Homoselenacalix[4]arenes: Synthetic exploration and metallosupramolecular chemistry

Article abstract of DOI:10.1039/c2ob25760b

Homoselenacalix[4]arenes were synthesized by a [2 + 2] reductive coupling protocol favouring the cyclotetramers. The inner and outer-rim decoration was varied and a bicyclic derivative was prepared by a similar one-pot procedure. Conformational analysis in solution and the solid state showed noticeable differences between the homoselenacalix[4]arenes and the analogous homothiacalix[4]arenes and provided insight into the metal binding potential of the Se-bridged macrocycles. The homoselenacalix[4]arenes were found to bind Ag(i). Complexation was visualized in the solid state and different packing networks were formed depending on the counter ions applied.

Full text of DOI:10.1039/c2ob25760b

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PAPER
Homoselenacalix[4]arenes: synthetic exploration and metallosupramolecular
chemistry†
Joice Thomas,a Liliana Dobrzańska,a Kristof Van Hecke,b,c Mahendra P. Sonawane,a Koen Robeyns,b,d
Luc Van Meervelt,b Krzysztof Woźniak,e Mario Smet,a Wouter Maes*a,f and Wim Dehaen*a
Received 20th April 2012, Accepted 21st June 2012
DOI: 10.1039/c2ob25760b
Homoselenacalix[4]arenes were synthesized by a [2 + 2] reductive coupling protocol favouring the
cyclotetramers. The inner and outer-rim decoration was varied and a bicyclic derivative was prepared by a
similar one-pot procedure. Conformational analysis in solution and the solid state showed noticeable
differences between the homoselenacalix[4]arenes and the analogous homothiacalix[4]arenes and
provided insight into the metal binding potential of the Se-bridged macrocycles. The homoselenacalix[4]-
arenes were found to bind Ag(I). Complexation was visualized in the solid state and different packing
networks were formed depending on the counter ions applied.
the subclass of homoheteracalixarenes, although the CH2XCH2
bridges (X = O, NR, S, Se) between the aromatic units provide
Introduction
Heteracalixarenes, in which the methylene bridges of traditional
calixarenes are replaced by heteroatoms (mostly S, N and O, but
also Se, Si, Ge, Sn and P), have recently attracted (renewed)
attention as a novel generation of macrocyclic receptors due to
their high adaptability in forming complementary three dimen-
sional cavities and their straightforward functionalization at both
the upper and lower rim.1–4 Moreover, the bridging heteroatoms
introduce additional potential binding sites for specific guests in
an induced-fit fashion. Comparably less studies have focused on
the opportunity to modulate the macrocycle’s host–guest proper-
ties to an even further extent, as they impose increased cavity
size and enhanced conformational flexibility.5–8 Among these
homoheteracalixarenes, the oxygenated analogues have been
investigated most intensively and supramolecular features have
been studied on a few occasions.5 The metallosupramolecular
chemistry of some homooxacalixarene derivatives in the pres-
ence of Ti and V has been studied and the resulting complexes
have been explored as catalytically active substances.5j,k Their
complexation ability towards charged (tetramethylammonium
ions) and neutral (fullerenes) organic molecules has also been
reported.5 The synthesis and host–guest properties of homoaza-
and homothiacalixarenes are much less developed.6,7 The homo-
heteracalixarene series has recently been expanded to the sel-
enium “isologues” of the chalcogen series, homoselenacalix[n]-
arenes (with CH2SeCH2 linkages), but their supramolecular
features have not been explored yet.8
Selenium-containing macrocycles are versatile platforms for
the construction of sophisticated molecular receptors for tran-
sition metals or electron deficient moieties because of the high
σ-donating ability of the Se atoms.9 Considerable efforts have
been directed to the synthesis of selenacrown ethers and mixed-
donor selenoether macrocycles, as well as to the study of their
ligation properties towards d- and p-block elements. In hetera-
cyclophane chemistry, the large Se atoms lead to increased cavity
size, which imposes electronic and conformational features that
are quite different from O-, N- or S-containing macrocycles. In
cyclic selena(n)alkynes, the non-bonding interactions between
the chalcogen atoms have afforded a columnar structure in the
solid state, with cavities allowing the inclusion of organic guest
species.10 The introduction of Se in calixarene chemistry has
aMolecular Design and Synthesis, Department of Chemistry,
KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium.
