Remarkable anion and cation effects on stille reactions in functionalised ionic liquids

Article abstract of DOI:10.1002/adsc.200505271

Task-specific ionic liquids bearing nitrile functional groups attached to the cation and nitrogen-donor-containing anions strongly affect the efficiency of the Stille cross-coupling, influencing the nature of the catalyst and its stability. The relative strengths of the coordinating power of the cations and anions are varied and compared, and under certain conditions nanoparticles are observed.

Full text of DOI:10.1002/adsc.200505271

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DOI: 10.1002/adsc.200505271
Remarkable Anion and Cation Effects on Stille Reactions in
Functionalised Ionic Liquids
Cinzia Chiappe,a,* Daniela Pieraccini,a Dongbin Zhao,b Zhaofu Fei,b
Paul J. Dysonb,*
a
Dipartimento di Chimica Bioorganica e Biofarmacia, Via Bonanno 33, 56126, Pisa, Italy
Fax: (þ39)-(0)50-221-9660, e-mail: cinziac@farm.unipi.it
b
´
´ ´
Institut des Sciences et Ingenierie Chimiques, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne,
Switzerland
Fax: (þ41)-21-693-9885, e-mail: paul.dyson@epfl.ch
Received: July 8, 2005; Accepted: October 20, 2005
Abstract: Task-specific ionic liquids bearing nitrile
functional groups attached to the cation and nitro-
gen-donor-containing anions strongly affect the effi-
ciency of the Stille cross-coupling, influencing the na-
ture of the catalyst and its stability. The relative
strengths of the coordinating power of the cations
and anions are varied and compared, and under cer-
tain conditions nanoparticles are observed.
clearly indicates this is not the case,[4] so that differences
between ILs may be apparent. Therefore, task-specific
(or functionalised) ILs able to interact with a metal cen-
tre via a coordination group attached to the IL backbone
(anion or cation) should further increase catalyst reten-
tion, thus avoiding the use of co-ligands and reducing
leaching.[5] Numerous functional groups have been at-
tached into imidazolium or pyridinium cations,[6] among
which many have been found to be able to stabilise tran-
sition metal nanoparticle catalysts/catalyst reservoirs,[5]
possibly via interaction of the functional group with
the surface of the nanoparticles, thereby preventing ag-
gregation.
Keywords: catalysis; immobilization; ionic liquids;
nanoparticles; palladium; Stille cross-coupling
While many efforts have been devoted to the func-
tionalisation of IL cations, and the influence of function-
Palladium-mediated cross-coupling reactions are alised ILs has been investigated in a few catalytic sys-
among the most widely studied type of catalysed reac- tems, there is little study of the influence of the anions.[7]
tions in ionic liquids (ILs).[1] The reason for such interest Recently, it has been shown that Stille cross-coupling re-
may be ascribed to the ability of the ionic reaction media actions are particularly sensitive to the structure of the
to overcome the drawbacks that generally accompany IL.[8] Formally, nitrogen-containing anions like [Tf2N]À
these reactions when performed in molecular solvents, ensure the highest reactivity, and facilitate a ligand-
limiting their applicability: namely, decomposition and free reaction protocol. Despite high activity, the stability
leaching of expensive catalysts/co-catalysts, poor re- of the catalytic system is low, so that recycling proce-
agent and catalyst solubility and difficulties in catalyst dures were ineffective. In contrast, the introduction of
recycling. In general, ionic transition metal catalysts a nitrile-functionality onto pyridinium-based ILs not
tend to be well retained in ILs during work-up proce- only reduces catalyst leaching, but improves catalyst sta-
dures, thus confirming their potential as the immobilis- bility.[5a]
ing phase. By varying and combining the ions, approxi-
Herein, we describe the synthesis of a series of sym-
mately one trillion ILs are accessible,[2] at least in princi- metrical and asymmetrical nitrile-functionalised imida-
ple, which makes further optimisation of palladium zolium-based ILs incorporating nitrogen-containing
cross-coupling reactions based on solvent selection a anions such as [Tf2N]À and [N(CN)2]À and assess their
daunting task. Until now it has been difficult to predict application as reaction media for the transfer of vinyl
which ILs are the best ones for certain applications, and methyl groups onto iodo- and bromobenzene.
