Stereochemical Stability of Planar-Chiral Benzazepine Tricyclics: Inversion Energies of P- and S-Alkene Ligands

Inversion barriers Delta G double dagger for planar chiral phosphine-alkene and sulfonamide-alkene hybrid ligands based on phenyl-dibenz-[b,f]-azepine have been determined by density-functional theory calculations. Analysis of the structural and electronic characteristics of the minima and transition states explains the magnitudes of Delta G double dagger and the geometrical changes during the inversion process. The steric repulsion caused by bulky substituents attached to the azepine nitrogen atom has a pronounced effect on the Delta G double dagger value, explaining, inter alia, the stereochemical stability of the P- and S-alkene ligands when compared to the fluxional parent compound where X = H.