Mimicking transition metals in borrowing hydrogen from alcohols

Area of Science:

• Organic Chemistry
• Catalysis
• Sustainable Chemistry

Background:

• Transition metal catalysts are typically used in borrowing hydrogen N-alkylation reactions.
• A transition metal-free system for storing and transferring hydrogen via a catalyst backbone is needed.
• Phenalenyl ligands offer a potential alternative to transition metals in catalytic hydrogen transfer.

Purpose of the Study:

• To establish a transition metal-free catalytic system for N-alkylation using the borrowing hydrogen mechanism.
• To demonstrate the ability of a phenalenyl ligand to store and transfer hydrogen.
• To achieve efficient alkylation of anilines with alcohols using this novel system.

Main Methods:

• Utilized a phenalenyl ligand as a transition metal-free catalyst.
• Investigated the mechanism using spectroscopic techniques and deuterium labeling.
• Performed density functional theory (DFT) calculations to elucidate the reaction pathway.

Main Results:

• The phenalenyl ligand successfully mediated borrowing hydrogen N-alkylation of anilines with alcohols.
• A wide substrate scope was achieved, demonstrating the versatility of the system.
• Mechanistic studies revealed a dearomatization process involving sequential addition of H+, H•, and an electron to the phenalenyl backbone.

Conclusions:

• Phenalenyl ligands can effectively replace transition metals in borrowing hydrogen catalysis.
• The developed system provides a sustainable and efficient route for N-alkylation.
• The study offers new insights into metal-free catalytic hydrogen storage and transfer.