but with increased understanding on how the structure
The ILs used as reaction media (see Scheme 1) were
of an IL affects its physical and chemical properties prepared by anion metathesis from their corresponding
the advantages of these solvents with respect to mo- chlorides, following reported procedures.[9] All the com-
lecular ones should emerge.[3] Here, it is worth noting pounds are liquid at room temperature and were charac-
that even if the anions generally used to make ILs are terised using electrospray ionisation-mass spectrometry
formally defined as non-coordinating, recent work (ESI-MS), IR and NMR spectroscopy (see Experimen-
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Anion and Cation Effects on Stille Reactions in Ionic Liquids
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Scheme 1. Ionic liquids employed.
tal Section). First, we evaluated the reaction of tributyl-
vinylstannane using Pd(OAc)2 as the catalyst source un-
der ligand-free conditions, following a literature proto-
col.[8] For comparison, reactions with palladium cata-
lyst/co-catalyst, Pd(0)/AsPh3, have been also per-
formed. The reduction of Pd(OAc)2 to Pd(0) in [Tf2N]-
based ILs is immediate, the solutions rapidly turn black,
Figure 1. Pd(OAc)2 solutions in [bmim][N(CN2)] (left) and in
[bmim][Tf2N] (right).
indicative of nanoparticle formation (see below). In al centre in Stille cross-coupling reactions is affected by
contrast, yellow solutions were obtained with the nature of the cation, that is, by the strength of ion
[N(CN)2]À-based ILs (Figure 1).
pairing through specific interactions,[8] and competition
Although Pd(OAc)2 rapidly dissolved in the ionic me- between the cation and the metal for the anion has been
dia, reagents and products were only slightly soluble, af- hypothesised. Moreover, Gordon et al. have shown that
fording a biphasic system, in principle enabling product there is a correlation between the basicity of the anion in
recovery directly by decantation. Practically, consider- ILs with the rate of nickel-catalysed reactions.[10]
ing the volume of IL used (1 mL), extraction with n-pen-
tane was preferred.
Considering that microscopic properties of
[bmim][Tf2N], determined through spectroscopic dyes
The degree of conversion, as well as the actual mass (Table 2), are practically the same as those of
balance, which is related to the ease of extraction of [C3CNmim][Tf2N] (i.e., the nucleophilicity of the anion
products and unreacted materials from the ionic me- is not modified by the cation structure), it is not unrea-
dium, were evaluated by GC analysis after the addition sonable to conclude that the increased efficiency of the
of an internal standard. The yields for the reactions in- nitrile-functionalised IL is due to the interaction of the
volving the transfer of a vinyl group onto iodobenzene nitrile pendant group with the metal centre. IR analysis
are generally high, considering that a relatively short confirmed that the palladium coordinates to the nitrile
reaction time was used; with the exception of group, since the nCN stretching frequency changes from
[C3CNmim][Tf2N], practically quantitative conversion 2251 cmÀ1 to 2359 and 2341 cmÀ1 (symmetric and asym-
can be obtained by increasing the reaction time. The re- metric stretching). In addition, TEM images reveal that
sults are summarised in Table 1 and show that the nature the near double conversion of the Stille reaction in the
of the cation in the [N(CN)2]-based ILs does not seem to CN-IL than that of the normal IL may be ascribed to dif-
have a major effect on the kinetics of the reaction, as the ferent states of the palladium nanoparticles in the differ-
percentage of conversion is almost the same on going ent ILs (Figure 2). Nanoparticles have been implicated
from [bmim][N(CN)2] to [(C4CN)2im][N(CN)2]. It is, as catalysts/catalyst reservoirs for numerous reactions
however, worth noting that, using the palladium-AsPh3 in ILs and in many cases they can be isolated and
system, the transfer of the vinyl group is almost quanti- reused.[11] In [bmim][Tf2N], the palladium nanoparticles
tative: indicating that [N(CN)2]À anions are not able to are small (2–4 nm), but highly aggregated, resulting in a
interact with the metal centre, if good ligands are em- low catalytically accessible area. Nanoparticle aggrega-
ployed.
tion during a catalytic process in ILs has been observed
Interestingly, visible increases in coupling yields char- previously,[12] but the CN group in the functionalised IL
acterise the reaction in [C3CNmim][Tf2N] with respect provides a stabilising effect. However, in spite of their
to the non-functionalised IL. It has previously been pro- larger size, the nanoparticles in the CN-IL are well dis-
posed that the ability of the anion to interact with a met- persed and are open to activation. Such an observation
Adv. Synth. Catal. 2006, 348, 68 – 74
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69

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Table 1. Stille coupling of iodobenzene with tributylvinylstannane in ILs.
