Phosphazene
From Wikipedia, the free encyclopedia
A phosphazene is any of a class of chemical compounds in which a phosphorus atom is covalently linked to a nitrogen atom by a double bond and to three other atoms or radicals by single bonds. Two examples are hexachlorocyclotriphosphazene and bis(triphenylphosphine)iminium chloride.
The corresponding polymers are polyphosphazenes.
[edit] Phosphazene bases
Phosphazene bases are strong non-metallic non-ionic and low-nucleophilic bases. They are stronger bases than regular amine or amidine bases such as Hünig's base or DBU. Protonation takes place at a doubly bonded nitrogen atom.
Two commercially available phosphazene bases are BEMP 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 after one of its inventors[1].
In one application t-Bu-P4 is employed in a nucleophilic addition converting the pival aldehyde to the alcohol[2] :
The active nucleophile is believed to be a highly reactive phosphazenium species with full negative charge on the arene sp2 carbon.
The related proazaphosphatrane superbases have a saturated P(NR)3 structure and protonation takes place at phosphorus.
[edit] External links
- Phosphazene bases Link
[edit] References
- ^ Peralkylated Polyaminophosphazenes - Extremely Strong, Neutral Nitrogen Bases Angewandte Chemie International Edition in English Volume 26, Issue 11, Date: November 1987, Pages: 1167-1169 Reinhard Schwesinger, Helmut Schlemper doi:10.1002/anie.198711671
- ^ Phosphazene base-promoted functionalization of aryltrimethylsilanes Koichi Suzawa, Masahiro Ueno, Andrew E. H. Wheatley and Yoshinori Kondo Chem. Commun., 2006, 4850 - 4852, doi:10.1039/b611090h
