In chemistry, the Verkade base (or Verkade superbase) is a powerful superbase with the formula P(MeNCH<sub>2</sub>CH<sub>2</sub>)<sub>3</sub>N. 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. Diverse analogues of the Verkade base are known, e.g. with isopropyl groups in place of methyl.
The Verkade base is generated by the reaction of N,N,N-trimethyltren with tris(dimethylamino)phosphine:
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.
The conjugate acid [HP(MeNCH<sub>2</sub>CH<sub>2</sub>)<sub>3</sub>N]<sup>+</sup> of the base has a pK<sub>a</sub> of 32.9 in acetonitrile. For comparison, the conjugate acid of triethylamine has a pK<sub>a</sub> near 17 in acetonitrile. Owing to its ability to deprotonate weak carbon acids, the Verkade base catalyzes a variety of condensation reactions.
Phosphazenes are phosphorus(V) derivatives with the formula RN=P(NR<sub>2</sub>)<sub>3</sub>.