Palladium complexes of N-heterocyclic carbenes as catalysts for cross-coupling reactions--a synthetic chemist's perspective.
Palladium-catalyzed C-C and C-N bond-forming reactions are among the most versatile and powerful synthetic methods. For the last 15 years, N-heterocyclic carbenes (NHCs) have enjoyed increasing popularity as ligands in Pd-mediated cross-coupling and related transformations because of their superior performance compared to the more traditional tertiary phosphanes. The strong sigma-electron-donating ability of NHCs renders oxidative insertion even in challenging substrates facile, while their steric bulk and particular topology is responsible for fast reductive elimination. The strong Pd-NHC bonds contribute to the high stability of the active species, even at low ligand/Pd ratios and high temperatures. With a number of commercially available, stable, user-friendly, and powerful NHC-Pd precatalysts, the goal of a universal cross-coupling catalyst is within reach. This Review discusses the basics of Pd-NHC chemistry to understand the peculiarities of these catalysts and then gives a critical discussion on their application in C-C and C-N cross-coupling as well as carbopalladation reactions.
Kantchev
Eric Assen B
EA
Institute of Bioengineering and Nanotechnology (IBN), 31 Biopolis way, no. 04-01, The Nanos, Singapore 138 669, Singapore.
O'Brien
Christopher J
CJ
Organ
Michael G
MG
D002384:Catalysis; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010165:Palladium / Q000737:chemistry*
D006571:Heterocyclic Compounds; D008024:Ligands; D010165:Palladium