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Superbase

From Wikipedia, the free encyclopedia
For similarly named articles, seeSuperbase (disambiguation).
Acids and bases
Diagrammatic representation of the dissociation of acetic acid in aqueous solution to acetate and hydronium ions.
Acidtypes
Basetypes

Asuperbaseis acompoundthat has a particularly high affinity forprotons.Superbases are of theoretical interest and potentially valuable inorganic synthesis.[1][2]Superbases have been described and used since the 1850s.[3][4]

Definitions

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GenericallyIUPACdefines a superbase as a "compound having a very highbasicity,such aslithium diisopropylamide."[5]Superbases are often defined in two broad categories,organicandorganometallic.

Organic superbases are charge-neutral compounds with basicities greater than that ofproton sponge(pKBH+= 18.6 in MeCN). "[1]In a related definition: any species with a higher absoluteproton affinity(APA = 245.3 kcal/mol) and intrinsic gas phase basicity (GB = 239 kcal/mol) than proton sponge.[6]Common superbases of this variety featureamidine,guanidine,andphosphazenefunctional groups. Strong superbases can be designed by utilizing various approaches[7][8][9]to stabilize the conjugate acid, up to the theoretical limits of basicity.[10]

Organometallic superbases, sometimes called Lochmann–Schlosser superbases, result from the combination ofalkali metalalkoxidesandorganolithiumreagents.[11]Caubère defines superbases as "bases resulting from a mixing of two (or more) bases leading to new basic species possessing inherent new properties. The termsuperbasedoes not mean a base is thermodynamically and/or kinetically stronger than another, instead it means that a basic reagent is created by combining the characteristics of several different bases. "[12]

Organic superbases

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Protonation ofVerkade base.Its conjugate acid has a pKaof 32.9 inacetonitrile.[13]

Organic superbases are mostly charge-neutral,nitrogencontaining species, where nitrogen act as a proton acceptor. These include thephosphazenes,phosphanes,amidines,andguanidines.Other organic compounds that meet the physicochemical or structural definitions of 'superbase' include protonchelatorslike the aromaticproton spongesand thebispidines.[14][15]Multicyclicpolyamines,likeDABCOmight also be loosely included in this category.[4]Phosphanesand carbodiphosphoranes are also strong organosuperbases.[16][17][18][19]

Despite enormous proton affinity, many organosuperbases can exhibit lownucleophilicity.

Superbases are used inorganocatalysis.[20][21]

Organometallic

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Deprotonation using LDA[22].

Organometallic compounds ofelectropositivemetals are superbases, but they are generally strong nucleophiles. Examples includeorganolithiumand organomagnesium (Grignard reagent) compounds. Another type of organometallic superbase has a reactive metal exchanged for a hydrogen on aheteroatom,such asoxygen(unstabilizedalkoxides) or nitrogen (metalamidessuch aslithium diisopropylamide).[23]

TheSchlosser base(or Lochmann-Schlosser base), the combination ofn-butyllithiumandpotassiumtert-butoxide,is commonly cited as a superbase.n-Butyllithiumandpotassiumtert-butoxideform a mixed aggregate of greater reactivity than either component reagent.[24]

Inorganic

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Inorganic superbases are typicallysalt-like compounds with small, highly charged anions, e.g.lithium hydride,potassium hydride,andsodium hydride.Such species are insoluble, but the surfaces of these materials are highly reactive andslurriesare useful in synthesis.Caesium oxideis probably the strongest base according to quantum-chemical calculations.[10]

