Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki-Miyaura cross-coupling

Article abstract of DOI:10.1039/c1dt10838g

The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27, 28-tetrabenzyloxy-calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1- imidazolylium)-25,26,27,28-tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b)

Full text of DOI:10.1039/c1dt10838g

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PAPER
Calix[4]arenes with one and two N-linked imidazolium units as precursors of
N-heterocyclic carbene complexes. Coordination chemistry and use in
Suzuki–Miyaura cross-coupling†
Eric Brenner,*a Dominique Matt,*a Mickae¨l Henrion,a Matthieu Tecia and Lo¨ıc Toupetb
Received 4th May 2011, Accepted 19th July 2011
DOI: 10.1039/c1dt10838g
The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxy-
calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1-imidazolylium)-25,26,27,28-
tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b) have been synthesised.
Reaction of 2 in dioxane with PdCl2 in the presence of CsCO3 and KBr (80 ◦C, 24 h) gives the carbene
complex trans-[PdBr2(calix-monocarbene)2] (14), containing two N-heterocyclic carbene ligands
derived from 2 (yield: 63%). Repeating the reaction in pyridine instead of dioxane gives the mixed
pyridine-carbene complex trans-[PdBr2(calix-carbene)(pyridine)] (15) in 75% yield. Treatment of the
bis-imidazolium salt 3a with [Pd(OAc)2] affords a chelate complex, trans-[PdI2{calix-bis(carbene)}]
(16), in which a metallo-(bis-carbene) fragment caps the upper rim of the calixarene basket. Complex
16, as well as its analogue 17, obtained from 3b, display apparent Cs-symmetry in solution. This is not
the case in the solid state, a single X-ray diffraction study carried out for 16 revealing a pinced cone
structure for the calixarene skeleton, which reduces the symmetry to C1. The chelate complex 17 shows
poor activity in Suzuki–Miyaura cross-coupling of phenyl boronic acid and p-tolyl halides, an
observation that suggests the presence of a strained metallocyclic unit preventing easy stereochemical
rearrangement to an active species. Unlike 17, complexes 14 and 15 show good activities in
cross-coupling. A comparative study using the carbene precursor 1-butyl-3-(2,6-diisopropylphenyl)-
imidazolium bromide (18), which is devoid of the receptor fragment, strongly suggests that the carbene
ligands of 14 and 15 operate typically as bulky NHC-ligands.
highly strained bidentates.17,18 The second valuable asset of the
calix[4]arene backbone is its capacity to function as a molecular
receptor, a property that is usually found only with calixarenes in
Introduction
From the point of view of a coordination chemist, the use
of the calix[4]arene skeleton has essentially two advantages.
the so-called cone conformation. By tethering functional groups
First, it constitutes an attractive platform for the construction
suitable for transition metal binding on such receptors, ligands
of sophisticated coordination spheres by assembling a set of
result that constitute potential candidates for supramolecular
convergent podand arms on one of the two calixarene rims.1–6
Ligands of this type often display unusual properties, most
catalysis. To date, the only known ligands of this class are
calixarene-monophosphines of type 1, which, once associated
depending upon the particular features of the calixarene core,
with palladium salts, become very efficient Suzuki cross-coupling
notably its flexibility,7–9 shape,10 and bulkiness11,12 as well as its
multifunctional character allowing, in particular, multiple metal
binding.13 Prominent examples of ligands of this type that have
found applications in transition metal chemistry include those
which are hemispherical,14,15 hemilabile,13 or chiral,16 as well as
catalysts.19 This property seemingly depends on the binding of
metal–arene units within the cavity of the conical calixarene.
Wondering whether calixarenes equipped with podand arms
other than a phosphino group would also be suitable for
supramolecular catalysis, we decided to synthesise and investigate
the properties of the calixarene-imidazolium salts 2 and 3a and
3b, which qualify as precursors for N-heterocylcic carbene (NHC)
ligands.20–25 In these derivatives, the NHC units are connected
through one of the nitrogen atoms to the calixarene upper rim,
without any linker, a feature which we expected would facilitate
metal–cavity interactions. The only reported calixarene complexes
having a NHC unit directly attached to the calixarene skeleton are
aLaboratoire de Chimie Inorganique Mole´culaire et Catalyse, Institut
de Chimie, UMR 7177 CNRS Universite´ de Strasbourg, 1 rue Blaise
Pascal, F-67008, Strasbourg Cedex, France. E-mail: brenner@unistra.fr,
dmatt@chimie.u-strasbg.fr
bGroupe Matie`re Condense´e et Mate´riaux UMR 6626, Universite´ de Rennes
1, Campus de Beaulieu, 35042, Rennes cedex, France
† CCDC reference numbers 748587 and 821364. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c1dt10838g
Dinares complexes 4a and 4b, which are active catalysts for the
`
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coupling between phenyboronic acid and aryl halides.26 The study
carried out with these complexes suggested that the catalytically
active species had the palladium centre bonded to only one NHC
ligand, although this was not certain. It is noteworthy that another,
more flexible calixarenyl-NHC recently reported by Schatz et al.
was also used in Suzuki cross coupling reactions.27 Overall, despite
their high catalytic potential, NHC-substituted calixarenes remain
relatively unexplored.
B separations are typical for those found in calixarenes adopting
a cone conformation (Dd > 0.7 ppm).33
The preparation of the bis-imidazolium salts 3a and 3b (Scheme
2) required the preparation of the proximally-dialkylated precur-
sor 10. The latter was obtained conveniently by treatment of 5 with
BnBr in the presence of NaH (yield 66%) using a methodology
described by Reinhoudt et al. for related dialkylated calixarenes.34
The following steps were similar to those described above for
the synthesis of the monoimidazolium salt: a) iodination of 10
with TCIA/KI giving 11 (91%); b) alkylation with BnBr/NaH
of the two free hydroxyl groups of 11 leading to 12 in 88%; c)
reaction of 12 with imidazole/CuI/DMEDA/K2CO3 to form the
bis-imidazolyl compound 13 in 80% yield; d) alkylation of 13 with
MeI or n-BuBr resulting quantitatively in 3a and 3b, respectively.
Both these calixarenes, as well as their precursors, adopt a cone
conformation.
Palladium complexes derived from monoimidazolium salt 2 and
bis-imidazolium salts 3a and 3b
NHC-complexes derived from the monoimidazolium salt 2 were
obtained using conventional procedures.35,36 Thus, reaction of
calixarene 2 with PdCl2 in dioxane at 80 ◦C in the presence
of Cs2CO3 and KBr (in excess) afforded the bis-NHC complex
14 in 63% yield (Scheme 3). The trans stereochemistry of 14
1
was inferred from the corresponding 13C{ H} NMR spectrum
(CDCl3), which showed a peak at 168.53 ppm for the carbenic
carbon atoms. This value is close to that reported in the literature
for other trans-[PdX2(NHC)2] complexes (X = halide; NHC =
imidazolylidene) (the Ccarbene of cis complexes typically appears
near 160 ppm).27,37,38 The coordination geometry of the complex
was further confirmed by a single crystal X-ray diffraction study
(Fig. 1). Applying conditions similar to those reported above for
the synthesis of 14, but carrying out the reaction in pyridine, gave
the PEPPSI-type complex 15 in 75% yield. We were unable to
assign with certainty a trans geometry to this complex, but this
stereochemistry is the more likely in view of the chemical shift of
the carbenic C atom (147.6 ppm), which is in keeping with that
found in other PEPPSI complexes having a crystallographically-
established trans configuration.39 It is also worth mentioning here
that the 1H NMR (CDCl3) spectra of complexes 14 and 15 revealed
that the p-H atom of the phenolic ring opposite to the one bearing
the heterocyclic ring appears as a doublet of doublets, so that
in fact these molecules display a pseudo Cs-symmetry. This is
Results and discussion
Syntheses of mono- and bis-imidazolium salts
The mono-imidazolium derivative 2 was prepared in five steps
according to Scheme 1. Its synthesis began with that of key inter-
mediate 6, which was obtained in 81% yield by tris-alkylation of
5 using benzyl bromide (BnBr) in the presence of Ba(OH)2·8H2O.
Note that the yield of this reaction significantly surpassed that of
the tris-alkylation procedure previously reported by Shinkai et al.28
Compound 6 was regioselectively iodinated with trichloroisocya-
nuric acid/sodium iodide (TCIA/NaI), leading to 7 in 69% yield.29
We observed that 7 is moderately stable in air. Upon benzylation
of 7 with BnBr/NaH in DMF, 8 formed quantitatively. Following
the procedure described in a recent publication of Dinare`s et al.30
the imidazolyl group was then introduced efficiently via Ullmann
coupling of 8 with imidazole in the presence of CuI/DMEDA and
K2CO3 in DMF (yield 88%). The final step was the quantitative
alkylation of the imidazolyl derivative 9 with n-BuBr in excess.
All of the above calixarenes have their backbone in the cone
conformation,31,32 as could be unambiguously deduced from the
corresponding 13C NMR spectra, which showed ArCH2 signals
lying in the range 31.5–30.0 ppm. In accord with Cs-symmetry, the
1H NMR spectrum of each compound showed two AB patterns
for the diastereotopic ArCH2 protons. In these systems the A and
˚
Fig. 1 The solid state structure of complex 14. Important distances (A)
and angles (◦): Pd–Br(1) 2.4280(4); Pd–Br(2) 2.4461(4); Pd–C(1) 2.016(3);
Pd–C(71) 2.024(3); Br(1)–Pd–Br(2) 175.27(2); C(1)–Pd–C(71) 176.30(11).
