Reductive Eliminations from Diarylpalladium(II) Complexes: A Combined Experimental and Computational Investigation

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Reductive elimination is a key step in many catalytic cycles involving palladium.
• Understanding the mechanisms of reductive elimination from diarylpalladium(II) complexes is crucial for designing efficient catalysts.
• Tetradentate ligands offer unique coordination environments that can influence reaction pathways.

Purpose of the Study:

• To investigate the diverse mechanisms for reductive elimination of biaryl compounds from diarylpalladium(II) complexes.
• To identify and characterize distinct chemical triggers that initiate reductive elimination.
• To elucidate the regioselectivity and mechanistic details of these transformations.

Main Methods:

• Combined experimental and computational study.
• Kinetic experiments to probe reaction rates and mechanisms.
• Density Functional Theory (DFT) calculations to model reaction pathways and intermediates.
• Thermal stability studies in inert solvents.
• Investigation of reactions in the presence of electron-donor ligands, oxidants, and organic acids.

Main Results:

• Identified at least four distinct chemical triggers for reductive elimination with specific regioselectivity.
• Demonstrated high thermal stability of diarylpalladium(II) complexes in inert solvents, indicating a high barrier for unimolecular elimination.
• Showed that electron-donor ligands (e.g., triphenylphosphine) promote facile reductive elimination via associative ligand exchange, consistent with computational findings.
• Revealed that oxidants (e.g., H2O2) can induce reductive elimination at room temperature through palladium(IV) intermediates.
• Observed that organic acids can facilitate reductive elimination with altered regiochemical outcomes due to complex rearrangement.

Conclusions:

• The reductive elimination of biaryl compounds from diarylpalladium(II) complexes is a versatile process controllable by various external stimuli.
• The choice of trigger dictates the reaction mechanism, regioselectivity, and efficiency of biaryl formation.
• This work provides fundamental insights into palladium catalysis, enabling the rational design of synthetic strategies for complex molecule synthesis.