Activation of alkynols on transition metal carbonyl clusters. Reactions of 1-ethynylcyclohexanol with Fe3(CO)12 and Co2(CO)8. Crystal structures of Co3(CO)9[μ3-CCH2(C6H10OH)], Fe3(CO)9(μ-CO)[μ3-η2-CC(C6H10)] and Co2Fe(CO)6(μ-CO)[μ3-η7-(C6H9)CC(H)C(H)C(H)(C6H10)]

Abstract

The reactions of Co₂(CO)₈ with 1-ethynylcyclohexanol (HCCC₆H₁₀OH, ECY) in benzene led mainly to Co₂(CO)₆(ECY) 1 and to smaller amounts of the methylidyne complex Co₃(CO)₉[μ₃-CCH₂(C₆H₁₀OH)] 2. The reactions of Fe₃(CO)₁₂ with ECY in the same solvent led to binuclear metallacyclic derivatives Fe₂(CO)₆(ECY)₂ (isomers 3a, 3b) or Fe₂(CO)₆[(ECY)₂ − H₂O] 3c as the main products; small yields of trinuclear complexes Fe₃(CO)₉(μ-CO)[μ₃-η²-1,2-HCC(C₆H₁₀OH)] 4, Fe₃(CO)₉(μ-CO)[μ₃-η²-1,2-CC(C₆H₁₀)] 5 and Fe₃(CO)₇[μ₃-η⁷-(C₆H₁₀OH)CCHCHC(C₆H₉)] 6 {containing respectively a parallel alkynol, an allenylidene and a dimeric metallacyclic ligand} were also obtained, together with 7, a thermal decomposition product of 6. Finally, when Co₂(CO)₈ was treated with ECY in benzene, and Fe₃(CO)₁₂ was added, the heterometallic complex Co₂Fe(CO)₆(μ-CO)[μ₃-η⁷-(C₆H₉)CC(H)C(H)C(H)(C₆H₁₀)] 8 was obtained in low yields. The complexes have been characterized by means of IR and ¹H NMR spectroscopies and by mass spectrometry. The structures of 2, 5, 8 have been determined by X-ray diffraction. Complex 2 contains an “hydrogenated” ECY ligand, 5 an allenylidene ligand formed upon dehydration of ECY (loss of the OH and of the terminal hydrogen), whereas 8 contains a ligand formed by tail-to-tail coupling of two ECY molecules, with loss of water and oxygen and shift of hydrogen. The elemental analysis of complex 8 gave a Co ∶ Fe ratio of 2 ∶ 1; on the basis of this analysis, the refinement of the diffraction data allowed a hypothesis on the distribution of the metal atoms in the cluster. Reaction pathways for the formation of these clusters are proposed and dehydration mechanisms for the ligand discussed.