Resorcin[4]arene-derived mono-, bis- and tetra-imidazolium salts as ligand precursors for Suzuki-Miyaura cross-coupling

Article abstract of DOI:10.1039/c1ob06404e

Eleven resorcinarene cavitands bearing either one, two or four (3-R-1-imidazolylium)-methyl substituents (R = ⁿBu, Ph, Mes, ⁱPr₂C₆H₃) anchored at resorcinolic "ortho" positions have been synthesised f

Full text of DOI:10.1039/c1ob06404e

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PAPER
Resorcin[4]arene-derived mono-, bis- and tetra-imidazolium salts as ligand
precursors for Suzuki–Miyaura cross-coupling†‡
Hani El Moll,a David Se´meril,*a Dominique Matt,*a Lo¨ıc Toupetb and Jean-Jacques Harrowfieldc
Received 16th August 2011, Accepted 14th September 2011
DOI: 10.1039/c1ob06404e
Eleven resorcinarene cavitands bearing either one, two or four (3-R-1-imidazolylium)-methyl
n
substituents (R = Bu, Ph, Mes, iPr2C6H3) anchored at resorcinolic “ortho” positions have been
synthesised from the appropriate bromomethylated precursor. Combining the imidazolium salts with
palladium acetate and Cs2CO3 gave active Suzuki–Miyaura cross coupling catalysts. The highest
activities were observed with the doubly functionalised cavitands, which all have the imidazolylium
groups attached to proximal resorcinol units.
example, Pd(II), in which the substituent-bearing phenyl groups
Introduction
are tilted in towards the cavity of the calixarene.12 In unrestricted
The palladium catalysed Suzuki–Miyaura cross-coupling of
cone calix[4]arenes, this tilting is usually outwards. An interesting
organoboron compounds has been established as one of the most
aspect of the structure of this particular Pd(II) complex is that
selective palladium-catalysed cross-coupling reactions, thereby
the metal ion is poised above the cavity, though it seems that
leading to many important developments in modern organic
the phenyl ring tilting may restrict access to the cavity, since
chemistry.1–4 While this reaction is usually performed in the
neither of the additional ligands on the metal are contained
presence of tertiary phosphines, recent studies have shown that
within it, a situation unlike that observed with some related
high catalytic efficiency can also be obtained with N-heterocyclic
carbenes (NHCs), ligands of this type being conveniently gener-
complexes where phosphorus ligating sites are present. Further,
although the Pd calixaryl(NHC)2 complex can be used as a
ated from imidazolium salts.5,6 To date research in this area has
catalyst precursor for the Suzuki–Miyaura reaction, it appears
mainly focused on mono-NHC ligands, although some palladium
complexes containing bis7–13 or tetrakis14-NHC ligands are known.
The present work concerns the use of NHC ligands supported
that chelation is not retained in the catalytically active species
and, more significantly, there is no evidence of a “cavity effect”
which might arise from substrate inclusion by the calixarene. Given
on a rigidified calixarene of the cavitand type. The term “cavi-
our interest in such determinants of catalyst activity, we have
tand” applies specifically to the sub-family of calixarenes termed
sought to clarify the situation concerning NHC functionalities
“resorcinarenes” where linking of the hydroxyl substituents on
grafted to a calix[4]arene scaffold by examining the properties
the macrocycles has been used to reinforce their structure,
of rigidified resorcinarenes bearing either a single substituent or
creating a well-defined cavity, usually of fourfold symmetry.15,16 In
calix[4]arene analogues, even those where phenolic-O alkylation
has been used to block conformational inversion, a degree
multiple substituents in which chelation by proximal groups might
be possible. For the species bearing multiple substituents, it may
be noted that the possibility of binding through a single site would
of conformational flexibility is retained, as is well illustrated
leave charged imidazolylium groups in the vicinity of the catalytic
by the fact that a cone calix[4]arene distally substituted with
imidazolylium-methyl groups is able, after deprotonation, to form
a trans chelate NHC (N-heterocyclic carbene) complex with, for
centre, providing another factor that might be used to influence
the catalyst properties.
Thus, we describe herein the synthesis of cavitands bearing one,
two and four imidazolium units (Scheme 1). These imidazolium
aLaboratoire de Chimie Inorganique Mole´culaire et Catalyse, Institut de
Chimie UMR 7177 CNRS, Universite´ de Strasbourg, 67008, Strasbourg
cedex, France. E-mail: dsemeril@unistra.fr, dmatt@unistra.fr
salts, which in fact are procarbenes, were assessed in Suzuki–
Miyaura cross-coupling between phenyl boronic acid and several
aryl bromides. A literature survey indicates that only three imida-
zolium salts built on a resorcinarene skeleton have been reported to
date, their use being restricted to molecular recognition studies.17–19
This is in marked contrast with the chemistry of the related
calix[4]arene analogues, which have already found numerous
applications in homogeneous catalysis.8,10–12,20 The present report
constitutes an extension of our previous work on functionalised
cavitands.21–23
bInstitut de Physique de Rennes, UMR 6251, Universite´ de Rennes 1, Campus
de Beaulieu, 35042, Rennes cedex, France
cUniversite´ de Strasbourg, ISIS, UMR 7006 CNRS, Universite´ de Stras-
bourg, 8 alle´e Gaspard Monge, BP 70028, F-67083, Strasbourg cedex, France
† Electronic supplementary information (ESI) available: Experimental
details. CCDC reference number 737674. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c1ob06404e
‡ Dedicated to Professor Christian Bruneau (CNRS – University of
Rennes) on the occasion of his 60th Birthday.
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Scheme 1 The three types of imidazolium salt synthesised in this study.
Results and discussion
Synthesis of resorcinarenyl-imidazolium salts
Eleven resorcinarene-derived imidazolium salts were synthesised,
all in high yields, according to the routes outlined in Scheme 2. The
general synthetic strategy consisted in reacting a mono- or multi-
bromomethylated resorcinarene with N-substituted imidazoles
in refluxing chloroform. All compounds were unambiguously
1
characterized by H and 13C NMR, elemental analysis and mass
spectrometry.
1
The H NMR spectra of mono-imidazolium salts 2–4 are in
keeping with Cs-symmetrical cavitands, each of them showing the
presence of two distinct AB patterns for the diastereotopic OCH2O
protons, and that of two methine triplets. The bis-imidazolium
salts 6–9 display Cs symmetry as well. Consistent with the presence
of a symmetry plane that bisects the two substituted resorcinol
1
Fig. 1 Molecular structure of resorcinarene 8 (hosting a molecule of
CHCl3). For clarity, the two CHCl3 molecules lying out of the cavity and
two the Br- anions are not shown.
rings, the H spectra of these latter compounds show three AB
patterns of intensity 1 : 2 : 1 for the four OCH2O groups and
three distinct methine triplets. An X-ray diffraction study was
carried out for one of the bis-imidazolium salts, namely 8 (Fig. 1),
which confirmed the presence of the two imidazolium moieties on
adjacent resorcinol rings. In the solid state, the two imidazolium
arms are bent towards the exterior of the cavity. The cavitand core
hosts a molecule of CHCl3, while two other molecules of CHCl3
were found remote from the cavity. Significantly, the bromide
counter anions are all remote from the cavity, although anion
inclusion in resorcinarene cavitands has already been observed.24
The tetra-imidazolium resorcinarenes 11–14 have C4v symmetry
and, accordingly, their 1H NMR spectra show a single AB pattern
for the four OCH2O groups. On going from the imidazole precur-
sors to the corresponding imidazolium salts the NCHN protons
undergo a deshielding of about 2 ppm (the imidazolium NCHN
signals appearing in the range 9.61–10.13 ppm). Consistent with
this apparent increase in acidity, the imidazolium-resorcinarenes
could easily be converted into coordinated NHC ligands under
basic conditions. For example, treatment of compound 7 with
1 equivalent of Ag2O in acetonitrile led to the white silver (I)
complex [(AgBr)2L] (15), in which L represents the bis-carbene
ligand derived from 7. The mass spectrum of 15 displayed a strong
peak at 1385.28, corresponding to the [M - Br]+ cation. In keeping
with carbene formation, the 1H NMR spectrum no longer revealed
the presence of a NCHN signal. The coordination of silver was
inferred from the 13C NMR spectrum, in which the carbenic
carbon atom appears at 181.47 ppm, which is a value typical for
coordinated NHCs. However, no Ag–C coupling was seen, as is
often the case, this finding probably reflecting the fluxional nature
of the complex.25
Utilisation of the resorcinarene-imidazolium salts in
Suzuki–Miyaura cross-coupling
Being potential precursors of carbenes, that is of strong 2-electron
donors, the above compounds were evaluated in Suzuki–Miyaura
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Scheme 2 Synthesis of the resorcinarene-imidazolium salts used in this study.
