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DOI: 10.1055/s-0031-1290666
Buchwald-Hartwig Amination of Aryl Chlorides Catalyzed by Easily Accessible Benzimidazolyl Phosphine-Pd Complexes
Publication History
Publication Date:
26 April 2012 (online)
Abstract
This study describes the efficacy of benzimidazolyl phosphine ligands, which are easily synthesized from inexpensive and commercially available o-phenylenediamine, 2-bormobenzoic acid, and chlorophosphines, in the Buchwald-Hartwig amination of aryl chlorides. Primary and secondary aromatic/aliphatic amines are effective substrates in this catalytic system. Functional groups such as keto and esters are also compatible. The catalyst loading can be reduced to 0.1 mol% Pd.
Key words
palladium - cross-coupling - amination - aryl chlorides - phosphine
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References and Notes
According to the list price from Aldrich (21-2-2011), o-phenylenediamine costs 0.18 USD/G and 2-bromobenzoic acid costs 0.88 USD/G.
17CCDC-865333 contains the supplementary crystallographic data for L2. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
18There was no detectable phosphine oxide signal of L2 in the ³¹P NMR spectrum when the solid form of the ligand was allowed to stand under air for one month.
19
Palladium-Catalyzed
Amination of Aryl Chlorides; General Procedure: A stock solution
of [Pd2 (dba)3] (0.023 g,
0.10 mmol) and ligand L (Pd/L = 1:4) were
loaded into a reaction tube equipped with a Teflon-coated magnetic
stir bar. The tube was evacuated and flushed with nitrogen (3 cycles).
A stock solution was prepared by adding freshly distilled toluene
(5.0 mL). Bases (2.5 mmol) were loaded into an array of Schlenk
tubes. The tubes were evacuated and flushed with nitrogen (3 cycles).
Aryl chlorides (1.0 mmol), amines (1.5 mmol) and the stock solution
(0.1 mol% Pd per 0.5 mL stock solution) were loaded
into the tubes. Toluene was then added to give a total volume of
3.0 mL in each tube. The solutions were stirred at room temperature
for several minutes and then placed into a preheated oil bath (135 ˚C) for
the time period indicated in the Tables. After completion of reaction
as judged by GC analysis, the reaction tube was allowed to cool
to room temperature and the reaction was quenched with water and
diluted with EtOAc. The organic layer was separated and the aqueous
layer was washed with EtOAc. The combined organic layer was dried,
filtered and concentrated under reduced pressure and the crude products were
purified by flash column chromatography on silica gel (230-400
mesh) to afford the desired product. 4-Methyl-
N
-phenylaniline
(Table 2, entry 1): ¹H NMR (400 MHz, CDCl3): δ = 2.50
(s, 3 H), 5.70 (s, 1 H), 7.05-7.09 (m,
1 H), 7.16-7.19 (m, 4 H), 7.26-7.30
(m, 2 H), 7.40-7.46 (m, 2 H); ¹³C
NMR (100 MHz, CDCl3): δ = 20.6, 116.8, 118.8,
120.1, 129.2, 129.7, 130.7, 140.2, 143.9; MS (EI):
m/z (%) = 183.1
(100) [M]+, 167.1 (20), 91.0(14),
77.1 (10).