Abstract The am bidentate chiral phosphinothioform am ides (-)-S- and (+)-R-Ph2P(X)C(S)NHCHMePh with X = 2e- (1a). O (1b), S (1c) were obtained from optically pure S- and R -l-phenylethylamine via the isothiocyanate interm ediates. Coordination of (-)-la to CpM(CO)3Cl(M = Mo, W) and ClMn(CO)5 in methanol proceeds with high stereoselectivity forming the P.S-chelate complexes (+)-2a (Mo), (+)-3a (W) and (-)-4a (Mn) which maintain their configuration in solid state. In solution, how ever, the primary diastereom ers 2aA and 3aA epimerize to 2aB and 3aB with inverted configuration at the metal centre. The equilibrial ratio of B /A ≥ 1 (40 °C) indicates only a slight optical induction. The epimerization rate was determined by polarimetry and follow s a formal first-order kinetics with an average free energy of activation ΔḠ* = 92 ± 5 kJ - mol-1 at 20-40 °C. The N .S-chelates (-)-2b, (-)-3b derived from the P-oxide (-)-lb are configurationally stable up to 80 °C suggesting both a kinetic and thermodynamic preference of the A diastereomer. The enantiomeric complexes (-)-2a, (-)-3a, (+)-2b, (+)-3b obtained from Rconfigurated (+)-la, b display mirror-symmetrical CD plots. In contrast to -1a, b, the P-sulfide 1c does not show any selectivity during coordination to the S.S-chelates 2c and 3c.