Organometallic complexes derived from alkyne-functionalized imidazolium salts

Article abstract of DOI:10.1021/om034248j

Two 1,3-dialkyne-functionalized imidazolium chlorides, 1,3-dipropynylimidazolium chloride and 1,3-dipentynylimidazolium chloride, have been prepared from the direct reaction between the appropriate chloroalkyne and (trimethylsily)imidazole. Replacement of the chloride counterion with BF₄^- or BPh₄^- gave four further imidazolium salts, three of which melt below 100°C and one of which is a liquid at room temperature. Reactions of the BF₄^-1 and BPh₄^- salts with Co₂(CO)₈ afforded complexes in which both of the alkyne functionalities coordinated to a Co₂(CO)₆ unit. One of these organometallic derivatives, viz. 1,3-dipentynylimidazolium bis(hexacarbonyldicobalt) tetrafluoroborate, can be classified as an ionic liquid on the basis of its melting point. The solid-state structures of three of these new salts have been elucidated by single-crystal X-ray diffraction, revealing extensive networks of C?H?π and π?π interactions. Attempts to prepare carbene derivatives from the functionalized imidazolium salts have also been made.

Full text of DOI:10.1021/om034248j

1622
Organometallics 2004, 23, 1622-1628
Or ga n om eta llic Com p lexes Der ived fr om
Alk yn e-F u n ction a lized Im id a zoliu m Sa lts
Zhaofu Fei, Dongbin Zhao, Rosario Scopelliti, and Paul J . Dyson*
Institut de Chimie Mole´culaire et Biologique, Ecole Polytechnique Fe´de´rale de Lausanne,
EPFL-BCH, CH-1015 Lausanne, Switzerland
Received October 21, 2003
Two 1,3-dialkyne-functionalized imidazolium chlorides, 1,3-dipropynylimidazolium chloride
and 1,3-dipentynylimidazolium chloride, have been prepared from the direct reaction between
the appropriate chloroalkyne and (trimethylsilyl)imidazole. Replacement of the chloride
-
-
counterion with BF4 or BPh4 gave four further imidazolium salts, three of which melt
-
below 100 °C and one of which is a liquid at room temperature. Reactions of the BF4 and
BPh4 salts with Co2(CO)8 afforded complexes in which both of the alkyne functionalities
-
coordinated to a Co2(CO)6 unit. One of these organometallic derivatives, viz. 1,3-dipentyn-
ylimidazolium bis(hexacarbonyldicobalt) tetrafluoroborate, can be classified as an ionic liquid
on the basis of its melting point. The solid-state structures of three of these new salts have
been elucidated by single-crystal X-ray diffraction, revealing extensive networks of C‚‚‚H‚
‚‚π and π‚‚‚π interactions. Attempts to prepare carbene derivatives from the functionalized
imidazolium salts have also been made.
In tr od u ction
liquids have found numerous applications in catalysis5
and have also been exploited in the synthesis of orga-
nometallic compounds such as transition-metal-arene
complexes. Lewis acidic [bmim]Cl-AlCl3 (bmim ) 1-bu-
tyl-3-methylimidazolium cation), combined with the
Brønsted acid [bmim][HCl2], aluminum powder, and an
arene, is an excellent medium for cyclopentadienyl ring
exchange reactions of ferrocene leading to compounds
of the general formula [Fe(η-C5H5)(η-arene)]+.6 In Lewis
acidic [bmim]Cl-AlCl3 ionic liquid, chromium(III) chlo-
ride may be reduced with aluminum in the presence of
an arene to afford sandwich complexes of the formula
[Cr(η-arene)2]+, and Mn(CO)5Br reacts with arenes to
afford the half-sandwich compounds [Mn(CO)3(η-are-
ne)]+.7 In these reactions the intrinsically high concen-
tration of the Lewis acid catalyst facilitates the reaction;
unfortunately, isolation of the complexes from these
reactions involves addition of an aqueous solution of
HBF4, resulting in the decomposition of the ionic liquid.
The acylation of ferrocene may also be conducted in
acidic choroaluminate ionic liquid. Ferrocene reacts with
ethanoyl chloride in [bmim]Cl-AlCl3 to afford 1-etha-
noylferrocene as the main product and 1,1′-diethanoyl-
ferrocene and 1,2-diethanoylferrocene in somewhat
lower yield.8
The application of ionic liquids to overcome a variety
of problems in catalysis has caught the imagination of
researchers across the world, and a number of excellent
reviews on this topic have been published in the past
few years.1 Many catalysts immobilized in ionic liquids
are organometallic species, are derived from organome-
tallics, or involve organometallic intermediates at cer-
tain stages of the reaction cycle. However, in addition
to these catalyst systems, classical organometallic reac-
tions have been carried out in ionic liquids and ionic
liquids containing organometallic components have also
been prepared.2
The organometallic alkylchloroaluminates were among
the first widely studied ionic liquids, and they were
employed in the first transition-metal-catalyzed reac-
tions to be conducted in ionic liquids. Chauvin and co-
workers combined them with various nickel complexes
to give solutions that catalyzed the dimerization of
alkenes.3 Around the same time, Carlin and Osteryoung
showed that the Ziegler-Natta catalyst Ti(η-C5H5)2Cl2
dissolved in alkylchloroaluminates was able to polymer-
ize ethylene.4 In both processes, the transition-metal
catalysts were only active when a Lewis acidic ionic
liquid was used.
Organometallic compounds have also been prepared
in basic ionic liquid; for example, [emim]Cl-AlCl3 (emim
Following the pioneering work of Chauvin, Carlin,
and Osteryoung, Lewis acidic chloroaluminate ionic
(5) For example see: (a) Adams, C. J .; Earle, M. J .; Seddon, K. R.
Chem. Commun. 1999, 1043. (b) Qiao, K.; Deng, Y. Q. J . Mol. Catal.
A: Chem. 2001, 171, 81. (c) McGuinness, D. S.; Mueller, W.; Wasser-
scheid, P.; Cavell, K. J .; Skelton, B. W.; White, A. H.; Englert, U.
Organometallics 2002, 21, 175.
* To whom correspondence should be addressed. E-mail:
paul.dyson@epfl.ch.
(1) (a) Seddon, K. R. J . Chem. Technol. Biotechnol. 1997, 68, 351.
