Mechanism of Pd-Catalyzed Decarbonylation of Biomass-Derived Hydrocinnamic Acid to Styrene Following Activation as an Anhydride

Ortuño, M. A.; Dereli, B.; Cramer, C. J.
Inorg. Chem. 2016, 55, 4124 (doi:10.1021/acs.inorgchem.5b02664).

All elementary steps in the mechanism of Pd-catalyzed decarbonylation of hydrocinnamic acid through formation of a mixed anhydride species have been characterized through electronic structure calculations. Oxidative addition of the mixed anhydride to a singly or doubly ligated Pd is followed by decarbonylation, alkene formation, and catalyst regeneration. Metal-assisted deprotonation of the alkyl-Pd species by a coordinated carboxylate is predicted to be the rate-determining step; theory suggests that bulkier phosphine ligands (e.g., P(o-Tol)₃) reduce the free energy of activation substantially, while variation of the auxiliary anhydride has little influence on efficiency.