Photochemische Reaktionen von Übergangsmetall-Organyl-Komplexen mit Olefinen, XVI [1]: Photochemisch induzierte Cycloadditionen von Diphenylacetylen an Tricarbonyl(η⁵-2,4-dimethyl-2,4-pentadien-1-yl)mangan / Photochemical Reactions of Transition Metal Organyl Complexes with Olefins, XVI [1]: Photochemically Induced Cycloadditions of Diphenylacetylene to Tricarbonyl(η⁵-2,4-dimethyl-2,4-pentadien-1-yl)manganese

Upon UV irradiation in THF at 208 K tricarbonyl(η⁵-2,4-dimethyl-2,4-pentadien-1-yl)- manganese (1) yields solvent stabilized, very reactive dicarbonyl(η5-2,4-dimethyl-2,4-pentadien-1-yl)(tetrahydrofuran)manganese (2), which reacts in situ with one or two molecules of diphenylacetylene (3) and yields four manganese complexes and 1,3-dimethyl-5,6-diphenyl-bicyclo[3.2.1]oct-2-ene-7-one (5), which were separated by HPL chromatography. In addition to tricarbonyl η⁵-4,6 -dimethyl-1,2-diphenyl-cyclohepta-2,4-dien-1-yl)manganese (4) formed by [5+2]cycloaddition and successive 1,4-H shift, tricarbonyl{ 1′,2′,5′-η-5-methyl-2,3 -diphenyl-5- (2′-methyl-4′,5′-diphenyl-penta-1′,4′-dien-1′,5′-diyl)cyclopent-2-en-1 -one-κ-O}manganese (6) is isolated with a ligand, formed from 2,4-dimethyl-2,4-pentadien-1-yl, two units of 3 and one carbon monoxide. The ligands of tricarbonyl{ 1-4,2′-η-4,6 -dimethyl-1,2-diphenyl-5-(E-1′,2′- diphenyl-vinylen)cyclohepta-1,3-diene}manganese (7), and tricarbonyl{η⁵-4,6 -dimethyl-1,2-diphenyl-7-(E-1′,2′-diphenyl-vinyl)cyclohepta-2,4-dien-1-yl}m anganese (8) are formed from 2,4-dimethyl-2,4-pentadien-1-yl and of two molecules of 3 each. The crystal and molecular structures of 5 and 6 have been determined by single crystal X-ray diffraction. 5 crystallizes in the triclinic space group P1̅ , a = 992.0(2) pm, b = 996.8(2) pm, c = 1021.0(2) pm, a = 77.67(3)°, β = 61.17(3)°, γ = 88.68(3)°. Complex 6 crystallizes also in the triclinic space group P1̅ ,a = 1023.2(2) pm, b - 1113.8(2) pm, c = 1567.9(3) pm, α = 82.88(3)°, β = 86.93(3)°, 7 = 63.53(3)°. The constitutions of 4, 7 and 8 were elucidated from the IR, NMR and mass spectra. Possible formation mechanisms for the compounds 4-8 are proposed. Complex 7 shows hindered rotations of two phenyl groups with different barriers of energy ΔG^≠₃₁₆ = 68.8 kJ/mol, „ΔH^≠ = 67.9 ± 0.7 kJ/mol, ΔS^≠ = -2 ± 2 J/mol · K and ΔG^≠₂₉₆ = 60.6 kJ/mol, ΔH^≠ = 57.7 ± 1.0 kJ/mol, ΔS^≠ = -10 ± 2 J/mol·K due to steric interactions.