Abstract
Tricarbonyl-η5-cyclopentadienyl-methyl-tungsten (1) reacts upon UV irradiation with conjugated dienes, like 1,3-butadiene (2), E-1,3-pentadiene (3), 2-methyl-1,3-butadiene (4), 2,3-dimethyl-1,3- butadiene (5), 1,3-cyclopentadiene (6) and 1,3-cyclohexadiene (7), to give the corresponding, quasisquare- pyramidal [(η5-C5H5)W(CO)(COCH3)(η4-diene)] complexes (8-13). With the unsymmetrically substituted dienes 3 and 4, only one of the possible diastereotopic complexes are obtained. At 200 to 230 K, 8-12 show two isomers, which are distinguished by the orientations (o or u) of the diene with respect to the other ligands. The interconversion of the o- and u-isomers was studied by dynamic 1H NMR spectroscopy and is explained by an intramolecular ±180° rotation of the diene ligands in the molecular plane. The barriers o f activation ⊿G* 300 are between 57.8 and 61.0 ± 1 kJ/mol.
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