Ligand Effects on Decarbonylation of Palladium-Acyl Complexes

The influences of perturbations of supporting phosphine ligands on the dehydrative decarbonylation of (L_n)­Pd^II(Cl)-hydrocinnamoyl complexes (L = P^tBu₃, 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: P^tBu₃ > 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 P^tBu₃ 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.