Table 1 Suzuki–Miyaura cross-coupling of 4-bromoanisole with phenyl-
boronic acid using 13 - the search for optimal catalytic conditionsa
cross-coupling between phenylboronic acid and aryl bromides in
the presence of a base (Scheme 3). For each test, the catalytic
system was generated in situ by mixing the imidazolium salt
and [Pd(OAc)2], a palladium complex which is routinely used for
generating carbene complexes.8,26 The runs were carried out using
an ArBr/Pd ratio of 10 000 and the conversions were determined
after one hour.
Entry
Solvent
Base
T/◦C
Conversion (%)
1
2
3
4
Dioxane
Dioxane
DMF
NaH
Cs2CO3
NaH
100
100
130
130
19.3
22.3
0.4
DMF
Cs2CO3
26.1
a Conditions: [Pd(OAc)2] (5 ¥ 10-5 mmol, 1 ¥ 10-2 mol%), imidazolium salt
13 (5 ¥ 10-5 mmol, 1 equiv./Pd), 4-bromoanisole (0.5 mmol), PhB(OH)2
(0.122 g, 1.0 mmol), base (1.0 mmol), solvent (1.5 mL), decane (0.05 mL),
1 h. The conversions were determined by GC, the calibrations being based
on decane.
Scheme 3 Suzuki–Miyaura cross-coupling reaction.
The first series of runs were aimed at optimisation of the
catalytic conditions with respect to solvent and base. Four tests
were carried out with the tetra-imidazolium salt 13 either in
dimethylformamide (DMF) or in dioxane and either with Cs2CO3
or NaH (Table 1). The highest conversion of 4-bromoanisole into
Ph–(p-OMe-C6H4) (26.1%) was observed when carrying out the
reaction in DMF at 130 C in the presence of Cs2CO3 (Table 1,
entry 4). It is likely that under these conditions the solubility of the
imidazolylium salt as well as that of Cs2CO3 is better in DMF than
◦
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Table 2 Suzuki–Miyaura cross-coupling of aryl bromides catalysed by [Pd(OAc)2]/mono-imidazolium salts using 10-2 mol% palladiuma
Mono-imidazolium salt
Entry
ArBr
Equiv./Pd
2
3
4
1
2
Conv. (%)
TOF
Conv. (%)
TOF
1
2
10.0
1000
10.5
1050
5.7
570
13.4
1340
3
Conv. (%)
TOF
2
7.9
790
12.4
1240
14.8
1480
4
5
Conv. (%)
TOF
2
2
50.2
5020
38.1
3810
51.7
5170
Conv. (%)
TOF
39.1
3910
45.3
4530
53.4
5340
6
7
Conv. (%)
TOF
2
2
6.5
650
13.0
1300
9.1
910
Conv. (%)
TOF
10.6
1060
8.2
820
5.2
520
8
9
Conv. (%)
TOF
2
2
4.4
440
7.0
700
4.8
480
Conv. (%)
TOF
7.5
750
7.9
790
11.2
1120
a Conditions: [Pd(OAc)2] (5 ¥ 10-5 mmol, 1 ¥ 10-2 mol%), mono-imidazolium salt, ArBr (0.5 mmol), PhB(OH)2 (0.122 g, 1.0 mmol), Cs2CO3 (0.326 g,
1.0 mmol), decane (0.05 mL), DMF (1.5 mL), 130 ◦C, 1 h. The conversions were determined by GC, the calibrations being based on decane. The TOFs
are expressed in mol(ArBr) mol(Pd)-1 h-1.
in dioxane. In none of the tests did the amount of homocoupling
product (Ph–Ph) exceed 9% of the products formed (see ESI†).
The three mono-imidazolium salts 2–4 were used in Suzuki–
Miyaura coupling of several aryl bromides. Under the optimal
conditions defined above, the mono-imidazolium salt 3 led to
slightly better conversions when using an imidazolium : Pd ratio of
2 : 1 instead of 1 : 1 (Table 2, entries 1 and 2). All subsequent runs
were therefore carried out with two equivalents of imidazolium per
Pd. It appears that the activity of the systems depends on both the
substrate and the mono-imidazolium employed. For example, the
crowded salt 4 was the more efficient proligand for the arylation
of 2-, and 4-bromoanisole, 2-bromo-6-methoxynaphthalene, 1-
bromonaphthalene and 4-bromotoluene (Table 2, entries 2–5 and
9). Whatever the mono-imidazolium employed, the reaction with
4-bromoanisole was relatively slow in comparison with that of
the sterically hindered 2-bromoanisole (Table 2, entries 2 and
3). The activities observed for 2-bromo-6-methoxynaphthalene
were 4–8 times higher than for 4-bromoanisole (Table 2, entries
2 and 4), this being rather surprising as these two substrates
usually show comparable reaction rates in Suzuki cross-coupling.
Bromobenzene and 3-bromotoluene reacted faster when mono-
imidazolium 3 was used (Table 2, entries 6 and 8). The highest
activity observed, 5340 mol(ArBr) mol(Pd)-1 h-1, was found in
the arylation of 1-bromonaphthalene with mono-imidazolium 4
(Table 2, entry 5). Unsurprisingly, for the whole series of substrates
nearly complete conversions could be obtained by increasing either
the catalyst loading or the reaction time (Table 3). For example,
2-bromo-6-methoxynaphthalene was nearly fully converted in 3 h
using 0.01 mol% of palladium or in 1 h with a palladium loading
of 0.1 mol% (Table 3, entries 5 and 6).
To test for any cavitand contribution, we investigated imida-
zolium 16 having a mesityl and a benzyl group as N-substituents
(Fig. 2). Using this salt and applying the conditions of Table 2
led to slightly higher activities than those observed with mono-
imidazolium 3 (Table S3†). For example, the activity of 16 was 5160
mol(ArBr) mol(Pd)-1 h-1 in the arylation of 1-bromonaphthalene
vs. 4530 mol(ArBr) mol(Pd)-1 h-1 using 3 (Table S3†, entry 3).
These findings strongly suggest that should 3 act as a receptor
during catalysis, then this would not have a beneficial role on the
catalyst performance. It also suggests that 3 does not function as
a hemilabile23 ligand via the oxygen atoms of the functionalised
resorcinol ring.
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Table 3 Suzuki-Miyaura cross-coupling of aryl bromides and phenylboronic acid using [Pd(OAc)2] and a mono-imidazolium salt – increasing the
palladium loading or the reaction timea
Entry
ArBr
Imidazolium salt
[Pd(OAc)2] (mol%)
Time (h)
Conversion (%)
1
2
4
4
0.1
0.01
2
16
92.8
94.9
3
4
4
4
0.1
0.01
2
16
89.3
95.7
5
6
4
4
0.1
0.01
1
3
98.6
98.5
7
8
4
4
0.1
0.01
1
3
99.1
97.6
9
10
3
3
0.1
0.01
2
16
93.7
94.8
11
12
2
2
0.1
0.01
2
16
87.9
91.6
13
14
3
3
0.1
0.01
2
16
81.6
76.7
15
16
4
4
0.1
0.01
2
16
90.3
89.1
a Conditions: [Pd(OAc)2], mono-imidazolium salt (2 equiv./Pd), ArBr (0.5 mmol), PhB(OH)2 (0.122 g, 1.0 mmol), Cs2CO3 (0.326 g, 1.0 mmol), decane
(0.05 mL), DMF (1.5 mL), 130 ◦C. The conversions were determined by GC, the calibrations being based on decane.
imidazoliums 7–9 in the arylation of 4-bromoanisole (14.7%) and
2-bromo-6-methoxynaphthalene (76.9%) (Table 4, entries 1 and
3). The highest activity (TOF = 9660 mol(ArBr) mol(Pd)-1 h-1)
was found in the cross-coupling of 1-bromonaphthalene with
bis-imidazolium 8 (substituted by two mesityl groups) (Table 4,
entry 4). Reduction of the palladium loading to 0.001 mol%
resulted with 1-bromonaphthalene in a TOF of 41600 mol(ArBr)
mol(Pd)-1 h-1 (Table 4, entry 5). It is interesting to mention
here that the activities observed with the bis-imidazolium salts
Fig. 2 Imidazolium salt 16 used as reference.
