Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips

Article abstract of DOI:10.1016/j.crci.2019.01.008

Three imidazolium salts having their two N-substituents equipped with remote calix[4]arenyl termini have been synthesised and converted into N-heterocyclic carbene (NHC) complexes of the type [PdCl₂(NHC)(pyridine)]. An X-ray diffraction study c

Full text of DOI:10.1016/j.crci.2019.01.008

C. R. Chimie xxx (xxxx) xxx
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ꢀ
Full paper/Memoire
Complexes featuring N-heterocyclic carbenes with bowl-
shaped wingtips
ꢁ
ꢀ ꢀ
ꢀ
ꢀ
ꢁ
Complexes de carbenes N-heterocycliques equipes de substituants a
ꢀ
ꢀ ꢀ
extremite receptrice
a
,
b
a
a
a
Hamze Almallah , Melodie Nos , Virgile Ayzac , Eric Brenner , **,
ꢀ
ꢀ
,
Dominique Matt a *, Christophe Gourlaouen c, Mohamad Jahjah b,
Akram Hijazi b
a
ꢀ
ꢀ
Universite de Strasbourg, Institut de chimie, UMR 7177 CNRS, Laboratoire de chimie inorganique moleculaire et catalyse, 4, rue Blaise-
Pascal, 67070 Strasbourg cedex, France
b Inorganic and Organometallic Coordination Chemistry Laboratory, Faculty of Sciences, Lebanese University, R. Hariri University
Campus, Beyrouth, Hadath, Lebanon
c
ꢀ
Universite de Strasbourg, Institut de chimie, UMR 7177 CNRS, Laboratoire de chimie quantique, 4, rue Blaise-Pascal, 67070 Strasbourg
cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Three imidazolium salts having their two N-substituents equipped with remote calix[4]
arenyl termini have been synthesised and converted into N-heterocyclic carbene (NHC)
complexes of the type [PdCl2(NHC)(pyridine)]. An X-ray diffraction study carried out for
one of the complexes, namely, trans-[1,3-bis(4-{25,26,27,28-tetrapropyloxycalix[4]aren-5-
yl}phenyl)imidazol-2-ylidene](pyridine)palladium(II) dichloride, revealed that in the solid
state the complex crystallises as a self-assembled dimer, its components being held
together by dispersion forces involving the polyphenoxy units, the pyridine ligands and
phenylene rings. This structure provides a new example of the diversity of interactions that
may occur in NHC complexes of catalytic relevance, which are thus not limited to intra-
molecular ones. There was no spectroscopic indication that such interactions also occur in
solution.
Received 11 December 2018
Accepted 24 January 2019
Available online xxxx
Keywords:
N-heterocyclic carbenes
Calixarenes
SuzukieMiyaura cross coupling
Palladium
© 2019 Académie des sciences. Published by Elsevier Masson SAS. This is an open access
article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/
).
r é s u m é
ꢀ
ꢀ
Trois sels d'imidazolium ayant leurs atomes d'azote substitues par des groupes arylcalixarenyle
ꢀ ꢀ
ꢀ
ꢀ
ꢀ
ꢁ
ont ete prepares et utilises pour la synthese de complexes de type [PdCl2(NHC)(pyridine)] (NHC
ꢀ ꢀ
ꢀ
Mots-cles:
ꢁ
¼ carbene N-heterocyclique). L'analyse par diffraction des rayons X du complexe trans-
ꢁ
ꢀ ꢀ
Carbenes N-heterocycliques
ꢀ
ꢁ
ꢀ
ꢁ
[1,3-bis(4-{25,26,27,28-tetrapropyloxycalix [4]aren-5-yl}phenyl)imidazol-2-ylidene](pyridine)
ꢁ
Calixarenes
* Corresponding author.
** Corresponding author.
E-mail addresses: eric.brenner@unistra.fr (E. Brenner), dmatt@unistra.fr (D. Matt).
https://doi.org/10.1016/j.crci.2019.01.008
1631-0748/© 2019 Académie des sciences. Published by Elsevier Masson SAS. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
Rendus Chimie, https://doi.org/10.1016/j.crci.2019.01.008

2
H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
ꢀ
ꢀ ꢁ
ꢁ
ꢁ
ꢀ
ꢀ
Couplage croise de SuzukieMiyaura
dichloropalladium(II) revele, de maniere inattendue, qu'a l'etat solide ce compose s'auto-
ꢁ
Palladium
assemble en formant un dimere dont les composantes sont maintenues ensemble par un jeu de
ꢀ
ꢀ
ꢀ
ꢁ
forces faibles impliquant des unites phenoxy, les coordinats pyridine et les noyaux phenylene.
ꢀ
ꢀ
ꢁ
Cette structure constitue un nouvel exemple de la complexite des phenomenes pouvant
ꢁ
ꢀ
ꢁ
ꢀ ꢀ
contribuer a influencer l'environnement sterique de complexes de carbenes N-heterocycliques
ꢀ ^
d'interet catalytique.
© 2019 Académie des sciences. Published by Elsevier Masson SAS. This is an open access
article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
volume parameter does not integrate steric effects due to
possible self-assembly phenomena.
Steric effects play a central role in the chemistry of N-
heterocyclic carbenes (NHCs) [1] and are largely controlled
by the size and shape of the substituents of their nitrogen
atoms [2e8]. Thus, bulky N-substituents provide kinetic
stabilisation of free NHCs with respect to dimerisation
[9,10]; when bound to a metal, they may both increase
complex stability and assist specific steps in catalytic re-
actions [11]. Typically, bulky NHCs such as IMes, IPr, IPent
or IPr* (Fig. 1) display a hemiovoidal umbrella shape,
thereby contrasting with the conical encumbrance brought
about by bulky tertiary phosphines. The most useful
parameter for the measure of their steric properties is the
so-called “buried volume” (%VBur), which expresses the
percentage of volume occupied by the ligand within the
first coordination sphere of the metal [12]. Actually, this
parameter is only helpful for the rough prediction of steric
effects; however, it does not enable prediction of regiose-
lectivities of catalytic reactions. These latter essentially
depend on subtle interactions in the catalytic process be-
tween specific locations of the ligand and coordinated
substrates. In this regard, it is useful to remind that a
number of NHCs (notably the IBiox ligands, see Fig. 1)
display in their complexes the flexible steric bulk [13], a
feature enabling these ligands to adapt to the steric re-
quirements of intermediates of catalytic cycles and conse-
quently improve the catalyst's performance. Thus, the value
expressing the %VBur of a NHC may vary during a catalytic
cycle. Finally, it should also be mentioned that the buried
As part of a programme aimed at the development of
NHCs displaying contours that delineate sterically
a
embracing environment, we have prepared the NHC pre-
cursors 1e3, both characterised by the presence of cavity-
shaped calixarene termini in their wingtips. We
wondered whether in NHC complexes derived from them,
the two bowl-shaped units could influence ligands of the
first coordination sphere. It is noteworthy that to date
double calixarenes [14e16] having the macrocyclic units
separated by an NHC spacer have not been documented
(see Fig. 2).
2. Results and discussion
The imidazolium salts 1e3 were each prepared in a
multistep sequence (Schemes 1 and 2) starting from bro-
mocalixarene 4. Only the synthesis of 1 is discussed here-
after. Full description of the preparations of 2 and 3, which
are basicallysimilartothatof1, isgiveninSection 4. Thus, the
preparation of 1 began with the synthesis of intermediate 5,
which was obtained from 4 by Br/Li exchange, followed by
reaction with B(OMe)3 and subsequent treatment with HCl
(Scheme 1). The boronic acid 5, which was used in its crude
form, was then reacted with tert-butyl N-(4-bromo-2,6-
dimethylphenyl)carbamate
under
SuzukieMiyaura
coupling conditions, affording the N-protected aniline 6.
Deprotection of the latter with CF3CO2H in dichloromethane
gave the primary amine 7.
Fig. 1. Conventional bulky NHCs.
Fig. 2. Imidazolium salts synthesised in the present study.
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
3
Scheme 1. Stepwise synthesis of arylamine 7.
