Trivalent phosphorus derivatives of group via : IV. Infrared and pmr studies of the protonation of M(CO)6−n(PA3)n Complexes (M = Mo,W; A = CH3, OCH3; n = 2, 3, 4)

The action of trifluoroacetic acid on the series M(CO)_6?n(PA₃)_n (M = Mo, W; A = CH₃, OCH₃; n = 2, 3, 4) has shown that protonation occurs if n ? 3. For n = 3 the basicity of the ligand PA₃ plays a more important role in the stability of HM(CO)₃(PA₃)₃]⁺complexes than for n = 4. Infrared and proton NMR give evidence of the stereochemical non-rigidity of the HM(CO)_6?n(PA₃)_n]⁺ heptacoordinated cation.