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Verkade base

Chemical compound From Wikipedia, the free encyclopedia

Verkade base
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In chemistry, the Verkade base (or Verkade superbase) is a powerful superbase with the formula P(MeNCH2CH2)3N. A colorless oil, it is an aminophosphine although its inventor John Verkade called it proazaphosphatrane. The trimethyl derivative or 2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane is the simplest.[1] Diverse analogues of the Verkade base are known, e.g. with isopropyl groups in place of methyl.

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Synthesis and reactions

The Verkade base is generated by the reaction of N,N,N-trimethyltren with tris(dimethylamino)phosphine:[2]

P(NMe2)3 + (MeNHCH2CH2)3N → P(MeNCH2CH2)3N + 3 Me2NH

The principal reaction of the Verkade base is protonation. The proton is attacked by the Verkade base at the phosphorus atom within, which induces the formation of a transannular P-N bond. The product exemplifies the structure of an atrane.

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Protonation of Verkade base.

The conjugate acid [HP(MeNCH2CH2)3N]+ of the base has a pKa of 32.9 in acetonitrile. For comparison, the conjugate acid of triethylamine has a pKa near 17 in acetonitrile. Owing to its ability to deprotonate weak carbon acids, the Verkade base catalyzes a variety of condensation reactions.

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Phosphazenes are phosphorus(V) derivatives with the formula RN=P(NR2)3.

References

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