Entry
Ionic liquid
Time [h]
Catalyst
Mass Balance[a] [%]
Conversion[b] [%]
1
2
[bmim][N(CN)2]
[bmim][N(CN)2][c]
1
1
1
1
1
1
1
1
1
2
1
1
2
1
2
1
1
1
1
1
Pd(OAc)2
Pd(OAc)2
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
65
70
79
>99
>99
>99
90
70
70
70
75
90
90
90
87
90
64
90
54
52
36
97
40
40
73
30
80
48
85
65
55
83
72
75
72
57
90
60
60
3[bmim][N(CN)
4
5
6
7
]
2
[bmim][Tf2N]
[bmim][Tf2N][c]
[bmim][Tf2N]
[bmim][BF4]
8
9
[C3CNmim][BF4]
[C3CNmim][BF4][c]
[C3CNmim][BF4]
10
11
12
13[C
14
15
16
17
18
19
20
[C3CNmim][BF4]
[C3CNmim][N(CN)2]
3CNmim][N(CN)2]
[C3CNmim][Tf2N]
[C3CNmim][Tf2N]
[C3CNmim][Tf2N]
[(C3CN)2im][N(CN)2]
[(C3CN)2im][Tf2N]
[(C4CN)2im][N(CN)2]
[(C4CN)2im][Tf2N]
70
[a]
Determined using benzonitrile as external standard.
Determined by GC analysis.
Water equilibrated.
[b]
[c]
T
Table 2. EN and Kamlet–Taft values for nitrile-functiona-
lised ionic liquids.
T
Solvent
EN
p*
a
b
[bmim][BF4]
[bmim][Tf2N]
[bmim][N(CN)2]
[C3CNmim][BF4]
[C3CNmim][N(CN)2]
[C3CNmim][Tf2N]
0.667
0.645
0.629
0.695
0.6531.124
0.677 1.029
0.984
0.971
1.129
1.078
0.665
0.635
0.464
0.638
0.451
0.248
0.708
0.337
0.516
0.646
0.508
0.219
Figure 2. Comparison of TEM images of the palladium nano-
particles isolated after the Stille reaction from [bmim][Tf2N]
(left) and [C3CNmim][Tf2N] (right).
can only be explained by the stabilisation effect from the
CN functionality incorporated into the IL, and may be
connected to the higher catalytic activity in the CN-ILs.
Further evidence that the nitrile pendant group is
chiefly responsible for the increased reaction rate in terms of coordination of the palladium only involving
the CN-IL with the [Tf2N]À anion arises from similar re- the anion. Unfortunately, it is not possible to confirm
sults obtained with respect to [C3CNmim][BF4]: given its this hypothesis by IR, due to overlap of the stretching
symmetrical shape and low charge density, the tetra- bands of the anion and cation counterparts. Moreover,
fluoroborate anion possesses a low nucleophilicity, and it was not possible to isolate palladium nanoparticles
therefore, it is generally considered as being effectively from these media, suggesting the involvement of anoth-
non-coordinating.
er catalyst state.
The low sensitivity of cross-coupling rates when
It is reasonably to propose that when ILs possessing
[N(CN)2]-based ILs are used may be rationalised in nucleophilic anions are used as solvents for palladium-
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Anion and Cation Effects on Stille Reactions in Ionic Liquids
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Figure 3. Recyclability of the Stille reaction between vinyltributylstannane and iodobenzene.
mediated cross-couplings, the stabilisation of the metal vinyl group from tributylvinyltin to bromobenzene.
centre involves mainly the anion and therefore is insen- Data reported in Table 3clearly reveal that
sitive to variation on the cation structure; however, [C3CNmim][Tf2N] is far superior to the [BF4] analogue,
when non-nucleophilic anions are used a positive effect even if the reaction rates are markedly lower to those
of the nitrile pendant group may be envisaged, as in characterising the reaction of iodobenzene (only 32%
[C3CNmim][BF4]. Tf2N-based ILs represent an inter- of product is recovered). Moreover, product yields are
mediate case as, in principle, both the anion and the cat- practically doubled on changing from [bmim][Tf2N] to
ion are able to stabilise a metal centre.
