Quasiclassical direct dynamics reveal new dynamical mechanisms for metal-alkyl to ethylene β-hydrogen transfer.

SbVF5 is generally assumed to oxidize methane through a methanium-to-methyl cation mechanism.

<div>The transfer of a -hydrogen from a metal-alkyl group to ethylene is a fundamental</div><div>organometallic transformation. Previously proposed mechanisms for this transformation involve either a</div><div>two-step -hydrogen elimination and migratory insertion sequence with a metal hydride intermediate</div><div>or a one-step concerted pathway. Here, we report density functional theory (DFT) quasiclassical direct</div><div>dynamics trajectories that reveal new dynamical mechanisms for the -hydrogen transfer of</div><div>[Cp*RhIII(Et)(ethylene)]</div><div>Despite the DFT energy landscape showing a two-step mechanism with a Rh-H</div><div>intermediate, quasiclassical trajectories commencing from the -hydrogen elimination transition state</div><div>revealed complete dynamical skipping of this intermediate. The skipping occurred either extremely fast</div><div>(typically <100 femtoseconds (fs)) through a dynamically ballistic mechanism or slower through a</div><div>dynamically unrelaxed mechanism. Consistent with trajectories begun at the transition state, all</div><div>trajectories initiated at the Rh-H intermediate show continuation along the reaction coordinate. All of</div><div>these trajectory outcomes are consistent with the Rh-H intermediate <1 kcal/mol stabilized relative to</div><div>the -hydrogen elimination and migratory insertion transition states. For Co, which on the energy</div><div>landscape is a one-step concerted mechanism, trajectories showed extremely fast traversing of the</div><div>transition-state zone (<50 fs), and this concerted mechanism is dynamically different than the Rh</div><div>ballistic mechanism. In contrast to Rh, for Ir, in addition to dynamically ballistic and unrelaxed</div><div>mechanisms, trajectories also stopped at the Ir-H intermediate. This is consistent with an Ir-H</div><div>intermediate that is stabilized by ~3 kcal/mol relative to the -hydrogen elimination and migratory</div><div>insertion transition states. Overall, comparison of Rh to Co and Ir provides understanding of the</div><div>relationship between the energy surface shape and resulting dynamical mechanisms of an</div><div>organometallic transformation.</div>