Bis(ethylene) complexes of molybdenum- and tungsten-(0) containing the CH3C(CH2PMe2)3 ligand: synthesis, solution conformation and reactivity
- 1 January 1997
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 20,p. 3749-3754
- https://doi.org/10.1039/a704748g
Abstract
The reaction of trans-[M(C2H4)2(PMe3)4] with the tripodal phosphine 1,1,1-tris[(dimethylphosphino)methyl]ethane (CP3) affords complexes trans-[M(C2H4)2(η2-CP3)(PMe3)2] (M = Mo 1a or W 1b). A detailed NMR study, including hetero- and homo-nuclear two-dimensional correlations, has been carried out for 1b which allows a complete assignment of signals and a structural spectroscopic determination. In solution, no ethylene rotation is observed at room temperature and the preferential conformer of the six-membered ring W[η2-CH3C(CH2PMe2)3] fragment is, on the basis of steric arguments, the skew-boat conformation. Interaction of compounds 1 with CO affords trans-[M(C2H4)2(η2-CP3)(CO)(PMe3)] (M = Mo 2a or W 2b), while reaction of 1a with CNBut furnishes the compound trans-[Mo(C2H4)2(η2-CP3)(CNBut)(PMe3)] 3. The bidentate co-ordination of CP3 induces chirality at the metal center and compounds 2 and 3 are obtained as a ca. 1∶1 mixture of diastereoisomers, identified by the presence of two different patterns of resonances in their 31P-{1H} NMR spectra at low temperature. At the fast regimen exchange, the isomers are interconverted through bis(ethylene) rotation. A variable-temperature 31P-{1H} NMR study carried out for 2a gives an approximate value of ΔG‡ for this process of 55 kJ mol–1 at 298 K.Keywords
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