161118-69-0Relevant articles and documents
Synthesis of electron-rich sterically hindered P1 phosphazene bases by the staudinger reaction
Alexandrova, Anastasia V.,Masek, Tomas,Polyakova, Svetlana M.,Cisarova, Ivana,Saame, Jaan,Leito, Ivo,Lyapkalo, Ilya M.
, p. 1811 - 1823 (2013/04/10)
The synthesis of electron-rich P1 phosphazene bases with a sterically protected basic center by a Staudinger reaction is reported. The initial products of the reaction between peralkylated triaminophosphanes and bulky alkyl azides, phosphazides 1a-f, were isolated in all cases in good to quantitative yield. The structures of 1d and 1e were confirmed by single-crystal X-ray diffraction. Acidic hydrolysis of pyrrolidino-substituted phosphazide (pyrr)3PN3tBu 1d led to the quantitative formation of aminophosphonium salt (pyrr)3PNH2+· BF4- 8, a direct precursor to a Schwesinger's "building block" synthetic unit. Thermally induced denitrogenation of the phosphazides, which is the second step performed in most cases under solvent-free conditions gave P1 phosphazene bases 2a-f in moderate to excellent yields. A "one-pot" two-step synthesis of phosphazene bases from commercially available triaminophosphanes was discovered. Most of the syntheses were performed on a large laboratory scale. The basicities of the newly synthesized bases 2e and 2f were determined. X-ray crystal structures were obtained for base 2e and for protonated species 2d·HBF4, 2e·HBF4, and 2f·HOTs, which provided the crucial geometrical parameters around the basic center. A rationale for the higher basicity of the pyrrolidino- (pyrr)3P=NR than the piperidino- (pip)3P=NR phosphazenes is presented. A Staudinger reaction was successfully used for the synthesis of a number of sterically congested electron-rich P1 phosphazene bases in moderate to quantitative yield. The intermediate phosphazides were isolated and characterized in all cases; their application in the preparation of higher-order phosphazenes is described. Copyright
