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]

Abstract

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.