10321
was evacuated, filled with dry N , and heated to 80°C with rapid stirring for 24 h. During this
2
time the colour changed from the initial dark blue to dark green and then to light green/yellow.
After 24 h bromobenzene (1.57 g, 10 mmol) was added and the reaction was stirred for a further
4
8 h at 80°C under dry N . After cooling the [bmim]PF was extracted with diethyl ether (3×20
2
6
mL) and after drying the combined extractions (MgSO ) removal of solvent and recrystallisation
4
1
2
gave the biphenyl (1.34 g, 87% yield).
It is interesting to note that in general the aryl bromides substituted at the ortho or para
position by an electron withdrawing substituent give lower yields of the biaryl than the simple
bromobenzene 2a, compound 2d giving the lowest yield of all. In the case of 2d it is unlikely that
this low yield is because we have employed an aryl iodide instead of an aryl bromide, as
aromatic iodides consistently give high yields for this reaction in DMF, except when there is acyl
substitution at the para or ortho position. The low yield is therefore consistent with these earlier
findings and is due to the influence of the ester group in the ortho position. It is also known that
aryl bromides show dramatic variations in yields of the biaryl as a result of substitution in the
1
3
aromatic ring.
The yields obtained using the ionic liquid [bmim]PF as the solvent for the reaction were
6
10
comparable to those yields obtained in the usual solvent for this reaction, DMF. However, we
were able to recycle the ionic liquid and the nickel catalyst. The used [bmim]PF containing the
6
spent catalyst was dried under vacuum at 60°C for 48 h and then deoxygenated. The
[
(PPh ) Ni(0)] could be reformed and used once more in the above procedure without requiring
3
n
the addition of further [(PPh ) Ni(II)Cl ]. There was however a small decrease in the yield of
3
2
2
biaryls, for example the second run for bromobenzene only produced an 81% yield of the
biphenyl.
References
1
2
. Wilkes, J. S.; Zaworotko, M. J. J. Chem. Soc., Chem. Commun. 1990, 965; Fuller, J.; Carlin, R. T.; De Long, H.
C.; Haworth, D. J. Chem. Soc., Chem. Commun. 1994, 299.
. Wilkes, J. S.; Levisky, J. A.; Wilson, R. A.; Hussey, C. L. Inorg. Chem. 1982, 21, 1263; Huddleston, J. G.;
Willauer, H. D.; Swatloski, R. P.; Visser, A. E.; Rogers, R. D. J. Chem. Soc., Chem. Commun. 1998, 1765.
. Fischer, T.; Sethi, A.; Woolf, J. Tetrahedron Lett. 1999, 40, 793.
3
4
5
. Earle, M. J.; McCormac, P. B.; Seddon, K. R. J. Chem. Soc., Chem. Commun. 1998, 2245.
. Chauvin, Y.; Olivier, H. CHEMTECH 1995, 26; Chauvin, Y.; Einloft, S.; Olivier, H. Ind. Eng. Chem. Res. 1995,
3
4, 1149; Suarez, P. A. Z.; Dullius, J. E. L.; Einloft, S.; De Souza, R. F.; Dupont, J. Polyhedron 1996, 15, 1217;
Simon, L. C.; Dupont, J.; De Souza, R. F. Appl. Catal. A: Gen. 1998, 175, 215.
6
7
. Chauvin, Y.; Mussmann, L.; Olivier, H. Angew. Chem., Int. Ed. Engl. 1995, 34, 2698.
. Kobryanskii, V. M.; Arnautov, S. A. J. Chem. Soc., Chem. Commun. 1992, 727; Arnautov, S. A. Synth. Metals
1
997, 84, 295; Goldenberg, L. M.; Osteryoung, R. A. Synth. Metals 1994, 64, 63.
8
9
. Howarth, J. Tetrahedron Lett. 2000, 41, 6627.
. Carmichael, A. J.; Earle, M. J.; Holbrey, J. D.; McCormac, P. B.; Seddon, K. R. Org. Lett. 1999, 1, 997;
Howarth, J.; Dallas, A. Molecules 2000, 5, 851.
10. Kende, A. S.; Liebeskind, L. S.; Braitsch, D. M. Tetrahedron Lett. 1975, 3375.
1
1. The solvent [bmim]PF is commercially available from Solvent Inovation, see http://www.solvent-innovation.com
6
for a catalogue. For a method of synthesis see Reference 8 and references cited therein.
1
13
1
1
2. The H and C NMR spectra for compounds 4a–g corresponded exactly to those cited in the literature, or
obtained from the commercially available biaryl, as did their melting points.
3. Tsou, T. T.; Kochi, J. K. J. Am. Chem. Soc. 1979, 101, 6319.
.