(b) Welton, T.; Chem. Rev. 1999, 99, 2071. (c) Wasserscheid, P.; Keim,
W. Angew. Chem., Int. Ed. 2000, 39, 3772.
(2) Dyson, P. J . Appl. Organomet. Chem. 2002, 16, 495.
(3) Chauvin, Y.; Gilbert, B.; Guibard, I. J . Chem. Soc., Chem.
Commun. 1990, 1715.
(6) Dyson, P. J .; Grossel, M. C.; Srinivasan, N.; Vine, T.; Welton,
T.; Williams, D. J .; White, A. J .; Zigras, T. J . Chem. Soc., Dalton Trans.
1997, 3465.
(7) Crofts, D.; Dyson, P. J .; Sanderson, K. M.; Srinivasan, N.; Welton,
T. J . Organomet. Chem. 1999, 573, 292.
(8) Stark A.; MacLean, B. L.; Singer, R. D. J . Chem. Soc., Dalton
Trans. 1999, 63.
(4) Carlin, R. T.; Osteryoung, R. A. J . Mol. Catal. 1990, 63, 125.
10.1021/om034248j CCC: $27.50 © 2004 American Chemical Society
Publication on Web 03/04/2004

Alkyne-Functionalized Imidazolium Salts
Organometallics, Vol. 23, No. 7, 2004 1623
Sch em e 1. Syn th esis of 1-6
) the 1-ethyl-3-methylimidazolium cation) has been
used as a medium to prepare a platinum carbene
complex from PtCl2, PtCl4, and ethylene.9 The reaction
exploits the fact that the proton in the 2-position of
imidazolium cations is acidic and may be removed under
basic conditions. Since palladium-carbene complexes
have been implicated as catalysts in C-C cross-coupling
reactions conducted in ionic liquids, there have been
some attempts to show under what conditions such
species are likely to be generated, under conditions more
characteristic of real catalytic systems; i.e., in the
presence of a phosphine ligand and base, palladium-
carbene complexes have been observed.10
a
Reagents and conditions: (i) (trimethylsilyl)imidazole; (ii)
NaBF4 for 3 and 5, NaBPh4 for 4 and 6.
In an interesting development, organometallic anions
have been combined with imidazolium cations to give
low-melting salts. For example, [bmim]Cl reacts with
Na[Co(CO)4] in propanone to afford [bmim][Co(CO)4],
and a similar approach has been used to prepare ionic
liquids containing [Mn(CO)5]- and [HFe(CO)4]-.11 The
cobalt-containing ionic liquid has also been shown to be
catalytically active. The Monsanto catalyst has also been
isolated in liquid form as [bmim][Rh(CO)2I2], prepared
from the direct reaction of [Rh(CO)2I]2 and 2 equiv of
[bmim]I in methanol.12 Since the submission of this
paper related, but different, alkyne-functionalized imi-
dazolium salts and their dicobalt hexacarbonyl deriva-
tives have been reported.13
Ta ble 1. Meltin g P oin t Da ta for 1-10
compd
mp (°C)
compd
mp (°C)
1
2
3
4
5
142
65
67
185
-23
6
7
8
9
10
135
110
115
100
132
Resu lts a n d Discu ssion
The reaction of the commercially available chloro-
alkynes with (trimethylsilyl)imidazole using a literature
method22 gave the alkyne-derivatized imidazolium salts
1 and 2 in a single step in high yield (see Scheme 1).
Compounds 1 and 2 were isolated as white solids
following washing with diethyl ether, but they were very
hygroscopic and became pale yellow oils when exposed
to air. Treatment of 1 and 2 with NaBF4 or NaBPh4 in
acetone afforded 3-6, which were isolated in pure form
following washing with diethyl ether. Compounds 2, 3,
and 5 melt below 100 °C (Table 1) and can be classified
as ionic liquids, with 5 being a liquid at room temper-
ature.
Characterization of 1-6 was achieved using a com-
bination of electrospray ionization (ESI) mass spectrom-
etry, IR, 1H, and 13C NMR spectroscopy, and elemental
analysis. Two of the salts (4 and 6) were also character-
ized in the solid state by single-crystal X-ray diffraction.
The ESI mass spectra of 1-6 in water recorded in
positive ion mode were dominated by a peak corre-
sponding to the intact parent ion. Similarly, the negative
ion spectra of 1-6 showed the presence of the anion.
The IR spectra of 1, 3, and 4 exhibit a sharp medium/
strong vibration in the region 2125-2132 cm-1, which
corresponds to the CtC bonds. In 2 a weak CtC
vibration at 2112 cm-1 is observed, and in 5 and 6 the
CtC bond does not afford a distinct vibration; instead,
weak split vibrations between 2120 and 1842 cm-1 are
observed, presumably due to interactions between the
CtC-H bond from the cation and the phenyl ring from
the anion. The two CtC-H groups in 4 and 6 are not
identical, as confirmed by a single-crystal X-ray diffrac-
tion analysis (see below). Compound 1 also contains a
vibration at 2410 cm-1, which could be due to an
intramolecular and/or intermolecular hydrogen bond
between the chloride anion and the hydrogen atoms
from the cation (the H atoms in the ring NCHdCHN,
NCHN, and the arms CH2CtCH are all acidic). Related
Inclusion of organometallic fragments as part of the
cationic component of the ionic liquid has yet to be
reported. However, a number of ionic liquids composed
of cations that have been derivatized with functionalized
groups that can complex to metal centers, albeit not
necessarily affording organometallic species, have been
reported. Functional groups that have been reported
include thiourea, thioether, and urea employed for the
extraction of metal ions from aqueous solutions,14,15
amines,13,14,16,17 amides,18 phosphines,19 and nitriles.20
In this paper we describe the synthesis and character-
ization of alkyne-functionalized imidazolium salts (some
of which are ionic liquids by virtue of their low melting
points) and their subsequent organometallic (dicobal-
thexacarbonyl) derivatives. One of these organometallic
ionic liquids has a melting point of 100 °C, which by
definition21 can be regarded as an ionic liquid.
(9) Husan, M.; Kozhevnikov, I. V.; Siddiqui, M. R. H.; Steiner, A.;
Winterton, N. J . Chem. Res., Synop. 2000, 392.
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Commun. 2001, 1862.
(12) Dyson, P. J .; McIndoe, J . S.; Zhao, D. Chem. Commun. 2003,
508.
