Dimeric Phosphazine Bases


Vol. 3, No. 1
Strong and Hindered Bases in Organic Synthesis
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Introduction / Phosphazene Bases / Verkade's Superbases / Traditional bases
Preservation of Reagents / Aldrich Schlenk-Type Glassware

 Phosphazene Bases Introduction / Monomeric Phosphazene Bases (P1)
Dimeric Phosphazene Bases (P2) / Tetrameric Phosphazene Bases (P4)

Dimeric Phosphazene Bases (P2)

Aldrich lists two P2 phosphazene bases (79416 and 79417), which differ with respect to their steric hindrance and basicity (Table 3).
 

Table 3. Order of Basicity of P2 Bases
Order of steric hindrance: P2-t-Bu >> P2-t-Et
Aldrich Product Number: 79416   79417
Basicity (MeCNpKBH+): 33.5   32.9

The phosphazene base P2-t-Bu is a solid at room temperature (m.p. 76 0C). and is available as a 2 M solution in THF (79416). P2-Et (79417) is offered as a stable, distillable liquid, which can easily be handled with syringe techniques. Both exhibit characteristics similar to those of DBU, but compared to DBU they are more hindered, much less sensitive towards hydrolysis, and 8.5-9 orders of magnitude more basic[2,3] See Table 4 for a list of our P2 bases with their properties, package size etc.
 

Table 4. Phospazene bases P2
79416

Phosphazene base P2-t-Bu solution

1-tert-Butyl-2,2,4,4,4-pentakis(dimethylamino)-2L5,4L5-catenadi(phosphazene)

tert-Butylimino-tris(dimethylamino)phosphorane

purum, ~2.0 M in THF   C14H39N7P2   Mr 367.5   [111324-03-9]   1 mL, 5 mL, 25 mL


 
79417

Phosphazene base P2-Et

1-Ethyl-2,2,4,4,4-pentakis(dimethylamino)-2L5,4L5-catenadi(phosphazene)

purum, 98.0% (NT)   C12H35N7P2   Mr 339.4   [165535-45-5]   1 mL, 5 mL


 

Applications: P2-Et 79417 is particularly suitable for E2-eliminations[3,4,5,6] being around 4 orders of magnitude more reactive than DBU. Deprotonations for spectroscopic investigations,[1] double bond shifts in vinyl sulfones,[7] and alkyl-lithium activation[8] have also been reported. The P2-t-Bu (79416) is particularly suitable for deprotonation (activation) of pronucleophiles. The P2 bases have attracted interest in the field of anionic polymerisation[8,9] and have been reported to support alkylation-,[10,11,12,13] michael addition-,[13,14] aldol condensation-,[13,15,16] and copper-induced coupling reactions.[17] Among the successfully converted low acidic substrates are alcohols,[10] phenols,[5] carbamates,[11] NH-acidic heterocycles,[6] phosphines,[12] benzyl sulfones,[13] glycin ester Schiff-bases,[14,15] a-azidoketones,[18] and N-alkylpyridinium salts.[3] Cinnamic esters,[13] chiral phenyloxiranes,[16] chiral amino acids,[14,15] biaryl thioethers,[17] and pyrazines[18] are thus efficiently synthesized.

References:

  1. Schwesinger, R. et al., Liebigs Ann. 1996, 1055.
  2. Angelaud, R., Landais, Y., Tetrahedron Lett. 1997, 38, 8841.
  3. Dega-Szafran, Z. et al., J. Phys. Org. Chem. 1999, 12, 39.
  4. Prinzbach, H. et al., Tetrahedron Lett. 1987, 28, 2517.
  5. Zundel, G. et al., J. Phys. Chem. 1996, 100, 9021; Sobczyk, L. et al., J. Chem. Res. (S) 1997, 151.
  6. Zundel, G. et al., J. Mol. Struct. 1997, 436, 103; Bauer, R., Zundel, G., J. Phys. Chem. A 2002, 106, 5828.
  7. Fuchs, P. L. et al., Tetrahedron Lett. 1996, 37, 5249; Fuchs, P. L. et al., Tetrahedron Lett. 1997, 38, 2601.
  8. Mvller, M. et al., Macromol. Symp. 1996 (Intern. Symposium on Ionic Polymerization 1995), 331; Molenberg, A., Mvller, M., Macromol. Chem. Phys. 1997, 198, 717.
  9. Memeger Jr., W. et al., Macromolecules 1996, 29, 6475, 8568.
  10. Schwesinger, R., Nachr. Chem. Tech. Lab. 1990, 38, 1214.
  11. Prinzbach, H. et al., Angew. Chem. Int Ed. Engl. 1989, 28, 1253.
  12. Uhlig, F. et al., Phosphorus, Sulfur & Silicon 1993, 81, 155; Uhlig, F. et al., Phosphorus, Sulfur & Silicon 1993, 84, 181.
  13. Najera, C. et al., J. Org. Chem. 2002, 67, 5216.
  14. Solladii-Cavallo, A. et al., Synlett. 1997, 217.
  15. Solladii-Cavallo, A. et al., Synlett. 2000, 327.
  16. Solladii-Cavallo, A. et al., Eur. J. Org. Chem. 2000, 1077; Solladii-Cavallo, A. et al., Tetrahedron Lett. 2000, 41, 7309.
  17. Palomo, C. et al., Tetrahedron Lett. 2000, 41, 1283.
  18. Winterfeldt, E. et al., Eur. J. Org. Chem. 1998, 2811.