Density Functional Theory Studies of the Catalyst Structure–Activity and Selectivity Relationships in Rh(I)-Catalyzed Transfer C–H Borylation of Alkenes

We report the results of a computational
investigation that shed
light on the catalyst structure–activity and selectivity relationships
for our recently developed Rh­(I)-xantphos-catalyzed transfer C–H
borylation of alkenes. Our study uncovered the influence that the
ligand properties have on the free energy surfaces of the reactions
catalyzed by a series of Rh catalysts bearing derivatives of the xantphos
ligand with varied electronic features and steric demands. We present
the full reaction profiles and provide a closer look on how different
modifications to the ligand structure influence each step of the catalytic
reaction. We observed that the increased steric effects have a large
effect on the free energy surfaces, increasing the energy barriers,
thereby decreasing the rates of the reaction. In turn, the electronic
effects can stabilize key transition states and destabilize crucial
intermediates, such as the resting of the catalyst, thus accelerating
the overall catalytic process. Additionally, the electronic effects
can modify the relative rates of the alternative pathways and therefore
affect the selectivity preferences. In general, our study provides
guidelines for the rational development of new catalysts to further
enhance the performance of the catalytic system and address the remaining
challenges.