Structural Requirements in Chiral Diphosphine–Rhodium Complexes. XIV. Heptagonal Chelating Ring Flexibility in Rhodium(I) Complexes of Trans‐1,2‐bis(Diphenylphosphinomethyl)cycloalkanes

Z‐N‐acyldehydroamino acids and esters were hydrogenated with in‐situ prepared rhodium(I) complexes, containing trans‐4,5‐bis(diphenylphosphinomethyl)‐2,2‐dimethyl‐1,3‐dioxolan (DIOP) or its carbocyclic analogues — trans‐1,2‐bis(diphenylphosphinomethyl)cycloalkanes. The optical purities of the N‐acylamino acid and ester products do not reflect a simple correlation with the PCH₂–C–C–CH₂P torsional angle within the diphosphine moiety of the catalytic complex, but are related to the flexibility of the heptagonal chelating ring. The relationship between the chiral sense of the major reduction product and the structure of the diastereomeric enamide adduct complexes is also discussed.