Reddy et al.
First generation catalyst systems included monodentate phos-
phines [e.g., P(o-tol)3]5c,6 while chelating bidentate phosphines
such as 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP)7a-d
or 1,1′-bis(diphenylphosphino)ferrocene (DPPF)7e comprise
second generation catalyst systems that greatly improved the
scope of amination reactions.
Third generation soft ligands [e.g., P(t-Bu)3,8 o-(biphenyl)P-
(t-Bu)2,9 and N-heterocyclic carbenes]10 are very active and
general for aminations because such bulky ligands promote
metal-ligand dissociation in the oxidative addition of aryl
halides to Pd(0).11 A generally important aspect of efficient
coupling reactions is the proper choice of ligand for stabilizing
catalytically active Pd(0) complexes. As has been recently
observed by Lloyd-Jones, “Often unpredictably, the choice of
ligand in Pd-catalyzed reactions can make surprisingly little
difference or can open up new avenues”.12a This factor is
particularly important with less reactive aryl bromide and
chloride substrates. Additional examples of ligands that have
been advanced in recent years for Pd-catalyzed C-N bond
formation include 2-dicyclohexylphosphanyl-1-trityl-1H-imida-
zole,13a pyrazole-based phosphines,13b [2-di(tert-butyl)phosphi-
noethyl]-N-methylaniline,13c di(tert-butyl)neopentylphosphine
(DTBNpP),13d 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phos-
pha-adamantane,13e chlorophosphine (CH2)2(NCMe3)2PCl,13f
clickphos,13g 1-(2-norbornyl)-2,2,6,6-tetramethylphosphorinane,13h
(1) For reviews on Buchwald-Hartwig amination, see, (a) Hartwig, J.
F. Angew. Chem., Int. Ed. 1998, 37, 2046-2067. (b) Hartwig, J. F. Acc.
Chem. Res. 1998, 31, 852-860. (c) Wolfe, J. P.; Wagaw, S.; Marcoux,
J.-F.; Buchwald, S. L. Acc. Chem. Res. 1998, 31, 805-818. (d) Yang, B.
H.; Buchwald, S. L. J. Organomet. Chem. 1999, 576, 125-146. (e) Hartwig,
J. F. In Modern Amination Methods; Ricci, A., Ed.; Wiley-VCH: Weinheim,
Germany, 2000. pp 195-262. (f) Prim, D.; Campagne, J.-M.; Joseph, D.;
Andrioletti, B. Tetrahedron 2002, 58, 2041-2075. (g) Hartwig, J. F. In
Modern Arene Chemistry; Astruc, D., Ed.; Wiley-VCH: Weinheim, 2002;
pp 107-168. (h) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2002,
219, 131-209 and cited therein. (i) Hartwig, J. F. In Handbook of
Organopalladium Chemistry for Organic Synthesis; Negishi, E.-i.; de
Meijere, A., Eds.; Wiley: New York, 2002; Vol. 1, pp 1051-1096. (j)
Schlummer, B.; Scholz, U. AdV. Synth. Catal. 2004, 346, 1599-1626. (k)
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(l) Schlummer, B.; Scholz, U. Spec. Chem. 2005, 25, 22-24. (m) Dehli, J.
R.; Legros, J.; Bolm C. Chem. Commun. 2005, 973-986. (n) Buchwald,
S. L.; Mauger, C.; Mignani, G.; Scholz, U. AdV. Synth. Catal. 2006, 348,
23-39. (o) Janey, J. M. Buchwald-Hartwig Amination. In Name Reactions
for Functional Group Transformations; Li, J. J., Ed.; John Wiley & Sons:
Hoboken, NJ, 2007; pp 564-611. (p) For the synthesis of aryl amines via
nucleophilic aromatic substitution, see, Yadav, J. S.; Reddy, B. V. S.; Basak
A. K.; Narsaiah, A. V. Tetrahedron Lett. 2003, 44, 2217-2220 and
references cited therein.
(2) Selected examples for the applications of Buchwald-Hartwig ami-
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di(1-adamantyl)-n-butylphosphine,13i
dicyclohexyl-2-(N-
arylindolyl)phosphine,13j N-aryl-2-(di-tert-butylphosphino)-
imidazoles,13k the 9-ethylfluorenyldicyclohexyl phosphonium
(7) (a) Wolfe, J. P.; Buchwald, S. L. J. Org. Chem. 2000, 65, 1144-
1157. (b) Wolfe, J. P.; Buchwald, S. L. Tetrahedron Lett. 1997, 38, 6359-
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1996, 118, 7215-7216. (d) Averin, A. D.; Ulanovskaya, O. A.; Fedotenko,
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