Selective Decarbonylation of Fatty Acid Esters to Linear α‑Olefins

Selective decarbonylation
of p-nitrophenol esters of fatty acids to the corresponding
linear α-olefins (LAOs) was achieved using palladium catalysis.
After extensive ligand screening, a mixed-ligand system exploiting
the trans-spanning diphosphine XantPhos and an N-heterocyclic carbene
(IPr) was identified as the most effective in yielding high α-selectivity
and high conversions of the ester (>98% selectivity, >90% conversion
using 2.5 mol % of PdCl2 and 5 mol % of the ligands, 190
°C, 2–2.5 h). On the basis of insights from modeling at
the density functional level of theory, we propose that the mixed-ligand
set achieves high α-selectivity by promoting olefin dissociation
from the palladium center following β-hydride elimination, which
is especially facilitated both by the combined steric bias of the
mixed-ligand set and by the ability of the XantPhos ligand to coordinate
in both mono- and bidentate fashions.