Balancing Stability and Reactivity: A Robust Pd(II) Biaryl Precatalyst for Rapid Generation of Catalytically Active Pd(0) Species

Abstract

Balancing long-term stability and rapid activation of Pd precatalysts in cross-coupling catalysis remains a fundamental challenge. Pd(0) precatalysts readily form active species but lack stability in air, whereas Pd(II) precatalysts often undergo undesired side reactions during the initial reduction step required to form the Pd(0) species. Herein, we report a robust Pd(II) biaryl precatalyst that combines excellent air stability with rapid and clean generation of Pd(0) species. The precatalyst design incorporates N,N,N′,N′-tetramethylethylenediamine (TMEDA), a chelating ligand, with a pentafluorophenyl moiety to suppress premature reductive elimination. The complex remains stable for several months in the solid state and for at least 48 h in solution under air. Upon addition of phosphine ligands, the precatalyst undergoes quantitative reductive elimination under mild heating to generate well-defined Pd(0) species without ligand oxidation, Pd black formation, or substrate consumption. The precatalyst exhibits high catalytic performance in the Suzuki-Miyaura coupling, Buchwald-Hartwig amination, and the synthesis of a hole-transporting material, achieving high turnover numbers at low catalyst loadings. In direct arylation polycondensation, the precatalyst delivers polymers free of structural defects arising from initiation-stage side reactions. These features establish the Pd(II) precatalyst as a practical and reliable platform for smallmolecule synthesis and material-oriented catalysis.