Synthesis and structural characterisation of trinuclear and tetranuclear ruthenium clusters containing diyne ligands derived from 1,4-bis(1-hydroxycyclopentyl)-1,3-butadiyne

Abstract

Three new ruthenium diyne clusters [Ru₃(CO)₇(µ-CO)(µ₃-η²∶η³∶η³-C₂₈H₃₄O₃)] 1a (10%), [Ru₃(CO)₇(µ-CO)(µ₃-η²∶η³∶η³-C₂₈H₃₄O₃)] 1b (4%) and [Ru₃(CO)₈(µ₃-η²∶η²∶η⁴-C₂₈H₃₂O₂)] 2 (12%) have been synthesized by reaction of 1,4-bis(1-hydroxycyclopentyl)-1,3-butadiyne with triruthenium dodecacarbonyl in chloroform under refluxing conditions. All have been fully characterised by spectroscopic and X-ray diffraction methods. The structures of 1a and 1b are based on a Ru₃ triangular skeleton containing a fragment of C₈ chain, which arises from the coupling of two diyne molecules with the formation of a ruthenacyclopentadienyl ring and a furyl ring. Complexes 1a and 1b are isomeric to each other and differ only in the spatial position of the pendant alkyne moiety in the C₈ hydrocarbyl fragment. The organic moiety in 2 is formed by coupling of two diyne ligands and is co-ordinated to a bent Ru₃ chain via a µ₃-η²∶η²∶η⁴ bonding mode. Cluster 2 is found to exhibit a charge-separated, zwitterionic formulation. Reaction of [Ru₃(CO)₁₀(NCMe)₂] with 1,4-bis(1-hydroxycyclopentyl)-1,3-butadiyne afforded another new cluster [Ru₃(CO)₉(µ-CO)(µ₃-η¹∶η¹∶η²-C₁₄H₁₈O₂)] 3, which consists of a diyne ligand bound to the triruthenium cluster unit via a typical µ₃-(η²-||) co-ordination mode. Thermolysis of 1a and 2, with 1,4-bis(1-hydroxycyclopentyl)-1,3-butadiyne and [Ru₃CO)₁₂], respectively, led to [Ru₃(CO)₅(µ₃-η⁵∶η⁵∶η⁶-C₄₃H₄₉O₅)] 4 and a tetraruthenium cluster [Ru₄(CO)₁₀(µ₄-η²∶η²∶η⁴∶η⁴-C₂₈H₃₂O₂)] 5. Cluster 4 is closely related to 1a by the coupling of one more diyne ligand to the triruthenium skeleton of 1a, resulting in an unusual µ₃-η¹∶η³∶η³ mode. The co-ordination mode of the organic ligand in 5 is very similar to that in 2, except that one more metal atom is involved, and one η³-allyl bond is formed.