The bis-imidazolium salts 6–9 were tested towards the same aryl
bromides as those used above (Table 4). The catalytic runs were
carried out in DMF at 130 ◦C using Cs2CO3 as base and with
an optimised bis-imidazolium/Pd ratio of 1 : 1 (Table 4, entries
9–11). Under these conditions, the bis-imidazolium salts led to
higher activities than those obtained with the mono-imidazolium
salts 2–4 (salt/Pd ratio = 2 : 1). As observed in those cases, the four
bis-carbene precursors 6–9 showed low activity in the arylation
of 4-bromoanisole. In fact, this reaction was about four times
slower than that with 2-bromo-6-methoxynaphthalene (Table 4,
entries 1 and 3). The bis-imidazolium salts 7 and 9 showed also
relatively low activities in the transformation of 3-bromotoluene,
this reagent displaying usually a reactivity lying between that of 2-
and 4-bromotoluene (Table 4, entries 7, 8 and 10).
6–9 were in general lower than those previously reported for
analogous cavitands bearing two –CH2PPh2 groups instead of (3-
R-1-imidazolylium)-methyl substituents.23
In contrast to the results obtained with the mono- and bis-
imidazolium salts described above, the tetra-carbene precursors
11–14 led to higher conversions when applying a tetraimida-
zolium/Pd ratio of 1 : 1 (i.e. a procarbene/Pd ratio of 4 : 1) (Table
5, entries 1–3). The bromotoluenes turned out to be converted
faster into coupling products when the bulky imidazolium 14
was employed (Table 5, entries 8–10). The highest activity was
obtained in the arylation of 1-bromonaphthalene using the
mesityl-substituted resorcinarene 13 (TOF = 7710 mol(ArBr)
mol(Pd)-1 h-1; Table 5, entry 6). Overall, the four tetra-imidazolium
salts were less efficient than the disubstituted derivates, but their
activities were significantly higher than those of the corresponding
mono-imidazoliums.
Unlike the observations usually made with NHCs, the n-butyl-
substituted 6 led to higher conversions than the more crowded
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Table 4 Suzuki–Miyaura cross-coupling of aryl bromides catalysed by [Pd(OAc)2]/bis-imidazolium saltsa
Bis-imidazolium salt
Entry
1
ArBr
Equiv./Pd
1
6
7
8
9
Conv. (%)
TOF
14.7
1470
10.9
1090
12.5
1250
11.6
1160
2
3
Conv. (%)
TOF
1
1
4.2
420
12.0
1200
17.5
1750
13.5
1350
Conv. (%)
TOF
76.9
7690
51.5
5150
61.1
6110
40.5
4050
4
Conv. (%)
TOF
Conv. (%)
TOF
1
1
52.4
5240
91.3
9130
37.2
96.6
9660
41.6
41.9
4190
5b
37200
41600
6
7
8
Conv. (%)
TOF
1
1
1
7.9
790
26.6
2660
43.3
4330
32.6
3260
Conv. (%)
TOF
6.1
610
29.6
2960
22.4
2240
14.1
1410
Conv. (%)
TOF
7.9
790
6.1
610
17.9
1790
22.9
2290
9
Conv. (%)
TOF
Conv. (%)
TOF
Conv. (%)
TOF
0.5
1
6.1
610
10
11
15.9
1590
39.6
3960
54.4
5440
53.2
5320
57.3
5730
2
a Conditions: [Pd(OAc)2] (5 ¥ 10-5 mmol, 1 ¥ 10-2 mol%), bis-imidazolium salt, ArBr (0.5 mmol), PhB(OH)2 (0.122 g, 1.0 mmol), Cs2CO3 (0.326 g,
1.0 mmol), decane (0.05 mL), DMF (1.5 mL), 130 ◦C, 1 h. The conversions were determined by GC, the calibrations being based on decane. The TOFs
are expressed in mol(ArBr) mol(Pd)-1 h-1. b [Pd(OAc)2] (5 ¥ 10-6 mmol, 1 ¥ 10-3 mol%)
An appealing rationalisation of the greater activity of catalysts
derived from tetrakis- and bis- rather than mono-imidazolium
salts is that the former may give rise to chelate species as the active
catalyst. Molecular modelling (Spartan) of the imidazolylium-
methyl-substituted resorcinarene cavitands 2–4, 6–9 and 11–14
shows that, as might be expected due to repulsions between the
cationic centres, the substituents are oriented away from the rigidi-
fied cavity (and this is as observed in the crystal structure of 8 as its
dibromide, where the cavity is occupied by a chloroform molecule
and note NOT the anion). Modelling of the Pd(II) complexes which
might be formed by deprotonation of the NHC-precursor sites
shows, nonetheless, that for the poly-imidazolylium derivatives
the carbene-C sites can be brought into an orientation such that
cis chelation by proximal sites is possible. It is worth mentioning
here that Schatz et al. have recently reported a structurally-related
chelate complex derived from a bis-imidazolium salt based on
the more flexible calix[4]arene platform.8 There, the metal atom
adopts a cis coordination geometry. However, in the present cases,
chelation as modelled involves either an endo-cavity orientation
where the metal is inserted rather deeply into the cavity and
where there would be no room for additional ligands on the
metal, or an exo-cavity orientation where there would be extreme
clashes between the (desirable) bulky substituents on the NHC
units. Thus, the expectation would be that ligands such as 2–4,
6–9 and 11–14 would most likely function as single-site NHC
sources, albeit ones with very large substituents and (except for
2–4) positive charges adjacent to the active centre. Hence, aside
from statistical factors associated with the number of substituents
and any possible influence of charge, all three ligands might be
anticipated to show similar properties as catalyst precursors for
the Suzuki–Miyaura reaction.
Indeed, the results presently reported are consistent with all the
substituted cavitands giving rise to catalysts of similar activity,
TOF values under identical conditions varying by little more than
a factor of two, clearly corresponding to rather minor activation
energy differences which might well be ascribed to differences in
solvation associated with the charge differences. If there is no
chelation by the carbene species, then the catalysts derived from
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Table 5 Suzuki–Miyaura cross-coupling of aryl bromides catalysed by [Pd(OAc)2]/tetra-imidazolium saltsa
Tetra-imidazolium salt
Entry
ArBr
Equiv./Pd
11
12
13
14
1
2
3
Conv. (%)
TOF
Conv. (%)
TOF
Conv. (%)
TOF
0.5
1
13.4
1340
26.1
2610
11.0
1100
14.1
1410
11.3
1130
23.8
2380
2
4
Conv. (%)
TOF
1
8.8
880
2.1
210
20.8
2080
23.4
2340
5
6
Conv. (%)
TOF
1
1
32.3
3230
30.9
3090
61.9
6190
35.1
3510
Conv. (%)
TOF
50.4
5040
58.4
5840
77.1
7710
57.7
5770
7
8
Conv. (%)
TOF
1
1
25.8
2580
26.9
2690
30.7
3070
28.9
2890
Conv. (%)
TOF
6.6
660
5.4
540
12.6
1260
23.5
2350
9
Conv. (%)
TOF
1
1
8.5
850
5.3
530
15.1
1510
31.1
3110
10
Conv. (%)
TOF
11.2
1120
21.9
2190
21.7
2170
32.0
3200
a Conditions: [Pd(OAc)2] (5 ¥ 10-5 mmol, 1 ¥ 10-2 mol%), tetra-imidazolium salt, ArBr (0.5 mmol), PhB(OH)2 (0.122 g, 1.0 mmol), Cs2CO3 (0.326 g, 1.0
mmol), decane (0.05 mL), DMF (1.5 mL), 130 ◦C, 1 h. The conversions were determined by GC, the calibrations being based on decane. The TOFs are
expressed in mol(ArBr) mol(Pd)-1 h-1.
