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A literature review on Melanie S. Sanford’s recent work. Presented by Guillaume Pelletier.

Palladium (II)/Palladium (IV) catalytic processes : new options to consider for C―H bonds activation. A literature review on Melanie S. Sanford’s recent work. Presented by Guillaume Pelletier. Outline of the presentation. Introduction to the concept of C-H bond activation Industrial processes

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A literature review on Melanie S. Sanford’s recent work. Presented by Guillaume Pelletier.

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  1. Palladium (II)/Palladium (IV) catalytic processes : new options to consider for C―H bonds activation. A literature review on Melanie S. Sanford’s recent work. Presented by Guillaume Pelletier.

  2. Outline of the presentation. • Introduction to the concept of C-H bond activation Industrialprocesses Interestingrecentwork in thisfield Applications in total synthesis • Oxidative C-H bond functionalizationusingPhI(OAc)2 and Pd(OAc)2. Crabtreeet al.work in the 1990’s. Melanie S. Sanford’sworkusingbenzo[h]quinoline Interestingmechanisticwork on the Pd(II)/Pd(IV) catalytic cycle Application of the Pd(II)/Pd(IV) concept to related and differentsystems. Formation of C-C bonds : mechanistic insights Formation of C-X bonds Synthesis of cyclopropanes throughenynes cyclisation Aminooxygenation of alkenes.

  3. Why C-H bonds are powerful tools to access to diversification of organic molecules? • Among the most abundant bonds… • …but also the least reactive bonds. • Could be a powerfull tool to convert a common bond into a linear alcohol, amines or α-olefins. • Direct conversion of a « unfunctionalized » bond (no oxidation/protection needed).

  4. A quick overview on the “C-H activation” in a simple industrial process. 2 CH4 + 4 H2SO4-Pd(II)  CH3CO2H + 4 SO4 + 6H2O Complimentary to the Mosento process 10% Overall Yield (could be improved by adding MeOH or CO) Harsh conditions used Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science, 1998, 280, 560.

  5. A more complex problematic : Applications of C-H bond functionalisation in total synthesis. Bore, L.; Honda, T.; Gribble, G. W. J. Org. Chem. 2000, 65, 6278-6282.

  6. A more complex problematic : Applications of C-H bond functionalisation in total synthesis. Johnson, J. A.; Li, N.; Sames, D. J. Am. Chem. Soc. 2002, 124, 6900-6903.

  7. What were the major problematics to C―H bond functionalisation before 1990’s… • Usually there is low level of regiochemistry. • Harsh conditions are often used. • Low TON • Low functional group tolerance • Significant formation of byproducts • Large excess of substrate/oxidant/catalyst loading are typically required. • In summary, there is an open space to a lot of groups to circumvent any of these factors and to propose a more efficient transformation.

  8. Classification of the reactions with two different concepts. Dick, A. R.; Sanford, M. S. Tetrahedron 2006, 62, 2439-2463.

  9. Some pionnier work on efficient C―H bond activation/transformation. Chen, H.; Schlech, S.; Semple, C. T.; Hartwig, J. F. Science, 2000, 287, 1995-1997.

  10. Some pionnier work on efficient C―H bond activation/transformation. A lot of additive were screened. TfOH promoted the reaction. (26 to 91 % Yields) A large elctronic dependance over the substrates (kobs(OMe) ~ kobs(H)>>kobs(CF3)) Slow C-H bond activation (kH/kD = 3.5) Boele, M. D. K.; Strijdonck, G. P. F. V.; De Vries, A. H. M.; Kamer, P. C. J.; De Vries, J. G.; Leeuwen, P. W. N. M. V. J. Am. Chem. Soc. 2002, 124, 1586-1587.

  11. Some pionnier work on efficient C―H bond activation/transformation. An efficient methodology to form 1,3-difunctionalized amines through a selective C─H bond oxidation. The sulfamate ester is forming a nitrene-metal intermediate with the rhodium. Espino, C. G.; When, P. M.; Chow, J.; Du Bois. J. J.Am. Chem. Soc.2001, 123, 6935.

  12. Formation of C-O bonds by using a more friendly oxidant : PhI(OAc)2 Stock et al. reported earlier that Cr2O7- anion did promoted the oxidation of PhPd(OAc) species. Eberson et al. proposed previously to use peroxydisulfate as the oxidant. Stock, L. M.; Tse, I. J.; Walstrum, S. A. J. Org. Chem. 1981, 46, 1757-1761. Eberson, L.; Jönsson, L. Acta Chem. Scand. B. 1976, 30, 361-364.

