Exploring the reductive CO₂ fixation with amines and hydrosilanes using readily available Cu(II) NHC-phenolate...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Green Chemistry

Background:

• N-methylation is crucial for synthesizing pharmaceuticals and valuable compounds.
• Utilizing inexpensive and non-toxic carbon dioxide (CO2) as a methylating agent is highly desirable.
• Developing efficient catalytic systems for CO2-based N-methylation is an active research area.

Purpose of the Study:

• To synthesize novel homoleptic Cu(II) complexes with hybrid N-Heterocyclic Carbene (NHC)-phenolate ligands.
• To explore the catalytic activity of these complexes in the N-methylation of amines using CO2 and hydrosilanes.
• To develop a new, efficient, and mild reaction protocol for N-methylation.

Main Methods:

• Synthesis of four novel Cu(II) complexes featuring NHC-phenolate ligands with specific trans coordination geometry.
• Catalytic N-methylation reactions employing the synthesized Cu(II) complexes, CO2, hydrosilanes, and an ionic liquid solvent ([BMMIM][NTf2]).
• Investigation of reaction pathways using different hydrosilanes and analysis of catalyst behavior under reaction conditions.

Main Results:

• Successful synthesis of four novel Cu(II) complexes with bidentate or tetradentate NHC-phenolate ligands.
• Development of a new protocol for high-yield N-methylation of secondary aromatic amines and dibenzylamine under mild conditions.
• Identification of distinct reaction pathways depending on the hydrosilane used and observation of Cu(II) complex reduction during catalysis.

Conclusions:

• Novel Cu(II)-NHC-phenolate complexes are effective catalysts for amine N-methylation using CO2.
• The developed protocol offers an efficient and mild route for synthesizing methylated amines.
• Understanding the catalytic mechanism, including catalyst reduction and pathway variations, is essential for further optimization.