In the next step (Scheme 2), a solution of glyoxal,
formaldehyde, acetic acid and ZnCl2 was heated at 60 ꢀC for
5 min, and then added to a mixture heated at 60 ꢀC of
amine 7, MgSO4 and AcOH. After 0.5 h, dichloromethane
was added to get a homogeneous solution. Treatment with
HCl followed by addition of NH4BF4 in excess gave imida-
zolium salt 1.
of the other two salts (
three compounds, the observed AB patterns (with J values
ranging from 13.2 to 13.5 Hz) are characterised by the
separation of the methylenic signals (1.22
1.34 ppm) typical of that of calix[4]arenes in the cone
conformation [19,20]. As expected, the BF4 anions appear
in the corresponding 19F NMR spectra as two broad peaks
with relative intensities of 1:4 (separation ca. 0.05 ppm),
this pattern being caused by the two boron isotopes, 10B
and 11B [21].
d
¼ 9.26 (2),
d
¼ 9.26 (3)). For all
< Dd <
The 1H NMR spectrum of each salt shows an imidazo-
lium NCHN signal appearing in the usual range [17,18], and
that of 1 being slightly less deshielded (
d
¼ 8.46) than that
Compounds 1e3 were converted into the Pd complexes
8e10 by their reaction with [PdCl2] in pyridine in the
presence of K2CO3 (Scheme 3). All three complexes were
purified by column chromꢀatography. The reaction leading
to 8 was carried out at 80 C, affording the product in 82%
yield. Those resulting in 9 and 10 required to be done at
room temperature to avoid product decomposition, this
presumably because of facile cyclometalation. Under these
conditions, 9 and 10 were obtained in, respectively, 60% and
68% yield.
The 1H and 13C{1H} NMR spectra of the three carbene
complexes present no anomalies. Thus, all 1H NMR spectra
show the presence of one NHC ring, one pyridine ligand
and two equivalent calixarene units. The carbene carbons
are observed at, respectively, 153.12 (8), 150.77 (9) and
151.53 (10) ppm in the 13C NMR spectra, these values being
close to those observed for related [PdCl2(NHC)(pyridine)]
complexes based on an imidazolylidene [22].
The crystal structure of complex 9 was determined by a
single-crystal X-ray diffraction study (Fig. 3). Crystal and
data collection are detailed in Section 4. The unit cell con-
sists of two pairs of self-assembled molecules of 9, this
considerably increases crowding about the palladium
atoms. The individual molecules of each dimer (denoted as
a
and b) present similar structural features. Thus, in both
molecules the palladium atom lies in a slightly distorted
square planar ligand environment (nonstrictly linear
ClePdeCl arrangements, see Table 1) with PdeCcarb
(1.946(3) Å in
2.099(3) Å in
a
; 1.954(3) Å in
b
), PdeN (2.135(3) Å in
a
a
;
;
Scheme 2. Multicomponent synthesis of imidazolium salt 1.
b) and PdeCl (2.312(1), 2.309(1) Å in
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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4
H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
Scheme 3. Syntheses of complexes 8e10.
2.310(1), 2.312(1) Å in
b
) bond lengths similar to those
pyridine ligand close to two calixarene phenoxy rings as
found in related molecules.
well as to the pyridine moiety of the partner molecule. As
could be inferred from the noncovalent interaction (NCI)
analysis of the density functional theory (DFT)-optimised
structure, the two components of the dimer are held
together by a network of attractive dispersion forces
(Fig. 4). For example, each pyridine ligand is wrapped in a
van der Waals surface involving interactions between the
All calixarene units adopt a typical pinched cone
conformation with interplanar angles between the facing
phenoxy rings of 11.8ꢀ/79.1ꢀ and 23.4ꢀ/69.2ꢀ in
a
and 20.8ꢀ/
72.6ꢀ and 22.0ꢀ/78.5ꢀ in
b. It is interesting that the two
phenoxy rings linked to the central NHC unit of each
molecule are different in nature, one belonging to the
pinched part of the corresponding calixarene moiety and
the other to the flared part of the second calixarene end.
Also noteworthy is the short separation between the o-
phenylene protons and the metal centre (shortest separa-
pyridine ligand (p stacking), a phenylene unit and a phe-
noxy(calix) ring of the partner molecule. Van der Waals
interactions also exist between one phenoxy ring of each
tions 2.79(1) and 3.08(1) Å in
suggesting that the phenylene units are prone to undergo
cyclometalation (vide supra).
a
; 2.73(1) and 2.84(1) Å in
b
),
Table 1
Selected distances (Å) and angles (ꢀ) in complex 9.
Distances
Examination of the solid state structure further reveals
that the bulky calixarene moieties themselves are not
responsible for the steric encumbrance created around the
metal atoms, the observed crowding resulting in fact from
the self-assembly phenomenon, which brings each
Molecule
C1ePd1
Pd1eN3
Molecule
C149ePd2
Pd2eN6
Angles
a
1.946(3)
2.135(3)
Pd1eCl1
Pd1eCl2
2.312(1)
2.309(1)
b
1.954(3)
2.099(3)
Pd2eCl3
Pd2eCl4
2.310(1)
2.312(1)
Molecule
a
C49ePd1eN3
C49ePd1eCl2
C49ePd1eCl1
179.13(11) N3ePd1eCl2
93.38(9)
94.40(9)
172.20(4)
86.37(10)
85.84(10)
N3ePd1eCl1
Cl2ePd1eCl1
Molecule
b
C149ePd2eN6
C149ePd2eCl3
C149ePd2eCl4
Interplanar angles
178.56(12) N6ePd2eCl3
92.79(10)
92.76(10)
174.24(3)
86.36(10)
92.96(10)
N6ePd2eCl4
Cl3ePd2eCl4
Molecule
a
Metal plane/pyridine plane 16.3(1)
Metal plane/
carbene ring
81.7(1)
Carbene plane/N-aryl
36.2(1)
Carbene plane/ 36.2(1)
plane 1
N-aryl plane 2
Molecule
b
Metal plane/pyridine plane 32.9(1)
Metal plane/
carbene ring
32.9(1)
Carbene plane/N-aryl
plane 1
48.2(1)
Carbene plane/ 39.2(1)
N-aryl plane 2
Fig. 3. Molecular structure of complex 9. Solvent molecules have been
omitted for clarity.
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
5
thereby rendering the metal more difficult of access.
However, one has to be careful in interpreting our findings,
as other phenomena may occur in a differentiated way for
the two complexes, notably the formation of nanoparticles.
3. Conclusions
We have synthesised the first double calixarenes having
their macrocyclic units linked through a symmetrically
substituted NHC spacer. The structural study of the
[PdCl2(NHC)(pyridine)] complex 9 unexpectedly revealed
how the presence of the calixarene termini may assist
dimer formation in the solid state, thereby considerably
increasing the steric crowding about the metal centres.
Consistent with a possible competitive aggregation phe-
nomenon of this type in solution, the performance of 8 in a
Suzuki cross-coupling reaction was lower than that
observed for a related, cavity-devoid analogue. Overall, the
present study provides a new example of the difficulty in
predicting steric effects in NHC complexes.
Fig. 4. NCIs in complex 9-dimer (optimised structure), with electrostatic in-
teractionsin blue, attractive dispersion forces in green and steric repulsions in red.
calixarene end and a specific phenylene-phenoxy fragment
of the other molecule. However, these steric interactions
could not be identified in solution (absence of cross-peaks
in the corresponding ROESY spectrum).
4. Experimental section
Wondering whether the ability of Pd complexes of type
9 to self-assemble would influence their catalytic proper-
ties, we examined the behaviour of complex 8 in the cross-
coupling of phenylboronic acid with 4-chlorotoluene at
80 ꢀC (Scheme 4). Complexes 9 and 10 were not considered
as appropriate for catalytic runs, as these readily under-
went decomposition when heated. Catalysis was carried
out in ethanol using 1 mol % of 8 in the presence of K2CO3
(1.5 equiv/mol of 4-chlorotoluene). After 1 h of reaction
time, 4-phenyltoluene was formed in 55% yield. Under
identical conditions, the related complex [PdCl2(IMes)(-
pyridine)] (11) [23], an analogue which is devoid of calix-
arene ends, resulted in 77% yield. Because carbene ligands
of 8 and 11 possess quite similar electronic properties
4.1. General procedures
The syntheses were performed in Schlenk-type flasks
under dry nitrogen. Solvents were dried by conventional
methods and distilled immediately before use. Routine 1H
and 13C{1H} NMR spectra were recorded using FT Bruker
Avance 500, 400 or 300 instruments at 25 ꢀC. 1H NMR
spectral data were referenced to residual protonated sol-
vent (CHCl3,
d
7.26); 13C chemical shifts are reported rela-
tive to deuterated solvent (CDCl3,
d
77.16). The 19F NMR
spectra of 1e3 were recorded using a FT Bruker Avance 300
apparatus (external reference CFCl3). In the NMR data given
hereafter, Cq denotes a quaternary carbon atom. The
bridging CH2 groups of the calixarene backbone are desig-
nated by the abbreviation ArCH2Ar. For column chroma-
tography, Geduran SI (E. Merck, 0.040e0.063 mm) silica
was used. Routine thin-layer chromatography analyses
were carried out using plates coated with Merck Kieselgel
60 GF254. Elemental analyses were performed by the
(d(Ccarb) ¼ 153.1 (8); 152.9 (11) ppm), one would have ex-
pected that the bulkier carbene ligand of 8 would facilitate
the reductive elimination step and thus result in a higher
catalytic activity. As the reverse is the case, it appears likely
that at least a fraction of the catalytic species self-assemble
in a manner similar to that observed for 9 in the solid state,
Scheme 4. SuzukieMiyaura cross-coupling reaction with 8 and 11.
