Electrophilic Pt(II) complexes catalyze efficient hydroaminations of olefins by sufforiamides and weakly basic anilines. Catalysts include the structurally characterized complex (COD)Pt(OTf)(2) (1) and the known dimer [PtCl2(C2H4)](2), activated by AgBF4. Experiments with substituted anilines establish an empirical pK(a) cutoff (conjugate acid pKa < 1) for the participation of nitrogen-containing substrates in this catalysis, Arylsulfonamides (conjugate acid pK(a). approximate to -6) with various para substituents hydroaminate olefins such as cyclohexene in yields greater than 95% at 90 degrees C. Hydroamination of propylene by p-toluenesulfonamide proceeds with Markovnikov selectivity, suggesting a mechanism that involves olefin activation at Pt. With norbornene and p-toluenesulfonamide as the substrates and 1 as the catalyst, intermediate [(COD)Pt(norbornene)(2)][OTf](2) (3) was identified and characterized by F-19 and Pt-195 NMR spectroscopies and mass spectrometry. Kinetic studies provide the empirical rate law, rate = k(obs)[Pt][sulfonamide], and are consistent with: a mechanism in which attack of a sulfonamide on the Pt-coordinated olefin is the rate-determining step.