Synthesis and Reactivity of N-Phosphanyl Phosphazenes

Chemoselective Staudinger Reactivity of Bis(azido)phosphines Supported with a π-Donating Imidazolin-2-iminato Ligand

“…Salt metathesis reactions of IPrNPCl 2 ( 1 ) with an excess of NaN 3 in acetonitrile, followed by an extraction using benzene, allowed for the facile production and the isolation of IPrNP­(N 3 ) 2 ( 2 ). Trimethylsilylazide (Me 3 SiN 3 ) was also explored as a method of synthesizing compound 2 but was found to concurrently generate mixtures of 2 (δ P = 123), a transient species IPrP­(N 3 )Cl ( 2 ′; δ P = 148), and a bis­(azido)­(trimethylsilyliminyl)­phosphine 3 (IPrNP­(NSiMe 3 )­(N 3 ) 2 ; δ P = −28). , The ambiphilic nature of 2 was noted by the spontaneous decomposition to a complex mixture of species in THF, likely containing oligomers of P–(N–P) n motifs via Staudinger reactions, while decomposition of 2 was much slower in less polar aromatic solvents (i.e., benzene or toluene). Using aromatic solvents allowed for longer time scale reactions to be performed at or below room temperature (i.e., in the syntheses of 4Ch , 7 ).…”

“…16 The ambiphilic nature of azidophosphines is also demonstrated by their ability to form a R 2 P−N�PR 3 motif or their reaction with an electrophilic azide to produce R 2 P(NPh)(N 3 ). 8,16,17 Bis-(azido)phosphines are scarcely reported due to poor thermal stability but have been isolated either using N-aryl 18 or cationic imidazolium ligands. 19 Phosphorus(V) bis(azido)phosphines are intriguing because the conversion of the first azide to a strongly π-donating phosphinimine has been reported to influence the ability of the remaining azide to perform a subsequent Staudinger reaction.…”

“…The use of an electron-deficient azide, more nucleophilic phosphine, or more polar solvents have all been demonstrated to increase the reaction rate, while electron-donating groups on the azide hinder the reaction . Staudinger reactions of P­(III) (azido)­phosphines (R 2 P–N 3 ) have also been reported, but their ambiphilic nature can result in spontaneous decomposition to oligomeric phosphazenes (RPN) n , and the reactivity can be attenuated by steric protection or by electron delocalization . The ambiphilic nature of azidophosphines is also demonstrated by their ability to form a R 2 P–NPR 3 motif or their reaction with an electrophilic azide to produce R 2 P­(NPh)­(N 3 ). ,, Bis­(azido)­phosphines are scarcely reported due to poor thermal stability but have been isolated either using N-aryl or cationic imidazolium ligands .…”