Dinuclear Tetrapyrazolyl Palladium Complexes Exhibiting Facile Tandem Transfer Hydrogenation/Suzuki Coupling Reaction of Fluoroarylketone

Herein, we report an example of dinuclear pyrazolyl-based Pd complexes exhibiting facile tandem catalysis for fluoroarylketone: tetrapyrazolyl dipalladium complexes with varying Pd-Pd distances efficiently catalyze the tandem reaction involving transfer hydrogenation of fluoroarylketone to the corresponding alcohol and Suzuki-Miyaura cross-coupling reaction of the resulting fluoroarylalcohol under moderate reaction conditions, to biaryl alcohol. The complex with the shortest Pd-Pd distance exhibits the highest tandem activity among its dimetallic analogues, and it exceeds, in terms of activity and selectivity, the analogous mononuclear compound. The kinetics of the reaction indicates clearly that reductive transformation of haloarylketone into haloaryalcohol is the rate-determining step in the tandem reaction. Interestingly, while fluoroarylketone undergoes the multistep tandem catalysis, the chloro- and bromo-arylketones undergo only a single step C-C coupling reaction, resulting in biarylketone as the final product. Unlike the pyrazole-based Pd compounds, the precursor PdCl₂ and the phosphine-based relevant complexes (PPh₃)₂PdCl₂ and (PPh₃)₄Pd are found to be unable to exhibit the tandem catalysis.