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HINDERED LIGAND MOVEMENTS IN TRANSITION-METAL COMPLEXES DECARBONYL (ETA-4-DIENE) TUNGSTEN(0)

1992-08-04
Özkar, Saim
KAYRAN, C
KREITER, CG
1,2-Bis(dimethylphosphino)ethane-dicarbonyl-eta-4-diene-tungsten(0) complexes (diene = 1,3-butadiene (1), E-1,3-pentadiene (2), E,E-2,4-hexadiene (3) and E-2-methyl-1,3-pentadiene (4)) were synthesized by UV irradiation of 1,2-bis(dimethylphosphino)ethane-tetracarbonyltungsten(0) and the corresponding dienes in toluene. The constitutions of these complexes were determined by IR and NMR spectroscopy (H-1, C-13, P-31). The spectral data indicate pseudo-octahedral structures for the complexes. When the dienes are assigned to the positions b and c of the coordination octahedron, the 1,2-bis(dimethylphosphino)ethane occupies a and d (e), the two carbonyls e (d) and f positions. 1 and 3 show temperature-dependent NMR signals according to hindered ligand movements with barriers of activation of 50 and 59 kJ mol-1. In contrast, as a consequence of very different isomer populations, no ligand movement is observed for 2 and 4 up to 353 K.