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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6
H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
Service de Microanalyse, Institut de Chimie (Unistra-CNRS),
Strasbourg. X-ray diffraction analysis of complex 9 was
performed by the Service de Radiocrystallographie, Institut
de Chimie de Strasbourg. tert-Butyl N-(4-bromo-2,6-
dimethylphenyl)carbamate, tert-butyl N-(4-iodophenyl)
carbamate and tert-butyl N-(3-bromophenyl)carbamate
were obtained according to the procedure reported for a
related compound [24] (vide infra). The procedure for the
preparation of the symmetrical imidazolium salts 1e3 was
inspired by that applied by Tarrieu et al. [25] for the
synthesis of unsymmetrically substituted imidazolium salts.
The structural formula of the N-protected compounds 60
and 600, both related to calixarene 6 and the amines 70 and
700, analogues of 7, are given in the Supplementary data. 5-
Bromo-25,26,27,28-tetrapropyloxycalix[4]arene 4 [26] and
[PdCl2(IMes)(pyridine)] (11) [23] were synthesised ac-
cording to the published methods. In the following “Py”
stands for pyridine.
4.46 mmol) in THF (50 mL) at ꢁ78 ꢀC. After 40 min,
B(OMe)3 (1.00 mL, 0.92 g, 8.95 mmol) was added dropwise
to the solution. After stirring for 1 h at room temperature,
the solution was quenched with aq HCl (1 M, 100 mL) and
the product extracted with CH2Cl2 (3 ꢂ 100 mL). The
combined organic layers were dried over MgSO4. The sol-
vent was removed in vacuum yielding the crude boronic
acid 5 as a white powder, which was used without further
purification. tert-Butyl (4-bromo-2,6-dimethylphenyl)
carbamate (1.34 g, 4.46 mmol), boronic acid 5, K2CO3
(0.92 g, 6.69 mmol) and [PdCl2(IMes)(pyridine)] (0.125 g,
0.222 mmol) were introduced in a Schlenk flask containing
absolute EtOH (50 mL). The mixture was stirred at 80 ꢀC for
24 h. After cooling to room temperature the mixture was
passed through Celite and the filtrate evaporated to dry-
ness. The crude product was purified by flash chromatog-
raphy (SiO2; AcOEt/petroleum ether, 7:93; Rf ¼ 0.28) to
afford 6 as a white solid (2.18 g, 60%). 1H NMR (CDCl3,
400 MHz), d 6.98 (2H, s, ArH), 6.85e6.63 (8H, m, ArH), 6.56
4.1.1. tert-Butyl N-(4-bromo-2,6-dimethylphenyl)carbamate
Boc2O (4.40 g, 20.0 mmol) was added to a solution of 4-
bromo-2,6-dimethylaniline (4.00 g, 20.0 mmol) in THF
(20 mL). The resulting mixture was stirred for 18 h at 65 ꢀC.
The solvent was removed in vacuo and the resulting res-
idue was recrystallised from CH2Cl2/petroleum ether
affording the aryl carbamate as a white solid (4.12 g, 69%).
The product did not require further purification. 1H NMR
(2H, d, 3J ¼ 7.3 Hz, ArH), 6.40 (1H, t, 3J ¼ 7.3 Hz, ArH), 5.92
(1H, br s, NH), 4.55 and 3.26 (4H, d, AB spin system, 2JAB
¼
13.4 Hz, ArCH2Ar), 4.53 and 3.21 (4H, d, AB spin system, 2JAB
¼ 13.4 Hz, ArCH2Ar), 4.01e3.83 (8H, m, OCH2), 2.32 (6H, s,
o-CH3), 2.07e1.92 (8H, m, CH2CH3), 1.56 (9H, br s, C(CH3)3),
1.13e1.01 (12H, m, CH2CH3) ppm. Because of the dynamic
conformation of the carbamate group, some 1H NMR peaks
were very broad. 13C{1H} NMR (CDCl3, 125 MHz),
d 156.83
(400 MHz, CDCl3),
(6H, s, 2CH3), 1.48 (9H, s, C(CH3)3). NMR spectroscopic data
are consistent with those of the literature [27].
d
7.19 (2H, s, ArH), 5.83 (1H, s, NH), 2.22
(2 ꢂ arom. CqeO), 156.36 (arom. CqeO), 156.06 (arom.
CqeO), 153.83 (NHCO), 140.42 (arom. CqeN), 135.50 (arom.
Cq),135.35 (arom. Cq),135.34 (arom. Cq),134.95 (arom. Cq),
134.82 (arom. Cq),132.33 (arom. Cq),128.41 (2 ꢂ arom. CH),
127.99 (arom. CH), 127.09 (arom. CH), 126.97 (arom. CH),
122.04 (2 ꢂ arom. CH), 79.84 (C(CH3)3), 76.88 (OCH2), 76.77
(3 ꢂ OCH2), 31.18 (ArCH2Ar), 31.07 (ArCH2Ar), 28.42 (CH3)3,
23.43 (CH2CH3), 23.40 (CH2CH3), 23.31 (2 ꢂCH2CH3), 18.61
(o-CH3) 10.53 (CH2CH3), 10.37 (CH2CH3) ppm. Found C,
77.89; H, 8.05; N,1.82. Calcd for C53H65NO6 (Mr ¼ 811.48): C,
78.38; H, 8.07; N, 1.73%. Despite several recrystallisations,
elemental C-analyses remained unsatisfactory.
4.1.2. tert-Butyl N-(4-iodophenyl)carbamate
Boc2O (5.00 g, 22.9 mmol) was added to a solution of 4-
iodoaniline (5.00 g, 22.8 mmol) in THF (20 mL). The
resulting mixture was stirred for 18 h at 65 ꢀC. Then the
solvent was removed in vacuo and the resulting residue
was recrystallised from CH2Cl2/petroleum ether affording
the aryl carbamate as a white solid (5.11 g, 70%). The
product did not require further purification. 1H NMR
(500 MHz, CDCl3),
d
7.55 (2H, d, 3J ¼ 8.5 Hz, ArH), 7.14 (2H,
d, 3J ¼ 8.5 Hz, ArH), 6.62 (1H, s, NH), 1.49 (9H, s, CH3). NMR
spectroscopic data are consistent with those of the litera-
ture [28].
4.1.5. 5-(4-tert-Butyloxycarbonylaminophenyl)-25,26,27,28-
tetrapropyloxycalix[4]arene (60)
A
1.5 M solution of n-BuLi in hexanes (6.2 mL,
9.80 mmol) was added dropwise to a solution of 5-bromo-
25,26,27,28-tetrapropyloxycalix[4]arene (4) (6.00 g,
8.93 mmol) in THF (120 mL) at ꢁ78 ꢀC. After 40 min,
B(OMe)3 (2.00 mL, 1.84 g, 17.9 mmol) was added dropwise
to the solution. After stirring for 1 h at room temperature,
the solution was quenched with aq HCl (1 M, 240 mL) and
the product extracted with CH2Cl2 (3 ꢂ 100 mL). The
combined organic layers were dried over MgSO4. The sol-
vent was removed in vacuum yielding the crude boronic
acid 5 as a white powder, which was used without further
purification. tert-Butyl (4-iodophenyl)carbamate (2.85 g,
8.93 mmol), crude boronic acid 5, K2CO3 (1.85 g,
13.39 mmol) and [PdCl2(IMes)(pyridine)] (0.250 g,
0.445 mmol) were introduced in a Schlenk flask containing
absolute EtOH (50 mL). The mixture was then stirred at
80 ꢀC for 24 h. After cooling to room temperature the so-
lution was passed through Celite and the filtrate evapo-
rated under reduced pressure. The residue was purified by
4.1.3. tert-Butyl N-(3-bromophenyl)carbamate
Boc2O (10.00 g, 58.1 mmol) was added to a solution of 3-
bromoaniline (12.70 g, 58.1 mmol) in THF (40 mL). The
resulting mixture was stirred for 18 h at 65 ꢀC. Then the
solvent was removed in vacuo and the resulting residue
was recrystallised from CH2Cl2/petroleum ether affording
the aryl carbamate as a white solid (10.30 g, 65%). The
product did not require further purification. 1H NMR
(300 MHz, CDCl3),
d 7.66 (1H, s, ArH), 7.23e7.08 (3H, m,
ArH), 6.47 (1H, s, NH), 1.51 (9H, s, CH3). NMR spectroscopic
data are consistent with those of the literature [29].
4.1.4. 5-(3,5-Dimethyl-4-tert-butyloxycarbonylaminophenyl)-
25,26,27,28-tetrapropyloxycalix[4]arene (6)
A
1.5 M solution of n-BuLi in hexanes (3.1 mL,
4.90 mmol) was added dropwise to a solution of 5-bromo-
25,26,27,28-tetrapropyloxycalix[4]arene (4) (3.00 g,
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
7
flash chromatography (SiO2; CH2Cl2/petroleum ether,
40:60; Rf ¼ 0.33) to afford 60 as a white solid (4.58 g, 65%).
