A Frustrated Phosphane-Borane Lewis Pair and Hydrogen: A Kinetics Study

The energy profile of a frustrated Lewis pair (FLP) dihydrogen splitting system was determined by a combined experimental kinetic and DFT study. A trimethylene‐bridged phosphane–borane FLP was converted into its endothermic H2‐cleavage product by sequential H+/H− addition. The system could be handled at low temperature, and the kinetics of the H2 elimination were determined to give a rate constant of kHH,exp(299 K)=(2.87±0.1)×10−4 s−1 in solution. The primary kinetic isotope effects were determined; for example, (kHH/kDD)exp=3.19. The system was accurately analyzed by DFT calculations. Retro‐kinetics: An evaluation of a dihydrogen splitting reaction utilizing a phosphane–borane frustrated Lewis pair was carried out by theory and experiment. The evaluation used the reverse reaction, namely, H2 elimination from a PH+/BH− zwitterion. H2 elimination kinetics gave a rate constant kHH,exp(299 K)=(2.87±0.1)×10−4 s−1, and kinetic isotope effects were determined; for example, (kHH/kDD)exp=3.19.