A new family of phosphido-bridged dinuclear ruthenium carbonyl complexes: Synthesis of [Ru₂(CO)₆{μ-P(C(CH)₃O)₂} (μ-η¹,η²-C(CH)₃O)] and its reactivity towards terminal alkynes

Thermal reaction of [Ru3(CO)12] with tri(2-furyl)phosphine affords the dinuclear phosphido-bridged complex [Ru2(CO)6{μ-P(C(CH)3O)2} (μ-η1,η2-C(CH)3O)] 1a in good yield via cleavage of Ru-Ru and P-C(furyl) bonds in the starting compounds and a small amount of the disubstitution product [Ru3(CO)10{P(C(CH)3O)3} 2] 1b. The X-ray structural analysis of 1a shows that it contains a dissociated furyl fragment bonded to the Ru2 unit in a μ-η1,η2 coordination mode through one σ and one π bond. This represents the first structurally characterised example of such a furyl-bonded dinuclear organometallic complex. Complex 1a readily reacts with two equivalents of terminal alkynes HC≡CR [R = Ph, p-C6H4Me, p-C6H4NO2, (C4H2S)C≡CH or (C4H2S)2C≡CH] 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-P(C(CH)3O)2} {μ-η1,η1,η2,η 3-RCC(H)C(R)C(H)-C(CH)3O}] [R = Ph 2, p-C6H4Me 3, p-C6H4NO2 4, (C4H2S)C≡CH 5 or (C4H2S)2C≡CH 6] in moderate to good yields, all of which have been characterised by spectroscopic and crystallographic methods. Assignments of the proton NMR spectra have been made with the aid of a 2-D 1H-1H COSY technique. On reaction with the thienyl-linked diyne ligands, only one free C≡CH group is involved in the coupling sequence while the other terminal alkyne functionality remains intact. All these new dinuclear complexes are electron precise with 34 cluster valence electrons.