Nuclear Quantum Effects on the Nature of Hydroboration Selectivity: Experimental Effects of First-Collision Tunneling.

The understanding of selectivity in reactions exhibiting nonstatistical dynamics is impeded by the limitations of trajectory studies with regard to nuclear quantum effects, especially tunneling. We described here the use of ring-polymer molecular dynamics (RPMD) to account for an unusual regiochemical isotope effect on the regioselectivity of hydroborations of alkenes with BH 3 /BD 3 . RPMD is able to account for the experimental observation, while statistical approaches and classical trajectories fail. The combination of experiment and RPMD trajectories suggests that tunneling in the initial collision of reactants is the major source of the nonstatistical selectivity.