Verkade base

Verkade base

File:P(MeNC2H4)3N.svg
Names
Preferred IUPAC name 2,8,9-Trimethyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane
Identifiers
CAS Number	120666-13-9
3D model (JSmol)	Interactive image
ChemSpider	3397532
ECHA InfoCard
E number
PubChem CID	4186723
UNII	LK9MJR52XE
CompTox Dashboard (EPA)	{{#property:P3117}}
InChI InChI=1S/C9H21N4P/c1-10-4-7-13-8-5-11(2)14(10)12(3)6-9-13/h4-9H2,1-3H3 Key: PCYSWBQHCWWSFW-UHFFFAOYSA-N
SMILES CN1CCN2CCN(P1N(CC2)C)C
Properties
Chemical formula	C9H21N4P
Molar mass	216.269 g·mol−1
Appearance	colorless oil
Boiling point	263.9 °C (507.0 °F; 537.0 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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. Diverse analogues of the Verkade base are known, e.g. with isopropyl groups in place of methyl.

Synthesis and reactions

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

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.

File:VerkadeProtn.svg

Protonation of Verkade base.

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

Related compounds

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