See also

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References

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  1. ^abPuleo, Thomas R.; Sujansky, Stephen J.; Wright, Shawn E.; Bandar, Jeffrey S. (2021). "Organic Superbases in Recent Synthetic Methodology Research".Chemistry – A European Journal.27(13): 4216–4229.doi:10.1002/chem.202003580.PMID32841442.S2CID221326865.
  2. ^Pozharskii, Alexander F.; Ozeryanskii, Valery A. (2012). "Proton Sponges and Hydrogen Transfer Phenomena".Mendeleev Communications.22(3): 117–124.doi:10.1016/j.mencom.2012.05.001.
  3. ^"BBC - h2g2 - History of Chemistry - Acids and Bases".Retrieved2009-08-30.
  4. ^abSuperbases for Organic SynthesisEd. Ishikawa, T., John Wiley and Sons, Ltd.: West Sussex, UK. 2009.
  5. ^IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "superacid".doi:10.1351/goldbook.S06135
  6. ^Raczynska, Ewa D.; Decouzon, Michele; Gal, Jean-Francois; Maria, Pierre-Charles; Wozniak, Krzysztof; Kurg, Rhio; Carins, Stuart N. (3 June 2010). "ChemInform Abstract: Superbases and Superacids in the Gas Phase".ChemInform.31(33): no.doi:10.1002/chin.200033267.
  7. ^Maksić, Zvonimir B.; Kovačević, Borislav; Vianello, Robert (2012-10-10)."Advances in Determining the Absolute Proton Affinities of Neutral Organic Molecules in the Gas Phase and Their Interpretation: A Theoretical Account".Chemical Reviews.112(10): 5240–5270.doi:10.1021/cr100458v.ISSN0009-2665.PMID22857519.
  8. ^Formica, Michele; Rozsar, Daniel; Su, Guanglong; Farley, Alistair J. M.; Dixon, Darren J. (2020). "Bifunctional Iminophosphorane Superbase Catalysis: Applications in Organic Synthesis".Accounts of Chemical Research.53(10): 2235–2247.doi:10.1021/acs.accounts.0c00369.PMID32886474.S2CID221503523.
  9. ^Vazdar, Katarina; Margetić, Davor; Kovačević, Borislav; Sundermeyer, Jörg; Leito, Ivo; Jahn, Ullrich (2021)."Design of Novel Uncharged Organic Superbases: Merging Basicity and Functionality".Accounts of Chemical Research.54(15): 3108–3123.doi:10.1021/acs.accounts.1c00297.PMID34308625.S2CID236430307.
  10. ^abKulsha, Andrey; Ragoyja, Ekaterina; Ivashkevich, Oleg (2022). "Strong Bases Design: Predicted Limits of Basicity".J. Phys. Chem. A.126(23): 3642–3652.Bibcode:2022JPCA..126.3642K.doi:10.1021/acs.jpca.2c00521.PMID35657384.S2CID249313043.
  11. ^Klett, Jan (2021)."Structural Motifs of Alkali Metal Superbases in Non‐coordinating Solvents".Chemistry – A European Journal.27(3): 888–904.doi:10.1002/chem.202002812.PMC7839563.PMID33165981.
  12. ^Caubère, P (1993). "Unimetal Super Bases".Chemical Reviews.93(6): 2317–2334.doi:10.1021/cr00022a012.
  13. ^Verkade, John G.; Urgaonkar, Sameer (2012). "Proazaphosphatrane".Encyclopedia of Reagents for Organic Synthesis.doi:10.1002/047084289X.rn00702.pub2.ISBN978-0471936237.
  14. ^Pozharskii, Alexander F.; Ozeryanskii, Valery A. (2012). "Proton Sponges and Hydrogen Transfer Phenomena".Mendeleev Communications.22(3): 117–124.doi:10.1016/j.mencom.2012.05.001.
  15. ^Barić, Danijela; Dragičević, Ivan; Kovačević, Borislav (2013-04-19)."Design of Superbasic Guanidines: The Role of Multiple Intramolecular Hydrogen Bonds".The Journal of Organic Chemistry.78(8): 4075–4082.doi:10.1021/jo400396d.ISSN0022-3263.PMID23445344.
  16. ^Kovačević, Borislav; Maksić, Zvonimir B. (2006)."High basicity of phosphorus–proton affinity of tris-(tetramethylguanidinyl)phosphine and tris-(hexamethyltriaminophosphazenyl)phosphine by DFT calculations".Chemical Communications(14): 1524–1526.doi:10.1039/b517349c.ISSN1359-7345.PMID16575448.
  17. ^Ullrich, Sebastian; Kovačević, Borislav; Xie, Xiulan; Sundermeyer, Jörg (2019)."Phosphazenyl Phosphines: The Most Electron-Rich Uncharged Phosphorus Brønsted and Lewis Bases".Angewandte Chemie International Edition.58(30): 10335–10339.doi:10.1002/anie.201903342.ISSN1521-3773.PMID31037821.S2CID140304424.
  18. ^Mehlmann, Paul; Mück-Lichtenfeld, Christian; Tan, Tristan T. Y.; Dielmann, Fabian (2017-05-02)."Tris(imidazolin-2-ylidenamino)phosphine: A Crystalline Phosphorus(III) Superbase That Splits Carbon Dioxide".Chemistry - A European Journal.23(25): 5929–5933.doi:10.1002/chem.201604971.PMID27779340.
  19. ^Ullrich, Sebastian; Kovačević, Borislav; Koch, Björn; Harms, Klaus; Sundermeyer, Jörg (2019)."Design of non-ionic carbon superbases: second generation carbodiphosphoranes".Chemical Science.10(41): 9483–9492.doi:10.1039/C9SC03565F.ISSN2041-6520.PMC6993619.PMID32055322.
  20. ^MacMillan, David W. C. (2008). "The advent and development of organocatalysis".Nature.455(7211): 304–308.Bibcode:2008Natur.455..304M.doi:10.1038/nature07367.PMID18800128.S2CID205215034.
  21. ^Ishikawa, Tsutomu, ed. (2009).Superbases for Organic Synthesis: Guanidines, Amidines, Phosphazenes and Related Organocatalysts.John Wiley & Sons.doi:10.1002/9780470740859.ISBN9780470740859.
  22. ^Jianshe Kong, Tao Meng, Pauline Ting, and Jesse Wong (2010)."Preparation of Ethyl 1-Benzyl-4-Fluoropiperidine-4-Carboxylate".Organic Syntheses.87:137.doi:10.15227/orgsyn.087.0137.{{cite journal}}:CS1 maint: multiple names: authors list (link)
  23. ^Trofimov, B.A.; Schmidt, E.Yu. (2022). "Superbases in Organic Synthesis".Chemical Problems.20(4): 325–340.doi:10.32737/2221-8688-2022-3-325-340.S2CID253832800.
  24. ^Schlosser, M. (1988)."Superbases for organic synthesis".Pure Appl. Chem.60(11): 1627–1634.doi:10.1351/pac198860111627.
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