Synthesis of -{Me2Si-eta(5)-C5H4Fe(CO)[P(OR)(3)]Me2Si-eta(5)-C5H4Fe(CO)[P(OR)(3)]}- via selective CO-substitution of -[Me2Si-eta(5)-C5H4Fe(CO)(2)Me2Si-eta(5)-C5H4Fe(CO)(2)]- by P(OR)(3) (R = Ph, Bu-n, Pr-n, Et, and Me) underphotochemical condition and molecular structure of trans-{Me2Si-eta(5)-C5H4Fe(CO)- [P(O Me)(3)]Me2Si-eta(5)-C5H4Fe(CO)[P(OMe)(3)]}-

Ultraviolet irradiation of -[Me2Si-eta (5)-C5H4Fe(CO)(2)Me2Si-eta (5)-C5H4F e (2) in the presence of P(OR)(3) leads to regioselective substitution of t wo CO groups at different iron centers to give -{Me2Si-eta (5)-C5H4Fe(CO)[P (OR)(3)]Me2Si-eta (5)-C5H4Fe(CO)[P(OR)](3)]}d- [R = Ph (3); Bu-n (4); Pr-n (5); Et (6); and Me (7)]. Complexes 3-7 are mixtures of cis and trans isome rs in ratios of ca. 1:1.4, as determined by H-1-NMR spectra. Both isomers o f 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 Ang strom) and hence strengthening of the geminal Fe-CO (1.725(3) Angstrom) coo rdination bond, which is most probably responsible for the regioselectivity of GO-substitution. (C) 2000 Published by Elsevier Science B.V. All rights reserved.