Well-Defined [Pd(NHC)(η³-methylnaphthyl)Br] Complexes in Cross-Coupling Reactions

Area of Science:

• Organometallic Chemistry
• Catalysis
• Synthetic Organic Chemistry

Background:

• Palladium-N-heterocyclic carbene (Pd-NHC) complexes are crucial in modern catalysis.
• Development of efficient and accessible pre-catalysts is essential for widespread application.
• N-heterocyclic carbenes (NHCs) offer strong sigma-donating properties, stabilizing palladium centers.

Purpose of the Study:

• To synthesize and characterize novel Pd(II)-NHC pre-catalysts.
• To evaluate the catalytic activity and activation rates of these pre-catalysts in key cross-coupling reactions.
• To explore alternative synthetic routes, such as using aqueous ammonia.

Main Methods:

• Synthesis of [Pd(NHC)(α/β-η³-MeNAP)Br] pre-catalysts via reaction of [Pd(α/β-η³-MeNAP)Br]₂ with NHC·HCl precursors.
• Utilizing potassium carbonate as a base in acetone for pre-catalyst synthesis.
• Employing aqueous ammonia as a base for the synthesis of a specific Pd(II)-NHC complex.

Main Results:

• A series of well-defined Pd(II)-NHC pre-catalysts were successfully synthesized.
• The synthesized pre-catalysts exhibited good to excellent catalytic activity.
• Rapid activation of the pre-catalysts was observed in Suzuki-Miyaura, Buchwald-Hartwig, and Miyaura borylation reactions.
• Successful synthesis of [Pd(IPr)(α-η³-MeNAP)Br] using aqueous ammonia was achieved.

Conclusions:

• The developed Pd(II)-NHC pre-catalysts are efficient, easily accessible, and rapidly activated.
• These pre-catalysts demonstrate broad utility in important organic transformations.
• The use of aqueous ammonia offers a greener synthetic alternative for certain Pd-NHC complexes.