Verkade base

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.

Verkade base

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
PubChem CID	4186723
UNII	LK9MJR52XE
CompTox Dashboard (EPA)	DTXSID90400494
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

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.

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.