PEPPSI

PEPPSI
Not to be confused with Pepsi.
General structure of PEPPSI catalysts. R stands for a small organic fragment.

PEPPSI is an abbreviation for pyridine-enhanced precatalyst preparation stabilization and initiation. It refers to a group of chemical catalysts developed around 2005 by Prof. Michael G. Organ and co-workers at York University,[1][2] which can accelerate various aminations and cross-coupling reactions. In comparison to many alternative palladium catalysts, PEPPSI catalysts are stable to air and moisture and are relatively easy to synthesize and handle.

Contents

Structure and synthesis

In the basic structure of PEPPSI, R is usually a methyl (CH3, Me), ethyl (C2H5, Et), isopropyl (C3H7, iPr) or isopentyl (C5H11, iPent) group, and the resulting catalysts are thus labeled as PEPPSI-IMes, PEPPSI-IEt, PEPPSI-IPr, and PEPPSI-IPent, respectively, with or without "Pd-" added in front.[3] Contrary to common palladium-based catalysts, such as tetrakis(triphenylphosphine)palladium(0), PEPPSI is stable to exposure to air[4] and moisture.[5] Even heating in dimethyl sulfoxide at 120 °C for hours does not result in significant decomposition or neutralization of PEPPSI catalysts.[6]

The synthesis and structure of PEPPSI catalysts were presented in 2005[6][7] and published in 2006.[8][9] PEPPSI catalysts are based on an organometallic complex palladium N-heterocyclic-carbene (NHC). They can be obtained by reacting imidazolium salt, palladium(II) chloride, and potassium carbonate in a 3-chloropyridine solvent, under vigorous stirring at 80 °C for 16 hours in air. The yield of PEPPSI in this reaction is 97–98%.[9][6]

Properties and applications

PEPPSI can catalyze various aminations and cross-coupling reactions including Negishi coupling,[4] Suzuki coupling, Kumada coupling,[10] Buchwald–Hartwig amination and Heck reaction.[11][6] In Negishi coupling, it promotes reaction of alkyl halides, aryl halides or alkyl sulfonates with alkylzinc halides,[12] and the important advantage of PEPPSI over alternative catalysts is that the reaction can be carried out in a general chemical laboratory, without a glove box. PEPPSI contains palladium in Pd(II) form and thus is a "precatalyst", that is palladium in it should be reduced to the active Pd(0) form. This is usually achieved automatically in the reaction being activated. Once activated, PEPPSI becomes rather sensitive to air and moisture.[4][13][14]

Suzuki coupling (left) and Buchwald Hartwig reaction (right) can be activated by PEPPSI

References

  1. ^ Organ, M. G. Rational catalyst design and its application in sp3-sp3 couplings. Presented at the 230th National Meeting of the American Chemical Society, Washington, DC, 2005; Abstract 308.
  2. ^ Hadei, Niloufar; Kantchev, Eric Assen B.; O'Brie, Christopher J.; Organ, Michael G. (2005). "The First Negishi Cross-Coupling Reaction of Two Alkyl Centers Utilizing a Pd−N-Heterocyclic Carbene (NHC) Catalyst†". Organic Letters 7 (17): 3805. doi:10.1021/ol0514909. PMID 16092880. 
  3. ^ Nasielski, Joanna; Hadei, Nilofaur; Achonduh, George; Kantchev, Eric Assen B.; O'Brien, Christopher J.; Lough, Alan; Organ, Michael G. (2010). "Structure-Activity Relationship Analysis of Pd-PEPPSI Complexes in Cross-Couplings: A Close Inspection of the Catalytic Cycle and the Precatalyst Activation Model". Chemistry - A European Journal 16 (35): 10844. doi:10.1002/chem.201000138. 
  4. ^ a b c Jie Jack Li, E. J. Corey Name reactions for homologations, Part 1, John Wiley and Sons, 2009, ISBN 047008507X p. 74
  5. ^ Valente, Cory; Belowich, Matthew E.; Hadei, Niloufar; Organ, Michael G. (2010). "Pd-PEPPSI Complexes and the Negishi Reaction". European Journal of Organic Chemistry: n/a. doi:10.1002/ejoc.201000359. 
  6. ^ a b c d PEPPSI Catalysts, Sigma Aldrich
  7. ^ Organ, M. G. Rational catalyst design and its application in sp3-sp3 couplings. Presented at the 230th National Meeting of the American Chemical Society, Washington, DC, 2005; Abstract 308.
  8. ^ Issue cover of Chemistry – A European Journal, June 2006
  9. ^ a b O'Brien, Christopher J.; Kantchev, Eric Assen B.; Valente, Cory; Hadei, Niloufar; Chass, Gregory A.; Lough, Alan; Hopkinson, Alan C.; Organ, Michael G. (2006). "Easily Prepared Air- and Moisture-Stable Pd–NHC (NHC=N-Heterocyclic Carbene) Complexes: A Reliable, User-Friendly, Highly Active Palladium Precatalyst for the Suzuki–Miyaura Reaction". Chemistry - A European Journal 12 (18): 4743. doi:10.1002/chem.200600251. 
  10. ^ Lutz Ackermann Modern arylation methods, Wiley-VCH, 2009, ISBN 3527319379 p. 52
  11. ^ S. V. Luis, Eduardo García-Verdugo Chemical Reactions and Processes Under Flow Conditions, Royal Society of Chemistry, 2010, ISBN 0854041923 p. 153
  12. ^ Catherine S. J. CazinHeterocyclic Carbenes in Transition Metal Catalysis and Organocatalysis, Springer, 2010, ISBN 904812865X pp. 169–173
  13. ^ Organ, MG; Avola, S; Dubovyk, I; Hadei, N; Kantchev, EA; O'Brien, CJ; Valente, C (2006). "A User-Friendly, All-Purpose Pd–NHC (NHC=N-Heterocyclic Carbene) Precatalyst for the Negishi Reaction: A Step Towards a Universal Cross-Coupling Catalyst". Chemistry (Weinheim an der Bergstrasse, Germany) 12 (18): 4749–55. doi:10.1002/chem.200600206. PMID 16568493. 
  14. ^ PEPPSI™: Instructions for Use, Sigma-Aldrich

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