P−C and C−H Bond Cleavages in the Photochemical Reactions of [Fe2(η5-C5H5)2(CO)4] with Bis(diphenylphosphino)methane

Abstract

The photochemical reactions of [Fe2Cp2(CO)4] (Cp = η5-C5H5) and the bidentate ligand Ph2PCH2PPh2 give a complex mixture of products. These include the known complexes [Fe2Cp2(μ-CO)2(μ-Ph2PCH2PPh2)] and cis-[Fe2Cp2(μ-PPh2)2(CO)2], as well as the new species [Fe2Cp(μ-η5:κ1-C5H4CH2PPh2)(μ-CO)2(CO)], cis-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2], [Fe2Cp(μ-η5:κ1-C5H4CH2PPh2)(μ-H)(μ-PPh2)(CO)], trans-[Fe2Cp2(μ-H)(μ-PPh2)(CO)(PMePh2)], and [Fe2Cp2(μ-PPh2)2(μ-CO)]. An intermediate species, trans-[Fe2Cp2(μ-CO)2(CO)(κ1-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 (1H, 31P, and 13C) data, as well as a single-crystal X-ray study on the (diphenylphosphinomethyl)cyclopentadienyl complex [Fe2Cp(μ-η5:κ1-C5H4CH2PPh2)(μ-CO)2(CO)]. A reassessment of the 31P chemical shifts for cis- and trans-[Fe2Cp2(μ-PPh2)2(CO)2] is also made.