The good yield of the cross-coupling product in the reaction with the benzyl bromide promoted further experimental and theoretical studies on its mechanism, which support the involvement of radical process in the reaction. Examining the rates of the reactions of 2 with a series of para-substituted benzyl bromides (30 equiv.) in THF revealed that the incorporation of electron-donating or electron-withdrawing substituent on the para-position of benzyl bromides can accelerate the consumption of 2 (Table ). Thus, plotting log(kX/kH) versus σp gave a nonlinear plot (Figure ). However, when taking both polar substituent and spin-delocalization constant parameters into consideration, the multiple linear regression for the dual-parameter equation for radical reactions [log(kX/kH) = ρmbσmb + ρJJ • σJJ • + C] using Jiang's σmb and σJJ • scales can give good linear correlation (Figure ). The value of |ρmb/ρJJ • | equals 1.36, emphasizing the significance of both polar and spin-delocalizing effects. Dual parameter correlation analysis has been successfully applied for the kinetic data of a bromo-abstraction reaction by a nucleophilic silyl radical, the aziridation reaction of iron imido species with substituted styrenes, and the cyclopropanation reaction of an iron ylide complex with styrenes. Furthermore, controlled experiment showed that in the presence of the radical quencher 2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO) the reaction of 2 with methyl 4-(bromomethyl)benzoate does not produce the cross-coupling product 5-CH2C6H4COOMe, but yields the coupling product of the benzylic radical with TEMPO, 6 (Figure ). The adduct of benzylic radical with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 7, was also detected by EPR in the reaction of 2 with methyl 4-(bromomethyl)benzoate and DMPO (Figure ). DFT studies on the reaction profile of the cross-coupling reaction of 2 with methyl 4-(bromomethyl)benzoate suggest that the reaction should start in an inner-sphere singleelectron transfer process and that reductive elimination reaction from Pd(III) intermediates should be responsible for the C-C bond formation step (Figure ). The calculation at the BP86/TZVP level of theory indicates that the single-electron-transfer step that generates a Pd(II) bromide species (IPr)Pd(Br)(Ar Trip -CF3-p) and the benzylic radical • CH2C6H4COOMe is nearly thermal neutral as indicated by the small change of Gibbs free energy of 2.8 kcal/mol (Figure ). The coordination of the benzylic radical to the Pd(II) intermediate forms a Pd(III) intermediate (IPr)Pd(Br)(Ar Trip -CF3-p)(CH2C6H4COOMe) (F) that lies above the reactant E in energy by about 10.3 kcal/mol. Notably, due to the steric demanding nature of IPr and the mterphenyl ligand, the palladium centers in the intermediates E and F are found to adapt T-shape and see-saw geometries, respectively, wherein their C(carbene)-Pd-C(aryl) alignments are nearly linear. The C-C bond forming reductive elimination reaction from F yields the cross-coupling product and Pd(I) species (IPr)PdBr. This step with a substantial change of Gibbs free energy reaching -47.1 kcal/mol is highly exothermic, resulting in an energy gain of 34 kcal/mol for the full conversion from 2 and methyl 4-(bromomethyl)benzoate to the adduct of the cross-coupling product and (IPr)PdBr (G). Among the transition-states throughout the path, the one of the reductive elimination step, TSE-F, that is 23.9 kcal/mol higher in energy than that of the initial starting materials, is the highest one in energy. The calculated low barrier is consistent with the observation that the cross-coupling reaction can readily take place at room temperature.