The rates of displacement of 5-aminoquinoline (5-Aq) and diethyl sulfide (SEt2) from cis-[PtPh2(CO)(L)] (L = 5-Aq or SEt2) by an extended series of aliphatic amines of comparable basicity (pK(a) = 10.6 +/- 0.4) and of widely different steric properties have been measured in dichloromethane solution. The reaction products cis-[PtPh2-(CO)(am)] (1-15) were characterized either as solids or in solution by their IR and H-1 and C-13 NMR spectra. Crystals of cis-diphenyl(pyridine)carbonyl platinum(II) (12) belong to the monoclinic space group P2(1)/n with lattice constants a = 11.756(2) angstrom, b = 9.853(2) angstrom, c = 13.552(2) angstrom, beta = 100.27(2)-degrees, and Z = 4. cis-diphenyl-(diisopropylamine)carbonyl platinum(II) 13 crystallizes in the monoclinic space group P2(1)/n) with lattice constants a = 8.926(2) angstrom, b = 14.439(2) angstrom, c = 14.468(2) angstrom, beta = 92.88(2)-degrees, and Z = 4. Least-squares refinement of the structures led to R factors of 1.93% and 3.08%, respectively. The substitution reactions take place by way of a direct bimolecular attack of the ligand on the substrate. The sulfide group is 100 times more labile than 5-Aq, but both complexes exhibit the same discrimination ability toward the entering amines. The sequence of reactivity observed is NH2(n)Pr almost-equal-to NH2(n)Pent almost-equal-to NH2(n)Hex > NH2Cy almost-equal-to NH2(n)BU > NH2(s)Bu > NH2Bz almost-equal-to pip almost-equal-to py > NH2(t)Bu > NHEt2 almost-equal-to NH(n)Bu2 > NH(i)Pr2, and it is determined by the number and the encumbrance of the substituents on the nitrogen atom. The difference of reactivity between the first and the last members of the series spans 2 orders of magnitude. For the most sterically hindered amines, such as NHCy2 or NEt3, the bimolecular attack is prevented and the reaction proceeds only by way of a nucleophile independent pathway, which most likely involves dissociation of a ligand (5-Aq or SEt2) from the coordination sphere of the metal. Different shapes of steric profiles for the two reactions were obtained by correlating the reactivity data with different sets of steric parameters such as the amine cone angles (theta) of space-filling CPK molecular models or the van der Waals steric repulsion (E(R)) as derived from molecular mechanics calculations. Limits and significance of such relationships are discussed in order to account for apparently conflicting interpretations.