Moderately Flexible Trans-Chelating Diphosphine Ligands Consisting of a Triazine Unit Showing High Ligand Acceleration Effect for Heck Reaction

摘要

Originally designed trans-chelating diphosphine ligands with moderate flexibility that allows trans-to cis-isomerization and bidentate to monodentate complex form were developed. The novel ligand shows high ligand acceleration effect (LAE) for Heck reaction. The catalyst loading was decreased to 0.0001 mol%, and the turnover number (TON) reached 970,000. The catalytic cycle was evaluated by DFT calculations. The calculations revealed the following: 1) the insertion step in monodentate pathway was the rate-determining step, 2) the high LAE effect of the novel ligand was due to a facile change of conformation from trans to cis form and flexibility to avoid steric repulsion between substrate and catalyst in the insertion step as well.