Phosphoranimines containing cationic N-imidazolinium moieties

Klaehn, John R.; Rollins, Harry W.; McNally, Joshua S.; Arulsamy, Navamoney; Dufek, Eric J.

September 2017 - Three new monomeric phosphoranimines (PAs; R′NPR3) were synthesized by the Staudinger route using 2-azido-1,3-dimethylimidazolinium hexafluorophosphate [ADMImPF] and various phosphines to form their respective PA salts of triphenylphosphine (1), tri(n-octyl)phosphine (2), and tris(2,2,2-trifluoroethoxy)phosphite (3). These PA salts have a cationic imidazolinium moiety attached to nitrogen. Interestingly, 2 is a room temperature ionic liquid (RTIL) with a melting point around −5 °C and a viscosity of 740cP at 25.5 °C. 1 and 2 show stability to moisture exposure and atmosphere for weeks whereas 3 is not stable toward atmospheric moisture undergoing decomposition to form 2-amino-1,3-dimethylimidazolinium phosphate (4). Thermal analyses reveal that 1 and 2 are stable to 90 °C under nitrogen, but 3 undergoes degradation by exposure to moisture and/or elevated temperature. All compounds exhibit similar multinuclear NMR chemical shifts as compared to their corresponding phosphine oxide counterparts. However, their respective X-ray structure determinations indicate that 2 has an open structure with the octyl groups that avoid the ionic charges, whereas 1 and 3 have tighter structural packing of the hexafluorophosphate to their pendant groups.

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