Quasi-equilibrium between catalytic reactive intermediates and reactant or product molecules is a common assumption. As process conditions vary, this assumption may cease to be valid because of kinetic coupling between steps in the catalytic cycle. In the case of coupled catalytic cycles, kinetic coupling manifests itself by substantial changes in selectivity. An elegant example of catalytic coupling in and between catalytic cycles is the change in enantioselection with H2 pressure for the asymmetric hydrogenation of a prochiral alkene, as discovered in the Halpern laboratory.