Secondary and tertiary phosphinothioformamides have proved to be flexible, ambidentate complex ligands. Structural differences in solid and dissolved state have been made observable by carbon-13 CP-MAS NMR techniques. The (CO)4M(PS) complexes (M = Cr, Mo, W) react with mono-dentate ligands under reversible fission of the metal-sulfur bond which favours the application of such systems in metal-catalyzed syntheses. We suggest three ways for the preparation of chiral phosphinothioformamides which show a high diastereoselectivity upon coordination to prochiral half-sandwich complexes.