conventional organic solvents. This suggests that for reactive
organometallic reagents in ionic liquids, we cannot extrapolate
their expected chemistry from conventional organic solvents.
Careful investigation for each case is warranted.
We thank NSERC of Canada, the RGC of Hong Kong (PolyU
5002/03P) as well as the University Grants Committee Area of
Excellence Scheme in Hong Kong (Project No AoE/P-10/01) for
financial support of this research.
Notes and references
1 (a) Green Chemistry: Theory and Practice, P. T. Anastas and
J. C. Warner, Oxford Science Publications, Oxford, 1998; (b) Clean
Solvents: Alternative Media for Chemical Reactions and Processing, ed.
M. Abraham and L. Moens, ACS Symposium Series No. 819,
American Chemical Society, Washington, DC, 2001.
2 Organic Reactions in Aqueous Media, C. J. Li and T. H. Chan, John
Wiley & Sons, New York, 1997.
3 Chemical Synthesis Using Supercritical Fluids, P. Jessop, Wiley-VCH,
Weinheim, 1999.
Scheme 2
Table 3 Chemical shifts of methylene protons of various ethylmag-
nesium compounds in different solvents17a,b
Compound
Et3Na Et2Oa THFa DBEb CD3CNc
EtMgBr
EtMgI
Et2Mg
EtMg species in [bpy][BF4]
20.51 20.61 20.71
—
—
—
—
0.45
4 Ionic Liquids: Industrial Applications to Green Chemistry, R. D. Rogers
and K. R. Seddon, Oxford University Press, Washington, 2002.
5 For the rather extensive study of less reactive organometallic reactions in
aqueous media, see for example: (a) C. J. Li and T. H. Chan,
Tetrahedron, 1999, 55, 11149; (b) C. Petrier and J. L. Luche, J. Org.
Chem., 1983, 50, 910; (c) C. C. K. Keh, C. Wei and C. J. Li, J. Am.
Chem. Soc., 2003, 125, 4062 and references therein.
—
—
—
—
20.67 20.78
—
20.62
—
—
—
—
a
b
Reference 17a. Reference 17b. This work, 1.5 M solution in
c
[bpy][BF4] with 2 mmol of pyridine dissolved in CD3CN.
6 (a) M. C. Law, K. Y. Wong and T. H. Chan, Green Chem., 2002, 4, 161;
(b) C. M. Gordon and C. Ritchie, Green Chem., 2002, 4, 124; (c)
T. Kitazume and K. Kasai, Green Chem., 2001, 3, 30; (d) C. M. Gordon
and A. Mccluskey, Chem. Commun., 1999, 1431.
7 B. Gorodetsky, T. Ramnial, N. R. Branda and J. A. C. Clyburne,
Chem. Commun., 2005, 325.
8 V. Jurcik and R. Wilhelm, Green Chem., 2005, 7, 844.
9 (a) M. C. Law, K. Y. Wong and T. H. Chan, Green Chem., 2004, 6, 241;
(b) M. C. Law, K. Y. Wong and T. H. Chan, J. Org. Chem., 2005, 70,
10434.
10 R. D. Rieke and P. M. J. Hudnall, J. Am. Chem. Soc., 1972, 94, 7178.
11 M. Gomberg and W. E. Bachmann, J. Am. Chem. Soc., 1927, 49, 236.
12 (a) W. C. Zhang and C. J. Li, J. Chem. Soc., Perkin Trans. 1, 1998, 3131;
(b) W. C. Zhang and C. J. Li, J. Org. Chem., 1999, 64, 3230.
13 (a) L. J. Guggenberger and R. E. Rundle, J. Am. Chem. Soc., 1964, 86,
5344; (b) L. J. Guggenberger and R. E. Rundle, J. Am. Chem. Soc.,
1968, 90, 5375.
14 W. E. Lindsell, in Comprehensive Organometallic Chemistry II, ed. E. W.
Abel, F. G. A. Stone and G. Wilkinson, Pergamon/Elsevier, Oxford,
1995, vol. 1, pp. 57–127.
15 J. Toney and G. D. Stucky, Chem. Commun., 1967, 1168.
16 E. J. Weiss, J. Organomet. Chem., 1965, 4, 101.
17 (a) G. Westera, C. Blomberg and F. J. Bickelhaupt, J. Organomet.
Chem., 1978, 155, C55; (b) H. W. H. J. Bodewitz, C. Blomberg and
F. Bickelhaupt, Tetrahedron, 1972, 29, 719.
species generated is likely to have an oligomeric structure
{EtMgI}n. This hypothesis is consistent with our 1H NMR studies
(Table 3). In general, the methylene protons of ethylmagnesium
halide in coordinating solvents such as ether or THF appear as a
clear quartet at about 20.5 to 20.7 ppm. The ethylmagnesium
species in [bpy][BF4], when observed directly, showed only broad
absorption and did not show any clear quartet in the 20.5 to
20.7 ppm region. This is consistent with the polymeric structure.
When the species was dissolved in a weakly coordinating solvent
such as CD3CN, the NMR signals sharpened, but there was still
no quartet in the 20.5 to 20.7 ppm region. Upon addition of
pyridine, a clear methylene quartet appeared at 0.45 ppm, much
lower field than 20.5 to 20.7 ppm. This is consistent with the fact
that pyridine is a coordinating ligand; de-aggregation of the
ethylmagnesium species in the IL thus occurred upon addition of
pyridine leading to the observed NMR signals.
In conclusion, we demonstrated that organomagnesium species
can be generated in the ionic liquid [Bpy][BF4]. They showed a
distinctly different reactivity pattern from Grignard reagents in
This journal is ß The Royal Society of Chemistry 2006
Chem. Commun., 2006, 2457–2459 | 2459