Gehinderte Ligandbewegungen in Übergangsmetallkomplexen, XLIV [1]: Photoreaktionen von Hexacarbonyl-μ-η5:5-fulvalen-dimolybdän mit Allen / Hindered Ligand Movements in Transition Metal Complexes, XLIV [1]: Photoreactions of Hexacarbonyl-μ-η5:5 -fulvalene-dimolybdenum with Allene

Abstract

Hexacarbonyl-μ-η5:5-fulvalene-dimolybdenum (1) reacts photochemically with allene to η2-allene-pentacarbonyl-μ-η5:5-fulvalene-dimolybdenum (2), μ-η2:2-allene-tetracarbonyl- μ-η5:5-fulvalene-dimolybdenum (4), and dicarbonyl-μ-η5:5-fulvalene-μ-η1:2:3-2-methylene- 4-penten-1,4-diyl-dimolybdenum (5). Complex 2 rearranges readily at room temperature to pentacarbonyl-μ-η1:3-2-propen-1,2-diyl-μ-η5:5-fulvalene-dimolybdenum (3). Upon UV irradiation 4 yields with an excess of allene μ-η2:2-Allene-pentacarbonyl-μ-η5:5-fulvalene-dimolyb-denum (2) shows a hindered rotation of the allene ligand with an energy barrier of ⊿G# 303 = 53.3 ± 2 kJ/mol. Hexacarbonyl-μ-η5:5-bis(cyclopentadiendiyl)methane-dimolybdenum (6) reacts with allene to μ-η2:2-ailene-tetracarbonyl-μ-η5:5-bis(cyclopentadiendiyl)methane- dimolybdenum (7) and octacarbonyl-bis{μ-η5:5:1-(cyclopentadiendiyl-cyclopentadientriyl)-methanejdihydrido-tetramolybdenum (8). For μ-η2:2-allene-tetracarbonyl-μ-η5:5-fulvalene-dimolybdenum (4) and 7 a hindered ligand movement was detected, by which the bridging allene ligand changes from one the side of the molecule to the other. The activation barriers of these pseudo rotations were determined for 4 with ⊿G# 303 = 57.4 ± 2 kJ/mol and for 7 with ⊿G# 293 = 63.4 ± 2 kJ/mol. Hexacarbonyl-μ-η5:5-fulvalene-ditungsten, hexacarbonyl-μ-η5-bis(cyclopentadiendiyl)ethane-dimolybdenum and hexacarbonyl-μ-η5:5-bis(cyclopen- tadiendiyl)propane-dimolybdenum form no stable photoproducts with allene.