Ligand Effects on Decarbonylation of Palladium-Acyl Complexes

The
influences of perturbations of supporting phosphine ligands
on the dehydrative decarbonylation of (Ln)­PdII(Cl)-hydrocinnamoyl complexes (L = PtBu3, n = 1; L = PPh3, n = 2; L = dppe, n = 1) to yield styrene were studied
through combined experiment and theory. Abstraction of chloride from
the complexes by silver and zinc salts, as well as sodium tetrakis­[3,5-bis­(trifluoromethyl)­phenyl]­borate,
enhanced the efficiency of styrene formation, according to the following
trend in L: PtBu3 > dppe > PPh3.
DFT calculations corroborated the experimental findings and provided
insights into the ligand influences on reaction step barriers and
transition state structures. Key findings include the following: a
stable intermediate forms after chloride abstraction, from which β-hydride
elimination is most affected by ligand choice, the low coordination
number for the PtBu3 case lowers reaction barriers
for all steps, and the trans disposition of two ligands
for L = PPh3 contributes to the low efficiency for styrene
production in that case.