6–9 and 11–14 would have residual cationic centres close to the
metal and it is conceivable that this could have some influence
on the binding of anionic boronate substrates. This may be a
partial explanation of the greater effectiveness of the bis- and
tetrakis-imidazolylium derivatives, though again it appears that
any such effect must be small. Attempts to isolate a well-defined
species by treatment of 9 with [Pd(OAc)2] failed, this reaction
leading to a mixture of compounds that could not be separated.
Analysis of the corresponding mass spectra revealed the presence
of an intense peak at m/z 1563.54, which could not be assigned
unequivocally, this peak corresponding either to the species
[PdBr2(bis-carbene)2 + H+] or its isomer [PdBr2(monocarbene-
monoimidazolium)]+ (see ESI†).
activity (TOF = 41 600 mol(ArBr) mol(Pd)-1 h-1) was observed
in the arylation of 1-bromonaphthalene using the proximally-
disubstituted cavitand 8. The relatively small differences in activity
observed within the three series of imidazolium salts suggest that
they all behave as single-site NHC sources.
Experimental
General remarks
All manipulations involving imidazolium derivatives were per-
formed in Schlenk-type flasks under dry nitrogen. Solvents
were dried by conventional methods and distilled immediately
prior to use. CDCl3 was passed down a 5 cm thick alumina
In summary, we have described the synthesis of eleven
resorcin[4]arenes substituted either by one, two, or four imida-
zolium units. In combination with [Pd(OAc)2] and a base, these
salts resulted in efficient Suzuki–Miyaura catalysts for the cross-
coupling of aryl bromides with phenylboronic acid. The highest
˚
column and stored under nitrogen over molecular sieves (4 A).
Routine H and 13C{ H} spectra were recorded with a Bruker
1
1
1
FT instrument (AC-300). H spectra were referenced to resid-
ual protiated solvents (7.26 ppm for CDCl3, 2.50 ppm for
378 | Org. Biomol. Chem., 2012, 10, 372–382
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DMSO-d6, 2.05 ppm for acetone-d6), 13C chemical shifts are
reported relative to deuterated solvents (77.16 ppm for CDCl3,
39.52 ppm for DMSO-d6, 29.84 ppm for acetone-d6). Chemical
shifts and coupling constants are reported in ppm and in Hz,
respectively. Elemental analyses were performed by the Service
de Microanalyse, Institut de Chimie, Universite´ de Strasbourg.
The catalytic solutions were analysed by using a Varian 3900
gas chromatograph equipped with a WCOT fused-silica column
(25 m ¥ 0.25 mm, inside diameter, 0.25 mm film thickness).
Bromomethylated cavitands 1, 5 and 10,22 N-substituted imida-
zoles (R¢ = Ph,27 R¢ = mesityl,28 R¢ = 2,6-diisopropylphenyl28),
and imidazolium salt 1629 were prepared according to proce-
dures described in the literature. NMR spectral data of the
resulting 4-methoxybiphenyl,30 biphenyl,30 4-methylbiphenyl,30 2-
methoxybiphenyl,31 1-phenylnaphthalene,31 2-methylbiphenyl,31
3-methylbiphenyl31 and 2-methoxy-6-phenylnaphthalene32 were in
agreement with those reported in the literature.
1H, arom. CH of resorcinarene), 6.99 (s, 2H, arom. CH of mes),
6.54 (s, 2H, arom. CH of resorcinarene), 6.47 (s, 1H, arom. CH of
resorcinarene), 6.00 and 4.56 (AB spin system, 4H, OCH2O, 2J =
7.3 Hz), 5.99 (s br, 2H, ArCH2N), 5.71 and 4.46 (AB spin system,
2
3
4H, OCH2O, J = 7.3 Hz), 4.74 (t, 2H, CHCH2, J = 7.9 Hz),
4.66 (t, 2H, CHCH2, 3J = 8.0 Hz), 2.32 (s, 3H, CH3 para of Mes),
2.27–2.10 (m, 8H, CHCH2), 2.05 (s, 6H, CH3 ortho of Mes), 1.39–
3
1.29 (m, 24H, CH2CH2CH2CH3), 0.89 (t, 12H, CH2CH3, J =
7.1 Hz); 13C NMR (75 MHz, CDCl3): d = 155.27–153.46 (arom.
Cquat), 141.45 (s, NCHN), 138.99–130.56 (arom. Cquat), 129.89
(s, arom. CH of Mes), 122.82 (s, arom. CH of resorcinarene),
122.26, 122.11 (2 s, NCHCHN), 120.33, 120.25 (2 s, arom. CH of
resorcinarene), 119.84 (s, arom. Cquat), 116.85, 116.67 (2 s, arom.
CH of resorcinarene), 100.55 (s, OCH2O), 99.56 (s, OCH2O),
44.17 (s, ArCH2N), 36.52 (s, CHCH2), 36.33 (s, CHCH2), 32.03 (s,
CH2CH2CH3), 31.92 (s, CH2CH2CH3), 29.92 (s, CHCH2), 29.77
(s, CHCH2), 27.56 (s, CHCH2CH2), 27.51 (s, CHCH2CH2), 22.68
(s, CH2CH3), 22.64 (s, CH2CH3), 21.07 (s, CH3 para of Mes),
17.46 (s, CH3 ortho of Mes), 14.09 (s, CH2CH3). Anal. calcd. for
C65H79O8N2Br (Mr = 1096.23): C 71.22, H 7.26, N 2.55%; found:
C 71.05, H 7.38, N 2.37%. MS (ESI-TOF): m/z = 1015.56 [M -
Br]+ expected isotopic profiles.
General procedure for the synthesis of imidazolium salts
A chloroform solution of the appropriate bromomethylated
resorcinarene and imidazole (1 equiv. of imidazole per –CH2Br
unit) was refluxed for 5 days. The reaction mixture was evaporated
to dryness and the solid residue was washed with Et2O (2 ¥ 15 mL)
to afford the imidazolium-resorcinarene as a white solid.
5-(3-(2,6-Diisopropylphenyl)-1-imidazolylium)-methyl-4(24),
6(10),12(16),18(22)-tetra-methylenedioxy-2,8,14,20-tetrapentyl-
resorcin[4]arene bromide (4). Yield: 0.607 g, 97%. 1H NMR
(300 MHz, CDCl3): d = 10.25 (s, 1H, NCHN), 7.54 (t, 1H, arom.
CH of iPr2C6H3, 3J = 7.7 Hz), 7.35 (s br, 1H, NCHCHN), 7.30 (d,
2H, arom. CH of iPr2C6H3, 3J = 7.7 Hz), 7.21 (s, 1H, arom. CH of
resorcinarene), 7.10 (s, 1H, arom. CH of resorcinarene), 7.08 (s,
2H, arom. CH of resorcinarene), 7.06–7.05 (m, 1H, NCHCHN),
6.55 (s, 2H, arom. CH of resorcinarene), 6.48 (s, 1H, arom. CH
of resorcinarene), 6.09 (s, 2H, ArCH2N), 6.00 and 4.57 (AB spin
system, 4H, OCH2O, 2J = 7.5 Hz), 5.72 and 4.47 (AB spin system,
5-(3-Phenyl-1-imidazolylium)-methyl-4(24),6(10),12(16),18(22)-
tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene bromide
(2). Yield: 0.562 g, 97%. 1H NMR (300 MHz, CDCl3): d = 10.90
(s, 1H, NCHN), 7.71–7.68 (m, 2H, arom. CH of NPh), 7.59–7.52
(m, 3H, arom. CH of NPh), 7.49 (s br, 1H, NCHCHN), 7.36 (s
br, 1H, NCHCHN), 7.20 (s, 1H, arom. CH of resorcinarene),
7.09 (s, 1H, arom. CH of resorcinarene), 7.08 (s, 2H, arom. CH of
resorcinarene), 6.55 (s, 2H, arom. CH of resorcinarene), 6.48 (s,
1H, arom. CH of resorcinarene), 6.18 and 4.55 (AB spin system,
4H, OCH2O, 2J = 7.4 Hz), 5.77 (s br., 2H, ArCH2N), 5.73 and 4.45
(AB spin system, 4H, OCH2O, 2J = 7.3 Hz), 4.72 (t, 2H, CHCH2,
2
3
4H, OCH2O, J = 7.3 Hz), 4.72 (t, 2H, CHCH2, J = 7.9 Hz),
3
4.70 (t, 2H, CHCH2, J = 7.7 Hz), 2.36–2.11 (m, 10H, CHCH2
and CH(CH3)2), 1.40–1.30 (m, 24H, CH2CH2CH2CH3), 1.20 (d,
6H, CH(CH3)2, 3J = 6.9 Hz), 1.14 (d, 6 H, CH(CH3)2, 3J =
6.8 Hz), 0.90 (t, 12H, CH2CH3, 3J = 7.1 Hz); 13C NMR (75 MHz,
CDCl3): d = 155.30–138.78 (arom. Cquat), 138.61 (s, NCHN),
3
3J = 7.9 Hz), 4.70 (t, 2H, CHCH2, J = 7.7 Hz), 2.32–2.11 (m,
8H, CHCH2), 1.38–1.30 (m, 24H, CH2CH2CH2CH3), 0.90 (t,
3
3
6H, CH2CH3, J = 6.2 Hz), 0.89 (t, 6H, CH2CH3, J = 6.2 Hz);
13C NMR (75 MHz, CDCl3): d = 155.27–137.37 (arom. Cquat),
136.24 (s, NCHN), 134.43 (arom. Cquat), 130.70 (s, arom. CH
of NPh), 130.42, 122.71 (2 s, NCHCHN), 122.25, 121,88 (2 s,
arom. CH of NPh), 120.38, 120.29, 120.13 (3 s, arom. CH of
resorcinarene), 119.71 (s, arom. Cquat), 116.79, 116.67 (2 s, arom.
