How Frustrated Lewis Acid/Base Systems Pass through Transition-State Regions: H2 Cleavage by [tBu3P/B(C6F5)3]

We investigate the transition-state (TS) region of the potential energy surface (PES) of the reaction tBu(3)P+H-2 +B(C6F5)(3)-> tBu(3)P-H(+)+H(-)-B(C6F5)(3) and the dynamics of the TS passage at room temperature. Owing to the conformational inertia of the phosphane center dot center dot center dot borane pocket involving heavy tBu(3)P and B(C6F5)(3) species and features of the PES E(P center dot center dot center dot H, B center dot center dot center dot H vertical bar B center dot center dot center dot P) as a function of P center dot center dot center dot H, B center dot center dot center dot H, and B center dot center dot center dot P distances, a typical reactive scenario for this reaction is a trajectory that is trapped in the TS region for a period of time (about 350 fs on average across all calculated trajectories) in a quasi-bound state (scattering resonance). The relationship between the timescale of the TS passage and the effective conformational inertia of the phosphane center dot center dot center dot borane pocket leads to a prediction that isotopically heavier Lewis base/Lewis acid pairs and normal counterparts could give measurably different reaction rates. Herein, the predicted quasi-bound state could be verified in molecular collision experiments involving femtosecond spectroscopy.