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Lukasser, J .; Polin, J .; McKenzie, J . M.; Raubenheimer, H. G. Dalton
Trans. 2003, 4275.
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Sheff, S.; Wierzbicki, A.; Davis, J . H., J r.; Rogers, R. D. Chem.
Commun. 2001, 135.
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Technol. 2002, 36, 2524.
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1079.
(19) Brauer, D. J .; Kottsieper, K.; Liek, C.; Stelzer, O.; Waffen-
schmidt, H.; Wasserscheid, P. J . Organomet. Chem. 2001, 630, 177.
(20) Zhao, D.; Fei, Z.; Scopelliti, R.; Dyson, P. J . Inorg. Chem., in
press.
(21) Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis; Wiley-
VCH: Weinheim, Germany, 2002.
(22) Harlow, K. J .; Hill, A. F.; Welton, T. Synthesis 1996, 697.

1624 Organometallics, Vol. 23, No. 7, 2004
Fei et al.
anion-cation interactions have been noted elsewhere.23,24
This may explain the difference in solubility of the
imidazolium salts; viz., compound 1 is soluble in water
and only sparingly soluble in dichloromethane, chloro-
form, and acetonitrile, whereas 2-6 are soluble in all
these solvents.
1
The H NMR spectra of 1-6 in CD3CN give rise to
signals between 7.47 and 9.00 ppm, which correspond
to the protons on the imidazolium ring. The exact
frequency is dependent on the concentration of the
solution, presumably due to the presence of hydrogen-
bonding interactions in solution, as observed previ-
ously.25 The CH2 units of 1, 3, and 4 display a doublet
at 5.00 ppm (4J (HH) ) 2.44 Hz), and no significant
influence of the anion could be observed. The alkyne
protons in 1, 3, and 4 are around 3 ppm and in 2, 5,
and 6 are around 2 ppm, and in all cases the two alkyne
groups attached to the imidazolium ring are equivalent.
Crystals of 4 and 6 suitable for X-ray diffraction
analysis were obtained from acetone by slow evapora-
tion at room temperature. The structures of 4 and 6 are
illustrated in Figures 1 and 2, respectively, and key
bond parameters are given in the captions. Both are
monoclinic crystal systems, but in 4 the cation displays
a pseudo S4 symmetry, whereas in 6 no particular
molecular symmetry is observed for the cation. The two
alkyne arms in 4 are trans to the imidazolium plane,
while in 6 they are cis. There are π‚‚‚π interactions
between the imidazolium ring and a phenyl ring from
the BPh4- anion, the centroid distances being the same
in both compounds (3.568(2) Å in 4 and 3.568(3) Å in
6). The CtC bonds in 4 and 6 are not involved in any
π‚‚‚π interactions, but there are several significant
C-H‚‚‚π interactions in the solid state of 4 and 6;
related C-H‚‚‚π interactions have been observed in
F igu r e 1. (top) Molecular structure of 4 in the solid state
(showing the labeling scheme for the asymmetric unit). Key
bond lengths (Å): N1-C3, 1.328(3); N1-C1, 1.379(3); N2-
C3, 1.329(3); N2-C2, 1.384(3); C1-C2, 1.351(3); C5-C6,
1.170(3); C8-C9, 1.177(3). (bottom) π‚‚‚π and C-H‚‚‚π
interactions around the imidazolium cation of 4.
imidazolium salts containing the BPh4 anion.26 In 4
-
and 6 the H atom from the CtC-H groups forms a
hydrogen bond with a phenyl ring from the anion. The
CtC-H‚‚‚π distances are very different; they are 2.92
Å for H6‚‚‚π and 2.46 Å for H9‚‚‚π in 4 and 2.81 Å for
H13‚‚‚π and 2.52 Å for H8‚‚‚π in 6. In compound 4, only
H1 from the imidazolium ring is involved in the C-H‚
‚‚π interaction (H1‚‚‚π ) 2.60 Å), but in compound 6,
all three hydrogens from the imidazolium ring form a
C-H‚‚‚π bond, with the strongest being that involving
H3 (2.35 Å); this is in accordance with the fact that the
H3 is the most acidic. In compound 4, the H atoms from
the sidearms (the CH2 groups) also form hydrogen bonds
with the phenyl rings from the anions. In contrast, in 6
none of the H atoms from the CH2 groups interact with
the phenyl rings of the anion. Presumably, the acidity
of the CH2 unit in 4 is enhanced by both the imidazo-
lium ring and the alkyne unit.
tetrahedral configurations. The different sidearms seem
to affect the geometry around the boron in the anion.
The B-C distances in 4 (1.642(3)-1.649(3) Å) are
slightly shorter than those in 6 (1.648(7)-1.669(6) Å).
The cis-{HCtC(CH2)3}N(CH)N{(CH2)3CtCH} group in
6 forms a cavity into which a phenyl ring of the anion
has inserted. The C-H‚‚‚π interaction is the strongest;
accordingly, the B1-C20 distance of 1.669(6) Å is the
longest and the C20-B1-C32 angle of 101.9(3)° is the
smallest. In comparison, the longest B-C distance in
1-butyl-3-methylimidazolium salts containing a tet-
raphenylborate anion substituted with the strongly
electron-withdrawing CF3 group at the para position is
1.647 Å, with the smallest C-B-C angle being 103.72°.27
Rea ction s of 3-6 w ith Co2(CO)8. Hexacarbonyldi-
cobalt-alkyne complexes have been known for many
years and are most conveniently obtained by direct
reaction of Co2(CO)8 with the alkyne, which acts as a
four-electron donor.28 Accordingly, reaction of the alkyne-
The CtC bond lengths are nearly the same in 4 and
6, ranging from 1.170(3) to 1.192(7) Å. The tetraphen-
ylborate anions in 4 and 6 have slightly distorted
(23) (a) Avent, A. G.; Chaloner, P. A.; Day, M. P.; Seddon, K. R.;
Welton, T. J . Chem. Soc., Dalton Trans. 1994, 3405. (b) Elaiwi, A.;
Hitchcock, P. B.; Seddon, K. R.; Srinivasan, N.; Tan, Y.-M.; Welton,
T.; Zora, J . A. J . Chem. Soc., Dalton Trans. 1995, 3467.
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Acta 2001, 320, 7.