CH of resorcinarene), 100.43 (s, OCH2O), 99.59 (s, OCH2O),
44.08 (s, ArCH2N), 36.65 (s, CHCH2), 36.33 (s, CHCH2), 32.02 (s,
CH2CH2CH3), 31.99 (s, CH2CH2CH3), 29.90 (s, CHCH2), 29.81
(s, CHCH2), 27.56 (s, CHCH2CH2), 22.68 (s, CH2CH3), 22.65
(s, CH2CH3), 14.09 (s, CH2CH3). Anal. calcd. for C62H73O8N2Br
(Mr = 1054.16): C 70.64, H 6.98, N 2.66%; found: C 70.56, H
7.07, N 2.47%. MS (ESI-TOF): m/z = 973.50 [M - Br]+ expected
isotopic profiles.
i
138.05, 137.23 (arom. Cquat), 131.99 (s, arom. CH of Pr2C6H3),
i
130.03 (arom. Cquat), 124.74 (s, arom. CH of Pr2C6H3), 123.70,
122.20 (2 s, NCHCHN), 122.06, 120.32, 120.22 (3 s, arom. CH of
resorcinarene), 120.00 (s, arom. Cquat), 116.88, 116.76 (2 s, arom.
CH of resorcinarene), 100.65 (s, OCH2O), 99.56 (s, OCH2O),
44.22 (s, ArCH2N), 36.49 (s, CHCH2), 36.33 (s, CHCH2), 32.04 (s,
CH2CH2CH3), 31.89 (s, CH2CH2CH3), 29.93 (s, CHCH2), 29.77
(s, CHCH2), 28.69 (s, CH(CH3)2), 27.56 (s, CHCH2CH2), 27.52 (s,
CHCH2CH2), 24.46 (s, CH(CH3)2), 24.10 (s, CH(CH3)2), 22.68 (s,
CH2CH3), 22.65 (s, CH2CH3), 14.09 (s, CH2CH3). Anal. calcd. for
C68H85O8N2Br (Mr = 1138.31): C 71.75, H 7.53, N 2.46%; found:
C 71.79, H 7.55, N 2.33%. MS (ESI-TOF): m/z = 1057.61 [M -
Br]+ expected isotopic profiles.
5-(3-(2,4,6-Trimethylphenyl)-1-imidazolylium)-methyl-4(24),
6(10),12(16),18(22)-tetra-methylenedioxy-2,8,14,20-tetrapentyl-
resorcin[4]arene bromide (3). Yield: 0.580 g, 96%. 1H NMR
(300 MHz, CDCl3): d = 10.18 (s, 1H, NCHN), 7.31 (s, 1H,
NCHCHN), 7.20 (s, 1H, NCHCHN), 7.09 (s, 1H, arom. CH of
resorcinarene), 7.08 (s, 2H, arom. CH of resorcinarene), 7.05 (s,
5,11-Bis(3-butyl-1-imidazolylium)-methyl-4(24),6(10),12(16),
18(22)-tetramethylene-dioxy-2,8,14,20-tetrapentylresorcin[4]arene
dibromide (6). Yield: 0.510 g, 97%. 1H NMR (300 MHz, CDCl3):
d = 9.95 (s, 2H, NCHN), 7.46 (s br, 2H, NCHCHN), 7.27 (s br,
2H, NCHCHN), 7.13 (s, 2H, arom. CH of resorcinarene), 7.05 (s,
2H, arom. CH of resorcinarene), 6.61 and 4.56 (AB spin system,
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2H, OCH2O, 2J = 7.5 Hz), 6.54 (s, 2H, arom. CH of resorcinarene),
6.12 and 4.54 (AB spin system, 4H, OCH2O, 2J = 7.4 Hz), 5.69 and
4.48 (AB spin system, 2H, OCH2O, 2J = 7.3 Hz), 5.54 and 5.45 (AB
spin system, 4H, ArCH2N, 2J = 14.3 Hz), 4.71 (t, 1H, CHCH2, 3J =
5.3 Hz), 4.68 (t, 2H, CHCH2, 3J = 5.5 Hz), 4.66 (t, 1H, CHCH2,
3J = 5.5 Hz), 4.31 (t, 4H, NCH2CH2, 3J = 7.3 Hz), 2.30–2.03 (m,
2H, NCHCHN), 7.29 (s, 2H, NCHCHN), 7.17 (s, 2H, arom. CH
of resorcinarene), 7.06 (s, 2H, arom. CH of resorcinarene), 6.96
(s, 4H, arom. CH of Mes), 6.58 and 4.61 (AB spin system, 2H,
2
OCH2O, J = 7.4 Hz), 6.53 (s, 2H, arom. CH of resorcinarene),
2
6.14 and 4.57 (AB spin system, 4H, OCH2O, J = 7.3 Hz), 5.88
and 5.68 (AB spin system, 4H, ArCH2N, 2J = 14.0 Hz), 5.67 and
3
2
8H, CHCH2), 1.86 (quint, 4H, NCH2CH2, J = 7.4 Hz), 1.42–
4.45 (AB spin system, 2H, OCH2O, J = 7.2 Hz), 4.71 (t, 1H,
1.25 (m, 28H, CH2CH2CH2CH3 and CH2CH3 of NnBu), 0.90 (t,
12H, CH2CH3 of resorcinarene, 3J = 7.1 Hz), 0.87 (t, 6H, CH2CH3
CHCH2, 3J = 7.9 Hz), 4.70 (t, 2H, CHCH2, 3J = 7.9 Hz), 4.68 (t,
3
1H, CHCH2, J = 7.9 Hz), 2.31 (s, 6H, CH3 para of Mes), 2.25–
◦
3
of NnBu, J = 6.9 Hz); 13C NMR (75 MHz, CDCl3, 25 C): d =
155.12–137.35 (arom. Cquat), 136.70 (s, NCHN), 122.21, 122.10
(2 s, NCHCHN), 121.82 (s, arom. CH of resorcinarene), 120.31
(s, arom. Cquat), 120.08, 116.95 (2 s, arom. CH of resorcinarene),
100.69 (s, OCH2O), 100.40 (s, OCH2O), 99.60 (s, OCH2O), 49.88
(s, NCH2CH2), 43.66 (s, ArCH2N), 36.77 (s, CHCH2), 36.61
(s, CHCH2), 36.33 (s, CHCH2), 32.12 (s, NCH2CH2), 31.98
(s, CH2CH2CH3 of resorcinarene), 29.92 (s, CHCH2), 29.68 (s,
CHCH2), 27.53 (s, CHCH2CH2), 27.52 (s, CHCH2CH2), 27.51
(s, CHCH2CH2), 22.68 (s, CH2CH3 of resorcinarene), 22.63 (s,
CH2CH3 of resorcinarene), 22.58 (s, CH2CH3 of resorcinarene),
19.45 (s, CH2CH3 of NnBu), 14.08 (s, CH2CH3 of resorcinarene),
13.42 (s, CH2CH3 of NnBu). Anal. calcd. for C68H90O8N4Br2 (Mr =
1251.27): C 65.27, H 7.25, N 4.48%; found: C 65.03, H 7.44, N
4.16%. MS (ESI-TOF): m/z = 1171.60 [M - Br]+ and 545.35 [M -
Br2]2+ expected isotopic profiles.
