Synthetic and Computational Studies on the Rhodium-Catalyzed Hydroamination of Aminoalkenes

The
influence of ligand structure on rhodium-catalyzed hydroamination
has been evaluated for a series of phosphinoarene ligands. These catalysts
have been evaluated in a set of catalytic intramolecular Markovnikov
hydroamination reactions. The mechanism of hydroamination catalyzed
by the rhodium­(I) complexes in this study was examined computationally,
and the turnover-limiting step was elucidated. These computational
studies were extended to a series of theoretical hydroamination catalysts
to compare the electronic effects of the ancillary ligand substituents.
The relative energies of intermediates and transition states were
compared to those of intermediates in the reaction catalyzed by the
unsubstituted catalyst. The experimental difference in the reactivities
of electron-rich and electron-poor catalysts was compared to the computational
results, and it was found that the activity for the electron-poor
catalysts predicted from the reaction barriers was overestimated.
Thus, the analysis of the catalysts in this study was expanded to
include the binding preference of each ligand, in comparison to that
of the unsubstituted ligand. This information accounts for the disparity
between observed reactivity and the calculated overall reaction barrier
for electron-poor ligands. The ligand-binding preferences for new
ligand structures were calculated, and ligands that were predicted
to bind strongly to rhodium generated catalysts for the experimental
catalytic reactions that were more reactive than those predicted to
bind more weakly.