Towards the Limit of Atropochiral Stability: H‐MIOP, an N‐Heterocyclic Carbene Precursor and Cationic Analogue of the H‐MOP Ligand

The configurational stability of biaryl motifs is addressed for the 1‐naphthyl‐ N ‐benzimidazolyl motif substituted by a single diphenylphosphinyl group at the 2‐position. The atropoenantiomers of the N‐methylated cation H‐MIOP, a less sterically locked analogue of the neutral H‐MOP ligand, were resolved by enantiospecific cleavage of the N 2 CP bond of the resolved enantiomers of BIMIONAP. The latter were obtained by enantiospecific N‐methylation of the previously resolved enantiomers of neutral BIMINAP. PdCl 2 complexes of the P,C‐chelating N ‐heterocyclic carbene (NHC)–phosphine ligands derived from ( R )‐ and ( S )‐H‐MIOP were prepared by two enantiospecific routes: by N 2 CP bond cleavage from the ( R )‐ and ( S )‐BIMIONAP–PdCl 2 complexes, or by simultaneous coordination of the P and C atoms of the in situ generated free NHC–phosphine. The enantiomerization pathways of H‐MOP, H‐MIOP, and corresponding NHC–phosphine have been investigated at the B3PW91/6‐31G(d,p) level of theory. The calculated enantiomerization barriers of H‐MOP and H‐MIOP in acetonitrile are equal to 176.0 and 146.4 kJ mol −1 , respectively, and are mainly determined by the distortion of the naphthalene and/or benzimidazole motifs in the transition state. Beyond the stability of their optical rotation at room temperature, the respective calculated Oki’s racemization temperatures of 334 and 225 °C allowed us to consider both ligands as configurationally stable.