[C3CNmim][Tf2N]. The [N(CN)2]-based ILs are the
Data collated in Table 1 also suggest that the introduc- least active for the ligandless Stille cross-coupling in-
tion of a second nitrile group on the cation determines, volving bromobenzene as substrate, even though a dif-
in the case of [Tf2N]-based ILs, a further increase in ference was observed on passing from the non-function-
the activity of the catalyst, even if the magnitude is not alised to the nitrile containing IL.
the same as when passing from non-functionalised to
Completely different behaviour was observed for the
mono-functionalised ILs. Moreover, a substantial drop transfer of a methyl group (see Table 4). In this case,
in catalytic activity is evidenced in [(C4CN)2im][Tf2N]: both cross-coupling and homocoupling are sensitive to
the high viscosity of this IL might well account for a re- the structure of the solvent. For example, nitrile-func-
duced mass transfer, determining a lower reaction rate. tionalised ILs do not improve the yields of the methyl
The effect of water has been also taken into consider- transfer reaction with respect to the non-functionalised
ation: as we might expect, water has detrimental effect derivatives in the presence of a ligand. [bmim][Tf2N]
on conversion for hydrophilic ILs, whereas it effects and [bmim][N(CN)2] ensure the highest conversion to-
no appreciable variation of the rate of conversion gether with the lowest percentage of homocoupling.
when [bmim][Tf2N] is used.
The situation deteriorates on application of the ligand-
The difference between reactions conducted in less protocol: in this case, only [C3CNmim][N(CN)2] en-
[N(CN)2]-based ILs with respect to the others is also ap- sured a conversion comparable to that obtained in the
parent in the recycling tests (see Figure 3). Although pal- presence of AsPh3.
ladium solutions in [N(CN)2]-based ILs generally yield
In conclusion, nitrile-functionalized ILs are consider-
colourless organic phases during extraction, indicating ably more-effective for the immobilisation of palladium
less pronounced leaching, they are generally less stable. catalysts for the transfer of a vinyl group in Stille reac-
Moreover, the catalyst immobilised in [C3CNmim][Tf2 tions with respect to 1-butyl-3-methylimidazolium de-
N] is much more stable than the non-functionalised ana- rivatives. TEM analysis of nanoparticles extracted
logue (after three cycles, there is no significant decrease from [Tf2N]-based ILs provides evidence for the stabil-
inactivity). Itisnoteworthythatthefourthcyclewascon- ising effect exerted by the nitrile pendant group on the
ducted seven days after the preceding one.
metal centre. Although such task-specific ILs may well
Nitrile-functionalised ILs of the type [C3CNmim][X] prove to be decisive in vinyl transfer, they do not appear
have also been tested as solvents for the transfer of the to be as effective in transferring a methyl group.
Adv. Synth. Catal. 2006, 348, 68 – 74
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Table 3. Stille coupling of bromobenzene and tributylvinylstannane in ILs.
Solvent
Time [h]
Catalyst
Mass Balance[a] [%]
Conversion[b] [%]
[bmim][N(CN)2]
[bmim][Tf2N]
[C3CNmim][BF4]
[C3CNmim][Tf2N]
[C3CNmim][N(CN)2]
24
24
24
24
24
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
65
81
86.2
80
62
2
16.3
12
32.5
14
[a]
Determined using benzonitrile as external standard.
Determined by GC analysis.
[b]
Table 4. Methyl transfer from tetramethyltin to iodobenzene in ionic liquids.
Entry Solvent
Catalyst
Ligand Time [h] Mass balance[a] [%] Ph-Me[b] [%] Tol/Biphenyl[b] [%]
1
2
[bmim][N(CN)2]
[bmim] [N(CN)2]
2N]
[bmim][Tf2N]
[C3CNmim][BF4]
[C3CNmim][BF4]
[C3CNmim][N(CN)2] Pd2(dba)3 AsPh3
[C3CNmim][N(CN)2] Pd(OAc)2
[C3CNmim][Tf2N]
[C3CNmim][Tf2N]
Pd2(dba)3 AsPh3
24
24
24
24
24
24
24
24
24
24
60
100
90
70
64
80
77
47
77
52.6[c]
–
1.40
–
2.29
0.617
1.45
–
0.993
1.77
0.303
0.786
Pd(OAc)2
Pd2(dba)3 AsPh3
Pd(OAc)2
Pd2(dba)3 AsPh3
Pd(OAc)2
–
3[bmim][Tf
4
5
6
7
8
9
10
62[c]
12[c]
23.4[c]
8[c]
–
–
33[c]
26[c]
9[c]
–
Pd2(dba)3 AsPh3
Pd(OAc)2
–
92
7[c]
[a]
[b]
[c]
Determined using benzonitrile as external standard.