  13. Kinetics of the reaction. • He found that PhPd(II)OAc intermediate fails to form the carbon-heteroatom bond. The most important fact to rememberisthat C-O bond isonlyformed on oxidation, presumably via a reductiveeliminationfrom a PhPd(IV)OAcspecies. Yoneyama, T.; Crabtree, R. H. J. Mol. Cat. A: Chem. 1996, 108, 35-40.

  14. Kinetics of the reaction and mechanism. • He found that k(H)/k(D) ~4.3 (C-H activation step is rate limiting). Yoneyama, T.; Crabtree, R. H. J. Mol. Cat. A: Chem. 1996, 108, 35-40.

  15. Some of Crabtree’s conclusions • Considering the regioslectivity of the acetoxylation of anisole (o:m:p = 44:5:51) the C-H insertion step is rather an electrophilic attack by the Pd (o:m:p ~ 60:0:30) than a oxidative addition/reductive elemination pathway (o:m:p = 12:76:12). • Sigma bond methathesis may be considered. • PhI(OAc)2 is a more selective and smooth oxidant than Cr2O7-. • PhI(OAc)2 favors the formation of C-O bonds from C-H bonds and not C-C homocoupling. Yoneyama, T.; Crabtree, R. H. J. Mol. Cat. A: Chem. 1996, 108, 35-40.

  16. About 10 years later… Dick, A. R.; Hull, K.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 2300-2301. Hartwell, G. E.; Lawrence, R. V.; Smas, M. J. J. Chem. Soc. Chem. Commun. 1970, 912.

  17. Melanie S. Sanford • She received her undergraduate degree in chemistry from Yale University in 1996 where she worked with Professor Robert Crabtree studying C-F bond functionalization. • She then moved to Caltech where she worked with Professor Robert Grubbs investigating the mechanism of ruthenium-catalyzed olefin metathesis reactions. • After receiving her PhD in 2001, she worked with Professor Jay Groves at Princeton University as an NIH post-doctoral fellow studying metalloporphyrin-catalyzed functionalization of olefins. • Melanie has been a professor at the University of Michigan since the summer of 2003.

  18. Her first paper about a Pd(II)/Pd(IV) oxidative functionalization of C-H bonds. • Very good yields were obtained without exclusion of air/moisture • She showed that the reaction tolerates variety of X = OAc, OMe, Br, Cl, OEt. • 2.5 equiv. PhI(OAc)2 gives the doubly acetylated products Dick, A. R.; Hull, K.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 2300-2301.

  19. Proposed catalytic cycle Using the cyclopalladated benzo[h]quinoline catalyst in the reaction without the oxidant does not form the product. Dick, A. R.; Hull, K.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 2300-2301.

  20. Precedents on the C-X bond formation in a similar mechanism. Han, R. Y.; Hillhouse, G. L. J. Am. Chem. Soc.1997, 119, 8135-8137 Williams, B. S.; Goldberg, K. I. J. Am. Chem. Soc. 2001, 123, 2576-2578

  21. Application of the concept to an sp3 carbon C-H bond. No β-hydroelimination product was observed due to Palladacycle rigidity. Desai, V. L.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 9542-9543

  22. High selectivity obtained at the ortho position. Kalyani, D.; Sanford, M. S. Org. Lett. 2005, 7, 4149-4172.

  23. An important observation : the selectivity of the reaction… Desai, V. L.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 9542-9543

  24. Other important observations… Oxidative cleavage of the C-O bond and C-H activation step are both highly stereoselective Desai, V. L.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 9542-9543

  25. Does Pd(IV) exist? Yamamoto, Y.; Kuwabara, S.; Matsuo, S.; Ohno, T.; Nishiyama, H.; Itoh, K. Organometallics, 2004, 23, 3898-3903. Canty, A. J.; Patel, J.; Rodemann, T.; Ryan, J. H. Skelton, B.W.; White, A. H. Organometallics, 2004, 23, 3466-3469.

  26. Does Pd(IV) exist? Càmpora, J.; Palma, P.; Del Rio, D.; Carmona, E.; Graiff, G.; Tiripiccio, A. Organometallics, 2003, 22, 3345-3349.

