DFT studies on the mechanisms of enantioselective Ni-catalyzed reductive coupling reactions to form 1,1-diarylalkanes

Abstract

The detail mechanisms of enantioselective Ni-catalyzed reductive coupling of 5-bromide-2-methoxypyridine (R1) and (1-chloropropyl) benzene (R2) to form 1,1-diarylalkanes (R, S)-P were studied using Density Functional Theory calculations. The overall catalytic cycles include the following basic steps: the oxidative addition, reduction, radical production, radical addition, reductive elimination and the catalyst regeneration. Our calculated results show that the favored way from the reactant (S)-R2 to get the products (R, S)-P is Path C (the NiI catalyst initially combined with alkyl chloride) where the energy barrier of the rate-determining step is the oxidative addition step with 9.1 kcal/mol (of TS1b), but the favored path starting from the reactant (R)-R2 to get the products (R, S)-P is Path A (the NiI catalyst initially combined with aryl bromide) or Path B (the Ni° catalyst initially combined with the aryl bromide) where the energy barrier of the rate-determining step is the radical production step with 12.7 kcal/mol (of (R)-TS2). Our calculated results also indicate that the formation of (R)-P is dominant over the product (S)-P, which meets the experimental results. The ligand effects have also been studied.