Kinetics and Inverse Temperature Dependence of a Tsuji-Trost Reaction in Aqueous Buffer

The palladium-catalyzed Tsuji-Trost reaction has been extensively studied under synthetically relevant conditions (millimolar concentrations of substrates and catalyst, aprotic solvents, no additives). Despite the increasing use of the Tsuji-Trost reaction in other areas (e.g., chemical biology), the paucity of kinetic studies at micromolar concentrations of substrates in water has impeded progress. Herein, we show that a fluorescence-based high-throughput method provided massive Eyring plot data and revealed three kinetic regimes. The associated turnover-limiting steps (TLSs) were assigned as the oxidative addition (regime 1; Delta H double dagger > 0), nucleophilic attack (regime 2; Delta H double dagger approximate to 0), and association (regime 3; Delta H double dagger < 0, inverse temperature dependence). A kinetic profile under particular conditions depended on the substrate concentration and reaction temperature. Density functional theory calculations supported these findings. This work indicates that a TLS under dilute conditions may be different from that under synthetically relevant conditions and may provide a path toward the development of faster and more reproducible Tsuji-Trost reactions for synthetic, analytical, and biological applications.