Quantifying the Electronic Effect of C4 and C4 & PRIME; Positions of Bipyridine Ligand on Pd(II)/Rh(I)-Catalyzed Conjugate Addition Reaction: A DFT Study

The electronic effects of the bidentate ligands play a vital role in the transition metal-catalyzed conjugate addition reactions. Here, the insertion step (rate-determining step (RDS) of the conjugate addition) catalyzed by Pd(II)/Rh(I)-complexes with 26 bipyridine-type (bpy) ligands linking different substituent groups in the opposite sides (C4, C4 & PRIME; position) are systematically studied by density functional theory (DFT). It is found that for both Pd(II)- and Rh(I)-catalysis, the stronger the electron-withdrawing group connecting to both C4 and C4 & PRIME; positions of bpy ligands can promote the insertion step. The predominance of & pi;-back donation in Rh(I) and & sigma;-donation in Pd(II) is the main reason for above different electronic properties of Pd(II) and Rh(I)-catalysis. This work gives enough theoretical guide to the rational design of the efficient transition metal-based catalyst for conjugate addition.