Ruthenium-Catalyzed Reductive Cleavage of Unstrained Aryl-Aryl Bonds: Reaction Development and Mechanistic Study

Area of Science:

• Organic Chemistry
• Catalysis
• Synthetic Methodology

Background:

• Carbon-carbon bond cleavage is crucial in industrial processes like petroleum cracking.
• Activating nonpolar, unstrained aryl-aryl bonds remains a significant challenge in synthetic chemistry.

Purpose of the Study:

• To develop a novel ruthenium-catalyzed method for the reductive cleavage of unstrained C(aryl)-C(aryl) bonds.
• To explore the scope and limitations of this new reaction.
• To elucidate the reaction mechanism.

Main Methods:

• Ruthenium-catalyzed reductive cleavage of biaryl compounds.
• Utilized directing groups (DGs) such as pyridine, quinoline, pyrimidine, and pyrazole.
• Employed various terminal reductants including hydrogen gas, Hantzsch ester, silanes, and alcohols.

Main Results:

• Successfully cleaved a wide range of unstrained C(aryl)-C(aryl) bonds in biaryl compounds with directing groups.
• Demonstrated tolerance of numerous functional groups due to the pH-neutral and oxidant-free conditions.
• Achieved a one-pot C-C activation/C-C coupling reaction.
• Identified the catalytic cycle involving a ruthenium(II) monohydride intermediate and a η⁴-coordinated ruthenium(II) dichloride resting state.

Conclusions:

• Developed an effective Ru-catalyzed reductive cleavage of challenging C(aryl)-C(aryl) bonds.
• The method offers broad substrate scope and functional group tolerance.
• Mechanistic insights provide a foundation for future catalytic transformations.