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A superbase is a compound that has a particularly high affinity for protons. Superbases are of theoretical interest and potentially valuable in organic synthesis. Superbases have been described and used since the 1850s. Superbases for Organic Synthesis Ed. Ishikawa, T., John Wiley and Sons, Ltd.: West Sussex, UK. 2009.
Organic superbases are charge-neutral compounds with basicities greater than that of proton sponge (1,8-bis(dimethylamino)naphthalene, pKBH+ = 18.6 in acetonitrile). In a related definition: any species with a higher absolute proton affinity (APA = 245.3 kcal/mol) and intrinsic gas phase basicity (GB = 239 kcal/mol) than proton sponge. Common superbases of this variety feature amidine, guanidine, and phosphazene functional groups. Strong superbases can be designed by utilizing various approaches to stabilize the conjugate acid, up to the theoretical limits of basicity.
Organometallic superbases, sometimes called Lochmann–Schlosser superbases, result from the combination of alkali metal and organolithium reagents. Caubère defines superbases as "bases resulting from a mixing of two (or more) bases leading to new basic species possessing inherent new properties. The term superbase does 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."
Despite enormous proton affinity, many organosuperbases can exhibit low Nucleophile.
Superbases are used in organocatalysis.
The Schlosser base (or Lochmann-Schlosser base), the combination of N-butyllithium and potassium tert-butoxide, is commonly cited as a superbase. n-Butyllithium and potassium tert-butoxide form a mixed aggregate of greater reactivity than either component reagent.
Organic superbases
Organic superbases are mostly charge-neutral, nitrogen containing species, where nitrogen act as a proton acceptor. These include the phosphazenes, organophosphine, amidines, and guanidines. Other organic compounds that meet the physicochemical or structural definitions of 'superbase' include proton Chelation like the aromatic proton sponges and the . Multicyclic , like DABCO might also be loosely included in this category. Phosphine and carbodiphosphoranes are also strong organosuperbases .
(2025). 9780470740859, John Wiley & Sons. ISBN 9780470740859
Organometallic
Organometallic compounds of electropositive metals are superbases, but they are generally strong nucleophiles. Examples include organolithium and organomagnesium (Grignard reagent) compounds. Another type of organometallic superbase has a reactive metal exchanged for a hydrogen on a heteroatom, such as oxygen (unstabilized ) or nitrogen (metal Azanide such as lithium diisopropylamide).
Inorganic
Inorganic superbases are typically salt-like compounds with small, highly charged anions, e.g., lithium hydride, potassium hydride, and sodium hydride. Such species are insoluble, but the surfaces of these materials are highly reactive and slurries are useful in synthesis. Caesium monoxide is probably the strongest base according to quantum-chemical calculations.
See also
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