Determined by GC and GM analysis.
The unreacted material is iodobenzene.
petted into a clean dry quartz cuvette. Residual dichlorome-
thane was evaporated under gentle stream of argon gas. The
ionic liquid was then added to the cuvette, the cuvette was cap-
ped and sealed, and the sample was mixed for an appropriate
time prior to experimental measurements. The dye concentra-
tion in the ionic liquid was such that it had an absorbance under
1 for aniline dyes and between 0.1 and 0.3for Reichardt dye. 4-
Nitroaniline (Fluka), N,N-diethyl-4-nitroaniline (Frinton),
Reichardtꢁs betaine dye (Aldrich), iodobenzene (99%), tribu-
tylvinylstannane, tetramethylstannane were used without puri-
fication. [bmim][Tf2N], [bmim][N(CN)2], [C3CNmim][BF4],
[C3CNmim][Tf2N], [C3CNmim][N(CN)2], [(C3CN)2im][Tf2N],
Experimental Section
General Remarks
GC-MS were carried out on a 30 m DB5 capillary column using
an instrument equipped with an ion trap detector. GC analyses
were carried out using an ECONOCAP EC-5 column (30 m).
ESI-MS analyses were performed on a Finnigan LCQ Advant-
age (Thermo Finnigan, San Jose, CA, USA) ion trap instru-
ment equipped with an Excalibur software (capillary tempera-
ture 493.15 K, flow rate 3 mL/min) as described previously.[13]
The UV-VIS spectroscopic measurements were performed us-
ing a Cary 2200 spectrometer at temperature of 25Æ0.28C. lmax
was measured by taking the middle point between the two po-
[(C3CN)2im][N(CN)2],
[(C4CN)2im][Tf2N],
[(C4CN)2im]
[N(CN)2] were prepared from the corresponding chlorides,
following the reported procedures.[9]
sitions of the band where the absorbance is equal to 0.90 Amax
.
Reactions were carried out in a screw cup with Teflon-faced
rubber septum vials under magnetic stirring. To a suspension of
Pd2(dba)3 (0.025 mmol) and Ph3As (0.05 mmol) or Pd(OAc)2
(0.025 mmol) in 1 mL of ionic liquid were added iodobenzene
Individual stock solutions of Reichardtꢁs betaine dye, 4-nitroa-
niline and N,N-diethyl-4-nitroaniline were prepared in di-
chloromethane. To prepare a given dye/ionic liquid solution,
the appropriate amount of the dye stock solution was micropi-
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Anion and Cation Effects on Stille Reactions in Ionic Liquids
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(0.5 mmol) and the organostannane (0.6 mmol). The mixture
was stirred at 808C for the times reported in Tables 1, 3and
4. The products were extracted with diethyl ether (10Â
1 mL), the organic layers were dried over MgSO4 and diluted
to an exactly known volume. A portion of this solution, exactly
measured, was analysed by GC-MS, the remainder by GC, af-
ter the addition of an appropriate amount of an internal stand-
ard (benzonitrile).
[(C4CN)2im][Tf2N]
The product was obtained as a deep yellow liquid; yield: 82%.
ESI-MS (CH3OH): positive ion, 231 [(C4CN)2im], 149
[C4CNim]; negative ion, 280 [Tf2N], 211 [CF3 loss], 147
[NSO2CF3]; 1H NMR (CD3CN): d¼8.48 (s, 1H), 7.40 (s, 2H),
4.15 (t, 4H, 2NCH2, J¼7.18 Hz), 2.45 (t, 4H, 2CH2CN, J¼
7.03Hz), 1.95 (m, 4H, 2CH 2), 1.65 (m, 4H, 2CH2); 13C NMR
(CD3CN): d¼136.88, 123.85, 121.13, 50.08, 29.94, 23.20,
17.42; IR: n¼3149, 3115, (nC-H aromatic), 2945, 2877 (nC-H ali-
phatic), 2249 (nCꢀN), 1618, 1566 cmÀ1 (nC N).
