Mechanism of the Stereomutation of an Azaplatinacyclobutane Complex

The diastereomerically pure azaplatinacyclobutane complex Unlabelled Image, bearing a single deuterium atom at Cα, undergoes stereomutation about the Cα–Cβ bond of the azaplatinacyclobutane moiety at 30°C with a half-life of 3.0 h. Kinetic analysis of the stereomutation of cis-6-α-d1 established the activation parameters ΔH‡ = 26 ± 2 kcal mol–1 and ΔS‡ = 6 ± 6 eu and a deuterium kinetic isotope effect resulting from deuteration of the Cβ atom of kH/kD = 1.32. These and related experiments support a mechanism for stereomutation involving rapid and reversible amine dissociation, reversible β-hydride elimination, and rate-limiting rotation about the Cα–Cβ bond of the resulting platinum enamine complex.