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K.; Gra¨tzel, M. Inorg. Chem. 1996, 35, 1168.
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Kintzinger, J .-.P. Chem. Eur. J . 2000, 6, 2377.
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L.; Deelman, B.-J .; van Koten, G. Eur. J . Inorg. Chem. 2003, 2798.
(28) For example see: (a) Sternberg, H. W.; Greenfield, H.; Friedel,
R. A.; Wotiz, J .; Markby, R. Wender, I. J . Am. Chem. Soc. 1954, 76,
1457. (b) Greenfield, H.; Sternberg, H.-W.; Friedel, R. A.; Wotiz, J .;
Markby, R.; Wender, I. J . Am. Chem. Soc. 1956, 78, 120. (c) Cetini.
G.; Gambino, O.; Rossetti, R.; Sappa, E. J . Organomet. Chem. 1967,
8, 149.

Alkyne-Functionalized Imidazolium Salts
Organometallics, Vol. 23, No. 7, 2004 1625
the same methods outlined for compounds 1-6. The
positive ion ESI mass spectra of 7-10 exhibit parent
peaks corresponding to the intact cation. The dominant
feature in the IR spectra of 7-10 are the ν(CO)
stretches, which exhibit the expected absorptions be-
tween 1990 and 2100 cm-1. The wavenumber of the
alkyne bond decreases to between 1600 and 1500 cm-1
,
indicating the bond order to be more reminiscent of a
CdC double bond. In comparison to the free imidazo-
lium salts, the most notable changes in the cobalt
carbonyl derivatized complexes 7-10 are observed in
1
the H NMR spectra, where the proton attached to the
alkyne unit changes from ca. 3 ppm in 3 and 4 and 2
ppm in 5 and 6 to 6.31-6.50 ppm in the Co complexes
7-10, reflecting the increased acidity induced by coor-
dination of the electron-withdrawing organometallic
fragment. The chemical shifts of the carbonyl carbon
atoms come at 202-203 ppm, shifted slightly lower than
for structurally similar compounds.29
Single crystals of 10 suitable for X-ray diffraction
analysis were grown from a solution of dichloromethane
and diethyl ether at 0 °C. The molecular structure of
10 is shown in Figure 3, and key bond lengths and
angles are listed in the caption.
The length of the CtC bonds in 10 (C7-C8 ) 1.32(2)
Å and C12-C13 ) 1.31(1) Å) are longer than those
observed in the precursor imidazolium salt 6 but
somewhat shorter than in related compounds, where the
CtC bond lengths range from 1.33 to 1.36 Å.30,31 In
comparison to the structures of the free salts, where the
1,3-dialkyne arms extrude from the same face of the
imidazolium ring, in 10 the arms adopt a trans confor-
mation. The slightly different Co-Co distances (Co1-
Co2 ) 2.468(3) Å and Co3-Co4 ) 2.474(3) Å) are shorter
32
than that in the parent Co2(CO)8 but are in keeping
with other dicobalt systems that are bridged by alkyne
ligands.
F igu r e 2. (top) Molecular structure of 6 in the solid state
(showing the labeling scheme for the asymmetric unit). Key
bond lengths (Å): N1-C3, 1.339(5); N1-C1, 1.376(5); N2-
C3, 1.339(5); N2-C2, 1.376(5); C1-C2, 1.350(6); C7-C8,
1.169(6); C12-C13, 1.192(7). (bottom) π‚‚‚π and C-H‚‚‚π
interactions around the imidazolium cation of 6.
The three different C-H‚‚‚π interactions observed in
the solid state of free imidazolium salts 6, viz.
NCHN‚‚‚π, NCHCHN‚‚‚π, and CtC-H‚‚‚π, are present
in the structure of 10. In addition, one of the H atoms
in the CH2 group is also involved in a C-H‚‚‚π interac-
tion with the phenyl ring from the anion. However, the
π‚‚‚π interactions between the imidazolium ring and the
phenyl ring in the anion are no longer present.
Sch em e 2. Syn th esis of 7-10
While imidazolium salts are currently attracting
considerable attention as ionic liquids, at least those
with low melting points, for many years they have been
(29) (a) Lang, H.; Rheinwald, R.; Lay, U.; Zsolnai, L.; Huttner, G.
J . Organomet. Chem. 2001, 634, 74. (b) Moreno, C.; Marcos, M.-L.;
Dom´ınguez, G.; Arnanz, A.; Farrar, D. H.; Teeple, R.; Lough, A.;
Gonza´lez-Velasco, J .; Delgado, S. J . Organomet. Chem. 2001, 631, 19.
(30) (a) Calvo-Perez, V.; Vega, A.; Cortes, C. P.; Spodine, E. Inorg.
Chim. Acta 2002, 333, 15. (b) Brook, M. A.; Ramacher, B.; Dallaire,
C.; Gupta, H. K.; Ulbrich, D.; Ruffolo, R. Inorg. Chim. Acta 1996, 250,
49.
(31) (a) McAdam, C. J .; Duffy, N. W.; Robinson, B. H.; Simpson, J .
J . Organomet. Chem. 1997, 527, 179. (b) Castro, J .; Moyano, A.;
Perica`s, M. A.; Riera, A.; Alvarez-Larena A.; Piniella, J . F. J . Orga-
nomet. Chem. 1999, 585, 53. (c) Moreno, C.; Marcos, M.-L.; Dom´ınguez,
G.; Arnanz, A.; Farrar, D. H.; Teeple, R.; Lough, A.; Gonza´lez-Velasco,
J .; Delgado, S. J . Organomet. Chem. 2001, 631, 19.
functionalized imidazolium salts 3-6 with 2.2 equiv of
Co2(CO)8 in dichloromethane under ambient conditions
gave the expected complexes 7-10 in high yield (see
Scheme 2). The slight excess of Co2(CO)8 is essential to
ensure complete derivatization of the alkyne function-
alities. The organometallic products are obtained in high
purity (as evidenced by elemental analysis) following
washing with diethyl ether.
In keeping with related compounds, 7-10 are stable
under an inert atmosphere but decompose slowly when
exposed to air/moisture. They were characterized using
(32) Housecroft, C. E.; J ohnson, B. F. G.; Khan, M. S.; Lewis, J .;
Raithby, P. R.; Robson, M. E.; Wilkinson, D. A. J . Chem. Soc., Dalton
Trans. 1992, 3171.

