Ligand Factors in the Isomerization of Olefins by Palladium Complexes

The double bond isomerization of 1-hexene in methylene chloride catalyzed by a series of l,3-dichloro-2-hex-1-ene-4 (p-Z-pyridine N-oxide)-palladium(ll) complexes has been studied. The reaction is very sensitive to the electronic nature of the trans N-oxide ligand, and olefin isomerization results only when the N-oxide ligand dissociates from the original palladium-olefin complex. When the complex contains a strongly electron-withdrawing nitro group on the N-oxide, the dissociative equilibrium is favored in the direction of free ligand and produces a very effective catalyst system. If the complex is structured with p-methylpyridine N-oxide, dissociation is negligible and minimal isomerization occurs. The experimental results support either the metal-hydride or a pseudo-π allyl mechanism for the isomerization. © 1970, American Chemical Society. All rights reserved