Experimental Pressure Dependence of Quantum Mechanical Exchange in a Metal Trihydride

The pressure dependence of the hydrogen-pair tunneling frequency in NbH3(cp ")(2)(cp " = C5H3(Si(CH3)(3))(2)) is measured by H-1-NMR spectroscopy in solution. Increasing the pressure to 5 kbar leads to a decrease of the scalar proton-proton coupling constant by 5-8 Hz, depending on the temperature. The pressure dependence of the tunneling frequency is rationalized in terms of the model III of Limbach et al. (Angew. Chem. 1992, 104, 1414) and in terms of solvent interactions.