Intraligand Charge Transfer Enables Visible-Light-Mediated Nickel-Catalyzed Cross-Coupling Reactions.

Area of Science:

• Organometallic Chemistry
• Photocatalysis
• Organic Synthesis

Background:

• Visible-light photocatalysis offers a sustainable approach to organic synthesis.
• Nickel-catalyzed cross-coupling reactions are fundamental in constructing complex molecules.
• Developing efficient and recyclable catalytic systems remains a key challenge.

Purpose of the Study:

• To develop a novel photoactive nickel precatalyst for visible-light-mediated cross-coupling reactions.
• To elucidate the activation mechanism of the nickel precatalyst under visible light.
• To engineer a recyclable heterogeneous catalyst from the developed system.

Main Methods:

• In situ formation of a photoactive nickel(II) precatalyst (Ni(Czbpy)Cl2) from a nickel salt and a bipyridine ligand.
• Visible-light irradiation to activate the precatalyst for cross-coupling reactions.
• Spectroscopic and theoretical investigations to understand the catalytic mechanism.
• Ligand polymerization to create a porous, recyclable organic polymer support for heterogeneous catalysis.

Main Results:

• The Ni(Czbpy)Cl2 precatalyst effectively mediates visible-light-driven carbon-heteroatom cross-coupling reactions.
• A novel activation mechanism involving intraligand charge transfer, distinct from metal-to-ligand charge transfer, was identified.
• Polymerization of the ligand resulted in a porous, recyclable organic polymer.
• The heterogeneous catalyst demonstrated stable performance in a packed-bed flow reactor over a week of continuous operation.

Conclusions:

• A new class of photoactive nickel catalysts activated by visible light has been developed.
• The catalytic system utilizes a unique intraligand charge transfer mechanism for efficient cross-coupling.
• The formation of a recyclable heterogeneous catalyst from ligand polymerization offers a sustainable approach to nickel catalysis.
• The demonstrated stability in flow conditions highlights the potential for industrial applications.