Gehinderte ligandbewegungen in übergangsmetallkomplexen XXXVI. Photoreaktivität von tricarbonyl-η5:1-(2-cyclopentadiendiyl)ethyl-wolfram gegenüber konjugierten dienen☆

Add time:09/02/2019    Source:sciencedirect.com

The quasi square pyramidal tricarbonyl-η5:1-(2-cyclopentadiendiyl)ethyl-tungsten (1) reacts photochemically with 1,3-butadiene (a), 2,3-dimethyl-2,4-butadiene (b), E,E-2,4-hexadiene (c), 4-methyl-1,3-pentadiene (d), and 2,5-dimethyl-2,4-hexadiene (e). Replacement of one CO ligand by a diene gives the [W(η5:1-C5H4C2H4)-(CO)2(η2-diene)] complexes 2a–2e, replacement of a second CO ligand gives the [W(η5:1-C5H4C2H4)(CO)(η4-diene)] complexes 3a, 3b, and 3d. In addition, insertion of the dienes into the tungsten carbon σ-bond yields the chelate complexes [W(η5:3-C5H4C2H4CnH2n-2)(CO)2] 4a–4e (n = 4, 6, 8). With the exception of 2b, the [W(η5:1-C5H4C2H4)(CO)2(η2-diene)] complexes form two rotamers each, which differ according to the orientation of the uncoordinated CC-double bond towards the C5H4-ring. Hindered olefin rotations interconvert the rotamers with barriers of activation of 58 to 73 kJ mol−1. However, no movements of the η4-diene ligands are observed for 3a, 3b, and 3d. An X-ray diffraction study of 3a shows the η4-diene ligand to have an unusual orientation towards the C5H4-ring.

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