Phosphine boranes azides

The synthesis of phosphorous-functionalized click ligands also requires special conditions. Phosphine building blocks need be protected as either the corresponding borane complex (l-2a and 4-5a) or oxide (l-2b and 4—5b) in order to prevent an undesirable Staudinger reaction with the azide synthons (Scheme 1). A range of bi-and tridentate P,N click ligands have been synthesized, and the free clickphines (3 and 6) are liberated by a final deprotection of the phosphine group with either DABCO in the case of the borane complexes [86-90] or reduction with tri-chlorosilane [88-92] in the case of the phosphine oxides. 

Phosphorylated 1,2,3-triazoles have been obtained in excellent yields via the 1,3-cycloaddition of m-phosphoryl azides to activated internal alkynes such as acetylenedicarboxylate and sodium azide to tetramethyl acetylenediphosphonate. These reactions proceed in water without any cosolvent or additive [100]. Moreover, sUyl-protected borane complexes of phosphinoalkynes may give rise to chiral and achiral P-stereogenic l,2,3-triazolyl-4-phosphines in moderate to good yields [101]. 

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