2.11 (m, 8H, CHCH2), 2.03 (s, 12H, CH3 ortho of Mes), 1.41–1.26
(m, 24H, CH2CH2CH2CH3), 0.88 (t, 12H, CH2CH3, 3J = 7.0 Hz);
13C NMR (75 MHz, CDCl3): d = 155.13–138.16 (arom. Cquat),
137.59 (s, NCHN), 137.26–130.72 (arom. Cquat), 129.79 (s, arom.
CH of Mes), 123.55, 122.94 (2 s, NCHCHN), 121.97 (s, arom. CH
of resorcinarene), 120.36 (arom. Cquat), 120.05, 116.94 (2 s, arom.
CH of resorcinarene), 100.87 (s, OCH2O), 100.68 (s, OCH2O),
99.64 (s, OCH2O), 43.96 (s, ArCH2N), 36.73 (s, CHCH2), 36.52
(s, CHCH2), 36.31 (s, CHCH2), 32.02 (s, CH2CH2CH3), 31.91 (s,
CH2CH2CH3), 31.79 (s, CH2CH2CH3), 29.95 (s, CHCH2), 29.84
(s, CHCH2), 29.54 (s, CHCH2), 27.57 (s, CHCH2CH2), 27.48 (s,
CHCH2CH2), 27.40 (s, CHCH2CH2), 22.68 (s, CH2CH3), 22.62
(s, CH2CH3), 22.58 (s, CH2CH3), 21.07 (s, CH3 para of Mes),
17.60 (s, CH3 ortho of Mes), 14.08 (s, CH2CH3). Anal. calcd. for
C78H92O8N4Br2 (Mr = 1373.39): C 68.21, H 6.75, N 4.08%; found:
C 68.25, H 6.84, N 4.18%. MS (ESI-TOF): m/z = 607.36 [M -
Br2]2+ expected isotopic profiles.
5,11-Bis(3-phenyl-1-imidazolylium)-methyl-4(24),6(10),12(16),
18(22)-tetramethylene-dioxy-2,8,14,20-tetrapentylresorcin[4]-
5,11-Bis(3-(2,6-diisopropylphenyl)-1-imidazolylium)-methyl-
4(24),6(10),12(16),18(22)-tetra-methylenedioxy-2,8,14,20-tetra-
pentylresorcin[4]arene dibromide (9). Yield: 0.810 g, 99%. 1H
NMR (300 MHz, CDCl3): d = 10.09 (s, 2H, NCHN), 7.55 (s br,
2H, NCHCHN), 7.51 (t, 2H, arom. CH of iPr2C6H3, 3J = 7.7 Hz),
1
arene dibromide (7). Yield: 0.527 g, 97%. H NMR (300 MHz,
CDCl3): d = 10.57 (s, 2H, NCHN), 7.87 (s br, 2H, NCHCHN),
7.80 (d, 4H, arom. CH ortho of NPh, 3J = 7.4 Hz), 7.56 (s br, 2H,
NCHCHN), 7.53 (t, 4H, arom. CH meta of NPh, 3J = 7.5 Hz), 7.49
3
(t, 2H, arom. CH para of NPh, J = 7.4 Hz), 7.16 (s, 2H, arom.
i
7.29 (s br, 2H, NCHCHN), 7.27 (d, 4H, arom. CH of Pr2C6H3,
CH of resorcinarene), 7.06 (s, 2H, arom. CH of resorcinarene),
6.84 and 4.64 (AB spin system, 2H, OCH2O, 2J = 7.0 Hz), 6.55 (s,
2H, arom. CH of resorcinarene), 6.30 and 4.58 (AB spin system,
3J = 7.7 Hz), 7.19 (s, 2H, arom. CH of resorcinarene), 7.07 (s, 2H,
arom. CH of resorcinarene), 6.58 and 4.60 (AB spin system, 2H,
2
OCH2O, J = 7.2 Hz), 6.54 (s, 2H, arom. CH of resorcinarene),
2
4H, OCH2O, J = 7.3 Hz), 5.75 and 5.58 (AB spin system, 4H,
2
6.14 and 4.60 (AB spin system, 4H, OCH2O, J = 7.5 Hz), 6.01
2
ArCH2N, J = 14.1 Hz), 5.69 and 4.45 (AB spin system, 2H,
and 5.72 (AB spin system, 4H, ArCH2N, 2J = 14.1 Hz), 5.68 and
OCH2O, 2J = 7.4 Hz), 4.73 (t, 1H, CHCH2, 3J = 8.2 Hz), 4.71 (t,
2H, CHCH2, 3J = 8.0 Hz), 4.70 (t, 1H, CHCH2, 3J = 7.9 Hz), 2.31–
2.06 (m, 8H, CHCH2), 1.41–1.25 (m, 24H, CH2CH2CH2CH3),
2
4.44 (AB spin system, 2H, OCH2O, J = 7.0 Hz), 4.74 (t, 1H,
3
3
CHCH2, J = 8.2 Hz), 4.68 (t, 2H, CHCH2, J = 8.4 Hz), 4.66
3
(t, 1H, CHCH2, J = 8.4 Hz), 2.32–2.09 (m, 12H, CHCH2 and
3
3
0.89 (t, 3H, CH2CH3, J = 6.8 Hz), 0.88 (t, 9H, CH2CH3, J =
6.9 Hz); 13C NMR (75 MHz, CDCl3): d = 155.13–137.34 (arom.
Cquat), 135.30 (s, NCHN), 134.51 (arom. Cquat), 130.50 (s, arom.
CH of NPh), 130.05, 123.49 (2 s, NCHCHN), 121.93 (s, arom.
CH of NPh), 121.88 (s, arom. CH of NPh), 120.82 (s, arom. CH
of resorcinarene), 120.31 (arom. Cquat), 120.06, 116.98 (2 s, arom.
CH of resorcinarene), 100.89 (s, OCH2O), 100.53 (s, OCH2O),
99.56 (s, OCH2O), 44.05 (s, ArCH2N), 36.89 (s, CHCH2), 36.66
(s, CHCH2), 36.33 (s, CHCH2), 32.00 (s, CH2CH2CH3), 29.92
(s, CHCH2), 29.69 (s, CHCH2), 27.55 (s, CHCH2CH2), 22.68
(s, CH2CH3), 22.63 (s, CH2CH3), 22.58 (s, CH2CH3), 14.08 (s,
CH2CH3). Anal. calcd. for C72H82O8N4Br2 (Mr = 1291.25): C
66.97, H 6.40, N 4.34%; found: C 67.03, H 6.35, N 4.29%. MS
(ESI-TOF): m/z = 565.31 [M - Br2]2+ expected isotopic profiles.
