Ruthenium polyhydrides supported by rigid PCP pincer ligands: dynamic behaviour and reactions with CO₂

Area of Science:

• Organometallic Chemistry
• Catalysis
• Coordination Chemistry

Background:

• Development of pincer ligands for transition metal catalysis.
• Ruthenium complexes as catalysts for CO2 transformations.
• Understanding fluxional processes in polyhydride complexes.

Purpose of the Study:

• Synthesize and characterize novel ruthenium pincer complexes.
• Investigate the reactivity of these complexes with CO2.
• Evaluate their potential as catalysts for CO2 hydrogenation.

Main Methods:

• Synthesis of rigid β-elimination immune PCcarbeneP pincer ligands and their ruthenium complexes.
• Conversion to hydrido chlorides and polyhydride complexes using dihydrogen and base.
• Spectroscopic studies (NMR) to elucidate speciation and fluxional processes.
• Reactions with CO2 to form formato hydride complexes.
• Catalytic testing for CO2 hydrogenation.

Main Results:

• Formation of novel ruthenium dichloride and polyhydride complexes.
• Dynamic behavior and fluxional processes observed in polyhydride complexes.
• Rapid reaction of polyhydrides with CO2 to yield formato hydrides.
• Reversible vs. irreversible hydride shifts depending on ligand substitution.
• CO2 exchange studies indicating a bimolecular mechanism.
• Poor catalytic performance for CO2 hydrogenation due to carbonate complex precipitation.

Conclusions:

• Novel ruthenium pincer complexes were successfully synthesized and characterized.
• The reactivity with CO2 and subsequent hydride shifts were elucidated.
• The investigated complexes are not efficient catalysts for CO2 hydrogenation due to catalyst deactivation by carbonate precipitation.