Verkade base

Verkade base
Names
	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, a Verkade base (or Verkade superbase) is a 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 attacks the Verkade base at phosphorus, inducing 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]⁺ has a pK_a of 32.9 in acetonitrile. For comparison, the conjugate acid of triethylamine has a pK_a's 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. They are about 10¹⁰ more basic than the Verkade base.[3]

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References

Verkade, John G.; Urgaonkar, Sameer (2012). "Proazaphosphatrane". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00702.pub2.
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.
Saame, Jaan; Rodima, Toomas; Tshepelevitsh, Sofja; Kütt, Agnes; Kaljurand, Ivari; Haljasorg, Tõiv; Koppel, Ilmar A.; Leito, Ivo (2016). "Experimental Basicities of Superbasic Phosphonium Ylides and Phosphazenes". The Journal of Organic Chemistry. 81 (17): 7349–7361. doi:10.1021/acs.joc.6b00872. PMID 27392255.

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[1] Verkade, John G.; Urgaonkar, Sameer (2012). "Proazaphosphatrane". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00702.pub2.

[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.

[3] Saame, Jaan; Rodima, Toomas; Tshepelevitsh, Sofja; Kütt, Agnes; Kaljurand, Ivari; Haljasorg, Tõiv; Koppel, Ilmar A.; Leito, Ivo (2016). "Experimental Basicities of Superbasic Phosphonium Ylides and Phosphazenes". The Journal of Organic Chemistry. 81 (17): 7349–7361. doi:10.1021/acs.joc.6b00872. PMID 27392255.