CH(CH3)2), 1.42–1.29 (m, 24H, CH2CH2CH2CH3), 1.20 (d, 3H,
3
3
CH(CH3)2, J = 6.7 Hz), 1.19 (d, 6H, CH(CH3)2, J = 6.7 Hz),
1.18 (d, 3H, CH(CH3)2, 3J = 6.8 Hz), 1.13 (d, 6H, CH(CH3)2, 3J =
6.6 Hz), 1.12 (d, 6H, CH(CH3)2, 3J = 6.6 Hz), 0.90 (t, 3H, CH2CH3,
3
3J = 6.8 Hz), 0.89 (t, 6H, CH2CH3, J = 7.0 Hz), 0.88 (t, 3H,
CH2CH3, 3J = 6.6 Hz); 13C NMR (75 MHz, CDCl3): d = 155.20–
138.50 (arom. Cquat), 138.28 (s, NCHN), 138.14, 137.19 (arom.
i
Cquat), 131.81 (s, arom. CH of Pr2C6H3), 130.21 (arom. Cquat),
124.63 (s, arom. CH of iPr2C6H3), 124.38, 122.86 (2 s, NCHCHN),
121.92 (s, arom. CH of resorcinarene), 120.59 (arom. Cquat), 120.44,
116.93 (2 s, arom. CH of resorcinarene), 100.95 (s, OCH2O),
100.93 (s, OCH2O), 99.70 (s, OCH2O), 43.95 (s, ArCH2N), 36.85
(s, CHCH2), 36.51 (s, CHCH2), 36.31 (s, CHCH2), 32.02 (s,
CH2CH2CH3), 31.91 (s, CH2CH2CH3), 31.88 (s, CH2CH2CH3),
29.93 (s, CHCH2), 29.87 (s, CHCH2), 29.61 (s, CHCH2), 28.62 (s,
CH(CH3)2), 27.58 (s, CHCH2CH2), 27.56 (s, CHCH2CH2), 27.52
(s, CHCH2CH2), 24.62 (s, CH(CH3)2), 24.57 (s, CH(CH3)2), 23.92
(s, CH(CH3)2), 23.90 (s, CH(CH3)2), 22.68 (s, CH2CH3), 22.63 (s,
5,11-Bis(3-(2,4,6-trimethylphenyl)-1-imidazolylium)-methyl-
4(24),6(10),12(16),18(22)-tetra-methylenedioxy-2,8,14,20-tetra-
pentylresorcin[4]arene dibromide (8). Yield: 0.570 g, 99%. 1H
NMR (300 MHz, CDCl3): d = 9.94 (s, 2H, NCHN), 7.52 (s,
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CH2CH3), 14.09 (s, CH2CH3), 14.08 (s, CH2CH3). Anal. calcd. for
C84H106O8N4Br2·CHCl3 (Mr = 1459.57 + 119.38): C 64.66, H 6.83,
N 3.55%; found: C 64.78, H 6.62, N 3.37%. MS (ESI-TOF): m/z =
649.91 [M - Br2]2+ expected isotopic profile.
CH2CH3, 3J = 6.9 Hz); 13C NMR (75 MHz, CDCl3): d = 153.55,
140.92, 138.62 (3 s, arom. Cquat), 137.22 (s, NCHN), 134.33, 130.77
(2 s, arom. Cquat), 129.71 (s, arom. CH of Mes), 124.08, 123.15
(2 s, NCHCHN), 122.09 (s, arom. CH of resorcinarene), 120.62
(arom. Cquat), 101.05 (s, OCH2O), 43.86 (s, ArCH2N), 36.77 (s,
CHCH2), 31.72 (s, CH2CH2CH3), 29.65 (s, CHCH2), 27.35 (s,
CHCH2CH2), 22.56 (s, CH2CH3), 21.09 (s, CH3 para of Mes),
17.65 (s, CH3 ortho of Mes), 14.09 (s, CH2CH3). Anal. calcd. for
C104H124O8N8Br4·CHCl3 (Mr = 1933.76 + 119.38): C 61.42, H 6.14,
N 5.46%; found: C 61.39, H 6.34, N 5.57%. MS (ESI-TOF): m/z =
403.09 [M - Br4]4+ expected isotopic profiles.
5,11,17,23-Tetra(3-butyl-1-imidazolylium)-methyl-4(24),6(10),
12(16),18(22)-tetra-methylenedioxy-2,8,14,20-tetrapentylresorcin-
[4]arene tetrabromide (11). Yield: 0.652 g, 92%. 1H NMR
(300 MHz, CDCl3): d = 9.79 (s, 4H, NCHN), 7.54 (s, 4H,
NCHCHN), 7.26 (s, 4H, NCHCHN), 7.10 (s, 4H, arom. CH
of resorcinarene), 6.58 and 4.58 (AB spin system, 8H, OCH2O,
3
2J = 6.2 Hz), 5.45 (s, 8H, ArCH2N), 4.67 (t, 4H, CHCH2, J =
7.7 Hz), 4.33 (t, 8H, NCH2CH2, 3J = 6.9 Hz), 2.18–2.10 (m, 8H,
CHCH2), 1.87 (quint, 8H, NCH2CH2, J = 6.9 Hz), 1.40–1.24 (m,
32H, CH2CH2CH2CH3 of resorcinarene and CH2CH3 of NnBu),
5,11,17,23-Tetra(3-(2,6-diisopropylphenyl)-1-imidazolylium)-
methyl-4(24),6(10),12(16), 18(22)-tetra-methylenedioxy-2,8,14,20-
tetrapentylresorcin[4]arene tetrabromide (14). Yield: 0.813 g,
92%. 1H NMR (300 MHz, acetone-d6): d = 10.12 (s, 4H, NCHN),
8.44 (s, 4H, NCHCHN), 7.78 (s, 4H, NCHCHN), 7.78 (s, 4H,
3
0.91 (t, 12H, CH2CH3 of resorcinarene, J = 7.3 Hz), 0.84 (t,
12H, CH2CH3 of NnBu, 3J = 7.0 Hz);13C NMR (75 MHz, CDCl3,
25 ◦C): d = 153.58, 138.51 (arom. Cquat), 136.54 (s, NCHN), 122.34,
122.23 (2 s, NCHCHN), 121.59 (s, arom. CH of resorcinarene),
120.68 (arom. Cquat), 100.76 (s, OCH2O), 49.89 (s, NCH2CH2),
43.40 (s, ArCH2N), 36.84 (s, CHCH2), 32.11 (s, NCH2CH2),
31.95 (s, CH2CH2CH3 of resorcinarene), 29.80 (s, CHCH2), 27.46
(s, CHCH2CH2), 22.55 (s, CH2CH3 of resorcinarene), 19.46 (s,
CH2CH3 of NnBu), 14.09 (s, CH2CH3 of resorcinarene), 13.51 (s,
CH2CH3 of NnBu). Anal. calcd. for C84H116O8N8Br4·CHCl3 (Mr =
1685.48 + 119.38): C 56.56, H 6.53, N 6.20%; found: C 56.48,
H 6.32, N 6.27%. MS (ESI-TOF): m/z = 481.94 [M - Br3]3+ and
341.23 [M - Br4]4+ expected isotopic profiles.
i
arom. CH of resorcinarene), 7.67 (t, 4H, arom. CH of Pr2C6H3,
i
3
3J = 7.8 Hz), 7.40 (d, 8H, arom. Pr2C6H3, J = 7.8 Hz), 6.70
2
and 4.68 (AB spin system, 8H, OCH2O, J = 7.9 Hz), 5.88 (s,
8H, ArCH2N), 4.82 (t, 4H, CHCH2, 3J = 8.1 Hz), 2.85–2.77
(m, 8H, CHCH2), 2.44 (hept, 8H, CH(CH3)2, 3J = 6.6 Hz),
1.48–1.30 (m, 24H, CH2CH2CH2CH3), 1.12 (d, 48H, CH(CH3)2,
3J = 6.6 Hz), 0.89 (t, 12H, CH2CH3, J = 6.8 Hz); 13C NMR
3
(75 MHz, acetone-d6): d = 153.42, 145.63, 139.40 (3 s, arom. Cquat),
i
138.84 (s, NCHN), 131.52 (s, arom. CH of Pr2C6H3), 130.72
(arom. Cquat), 126.01, 124.61 (2 s, NCHCHN), 124.47 (s, arom.
i
CH of Pr2C6H3), 122.93 (s, arom. CH of resorcinarene), 120.65
(arom. Cquat), 101.60 (s, OCH2O), 43.94 (s, ArCH2N), 37.86 (s,
CHCH2), 31.46 (s, CH2CH2CH3), 29.93 (s, CHCH2), 28.29 (s,
CH(CH3)2), 27.77 (s, CHCH2CH2), 24.04 (s, CH(CH3)2), 23.16 (s,
CH(CH3)2), 22.58 (s, CH2CH3), 13.58 (s, CH2CH3). Anal. calcd.
for C116H148O8N8Br4·CHCl3 (Mr = 2102.08 + 119.38): C 63.26, H
6.76, N 5.04%; found: C 63.01, H 6.51, N 4.87%. MS (ESI-TOF):
m/z = 620.70 [M - Br3]3+ and 445.54 [M - Br4]4+ expected isotopic
profiles.
