Influence of Anionic Ligand Exchange in Latent Sulfur-Chelated Ruthenium Precatalysts

Area of Science:

• Organometallic Chemistry
• Catalysis
• Ruthenium Complexes

Background:

• Ruthenium benzylidenes are vital catalysts for olefin metathesis.
• Developing room-temperature-latent precatalysts is crucial for practical applications.
• Tuning catalyst activity through ligand modification and solvent effects is an ongoing area of research.

Purpose of the Study:

• To synthesize and characterize novel cis-dianionic S-chelated ruthenium benzylidene complexes.
• To investigate the influence of ligand exchange and solvent on precatalyst latency and activity.
• To explore the distinct catalytic behaviors, including metathesis and cycloisomerization, of these complexes.

Main Methods:

• Synthesis of ruthenium benzylidenes via chloride ligand exchange.
• Anion exchange reactions to generate various precatalysts.
• Catalytic testing in ring-closing metathesis and cycloisomerization reactions.
• Solvent screening and cocatalyst addition studies.

Main Results:

• Four new cis-dianionic S-chelated ruthenium benzylidenes were successfully synthesized.
• Room-temperature-latent precatalysts were generated through facile anion exchange.
• Catalytic activity was highly dependent on the solvent and counterion.
• The iodide complex efficiently catalyzed ring-closing metathesis in toluene.
• Carboxylate complexes showed poor activity but could be activated by abstracting chlorides from solvents.
• In THF, the dichloro complex promoted cycloisomerization, but metathesis activity was restored with phenylacetylene.

Conclusions:

• The cis-dianionic S-chelate conformation facilitates anion exchange and precatalyst activation.
• Solvent choice and ligand identity significantly dictate the catalytic pathway (metathesis vs. cycloisomerization).
• These findings offer insights into designing tunable ruthenium catalysts for specific transformations.