9890 | Dalton Trans., 2011, 40, 9889–9898
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Scheme 1 Stepwise construction of imidazolium salt 2.
Scheme 2 Synthesis of imidazolium salts 3a and 3b.
likely to arise from the unsymmetrical structure of the heterocycle
which adopts a sideways orientation enabling its conjugation with
the phenolic ring to which it is connected.40 Unsurprisingly, the
spectra of 2 and 9 showed the same feature.
The carbenes derived from salts 3a and 3b turned out to
be suitable for forming chelate complexes, but the yields were
moderate. Thus, reaction of 3a and 3b with [Pd(OAc)2] (Scheme
4) in DMF gave complexes 16 and 17, respectively, in ca. 37%
yield. Chromatographic separation revealed the formation, beside
that of 16 or 17, of coloured by-products, possibly oligomeric
complexes, which were not identified. The monomeric nature of the
complexes was deduced from the corresponding mass spectra (see
experimental section). The trans configuration of the complexes
1
was again inferred from the corresponding 13C{ H} NMR spectra
(carbene peaks at 167.0 (16) and 168.24 (17) ppm). As expected for
1
Cs-symmetrical complexes, both H NMR spectra showed three
AB systems (intensity 1 : 2 : 1) for the bridging methylene units.
One of the two H atoms of the NHC-substituted phenolic rings
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Scheme 3 Synthesis of palladium complexes 14 and 15.
renders the NHC units inequivalent. Note that in the NMR spectra
of 16 the two heterocycles appear equivalent over the range -80
to 25 ◦C, showing that the formation of a metallo-bridge does not
prevent “breathing” of the calixarene backbone.6
Suzuki–Miyaura cross-coupling
For the catalytic tests, phenyl boronic acid was reacted with either
p-tolyl bromide or p-tolyl chloride. The runs were carried out with
the complexes 14, 15 and 17. The conditions applied were those
used by Dinare`s et al. for the study of 4a and 4b (dioxane, 80 ◦C,
2 h, Cs2CO3). The results are summarised in Table 1.
Scheme 4 Synthesis of palladium complexes 16 and 17.
of both complexes is considerably low-field shifted with respect to
the other one (ca. 2 ppm), reflecting hydrogen bond interactions
with one of the palladium-bonded halogen atoms.
Table 1 Suzuki–Miyaura cross-coupling of phenyl boronic acid with p-
tolyl halidesa
This was confirmed by an X-ray diffraction study of 16 (H(6)–
˚
˚
I(2): 3.179 A; H(9)–I(2) 3.334 A) (Fig. 2). This further revealed
that the calixarene adopts a pinced cone structure which therefore
Entry
Complex
X
[Pd] (mol%)
yield (%)b
1
2
3
4
5
6
7
8
14
14
14
14
15
15
15
15
17
17
19
19
Br
Br
Br
Cl
Br
Br
Br
Cl
Br
Br
Br
Cl
0.1
0.05
0.01
1
0.1
0.05
0.01
1
0.1
0.1
0.05
1
100
92
1
67
100
84
2
45
100c
4
61
64
9
10
11
12
a Aryl halide (1 mmol), phenylboronic acid (1.5 mmol), Cs2CO3
(2 mmol), dioxane (3 mL). b Yields determined by 1H NMR using 1,4-
dimethoxybenzene as internal standard. Averaged over two runs. c After
24 h of reaction.
˚
Fig. 2 The solid state structure of complex 16. Important distances (A)
and angles (◦): Pd–I(1) 2.5984(3); Pd–I(2) 2.6297(2); Pd–C(35) 2.015(2);
Pd–C(31) 2.035(2); I(1)–Pd–I(2) 169.28(1); C(31)–Pd–C(35) 176.1(1).
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The mono-NHC calixarene complexes 14 and 15 showed good
activities in the coupling with the p-tolyl halides, the reactivity
towards the bromide being, as expected, higher than that towards
the chloride (Table 1, entries 1–8). Interestingly, the association of
two calixarene ligands with the palladium centre (as in complex
14) does not significantly improve the reaction rate with respect
to the reactions where only one equivalent of NHC is present (see
entries 2 and 6).
The activities observed with the chelate complex 17 were
disappointingly low when compared with the performances of
14 and 15 (compare entries 9 and 10 with entries 1 and 5,
respectively). This may reflect the high stability of the chelate
complex which does not favour dissociation of a carbenic ligand
with concomitant formation of a mono-NHC complex similar to
those obtained with 14 or 15. This behaviour markedly contrasts
with that of the Dinare`s complexes 4a and 4b, which displayed 10–
20 times higher activities than 17.26 It is likely that complexes 4a
and 4b undergo easy stereochemical rearrangements facilitating
either the formation of mono-NHC intermediates, or that of a
cis-chelate complex, both types of complexes having intrinsically
higher activities than the trans complexes 4. The fact that the
reactions rates obtained with 14 and 15 were of the same order
of magnitude as those of 4a (in fact their activity is roughly twice
that of 4a), suggests that with the latter the active species is a
mono-NHC-ligand complex.
the usual breathing motion observed for conical calix[4]arenes.
The chelate complex 17 showed poor activity in the cross-coupling
of phenylboronic acid and p-tolyl halides, suggesting that the
generation of an active species is made difficult by the presence of
a rather rigid trans-spanning bis-carbene ligand. In contrast, the
palladium complexes obtained from the mono-imidazolium salts
displayed good activities in Suzuki cross-coupling. Comparison of
their activity with a related calixarene complex lacking a receptor
moiety shows that no supramolecular effect is involved in the
catalysis with complexes 14 and 15.
Experimental section
General procedures
All commercial reagents were used as supplied. The syntheses were
performed in Schlenk-type flasks under dry nitrogen. Solvents
were dried by conventional methods and distilled immediately
1
prior to use. Routine 1H and 13C{ H} NMR spectra were recorded
on a FT Bruker AVANCE 300 (1H: 300.1 MHz, 13C: 75.5 MHz)
◦
1
instrument at 25 C. H NMR spectral data were referenced to
residual protonated solvents (CHCl3, d 7.26; DMSO, d 2.50),
13C chemical shifts are reported relative to deuterated solvents
(CDCl3, d 77.16; DMSO-d6, d 39.52). For column chromatog-
raphy Geduran SI (E. Merck, 0.040–0.063 mm) silica was used.
Routine thin-layer chromatography analyses were carried out by
using plates coated with Merck Kieselgel 60 GF254. Mass spectra
were recorded either with a Bruker MicroTOF spectrometer
(ESI-TOF) using CH2Cl2 or CH3CN as solvent, or with a
Bruker MaldiTOF spectrometer (MALDI-TOF) using dithranol
as matrix. Elemental analyses were performed by the Service de
Microanalyse, Institut de Chimie (CNRS), Strasbourg. Melting
points were determined with a Bu¨chi 535 capillary melting-point
apparatus and are uncorrected. Tetrahydroxycalix[4]arene (5)41
and 1-butyl-3-(2,6-diisopropylphenyl)imidazolium bromide (18)42
were prepared as described in the literature. In the NMR data given
hereafter, the bridging CH2 groups of the calixarene backbone
are designated by the abbreviation “ArCH2Ar”. Cq denotes a
quaternary carbon atom.
One question that arises is whether the mono-NHC ligand
of complex 15 operates in a supramolecular manner like the
previously reported phosphine ligand 1 when used in Suzuki–
Miyaura cross-coupling. To answer this question, complex 19
was prepared, which is structurally close to 15, but which lacks
a receptor unit. The synthesis of 19 was similar to that of 15
(Scheme 5).
Syntheses
Scheme 5 Synthesis of palladium complex 19.
25,26,27-Tribenzyloxy-28-hydroxycalix[4]arene (cone) (6). To
a stirred mixture of calix[4]arene 5 (5.00 g, 11.8 mmol) and
benzyl bromide (7.06 g, 41.3 mmol) in DMF (80 mL), at room
temperature, was added portionwise Ba(OH)2·8H2O (18.6 g,
59.0 mmol). The reaction mixture was stirred for 4 h at room
temperature before cooling with an ice bath. Aqueous HCl (1
N, 100 mL) was then slowly added to the mixture, followed by
CHCl3 (150 mL). The organic layer was separated and the aqueous
phase was extracted with CHCl3 (2 ¥ 100 mL). The extracts were
combined and washed with water (3 ¥ 100 mL). The organic
layer was dried over Na2SO4, and the solvent was evaporated
under reduced pressure. The crude product was purified by flash
chromatography (SiO2, CH2Cl2/petroleum ether, 25 : 75, v/v) to
afford 6 as a white solid (Rf 0.47, SiO2, CH2Cl2/petroleum ether,
40 : 60, v/v). Yield: 6.66 g, 81%; mp 178–180 ◦C. 1H NMR
(300 MHz, CDCl3): d 7.47–7.22 (13H, m, ArH), 7.20–7.05 (6H, m,
ArH), 6.94 (1H, t, 3J = 7.4 Hz, ArH), 6.80 (1H, t, 3J = 7.4 Hz, ArH),
In fact, the catalytic runs performed with 19 revealed catalytic
activities similar to those observed with 15 (Table 1, entries 11 and
12; compare with entries 6 and 8). These findings suggest that the
NHC of 15 simply operates as a bulky ligand and not as a receptor
unit able to enhance the catalytic activity.
