Metallocenium incorporated charge-enhanced thiourea catalysts

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Metallocenium salts are cationic organometallic compounds with potential catalytic applications.
• Friedel-Crafts alkylation is a fundamental reaction in organic synthesis for forming carbon-carbon bonds.

Purpose of the Study:

• To synthesize and characterize novel metallocenium derivatives as catalysts.
• To evaluate the catalytic activity of these compounds in Friedel-Crafts alkylation reactions.
• To explore the role of Lewis and Brønsted acidity in their catalytic performance.

Main Methods:

• Synthesis of N-ferrocenium-N'-phenylthiourea and N-cobaltocenium-N'-phenylthiourea derivatives.
• Catalytic testing in the Friedel-Crafts alkylation of indoles with trans-β-nitrostyrenes.
• Characterization of compounds, including X-ray crystallography for the cobalt analog.

Main Results:

• Successfully prepared three metallocenium salts (4a, 4b, 5) with tetrakis-[3,5-bis(trifluoromethyl)phenyl]borate (BArF4) counterions.
• Demonstrated high catalytic activity in Friedel-Crafts alkylation, outperforming reduced, neutral analogues.
• Identified dual Lewis and Brønsted acidic sites enabling charge-activated catalysis.

Conclusions:

• Metallocenium salts are effective catalysts for Friedel-Crafts alkylation.
• The cationic nature and dual acidity of these compounds are key to their enhanced catalytic activity.
• Cobalt-containing metallocenium thiourea offers superior stability for isolation and characterization.