TETRAHEDRON LETTERS Tetrahedron Letters 42 (2001) 5689–5692 Pergamon Nickel-catalysed amination of aryl chlorides using a dihydroimidazoline carbene ligand Benoı ˆt Gradel, Eric Brenner, Raphae ¨l Schneider and Yves Fort* Synthe `se Organique et Re ´activite ´ , UMR CNRS -UHP 7565, Universite ´ Henri Poincare ´ , Nancy I, Faculte ´ des sciences, BP 239, 54506 Vandoeuvre les Nancy cedex, France Received 19 June 2001 Abstract—A new arylamination protocol has been developed using a catalyst combination prepared from Ni(acac) 2 associated to a sterically hindered dihydroimidazoline carbene ligand. A high efficiency was attained using, in most cases, only 2 mol% Ni/carbene clusters. © 2001 Elsevier Science Ltd. All rights reserved. The synthesis of aromatic amines has attracted consid- erable attention since these compounds are found in biologically active products as well as in materials with useful electronic and mechanical properties. 1 Palla- dium-catalysed carbonnitrogen bond-forming reac- tions has been the area of intensive research in recent literature. These studies have shown that the supporting ligands on the metal centre play a crucial role in dictating the efficiency of the catalytic system. 2 Recently, bulky N -heterocyclic carbenes have attracted considerable attention as ligands in carboncarbon 3 and carbonnitrogen 4 coupling reactions. These reports have demonstrated that such strong electron donating ligands can be incorporated into palladium catalysts and that an excess of ligand is not required to prevent aggregation of the metal. Alternatively, nickel-catalysed amination reactions have received less attention. Buchwald reported first the use of Ni(COD) 2 associated to 1,1-bis(diphenylphosphino) ferrocene (dppf) or 1,10-phenanthroline for the synthe- sis of arylamines. 5 Bolm extended this N -arylation method for the coupling of sulfoximines with aryl tosy- lates using Ni(COD) 2 liganded with BINAP. 6 An het- erogeneous Ni/C catalyst liganded with dppf was also recently developed by Lipshutz. 7 For our part, we have reported the use of a catalyst combination of in situ generated colloidal Ni(0) associa- ted to 2,2-bipyridine which provided an efficient route to substituted anilines. 8 In addition to its utility in catalytic amination reactions of aryl chlorides sub- strates, the Ni/2,2-bipyridine has also shown to be effective for a wide variety of carbonnitrogen bond- forming processes including N -monoarylation of piperazine 9 and polyamination or selective monoamina- tion of aryl di- and trichlorides. 10 Although a good catalytic activity and the synthesis of elaborated aryl amines were attained, ligand effect in nickel-catalysed arylamination reactions is still of interest. We therefore, wondered if such reactions could be performed and improved using carbene ligands. Herein, we wish to report our initial results on the synthesis of aromatic amines from aryl- or heteroaryl chlorides and secondary amines based on a Ni(0)/dihy- droimidazoline carbene catalysed cross-coupling reac- tions. To select the most effective ligand, a number of 1,3-diaryl substituted imidazolium and dihydroimida- zolium salts were used in a model reaction (Table 1). 1,3-Bis(2,4,6-trimethyl)substituted imidazolium salts 1 and 2 afforded the desired arylamine in poor yields (entries a–c). The sterically hindered 1,3-bis(2,6-diiso- propylphenyl) imidazol-2-ylidenes, in situ generated from the corresponding imidazolium chlorides 3 and 4b, were found to be the most effective carbene precur- sors leading to N -phenylmorpholine in a 99% isolated yield (Table 1, entries d and f). The results obtained with unsaturated and saturated imidazolium chlorides 3 and 4b indicate clearly that their higher performances are due to their steric hindrance. The counter-ion asso- ciated to the dihydroimidazolium salt was however Keywords : nickel clusters; arylamination; carbene ligand; dihydro- imidazoline. * Corresponding author. Tel.: +33 (0)3 83 91 21 03; fax: +33 (0)3 83 40 45 58; e-mail: yves.fort@sor.uhp-nancy.fr 0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0040-4039(01)01079-6