Conclusion
In summary, we have described the first calix[4]arenes substituted
by a single imidazolylium moiety, as well as the first calix[4]arenes
proximally-substituted by two such units. N-heterocyclic carbene
complexes were conveniently obtained from both types of salts
using conventional procedures. Chelate palladium complexes of
trans stereochemistry could be obtained from the calixarenes with
the proximal substitution pattern, thereby leading to metallo-
capped calix[4]arenes, the backbone of which retains, in solution,
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6.55–6.42 (6H, m, ArH), 5.35 (1H, s, OH), 5.11 (2H, s, OCH2),
122–124 ◦C. 1H NMR (300 MHz, CDCl3): d 7.41–7.14 (21H, m,
4.80 and 4.75 (4H, AB spin system, 2JAB = 11.7 Hz, OCH2), 4.39
ArH), 6.74–6.62 (8H, m, ArH), 6.45 (2H, d, J = 7.5 Hz, ArH),
3
2
and 3.20 (4H, AB spin system, JAB = 13.6 Hz, ArCH2Ar), 4.17
5.03 and 4.98 (4H, AB spin system, 2JAB = 11.8 Hz, OCH2), 4.90
1
and 3.02 (4H, AB spin system, 2JAB = 13.2 Hz, ArCH2Ar). 13C{ H}
(2H, s, OCH2), 4.85 (2H, s, OCH2), 4.27 and 3.02 (4H, AB spin
2
(75 MHz, CDCl3): d 155.34 (s, arom. Cq–O), 153.91 (s, 2x, arom.
Cq–O), 153.49 (s, arom. Cq–O), 137.54, 137.33, 133.76, 133.07
and 131.07 (5 s, arom. Cq), 130.45, 129.09, 128.71, 128.54, 128.47,
128.21, 128.09, 128.02, 127.67, 123.61, 123.16 and 119.43 (12 s,
arom. CH), 77.65 (s, 2x, OCH2), 75.69 (s, OCH2), 31.42 and 31.17
(2 s, ArCH2Ar). Found: C, 84.80; H, 6.33. Calc. for C49H42O4 (Mr =
694.86): C, 84.70; H, 6.09%.
system, JAB = 13.7 Hz, ArCH2Ar), 4.10 and 2.84 (4H, AB spin
2
1
system, JAB = 13.7 Hz, ArCH2Ar). 13C{ H} (75 MHz, CDCl3):
d 155.52 (s, 2x, arom. Cq–O), 155.39 (s, arom. Cq–O), 155.33
(s, arom. Cq–O), 137.88, 137.74, 137.66 and 137.32 (4 s, arom.
Cq), 136.80 (s, arom. CH), 136.12, 135.25 and 134.79 (3 s, arom.
Cq), 129.93, 129.56, 129.37, 128.94, 128.36, 128.31, 128.14, 128.09,
128.05, 127.95, 122.81 and 122.54 (12 s, arom. CH), 86.43 (s, arom.
Cq–I), 76.79 and 76.73 (2 s, OCH2), 76.26 (s, 2x, OCH2), 31.46
and 31.12 (2 s, ArCH2Ar). Found: C, 74.18; H, 5.48. Calc. for
C56H47IO4 (Mr = 910.87): C, 73.84; H, 5.20%.
5-Iodo-25,26,27-tribenzyloxy-28-hydroxycalix[4]arene
(cone)
(7). A stirred mixture of calix[4]arene 6 (1.70 g, 2.45 mmol),
NaOH (0.137 g, 3.43 mmol) and NaI (0.514 g, 3.43 mmol)
in MeOH/CH2Cl2 (30 mL, 1 : 1, v/v) was cooled at 0 ◦C and
protected from light. Trichloroisocyanuric acid (TCIA, 0.265 g,
1.14 mmol) in MeOH (3 mL) was added dropwise to the mixture
which was then allowed to reach room temperature. After 5 h,
CH2Cl2 (100 mL), water (50 mL) and aqueous HCl (1 N, 15 mL)
were successively added to the mixture. The organic layer was
separated and the aqueous layer was extracted with CH2Cl2
(2 ¥ 50 mL). The extracts were combined and washed with
aqueous Na2S2O3 (5%, 100 mL). The organic layer was dried over
Na2SO4, and the solvent was evaporated under reduced pressure.
The crude product was purified by flash chromatography (SiO2,
CH2Cl2/petroleum ether, 30 : 70, v/v) to afford 7 as a white
solid (Rf 0.37, SiO2, CH2Cl2/petroleum ether, 30 : 70, v/v). Yield:
1.39 g, 69%; mp 174–175 ◦C. 1H NMR (300 MHz, DMSO-d6): d
7.64 (1H, s, OH), 7.41 (2H, s, ArH), 7.39–7.30 (12H, m, ArH),
5-(N-imidazolyl)-25,26,27,28-tetrabenzyloxycalix[4]-arene (cone)
(9). To a mixture of iodocalix[4]arene 8 (1.50 g, 1.65 mmol),
imidazole (0.168 g, 2.47 mmol), K2CO3 (0.569 g, 4.12 mmol) and
DMEDA (0.073 g, 0.828 mmol) was added 10 mL of degassed
DMF. CuI (0.156 g, 0.820 mmol) was added and the reaction
mixture was stirred under exclusion of light at 120 ◦C for 5 days.
After cooling to room temperature, water (50 mL) was added
followed by CHCl3 (50 mL). The organic layer was separated
and the aqueous phase was extracted with CHCl3 (2 ¥ 50 mL).
The extracts were combined and washed with aqueous Na4EDTA
0.2 N by vigorous stirring of the biphasic mixture over 1 h (3 ¥
80 mL). The organic layer was dried over Na2SO4, then the solvent
was evaporated under reduced pressure. The crude product was
purified by flash chromatography (SiO2, MeOH/CH2Cl2, 1 : 99,
v/v) to afford 9 as a white solid (Rf 0.34, SiO2, MeOH/CH2Cl2,
2 : 98, v/v). Yield: 1.23 g, 88%; mp 177–178 ◦C. 1H NMR
(300 MHz, CDCl3): d 7.50–7.24 (17H, m, ArH and NCHN), 7.22–
7.12 (4H, m, ArH), 7.07 (1H, s, NCHC), 7.01 (2H, dd, 3J = 7.0 Hz,
4J = 2.1 Hz, ArH), 6.96–6.84 (4H, m, ArH), 6.80 (1H, s, NCHC),
6.24 (2H, d, 3J = 7.5 Hz, ArH), 6.19 (2H, s, ArH), 6.12 (1H, dd,
3J = 8.2 Hz, 3J¢ = 6.7 Hz, p-H of Ar opposite to Ar–N), 5.22 and
5.15 (4H, AB spin system, 2JAB = 11.9 Hz, OCH2), 4.82 (2 ¥ 2H,
3
7.29–7.22 (3H, m, ArH), 7.17 (2H, d, J = 7.6 Hz), 6.90 (2H,
3
4
dd, J = 7.6 Hz, J = 1.4 Hz, ArH), 6.85–6.76 (3H, m, ArH),
3
3
6.65 (2H, dd, J = J¢ = 7.6 Hz, ArH), 4.86 (2H, s, OCH2), 4.73
2
and 4.68 (4H, AB spin system, JAB = 11.7 Hz, OCH2), 4.13 and
2
3.11 (4H, AB spin system, JAB = 12.4 Hz, ArCH2Ar), 3.92 and
2
1
3.18 (4H, AB spin system, JAB = 13.1 Hz, ArCH2Ar). 13C{ H}
(75 MHz, DMSO-d6): d 154.52 (s, arom. Cq–O), 153.10 (s, 2x,
arom. Cq–O), 152.95 (s, arom. Cq–O), 137.57 and 136.75 (2 s,
arom. Cq), 136.36 (s, arom. CH), 135.82, 134.52, 132.46 and
131.43 (4 s, arom. Cq), 128.84, 128.75, 128.71, 128.62, 128.41,
128.33, 128.15, 127.76, 127.54, 124.05 and 123.58 (11 s, arom.
CH), 81.32 (s, arom. Cq–I), 77.42 (s, 2x, OCH2), 75.44 (s, OCH2),
30.26 and 30.08 (2 s, ArCH2Ar). Found: C, 71.47; H, 5.08. Calc.
for C49H41IO4 (Mr = 820.75): C, 71.71; H, 5.04%.
