Mechanistic Insights and Implications of Dearomative Rearrangement in Copper-Free Sonogashira Cross-Coupling Catalyzed by Pd-Cy*Phine

The
reaction mechanism for the in situ prepared Pd-Cy*Phine
catalyst used in copper-free Sonogashira coupling was investigated
using density functional theory. In addition, the significance of
the meta-terarylphosphine ligand architecture of
Cy*Phine was probed, as it had been previously shown experimentally
to augment catalytic activity relative to its biarylphosphine analogue,
XPhos. The calculated reaction barriers and free energies for the
steps in the catalytic cycle suggest that the suppression of a dearomative
rearrangement pathway is likely to be an important feature for the
improved catalytic performance observed for the Pd-Cy*Phine system.