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)tBu(3))Mo-(PMe3)(2)H-3 ((CpMoH3)-Mo-tBu) and (C(5)HiPr(4))Mo(PMe3)(2)H-3 ((CpMoH3)-Mo-iPr) undergo oxidatively induced reductive elimination of dihydrogen (H-2), slowly forming the 15-electron monohydride species in tetrahydrofuran and acetonitrile. The 17-electron [(CpMoH3)-Mo-tBu](+) derivative was stable enough to be characterized by X-ray diffraction, while [(CpMoH3)-Mo-iPr](+) 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 [(CpMoH3)-Mo-iPr](+) has a lower barrier than that from [(CpMoH3)-Mo-tBu](+). Further, a specific solveht association, which is stronger for [(CpMoH3)-Mo-tBu](+) than for [(CpMoH3)-Mo-iPr](+), contributes to the stability of the former. In agreement with the experimental observations, the calculations predict that [(CpMoH3)-Mo-tBu](+) j would be in a quartet state at room temperature and a doublet state at 4.2 K, while [(CpMoH3)-Mo-iPr](+) is in a doublet state even at room temperature.