RESUMEN
Phosphoranides are interesting hypervalent species which serve as model compounds for intermediates or transition states in nucleophilic substitution reactions at trivalent phosphorus substrates. Herein, the syntheses and properties of stable trifluoromethylphosphoranide salts are reported. [K(18-crown-6)][P(CF3 )4 ], [K(18-crown-6)][P(CF3 )3 F], and [NMe4 ][P(CF3 )2 F2 ] were obtained by treatment of trivalent precursors with sources of CF3 - or F- units. These [P(CF3 )4-n Fn ]- (n=0-2) salts exhibit fluorinating (n=1-2) or trifluoromethylating (n=0) properties, which is disclosed by studying their reactivity towards selected electrophiles. The solid-state structures of [K(18-crown-6)][P(CF3 )4 ] and [K(18-crown-6)][P(CF3 )3 F] are ascertained by single crystal X-ray crystallography. The dynamics of these compounds are investigated by variable temperature NMR spectroscopy.
RESUMEN
The P(CF(3))(3)CH(3)(+) ion is synthesized as P(CF(3))(3)CH(3)(+)AsF(6)(-) by methylation in a MeF/SO(2)/AsF(5) system or as P(CF(3))(3)CH(3)(+)Sb(2)F(11)(-) in a MeF/HF/SbF(5) system at low temperatures. In contrast to (CF(3))(3)(CH(3))P(+)AsF(6)(-), P(CF(3))(3)CH(3)(+)Sb(2)F(11)(-) is a stable, colorless crystalline solid. A crystal structure determination shows the presence of a slightly distorted tetrahedral phosphonium cation with P-C(F) distances of 188.1-188.7(4) and a P-C(H) bond length of 176.7(4) pm. The phosphonium salt (CF(3))(3)(CH(3))P(+)AsF(6)(-) was also obtained by abstraction of a fluoride ion from the anion [(CF(3))(3)(CH(3))PF(2)](-) salt using AsF(5).