Synthesis, structure, and hydride-deuteride exchange studies of CpMoH(3)(PMe(2)Ph)(2) and theoretical studies of the CpMoH(3)(PMe(3))(2) model system
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The synthesis and characterization of CpMoH3(PMe2Ph)2,1, is described. Compound 1 is obtained from the reaction between CpMoCl3, PMe2Ph, and LiAlH4, in 61% yield. Compound 1 has also been obtained from the reaction of CpMo(o-C6H4PMe2)(PMe2Ph)2 with H2. Characterization of 1 by 1H- and 31P-NMR spectroscopies shows a high degree of fluxionality for the hydride atoms, even at low temperatures. A single-crystal X-ray structure indicates that the geometry is pseudo-octahedral, with a relative mer arrangement of the three H ligands and the two PMe2Ph ligands occupying relative trans positions. This is in contrast with the only other previously reported structure of a Mo(IV) trihydride, Cp*MoH3(dppe), which adopts a pseudo trigonal prismatic structure. The Mo-P (average 2.41(8) ) and Mo-H distances (average 1.64(4) ) are similar to those found in Cp*MoHs(dppe). The closest H-H distance is 1.79 , consistent with a classical hydride. The results of ab initio calculations for the CpMoH3CPMe3)2 model in different configurations agree with the experimental observations and suggest that a mechanism of hydride exchange consisting of a Bailar twist, which interconverts pseudo-octahedral mer, trans and fac geometries, is possible. The process of hydride-deuteride exchange of 1 in C6D6 is also examined. 1997 American Chemical Society.