2
s, OCH2), 4.33 and 3.06 (4H, AB spin system, JAB = 13.6 Hz,
2
ArCH2Ar), 4.24 and 2.95 (4H, AB spin system, JAB = 13.8 Hz,
1
ArCH2Ar). 13C{ H} (75 MHz, CDCl3): d 155.67 (s, 2x, arom. Cq–
O), 155.10 and 154.29 (2 s, arom. Cq–O), 137.68, 137.51, 137.17,
137.09, 136.31 and 135.91 (6 s, arom. Cq), 135.51 (s, arom. CH),
133.84 and 131.70 (2 s, arom. Cq), 129.42, 129.36, 129.21, 129.02,
128.61, 128.45, 128.43, 128.25, 128.06, 127.92, 127.87, 127.61,
122.57, 122.40, 120.51 and 118.16 (16 s, arom. CH), 77.28 and
75.83 (2 s, 2x, OCH2), 31.47 and 31.39 (2 s, ArCH2Ar). Found:
C, 82.80; H, 6.05; N, 3.01. Calc. for C59H50N2O4·0.4 H2O (Mr =
851.04 + 7.21): C, 82.57; H, 5.97; N, 3.26%.
5-Iodo-25,26,27,28-tetrabenzyloxycalix[4]arene (cone) (8). To
a stirred mixture of calix[4]arene 7 (1.65 g, 2.01 mmol) and
benzyl bromide (0.514 g, 3.02 mmol) in DMF (10 mL), at room
temperature, was added portionwise NaH (0.121 g of a 60%
dispersion in paraffin, 3.02 mmol). After stirring for◦1 h at room
temperature, the reaction mixture was heated at 70 C for 24 h.
After cooling to room temperature, aqueous HCl (0.5 N, 20 mL)
was added followed by CHCl3 (80 mL). The organic layer was
separated and the aqueous phase was extracted with CHCl3 (2 ¥
50 mL). The extracts were combined and washed with water
(4 ¥ 80 mL). The organic layer was dried over Na2SO4, and the
solvent was evaporated under reduced pressure. The crude product
was purified by flash chromatography (SiO2, CH2Cl2/petroleum
ether, 24 : 76, v/v) to afford 8 as a white solid (Rf 0.46, SiO2,
CH2Cl2/petroleum ether, 30 : 70, v/v). Yield: 1.80 g, 98%; mp
5-(3-Butyl-1-imidazolylium)-25,26,27,28-tetrabenzyl-oxycalix[4]-
arene bromide (cone) (2). A stirred solution of 9 (0.775 g,
0.910 mmol) in n-butyl bromide (6 mL), was heated under reflux
for 24 h. The precipitate formed was collected by filtration and
washed with petroleum ether. The white solid (2) was dried under
vacuum and used without further purification. Yield: 0.896 g,
99%; mp 128–130 ◦C. 1H NMR (300 MHz, CDCl3): d 10.15
(1H, s, NCHN), 7.69 (1H, s, NCHC), 7.43–7.09 (20H, m, ArH),
6.97–6.69 (7H, m, ArH and NCHC), 6.45 (2H, s, ArH), 6.28
(2H, d, 3J = 7.5 Hz, ArH), 6.12 (1H, dd, 3J = 7.8 Hz, 3J¢ =
7.0 Hz, p-H of Ar opposite to Ar–N), 5.08 and 5.01 (4H, AB spin
9894 | Dalton Trans., 2011, 40, 9889–9898
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©

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2
system, JAB = 11.8 Hz, OCH2), 4.79 (4H, s, OCH2), 4.53 (2H, t,
pressure. The crude product was purified by flash chromatography
(SiO2, CH2Cl2/petroleum ether, 30 : 70, v/v) to afford 11 as a
white solid (Rf 0.61, SiO2, CH2Cl2/petroleum ether, 50 : 50, v/v).
Yield: 2.37 g, 91%; mp 245–248 ◦C. 1H NMR (300 MHz, CDCl3):
d 8.98 (2H, s, OH), 7.52–7.45 (4H, m, ArH), 7.44–7.36 (6H, m,
3J = 7.4 Hz, NCH2), 4.23 and 2.96 (4H, AB spin system, JAB
=
=
2
2
13.4 Hz, ArCH2Ar), 4.11 and 2.92 (4H, AB spin system, JAB
13.7 Hz, ArCH2Ar), 1.89 (2H, tt, 3J = J¢ = 7.4 Hz, NCH2CH2),
1.37 (2H, tq, 3J = 3J¢ = 7.4 Hz, CH2CH3), 0.92 (3H, t, 3J =
3
7.4 Hz, CH3). 13C{ H} (75 MHz, CDCl3): d 156.55 and 155.35
ArH), 7.27 (2H, d, J = 2.2 Hz, ArH), 7.20 (2H, d, J = 2.2 Hz,
3 4
1
4
4
(2 s, arom. Cq–O), 155.31 (s, 2x, arom. Cq–O), 137.45, 137.34,
137.20, 136.54, 136.40 and 135.45 (6 s, arom. Cq), 134.89 (s,
arom. CH), 134.49 (s, arom. Cq), 130.08, 129,38, 129.19, 129.16
and 128.71 (5 s, arom. CH), 128.58 (s, arom. Cq), 128.39, 128.29,
128.04, 127.98, 127.90, 127.56, 122.82, 122.68, 121.60, 121,13 and
120.51 (11 s, arom. CH), 77.16 and 75.99 (2 s, 2x, OCH2), 50.03
(s, NCH2), 32.28 (s, NCH2CH2), 31.28 (s, 4x, ArCH2Ar), 19.43
(s, CH2CH3), 13.52 (s, CH3). Found: C, 76.12; H, 6.01; N, 2.66.
Calc. for C63H59BrN2O4·0.3 H2O (Mr = 988.06 + 5.40): C, 76.17;
H, 6.05; N, 2.82%.
ArH), 7.13 (2H, dd, J = 7.5 Hz, J = 1.7 Hz, ArH), 6.97 (2H,
3 4 3 3
dd, J = 7.5 Hz, J = 1.7 Hz, ArH), 6.86 (2H, dd, J = J¢ =
7.5 Hz, ArH), 5.06 and 4.86 (4H, AB spin system, 2JAB = 11.3 Hz,
2
OCH2), 4.46 and 3.36 (2H, AB spin system, JAB = 12.6 Hz,
2
ArCH2Ar), 4.11 and 3.18 (2H, AB spin system, JAB = 13.6 Hz,
2
ArCH2Ar), 4.01 and 3.17 (4H, AB spin system, JAB = 13.0 Hz,
1
ArCH2Ar). 13C{ H} (75 MHz, CDCl3): d 153.11 and 151.29 (2 s,
arom. Cq–O), 137.17 and 136.80 (2 s, arom. CH), 136.35, 134.73,
133.51, 132.03 and 130.50 (5 s, arom. Cq), 129.38, 129.30 and
129.05 (3 s, arom. CH), 128.78 and 128.75 (2 s, arom. CH), 125.32
(s, arom. CH), 82.65 (s, arom. Cq–I), 78.68 (s, OCH2), 31.60 (s,
2x, ArCH2Ar), 31.10 and 30.56 (2 s, ArCH2Ar). Found: C, 59.14;
H, 4.09. Calc. for C42H34I2O4 (Mr = 856.53): C, 58.89; H, 4.00%.
25,26-Dibenzyloxy-27,28-dihydroxycalix[4]arene (cone) (10).
To a stirred mixture of calix[4]arene 5 (5.00 g, 11.8 mmol) and
benzyl bromide (4.43 g, 25.9 mmol) in DMF (125 mL), was
added portionwise NaH (2.83 g of a 60% dispersion in paraffin,
70.7 mmol). The reaction mixture was stirred for 2.5 h at room
temperature before cooling with an ice bath. Aqueous HCl (1 N,
100 mL) was then slowly added to the mixture, upon which the
precipitate formed was collected on a Bu¨chner funnel and washed
with water (ca. 100 mL). The white solid was dissolved in CH2Cl2
(ca. 60 mL), and the resulting solution was dried with Na2SO4,
then evaporated to dryness. The crude product was purified by
flash chromatography (SiO2, CH2Cl2/petroleum ether, 35 : 65, v/v)
to afford 10 as a white solid (Rf 0.44, SiO2, CH2Cl2/petroleum
ether, 50 : 50, v/v). Yield: 4.69 g, 66%; mp 224–227 ◦C. 1H NMR
(300 MHz, CDCl3): d 8.97 (2H, s, OH), 7.52–7.46 (4H, m, ArH),
5,11-Diiodo-25,26,27,28-tetrabenzyloxycalix[4]arene
(cone)
(12). To a stirred mixture of calix[4]arene 11 (1.65 g, 1.93 mmol)
and benzyl bromide (0.990 g, 5.79 mmol) in DMF (15 mL)
was added portionwise NaH (0.232 g of a 60% dispersion in
paraffin, 5.79 mmol). After stirring for 1 h at room temperature,
◦
the reaction mixture was heated at 70 C for 24 h. After cooling
to room temperature, aqueous HCl (1 N, 20 mL) was added
followed by AcOEt (50 mL). The organic layer was separated
and the aqueous phase was extracted with AcOEt (2 ¥ 50 mL).
The extracts were combined and washed with water (4 ¥ 50 mL).
