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Phosphazene

1=Organophosphorus compound with pentavalent phosphorus having P=N bonds

1=Organophosphorus compound with pentavalent phosphorus having P=N bonds

Phosphazenes refer to various classes of organophosphorus compounds featuring phosphorus(V) with a double bond between P and N. One class of phosphazenes have the formula . These phosphazenes are also known as iminophosphoranes and phosphine imides. They are superbases.

BEMP and ''t''-Bu-P4

Well known phosphazene bases are BEMP (2-tert-Butylimino-2-diEthylamino-1,3-diMethylperhydro-1,3,2-diazaPhosphorine) with an acetonitrile pKa of the conjugate acid of 27.6 and the phosphorimidic triamide t-Bu-P4 (pKBH+ = 42.7) also known as Schwesinger base. BEMP and P4-t-Bu|t-Bu-P4 have attracted attention because they are low-nucleophilic, which precludes their participating in competing reactions. Being non-ionic ("charge-neutral"), they are soluble in nonpolar solvents. Protonation takes place at a doubly bonded nitrogen atom. The pKa's of , where R = Me and pyrrolidinyl, are 42.7 and 44, respectively. These are the highest pKa recorded for the conjugate acid of charge-neutral molecular base.

P4-t-Bu_Strukturformel.svg|t-Bu-P4 BEMP Phosphazene.svg|BEMP

In one implementation, t-Bu-P4 catalyzes the conversion of pivaldehyde to the alcohol: Phosphazene bases have been used as basic titrants in non-aqueous acid–base titrations.

Other classes of phosphazenes

Also called phosphazenes are represented with the formula , where X = halogen, alkoxy group, amide and other organyl groups. One example is hexachlorocyclotriphosphazene . Bis(triphenylphosphine)iminium chloride is also referred to as a phosphazene, where Ph = phenyl group. The present article focuses on those phosphazenes with the formula .

References

References

  1. ''Superbases for Organic Synthesis: Guanidines, Amidines, Phosphazenes and Related Organocatalysts'' Tsutomu Ishikawa {{ISBN. 978-0-470-51800-7
  2. (1987). "Peralkylated Polyaminophosphazenes— Extremely Strong, Neutral Nitrogen Bases". Angewandte Chemie International Edition in English.
  3. (1993). "How Strong and How Hindered Can Uncharged Phosphazene Bases Be?". Angewandte Chemie International Edition in English.
  4. (2016). "Experimental Basicities of Superbasic Phosphonium Ylides and Phosphazenes". The Journal of Organic Chemistry.
  5. (2006). "Phosphazene base-promoted functionalization of aryltrimethylsilanes". Chemical Communications.
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nitrogen-compounds non-nucleophilic-bases superbases phosphazenes
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