metal complexes, proceeding either through radical or polar
reaction pathways, also are supported in these new reaction media.
Funding was provided by the Natural Sciences and Engineering
Council of Canada (NSERC) through the Discovery Grants
Program to JACC and CJW. CJW is grateful for funding from
Simon Fraser University. JACC acknowledges generous support
from the Canada Research Chairs Program, the Canadian
Foundation for Innovation and the Nova Scotia Research and
Innovation Trust Fund.
Notes and references
{ Coupling reactions of Grignard reagents in PILs: A stock solution of 1.0 M
PhMgBr in THF (5 mL, 5 mmol) was added to cold PIL-C9H19COO
(5.0 mL) at 278 uC. The reaction mixture was warmed to room
temperature and THF was removed in vacuo. Toluene (0.5 mL) was
added to reduce viscosity, followed by the addition of one equivalent (with
respect to PhMgBr) of: 4-fluorotoluene; 4-chlorotoluene; 4-bromotoluene;
or 4-iodotoluene. To this solution, 0.05 mol% of the complex bis[1,3-
di(29,69-diisopropylphenyl)imidazolin-2-ylidene]nickel(0), prepared in situ
by the reaction of nickel dicyclooctadiene and the N-heterocyclic carbene,
in PIL-C9H19COO, was added. On addition of nickel dicyclooctadiene a
colour change from pale yellow to dark green was observed. The reaction
mixture was stirred for 18 hours at room temperature under nitrogen and
then quenched with a few drops of methanol. Extraction was carried out
using dichloromethane and water. The dichloromethane layer was then
dried using anhydrous magnesium sulfate and then analyzed by GC–MS.
In all cases a small amount (,2%) of biphenyl was observed.
Fig. 2 EPR spectrum of PIL-C9H19COO–PhMgBr with DMPO (diluted
with toluene).
Scheme 2 Kumada–Corriu reaction in PILs.
Mg–Br exchange: For example, to cold PIL-C9H19COO, ethylmagne-
sium bromide in THF was added and the molecular solvent (THF) was
removed under vacuum. To this ether free solution (as tested by 1H NMR
spectroscopy) bromobenzene was added and stirred for 6 hours.
Benzaldehyde was added and the mixture was stirred for 16 hours. After
an aqueous quench and extraction with dichloromethane, diphenyl-
methanol was detected in 83% yield. A small amount (6%) of 1-phenyl-
propan-1-ol was also observed in the reaction mixtures.
reactions that involve either radicals or charge-separated inter-
mediates, which are important synthetic tools in carbon–carbon
bond formation reactions. Unfortunately, some of the most active
catalysts that support these reaction types involve species that are
clearly incompatible with most ionic liquids, namely: (1) a low-
valent metal centre in the presence of (2) a strongly nucleophilic
ligand in (3) basic reaction media.8 To illustrate the ability of our
PIL–Grignard solutions to support such reactions, we examined
the Kumuda–Corriu reaction, which involves coupling aryl-
Grignard reagents with aryl halides in the presence of a Ni(0)
complex of a nucleophilic carbene, as shown in Scheme 2.19 The
coupling reaction proceeds with high yield in the case of
4-bromotoluene and 4-iodotoluene, although transmetallation
occurs with concomitant generation of y25% 4,49-dimethylbiphe-
nyl.{ The reaction also proceeds well for chlorotoluene, and
surprisingly facilitates C–F bond activation.20 The yield of the
heterocoupling reaction in PILs is slightly lower than in molecular
solvent (THF); however, different side products are obtained due
to homocoupling, indicating that rapid transmetallation reactions
are occurring.
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Finally, the dramatic shift in the Schlenk equilibrium in favour
of R2Mg?S2, where S = decanoate, as well as the results from the
Kumuda–Corriu reaction above, suggested to us that transme-
tallation reactions would be facile in the ionic liquid, recognizing
the structural similarity to dialkylmagnesium compounds recently
reported.21 Indeed, transmetallations occur smoothly,{ suggesting
that PIL solutions of Grignard solutions are excellent reaction
media for Mg–Br exchanges.21
16 Nitrones, Nitronates, and Nitroxides, ed. E. Breuer, H. G. Aurich and
A. Nielsen, John Wiley and Sons, Chichester, UK, 1989.
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W. A. Herrmann, Angew. Chem., Int. Ed., 2001, 40, 3387.
20 J. Terao, A. Ikumi, H. Kuniyasu and N. Kambe, J. Am. Chem. Soc.,
2003, 125, 5646.
In summary, ether-free solutions of Grignard reagents dissolved
in PILs support a variety of strong bases and are good solvents for
the generation of radicals. Ionic liquids may be used to evoke new
chemistry for Grignard reagents. Reactions catalysed by transition
21 A. Krasovskiy, B. F. Straub and P. Knochel, Angew. Chem., Int. Ed.,
2006, 45, 159.
2068 | Chem. Commun., 2007, 2066–2068
This journal is ß The Royal Society of Chemistry 2007