PHOTOCHEMICAL-REACTIONS OF TRANSITION-METAL ORGANYL COMPLEXES WITH OLEFINS .12. PHOTOCHEMICALLY INDUCED [5+2, 3+2] CYCLOADDITIONS OF ALKYNES TO TRICARBONYL-ETA(5)-CYCLOHEXADIENYL-MANGANESE

Upon UV irradiation in hexane at 243 K tricarbonyl-eta(5)-cyclohexadienyl-manganese (1) and two equivalents of 2-butyne (2) or diphenylacetylene (4) yield in successive [5 + 2, 3 + 2] cycloadditions tricarbonyl-eta(2:2:1)-1,2,3,10-tetramethyl-tricyclo[5.2.1.0(4,9)]-deca-2,5-dien-10-yl-manganese (6), or tricarbonyl-eta(2:2:1)-1,2,3,10-tetraphenyl-tricyclo[5.2.1.0(4,9)]-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 I,bH-shift to tricarbonyl-eta(2:2:1)-1,2,3-triethyl-10-ethylidene-tricyclo[5.2.1.0(4,9)]dec-2-en-5-yl-manganese (7). Identical products are also obtained when 1 is first irradiated in THF at 208 K and the thermolabile intermediate, dicarbonyl-eta(5)-cyclohexadienyl-tetrahydrofurane-manganese (11), is treated with an excess of the alkynes 2-4. In contrast, bis(trimethylsilyl)acetylene (5) substitutes photochemically in 1 only a CO ligand to yield dicarbonyl-eta(5)-cyclohexadienyl-eta(2)-bis(trimethylsilyl)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 P (1) over bar, a = 822.6(2) pm, b = 882.5(2) pm, c = 1344.6(2) pm, gamma = 92.36(2)degrees, beta = 107.13(2)degrees, gamma = 99.71(2)degrees, V = 0.9152(3) nm(3), 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.