An Easy Conversion from Platinum(II) Reagents to Platinum(IV) Products: κ³ to κ² Coordination Mode Interconversion, Phenyl Migration, and Ortho C–H Activation Cascade in a Hemilabile “Click”-Triazole Scorpionate Platinum System

A series of platinum phenyl olefin complexes has been prepared that bear hemilabile “Click”-triazole based scorpionate ligands (Tt^R). Mild heating of the olefin adducts initiates a reaction sequence to form stable, cationic Pt­(IV) hydride metallacycles. An attractive mechanism involves κ³/κ² conversion, phenyl migration, and ortho C–H activation. Activation parameters for the overall C–C bond-forming and C–H bond-breaking process were obtained. Insertion products from mono- and disubstituted olefins reveal a kinetic preference for phenyl migration to the less sterically hindered olefin position but a thermodynamic preference for the β-substituted metallacycle isomer, in which steric bulk is further away from the metal center and the Tt^R ligand. Thermolysis converts the kinetically favored products to their thermodynamically stable isomers via a reversible C–C bond cleavage and formation reaction. EXSY NMR and deuterium-labeling studies reveal facile scrambling processes in the metallacycles due to the hemilabile ligand