Palladium-Catalyzed Ethylene Methoxycarbonylation Using Bidentate Phosphines: How the Stereochemistry of the Ligand...

To elucidate the diastereomeric control of bidentate P-ligands in the ethylene methoxycarbonylation, a comparative and systematic experimental and computational investigation was conducted on the catalytic activity of the Pd-complexes of the racemic, meso, and epimerized LIKATphos ligands (py^tbpx, B) as well as the Lucite ligand (d^tbpx, A). The experimental study revealed that the racemic ligand (py^tbpx, B) exhibited the highest catalytic activity, while the Lucite ligand (d^tbpx, A) exhibited the lowest activity, and the meso ligand (py^tbpx, B) exhibited moderate activity. This activity order follows the same trend as the CO coordination energy to the palladium hydride complex for B, while the methanolysis is the rate-limiting step with A. The enhanced catalytic activity exhibited by the chiral py^tbpx (B) is attributed to the higher stability of the hydride complex and lower stability of the CO complex compared to the meso py^tbpx (B). The higher activity of the Pd-complexes of py^tbpx (B) over the Pd-complexes of d^tbpx (A) is attributed to the built-in base effect.