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

Overview & Synopsis

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) Å) and Mo−H distances (average 1.64(4) Å) are similar to those found in Cp*MoH3(dppe). The closest H−H distance is 1.79 Å, consistent with a classical hydride. The results of ab initio calculations for the CpMoH3(PMe3)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.