Dissociative pathway of the [Pd(2,2′-bipyridyl)(2-picoline)2]2+ cation

Pyridines of Cs symmetry coordinated to [Pd(bipy)(pyr)2]2+ cations (bipy = 2,2′-bipyridyl; pyr = substituted pyridines) lead to syn and anti isomers due to their perpendicular orientation. Rate constants of syn–anti isomerizations of [Pd(bipy)(2pic)2]2+ (2pic = 2-methyl-pyridine) have been measured by quantitative 2D-EXSY NMR. Results suggest a dissociative (D) pathway involving an unsaturated 14-electrons PdII intermediate stabilized by γ-agostic interactions. Kinetic isotope effect, activation parameters, and crystal structure of the anti isomer support the D mechanism.