Buchwald-Hartwig amination carbenes

The first examples utilising A-heterocyclic carbenes as ligands in the Buchwald-Hartwig amination involved the in situ formation of the catalyst from the corresponding imidazolium salt and a Pd(0) source. Nolan reported IPr-HCl/PdjCdbalj as a catalytic system for the amination of aryl chlorides in excellent yields, using different types of amines, anilines, and also imines or indoles [142,143] (Scheme 6.46). Hartwig showed later that in some cases the reactions could be performed at room temperature and without anhydrous conditions even for aryl chlorides [ 144]. This was later shown for the less challenging bromides and iodides [145,146]. 

N-Aryl amination, or the Buchwald-Hartwig reaction, has proven to be a useful and versatile method to obtain aryl amines, which are of great synthetical and industrial interest [145]. The first examples of carbene/palladium-catalyzed amination of aryl halides showed that in situ-generated catalyst could efficiently mediate the coupling of aryl halides with primary and secondary amines, imines and indoles [ 146-148]. Even if most of these reactions could be carried out at room temperature with aryl iodides and bromides, elevated temperatures were required in order to couple aryl chlorides. 

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