Formation of a bridged vinylidenedi-iron complex by nucleophilic attack on a carbonyl ligand of [Fe2(CO)4(η-C5H5)2], and the synthesis and X-ray crystal structure of [(OC)3Fe((µ-Ph2PCHPPh2)FeH(CO)3

Abstract

Reaction of [Fe2(µ-CO)2(CO)2(η-C5H5)2] with an excess of methyl-lithium in tetrahydrofuran followed by treatment with CF3CO2H at low temperatures affords a mixture of cis- and trans-[Fe2(µ-CCH2)(µ-CO)(CO)2(η-C5H5)2]. The isomers can be separated by column chromatography, and are thermally interconvertible. Reaction of the trans- vinylidenedi -iron complex with HBF4·Et2O affords the salt [Fe2(µ-CCH3)(µ-CO)(CO)2(η-C5H5)2][BF4], which deprotonates on treatment with NEt3 to form a mixture of cis- and trans-[Fe2(µ-CCH2)(µ-CO)(CO)2(η-C5H5)2]. In contrast, [Fe2(µ-CO)(µ-dppm)(CO)6](dppm = Ph2PCH2PPh2) is deprotonated by methyl-lithium to form an anionic species, which on protonation (CF3CO2H) affords the dinuclear iron complex [(OC)3Fe(µ-Ph2PCHPPh2)FeH(CO)3], characterised by n.m.r. spectroscopy and X-ray crystallography. Crystals are triclinic, space group P, Z= 4, in a unit cell with a= 10.504(3), b= 15.189(5), c= 19.552(5)A, α= 104.43(2), β= 103.04(2), and γ= 98.57(2)°. There are two independent molecules in the asymmetric unit, and the structure has been refined to R 0.073 (R′ 0.072) for 2 669 reflections with 2θ⩽ 40°(Mo-KαX-radiation) collected at 298 K. The two molecules have very similar geometries and contain a novel 1,2-diferra-3,5-diphosphabicyclo[2.1.0] pentane ring [mean separations within the ring system Fe–Fe 2.687(4), Fe–P 2.197(5) and 2.271(6), Fe–µ-C 2.15(2), and µ-C–P 1.79(2) and 1.76(2)A]. Both iron atoms are bonded to three carbonyl groups, but one of these ligands semi-bridges the metal–metal bond [Fe–C–O 152.6(14)°]. The hydrido-ligand was not located by the X-ray diffraction study but from potential-energy minimisation methods was calculated to be bridging the metal–metal bond, in accord with the 1H n.m.r. data for the compound.