The organic layer was dried over Na2SO4, then the solvent was
evaporated under reduced pressure. The crude product was
purified by flash chromatography (SiO2, CH2Cl2/petroleum
ether, 25 : 75, v/v) to afford 12 as a white solid (Rf 0.44, SiO2,
CH2Cl2/petroleum ether, 30 : 70, v/v). Yield: 1.75 g, 88%; mp
182–185 ◦C. 1H NMR (300 MHz, CDCl3): d 7.35–7.20 (20H, m,
3
4
7.39–7.28 (6H, m, ArH), 7.06 (2H, dd, J = 7.5 Hz, J = 1.5 Hz,
3
3
ArH), 6.98–6.89 (6H, m, ArH), 6.78 (2H, dd, J = J¢ = 7.5 Hz,
ArH), 6.57 (2H, dd, 3J = J¢ = 7.5 Hz, ArH), 5.05 and 4.86 (4H, AB
3
spin system, 2JAB = 11.3 Hz, OCH2), 4.47 and 3.32 (2H, AB spin
2
4
3
3
system, JAB = 12.7 Hz, ArCH2Ar), 4.23 and 3.30 (2H, AB spin
ArH), 6.87 (2H, d, J = 2.2 Hz, ArH), 6.80 (2H, dd, J = J¢ =
7.5 Hz, ArH), 6.80 (2H, d, 4J = 2.2 Hz, ArH), 6.61 (2H, dd, 3J =
7.5 Hz, 4J = 1.5 Hz, ArH), 6.55 (2H, dd, 3J = 7.5 Hz, 4J = 1.5 Hz,
ArH), 5.01–4.84 (8H, m, OCH2), 4.29 and 3.05 (2H, AB spin
2
system, JAB = 13.6 Hz, ArCH2Ar), 4.11 and 3.21 (4H, AB spin
system, 2JAB = 13.0 Hz). 13C{ H} (75 MHz, CDCl3): d 153.28 and
1
151.17 (2 s, arom. Cq–O), 136.64, 134.74 and 134.48 (3 s, arom.
Cq), 129.27 (s, 2x, arom. Cq and arom. CH), 129.03, 128.97, 128.80
and 128.70 (4 s, arom. CH), 128.64 (s, arom. Cq), 128.57, 128.12,
125.00 and 120.53 (4 s, arom. CH), 78.51 (s, OCH2), 31.95 (s, 3x,
ArCH2Ar), 30.63 (s, ArCH2Ar). The spectroscopic data are in full
agreement with the literature.43 Found: C, 83.15; H, 6.07. Calc. for
C42H36O4 (Mr = 604.73): C, 83.42; H, 6.00%.
2
system, JAB = 13.8 Hz, ArCH2Ar), 4.13 and 2.89 (4H, AB spin
2
system, JAB = 13.8 Hz, ArCH2Ar), 3.96 and 2.70 (2H, AB spin
1
system, 2JAB = 13.9 Hz, ArCH2Ar). 13C{ H} (75 MHz, CDCl3): d
155.41 (s, 4x, arom. Cq–O), 138.34, 137.62 and 137.48 (3 s, arom.
Cq), 137.35 (s, arom. CH), 137.08 (s, arom. Cq), 136.66 (s, arom.
CH), 135.43 and 134.58 (2 s, arom. Cq), 129.79, 129.61, 128.71,
128.21, 128.05 and 122.94 (6 s, arom. CH), 86.43 (s, arom. Cq–I),
76.68 and 76.47 (2 s, OCH2), 31.41 (s, ArCH2Ar), 31.11 (s, 2x,
ArCH2Ar), 30.74 (s, ArCH2Ar). Found: C, 65.03; H, 4.53. Calc.
for C56H46I2O4 (Mr = 1036.77): C, 64.87; H, 4.47%.
5,11-Diiodo-25,26-dibenzyloxy-27,28-dihydroxycalix-[4]arene
(cone) (11). A stirred mixture of calix[4]arene 10 (1.83 g,
3.03 mmol), NaOH (0.291 g, 7.27 mmol) and KI (1.21 g,
7.27 mmol) in MeOH/CH2Cl2 (40 mL, 1 : 1, v/v) was cooled at
0 ◦C and protected from light. Trichloroisocyanuric acid (TCIA,
0.561 g, 2.42 mmol) in MeOH (4 mL) was added dropwise to
the mixture, which was then allowed to reach room temperature.
After 4 h, CH2Cl2 (100 mL), water (50 mL) and aqueous HCl (1
N, 20 mL) were successively added to the mixture. The organic
layer was separated and the aqueous layer was extracted with
CH2Cl2 (2 ¥ 50 mL). The extracts were combined and washed
with aqueous Na2S2O3 (5%, 100 mL). The organic layer was dried
over Na2SO4, and the solvent was evaporated under reduced
5,11-Bis(N -imidazolyl)-25,26,27,28-tetrabenzyloxy-calix[4]-
arene (cone) (13). To a mixture of diiodocalix[4]arene 12 (2.00 g,
1.93 mmol), imidazole (0.394 g, 5.79 mmol), K2CO3 (1.33 g,
9.65 mmol) and DMEDA (0.170 g, 1.93 mmol) was added 15 mL
of degassed DMF. CuI (0.367 g, 1.93 mmol) was added and the
reaction mixture was stirred under exclusion of light at 120 ◦C
for 3 days. After cooling to room temperature, water (50 mL)
was added followed by CHCl3 (50 mL). The organic layer was
separated and the aqueous phase was extracted with CHCl3
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©

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2
(2 ¥ 50 mL). The extracts were combined and washed with
aqueous Na4EDTA 0.2 N by vigorous stirring of the biphasic
mixture over 1 h (3 ¥ 80 mL). The organic layer was dried over
Na2SO4, and the solvent was evaporated under reduced pressure.
The crude product was purified by flash chromatography (SiO2,
MeOH/CH2Cl2, 5 : 95, v/v) to afford 13 as a white solid (Rf 0.39,
SiO2, MeOH/CH2Cl2, 6 : 94, v/v). Yield: 1.41 g, 80%; mp 171–
174 ◦C. 1H NMR (300 MHz, CDCl3): d 7.56 (2H, s, NCHN), 7.36–
7.21 (20H, m, ArH), 7.11 (2H, s, NCHC), 6.98 (2H, s, NCHC),
6.66–6.42 (10H, m, ArH), 5.05–4.87 (8H, m, OCH2), 4.29 and
sytem, JAB = 13.8 Hz, ArCH2Ar), 4.04 and 2.99 (2H, AB spin
sytem, 2JAB = 13.7 Hz, ArCH2Ar), 1.91 (4H, tt, 3J = J¢ = 7.4 Hz,
3
NCH2CH2), 1.35 (4H, tq, 3J = J¢ = 7.4 Hz, CH2CH3), 0.90 (6H, t,
3
3J = 7.4 Hz, CH3). 13C{ H} (75 MHz, CDCl3): d 156.31 and 155.33
1
(2 s, arom. Cq–O), 138.11, 137.12, 137.03, 136.27 and 135.49 (5
s, arom. Cq), 135.18 (s, arom. CH), 134.33 (s, arom. Cq), 129.75
and 129.62 (2 s, arom. CH), 128.83 (s, arom. Cq), 128.60, 128.45,
128.28, 128.18, 123.14, 122.36, 121.71, 121.22 and 120.84 (9 s,
arom. CH), 76.84 and 76.73 (2 s, OCH2), 49.99 (s, NCH2), 32.14
(s, NCH2CH2), 31.29 (s, 2x, ArCH2Ar), 31.18 (s, ArCH2Ar), 31.11
(s, ArCH2Ar), 19.42 (s, CH2CH3), 13.46 (s, CH3). Found: C, 69.29;
H, 6.04; N, 4.49. Calc. for C70H70Br2N4O4·H2O (Mr = 1191.14 +
18.02): C, 69.53; H, 6.00; N, 4.63%.
2
3.04 (2H, AB spin system, JAB = 13.6 Hz, ArCH2Ar), 4.22 and
2
2.94 (4H, AB spin system, JAB = 13.8 Hz, ArCH2Ar), 4.16 and
2
1
2.85 (2H, AB spin system, JAB = 14.0 Hz, ArCH2Ar). 13C{ H}
(75 MHz, CDCl3): d 155.48 and 154.54 (2 s, arom. Cq–O), 137.54,
137.42, 136.90 and 136.56 (4 s, arom. Cq), 135.60 (s, arom. CH),
135.55 and 134.63 (2 s, arom. Cq), 131.84 (s, arom. Cq–N), 129.89,
129.71, 128.78, 128.34, 128.27, 128.18 and 128.04 (7 s, arom. CH),
76.90 and 76.60 (2 s, OCH2), 31.62 (s, ArCH2Ar), 31.50 (s, 2x,
ArCH2Ar), 31.35 (s, ArCH2Ar). Found: C, 81.04; H, 5.75; N,
5.97. Calc. for C62H52N4O4 (Mr = 917.10): C, 81.20; H, 5.72; N,
6.11%.
Palladium complexes
trans-Bis[5-(3-butylimidazol-2-yliden-1-yl)-25,26,27, 28-tetra-
benzyloxycalix[4]arene] palladium(II) dibromide (cone) (14).