1626 Organometallics, Vol. 23, No. 7, 2004
Fei et al.
Sch em e 3. Attem p ts To P r ep a r e Ca r ben es fr om 2
a n d 11
{Co2(CO)6}2]2PdCl2] (13), although we have established
a related chemistry for other functionalized imidazolium
salts that will be reported in due course. The reaction
of any of the dicobalt hexacarbonyl derivatized ionic
liquids reported herein with base, not surprisingly, leads
to reaction at the metal carbonyl site, resulting in
decomposition; thus, carbenes have not as yet been
identified.
In conclusion, we have prepared a series of alkyne-
functionalized imidazolium salts (including ionic liquids)
and derivatized them with the dicobalt hexacarbonyl
fragment to yield novel organometallic materials. Di-
cobalt hexacarbonyl alkyne complexes have previously
been prepared in ionic liquids,34 but this differs from
our work, in which the alkyne is part of the ionic liquid.
The spectroscopic and structural properties of the
materials prepared in this study have been examined
in some detail, and in the future we intend to explore
their chemical properties.
F igu r e 3. (top) Molecular structure of 10 in the solid state
(showing the labeling scheme for the asymmetric unit;
solvent molecules have been omitted for clarity). Key bond
lengths (Å): Co1-C7, 1.938(12); Co1-C8, 1.946(12); Co1-
Co2, 2.468(3); Co2-C8, 1.945(12); Co2-C7, 1.985(13); Co3-
C13, 1.916(12); Co3-C12, 1.942(11); Co3-Co4, 2.474(3);
Co4-C13, 1.952(11); Co4-C12, 1.972(10); N1-C3, 1.302(12);
N1-C1, 1.390(11); N2-C3, 1.335(12); N2-C2, 1.385(11);
C1-C2, 1.309(14); C7-C8, 1.318(16); C12-C13, 1.310(14).
(bottom) C-H‚‚‚π interactions around the imidazolium
cation of 10.
Exp er im en ta l Section
Starting materials were purchased from Acros and used as
received without further purification. The reactions were
performed under an inert atmosphere of dry nitrogen using
standard Schlenk techniques, in solvents dried using appropri-
ate reagents and distilled prior to use. IR spectra were
recorded on a Perkin-Elmer FT-IR 2000 system. NMR spectra
of interest as precursors to carbenes.33 Attempts have
also been made to convert the functionalized imidazo-
lium chlorides 2 and [{µ2-HCC(CH2)3NdC(H)N(µ2-
1
CCH(CH2)3CHdCH}{Co2(CO)6}2]Cl (11) (obtained from
2 by reaction with Co2(CO)8 in dichloromethane for 2
h) to carbenes. In the first step salts 2 and 11 were
treated with PdCl2 in a 2:1 ratio to give a polymeric
material (a clear plasticlike substance) and [{µ2-HCC-
were measured on a Bruker DMX 400, using SiMe4 for H and
13C as external standards at 20 °C. Electrospray ionization
mass spectra (ESI-MS) were recorded on a ThermoFinnigan
LCQ Deca XP Plus quadrupole ion trap instrument on samples
dissolved in water (1-6) and dichloromethane (7-10) using a
method described elsewhere.35 Differential scanning calorim-
etry (DSC) used to determine the melting points of the room-
temperature liquid salts was performed with a SETARAM
DSC 131 instrument. Elemental analysis was carried out at
the Institute of Molecular and Biological Chemistry at the
EPFL.
(CH2)3NdC(H)N(µ2-CCH(CH2)3CHdCH}{Co2(CO)6}2]2-
[PdCl4] (12), respectively (Scheme 3). Further reaction
of 12 with Ag2O does not afford the expected carbene
complex [HCC(CH2)3NdCN(µ2-CCH(CH2)3CHdCH}-
Syn th esis of [HCtCCH2NdC(H)N(CH2CtCH)CHdCH]-
Cl (1). A mixture of (trimethylsilyl)imidazole (14.026 g, 0.100
(33) For reviews, see: (a) Herrmann, W. A.; Ko¨cher, C. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2162. (b) Lappert, M. F. J . Organomet.
Chem. 1988, 358, 185. (c) Bourissou, D.; Guerret, O.; Gabba¨ı, F. P.;
Bertrand, G. Chem. Rev. 2000, 100, 39. (d) Carmalt, C. J .; Cowley, A.
H. Adv. Inorg. Chem. 2000, 50, 1.
(34) Becheanu, A.; Laschat, S. Synlett 2002, 11, 1865.
(35) Dyson, P. J .; McIndoe, J . S. Inorg. Chim. Acta 2003, 354, 68.

Alkyne-Functionalized Imidazolium Salts
Organometallics, Vol. 23, No. 7, 2004 1627
3050 (m, H-CdC), 2129 (m, CtC). Anal. Calcd for C33H29
BN2: C, 85.35; H, 6.29; N, 6.03. Found: C, 85.51; H, 6.31; N,
6.10.
mol) and ClCH2CtCH (21.502 g, 0.202 mol, 70 wt % in toluene
solution) was refluxed at 60 °C for 24 h. The resulting solid
was filtered, washed with diethyl ether (3 × 30 mL), and dried
under vacuum for 24 h. Yield: 28.5 g, 98%. Mp: 142 °C. ESI-
-
Syn t h esis of [H CtC(CH 2)3NdC(H )N{(CH 2)3CtCH }-
MS (H2O; m/z): positive ion, 145 [HCtCCH2NdC(H)N(CH2Ct
CHdCH]BF 4 (5). Compound 5 was obtained as a colorless
liquid in a similar manner as for 3 from 2 (2.367 g, 0.01 mol)
and NaBF4 (1.098 g, 0.01 mol). Yield: 2.70 g, 94%. Oil.
Viscosity: 512 mPa s-1. ESI-MS (H2O; m/z): positive ion, 201
CH)CHdCH]+; negative ion, 35, 37 [Cl]-. 1H NMR (D2O): δ
9.00 (s, 1H, NCHN), 7.56 (s, 2H, NCHdCHN), 4.93 (d, 4J (HH)
) 2.44 Hz, 4H, 2 × CH2CtCH), 2.98 (t, 4J (HH) ) 2.44 Hz,
2H, 2 × CH2CtCH). 13C NMR (D2O): δ 138.91 (s, NCHN),
125.77 (s, NCHdCHN), 81.16 (s, CH2CtCH), 74.82 (s, CH2Ct
CH), 42.55 (s, NCH2CtCH). IR (cm-1): 3394 (s, H-Ct
CCH2N), 3208, 3086, 3010 (m, H-CdC), 2125 (m, CtC). Anal.
