The mononuclear complexes Pt(P-P')Cl2 (1-3), where P-P' are the chiral ligands (S)-1-diphenylphosphino-2-(diphenylphosphinomethyl)pyrrolidine (S-promephos), (S,S')-1,1'-bis(diphenylphosphino)-2,2'-bipyrrolidine (S-bipyrphos) and (S)-1-diphenylphosphino-2-(diphenylphosphinoxymethyl)pyrrolidine (S-prolophos), resp., were synthesized and studied by NMR spectroscopy and x-ray structure anal. The cis influence on the platinum aminophosphine bond in 1-3 was characterized by the coupling const. 1J(Pt-Pa) which is dominated by the Fermi contact term and varies mainly with the electron d. in the platinum 6s valence orbital. The magnitude of the cis influence is too small to be detected by x-ray anal. because Pt-P bond lengths vary only by .apprx.1 pm. 1 Crystallizes in two different mol. geometries; the six-membered chelate ring adopts either a half-boat or a half-chair conformation. The seven-membered platinum chelate 2 has a boat form. All conformations are fixed by the square planar platinum environment and the fused L-proline mols. In both compds. the Ph groups occupy isoclinal positions but not alternating axial/edge and equatorial/face arrangements. Crystal data: 1.PhMe, monoclinic, space group P21, R = 0.0462; 2.CHCl3, orthorhombic, space group P212121, R = 0.0579.