Liberation of H 2 from (o-C 6 H 4 Me) 3 P-H (+) + (-) H-B(p-C 6 F 4 H) 3 ion-pair: A transition-state in the minimum energy path versus the transient species in Born-Oppenheimer molecular dynamics.

Using Born-Oppenheimer molecular dynamics (BOMD) with density functional theory, transition-state (TS) calculations, and the quantitative energy decomposition analysis (EDA), we examined the mechanism of H2 -liberation from LB-H(+) + (-) H-LA ion-pair, 1, in which the Lewis base (LB) is (o-C6 H4 Me)3 P and the Lewis acid (LA) is B(p-C6 F4 H)3 . BOMD simulations indicate that the path of H2 liberation from the ion-pair 1 goes via the short-lived transient species, LB⋯H2 ⋯LA, which are structurally reminiscent of the TS-structure in the minimum-energy-path describing the reversible reaction between H2 and (o-C6 H4 Me)3 P/B(p-C6 F4 H)3 frustrated Lewis pair (FLP). With electronic structure calculations performed on graphics processing units, our BOMD data-set covers more than 1 ns of evolution of the ion-pair 1 at temperature T ≈ 400 K. BOMD simulations produced H2 -recombination events with various durations of H2 remaining fully recombined as a molecule within a LB/LA attractive "pocket"-from very short vibrational-time scale to time scales in the range of a few hundred femtoseconds. With the help of perturbational approach to trajectory-propagation over a saddle-area, we directly examined dynamics of H2 -liberation. Using EDA, we elucidated interactions between the cationic and anionic fragments in the ion-pair 1 and between the molecular fragments in the TS-structure. We have also considered a model that qualitatively takes into account the potential energy characteristics of H-H recombination and H2 -release plus inertia of molecular motion of the (o-C6 H4 Me)3 P/B(p-C6 F4 H)3 FLP.