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-tetraza-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-tetraza-1-phosphabicyclo[3.3.3]undecane
Identifiers
3D model (JSmol)
ChemSpider
UNII
  • 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
  • CN1CCN2CCN(P1N(CC2)C)C
Properties
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 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.

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

References
  1. Verkade, John G.; Urgaonkar, Sameer (2012). "Proazaphosphatrane". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00702.pub2. ISBN 978-0471936237.
  2. Schmidt, H.; Lensink, C.; Xi, S. K.; Verkade, J. G. (1989). "New Prophosphatranes: Novel intermediates to five-coordinate phosphatranes". Zeitschrift für Anorganische und Allgemeine Chemie. 578: 75–80. doi:10.1002/zaac.19895780109.
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