Synthesis and characterization of phosphonium and phosphine oxide linked to a tetrairon cluster

Reaction of Cp3Fe4(CO)4(C5H4PPh2) (1) with Me3OBF4 or MeI leads to methylation of the phosphine group to give the phosphonium compound [Cp3Fe4(CO)4(C5H4PPh2Me)]Y (2a, Y = BF4−; 2b, Y = I−) in high yields. On the other hand, treating 1 with H2O2 generates the phosphine oxide complex Cp3Fe4(CO)4(C5H4PPh2(O)) (3). Compounds 2 and 3 have been characterized by 1H, 13C and 31P NMR, and mass spectroscopies together with a single-crystal X-ray diffraction study. The electrochemistry of 1, 2a and 3 were investigated by cyclic voltammetry. The positive charge on the PPh2Me+ group may be delocalized to the tetrairon cluster through a ylide-like Ph2MePC5H4 resonance structure.