Mechanistic Understanding of Arylation vs Alkylation of Aliphatic Csp3-H Bonds by Decatungstate-Nickel Catalysis

Computational analysis of the arylation of aliphatic C-sp3-H bonds catalyzed by decatungstate-nickel validates the reaction mechanism and provides valuable insights into how to accomplish the corresponding alkylation. Our analysis indicates that the light-excited decatungstate photocatalyst activates one of the C-sp3-H bonds by a hydrogen atom transfer reaction involving the bridging O atoms of decatungstate. The generated alkyl radical reacts with a bipyridine-based Ni catalytic species to form a Ni-I-alkyl intermediate. Oxidative addition of aryl bromide to this intermediate leads to a Ni-III complex, from which the cross coupling product is liberated via reductive elimination. We also investigated the corresponding prototype reaction where the aryl bromide is replaced by an alkyl bromide, which suggested a too high energy barrier for the oxidative addition of the alkyl bromide to the Ni-I-alkyl intermediate. Variation of the steric and electronic properties of the bipyridine ligand suggests that steric encumbrance in the 6,6 ' position can promote oxidative addition of the alkyl bromide as verified by ad hoc experimental tests.

Automated summary

The study validates the mechanism of arylation of aliphatic C-sp3-H bonds and provides valuable insights into achieving the corresponding alkylation, revealing that steric and electronic properties of the bipyridine ligand play a crucial role in promoting oxidative addition of alkyl bromide. The experimental tests confirmed that steric hindrance at the 6,6' position of the bipyridine ligand can facilitate the oxidative addition reaction.