ONE-DIMENSIONAL AND 2-DIMENSIONAL MULTINUCLEAR NMR-SPECTROSCOPY OF THE ISOMERIC SEMI-SANDWICH COMPLEXES CIS-[(ETA5-C5H5)W(CO)2(H)PME3] AND TRANS-[(ETA5-C5H5)W(CO)2(H)PME3]

The 1:1 mixture of the complexes cis and trans-[(η5-C5H5)W(CO)2(H)PMe3] (1a.b) has been studied by multinuclear magnetic resonance (1H, 13C, 31P, 183W) at variable temperature, with one- and two-dimensional (2d) NMR techniques. This has led to the unambiguous assignment of the 1H(WH), 13C(CO) and all other 13C resonances as well as of the 31P and 183W resonance signals. The sign of the coupling constants 1J(183W13C), 1J183W1H) and 1J(183W31P) was shown to be positive by the consistent results of various 2D X/1H- and inverse 2D 1H{183W} heteronuclear shift correlations. In contrast, a negative sign of 2J(31PW1H)cis/trans and 2J(31PW13C)cis emerged from these experiments. The 13C(CO) resonance signals of the cis-isomer 1a are broadened, even at -40°C, indicating that the cis-cis rearrangement occurs more readily than the cis-trans rearrangement. © 1990.