Photochemische Reaktionen von Übergangsmetall‐Organyl‐Komplexen mit Olefinen, 3. [4 + 5]‐Cycloaddition konjugierter Diene an Tricarbonyl(η5‐2,4‐dimethyl‐2,4‐pentadienyl)mangan

Photochemical Reactions of Transition Metal Organyl Complexes with Olefines, 31). – [4 + 5] Cycloaddition of Conjugated Dienes to Tricarbonyl(η5‐2,4‐dimethyl‐2,4‐pentadienyl)manganese Tricarbonyl(η5‐2,4‐dimethyl‐2,4‐pentadienyl)manganese [1] reacts photochemically with the acyclic conjugated dienes 1,3‐butadiene [A], 2‐methyl‐1,3‐butadiene [B], (E)‐1,3‐pentadiene (C), (E,E)‐2,4‐hexadiene (D), 2,4‐dimethyl‐1,3‐pentadiene (E), 2,4‐hexadien‐1‐ol (F), and methyl 2,4‐hexadienoate (G) in a formal [4 + 5] cycloaddition to give tricarbonylmanganese complexes with η3:2‐2,6‐cyclononadien‐1‐yl ligands (2A‐2G). In addition, the reaction of 1 with A yields thermolabile [η3:2:2‐1‐(3‐butene‐1,2‐diyl)‐1,3‐dimethyl‐2,6‐cyclononadiene]dicarbonylmanganese (3A) and E,E and E,Z isomers of [η3‐1‐(2‐butene‐1,1‐diyl)‐1,3‐dimethyl‐2,6‐cyclononadiene]tetracarbonylmanganese (4A, 4A] as byproducts. Similarly, 1 reacts with B to form tetracarbonyl[η3‐1‐(3‐methyl‐2‐butene‐1,1‐diyl)‐1,3,6‐trimethyl1‐2,6‐cyclononadiene]manganese (4B) in a side reaction. The crystal and molecular structures of tricarbonyl(η3:2‐1,3,5,5,7‐pentamethyl‐2,6‐cyclononadien‐1‐yl]manganese (2E) and of 3A are determined by X‐ray structure analyses. In each of the formally octahedral complexes unusual long manganese–carbon bonds are found for one coordinated CC double bond of the hydrocarbon ligands.