Synthesis, characterization and crystal structures of new difurylphosphido-bridged dinuclear ruthenium carbonyl complexes derived from ferrocenylacetylene ligands

The difurylphosphido-bridged dinuclear complex [Ru₂(CO) ₆(μ-PFu₂)(μ-η¹,η²-Fu)] (Fu = 2-furyl) 1 readily reacts with two equivalents of each of the terminal alkynes HC = CR (R = Fc, p-C₆H₄Fc, p-C₆H ₄NO₂, Fc = Fe(η⁵-C₅H ₅)(η⁵-C₅H₄)) by an interesting head-to-tail ynyl coupling with a furan group to form a series of phosphido-bridged diruthenium compounds containing a novel furyl-substituted C₄ hydrocarbyl chain of stoichiometry [Ru₂(CO) ₄(μ-PFu₂){μ-η¹,η¹, η²,η³-RCC(H)C(R)C(H)Fu}] (R = Fc 2, p-C ₆H₄Fc 3, p-C₆H₄NO₂ 4) in moderate to good yields. Reaction of 1 with an equimolar amount of HC = CFc and HC= C(p-C₆H₄NO₂) afforded a pair of isomers of [Ru₂(CO)₄(μ-PFu₂){μ-η¹, η¹,η²,η³-R¹CC(H)C(R ²)C(H)Fu}] (R¹ = Fc, R² = p-C₆H ₄NO₂ 5a; R¹ = p-C₆H ₄NO₂, R² = Fc 5b) together with a small mixture of 4. X-ray crystal structures of 2, 3, 5a and 5b are reported. All of these new alkyne-derived dinuclear complexes are electron precise with 34 cluster valence electrons in which the μ-η¹,η²-furyl ligand acts as a three-electron donor and the μ-phosphido Ru₂ framework is retained in the products upon alkyne coupling reactions. The resulting organic fragment of each complex is coordinated to the Ru atoms via a π, a π-allyl and two σ bonds, and donates seven electrons to the metal core.