Add time:09/27/2019         Source:sciencedirect.com

Upon UV irradiation in hexane at 243 K tricarbonyl-η5-cyclohexadienyl-manganese (1) and two equivalents of 2-butyne (2) or diphenylacetylene (4) yield in successive [5 + 2, 3 + 2] cycloadditions tricarbonyl-η2:2:1-1,2,3,10-tetramethyl-tricyclo[5.2.1.04,9]-deca-2,5-dien-10-yl-manganese (6), or tricarbonyl-η2:2:1-1,2,3,10-tetraphenyl-tricyclo[5.2.1.04,9]-deca-2,5-dien-10-yl-manganese (8), respectively. 3-Hexyne (3) reacts with 1 under the same conditions by successive [5 + 2, 3 + 2] cycloadditions and 1,4-H-shift to tricarbonyl-η2:2:1-1,2,3-triethyl-10-ethylidene-tricyclo[5.2.1.04,9]dec-2-en-5-yl-manganse (7). Identical products are also obtained when 1 is first irradiated in THF at 208 K and the thermolabile intermediate, dicarbonyl-η5-cyclohexadienyl-tetrahydrofurane-manganese (11), is treated with an excess of the alkynes 2–4. In contrast, bis(trimethylsily)acetylene (5) substitutes photochemically in 1 only a CO ligand to yield dicarbonyl-η5-cyclohexadienyl-η2-bis(trimethylsily)Acetylene-manganese (9). The crystal and molecular structure of 7 was determined by an X-ray diffraction analysis. Complex 7 crystallizes in the triclinic space group P1, a = 822.6(2) pm, b = 882.5(2) pm, c = 1344.6(2) pm, α = 92.36(2)°, β = 107.13(2)°, γ = 99.71(2)°, V = 0.9152(3) nm3, Z = 2. The complexes 6–9 were studied in solution by IR and NMR spectroscopy. The structures of 6,8 and 9 were elucidated from the NMR spectra. A possible formation mechanism for the complexes 6–9 will be discussed.

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