5,11,17,23-Tetra-(3-phenyl-1-imidazolylium)-methyl-4(24),
6(10),12(16),18(22)-tetra-methylenedioxy-2,8,14,20-tetrapen-
tylresorcin[4]arene tetrabromide (12). Yield: 0.723 g, 97%. 1H
NMR (300 MHz, DMSO): d = 10.13 (s, 4H, NCHN), 8.38 (s, 4H,
NCHCHN), 7.89 (s, 4H, NCHCHN), 7.87–7.84 (m, 12H, arom.
CH of NPh), 7.71–7.59 (m, 12H, arom. CH of resorcinarene and
NPh), 6.47 and 4.54 (AB spin system, 8H, OCH2O, 2J = 7.7 Hz),
5.42 (s, 8H, ArCH2N), 4.67 (t, 4H, CHCH, 3J = 7.7 Hz), 2.48–2.42
(m, 8H, CHCH2), 1.38–1.24 (m, 24H, CH2CH2CH2CH3), 0.82 (t,
Dibromido-5,11-bis{(3-diisopropyl-1-imidazol-2-idenyl-1-yl)-
methyl}-4(24),6(10),12(16),18(22)-tetramethylene-dioxy-2,8,14,
20-tetrapentylresorcin[4]arene disilver(I) (15). To a stirred solu-
tion of 9 (0.150 g, 0.12 mmol) in acetonitrile (30 mL) was added
Ag2O (0.028 g, 0.12 mmol). The solution was refluxed for 12 h.
The reaction mixture was allowed to reach room temperature
and was then filtered through a pad of Celite. The solvent was
removed under vacuum. The residue was washed with hexane
3
12H, CH2CH3, J = 7.0 Hz); 13C NMR (75 MHz, DMSO): d =
155.40, 139.06 (arom. Cquat), 135.85 (s, NCHN), 135.04 (arom.
Cquat), 130.59, 130.34 (2 s, arom. CH of NPh), 124.61 (s, arom.
CH of resorcinarene), 123.77 (s, NCHCHN), 122.55 (s, arom.
CH of NPh), 122.13 (s, NCHCHN), 120.81 (arom. Cquat), 100.36
(s, OCH2O), 43.37 (s, ArCH2N), 37.61 (s, CHCH2), 31.82 (s,
CH2CH2CH3), 29.63 (s, CHCH2), 27.72 (s, CHCH2CH2), 22.64
(s, CH2CH3), 14.37 (s, CH2CH3). Anal. calcd. for C92H100O8N8Br4
(Mr = 1765.44): C 62.59, H 5.71, N 6.35%; found: C 6.43, H 5.75, N
6.12%. MS (ESI-TOF): m/z = 1685.59 [M - Br]+ expected isotopic
profiles.
1
(2 ¥ 10 mL) to afford 15 as a white solid (0.161 g, 92%). H
NMR (300 MHz, CDCl3): d = 7.15 (s, 2H, CH of resorcinarene),
7.13 (d, 2H, NCHCHN, 3J = 1.6 Hz), 7.11 (s, 2H, CH of
3
resorcinarene), 6.90 (d, 2H, NCHCHN, J = 1.6 Hz), 6.53 (s,
2H, CH of resorcinarene), 6.52 and 4.57 (AB spin system, 2H,
OCH2O, 2J = 6.8 Hz), 6.05 and 4.46 (AB spin system, 4H,
OCH2O, 2J = 7.0 Hz), 5.76 and 4.43 (AB spin system, 2H, OCH2O,
2J = 7.1 Hz), 5.17 and 5.05 (AB spin system, 4H, ArCH2N,
5,11,17,23-Tetra(3-(2,4,6-trimethylphenyl)-1-imidazolylium)-
methyl-4(24),6(10),12(16), 18(22)-tetra-methylenedioxy-2,8,14,20-
tetrapentylresorcin[4]arene tetrabromide (13). Yield: 0.773 g,
1
3
95%. H NMR (300 MHz, CDCl3): d = 9.61 (s, 4H, NCHN),
2J = 13.8 Hz), 4.73 (2 overlapping t, 3H, CHCH2, J = 7.9 Hz),
7.51 (s, 4H, NCHCHN), 7.39 (s, 4H, NCHCHN), 7.21 (s, 4H,
arom. CH of resorcinarene), 6.91 (s, 8H, arom. CH of Mes), 6.51
and 4.63 (AB spin system, 8H, OCH2O, 2J = 7.3 Hz), 5.67 (s br, 8H,
4.71 (t, 1H, CHCH2, 3J = 7.7 Hz), 4.16–4.00 (m, 4H, NCH2CH2),
3
2.30–2.10 (m, 8H, CHCH2), 1.77 (quint, 4H, NCH2CH2, J =
7.5 Hz), 1.43–1.28 (m, 28H, CH2CH2CH2CH3 of resorcinarene
and CH2CH3 of NnBu), 0.93 (t, 12H, CH2CH3 of resorcinarene,
3J = 7.3 Hz), 0.90 (t, 6H, CH2CH3 of NnBu, 3J = 7.0 Hz); 13C NMR
(75 MHz, CDCl3): d = 181.42 (s, NCN), 155.10–121.84 (arom.
3
ArCH2N), 4.69 (t, 4H, CHCH2, J = 7.7 Hz), 2.29 (s, 12H, CH3
para of Mes), 2.25–2.13 (m, 8H, CHCH2), 1.98 (s, 24H, CH3 ortho
of Mes), 1.36–1.25 (m, 24H, CH2CH2CH2CH3), 0.84 (t, 12H,
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Cquat), 121.37, 121.17 (2 s, NCHCHN), 120.87, 120.43, 116.62 (3 s,
arom. CH of resorcinarene), 99.54 (s, OCH2O), 99.52 (s, OCH2O),
99.50 (s, OCH2O), 51.77 (s, NCH2CH2), 45.62 (s, ArCH2N),
36.92 (s, CHCH2), 36.73 (s, CHCH2), 36.40 (s, CHCH2), 33.50
(s, NCH2CH2), 32.06 (s, CH2CH2CH3 of resorcinarene), 32.03
(s, CH2CH2CH3 of resorcinarene), 32.01 (s, CH2CH2CH3 of
resorcinarene), 29.99 (s, CHCH2), 29.92 (s, CHCH2), 29.87 (s,
CHCH2), 27.60 (s, CHCH2CH2), 27.55 (s, CHCH2CH2), 27.52
(s, CHCH2CH2), 22.72 (s, CH2CH3 of resorcinarene), 22.68 (s,
CH2CH3 of resorcinarene), 22.64 (s, CH2CH3 of resorcinarene),
19.78 (s, CH2CH3 of NnBu), 14.11 (s, CH2CH3 of resorcinarene),
13.70 (s, CH2CH3 of NnBu). Anal. calcd. for C68H88Ag2O8N4Br2
(Mr = 1465.00) C 55.75, H 6.05, N 3.82%; found: C 55.62, H 5.87,
N 4.08%. MS (MALDI-TOF): m/z = 1385.28 [M - Br]+ expected
isotopic profile.
Acknowledgements
The French Agence Nationale de la Recherche is gratefully ac-
knowledged (ANR MATMALCAT). We thank Johnson Matthey
for a generous gift of palladium.
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˚
P21/c, a = 15.9979(3), b = 29.8312(5), c = 20.5629(5) A, b =
◦
3
-3
˚
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˚
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˚
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In a Schlenk tube under an inert atmosphere a solution of
[Pd(OAc)2] in DMF, a solution of the ligand in DMF, aryl bromide
(0.5 mmol), phenylboronic acid (0.122 g, 1.0 mmol), Cs2CO3
(0.326 g, 1.0 mmol), decane (0.05 mL, internal reference) and an
additional amount of DMF (so that the total reaction volume was
1.5 mL) were introduced. The reaction mixture was then heated
for 1 h at 100 ◦C. Thus, the 1 h reaction period included the period
of time needed for generating the active species. After cooling
to room temperature, a small amount (0.5 mL) of the resulting
solution was passed through a Millipore filter and analyzed by
GC.
382 | Org. Biomol. Chem., 2012, 10, 372–382
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The Royal Society of Chemistry 2012
©