Synthesis of {Me2Si-η5-C5H4Fe(CO)[P(OR)3]Me2Si-η5-C5H4Fe(CO)[P(OR)3]} via selective CO-substitution of [Me2Si-η5-C5H4Fe(CO)2Me2Si-η5-C5H4Fe(CO)2] by P(OR)3 (R=Ph, nBu, nPr, Et, and Me) under photochemical condition and molecular structure of trans-{Me

Ultraviolet irradiation of [Me2Si-η5-C5H4Fe(CO)2Me2Si-η5-C5H4Fe(CO)2] (2) in the presence of P(OR)3 leads to regioselective substitution of two CO groups at different iron centers to give {Me2Si-η5-C5H4Fe(CO)[P(OR)3]Me2Si-η5-C5H4Fe(CO)[P(OR)]3]} [R=Ph (3); nBu (4); nPr (5); Et (6); and Me (7)]. Complexes 3–7 are mixtures of cis and trans isomers in ratios of ca. 1:1.4, as determined by 1H-NMR spectra. Both isomers of 3 and 7 were isolated by exploiting their differing solubility while only the trans isomers were obtained for 4, 5 and 6. The molecular structure of trans-7 has been determined by X-ray diffraction. It is demonstrated that coordination of P(OMe)3 at the iron center leads to shortening (0.036 Å) and hence strengthening of the geminal FeCO (1.725(3) Å) coordination bond, which is most probably responsible for the regioselectivity of CO-substitution.