Calcd for C9H9ClN2: C, 59.84; H, 5.02; N, 15.51. Found: C,
60.01; H, 5.08; N, 15.65.
[HCtC(CH2)3NdC(H)N{(CH2)3CtCH}CHdCH]+; negative ion,
1
87 [BF4]-. H NMR (CD3CN): δ 8.52 (s, 1H, NCHN), 7.43 (s,
2H, NCHdCHN), 4.26 (t, 4H, 3J (HH) ) 7.00 Hz, 2 × CH2CH2-
CH2CtCH), 2.29 (m, 4H, 2 × CH2CH2CH2CtCH), 2.03 (m,
4H, 2 × CH2CH2CH2CtCH), 1.95 (m, 2H, 2 × CH2CH2CH2Ct
CH). 13C NMR (CD3CN): δ 138.76 (s, NCHN), 125.62 (s,
NCH)CHN), 84.99 (s, CH2CH2CH2CtCH), 73.27 (s, CH2CH2-
CH2CtCH), 51.43 (s, CH2CH2CH2CtCH), 31.10 (s, CH2-
CH2CH2CtCH), 17.74 (s, H2CH2CH2CtCH). IR (cm-1): 3282
(s, H-CtCCH2N), 3151, 3138 (m, H-CdC), 2125 (m, CtC).
Anal. Calcd for C13H17BF4N2: C, 54.20; H, 5.95; N, 9.72.
Found: C, 54.29; H, 6.01; N, 9.75.
Syn t h esis of [H CtC(CH 2)3NdC(H )N{(CH 2)3CtCH }-
CHdCH]Cl (2). 2 was prepared in a manner similar to that
for 1 from (trimethylsilyl)imidazole (1.403 g, 0.010 mol) and
ClCH2CH2CH2CtCH (2.0718 g, 0.0202 mol) in toluene (10
mL). Yield: 3.23 g, 94%. Mp: 65 °C. ESI-MS (H2O; m/z):
positive ion, [HCtC(CH2)3NdC(H)N{(CH2)3CtCH}CHdCH]+
Syn t h esis of [H CtC(CH 2)3NdC(H )N{(CH 2)3CtCH }-
1
201; negative ion, 35, 37 [Cl]-. H NMR (CD3CN): δ 9.02 (s,
3
1H, NCHN), 7.47 (s, 2H, NCHdCHN), 4.30 (t, 4H, J (HH) )
CHdCH]BP h 4 (6). Compound 6 was obtained as a colorless
solid in a similar manner from 2 (2.367 g, 0.010 mol) and
NaBPh4 (3.422 g, 0.010 mol). Yield: 5.15 g, 99%. Mp: 135 °C.
7.45 Hz, 2 × CH2CH2CH2CtCH), 2.29 (m, 4H, 2 x CH2CH2-
CH2CtCH), 2.08 (m, 4H, 2 × CH2CH2CH2CtCH), 1.96 (dd,
2H, 4J (HH) ) 2.73 Hz, 2 × CH2CH2CH2CtCH). 13C NMR
(CD3CN): δ 140.31 (s, NCHN), 125.60 (s, NCHdCHN), 84.38
(s, CH2CH2CH2CtCH), 73.57 (s, CH2CH2CH2CtCH), 51.51 (s,
CH2CH2CH2CtCH), 31.91 (s, CH2CH2CH2CtCH), 18.31 (s,
CH2CH2CH2CtCH). IR (cm-1): 3377 (s, H-CtC(CH2)3N),
3280, 3078 (m, H-CdC), 2112 (m, CtC). Anal. Calcd for
ESI-MS (H2O; m/z): positive ion, 201 [HCtC(CH2)3NdC(H)N-
{(CH2)3CtCH}CHdCH]+; negative ion, 319 [BPh4]-. 1H NMR
(CD3CN): δ 8.47 (s, 1H, NCHN), 7.41 (s, 2H, NCHdCHN),
7.29 (m, 8H, C6H5 ortho), 7.02 (m, 8H, C6H5 meta), 6.86 (m,
3
4H, C6H5 para), 4.24 (t, 4H, J (HH) ) 7.17 Hz, 2 × CH2CH2-
C
13H17ClN2: C, 65.95; H, 7.24; N, 11.83. Found: C, 66.01; H,
CH2CtCH), 2.29 (m, 2H, 2 × CH2CH2CH2CtCH), 2.24 (m,
4H, 2 × CH2CH2CH2CtCH), 1.97 (m, 4H, 2 × CH2CH2CH2Ct
CH). 13C NMR (CD3CN): δ 166.80 (q, 1J (BC) ) 49.43 Hz, C6H5
ipso), 138.71, 138.35, 128.70, 125.48, 124.84, 84.87 (s, CH2Ct
CH), 73.34 (s, CH2CtCH), 51.36 (s, CH2CH2CH2CtCH), 31.05
(s, CH2CH2CH2CtCH), 17.78 (s, CH2CH2CH2CtCH). IR (cm-1):
3268 (s, H-CtCCH2N), 3077, 3051, 3035 (m, H-CdC), 2120
(m, CtC), Anal. Calcd for C37H37BN2: C, 85.38; H, 7.16; N,
5.38. Found: C, 84.01; H, 7.21; N, 5.41.
7.31; N, 11.95.
Syn th esis of [HCtCCH2NdC(H)N(CH2CtCH)CHdCH]-
BF 4 (3). A mixture of 1 (1.806 g, 0.01 mol) and NaBF4 (1.098
g, 0.01 mol) in acetone (30 mL) was stirred at room temper-
ature for 24 h. The resulting solid was filtered off, and the
solid was washed with diethyl ether (2 × 5.0 mL). The filtrates
were collected, and the solvent was removed under vacuum.
