P-C and C-H bond cleavages in the photochemical reactions of [Fe2(η5-C5H5)2(CO)4] with bis(diphenylphosphino)methane

The photochemical reactions of [Fe2Cp2(CO)(4)] (Cp = eta(5)-C5H5) and the bidentate ligand Ph2PCH2PPh2 give a complex mixture of products. These include the known complexes [Fe2Cp2(mu-CO)(2)(mu-Ph2PCH2PPh2)] and cis-[Fe2Cp2(mu-PPh2)(2)(CO)(2)], as well as the new species [Fe2Cp(mu-eta(5):kappa(1)-C5H4CH2PPh2)(mu-CO)(2)(CO)], cis-[Fe2Cp2(mu-H)(mu-PPh2)(CO)(2)], [Fe2Cp(mu-eta(5):kappa(1)-C5H4CH2PPh2)(mu-H)(mu-PPh2)(CO)], trans-[Fe2Cp2(mu-H)(mu-PPh2)(CO)(PMePh2)], and [Fe2Cp2(mu-PPh2)(2)(mu-CO)]. An intermediate species, trans- [Fe2Cp2(mu-CO)(2)(CO)(kappa(1)-Ph2PCH2PPh2)], having an intact diphosphine ligand coordinated through one of the P atoms, can be detected at the early stages of the reaction. Separate experiments indicate that the latter species is the precursor of the unique diphosphine-bridged complex, but of none of the other products. The above results indicate that different P-C (diphosphine) and C-H (cyclopentadienyl) bond cleavage processes are operative under the conditions examined, as well as novel C-C bond formations. The structures of the new complexes are analyzed on the basis of the corresponding IR and NMR (H-1, P-31, and C-13) data, as well as a single-crystal X-ray study on the (diphenylphosphinomethyl)cyclopentadienyl complex [Fe2Cp(mu-eta(5):kappa(1)-C5H4CH2PPh2)(mu-CO)(2)(CO)]. A reassessment of the P-31 chemical shifts for cis- and trans-[Fe2Cp2(mu-PPh2)(2)(CO)(2)] is also made.