An analysis of product distributions in the Tsuji-Trost reaction indicates that several instances of reported memory effects can be attributed to slow interconversion of the initially formed syn- and anti-[Pd(eta3-allyl)] complexes. Addition of chloride triggers a true memory effect, in which the allylic terminus originally bearing the leaving group has a higher reactivity. The latter effect, termed regioretention, can be rationalized by ionization from a palladium complex bearing a chloride ion, forming an unsymmetrically substituted [Pd(eta3-allyl)] complex. DFT calculations verify that the position trans to the phosphine ligand is more reactive both in the initial ionization and in the subsequent nucleophilic attack.
Fristrup, P., Jensen, T., Hoppe, J., & Norrby, P-O. (2006). Deconvoluting the memory effect in Pd-catalyzed allylic alkylation; effect of leaving group and added chloride. Chemistry: A European Journal, 12(20), 5352-5360. https://doi.org/10.1002/chem.200600152