A
mixture of bromide 2 (0.412 g, 0.416 mmol), PdCl2 (0.037 g,
0.208 mmol), Cs2CO3 (0.677 g, 2.08 mmol) and KBr (0.495 g,
4.16 mmol) in dioxane (5 mL) was stirred at 80 ◦C for 24 h. After
cooling to room temperature, the mixture was filtered through
Celite and the filtrate evaporated to dryness. The crude mixture
was purified by flash chromatography (SiO2, CH2Cl2/petroleum
ether, 70 : 30, v/v) to afford 14 as a yellow solid (Rf 0.43, SiO2,
CH2Cl2/petroleum ether, 70 : 30, v/v). Yield: 0.272 g, 63%; mp
134–136 C. H NMR (300 MHz, CDCl3): d 7.48–7.41 (4H, m,
ArH), 7.39–7.25 (28H, m, ArH), 7.24–7.16 (8H, m, ArH and
NCHC), 7.07 (4H, s, ArH), 6.86–6.78 (6H, m, ArH), 6.77–6.67
(8H, m, ArH), 6.53–6.48 (2H, m, ArH), 6.48–6.41 (4H, m, ArH),
5,11-Bis(3-methyl-1-imidazolylium)-25,26,27,28-tetra-benzyl-
oxycalix[4]arene diiodide (cone) (3a). A stirred mixture of 13
(0.300 g, 0.33 mmol) and methyl iodide (65 mL, 1.04 mmol)
in CHCl3 (8 mL) was heated at 40 ◦C for 24 h. The reaction
mixture was then evaporated to dryness to afford a yellow-brown
solid, which was collected by filtration and washed with petroleum
ether. The solid (3a) was dried under vacuum and used without
further purification. Yield: 0.393 g, 99%; mp 152–154 ◦C.1H NMR
(300 MHz, CDCl3): d 10.23 (2H, s, NCHN), 7.80 (2H, s, NCHC),
7.43 (2H, s, NCHC), 7.37–7.23 (20H, m, ArH), 7.20 (2H, d, 4J =
◦
1
3
3
6.38 (2H, dd, J = 8.7 Hz, J¢ = 6.0 Hz, p-H of Ar opposite to
Ar–N), 5.08 (8H, s, OCH2), 4.95 (4H, s, OCH2), 4.88 (4H, s,
OCH2), 4.42 (4H, t, 3J = 6.6 Hz, NCH2), 4.33 and 3.10 (8H, AB
4
2.6 Hz, ArH), 6.84 (2H, d, J = 2.6 Hz, ArH), 6.69–6.62 (4H,
3
3
2
m, ArH), 6.51 (2H, dd, J = J¢ = 7.5 Hz, ArH), 5.04–4.86 (8H,
spin system, JAB = 13.5 Hz, ArCH2Ar), 4.25 and 2.97 (8H, AB
2
spin system, 2JAB = 13.7 Hz, ArCH2Ar), 1.82 (4H, tt, 3J = 7.4 Hz
m, OCH2), 4.29 and 3.17 (2H, AB spin system, JAB = 13.7 Hz,
2
3J¢ = 6.6 Hz, NCH2CH2), 1.30 (4H, tq, 3J = J¢ = 7.4 Hz, CH2CH3),
3
ArCH2Ar), 4.22 and 3.02 (4H, AB spin system, JAB = 13.8 Hz,
0.84 (6H, t, J = 7.4 Hz, CH3). 13C{ H} (75 MHz, CDCl3): d
168.53 (s, NCN), 155.35 (s, arom. Cq–O), 155.30 (s, 2x, arom.
Cq–O), 155.06 (s, arom. Cq–O), 137.75, 137.39, 135.98, 135.43,
135.20, 135.00 and 134.82 (7 s, arom. Cq), 130.01, 129.51, 129.35,
129.04, 128.79, 128.54, 128.26, 128.12, 128.01, 127.95, 127.90,
125.46, 122.77, 122.54, 122.22 and 120.04 (16 s, arom. CH), 77.24
and 76.93 (2 s, OCH2), 76.11 (s, 2x, OCH2), 50.42 (s, NCH2),
32.20 (s, NCH2CH2), 31.50 (s, 4x, ArCH2Ar), 20.19 (s, CH2CH3),
14.15 (s, CH3). Found: C, 72.71; H, 5.68; N, 2.56. Calc. for
C126H116Br2N4O8Pd (Mr = 2080.52): C, 72.74; H, 5.62; N, 2.69%.
3
1
ArCH2Ar), 4.17 (6H, s, CH3), 4.15 and 3.04 (2H, AB spin system,
1
2JAB = 13.6 Hz, ArCH2Ar). 13C{ H} (75 MHz, CDCl3): d 156.31
and 155.08 (2 s, arom. Cq–O), 138.08, 136.86, 136.11 and 135.27
(4 s, arom. Cq), 135.05 (s, arom. CH), 134.03 (s, arom. Cq), 129.54
and 129.45 (2 s, arom. CH), 128.64 (s, arom. Cq), 128.44, 128.29,
128.21, 128.14, 128.00, 124.28, 122.34, 121.64, 121.43 and 120.68
(10 s, arom. CH), 76.65 and 76.61 (2 s, OCH2), 37.11 (s, CH3),
31.04 (s, 3x, ArCH2Ar), 30.83 (s, ArCH2Ar). Found: C, 63.70; H,
5.13; N, 4.47. Calc. for C64H58I2N4O4 (Mr = 1200.98): C, 64.00; H,
4.87; N, 4.67%.
5,11-Bis(3-butyl-1-imidazolylium)-25,26,27,28-tetra-benzyl-
oxycalix[4]arene dibromide (cone) (3b). A stirred solution of 13
(0.400 g, 0.436 mmol) in n-butyl bromide (8 mL), was heated at
reflux for 24 h. The precipitate formed was collected by filtration
and washed with petroleum ether. The white solid (3b) was
dried under vacuum and used without further purification. Yield:
trans-[5-(3-Butylimidazol-2-iden-1-yl)-25,26,27,28-tetrabenzyl-
oxycalix[4]arene](pyridine) palladium(II) dibromide (cone) (15).
A
mixture of bromide 2 (0.205 g, 0.207 mmol), PdCl2 (0.044 g,
0.248 mmol), K2CO3 (0.143 g, 1.04 mmol) and KBr (0.492 g,
4.14 mmol) in pyridine (2 mL), was stirred at 80 ◦C for 18 h. After
cooling to room temperature, the mixture was filtered through
Celite and the filtrate evaporated to dryness. The crude mixture
was purified by flash chromatography (SiO2, CH2Cl2/petroleum
ether, 60 : 40, v/v) to afford 15 as a yellow solid (Rf 0.32, SiO2,
CH2Cl2/petroleum ether, 60 : 40, v/v). Yield: 0.194 g, 75%; mp
◦
1
0.514 g, 98%; mp 158–160 C. H NMR (300 MHz, CDCl3): d
10.65 (2H, s, NCHN), 7.81 (2H, s, NCHC), 7.48 (2H, s, NCHC),
4
7.34–7.06 (22H, m, ArH), 6.73 (2H, d, J = 2.3 Hz, ArH), 6.58
3
3
(2H, d, J = 7.5 Hz, ArH), 6.51 (2H, d, J = 7.5 Hz, ArH), 6.39
◦
(2H, dd, 3J = J¢ = 7.5 Hz, ArH), 5.00–4.78 (8H, m, OCH2), 4.51–
105–108 C. H NMR (300 MHz, CDCl3): d 8.91–8.85 (2H, m,
o-NC5H5), 7.66 (1H, tt, 3J = 7.6 Hz 4J = 1.7 Hz, p-NC5H5), 7.40–
7.13 (22H, m, ArH), 7.12–7.05 (2H, m, m-NC5H5), 6.96 (1H, d,
3
1
4.30 (4H, ABX2 spin system, NCH2), 4.24 and 3.04 (2H, AB spin
2
sytem, JAB = 13.7 Hz, ArCH2Ar), 4.15 and 2.91 (4H, AB spin
9896 | Dalton Trans., 2011, 40, 9889–9898
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3J = 2.0 Hz, NCHC), 6.83 (1H, d, 3J = 2.0 Hz, NCHC), 6.72–6.62
(4H, m, ArH), 6.57 (1H, dd, 3J = 8.3 Hz, 3J¢ = 6.4 Hz, p-H of Ar
1.5 Hz, NCHC), 6.81 (2H, dd, 3J = 6.6 Hz, 4J = 2.2 Hz, ArH), 6.69
(2H, d, 4J = 2.4 Hz, ArH), 6.64–6.54 (4H, m, ArH), 5.01 and 4.92
(4H, AB spin system, 2JAB = 11.6 Hz, OCH2), 4.93 and 4.88 (4H,
AB spin system, 2JAB = 11.3 Hz, OCH2), 4.78–4.51 (4H, ABX2 spin
system, NCH2), 4.39 and 3.32 (2H, AB spin system, 2JAB = 12.4 Hz,
opposite to Ar–N), 6.42–6.30 (4H, m, ArH), 5.04 (2H, s, OCH2),
2
4.99 (2H, s, OCH2), 4.91 and 4.85 (4H, AB spin system, JAB
=
3
11.6 Hz, OCH2), 4.57 (2H, t, J = 7.5 Hz, NCH2), 4.23 and 2.96
2
2
(4H, AB spin system, JAB = 13.7 Hz, ArCH2Ar), 4.18 and 2.95
ArCH2Ar), 4.23 and 2.85 (4H, AB spin system, JAB = 13.0 Hz,
(4H, AB spin system, 2JAB = 13.7 Hz, ArCH2Ar), 2.11 (2H, tt, 3J =
ArCH2Ar), 4.12 and 2.91 (2H, AB spin system, JAB = 13.3 Hz,
2
3J¢ = 7.5 Hz, NCH2CH2), 1.52 (2H, tq, 3J = J¢ = 7.5 Hz, CH2CH3),
ArCH2Ar), 2.11 (4H, tt, 3J = J¢ = 7.4 Hz, NCH2CH2), 1.52 (4H,
3
3
1.04 (3H, t, 3J = 7.5 Hz, CH3). 13C{ H} (75 MHz, CDCl3): d 155.70
tq, J = J¢ = 7.4 Hz, CH2CH3), 1.04 (6H, t, J = 7.4 Hz, CH3).
