Synthesis and structural characterisation of ruthenium carbonyl clusters containing hydrocarbyl ligands derived from (hydroxy)alkynes HCCC(H)(OH)CH3

Abstract

Five new ruthenium ketonic clusters [Ru₄(CO)₁₂{µ₄-η¹∶η¹∶η²∶η²-CH₃C(H)CCC(H)CH₂C(O)CH₃}] 1 (10%), [Ru₅(CO)₁₄(µ-H)₂{µ₄-η¹∶η¹∶η²∶η²-CC(H)C(O)CH₃}] 2 (15%), [Ru₆(CO)₁₆{µ₄-η¹∶η¹∶η²∶η²-CC(H)C(O)CH₃}₂] 3 (15%), [Ru₇(CO)₁₉{µ₄-η¹∶η¹∶η²∶η²-CC(H)C(O)CH₃}{µ₅-η¹∶η¹∶η¹∶η¹∶η²-CCC(H)CH₃}] 4 (8%), and [Ru₅(CO)₁₂(µ-CO){µ₄-η¹∶η¹∶η²∶η²-CC(H)C(O)CH₃}(µ₄-η²-HCCCH₂CH₃)] 5 (10%) have been synthesised by reaction of but-3-yn-2-ol with triruthenium dodecacarbonyl, in cyclohexane, under reflux. All the compounds have been fully characterised by spectroscopic and X-ray diffraction methods. The structure of 1 is based on a Ru₄ butterfly skeleton containing a fragment of C₈ ketonic chain which arises from the coupling of two ligand molecules with the elimination of a water molecule. An interesting feature in clusters 2, 3, 4 and 5 is the formation of a metallocycloketonic ring with a µ₄-η¹∶η¹∶η²∶η² coordination mode which is derived from the activation of the CC triple bond. Both 2 and 5 consist of a wingtip bridged butterfly core, which is also bonded with two bridged hydrides in 2 and a µ₄-η² acetylide fragment in 5 respectively. Cluster 2 is also closely related to cluster 3, in that it seems to be a monomeric unit of 3 forming a six atom raft geometry with two metallocycloketonic rings. The metal core of 4 is similar to 3, except that one Ru–Ru bond in 4 is broken to form two more metal–metal bonds with an additional Ru atom to give a novel Ru₇ core, which is best described as a distorted Ru₄ square plane sharing an edge with an edge-bridged butterfly. Moreover, one of the metallocycloketonic rings in 3 is replaced by an allenyl CCC(H)CH₃ ligand, which is coordinated to an edge-bridged butterfly in 4.