The PN2S chelate N-[N-(3-diphenylphosphinopropionyl)glycyl]-S-tritylcysteine methyl ester [PN2S(Trt)-OMe] was synthesized and reacted with ReOCl3(PPh3)(2) and Ph4P[ReOCl4]. The reactions of both tritylated and detritylated ligands with (ReO)-O-V precursors gave two diastereomers, 9a and 9b, of the ReO(PN2S-OMe) complex. The two isomers, produced in a 1:1 molar ratio, are stable and do not interconvert. They were separated by reverse-phase HPLC and characterized by NMR, FT-IR, and UV-visible spectroscopy and electrospray mass spectrometry. X-ray analysis established for 9a the presence in the solid of the syn isomer. Compound 9a, C21H23N2O5PSRe, crystallized from warm acetonitrile in the triclinic space group P (1) over bar, a = 9.828(2) Angstrom, b = 11.163(2) Angstrom, c = 11.641(2) Angstrom, alpha = 106.48(3)degrees, beta = 109.06(3)degrees, gamma = 102.81(3)degrees, V = 1085.7(4) Angstrom(3), Z = 2. The PN2S coordination set is in the equatorial plane, and the complex shows a distorted square pyramidal coordination. The anti configuration assigned to 9b is consistent with all the available physicochemical data. Follow-up of the reaction of the detritylated ligand with Ph4P[ReOCl4] in ethanol or acetonitrile indicated that the phosphorus atom of the chelate binds first to the metal and that this bond acts as the driving force for coordination.