1
3
3
3
1
and 155.41 (2 s, arom. Cq–O), 155.08 (s, 2x, arom. Cq–O), 152.65
(o-NC5H5), 147.61 (s, NCN), 137.77 (s, arom. Cq), 137.63 (p-
NC5H5), 137.17, 136.81, 136.02, 134.60, 134.23 and 133.74 (6 s,
arom. Cq), 130.17, 129.83, 129.52, 128.80, 128.42, 128.22, 128.07,
128.05, 127.97, 127.93, 127.90, 126.13, 124.42, 123.11, 122.73,
122.08 and 121.50 (17 s, arom. CH), 76.73 (s, 2x, OCH2), 76.37 and
76.31 (2 s, OCH2), 51.30 (s, NCH2), 32.14 (s, NCH2CH2), 31.42
(s, 4x, ArCH2Ar), 20.12 (s, CH2CH3), 13.93 (s, CH3). Found: C,
65.48; H, 5.37; N, 3.21. Calc. for C68H63Br2N3O4Pd (Mr = 1252.47):
C, 65.21; H, 5.07; N, 3.35%.
13C{ H} (75 MHz, CDCl3): d 168.24 (s, NCN), 154.80 and 154.41
(2 s, arom. Cq–O), 137.91, 137.58, 135.97, 135.37, 134.95, 134.65
and 133.48 (7 s, arom. Cq), 130.05, 129.70, 129.32, 128.89, 128.38,
128.18, 128.01, 127.85, 125.85, 123.43, 122.57, 121.12 and 120.94
(13 s, arom. CH), 77.89 and 76.02 (2 s, OCH2), 51.50 (s, NCH2),
32.58 (s, NCH2CH2), 31.80 (s, ArCH2Ar), 31.09 (s, 2x, ArCH2Ar),
30.46 (s, ArCH2Ar), 20.47 (s, CH2CH3), 14.03 (s, CH3). MALDI-
TOF mass spectrum: m/z (%) 1295.28 (44) [M + H]+, 1134.42
(100) [M - 2Br]2+, 1216.35 (37) [M - Br + H]2+. Found: C, 65.19;
H, 5.45; N, 4.14. Calc. for C70H68Br2N4O4Pd (Mr = 1295.54): C,
64.90; H, 5.29; N, 4.32%.
trans-[5,11-Bis(3-methylimidazol-2-yliden-1-yl)-25,26,27,28-
trans-[1-Butyl-3-(2,6-diisopropylphenyl)imidazol-2-ylidene]-
(pyridine) palladium(II) dibromide (19). A mixture of bromide 18
(0.502 g, 1.37 mmol), PdCl2 (0.268 g, 1.51 mmol), K2CO3 (0.949 g,
6.87 mmol) and KBr (3.27 g, 27.5 mmol) in pyridine (7 mL), was
stirred at 80 ◦C for 16 h. After cooling to room temperature, the
mixture was filtered through Celite and the filtrate evaporated to
dryness. The crude mixture was purified by flash chromatography
(SiO2, CH2Cl2/petroleum ether, 60 : 40, v/v) to afford 19 as a
yellow solid (Rf 0.39, SiO2, CH2Cl2/petroleum ether, 70 : 30, v/v).
Yield: 0.603 g, 70%; mp 179–180 ◦C. 1H NMR (300 MHz, CDCl3):
tetrabenzyloxycalix[4]arene] palladium(II) diiodide (cone) (16).
A
solution of diiodide 3a (0.250 g, 0.208 mmol) and Pd(OAc)2
(0.047 g, 0.208 mmol) in DMF (50 mL), was stirred at 50 ◦C
for 1.5 h, then at 80 ◦C for 2 h and finally at 130 ◦C for 2 h.
The mixture was cooled at room temperature and evaporated to
dryness to afford a brown solid. The crude product was purified
by flash chromatography (SiO2, CH2Cl2/petroleum ether, 90 : 10,
v/v) to afford 16 as a yellow solid (Rf 0.38, SiO2, CH2Cl2). Yield:
0.104 g, 38%; mp > 200 ◦C. 1H NMR (300 MHz, CDCl3): d 8.87
(2H, d, 4J = 2.6 Hz, m-ArH), 7.47–7.02 (20H, m, ArH), 7.15 (2H,
d, 3J = 1.8 Hz, NCHC), 6.97 (2H, d, 3J = 1.8 Hz, NCHC), 6.90 (2H,
dd, 3J = 6.5 Hz, 4J = 2.6 Hz, ArH), 6.74 (2H, d, 4J = 2.6 Hz, ArH),
3
4
d 8.81–8.75 (2H, m, o-NC5H5), 7.64 (1H, tt, J = 7.6 Hz, J =
3
1.6 Hz, p-NC5H5), 7.49 (1H, t, J = 7.8 Hz, ArH), 7.33 (2H, d,
3J = 7.8 Hz, ArH), 7.24–7.17 (2H, m, m-NC5H5), 7.12 (1H, d, 3J =
6.69–6.58 (4H, m, ArH), 5.06 and 4.92 (4H, AB spin system, 2JAB
=
3
2.0 Hz, NCHC), 6.96 (1H, d, J = 2.0 Hz, NCHC), 4.79 (2H, t,
11.7 Hz, OCH2), 4.99 (2H, s, OCH2), 4.95 (2H, s, OCH2), 4.38 and
3
3J = 7.9 Hz, NCH2), 3.01 (2H, qq, 3J = J¢ = 6.7 Hz, CHMe2), 2.19
2
3.30 (2H, AB spin system, JAB = 12.5 Hz, ArCH2Ar), 4.28 and
3
3
3
2.91 (4H, AB spin system, 2JAB = 13.0 Hz, ArCH2Ar), 4.14 and 2.94
(2H, AB spin system, 2JAB = 13.2 Hz, ArCH2Ar), 4.08 (6H, s, CH3).
(2H, tt, J = 7.9 Hz J¢ = 7.5 Hz, NCH2CH2), 1.58 (2H, tq, J =
3J¢ = 7.5 Hz, CH2CH3), 1.41 (6H, d, 1.04, 3J = 6.7 Hz, CH3 of iPr),
1.10 (3H, t, 3J = 7.5 Hz, CH2CH3), 1.04 (6H, d, 1.04, 3J = 6.7 Hz,
1
13C{ H} (75 MHz, CDCl3): d 167.00 (s, NCN), 154.77 and 154.34
i
1
CH3 of Pr). 13C{ H} (75 MHz, CDCl3): d 152.65 (o-NC5H5),
150.26 (NCN), 147.21 (s, arom. Cq), 137.60 (p-NC5H5), 134.69
(s, arom. Cq–N), 130.37 and 126.26 (2 s, arom. CH), 124.35 and
124.13 (2 s, NCH), 120.73 (s, arom. CH), 52.14 (s, NCH2), 32.30 (s,
NCH2CH2), 28.67 (s, CHMe2), 26.66 (CHCH3), 23.48 (CHCH3),
20.20 (s, CH2CH3), 14.01 (s, CH2CH3). Found: C, 45.34; H, 5.32;
N, 6.43. Calc. for C24H33Br2N3Pd (Mr = 629.77): C, 45.77; H, 5.28;
N, 6.67%.
(2 s, arom. Cq–O), 137.79, 137.46, 136.05, 135.12, 134.92, 134.51
and 133.41 (7 s, arom. Cq), 129.98, 129.62, 129.37, 128.79, 128.35,
128.18, 127.97, 127.82, 125.44, 123.57, 122.82, 122.32 and 121.31
(13 s, arom. CH), 77.82 and 76.01 (2 s, OCH2), 39.28 (s, CH3),
31.66 (s, ArCH2Ar), 31.18 (s, 2x, ArCH2Ar), 30.26 (s, ArCH2Ar).
ESI-TOF mass spectrum: m/z (%) 1343.11 (18) [M + K]+, 1327.15
(16) [M + Na]+, 1177.25 (100) [M - I]+. Found: C, 58.24; H, 4.64; N,
4.13. Calc. for C64H56I2N4O4Pd·0.6 H2O (Mr = 1305.38 + 10.81):
C, 58.40; H, 4.38; N, 4.26%.
General procedure for palladium-catalysed Suzuki–Miyaura
cross-coupling reactions
trans-[5,11-Bis(3-butylimidazol-2-yliden-1-yl)-25,26,27,28-
tetrabenzyloxycalix[4]arene] palladium(II) dibromide (cone) (17).
