Organic chemistry of dinuclear metal centres. Part 8. Organo–iron–ruthenium chemistry. X-Ray structure of trans-[FeRu(CO)2(µ-CO)2(η-C5H5)2

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The iron–ruthenium complex [FeRu(CO)4(η-C5H5)2] is obtained in 60% yield from the reaction of Na[Fe(CO)2(η-C5H5)] with [RuI(CO)2(η-C5H5)]. In the solid state a trans-[FeRu(CO)2(µ-CO)2(η-C5H5)2] structure has been established by X-ray diffraction. Crystals are monoclinic, space group P21/c (no. 14), with Z= 2 in a unit cell for which a= 7.064(2), b= 12.518(3), c= 8.011(2)Å, and β= 106.23(2)°. The structure was solved by heavy-atom methods and refined to R 0.0275 (R′ 0.0313) for 1 532 independent intensities. The molecule is disordered about a centre of inversion at the mid-point of the metal–metal bond, each metal site being occupied by half an iron and half a ruthenium atom, with an iron–ruthenium bond length of 2.626(1)Å. In solution the cis-[FeRu(CO)2(µ-CO)2(η-C5H5)2] isomer is dominant, and shown by 13C n.m.r. to be undergoing cis⇌trans isomerisation with bridge ⇌ terminal carbonyl exchange at room temperature, but to be static at –80 °C. The complex is an excellent precursor of organo-iron–ruthenium chemistry. Treatment with alkynes R1C2R2(R1= R2= H, Me, Ph, or CO2Me; R11= Me or Ph, R2= H) under u.v. irradiation gives complexes [FeRu(CO)(µ-CO){µ-C(O)CR1CR2}(η-C5H5)2] in 20–65% yield as a result of alkyne–CO linkage. This link in the complexes derived from ethyne, propyne, and but-2-yne is broken upon protonation, generating µ-vinyl cations [FeRu(CO)2(µ-CO)(µ-CR1CHR2)(η-C5H5)2]+(R1= R2= H or Me; R1= H, R2= Me). These are attacked by hydride at the β carbon of the µ-vinyl to give µ-alkylidene complexes [FeRu(CO)2(µ-CO)(µ-CR1R2)(η-C5H5)2](R1= H, R2= Me or Et; R1= Me, R2= Et). Reaction of [FeRu(CO)(µ-CO){µ-C(O)CPhCPh}(η-C5H5)2] with Ph3PCHR or CH(CO2Et)N2 in boiling toluene also gives µ-alkylidene complexes [FeRu(CO)2(µ-CO)(µ-CHR)(η-C5H5)2](R = H, Me, or CO2Et) in good yield, through ready displacement of diphenylacetylene. The µ-CH2 complex is best obtained (75%) by treating [FeRu(CO)4(η-C5H5)2] with LiBHEt3 then water, and in a related manner sequential addition of methyl-lithium, HBF4·OEt2, and NaBH4 affords [FeRu(CO)2(µ-CO)(µ-CHMe)(η-C5H5)2]. Under u.v. irradiation alkynes react with µ-alkylidene complexes [FeRu(CO)2(µ-CO)(µ-CHR1)(η-C5H5)2] to give products of alkyne–alkylidene linking [FeRu(CO)(µ-CO)(µ-CR3CR2CHR1)(η-C5H5)2](R1= H or Me, R2= R3= H, Me, Ph, or CO2Me; R1= H or Me, R2= Me or Ph, R3= H). These exist as non-interconverting isomers in which the new C3 ligand is either bound σ to iron and σ, η2 to ruthenium or vice versa. The scope of organo-iron–ruthenium chemistry closely resembles that of the di-iron system but it is apparent that in reactivity terms there is an order: FeRu > Fe2 > Ru2.