128.07 (arom. CH), 126.94 (arom. CH), 122.08 (2 ꢂ arom.
CH), 121.92 (arom. CH), 117.21 (arom. CH), 116.58 (arom.
CH), 80.53 (C(CH3)3), 76.89 (OCH2), 76.80 (3 ꢂ OCH2), 31.28
(ArCH2Ar), 31.10 (ArCH2Ar), 28.49 ((CH3)3), 23.44 (CH2CH3),
23.41 (CH2CH3), 23.35 (2 ꢂ CH2CH3), 10.54 (CH2CH3), 10.42
(CH2CH3) ppm. Found C, 77.92; H, 7.82; N, 1.98. Calcd for
1H NMR (CDCl3, 500 MHz),
d
7.39 (2H, d, 3J ¼ 8.5 Hz, ArH),
7.25 (2H, d, 3J ¼ 8.5 Hz, ArH), 6.93e6.83 (4H, m, ArH), 6.78
(2H, dd, 3J ¼ 3J’ ¼7.4 Hz, ArH), 6.73 (2H, s, ArH), 6.64 (1H, s,
NH), 6.50 (2H, d, 3J ¼ 7.4 Hz, ArH), 6.33 (1H, t, 3J ¼ 7.4 Hz,
ArH), 4.59 and 3.29 (4H, d, AB spin system, 2JAB ¼ 13.5 Hz,
C
51H61NO6 (Mr ¼ 784.05): C, 78.13; H, 7.84; N, 1.79%.
2
ArCH2Ar), 4.57 and 3.25 (4H, d, AB spin system, JAB
¼
13.5 Hz, ArCH2Ar), 4.07e3.98 (4H, m, OCH2), 3.97e3.86 (4H,
m, OCH2), 2.13e1.95 (8H, m, CH2CH3), 1.62 (9H, s, C(CH3)3),
1.19e1.04 (12H, m, CH2CH3) ppm. 13C{1H} NMR (CDCl3,
4.1.7. 5-(4-Amino-3,5-dimethylphenyl)-25,26,27,28-
tetrapropyloxycalix[4]arene (7)
Trifluoroacetic acid (1.82 g, 15.9 mmol) was added
dropwise to a stirred solution of calix[4]arene 6 (1.00 g,
1.23 mmol) in CH2Cl2 (12 mL) cooled at 0 ꢀC. After 15 min,
the reaction mixture was allowed to reach room tempera-
ture and stirred for a further 2 h. The mixture was washed
with an aqueous solution of K2CO3 (20%, 150 mL) and the
two phases were separated. The aqueous phase was treated
with dichloromethane (2 ꢂ 100 mL) and the organic phases
were then combined. The solvent was removed under
reduced pressure to afford 7 as a beige solid (0.816 g, 93%),
which did not need further purification. 1H NMR (CDCl3,
125 MHz),
d
157.07 (2 ꢂ arom. CqeO), 156.17 (arom. CqeO),
155.79 (arom. CqeO), 152.91 (NHCO), 136.70 (arom. CqeN),
136.45 (arom. Cq), 135.79 (arom. Cq), 135.60 (arom. Cq),
134.86 (arom. Cq), 134.56 (arom. Cq), 134.23 (arom. Cq),
128.51 (arom. CH), 128.49 (arom. CH), 127.83 (arom. CH),
127.34 (arom. CH), 126.42 (arom. CH), 122.10 (arom. CH),
121.99 (arom. CH), 118.57 (arom. CH), 80.46 (C(CH3)3), 76.86
(OCH2), 76.73 (OCH2), 76.71 (2 ꢂ OCH2), 31.19 (ArCH2Ar),
31.07 (ArCH2Ar), 28.42 (C(CH3)3), 23.43 (CH2CH3), 23.26
(CH2CH3), 10.58 (CH2CH3), 10.28 (CH2CH3) ppm. Found C,
77.97; H, 7.99; N,1.66. Calcd for C51H61NO6 (Mr ¼ 784.05): C,
78.13; H, 7.84; N, 1.79%.
500 MHz), d 6.98 (2H, s, ArH), 6.84 (2H, s, ArH), 6.67 (4H, d,
3J ¼ 7.4 Hz, ArH), 6.63e6.55 (4H, m, ArH), 6.53 (1H, t, 3J ¼
2
7.4 Hz, ArH), 4.53 and 3.24 (4H, d, AB spin system, JAB
¼
4.1.6. 5-(3-tert-Butyloxycarbonylaminophenyl)-25,26,27,28-
tetrapropyloxycalix[4]arene (600)
13.3 Hz, ArCH2Ar), 4.51 and 3.20 (4H, d, AB spin system, 2JAB
¼ 13.3 Hz, ArCH2Ar), 3.98e3.85 (8H, m, OCH2), 3.50 (2H, br
s, NH2), 2.26 (6H, s, o-CH3), 2.06e1.92 (8H, m, CH2CH3),
1.11e0.99 (12H, m, CH2CH3) ppm. 13C{1H} NMR (CDCl3,
A
1.5 M solution of n-BuLi in hexanes (6.2 mL,
9.80 mmol) was added dropwise to a solution of 5-bromo-
25,26,27,28-tetrapropyloxycalix[4]arene (4) (6.00 g,
8.93 mmol) in THF (120 mL) at ꢁ78 ꢀC. After 40 min,
B(OMe)3 (2.00 mL, 1.84 g, 17.9 mmol) was added dropwise
to the solution. After stirring for 1 h at room temperature,
the solution was quenched with aq HCl (1 M, 240 mL) and
the product extracted with CH2Cl2 (3 ꢂ 100 mL). The
combined organic layers were dried over MgSO4. The sol-
vent was removed in vacuum yielding the crude boronic
acid 5 as a white powder, which was used without further
purification. tert-Butyl (3-bromophenyl)carbamate (2.43 g,
8.93 mmol), boronic acid 5, K2CO3 (1.850 g, 13.39 mmol)
and [PdCl2(IMes)(pyridine)] (0.250 g, 0.445 mmol) were
introduced in a Schlenk flask containing absolute EtOH
(50 mL). The mixture was stirred at 80 ꢀC for 24 h. After
cooling to room temperature the mixture was passed
through Celite and the filtrate evaporated to dryness. The
crude product was purified by flash chromatography (SiO2;
CH2Cl2/petroleum ether, 40:60; Rf ¼ 0.27) to afford 600 as a
white solid (4.55 g, 65%). 1H NMR (CDCl3, 500 MHz),
125 MHz),
d
156.76 (arom. CqeO),156.54 (2 ꢂ arom. CqeO),
155.69 (arom. CqeO), 141.41 (arom. CqeN), 135.38 (arom.
Cq), 135.27 (arom. Cq), 135.03 (3 ꢂ arom. Cq), 131.89 (arom.
Cq), 128.30 (arom. CH), 128.21 (arom. CH), 128.13 (arom.
CH), 127.12 (arom. CH), 126.62 (arom. CH), 122.00 (2 ꢂ
arom. CH), 121.76 (arom. Cq), 76.81 (3 ꢂ OCH2), 76.72
(OCH2), 31.22 (ArCH2Ar), 31.10 (ArCH2Ar), 23.39 (3
ꢂCH2CH3), 23.35 (CH2CH3), 17.92 (o-CH3), 10.51 (2 ꢂ
CH2CH3), 10.44 (CH2CH3), 10.43 (CH2CH3) ppm. Found C,
80.69; H, 8.11; N, 2.09. Calcd for C48H57NO4 (Mr ¼ 711.99): C,
80.97; H, 8.07; N, 1.97%.
