Molybdenum Trihydride Complexes: Computational Model of Oxidatively Induced Reductive Elimination of Dihydrogen

Recent experimental work shows that the 18-electron molybdenum complexes (1,2,4-C 5 H 2 t Bu 3 )Mo(PMe 3 ) 2 H 3  (Cp t Bu MoH 3 ) and (C 5 H i Pr 4 )Mo(PMe 3 ) 2 H 3  (Cp i Pr MoH 3 ) undergo oxidatively induced reductive elimination of dihydrogen (H 2 ), slowly forming the 15-electron monohydride species in tetrahydrofuran and acetonitrile. The 17-electron [Cp t Bu MoH 3 ] +  derivative was stable enough to be characterized by X-ray diffraction, while [Cp i Pr MoH 3 ] +  was not. Density functional theory calculations of the H 2  elimination pathways for both complexes in the gas phase and in a continuum solvent model indicate that H 2  elimination from [Cp i Pr MoH 3 ] +  has a lower barrier than that from [Cp t Bu MoH 3 ] + . Further, a specific solvent association, which is stronger for [Cp t Bu MoH 3 ] +  than for [Cp i Pr MoH 3 ] + , contributes to the stability of the former. In agreement with the experimental observations, the calculations predict that [Cp t Bu MoH 3 ] +  would be in a quartet state at room temperature and a doublet state at 4.2 K, while [Cp i Pr MoH 3 ] +  is in a doublet state even at room temperature.