Design of a Highly Active Pd Catalyst with P,N Hemilabile Ligands for Alkoxycarbonylation of Alkynes and Allenes: A Density Functional Theory Study

In the palladium‐catalysed methoxycarbonylation of technical propyne, the presence of propadiene poisons the hemilabile Pd(P,N) catalyst. According to density functional theory calculations (B3PW91‐D3/PCM level), a highly stable π‐allyl intermediate is the reason for this catalyst poisoning. Predicted regioselectivities suggest that at least 11 % of propadiene should yield this allyl intermediate, in which the reaction gets stalled under the turnover conditions due to an insurmountable methanolysis barrier of 25.8 kcal mol −1 . The results obtained for different ligands and substrates are consistent with the available experimental data. A new ligand, (6‐Cl‐3‐Me‐Py)PPh 2 , is proposed, which is predicted to efficiently control the branched/linear selectivity, avoiding rapid poisoning (with only 0.2 % of propadiene being trapped as the Pd allyl complex), and to tremendously increase the catalytic activity by decreasing the overall barrier to 9.1 kcal mol −1 .