Organometallic Chemistry Name:__________________________________ CHEM 534 Final Exam December 16/18, 2008 Prof. Malachowski 1H NMR chemical shifts 13C NMR chemical shifts2 1. In the following reaction, draw the metal complex which would be the intermediate in the catalytic cycle immediately before the reductive elimination to form the product shown. (8 pts.) Bunnai Saito and Gregory C. Fu. J. Am. Chem. Soc., 2008, 130 (21), pp 6694–6695. 2. White et al. (J. Am. Chem. Soc. 2008, 130(43), pp. 14090-14091) recently reported alkylation reactions with Pd-allyl complexes. Key to the process was the formation of a Pd-allyl complex. During the course we discussed several different ways to make metal-allyl complexes. Provide two examples of reactions that form metal-allyl complexes. Be as explicit as possible with your answers. (10 pts.) _______/18 pts.3 3. Propose a mechanism or catalytic cycle for the following reaction. Label each step with the reaction type shown. (12 pts.) Manon Chaumontet, Riccardo Piccardi, Nicolas Audic, Julien Hitce, Jean-Louis Peglion, Eric Clot and Olivier Baudoin. J. Am. Chem. Soc., 2008, 130 (45), pp. 15157–15166 _______/12 pts.4 4. Answer the following questions about the uranium complex, U(cot)2, shown below. U a) What is the oxidation state of the uranium? (2 pts.) b) What is the coordination number of the uranium? (2 pts.) c) What is the electron count of the uranium? (2 pts.) d) Why doesn’t the uranium complex obey the 18 electron rule? (3 pts.) 5. a) In the following scheme, identify the thermodynamic and kinetic product by writing ‘thermo’ or ‘kinetic’ next to each. Note: calculated energy values are written beneath each intermediate or product. (4 pts.) Liam P. Spencer, Ping Yang, Brian L. Scott, Enrique R. Batista, and James M. Boncella. J. Am. Chem. Soc., 2008, 130 (10), pp 2930–2931 Path 1Path 2OCNPh b) What is the reaction shown in the first step of path 1 and 2 to form compound 7 and 9? (2 pts.) c) The reaction to form 7 and 9 was NOT a reaction that we discussed during the course, but it was very similar to a reaction that we did discuss. Name this reaction and show a brief example.(4 pts.) _______/19 pts.5 6. Answer the following questions about the structure shown below which comes from Karsten Meyer et al. J. Am. Chem. Soc., 2008, 130 (37), pp 12536–12546. a) Identify all the X-type and L-type ligands on the uranium atom. (5 pts.) b) What is the oxidation state of the uranium? (3 pts.) c) The authors of the research on uranium compounds 2 reported a crystal structure of 2-tBu (below). What about the crystal structure told them that there was an imido bond or U=N in the structure? (3 pts.) 7. Three different phosphines, P(tBu)3, P(tBu)2nBu and P(1-Ad)2nBu, were analyzed in the aryl bromide hydroformylation study reported by Beller et al. (J. Am. Chem. Soc. 2008, 130(46), pp. 15549-15563). 1-Ad= a) Briefly discuss the steric and electronic properties of these phosphines relative to the full range of phosphines that we discussed in the course. (5 pts.) b) As we heard on several occasions over the last two weeks of the course, the slow step in Pd catalytic cycles is often the oxidative addition. How would these type of ligands facilitate the oxidation step? (4 pts.) _______/20 pts.6 8. The following reaction was reported by Beller et al. (J. Am. Chem. Soc. 2008, 130(46), pp. 15549-15563) as the hydrogenolysis step in the formylation of aryl bromides. LPdOArBrHHNNMeMeMeMe(T MEDA)ArOH+ Pd-LA a) This semester we discussed two basic types of transition metal complexes with hydrogen. List both types of complexes, identify which type complex A is and, using complex A as an example compound, draw the second type of metal complex with hydrogen. (6 pts.) b) Beller et al. state that the dihydride version is very unstable and prone to reductive elimination. Explain why this would be. (2 pts.) c) In the case of L=P(t-Bu)2n-Bu or P(1-Ad)2n-Bu the reaction of complex A succeeded in forming the benzaldehyde product as shown. What role did TMEDA play in this case? Be as explicit as possible. (2 pts.) d) In the case of L=P(t-Bu)3, complex A failed and it formed another Pd complex. Draw the structure of that Pd complex below. (2 pts.) _______/12 pts.7 9. After some experimentation, path C, shown below, was selected by Hartwig et al. (J. Am. Chem. Soc., 2008, 130 (46), pp 15627–15635) as the most likely path for the beta-hydride elimination of Pt enolates. The authors highlighted two classic mechanistic experiments as evidence that supported path C. Briefly describe the experiments that supported path C shown below. (Note: these experiments did not rule out another path (E); a second set of considerations lead them to favor path C.) (9 pts.) 10. Complete the synthesis of complex 1 from the pyridine starting material by filling in the necessary reagents or reactants in the boxes. (8 pts.) NB r B rNNN 1, R1,R2=H _______/17 pts.8 11. a) What type of geometry would be expected for complex 1 in the previous problem? (3 pts.) b) Show the d orbital arrangement for Ru based on this geometry and the metal’s oxidation state. Label the d and d orbital groups. (4 pts.) c) One key to the success of complex 1 in the photosensitization studies of Hammarstrom et al. (J. Am. Chem. Soc. 2008, 130(46), pp. 15533-15542.) was the angle of the N-Ru-N bonds and the close adherence of the structure to the geometry as noted in part a of this question. Based on crystal field theory, what happens to the relative energies of the d orbitals in your diagram of part b if the N-Ru-N angle becomes smaller and the geometry departs from the standard structure? (4 pts.) _______/11 pts.9 12. In their recent publication (J. Am. Chem. Soc. 2008, 130(47), pp. 15764-15765), Meggers et al. generated a range of Ru complexes to test as inhibitors of kinase enzymes. The authors used a variety of techniques or tricks to substitute groups on the Ru complex. a) One such substitution is shown below for complex 3.