4.1.8. 5-(4-Aminophenyl)-25,26,27,28-tetrapropyloxycalix[4]
arene (70)
Trifluoroacetic acid (4.20 g, 36.8 mmol) was added
dropwise to a stirred solution of calix[4]arene 60 (2.17 g,
2.77 mmol) in CH2Cl2 (20 mL) cooled at 0 ꢀC. After 15 min,
the reaction mixture was allowed to reach room tempera-
ture and stirred for a further 2 h. The mixture was washed
with an aqueous solution of K2CO3 (20%, 100 mL) and the
two phases were separated. The aqueous phase was treated
with dichloromethane (2 ꢂ 100 mL) and the organic phases
were then combined. The solvent was removed under
reduced pressure to afford 70 as a white solid (1.66 g, 88%),
which did not need further purification. 1H NMR (CDCl3,
d
7.38e7.30 (1H, m, ArH), 7.27 (1H, dd, 3J ¼ 3J’ ¼ 7.6 Hz,
ArH), 7.23 (1H, s, ArH), 6.94 (2H, d, 3J ¼ 7.6 Hz, ArH), 6.77
(2H, s, ArH), 6.74e6.67 (4H, m, ArH), 6.64 (2H, dd, 3J ¼ 3J’ ¼
7.5 Hz, ArH), 6.53 (2H, d, 3J ¼ 7.5 Hz, ArH), 6.50 (1H, s, NH),
6.37 (1H, t, 3J ¼ 7.5 Hz, ArH), 4.51 and 3.22 (4H, d, AB spin
2
system, JAB ¼ 13.3 Hz, ArCH2Ar), 4.48 and 3.17 (4H, d, AB
2
spin system, JAB ¼ 13.3 Hz, ArCH2Ar), 3.95e3.81 (8H, m,
500 MHz),
d
7.16 (2H, d, 3J ¼ 8.3 Hz, ArH), 6.80 (2H, d, 3J ¼
OCH2), 2.03e1.88 (8H, m, CH2CH3), 1.55 (9H, s, C(CH3)3),
1.08e0.97 (12H, m, CH2CH3) ppm. 13C{1H} NMR (CDCl3,
7.5 Hz, ArH), 6.76 (2H, s, ArH), 6.75 (2H, d, 3J ¼ 8.3 Hz, ArH),
6.72e6.66 (4H, m, ArH), 6.55 (2H, d, 3J ¼ 7.5 Hz, ArH), 6.41
(1H, t, 3J ¼ 7.5 Hz, ArH), 4.55 and 3.26 (4H, d, AB spin sys-
tem, 2JAB ¼ 13.4 Hz, ArCH2Ar), 4.54 and 3.22 (4H, d, AB spin
125 MHz),
d
156.82 (2 ꢂ arom. CqeO),156.49 (arom. CqeO),
156.45 (arom. CqeO), 152.83 (NHCO), 142.55 (arom. CqeN),
138.42 (arom. Cq), 135.49 (arom. Cq), 135.26 (arom. Cq),
135.23 (arom. Cq), 135.01 (arom. Cq), 134.48 (arom. Cq),
129.01 (arom. CH), 128.43 (arom. CH), 128.39 (arom. CH),
2
system, JAB ¼ 13.4 Hz, ArCH2Ar), 3.96 (4H, t, 3J ¼ 7.6 Hz,
OCH2), 3.93e3.87 (4H, m, OCH2), 3.63 (2H, br s, NH2),
2.06e1.94 (8H, m, CH2CH3), 1.14e1.01 (12H, m, CH3) ppm.
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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8
H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
13C{1H} NMR (CDCl3, 125 MHz),
d
156.87 (2 ꢂ arom. CqeO),
stirred for 1 h at room temperature. The organic layer was
separated. Water (20 mL) and ammonium tetra-
fluoroborate (0.313 g, 2.99 mmol) were added, and the
mixture was stirred at room temperature for 1 h. The
organic layer was separated, dried over Na2SO4, filtered,
and the solvent was removed under reduced pressure. The
crude product was purified by flash chromatography (SiO2;
EtOAc/petroleum ether, 50:50; Rf ¼ 0e0.47) to afford 1 as a
156.41 (arom. CqeO), 155.51 (arom. CqeO), 144.94 (arom.
CqeN), 135.50 (arom. Cq), 135.40 (arom. Cq), 134.98 (arom.
Cq),134.92 (arom. Cq),134.78 (arom. Cq),132.20 (arom. Cq),
128.40 (arom. CH), 128.35 (arom. CH), 127.99 (arom. CH),
127.81 (arom. CH), 126.20 (arom. CH), 122.06 (arom. CH),
121.97 (arom. CH), 115.17 (arom. CH), 76.86 (OCH2), 76.75 (3
ꢂ OCH2), 31.21 (ArCH2Ar), 31.08 (ArCH2Ar), 23.43 (CH2CH3),
23.39 (CH2CH3), 23.32 (2 ꢂCH2CH3), 10.53 (CH3), 10.38
(CH3) ppm. Found C, 80.67; H, 7.82; N, 2.06. Calcd for
C46H53NO4 (Mr ¼ 683.93): C, 80.78; H, 7.81; N, 2.05%.
tan solid (1.33 g, 71%). 1H NMR (CDCl3, 500 MHz),
d 8.45
(1H, s, NCHN), 7.67 (2H, s, NCH), 7.14 (4H, s, ArH), 6.81 (4H,
s, ArH), 6.73 (4H, d, 3J ¼ 7.4 Hz, ArH), 6.69e6.61 (8H, m,
ArH), 6.57 (4H, d, 3J ¼ 7.4 Hz, ArH), 6.40 (2H, t, 3J ¼ 7.4 Hz,
2
4.1.9. 5-(3-Aminophenyl)-25,26,27,28-tetrapropyloxycalix[4]
arene (700)
ArH), 4.54 and 3.23 (8H, d, AB spin system, JAB ¼ 13.5 Hz,
2
ArCH2Ar), 4.50 and 3.16 (8H, d, AB spin system, JAB
¼
Trifluoroacetic acid (7.56 g, 66.3 mmol) was added
dropwise to a stirred solution of calix[4]arene 600 (4.00 g,
5.10 mmol) in CH2Cl2 (20 mL) cooled at 0 ꢀC. After 15 min,
the reaction mixture was allowed to reach room tempera-
ture and stirred for a further 2 h. The mixture was washed
with an aqueous solution of K2CO3 (20%, 150 mL) and the
two phases were separated. The aqueous phase was treated
with dichloromethane (2 ꢂ 100 mL) and the organic phases
were then combined. The solvent was removed under
reduced pressure to afford 700 as a white solid (3.43 g, 97%),
which did not need further purification. 1H NMR (CDCl3,
13.4 Hz, ArCH2Ar), 3.99e3.82 (16H, m, OCH2), 2.18 (12H, s,
o-CH3), 2.05e1.91 (16H, m, CH2CH3), 1.13e0.97 (24H, m,
CH2CH3) ppm. 13C{1H} NMR (CDCl3, 125 MHz),
d 157.12
(arom. CqeO), 156.65 (2 ꢂ arom. CqeO), 156.53 (arom.
CqeO), 144.63 (arom. CqeN), 136.54 (NCHN), 135.67 (arom.
Cq), 135.33 (arom. Cq),135.05 (arom. Cq), 134.91 (arom. Cq),
134.23 (arom. Cq), 132.98 (arom. Cq), 131.10 (arom. Cq),
128.43 (arom. CH), 128.36 (arom. CH), 127.99 (arom. CH),
127.79 (arom. CH), 127.12 (arom. CH), 125.52 (arom. CH),
122.15 (arom. CH),121.85 (arom. CH), 76.91 (OCH2), 76.80 (2
ꢂ OCH2), 76.77 (OCH2), 31.12 (ArCH2Ar), 31.00 (ArCH2Ar),
23.39 (CH2CH3), 23.34 (CH2CH3), 23.30 (2 ꢂCH2CH3), 17.57
(o-CH3), 10.45 (CH2CH3), 10.37 (CH2CH3) ppm. 19F NMR
(CDCl3, 282 MHz), ꢁ152.32 (br s, 19F-10B), ꢁ152.37 to
ꢁ152.39 (m, 19F-11B) ppm. Found C, 76.55; H, 7.40; N, 1.75.
Calcd for C99H113BF4N2O8 (Mr ¼ 1545.80): C, 76.92; H, 7.37;
N, 1.81%.
500 MHz),
d
7.14 (1H, dd, 3J ¼ 3J’ ¼ 7.7 Hz, ArH), 6.77e6.68
(7H, m, ArH), 6.66e6.60 (3H, m, ArH), 6.59 (1H, dd, 3J ¼
7.7 Hz, 4J ¼ 1.9 Hz, ArH), 6.51 (2H, d, 3J ¼ 7.4 Hz, ArH), 6.38
(1H, t, 3J ¼ 7.4 Hz, ArH), 4.51 and 3.21 (4H, d, AB spin sys-
tem, 2JAB ¼ 13.3 Hz, ArCH2Ar), 4.48 and 3.17 (4H, d, AB spin
system, 2JAB ¼ 13.3 Hz, ArCH2Ar), 3.94e3.81 (8H, m, OCH2),
3.65 (2H, br s, NH2), 2.02e1.89 (8H, m, CH2CH3), 1.09e0.96
(12H, m, CH3), ppm. 13C{1H} NMR (CDCl3, 125 MHz),
4.1.11. 1,3-Bis[4-(25,26,27,28-tetrapropyloxycalix[4]aren-5-yl)
d
156.88 (2 ꢂ arom. CqeO), 156.44 (arom. CqeO), 156.24
phenyl]imidazolium tetrafluoroborate (2)
(arom. CqeO), 146.26 (arom. CqeN), 142.87 (arom. Cq),
135.56 (arom. Cq), 135.34 (arom. Cq), 135.06 (arom. Cq),
134.95 (arom. Cq), 134.93 (arom. Cq), 129.28 (arom. CH),
128.42 (2 ꢂ arom. CH), 128.03 (arom. CH), 126.87 (arom.
