Remote Hydrogen Bonding between Ligand and Substrate Accelerates C-H Bond Activation and Enables Switchable Site...

Area of Science:

• Organic Chemistry
• Catalysis
• Synthetic Methodology

Background:

• Transition-metal catalysis is crucial for activating inert C-H bonds, enabling streamlined organic synthesis.
• Designing catalysts that utilize noncovalent interactions for substrate recognition offers a promising route to control reactivity and selectivity.
• Selective functionalization of organic molecules remains a significant challenge in synthetic chemistry.

Purpose of the Study:

• To develop a novel metal catalyst for site-selective C-H borylation of organic substrates.
• To investigate the role of noncovalent interactions, specifically hydrogen bonding, in controlling catalytic selectivity.
• To demonstrate a generalizable strategy for designing recognition elements in ligands for enhanced catalytic performance.

Main Methods:

• Synthesis of a spirobipyridine ligand featuring a hydroxyl group for hydrogen bonding interactions.
• Combination of the synthesized ligand with an iridium catalyst to form a catalytic system.
• Evaluation of the catalytic system's performance in C-H borylation reactions with pyridine and quinoline substrates.

Main Results:

• The iridium catalyst, utilizing the designed spirobipyridine ligand, achieved site-selective C-H borylation.
• The hydroxyl group on the ligand facilitated hydrogen bonding, enabling recognition and selective functionalization of pyridine and quinoline substrates.
• Site selectivity was tunable by altering the hydroxyl group's position on the ligand, and the catalyst demonstrated enhanced reaction rates and overcame steric hindrance.

Conclusions:

• A novel ligand-metal catalyst system enables highly selective C-H borylation through hydrogen-bonding-mediated substrate recognition.
• The ability to switch selectivity by modifying the ligand's recognition moiety highlights a generalizable strategy for catalyst design.
• This approach mimics enzymatic catalysis, offering a powerful tool for efficient and selective functionalization of organic molecules.