Verkade base

Verkade base
Names
	Preferred IUPAC name 2,8,9-Trimethyl-2,5,8,9-tetraza-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

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.

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.

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.

References

^ Verkade, John G.; Urgaonkar, Sameer (2012). "Proazaphosphatrane". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00702.pub2. ISBN 978-0471936237.
^ 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.

[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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