CH), 122.08 (arom. CH), 122.05 (arom. CH), 117.78 (arom.
CH), 114.03 (arom. CH), 113.30 (arom. CH), 76.92 (OCH2),
76.79 (3 ꢂ OCH2), 31.23 (ArCH2Ar), 31.11 (ArCH2Ar), 23.46
(CH2CH3), 23.42 (CH2CH3), 23.34 (2 ꢂCH2CH3), 10.55 (CH3),
10.40 (CH3) ppm. Found C, 80.57; H, 7.76; N, 2.09. Calcd for
A
mixture
of
5-(4-aminophenyl)-25,26,27,28-
tetrapropyloxycalix[4]arene (70) (6.65 g, 9.72 mmol) and
acetic acid (1.25 mL, 1.31 g, 21.9 mmol) was heated at 60 ꢀC
for 5 min and MgSO4 (1.17 g, 9.72 mmol) was added
(mixture A). In another flask,
a mixture of glyoxal
(0.555 mL, 0.705 g, 4.86 mmol, 40 wt % in water), formal-
dehyde (0.361 mL, 0.394 g, 4.86 mmol, 37 wt % in water)
and acetic acid (1.25 mL, 1.31 g, 21.9 mmol) was heated at
60 ꢀC for 5 min and ZnCl2 (0.794 g, 5.83 mmol) was added
(mixture B). At 60 ꢀC mixture B was added to mixture A, the
resulting mixture was stirred at 60 ꢀC for 25 min and then
cooled to room temperature. CH2Cl2 (70 mL) and a 3 M
aqueous solution of HCl (100 mL) were added and the
resulting mixture was stirred for 1 h at room temperature.
The organic layer was separated. Water (40 mL) and
ammonium tetrafluoroborate (1.02 g, 9.72 mmol) were
added, and the mixture was stirred at room temperature
for 1 h. The organic layer was separated, dried over Na2SO4,
filtered, and the solvent was removed under reduced
pressure. The crude product was purified by flash chro-
C
46H53NO4 (Mr ¼ 683.93): C, 80.78; H, 7.81; N, 2.05%.
4.1.10. 1,3-Bis[2,6-dimethyl-4-(25,26,27,28-tetrapropyloxycalix
[4]aren-5-yl)phenyl]imidazolium tetrafluoroborate (1)
A
mixture
of
5-(4-amino-3,5-dimethylphenyl)-
25,26,27,28-tetrapropyloxycalix[4]arene (7) (1.71 g,
2.41 mmol) and acetic acid (0.310 mL, 0.325 g, 5.42 mmol)
was heated at 60 ꢀC for 5 min and MgSO4 (0.290 g,
2.41 mmol) was added (mixture A). In another flask, a
mixture of glyoxal (0.137 mL, 0.174 g, 1.20 mmol, 40 wt % in
water), formaldehyde (0.090 mL, 0.097 g, 1.20 mmol,
37 wt % in water) and acetic acid (0.310 mL, 0.325 g,
5.42 mmol) was heated at 60 ꢀC for 5 min and ZnCl2
(0.196 g, 1.44 mmol) was added (mixture B). At 60 ꢀC
mixture B was added to mixture A, the resulting mixture
was stirred at 60 ꢀC for 25 min and then cooled to room
temperature. CH2Cl2 (30 mL) and a 3 M aqueous solution of
HCl (50 mL) were added and the resulting mixture was
matography (SiO2; EtOAc/petroleum ether, 50:50, Rf
¼
0e0.51) to afford 2 as a tan solid (4.40 g, 61%). 1H NMR
(CDCl3, 500 MHz),
d 9.26 (1H, s, NCHN), 7.73 (2H, s, NCH),
7.64 (4H, d, 3J ¼ 7.7 Hz, ArH), 7.39 (4H, d, 3J ¼ 7.7 Hz, ArH),
6.80 (4H, d, 3J ¼ 7.4 Hz, ArH), 6.77 (4H, d, 3J ¼ 7.4 Hz, ArH),
6.70 (4H, dd, 3J ¼ 3J’ ¼ 7.4 Hz), 6.65 (4H, s, ArH), 6.36 (4H, d,
3J ¼ 7.4 Hz, ArH), 6.16 (2H, t, 3J ¼ 7.4 Hz, ArH), 4.50 and 3.19
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
9
2
(8H, d, AB spin system, JAB ¼ 13.4 Hz, ArCH2Ar), 4.45 and
(ArCH2Ar), 31.05 (ArCH2Ar), 23.43 (CH2CH3), 23.39
(CH2CH3), 23.29 (2 ꢂCH2CH3),10.52 (CH3),10.34 (CH3) ppm.
19F NMR (CDCl3, 282 MHz), ꢁ150.31 (br s, 19F-10B), ꢁ150.36
(br s, 19F-11B) ppm. Found C, 72.97; H, 6.92; N,1.73. Calcd for
2
3.12 (8H, d, AB spin system, JAB ¼ 13.4 Hz, ArCH2Ar),
3.97e3.88 (8H, m, OCH2), 3.85 (4H, t, 3J ¼ 7.2 Hz, OCH2),
3.77 (4H, t, 3J ¼ 7.2 Hz, OCH2), 2.01e1.85 (16H, m, CH2CH3),
1.07 (6H, t, 3J ¼ 7.4 Hz, CH3), 1.04 (6H, t, 3J ¼ 7.4 Hz, CH3),
0.98 (12H, t, 3J ¼ 7.4 Hz, CH3) ppm. 13C{1H} NMR (CDCl3,
C
95H105BF4N2O8$CH2Cl2 (Mr ¼ 1489.69 þ 84.93): C, 73.23;
H, 6.85; N, 1.78%.
125 MHz),
d
157.03 (2 ꢂ arom. CqeO), 157.00 (arom. CqeO),
156.20 (arom. CqeO), 144.02 (arom. CqeN), 135.89 (arom.
Cq),135.48 (arom. Cq),135.37 (arom. Cq), 134.60 (arom. Cq),
132.35 (arom. Cq), 131.95 (NCHN), 128.73 (arom. CH),
128.71 (arom. CH), 128.51 (arom. CH), 127.79 (arom. CH),
126.76 (arom. CH), 122.39 (arom. CH), 122.24 (arom. CH),
122.16 (arom. CH), 121.89 (arom. CH), 77.00 (OCH2), 76.85
(OCH2), 76.75 (2 ꢂ OCH2), 31.17 (ArCH2Ar), 31.04 (ArCH2Ar),
23.50 (CH2CH3), 23.45 (CH2CH3), 23.26 (2 ꢂCH2CH3), 10.63
(CH3), 10.27 (CH3) ppm. 19F NMR (CDCl3, 282 MHz), ꢁ151.00
(br s, 19F-10B), ꢁ151.05 (br s, 19F-11B) ppm. Found C, 76.23; H,
7.22; N, 2.10. Calcd for C95H105BF4N2O8 (Mr ¼ 1489.69): C,
76.60; H, 7.10; N, 1.88%.
4.1.13. trans-[1,3-Bis-{2,6-dimethyl-4-(25,26,27,28-
tetrapropyloxycalix[4]aren-5-yl)phenyl}imidazol-2-
ylidene](pyridine)palladium(II) dichloride (8)
A
suspension of imidazolium salt
1
(0.200 g,
0.133 mmol), finely crushed K2CO3 (0.092 g, 0.665 mmol)
and PdCl2 (0.028 g, 0.159 mmol) in pyridine (4 mL) was
heated at 80 ꢀC for 18 h under vigorous stirring. The
mixture was cooled to room temperature, filtered through
Celite and the collected solid washed with CH2Cl2 (ca.