A solution of dibromide 3b (0.337 g, 0.282 mmol) and Pd(OAc)2
(0.063 g, 0.282 mmol) in DMF (70 mL), was stirred at 50 ◦C for 1.5
h, then at 80 ◦C for 2 h and finally at 130 ◦C for 2 h. The mixture
was cooled at room temperature and evaporated to dryness to
afford a brown solid. The crude product was purified by flash
chromatography (SiO2, CH2Cl2) to afford 17 as a yellow solid (Rf
0.35, SiO2, CH2Cl2). Yield: 0.131 g, 36%; mp > 240 ◦C. 1H NMR
(300 MHz, CDCl3): d 8.92 (2H, d, 4J = 2.4 Hz, m-ArH), 7.44–7.17
(20H, m, ArH), 7.08 (2H, d, 3J = 1.5 Hz, NCHC), 6.93 (2H, d, 3J =
In a Schlenk tube under nitrogen were introduced phenylboronic
acid (0.183 g, 1.50 mmol), Cs2CO3 (0.652 g, 2 mmol) and a
solution of the palladium complex in CH2Cl2. The solvent was
removed under vacuum and 3 mL of dioxane were added. The
stirred mixture was degassed by nitrogen bubbling (2 min), upon
which the halide (1 mmol) was added and the mixture vigorously
stirred at 80 ◦C for 2 h. The hot mixture was filtered through
Celite. Then 1,4-dimethoxybenzene (0.069 g, 0.5 mmol; internal
standard) was added to the filtrate. The solvent was removed under
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1
reduced pressure and the crude mixture analysed by H NMR.
8 C. B. Dieleman, D. Matt, I. Neda, R. Schmutzler, H. Tho¨nnessen, P.
G. Jones and A. Harriman, J. Chem. Soc., Dalton Trans., 1998, 2115–
2121.
9 F. J. Parlevliet, C. Kiener, J. Fraanje, K. Goubitz, M. Lutz, A. L. Spek,
P. C. J. Kamer and P. W. N. M. van Leeuwen, J. Chem. Soc., Dalton
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10 D. Se´meril, C. Jeunesse, D. Matt and L. Toupet, Angew. Chem., Int.
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11 P. Faidherbe, C. Wieser, D. Matt, A. Harriman, A. De Cian and J.
Fischer, Eur. J. Inorg. Chem., 1998, 451–457.
The yields were determined by comparing the intensity of methyl
signal of the product (d(Me) = 2.41 ppm) with that of the internal
reference (d(Me) = 3.78 ppm). In some experiments the product
was isolated chromatographically. The isolated yield turned out to
be very close (deviation less than 5%) to that determined using the
internal reference.
12 P. Kuhn, D. Se´meril, C. Jeunesse, D. Matt, P. Lutz, R. Louis and M.
Neuburger, Dalton Trans., 2006, 3647–3649.
X-Ray crystallography
13 S. Steyer, C. Jeunesse, D. Matt, R. Welter and M. Wesolek, J. Chem.
Soc., Dalton Trans., 2002, 4264–4272.
14 D. Se´meril, D. Matt and L. Toupet, Chem.–Eur. J., 2008, 14, 7144–7155.
15 L. Monnereau, D. Se´meril and D. Matt, Eur. J. Org. Chem., 2010,
3068–3073.
Crystal data for 14: crystals suitable for X-ray diffraction were
obtained by slow diffusion of cyclohexane into a thf solution
of the complex: C127.50H119Br2N4O8Pd, M = 2101.49, monoclinic,
space group P21/a, a = 21.6895(4), b = 21.7815(3), c = 23.3319(4)
A, b = 106.156(2), V = 10587.4(3) A , Z = 4, m = 0.991 mm ,
F(000) = 4368. Crystals of the compound were mounted on a
Oxford Diffraction CCD Saphire 3 Xcalibur diffractometer. Data
16 C. B. Dieleman, S. Steyer, C. Jeunesse and D. Matt, J. Chem. Soc.,
3
-1
˚
˚
Dalton Trans., 2001, 2508–2517.
17 M. Lejeune, C. Jeunesse, D. Matt, D. Se´meril, F. Peruch, L. Toupet and
P. J. Lutz, Macromol. Rapid Commun., 2006, 27, 865–870.
18 D. Se´meril, C. Jeunesse and D. Matt, C. R. Chim., 2008, 11, 583–594.
19 L. Monnereau, D. Se´meril, D. Matt and L. Toupet, Chem.–Eur. J.,
2010, 16, 9237–9247.
˚
collection with Mo-Ka radiation (l = 0.71073 A) was carried
out at 140 K. 80046 reflections were collected (2.55 < q <
27.00◦), 22899 were found to be unique and 11333 were observed
(merging R = 0.0537). The structure was solved with SHELXS-
97.44 Final results: R2, R1, wR2, wR1, Goof; 0.1037, 0.0383, 0.0863,
0.0783, 0.799. Residual electron density minimum/maximum =
20 A. A. D. Tulloch, A. A. Danopoulos, S. Winston, S. Kleinhenz and G.
Eastham, J. Chem. Soc., Dalton Trans., 2000, 4499–4506.
21 W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290–1309.
22 S. D´ıez-Gonza´lez and S. P. Nolan, Coord. Chem. Rev., 2007, 251, 874–
883.
-3
˚
-0.601/0.606 e A . Important bond lengths and angles are given
23 N. Marion, S. D´ıez-Gonza´lez and S. P. Nolan, Angew. Chem., Int. Ed.,
2007, 46, 2–15.
in Fig. 1. CCDC 821364.†
24 E. A. B. Kantchev, C. J. O’Brien and M. G. Organ, Angew. Chem., Int.
Ed., 2007, 46, 2768–2813.
Crystal data for 16: crystals suitable for X-ray diffraction were
obtained by slow evaporation of a dichloromethane solution of
the complex: C66H60Cl4I2N4O4Pd, M = 1475.18, triclinic, space
25 S. Diez-Gonzalez, N. Marion and S. P. Nolan, Chem. Rev., 2009, 109,
3612–3676.
26 I. Dinare`s, C. Garcia de Miguel, M. Font-Bacia, X. Solans and E.
Alcade, Organometallics, 2007, 26, 5125–5128.
¯
˚
group P1, a = 13.2867(2), b = 13.6636(2), c = 19.0656(3) A,
a = 98.340(1), b = 94.964(1), g = 117.181(1), V = 3000.2(1)
27 T. Fahlbusch, M. Frank, G. Maas and J. Schatz, Organometallics, 2009,
28, 6183–6193.
3
-1
˚
A , Z = 2, m = 1.569 mm , F(000) = 1472. Crystals of the
compound were mounted on a Oxford Diffraction CCD Saphire
3 Xcalibur diffractometer. Data collection with Mo-Ka radiation
28 K. Iwamoto, K. Araki and S. Shinkai, J. Org. Chem., 1991, 56, 4955–
4962.
29 X. Liu, H. Wang, Q. Zhang, M. Cai and S. Jiang, Chinese Patent CN
101318881, 2008.
˚
(l = 0.71073 A) was carried out at 150 K. 59591 reflections were
collected (2.56 < q < 27.00◦), 12097 were found to be unique
and 9678 were observed (merging R = 0.0291). The structure
was solved with SHELXS-97.44 Final results: R2, R1, wR2, wR1,
Goof; 0.0369, 0.0266, 0.0689, 0.0671, 0.952. Residual electron
30 I. Dinares, C. G. de Miguel, N. Mesquida and E. Alcalde, J. Org. Chem.,
2009, 74, 482–485.
31 C. Jaime, J. de Mendoza, P. Prados, P. M. Nieto and C. Sa´nchez, J. Org.
Chem., 1991, 56, 3372–3376.
32 C. B. Dieleman, C. Marsol, D. Matt, N. Kyritsakas, A. Harriman and
J.-P. Kintzinger, J. Chem. Soc., Dalton Trans., 1999, 4139–4148.
33 C. D. Gutsche, in Calixarenes, Monographs in Supramolecular Chem-
istry, ed. J. F. Stoddart, The Royal Society of Chemistry, Cambridge,
1989.
-3
˚
density minimum/maximum = -0.718/1.110 e A . Important
bond lengths and angles are given in Fig. 2. CCDC 748587.†
Acknowledgements
34 L. C. Groenen, B. H. M. Ruel, A. Casnati, P. Timmerman, W. Verboom,
S. Harkema, A. Pochini, R. Ungaro and D. N. Reinhoudt, Tetrahedron
Lett., 1991, 32, 2675–2678.
35 H. Lebel, M. K. Janes, A. B. Charette and S. P. Nolan, J. Am. Chem.
Soc., 2004, 126, 5046–5047.
36 C. J. O’brien, E. A. B. Kantchev, C. Valente, N. Hadei, G. A. Chass, A.
Lough, A. C. Hopkinson and M. G. Organ, Chem.–Eur. J., 2006, 12,
4743–4748.
We thank Dr C. Jeunesse (University of Strasbourg) for interesting
discussion. Johnson Matthey is gratefully acknowledged for a
generous gift of palladium.
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9898 | Dalton Trans., 2011, 40, 9889–9898
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The Royal Society of Chemistry 2011
©