Non-nucleophilic base

As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile. Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions. Typical non-nucleophilic bases are bulky, such that protons can attach to the basic center but alkylation and complexation is inhibited.

Non-nucleophilic bases

A variety of amines and nitrogen heterocycles are useful bases of moderate strength

N,''N-Diisopropylethylamine, pK_a = 10.75
1,8-Diazabicycloundec-7-ene - useful for E2 elimination reactions, pK_a = 13.5
1,5-Diazabicyclonon-5-ene - comparable to DBU
2,6-Di-tert-butylpyridine, a weak non-nucleophilic base pK_a = 3.58
Phosphazene bases, such as t''-Bu-P₄

Non-nucleophilic bases of high strength are usually anions. For these species, the pK_as of the conjugate acids are around 35–40.

Lithium diisopropylamide, pK_a = 36
Silicon-based amides, such as sodium and potassium bisamide
Lithium tetramethylpiperidide

Other strong non-nucleophilic bases are sodium hydride and potassium hydride. These compounds are dense, salt-like materials that are insoluble and operate by surface reactions.
Some reagents are of high basicity but of modest but not negligible nucleophilicity. Examples include sodium tert-butoxide and potassium tert-butoxide.

Example

The following diagram shows how the hindered base, lithium diisopropylamide, is used to deprotonate an ester to give the enolate in the Claisen ester condensation, instead of undergoing a nucleophilic substitution.
This reaction is commonly used to generate enolates.