The product 3 was obtained as a white solid. Yield: 2.10 g,
91%. Mp: 67 °C. ESI-MS (H2O; m/z): positive ion, 145 [HCt
Syn th esis of [{µ2-HCCCH2NdC(H)N(µ2-CCHCH2)CHd
CCH2NdC(H)N(CH2CtCH)CHdCH]+; negative ion, 87 [BF4]-
. 1H NMR (CD3CN): δ 8.79 (s, 1H, NCHN), 7.57 (s, 2H, NCHd
CHN), 5.05 (d, 4J (HH) ) 2.44 Hz, 4H, 2 × CH2CtCH), 3.07
(t, 4J (HH) ) 2.44 Hz, 2H, 2 × CH2CtCH). 13C NMR
(CD3CN): δ 139.21 (s, NCHN), 125.86 (s, NCHdCHN), 80.98
(s, CH2CtCH), 75.00 (s, CH2CtCH), 42.15 (s, NCH2CtCH).
IR (cm-1): 3277 (s, H-CtCCH2N), 3265, 3176, 3159 (m,
H-CdC), 2132 (m, CtC). Anal. Calcd for C9H9BF4N2: C,
46.60; H, 3.91; N, 12.08. Found: C, 46.71; H, 3.96; N, 12.15.
CH}{Co2(CO)6}2]BF 4 (7). Co2(CO)8 (0.700 g, 2.05 mmol) was
added to a solution of 3 (0.232 g, 1.0 mmol) in dichloromethane
(10 mL). The reaction mixture was stirred at room temperature
for 2 h, during which time the CO gas bubbled out from the
reaction solution completely. The solvent was removed under
vacuum. The remaining solid was washed with diethyl ether
(3 × 10 mL) to give the product 7 as a dark red solid. Yield:
0.65 g, 81%. Mp: 110 °C. ESI-MS (CH2Cl2; m/z): positive ion,
717 [{µ2-HCCCH2NdC(H)N(µ2-CCHCH2)CHdCH}{Co2(CO)6}2]+;
negative ion, 87 [BF4]-. 1H NMR (CD3CN): δ 8.90 (s, 1H,
NCHN), 7.68 (s, 2H, NCHdCHN), 6.49 (broad signal, 2H, 2 ×
CH2CtCH), 5.56 (broad signal, 4H, 2 × CH2CtCH). 13C NMR
(CD3CN): δ 201.96, 138.85, 126.22, 90.80, 74.81, 54.86. IR
(cm-1): 3153 (w, H-CCCo2(CO)6), 3121, (w, H-CdC), 2001,
2014, 2100 (s, CtO), 1559 (m, CCCo2(CO)6). Anal. Calcd for
Syn th esis of [HCtCCH2NdC(H)N(CH2CtCH)CHdCH]-
BP h 4 (4). A mixture of 1 (1.806 g, 0.01 mol) and NaBPh4 (3.422
g, 0.01 mol) in acetone (30 mL) was stirred at room temper-
ature for 48 h. The resulting solid was filtered off, and the
solid was washed with diethyl ether (2 × 5.0 mL). The filtrates
were collected, and solvent was removed under vacuum. The
product 4 was obtained as a white solid. Yield: 4.41, 95%.
Mp: 185 °C. ESI-MS (H2O; m/z): positive ion, 145 [HCt
C
21H9BCo4F4N2O12: C, 31.38; H, 1.13; N, 3.48. Found: C,
31.21; H, 1.11; N, 3.45.
CCH2NdC(H)N(CH2CtCH)CHdCH]+; negative ion, 319
[BPh4]-. 1H NMR (CD3CN): δ 8.61 (s, 1H), 7.57 (s, 2H, NCHd
CHN), 7.30 (m, 8H, C6H5 ortho), 7.02 (m, 8H, C6H5 meta), 6.86
(m, 4H, C6H5 para), 4.73 (s, 4H, 2 × CH2CtCH), 3.05 (t,
4J (HH) ) 2.44 Hz, 2H, 2 × CH2CtCH). 13C NMR (CD3CN): δ
Syn th esis of [{µ2-HCCCH2NdC(H)N(µ2-CCHCH2)CHd
CH}{Co2(CO)6}2]BP h 4 (8). Compound 8 was obtained as a
dark red solid in a manner similar to that for 7 from 4 (0.464
g, 1 mmol) and Co2(CO)8 (0.7000 g, 2.05 mmol) in dichlo-
romethane (30 mL). Yield: 0.78 g, 75%. Mp: 115 °C. ESI-MS
1
166.80 (q, J (BC) ) 49.73 Hz, C6H5 ipso), 138.68 (s, NCHN),
128.69 (s, C6H5 ortho), 125.42 (s, NCHdCHN), 124.85 (s, C6H5
meta), 80.64 (s, CH2CtCH), 74.84 (s, CH2CtCH), 42.27 (s,
NCH2CtCH). IR (cm-1): 3256 (s, H-CtCCH2N), 3160, 3131,
(CH2Cl2; m/z): positive ion, 717 [{µ2-HCCCH2NdC(H)N(µ2-
CCH CH2)CHdCH}{Co2(CO)6}2]+; negative ion, 319 [BPh4]-.

1628 Organometallics, Vol. 23, No. 7, 2004
Fei et al.
1H NMR (CD3CN): δ 8.89 (s, 1H, NCHN), 7.68 (s, 2H, NCHd
CHN), 7.28 (m, 8H, C6H5 ortho), 7.00 (m, 8H, C6H5 meta), 6.86
(m, 4H, C6H5 para), 6.50 (broad signal, 2H, 2 × CH2CtCH),
5.53 (broad signal, 4H, 2 × CH2CtCH). 13C NMR (CD3CN): δ
201.82 (broad signal, CtO), 167.18 (q, 1J (BC) ) 48.50 Hz, C6H5
ipso), 138.75, 128.71, 126.11, 124.94. 94.42, 74.95, 54.86. IR
(cm-1): 3155 (w, H-CCCo(CO)6), 3058 (w, H-CdC), 2099,
2057, 1999 (s, CtO), 1548 (m, CCCo2(CO)6). Anal. Calcd for
Ta ble 2. Cr ysta l Da ta a n d Deta ils of th e Str u ctu r e
Deter m in a tion for 4, 6, a n d 10
4
6
10
chem formula
C
33H29BN2
C37H37BN2
C50H41BCl2-
Co4N2O13
1195.28
monoclinic
C2/c
35.331(18)
19.2780(17)
16.489(9)
90
110.76(5)
90
10502(8)
8
formula wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
464.39
monoclinic
P21/c
14.606(6)
8.780(4)
20.378(2)
90
95.701(19)
90
2600.4(16)
4
520.50
monoclinic
P21/n
10.7263(16)
17.092(2)
16.239(2)
90
92.631(12)
90
2974.1(7)
4
C
45H29BCo4N2O12: C, 52.16; H, 2.82; N, 2.70. Found: C, 52.21;
H, 2.81; N, 2.75.
