Platinum-Based Catalysts for the Hydroamination of Olefins with Sulfonamides and Weakly Basic Anilines

Electrophilic Pt(II) complexes catalyze efficient hydroaminations of olefins by sulfonamides 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
pKa cutoff (conjugate acid pKa < 1) for the participation of nitrogen-containing substrates in this catalysis.
Arylsulfonamides (conjugate acid pKa ≈ −6) with various para substituents hydroaminate olefins such as
cyclohexene in yields greater than 95% at 90 °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 19F and 195Pt NMR spectroscopies and mass
spectrometry. Kinetic studies provide the empirical rate law, rate = kobs[Pt][sulfonamide], and are consistent
with a mechanism in which attack of a sulfonamide on the Pt-coordinated olefin is the rate-determining
step.