Chelate assisted oxidative addition of one equivalent of 2-phosphinothiols (2-(diphenylphosphino)ethanethiol 1, 1-(benzyloxy)-2-(diphenylphosphino) ethanethiol 2 and 2-(diphenylphosphino)-cyclohexanethiol 3) to tetrakis(triphenylphosphine) platinum(0) gives the corresponding hydrido[2-(phosphino-kappa P)thiolato-kappa S]triphenylphosphineplatinum(II) complexes 8-10. Temperature variable NMR studies show that these complexes display a chemical equilibrium between the cis-P,P and trans-P,P geometries, strongly displaced toward the trans-P,P configuration (70-90%). XRD studies carried out on crystals of 8 indicate that although the two geometric isomers are present in solution, only the trans-P,P is obtained in the solid state. These results differ from the cis-P,N geometry observed for the related hydrido[2-(amino-kappa N)thiolato-kappa S] triphenylphosphineplatinum(II) complexes 5-7 in solution. The crystal structures obtained for these aminothiolate hydrides show that the cis-P, N configuration is the only one observed in the solid state. Chelate assisted oxidative addition of one equivalent of 3-(diphenylphosphino) propanethiol 4 to tetrakis(triphenylphosphine) platinum(0) gives the resultant hydrido[3-(phosphino-kappa P)thiolato-kappa S]triphenylphosphineplatinum(II) complex 11. This 3-phosphinothiolate hydride shows in solution only a trans-P, P geometry but presents two chelate ring conformational isomers. Density functional theory calculations have been used to explore the ligand-based stereoelectronic effects that are determinant in the different diastereoisomerism observed in these platinum(II) hydrides (5-11).