¼
[C3CNmim][Tf2N]
[(C4CN)2im][N(CN)2]
The product was obtained as a colourless liquid; yield: 85%.
ESI-MS (CH3OH): positive ion, 150 [C3CNmim]; negative
The product was obtained as a deep yellow liquid; yield: 75%.
ESI-MS (CH3OH): positive ion, 231 [(C4CN)2im], 149
[C4CNim]; negative ion, 66 [N(CN)2]; 1H NMR (CD3CN):
d¼8.58 (s, 1H), 7.42 (s, 2H), 4.16 (t, 4H, 2NCH2, J¼7.05 Hz),
2.45 (t, 4H, 2CH2CN, J¼7.04 Hz), 1.95 (m, 4H, 2CH2), 1.65
(m, 4H, CH2); 13C NMR (CD3CN): d¼136.48, 123.45, 120.74,
1
ion, 280 [Tf2N]; H NMR (CD3CN): d¼8.43(s, 1H), 7.38 (s,
1H), 7.35 (s, 1H), 4.21 (t, 2H, NCH2, J¼7.11 Hz), 3.82 (s, 3H,
NCH3), 2.46 (t, 2H, CH2CN, J¼7.08 Hz), 2.16 (m, 2H, CH2);
13C NMR (CD3CN): d¼137.11, 124.88, 123.28, 117.67, 48.96,
36.84, 26.46, 14.63; IR: n¼3159, 3122 (nC-H aromatic); 2251
(nCꢀN); 1577 cmÀ1 (nC N).
¼
49.68, 29.53, 22.78, 17.02; IR: n¼3144, 3103 (nCÀ aromatic),
H
2943, 2874 (nCÀH aliphatic), 2231, 2193, 2135 (nCꢀN), 1566 cmÀ1
(nC N).
¼
[C3CNmim][N(CN)2]
Acknowledgements
The product was obtained as a colourless liquid; yield: 78%.
ESI-MS (CH3OH): positive ion, 150 [C3CNmim], 82 [mim];
negative ion, 66 [N(CN)2], 282 [anion-cation-anion]; 1H
NMR (CD3CN): d¼8.64 (s, 1H), 7.44 (s, 1H), 7.40 (s, 1H),
4.20 (t, 2H, NCH2, J¼7.08 Hz), 3.83 (s, 3H, NCH3), 2.48 (t,
2H, CH2CN, J¼7.12 Hz), 2.17 (m, 2H, CH2); 13C NMR
(CD3CN): d¼137.32, 124.75, 123.21, 120.42, 119.85, 48.87,
We thank MIUR (PRIN 2003035403 002), the Swiss National
Science Foundation and the EPFL for the financial support.
References
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H
2197, 2139 cmÀ1 (nCꢀN).
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[(C3CN)2im][Tf2N]
The product was obtained as a yellow liquid; yield: 80%. ESI-
MS (CH3OH): positive ion, 203[(C CN)2im], 137 [C3CNim];
3
1
negative ion, 280 [Tf2N], 211[CF3 loss], 147 [NSO2CF3]; H
NMR (CD3CN): d¼8.53(s, 1H), 7.44 (s, 2H), 4.23(t, 4H,
2NCH2, J¼7.05 Hz), 2.47 (t, 4H, 2CH2CN, J¼7.12 Hz), 2.19
(m, 4H, 2CH2); 13C NMR (CDCl3): d¼136.78, 123.74, 117.63,
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¼
[(C3CN)2im][N(CN)2]
The product was obtained as a light yellow liquid; yield: 82%.
ESI-MS (CH3OH): positive ion, 203[(C 3CN)2im], 137 [C3
CNim]; negative ion, 66 [N(CN)2], 335 [anion-cation-anion];
1H NMR (CD3CN): d¼8.65 (s, 1H), 7.46 (s, 2H), 4.24 (t, 4H,
2NCH2, J¼7.05 Hz), 2.49 (t, 4H, 2CH2CN, J¼7.07 Hz), 2.18
(m, 4H, 2CH2); 13C NMR (CD3CN): d¼136.96, 123.74,
119.82, 49.17, 26.34, 14.71; IR: n¼3499, 3425, 3144, 3107 (nC-H
aromatic), 2958 (nC-H aliphatic), 2235, 2195, 2135 (nCꢀN), 1624,
1566 cmÀ1 (nC N).
¼
Adv. Synth. Catal. 2006, 348, 68 – 74
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