Enantiomerization pathway and atropochiral stability of the BINAP ligand: a density functional theory study

A theoretical study of the enantiomerization pathway of BINAP, the paradigm of atropochiral ligands in asymmetric organometallic catalysis, is reported. Density functional theory was used with the B3PW91 functional and the 6-31G(d,p) basis set. The calculation level was validated through the study of the syn and anti enantiomerization pathways of the 1,1′-binaphthyl reference for which the enantiomerization barrier was calculated to be in good agreement with experimental data. Calculations were then performed on BINAP itself using the same level of theory, and showed that its enantiomerization mechanism follows the syn route through a concerted, yet highly asynchronous, all-chiral process. The enantiomerization barrier was computed at 213 kJ mol(−1) and proved little sensitive to the functional or to the basis set used, with values always larger than 200 kJ mol(−1). The configurational stability of BINAP was finally characterized by a computed Oki’s racemization temperature of 491 °C.