Computational Study on the Mechanism of the Palladium-Catalyzed Arylation of α,β-Unsaturated Aldehydes

The
origin of the regio- and stereocontrol in the Pd-catalyzed γ-arylation
of α,β-unsaturated aldehydes was theoretically investigated.
The reaction proceeds via isomerization of different Pd intermediates
followed by reductive elimination. Up to 10 Pd isomers were identified
and are in equilibrium controlled by an unprecedented swinging palladium
mechanism. The subsequent reductive elimination step showed that the
formation of the favored γ-arylated product was achieved by
a bending of the aryl moiety. Computational studies also shed light
on the mechanism of the arylation reaction and are in good agreement
with the experimental observations where only the γ-arylated
product was detected. All geometries were optimized by density functional
theory using the B3LYP functional with standard double-ζ basis
set (LANL2DZ) and effective core potentials for the palladium center
and the 6-311G­(d,p) basis sets for other atoms. The addition of dispersion
forces and solvent corrections were found to play an important role
in the description of the system.