  27. To study the system, Pt(IV) is more suitable… Dick, A. R.; Kampf, J. W.; Sanford, S. M. Organometallics, 2005, 24, 482-485.

  28. Pt(II) is like Pd(II)… Huang, T. S.; Chen, J. T.; Lee, G. H.; Wang, Y. Organometallics, 1991, 10, 175-180.

  29. Design of new Pt(III) and Pt(IV) complexes Dick, A. R.; Kampf, J. W.; Sanford, S. M. Organometallics, 2005, 24, 482-485.

  30. Platinum (III) complex Treatment of this complex with 10 PhI(OAc)2 does not over oxidize it. Dick, A. R.; Kampf, J. W.; Sanford, S. M. Organometallics, 2005, 24, 482-485.

  31. Platinum (IV) complex synthesis With benzo[h] quinoline, with R = OMe, the ratio A:B is 2:1 and with R = OiPr A:B = 0.4:1. Stable (purified by chromatography) Dick, A. R.; Kampf, J. W.; Sanford, S. M. Organometallics, 2005, 24, 482-485.

  32. Platinum (IV) synthesis C-N ligand = Benzo[h]quinoline ROH = MeOH Dick, A. R.; Kampf, J. W.; Sanford, S. M. Organometallics, 2005, 24, 482-485.

  33. Various tests with the 8-Methylquinoline We see the same trend that the one observed with the palladium complex. When R is big for ROH, the ratio of product with 8-methylquinoline is less interesting than the one observed with small R group Dick, A. R.; Kampf, J. W.; Sanford, S. M. Organometallics, 2005, 24, 482-485.

  34. New Pd (IV) catalysts isolation Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791.

  35. New Pd (IV) X-Ray Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791.

  36. Reductive elimination step pathways Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791.

  37. Reductive elimination step pathways: first approach. • If mechanism A is the right one, thenthereshouldbe a radical solventeffect on the speed rate of the reaction. BUT!! In polar acetone : ε = 21, krel = 1.0 ± 0.1 In apolarsolvent : ε = 2.3 krel = 1.0 ± 0.1 Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791. Willams, B. S.; Goldberg, K. I. J. Am. Chem. Soc. 2001, 123, 2576-2578. Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791.

  38. Reductive elimination step pathways: Erying studies. • Erying studies gives a value of +4.2 ± 0.4 and -1.4 ± 1.9 in DMSO and CDCl3 for ∆S†. • Typically, we see a value of -13 to -49 for C-C and C-Se reductive elimination with Pd(IV) Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791. Canty, A. J.; Jin, H.; Skelton, B. W.; White, A. H. Inorg. Chem. 1998, 37, 3975-3978.

  39. Hammet studies with various X substituents. • Benzoate acts as a nucleophilic partner in the transformation (σ = -1.36 ± 0.04) • σ value of -1.5 with C-S coupling with Pd(II) which goes through a Mechanism type B • σ value of + 1.44 for reductive elimination from Pt(IV) (stabilization of the –OR moiety). Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791.

  40. Reductive elimination step pathways : crossover reactions. • With these observations, mechanism A can be ruled out. Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791.

  41. How to dicriminate between B and C? • Mechanism B and C are kinetically indistinguishable… Dick, A. R.; Kampf, J. W.; Sanford, S. M. J. Am. Chem. Soc. 2005, 127, 12790-12791.

  42. How can we push further the concept? Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047-14049.

  43. Possible mechanisms Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047-14049.

  44. Possible mechanisms Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047-14049.

  45. Important results Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047-14049.

  46. Important results • With these observations, mechanisms C and D can be ruled out. Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047-14049.

  47. Important results Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 14047-14049.

  48. Other methodologies: C-F bond formation. Hull, K. L.; Anani, Q. W.; Sanford, M. S. J. Am. Chem. Soc. 2007, 128, 7134-7135.

  49. Other methodologies: C-Cl, C-Br and C-I bond formation. Kalyani, D.; Dick, A. R.; Anani, W. Q.; Sanford, M. S. Org. Lett. 2006, 8, 2523-2526.

  50. Other methodologies: C-Cl, C-Br and C-I bond formation. Whitfield, S. R.; Sanford, M. S. J. Am. Chem. Soc. 2007, 129, 15142-15143.c

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