 1832. This paper centers on a topic (molecular hydrogen complexes) covered in one of the individual student presentations. It was not covered explicitly in the presentation, however.
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