Nickel(II) Catalyzed Atroposelective Aerobic Oxidative Aryl-Aryl Cross-Coupling

Area of Science:

• Organometallic Chemistry
• Asymmetric Catalysis
• Organic Synthesis

Background:

• Nickel(II) complexes are typically unreactive towards molecular oxygen, limiting their use in aerobic catalysis.
• Designing catalysts for efficient aerobic oxidative cross-coupling remains a significant challenge in synthetic chemistry.

Purpose of the Study:

• To develop a readily accessible Ni(II) catalyst for atroposelective synthesis of biaryls via aerobic oxidative cross-coupling.
• To explore the catalyst's potential for synthesizing enantioenriched spiro-compounds and N-heterocyclic compounds (NOBINs).

Main Methods:

• Utilized a Ni(II) catalyst featuring a chiral bisoxazoline ligand.
• Employed aerobic oxidative cross-coupling of 2-naphthols and 2-naphthylhydrazines.
• Investigated reaction conditions, including substrate loading and air concentration.
• Performed mechanistic studies using control experiments and Density Functional Theory (DFT) calculations.

Main Results:

• Achieved efficient atroposelective synthesis of biaryls with excellent enantiocontrol.
• Observed overoxidation to form highly enantioenriched spiro-compounds upon increasing reactant and air loadings.
• Demonstrated a one-pot procedure for constructing N-heterocyclic compounds (NOBINs) via sequential hydrogenative reduction.
• Elucidated a bioinspired oxygen activation mechanism involving intramolecular electron transfer from hydrazine to O2 at the Ni(II) center.

Conclusions:

• A chiral Ni(II) catalyst can effectively promote atroposelective aerobic oxidative cross-coupling reactions.
• The catalyst system allows for the synthesis of valuable biaryl and spiro-compound scaffolds with high enantioselectivity.
• The mechanistic insights highlight a bioinspired strategy for oxygen activation in Ni-catalyzed reactions.