Syn th esis of [{µ2-HCC(CH2)3NdC(H)N(µ2-CCH(CH2)3-
CHdCH}{Co2(CO)6}2]BF 4 (9). Compound 9 was obtained as
a dark red solid in a manner similar to that for 7 from 5 (0.288
g, 1 mmol) and Co2(CO)8 (0.7000 g, 2.05 mmol) in dichlo-
romethane (30 mL). Yield: 0.76 g, 88%. Mp: 100 °C. ESI-MS
Z
Dcalcd (g cm-3
F(000)
)
1.186
984
0.068
140
1.162
1112
0.066
140
1.512
4848
1.407
140
(CH2Cl2; m/z): positive ion, 772 [{µ2-HCCCH2NdC(H)N(µ2-
µ (mm-1
)
1
CCHCH2)CHdCH}{Co2(CO)6}2]+; negative ion, 87 [BF4]-. H
temp (K)
wavelength (Å)
no. of measd rflns
no. of unique rflns
no. of unique rflns
(I > 2σ(I))
no. of data/params
R1a (I > 2σ(I))
wR2a (all data)
GOFb
0.710 70
15 846
4344
0.710 73
17 251
4938
0.710 70
32 633
8973
NMR (CD3CN): δ 8.57 (s, 1H, NCHN), 7.47 (s, 2H, NCHd
CHN), 6.31 (broad signal, 2H, 2 × CH2CH2CH2CtCH), 4.28
(broad signal, 4H, 2 × CH2CH2CH2CtCH), 2.92 (m, 4H, 2 ×
2958
1976
3166
CH2CH2CH2CtCH), 1.98 (m, 4H, 2 × CH2CH2CH2CtCH). 13
C
NMR (CD3CN): δ 203.09, 138.47, 125.55, 98.22, 76.66, 51.89,
34.61, 32.98. IR (cm-1): 3156 (w, H-CCCo2(CO)6), 3098 (w,
H-CdC), 2043, 2012, 1988 (s, CtO), 1565 (m, CCCo2(CO)6).
Anal. Calcd for C25H17BCo4F4N2O12: C, 34.92; H, 1.99; N, 3.26.
Found: C, 34.99; H, 2.01; N, 3.31.
4344/326
0.0492
0.1526
1.072
4938/362
0.0504
0.1692
0.868
8973/659
0.0887
0.2860
0.972
R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
GOF ) {∑[w(Fo - Fc2)2]/(n - p)}1/2, where n is the number of
data and p is the number of parameters refined.
b
2
Syn th esis of [{µ2-HCC(CH2)3NdC(H)N(µ2-CCH(CH2)3-
CHdCH}{Co2(CO)6}2]BP h 4 (10). Compound 9 was obtained
as a dark red solid in a manner similar to that for 7 from 6
(0.521 g, 1 mmol) and Co2(CO)8 (0.7000 g, 2.05 mmol) in
dichloromethane (30 mL). Yield: 0.88 g, 81%. Mp: 132 °C. ESI-
were measured at room temperature on a Marresearch mar345
IPDS instrument. Data reduction was carried out with CrysA-
lis RED, release 1.7.0.36 An empirical absorption correction37
was applied to all data sets. Structure solution and refinement
as well as molecular graphics and geometrical calculations
were performed for all structures with the SHELXTL software
package, release 5.1.38 The structures were refined using full-
matrix least squares on F2 with all non-H atoms anisotropi-
cally defined. H atoms were placed in calculated positions
using the riding model.
MS (CH2Cl2; m/z): positive ion, 772 [{µ2-HCC(CH2)3NdC(H)N-
(µ2-CCH(CH2)3CHdCH}{Co2(CO)6}2]+; negative ion, 319 [BPh4]-.
1H NMR (CD3CN): δ 8.40 (s, 1H, NCHN), 7.43 (s, 2H, NCHd
CHN), 7.27 (m, 8H, C6H5 ortho), 7.00 (m, 8H, C6H5 meta), 6.84
(m, 4H, C6H5 para), 6.31 (broad signal, 2H, 2 × CH2CH2CH2Ct
CH), 4.23 (broad signal, 4H, 2 × CH2CH2CH2CtCH), 2.86 (m,
4H, 2 × CH2CH2CH2CtCH), 1.95 (m, 4H, 2 × CH2CH2CH2Ct
CH). 13C NMR (CD3CN): δ 203.29 (broad signal, C)O), 166.59
(q, 1J (BC) ) 48.00 Hz, C6H5 ipso), 138.70, 138.11, 128.69,
125.45, 124.82, 98.18, 76.76, 51.83, 34.66, 33.07. IR (cm-1):
3108 (w, H-CCCo2(CO)6), 3056 (w, H-CdC), 2090, 2045, 1989
Ack n ow led gm en t. We thank the EPFL and Swiss
National Science Foundation for financial support.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data, as CIF files. This material is available free of charge via
the Internet at http://pubs.acs.org.
(s, CtO), 1557 (w, H-CCCo2(CO)6). Anal. Calcd for C49H37
-
BCo4N2O12: C, 53.88; H, 3.41; N, 2.56. Found: C, 53.91; H,
3.45; N, 2.60.
X-r a y Deter m in a tion of 4, 6, a n d 10. Details about the
crystals and their structure refinement are given in Table 2,
whereas relevant geometrical parameters, including bond
lengths and angles, are included in the captions to Figures
1-3. Data collections were performed at 140 K on a four-circle
Kappa goniometer equipped with an Oxford Diffraction KM4
Sapphire CCD for compound 6. Diffraction data for 4 and 10
OM034248J
(36) Oxford Diffraction Ltd., Abingdon, Oxfordshire, U.K., 2003.
(37) DELABS: Walker, N.; Stuart, D. Acta Crystallogr., Sect A 1983,
39, 158-166.
(38) Sheldrick, G. M. University of Go¨ttingen, Go¨ttingen, Germany,
1997 (Bruker AXS, Inc., Madison, WI 53719, 1997).