59888-71-0Relevant academic research and scientific papers
Phosphoranes. 3. New tris(trifluoromethyl)phosphoranes (CF3)3PXY with monofunctional [F, Cl, N(CH3)2, OCH3, SCH3, OSi(CH3)3] substituents
The, Kwat I.,Cavell, Ronald G.
, p. 2518 - 2525 (2007/10/12)
New five-coordinate molecular phosphoranes of the types (CF3)3PY2 (Y = OCH3) and (CF3)3P(F)Y (Y = N(CH3)2, OCH3, SCH3, OSi(CH3)3) have been prepared from (CF3)3PF2 and the trimethylsilyl reagent (CH3)3SiY or dimethylamine. An improved synthesis of (CF3)3P(Cl)N(CH3)2 is also described. Formulation of the monofluoro- and disubstituted phosphoranes as the isomeric phosphonium salts can be clearly ruled out by NMR spectroscopic studies. At low temperatures, 19F, 31P, and, in the case of (CF3)3P(Cl)N(CH3)2, 13C NMR spectra of the phosphoranes show the presence of different CF3 environments consistent with substitution at axial or equatorial positions of the (assumed) trigonal-bipyramidal framework. The former are characterized by relatively small 2JPF and the latter by relatively large 2JPF values. Ground-state structures are consistent with the preferential location of halogen (F, Cl) in the axial positions and of OCH3, SCH3, or N(CH3)2 groups in the equatorial positions. The CF3 groups which occupy the remaining axial and equatorial sites are, in most cases, distinguishable by 19F NMR with only moderate cooling of the sample. New 31P NMR data for (CF3)3P[N(CH3)2]2 strongly support the location of both N(CH3)2 groups in the equatorial plane as suggested earlier. The barrier to the averaging of CF3 environments appears to decrease in the order N(CH3)2 > SCH3 > OCH3. The presence of a halogen substituent appears to lower the barrier to the averaging process compared to the doubly substituted molecules and a chlorophosphorane appears to have a lower barrier than the corresponding fluorophosphorane.
