Reactions of IrHCl₂(PPh₃)₂{P(OEt)₃} with Organic Azides: Formation of Aminophosphonium Salts

Abstract

Aminophosphonium salts [Ph3PN(H)R]BPh4 (1) [R = C6H5CH2 (1a), 4‐CH3C6H4CH2 (1b), C6H5 (1c)] were obtained by allowing hydride IrHCl2(PPh3)2{P(OEt)3} to react first with triflic acid and then with the organic azide RN3. The compounds were characterized spectroscopically and by X‐ray crystal structure determination of [Ph3PN(H)CH2C6H4‐4‐CH3]BPh4 (1b). A reaction path for the formation of aminophosphonium cations is also proposed.

Significance of reagent addition sequence in the amidation of carboxylic acids mediated by PPh3 and I2

“…When benzylamine was added to the PPh 3 -I 2 mixture, followed by addition of Et 3 N then benzoic acid (method B), no trace of the corresponding amide could be detected either. Nevertheless, we were able to isolate a major component from this reaction which was identied as (benzylamino)triphenylphosphonium iodide 11 based on spectroscopic analysis. To our delight, it was found that when the amine base was added in the last step (methods C and D), N-benzylbenzamide was obtained quantitatively within 10 min.…”

“…In method B, treatment of the intermediates I with benzylamine led to a rapid formation of solid precipitate. 31 P{H} NMR spectrum of the solution showed an appearance of a 31 P signal at 39.20 ppm (major) as well as two minor peaks at À18.70 and 35.50 ppm (broad) which could be attributed to the presence of aminophosphonium iodide, 11 and possibly a pentavalent phosphorus species IV as well as an iminiumphosphorane V, respectively. 5a,30 Upon addition of Et 3 N, the solids which could be ammonium salts including IV and V became dissolve.…”