Metal-Ligand Cooperativity via Π-Π Interactions Supporting Outer-Sphere Hydride Transfer

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Ruthenium (Ru) pincer complexes are vital catalysts in organic synthesis.
• Developing phosphine-free catalysts is crucial for sustainability and avoiding catalyst poisoning.
• Understanding reaction mechanisms, including metal-ligand cooperativity, is key to catalyst design.

Purpose of the Study:

• To synthesize and characterize novel phosphine-free Ru(II)-CNC pincer complexes.
• To evaluate their catalytic performance in the α-alkylation of ketones using primary alcohols.
• To elucidate the reaction mechanism, particularly the role of metal-ligand cooperativity.

Main Methods:

• Synthesis and characterization of Ru(II)-CNC pincer complexes.
• Catalytic testing for α-alkylation of ketones with primary alcohols.
• Density Functional Theory (DFT) calculations to investigate reaction pathways.

Main Results:

• The synthesized phosphine-free Ru(II)-CNC pincer complexes exhibit excellent catalytic activity.
• DFT studies indicate a dual mechanism (inner- and outer-sphere) for alcohol dehydrogenation, with a preference for the outer-sphere pathway in subsequent steps.
• An unprecedented metal-ligand cooperativity mechanism involving π-π interactions was identified.

Conclusions:

• Phosphine-free Ru(II)-CNC pincer complexes are highly effective catalysts for ketone α-alkylation.
• The catalytic process is facilitated by an outer-sphere mechanism driven by π-π interactions and metal-ligand cooperativity.
• This work offers new insights into catalytic mechanisms and the design of sustainable catalytic systems.