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

Upon UV irradiation in hexane at 243 K tricarbonyl-eta(5)-cyclohexadie nyl-manganese (1) and two equivalents of 2-butyne (2) or diphenylacety lene (4) yield in successive [5 + 2, 3 + 2] cycloadditions icyclo[5.2. 1.0(4,9)]-deca-2,5-dien-10-yl-manganese (6), or icyclo[5.2.1.0(4,9)]-d eca-2,5-dien-10-yl-manganese (8), respectively. 3-Hexyne (3) reacts wi th 1 under the same conditions by successive [5 + 2, 3 + 2] cycloaddit ions and I,bH-shift to dene-tricyclo[5.2.1.0(4,9)]dec-2-en-5-yl-mangan ese (7). Identical products are also obtained when 1 is first irradiat ed in THF at 208 K and the thermolabile intermediate, -eta(5)-cyclohex adienyl-tetrahydrofurane-manganese (11), is treated with an excess of the alkynes 2-4. In contrast, bis(trimethylsilyl)acetylene (5) substit utes photochemically in 1 only a CO ligand to yield enyl-eta(2)-bis(tr imethylsilyl)acetylene-manganese (9). The crystal and molecular struct ure of 7 was determined by an X-ray diffraction analysis. Complex 7 cr ystallizes in the triclinic space group P (1) over bar, a = 822.6(2) p m, 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 .