| Popis: |
The transfer of a -hydrogen from a metal-alkyl group to ethylene is a fundamentalorganometallic transformation. Previously proposed mechanisms for this transformation involve either atwo-step -hydrogen elimination and migratory insertion sequence with a metal hydride intermediateor a one-step concerted pathway. Here, we report density functional theory (DFT) quasiclassical directdynamics trajectories that reveal new dynamical mechanisms for the -hydrogen transfer of[Cp*RhIII(Et)(ethylene)]Despite the DFT energy landscape showing a two-step mechanism with a Rh-Hintermediate, quasiclassical trajectories commencing from the -hydrogen elimination transition staterevealed complete dynamical skipping of this intermediate. The skipping occurred either extremely fast(typically dynamically unrelaxed mechanism. Consistent with trajectories begun at the transition state, alltrajectories initiated at the Rh-H intermediate show continuation along the reaction coordinate. All ofthese trajectory outcomes are consistent with the Rh-H intermediate the -hydrogen elimination and migratory insertion transition states. For Co, which on the energylandscape is a one-step concerted mechanism, trajectories showed extremely fast traversing of thetransition-state zone (ballistic mechanism. In contrast to Rh, for Ir, in addition to dynamically ballistic and unrelaxedmechanisms, trajectories also stopped at the Ir-H intermediate. This is consistent with an Ir-Hintermediate that is stabilized by ~3 kcal/mol relative to the -hydrogen elimination and migratoryinsertion transition states. Overall, comparison of Rh to Co and Ir provides understanding of therelationship between the energy surface shape and resulting dynamical mechanisms of anorganometallic transformation. |
