REACTIVITY OF ALLENE AT PHOSPHINE-BRIDGED DIIRON CENTERS - X-RAY CRYSTAL-STRUCTURES OF [FE2(CO)S(MU-SIGMA,ETA-3-C(O)C(CH2)2)-(MU-DPPM)] AND [FE2(CO)4(MU-ETA-3,ETA-3'-(CH2)2C2(CH2)2)(MU-DPPM)].ET2O

Photochemically induced reaction of [Fe2(CO)6(mu-CO)(mu-dppm)] (1) (dppm=bis(diphenylphosphino)methane) with allene gave [Fe2(CO)5{mu-sigma,eta3-C(O)C(CH2)2(mu-dppm)] (3), as a result of allene-CO linking, [Fe2(CO)5{mu-sigma,eta3-C(CH2)2}(mu-dppm)] (4) and [Fe2(CO)4{mu-eta3,eta3'-(CH2)2C2(CH2)2}(mu-dppm)] (5), formed by linking of two allene molecules via the central carbons. On heating in tetrahydrofuran complex 3 decarbonylated to give 4, which in refluxing toluene isomerised to [Fe2(CO)5(PPh2Me)(mu-sigma,eta4-CHCHCHPPh2)] (8) and [Fe2(CO)5(mu-eta4-CHPhCHCHPPhMe)(mu-PPh2)] (9) via cleavage of a P-CH2 bond of the dppm ligand and subsequent P-C bond formation, hydrogen shifts and, in the case of 9, phenyl migration. Reaction of [Fe2(CO)6(mu-CH2PPh2)(mu-PPh2)] (2) with allene gave [Fe2(CO)5{mu-PPh2C(CH2)2}(mu-CH2PPh2)] (10), which contains a novel phospha-trimethylenemethane ligand produced by the insertion of allene into the phosphido bridge. Protonation of 10 in the presence of carbon monoxide gave [Fe2(CO)7{eta1-PPh2C(Me)=CH2}(mu-CH2PPh2)][BF4] (11), containing a 2-propenylphosphine ligand. The structures of 3 and 5.Et2O were determined by X-ray diffraction.