II
0
I
§ Representative procedure (Table 2, entry 16): A Schlenk tube was charged
with 3b (33.9 mg, 0.0489 mmol), THF (2 cm ) and chlorobenzene (0.22 g,
radical anion reduces the Ni complex to a Ni or Ni complex
which catalyses the following coupling reaction. Namely, aryl
halides act as an intermedium of the SET at the initial stage of
the reaction and such behavior of aryl halides as intermedia in
3
1.95 mmol). To the homogeneous solution formed was added dropwise a
solution of p-MeC H MgBr in THF (2.2 mmol, ca. 1 M in THF) at room
6
4
temperature with stirring. Stirring was continued at room temperature for
12 h. The reaction was ceased by addition of water (6 cm ). The mixture
3
6
SET processes have been proved. Reactions of Grignard reagents
3
was extracted with Et
dried over anhydrous Na
washed with Et O. The resulting Et O solution was concentrated by rotary
2
O (3 6 5 cm ) and the combined organic layers were
with organic compounds via SET processes have also been
7
reported.
2 4 2 4
SO . The Na SO was removed by filtration and
2
2
evaporation and the residue was purified by column chromatography on
silica gel (hexane) to afford p-MeC Ph (0.323 g, 98.4%) as colorless
crystals.
In the catalytic system we tested, the coupling reactions using an
aryllithium instead of a Grignard reagent often gave different
6 4
H
results. For example, reaction of p-MeC
by 2.5 mol% of 3b in toluene at 70 uC gave the homocoupling
product of p-MeC Li in 75.2% yield (based on the amount of
p-MeC Li added), while the reaction of p-MeC MgBr with
6 4
H Li with PhCl catalysed
1
(a) E. I. Negishi and F. Liu, in Metal-Catalyzed Cross-Coupling
Reactions, ed. F. Diederich and P. J. Stang, Wiley-VCH, Weinheim,
6 4
H
1998; (b) J. Tsuji, Palladium Reagents and Catalysis, Wiley, Chichester,
6
H
4
6 4
H
1995; (c) T. Takahashi and K. I. Kanno, in Modern Organonickel
PhCl under the same conditions afforded the sole cross-coupling
product in 97.8% yield. This showed that metal ion on nucleophiles
played an important role in the reaction. Recently, Nakamura and
co-workers indicated that a Ni/Mg bimetallic synergy accelerated
Chemistry, ed. Y. Tamaru, Wiley-VCH, Weinheim, 2005; (d) J. Tsuji,
Transition Metal Reagents and Catalysts: Innovations in Organic
Synthesis, John Wiley & Sons, Chichester, 2000; (e) L. Pu, Chem. Rev.,
1
998, 98, 2405.
(a) K. Tamao, K. Sumitani and M. Kumada, J. Am. Chem. Soc., 1972,
4, 4374; (b) R. J. P. Corriu and J. P. Masse, J. Chem. Soc., Chem.
Commun., 1972, 144.
(a) R. B. Bedford, C. S. J. Cazin and D. Holder, Coord. Chem. Rev.,
2
3
4
5
c
nickel-catalysed Kumada cross-coupling reactions. The selectivity
of the reactions we tested may be also a result of Ni/Mg bimetallic
cooperation.
9
2004, 248, 2283; (b) A. F. Littke and G. C. Fu, Angew. Chem., Int. Ed.,
In summary, we have demonstrated that amido pincer
complexes of nickel are highly active catalysts in cross-coupling
of aryl Grignard reagents and aryl halides. Among the catalysts
tested, the P,N,P-chelate nickel complexes showed relatively low
catalytic activity compared with those with N,N,P- and N,N,N-
chelate ligands. Steric congestion of reactants did not intensively
affect the reactions tested. However, excessive steric hindrance of
ligands led to a decline of catalytic activity of the complexes in
most cases. The reactions probably proceed through single electron
transfer processes from Grignard reagents to aryl halides at the
initial stage of the reactions.
2002, 41, 4176.
(a) S. Y. Park, M. Kang, J. E. Yie, J. M. Kim and I.-M. Lee, Tetrahedron
Lett., 2005, 46, 2849; (b) J. Huang and S. P. Nolan, J. Am. Chem. Soc.,
1999, 121, 9889; (c) C. Dai and G. C. Fu, J. Am. Chem. Soc., 2001, 123,
2719; (d) V. P. W. Bohm, T. Weskamp, C. W. K. Gstottmayr and
W. A. Herrmann, Angew. Chem., Int. Ed., 2000, 39, 1602; (e)
B. H. Lipshutz, T. Tomiolka, P. A. Blomgren and J. A. Sclafani,
Inorg. Chim. Acta, 1999, 296, 164; (f) G. Y. Li and W. J. Marshall,
Organometallics, 2002, 21, 590.
5
6
(a) G. Y. Li, Angew. Chem., Int. Ed., 2001, 40, 1513; (b) S. Tasler and
B. H. Lipshutz, J. Org. Chem., 2003, 68, 1190; (c) N. Yoshikai,
H. Mashima and E. Nakamura, J. Am. Chem. Soc., 2005, 127, 17978; (d)
J.-P. Corbet and G. Mignani, Chem. Rev., 2006, 106, 2651; (e)
L. Ackermann, C. J. Gschrei, A. Althammer and M. Riederer, Chem.
Commun., 2006, 1419.
H. Zhao, D.-J. Li, L. Deng, L. Liu and Q.-X. Guo, Chem. Commun.,
2003, 506.
Notes and references
{
CCDC 632195–632198 for complexes 1c, 2b, 3c and 4b. For crystal-
7 A. Albert, M. Benaglia, B. F. Bonini, M. Fochi, D. Macciantelli,
M. Marcaccio, F. Paolucci and S. Roffia, J. Phys. Org. Chem., 2004, 17,
1084, and references therein.
lographic data in CIF or other electronic format see DOI: 10.1039/
b702027a
This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 2423–2425 | 2425