Earth-Abundant Metal Catalysts for the Dehydrodecarbonylation of Carboxylic Acids to Olefins

John, A.; Miranda, M. O.; Ding, K.; Dereli, B.; Ortuño, M. A.; LaPointe, A. M.; Coates, G. W.; Cramer, C. J.; Tolman, W. B.
Organometallics 2016, 35, 2391 (doi:10.1021/acs.organomet.6b00415).

Combining high-throughput experimentation with conventional experiments expedited discovery of new first-row nickel catalysts for the dehydrodecarbonylation of the bio-derived substrates hydrocinnamic acid and fatty acids to their corresponding alkenes. Conventional experiments using a continuous distillation process (180 ^oC) revealed that catalysts comprised of Ni^II or Ni⁰ precursors (NiI₂, Ni(PPh₃)₄) and simple aryl phosphine ligands were the most active. In the reactions with fatty acids, the nature of the added phosphine influenced the selectivity for α-alkene, which reached a maximum value of 94%. Mechanistic studies of the hydrocinnamic reaction using Ni(PPh₃)₄ as catalyst implicate a facile first turnover to produce styrene at room temperature, but deactivation of the Ni⁰ catalyst by CO poisoning occurs subsequently, as evidenced by the formation of a Ni(CO)(PPh₃)₃, which was isolated and structurally characterized. Styrene dimerization is a major side reaction. Analysis of the reaction mechanism using density functional theory supported catalyst regeneration along with alkene formation as the most energetically demanding reaction steps.