20 mL). The filtrate was evaporated to dryness and the
residue purified by flash chromatography (SiO2; CH2Cl2/
petroleum ether, 60:40; Rf ¼ 0.68) to afford 8 as a yellow
solid (0.187 g, 82%). 1H NMR (CDCl3, 500 MHz),
d 8.51e8.47
4.1.12. 1,3-Bis[3-(25,26,27,28-tetrapropyloxycalix[4]aren-5-yl)
phenyl]imidazolium tetrafluoroborate (3)
(2H, m, o-NC5H5), 7.54 (1H, tt, 3J ¼ 7.6 Hz, 4J ¼ 1.7 Hz, p-
NC5H5), 7.19 (4H, s, ArH), 7.13 (2H, s, NCH), 7.10e7.05 (2H,
m, m-NC5H5), 6.93 (4H, s, ArH), 6.73e6.66 (4H, m, ArH),
6.64e6.57 (12H, m, ArH), 6.48 (2H, t, 3J ¼ 7.5 Hz, ArH), 4.53
A
mixture
of
5-(3-aminophenyl)-25,26,27,28-
tetrapropyloxycalix[4]arene (700) (2.04 g, 2.99 mmol) and
acetic acid (0.384 mL, 0.404 g, 6.73 mmol) was heated at
60 ꢀC for 5 min and MgSO4 (0.359 g, 2.99 mmol) was added
(mixture A). In another flask, a mixture of glyoxal (0.170 mL,
0.216 g, 1.49 mmol, 40 wt % in water), formaldehyde
(0.111 mL, 0.121 g, 1.49 mmol, 37 wt % in water) and acetic
acid (0.384 mL, 0.404 g, 6.73 mmol) was heated at 60 ꢀC for
5 min and ZnCl2 (0.244 g, 1.79 mmol) was added (mixture
B). At 60 ꢀC mixture B was added to mixture A, the resulting
mixture was stirred at 60 ꢀC for 25 min and then cooled to
room temperature. CH2Cl2 (30 mL) and a 3 M aqueous so-
lution of HCl (50 mL) were added and the resulting mixture
was stirred for 1 h at room temperature. The organic layer
was separated. Water (20 mL) and ammonium tetra-
fluoroborate (0.313 g, 2.99 mmol) were added, and the
mixture was stirred at room temperature for 1 h. The
organic layer was separated, dried over Na2SO4, filtered,
and the solvent was removed under reduced pressure. The
crude product was purified by flash chromatography (SiO2;
EtOAc/petroleum ether, 50:50; Rf ¼ 0e0.5) to afford 3 as a
2
and 3.25 (8H, d, AB spin system, JAB ¼ 13.3 Hz, ArCH2Ar),
2
4.48 and 3.17 (8H, d, AB spin system, JAB ¼ 13.3 Hz,
ArCH2Ar), 3.93 (4H, t, 3J ¼ 7.4 Hz, OCH2), 3.90e3.84 (12H, m,
OCH2), 2.43 (12H, s, o-CH3), 2.02e1.88 (16H, m, CH2CH3),
1.06e0.98 (24H, m, CH2CH3) ppm. 13C{1H} NMR (CDCl3,
125 MHz),
d 156.81 (arom. CqeO), 156.72 (arom. CqeO),
156.65 (2 ꢂ arom. CqeO), 153.12 (NCN), 151.67 (arom. CH o-
Py), 142.39 (arom. CqeN), 137.52 (arom. CH p-Py), 136.67
(arom. Cq), 136.01 (arom. Cq), 135.62 (arom. Cq), 135.33
(arom. Cq), 135.23 (arom. Cq), 135.00 (arom. Cq), 134.05
(arom. Cq), 128.47 (arom. CH), 128.33 (arom. CH), 128.17
(arom. CH), 127.20 (arom. CH), 127.18 (arom. CH), 124.34
(arom. CH), 124.05 (arom. CH), 122.22 (arom. CH), 122.13
(arom. CH), 76.91 (OCH2), 76.87 (2 ꢂ OCH2), 76.79 (OCH2),
31.29 (ArCH2Ar), 31.16 (ArCH2Ar), 23.46 (CH2CH3), 23.41 (3
ꢂCH2CH3), 19.52 (o-CH3), 10.50 (CH2CH3), 10.48 (CH2CH3)
ppm. Found C, 72.64; H, 6.97; N, 2.53. Calcd for
C
104H117Cl2N3O8Pd (Mr ¼ 1714.41): C, 72.86; H, 6.88; N,
2.45%.
tan solid (0.508 g, 23%). 1H NMR (CDCl3, 500 MHz),
d 9.26
(1H, s, NCHN), 7.74 (2H, s, NCH), 7.63e7.42 (4H, m, ArH),
7.40e7.20 (4H, m, ArH), 6.93e6.75 (8H, m, ArH), 6.71 (4H, d,
3J ¼ 7.3 Hz, ArH), 6.66 (4H, dd, 3J ¼ 3J’ ¼ 7.3 Hz), 6.49 (4H, d,
3J ¼ 7.3 Hz, ArH), 6.26 (2H, t, 3J ¼ 7.3 Hz, ArH), 4.51 and 3.29
4.1.14. trans-[1,3-Bis{4-(25,26,27,28-tetrapropyloxycalix[4]
aren-5-yl)phenyl}imidazol-2-ylidene](pyridine)palladium(II)
dichloride (9)
A
suspension of imidazolium salt
2
(0.429 g,
2
(8H, d, AB spin system, JAB ¼ 13.2 Hz, ArCH2Ar), 4.48 and
0.298 mmol), finely crushed K2CO3 (0.206 g, 1.49 mmol)
and PdCl2 (0.063 g, 0.357 mmol) in pyridine (6 mL) was
stirred at room temperature for 18 h. The mixture was
filtered through Celite and the filtered solid washed with
CH2Cl2 (ca. 20 mL). The filtrate was evaporated to dryness
and the residue purified by flash chromatography (SiO2;
CH2Cl2/petroleum ether, 50:50; Rf ¼ 0.59) leading to 9 as a
yellow solid (0.296 g, 60%). 1H NMR (CDCl3, 500 MHz),
2
3.16 (8H, d, AB spin system, JAB ¼ 13.3 Hz, ArCH2Ar),
3.97e3.85 (12H, m, OCH2), 3.83 (4H, t, 3J ¼ 7.4 Hz, OCH2),
2.03e1.88 (16H, m, CH2CH3), 1.10e0.96 (24H, m, CH3) ppm.
13C{1H} NMR (CDCl3, 125 MHz),
d 157.25 (arom. CqeO),
156.85 (2 ꢂ arom. CqeO), 156.45 (arom. CqeO), 144.06
(arom. CqeN), 135.80 (arom. Cq), 135.53 (arom. Cq), 135.25
(arom. Cq), 134.96 (arom. Cq), 134.44 (arom. Cq), 132.37
(NCHN),132.19 (arom. Cq),130.76 (arom. CH),128.86 (arom.
CH), 128.56 (arom. CH), 128.47 (arom. CH), 127.88 (arom.
CH), 126.98 (arom. CH), 122.72 (arom. CH), 122.14 (arom.
CH), 121.77 (arom. CH), 120.27 (arom. CH), 120.10 (arom.
CH), 76.96 (OCH2), 76.85 (OCH2), 76.77 (2 ꢂ OCH2), 31.10
d
8.69 (2H, d, 3J ¼ 5.2 Hz, o-NC5H5), 8.10 (4H, d, 3J ¼ 8.2 Hz,
ArH), 7.66 (1H, t, 3J ¼ 7.7 Hz, p-NC5H5), 7.47 (4H, d, 3J ¼
8.2 Hz, ArH), 7.33 (2H, s, NCH), 7.22 (2H, dd, 3J ¼ 7.7 Hz, 3J’ ¼
5.2 Hz, m-NC5H5), 6.90 (4H, d, 3J ¼ 7.4 Hz, ArH), 6.85 (4H, d,
3J ¼ 7.4 Hz, ArH), 6.82e6.74 (7H, m, ArH), 6.45 (4H, d, 3J ¼
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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10
H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
7.4 Hz, ArH), 6.30 (2H, t, 3J ¼ 7.4 Hz, ArH), 4.58 and 3.29 (8H,
4.1.16. General procedure for palladium-catalysed
SuzukieMiyaura cross-coupling reactions
2
d, AB spin system, JAB ¼ 13.3 Hz, ArCH2Ar), 4.52 and 3.21
2
(8H, d, AB spin system, JAB ¼ 13.3 Hz, ArCH2Ar), 3.99 (8H,
A mixture of the palladium complex (0.01 mmol), phe-
nylboronic acid (0.146 g, 1.20 mmol) and K2CO3 (0.207 g,
1.50 mmol) was suspended in absolute ethanol (3 mL).
After addition of p-tolyl chloride (0.126 g, 1 mmol), the
mixture was vigorously stirred at 80 ꢀC for 1 h. The hot
mixture was filtered through Celite. 1,4-Dimethoxybenzene
(0.069 g, 0.5 mmol), used as internal standard, was then
added to the filtrate. The solvent was removed under
reduced pressure, and the crude mixture was analysed by
1H NMR spectroscopy. The yields were determined by
comparing the intensity of the methyl signal of the product
dd, 3J ¼ 3J’ ¼7.1 Hz, OCH2), 3.91 (4H, t, 3J ¼ 7.1 Hz, OCH2),
3.85 (8H, t, 3J ¼ 7.1 Hz, OCH2), 2.12e1.91 (16H, m, CH2CH3),
1.12 (6H, t, 3J ¼ 7.3 Hz, CH3), 1.09 (6H, t, 3J ¼ 7.3 Hz, CH3),
1.03 (12H, t, 3J ¼ 7.3 Hz, CH3) ppm. 13C{1H} NMR (CDCl3,
125 MHz),
d
157.07 (2 ꢂ arom. CqeO), 156.43 (arom. CqeO),
156.14 (arom. CqeO), 151.25 (arom. CH o-Py), 150.77 (NCN),
142.05 (arom. CqeN), 137.77 (arom. CH p-Py), 137.64 (arom.
