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-CC(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.