Facile synthesis, X-ray analysis, and spectroscopic studies of di-iron propanedithiolate complexes with tris(aromatic)phosphine ligands

Three new propanedithiolate-type iron-sulfur complexes containing tris(aromatic)phosphine ligands, [{(mu-SCH2)(2)CH2}Fe-2(CO)(5)L] (L = P(PhOMe-p)(3), 1; P(PhMe-p)(3), 2; P(PhF-p)(3), 3), have been prepared through carbonyl substitution in the presence of Me3NO. The new complexes 1-3 were characterized by elemental analysis, IR, H-1, C-13{H-1}, and P-31{H} NMR spectra. The molecular structures of 1-3 were unequivocally determined by single crystal X-ray diffraction, in which the tris(aromatic)phosphine coordinated to Fe resides in an apical position of the pseudo-square-pyramidal geometry. IR spectroscopy and X-ray crystallographic analysis for 1-3 have indicated that the highly electron rich tris(aromatic)phosphine ligands (where the corresponding electron-donating abilities display the following order of P(PhOMe-p)(3) > P(PhMe-p)(3) > P(PhF-p)(3)) result in a considerable red shift of the CO-stretching frequencies and a clear change of the Fe-Fe bond distances in 1-3.