Cq), 135.89 (arom. Cq), 135.51 (arom. Cq), 135.11 (arom. Cq),
134.53 (arom. Cq), 133.47 (arom. Cq), 128.67 (arom. CH),
128.52 (arom. CH), 127.85 (arom. CH), 127.61 (arom. CH),
126.81 (arom. CH), 125.94 (arom. CH), 124.36 (arom. CH),
123.56 (arom. CH), 122.18 (arom. CH), 122.04 (arom. CH),
76.94 (OCH2), 76.78 (OCH2), 76.72 (2 ꢂ OCH2), 31.21
(ArCH2Ar), 31.07 (ArCH2Ar), 23.47 (CH2CH3), 23.43
(CH2CH3), 23.25 (2 ꢂ CH2CH3), 10.61 (CH3), 10.26 (CH3)
ppm. Found C, 72.22; H, 6.71; N, 2.45. Calcd for
[
[
d
(Me) ¼ 2.41 ppm] with that of the internal reference
d(Me) ¼ 3.78 ppm]. The isolated yield (concerning exper-
iments with chromatographic product separation) turned
out to be very close to that determined by using the internal
reference (deviation less than 5%).
C
100H109Cl2N3O8Pd (Mr ¼ 1658.31): C, 72.43; H, 6.63; N,
4.1.17. Crystal data for complex 9
Crystals suitable for X-ray analysis were obtained by
slow diffusion of pentane into a chloroform solution of the
2.53%.
4.1.15. trans-[1,3-Bis-{3-(25,26,27,28-tetrapropyloxycalix[4]
aren-5-yl)phenyl}imidazol-2-ylidene](pyridine)palladium(II)
dichloride (10)
complex. Crystal data: C100H109Cl2N3O8Pd$CHCl3, Mr
¼
1777.56 g molꢁ1, triclinic, space group P1, a ¼ 13.7011(5) Å,
b ¼ 22.8400(8) Å, c ¼ 35.5075(13) Å,
a
¼ 73.332(2)ꢀ,
b
¼
A
suspension of imidazolium salt
3
(0.200 g,
83.700(2)ꢀ,
1.130 g cmꢁ3
g
¼ 79.678(2)ꢀ, V ¼ 10,452.3(7) Å3, Z ¼ 4, D ¼
0.139 mmol), finely crushed K2CO3 (0.096 g, 0.695 mmol)
and PdCl2 (0.029 g, 0.166 mmol) in pyridine (4 mL) was
stirred at room temperature for 18 h. The mixture was
filtered through Celite and the collected solid washed
with CH2Cl2 (ca. 20 mL). The filtrate was evaporated to
dryness and the residue purified by flash chromatography
(SiO2; CH2Cl2/petroleum ether, 60:40; Rf ¼ 0.56) to afford
10 as a yellow solid (0.157 g, 68%). 1H NMR (CDCl3,
,
m
¼ 3.004 mmꢁ1, F(000) ¼ 3728, T ¼ 173(2) K.
The sample was studied using a Kappa APEX II diffrac-
tometer (graphite monochromated Cu K
a
radiation,
l
¼
1.54178 Å). The data collection (2qmax ¼ 133.7ꢀ, omega
omegascan frames by using 2ꢀomega rotation and 10 s per
frame, range hkl: h ꢁ16, 16; k ꢁ27, 23; l ꢁ42, 40) gave
204,167 reflections. The structure was solved using
SHELXS-2013 [30], which revealed the non-hydrogen
atoms of the molecule. After anisotropic refinement, all
hydrogen atoms were found using a Fourier difference map.
The structure was refined using SHELXL-2013 [31] by the
full-matrix least-squares technique (use of F2 magnitude; x,
y, z, bij for C, Cl, N and Pd atoms; x, y, z in riding mode for H
atoms); 2138 variables and 27,946 observations with I > 2.0
500 MHz),
d
8.68 (2H, d, 3J ¼ 5.2 Hz, o-NC5H5), 8.32 (2H, s,
ArH), 8.14 (2H, d, 3J ¼ 7.5 Hz, ArH), 7.65e7.55 (4H, m,
ArH), 7.53 (1H, t, 3J ¼ 7.3 Hz, p-NC5H5), 7.42 (2H, s, NCH),
7.18 (4H, s, ArH), 7.06 (2H, dd, 3J ¼ 7.3 Hz, 3J’ ¼ 5.2 Hz, m-
NC5H5), 6.76 (4H, d, 3J ¼ 7.5 Hz, ArH), 6.60 (2H, t, 3J ¼
7.4 Hz, ArH), 6.57e6.53 (4H, m, ArH), 6.41e6.43 (8H, m,
ArH), 4.51 and 3.21 (8H, d, AB spin system, JAB ¼ 13.2 Hz,
s
(I); calcd w ¼ 1/[
s
2(Fo2) þ (0.1202P)2 þ 1.2609P] where P ¼
2
2
ArCH2Ar), 4.49 and 3.17 (8H, d, AB spin system, JAB
¼
(Fo2 þ 2F2c)/3, with the resulting R ¼ 0.0601, RW ¼ 0.1837 and
SW ¼ 1.081, Dr < 1.149 eÅꢁ3. CCDC 1882970.
13.2 Hz, ArCH2Ar), 3.97 (4H, t, 3J ¼ 7.4 Hz, OCH2), 3.93
(4H, t, 3J ¼ 7.4 Hz, OCH2), 3.83 (8H, t, 3J ¼ 7.4 Hz, OCH2),
2.02e1.87 (16H, m, CH2CH3), 1.06 (12H, t, 3J ¼ 7.4 Hz, CH3),
1.01 (6H, t, 3J ¼ 7.4 Hz, CH3), 0.99 (6H, t, 3J ¼ 7.4 Hz, CH3)
4.2. Computational details
ppm. 13C{1H} NMR (CDCl3, 125 MHz),
d
157.37 (arom.
All calculations were performed with the Gaussian 09
program [32], using the functional PBEPBE [33]. Dispersion
corrections were included [34]. All atoms were described
using the def2-SVP basis set [35] and associated pseudo-
potential for the palladium atom. To get an optimised
structure, the geometry was simplified by replacing the
propoxy groups of the calixarenes by methoxy groups. The
structure was fully optimised and the wavefunction saved.
The NCI analysis [36] was performed on this geometry. All
calculations were performed in the gas phase.
CqeO), 157.07 (arom. CqeO), 156.21 (2 ꢂ arom. CqeO),
151.53 (NCN), 151.29 (arom. CH o-Py), 142.71 (arom.
CqeN), 139.73 (arom. Cq), 137.65 (arom. CH p-Py), 136.27
(arom. Cq), 135.82 (arom. Cq), 134.62 (arom. Cq), 134.34
(arom. Cq), 133.31 (arom. Cq), 129.51 (arom. CH), 128.39
(arom. CH), 128.24 (arom. CH), 128.07 (arom. CH), 127.27
(arom. CH), 127.18 (arom. CH), 124.42 (arom. CH), 123.77
(arom. CH), 123.48 (arom. CH), 122.19 (arom. CH), 122.00
(arom. CH), 76.92 (2 ꢂ OCH2), 76.81 (OCH2), 76.70 (OCH2),
31.24 (ArCH2Ar), 31.10 (ArCH2Ar), 23.45 (2 ꢂ CH2CH3),
23.33 (CH2CH3), 23.29 (CH2CH3), 10.61 (CH3), 10.32 (CH3)
ppm. Found C, 71.84; H, 6.69; N, 2.43. Calcd for
Acknowledgements
C
100H109Cl2N3O8Pd$0.25 CH2Cl2 (Mr ¼ 1658.31 þ 21.23): C,
H.A. gratefully acknowledges the "Association de
ꢀ
71.69; H, 6.52; N, 2.50%.
specialisation et d'orientation scientifique" (Lebanon) for
Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
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H. Almallah et al. / C. R. Chimie xxx (xxxx) xxx
11
[19] C. Wieser, D. Matt, J. Fischer, A. Harriman, J. Chem. Soc. Dalton
financial support. We thank Mr. Vincent Bruno (Unistra) for
assistance in obtaining NMR data.
(1997) 2391e2402.
€
[20] I.A. Bagatin, D. Matt, H. Thonnessen, P.G. Jones, Inorg. Chem. 38
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44 (2015) 9260e9268.
[23] M. Teci, E. Brenner, D. Matt, L. Toupet, Eur. J. Inorg. Chem. (2013)
2841e2848.
Appendix B. Supplementary data
1H and 13C NMR spectra of 1e3 and 8e10 and 19F NMR
spectra of 1e3
Supplementary data to this article can be found online
at https://doi.org/10.1016/j.crci.2019.01.008.
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Please cite this article as: H. Almallah et al., Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips, Comptes
Rendus Chimie, https://doi.org/10.1016/j.crci.2019.01.008