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)Å, 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-K_αX-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)Å]. 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.