N-Heterocyclic Carbenes as Ligands

N-heterocyclic carbenes (NHCs) have demonstrated their utility as ligands in a variety of cross-coupling reactions [173-176]. The oxidative addition of aryl halides 

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Nolan SP, Viciu MS (2005) The Use of N-Heterocyclic Carbenes as Ligands in Palladium Mediated Catalysis. 14 241-278... 

Despagnet-Ayoub E, Ritter T (2006) N-Heterocyclic Carbenes as Ligands for Olefin Metathesis Catalysts. 2f 193-218... 

Rogers MM, Stahl SS (2006) N-Heterocyclic Carbenes as Ligands for High-Oxidation-State Metal Complexes and Oxidation Catalysis. 21 21-46 Roland S, Mangeney P (2005) Chiral Diaminocarbene Complexes, Synthesis and Application in Asymmetric Catalysis. 15 191-229 Roll R, see Behr A (2008) 23 19-52... 

The attractivity of N-heterocyclic carbenes as ligands for transition metal catalysis is a result of the following features. 

N-Heterocyclic Carbenes as Ligands for Olefin Metathesis Catalysts... 

R. Noyori (1994) supercritical fluid (CO2) in homogeneous catalysis W. A. Herrmann (1994) N-heterocyclic carbenes as ligands in catalysis J.-M. Basset (>1991) surface organometallic chemistry... 

On the nature of the active species in palladium catalyzed Mizoroki-Heck and Suzuki-Miyaura couplings (particularly, Pd complexes with imi-nopyridine and N-heterocyclic carbenes as ligands) 06ASC609. 

N -heterocyclic carbenes as ligands in this process. In particular complex (2.115) where the oxazoline moiety has been replaced with an imidazolylidine group has been shown to be as effective as some PHOX ligands in the hydrogenation of ( )-arylethenes. ... 

In recent years, there has been a considerable focus on the development of new reaction conditions that use only molecular oxygen as the co-oxidant and do not require DMSO solvent [19]. Considerable progress has been made through the use of palladium catalysts supported by pyridine or N-heterocyclic carbenes as ligands. For example, Stahl has demonstrated that the 2-allylaniline derivative 14 is transformed to indoline 15 in 79% yield upon treatment with 5 mol% IMesPd(TFA)2 and 10 mol% benzoic acid (Eq. (1.8)) 19d]. Stoltz has reported the conversion ofamide 16 to lactam 17 under similar reaction conditions (Eq. (1.9)) [19b]. Through elegant mechanistic studies Stahl has shown that the stereochemistry of the aminopalladation step is dependent on reaction conditions, and both syn- and antt-aminopalladation mechanistic pathways are accessible in oxidative amination reactions [20]. 

Scheme 1.17 Oxidative addition products with N-heterocyclic carbenes as ligands.

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