Mononuclear Palladium(I) Aryl Complexes Performs Cross-Coupling Reactions with Organic Halides

Mononuclear Pd(I) species represent the least understood Pd intermediates in Pd-catalyzed reactions and isolable complexes of the type are exceedingly rare. Herein, we report the synthesis and characterization of mononuclear Pd(I) complexes bear-ing aryl ligands, namely [(IPr)Pd(ArTrip-R-p)] (ArTrip-R-p = 4-R-2,6-bis(2’,4’,6’-triisopropylphenyl)phenyl, R = H, CF3), as well as their reactions with organic halides. The Pd(I) aryl complexes were prepared from the reactions of [(IPr)PdCl2]2 with the corresponding aryl lithium salts and have been characterized by various spectroscopic methods. EPR spectroscopy and calculation studies suggest their Pd(I) nature. Reactivity studies using [(IPr)Pd(ArTrip-CF3-p)] as the representative revealed the capability of the Pd(I) aryl complex in activating the carbon-halogen bonds of organic iodide and benzyl halides. In the reactions with para-substituted benzyl bromides, C(aryl)-C(benzyl) cross-coupling products are formed in moderate to good yields. Kinetic studies, radical trapping experiments, and theoretical calculations point out that the cross-coupling products are likely formed from the sequential steps of stepwise oxidative addition reaction of Pd(I) aryl complex with benzyl bromide involving Pd(II) intermediate followed by reductive elimination reactions of the resulting Pd(III) intermediates.