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

Abstract

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 HCCR [R = Ph, p-C₆H₄Me, p-C₆H₄NO₂, (C₄H₂S)CCH or (C₄H₂S)₂CCH] 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,η³-RCC(H)C(R)C(H)C(CH)₃O}] [R = Ph 2, p-C₆H₄Me 3, p-C₆H₄NO₂4, (C₄H₂S)CCH 5 or (C₄H₂S)₂CCH 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 CCH 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.