The Development of Bulky Palladium NHC Complexes for the Most-Challenging Cross-Coupling Reactions

• Published in: Angewandte Chemie International Edition Vol. 51; no. 14; pp. 3314 - 3332
• Main Authors: Valente, Cory, Çalimsiz, Selçuk, Hoi, Ka Hou, Mallik, Debasis, Sayah, Mahmoud, Organ, Michael G.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 02.04.2012; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Aromatic compounds; bulky ligands; Carbenes; Catalysis; Catalysts; Chemists; cross-coupling; homogeneous catalysis; Ligands; N-heterocyclic carbenes; Palladium; PEPPSI; Phosphines; Stabilization
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201106131

Palladium‐catalyzed cross‐coupling reactions enable organic chemists to form CC bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross‐coupling catalysts attention has recently turned to the use of N‐heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine‐enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki–Miyaura, Negishi, and Stille–Migita cross‐couplings as well as in amination and sulfination reactions. Adding fizz to catalysis: The Pd‐PEPPSI series of catalysts (see scheme) is very active for the Suzuki–Miyaura, Negishi, Stille–Migita, aryl amination, and aryl sulfination reactions. The high reactivities of Pd‐PEPPSI‐IPr and Pd‐PEPPSI‐IPent catalysts with N‐heterocyclic carbene (NHC) ligands are compared with other state‐of‐the‐art catalysts. Pd‐PEPPSI‐IPent is shown to be one of the most active and general catalysts for cross‐coupling reactions.