E-mail: wim.dehaen@chem.kuleuven.be; Fax: +32 16327990;
Tel: +32 16327439
bBiomolecular Architecture, Department of Chemistry, KU Leuven,
Celestijnenlaan 200F, 3001 Leuven, Belgium
cDepartment of Inorganic and Physical Chemistry Group, Ghent
University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium
dInstitute of Condensed Matter and Nanosciences (IMCN), Université
Catholique de Louvain (UCL), Bâtiment Lavoisier, Place Louis Pasteur
1 (Bte 3), 1348 Louvain-la-Neuve, Belgium
eDepartment of Chemistry, Warsaw University, Pasteura 1, 02-093
Warsaw, Poland
fDesign & Synthesis of Organic Semiconductors (DSOS), Institute for
Materials Research (IMO-IMOMEC), Hasselt University, Universitaire
Campus, Agoralaan 1 – Building D, 3590 Diepenbeek, Belgium.
E-mail: wouter.maes@uhasselt.be; Fax: +32 11268299;
Tel: +32 11268312
†Electronic supplementary information (ESI) available: 1H, 13C and
77Se NMR spectra for the novel precursors and homoselenacalix[n]-
arenes, X-ray crystallographic general experimental data and additional
figures for the structures of homoselenacalix[n]arenes 4·THF, 10, 19, 20,
21 and 22, and FTMS (ESI+) isotopic patterns for homoselenacalix[4]-
arene 10 and metal complexes 21 and 22. CCDC 848952–848956. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2ob25760b
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Scheme 1 Synthetic pathways towards homoselenacalix[n]arenes 3–8.
Scheme 2 Synthesis of inner-rim functionalized homoselenacalix[n]-
arenes 10 and 11.
been limited to the periphery of the macrocycles and the con-
struction of calix(selena)crown ethers aiming at selective metal
extraction.11 More in general, organoselenium compounds are
also of significant importance because of their potential impact
in biological and pharmaceutical sciences.12
the cavity size, thereby changing its ligand features. It has pre-
viously been observed for both Se and S-bridged homocalixar-
enes that the introduction of intraannular methoxy groups is
crucial to direct the macrocyclization to the cyclic tetramers
rather than the cyclic dimers (diselena[3.3]-metacyclopha-
nes).7g,8 An initial attempt to deprotect the methoxy groups of
parent homoselenacalix[4]arene 4 with BBr3 was not successful,
as it was difficult to selectively deprotect the methoxy groups
without affecting the macrocycle. Therefore, the desired intra-
annular substituents should be introduced prior to macrocycliza-
tion. First of all, an asymmetrical homoselenacalix[4]arene
macrocycle 10 was synthesized, carrying alternate methoxy and
tert-butyl ester groups at the intraannular positions (Scheme 2).
Initially, the optimized conditions reported for the synthesis of 4
were applied.8 However, the [2 + 2] reductive coupling reaction
between tert-butyl 2-[2,6-bis(bromomethyl)-4-tert-butylphe-
noxy]acetate (9) and bisselenocyanate 2 using an excess of
NaBH4 under high dilution conditions (2.6 mM of each of the
building blocks) afforded the desired macrocycle 10 in negligible
amounts only. Analysis of the crude reaction mixture by ESI-MS
(electrospray ionization-mass spectrometry) revealed, besides the
formation of the [2 + 2] coupling product and some higher
homologues, the presence of products with a single diselenide
linkage within the macrocyclic skeleton (in spite of the reductive
conditions employed). As these macrocycles all have comparable
polarity, they could not be separated and purified effectively by
standard column chromatography (on silica). Deaeration of the
reaction mixture over a longer time and/or slight changes in the
reaction parameters (e.g. adding an excess of NaBH4 or proceed-
ing to reflux conditions) did not enable us to exclude the intro-
duction of a diselenide linkage. A possible hypothesis as to why
the diselenide formation is only observed in this case (and not
during the synthesis of 4)8 might be that there is a higher ten-
dency to relieve ring strain when the more bulky tert-butyl
The unique properties of Se, taken together with the consider-
able difference in the physical characteristics of (homo)hetera-
calixarenes, prompted us to continue our work on (homo)-
selenacalix[n]arene macrocycles. In a previous communication,
we have reported synthetic routes towards both symmetrical and
asymmetrical homoselenacalix[n]arenes of varying ring size by
two different approaches (Scheme 1).8 The first method
employed the nucleophilic substitution reaction of sodium
hydrogen selenide (NaSeH) with 1,3-bis(bromomethyl)-5-tert-
butyl-2-methoxybenzene (1) and afforded a mixture of sym-
metrical homoselenacalix[n]arenes 3–8 (n = 3–8), with some
selectivity for the smallest homoselenacalix[3]arene 3. The
second approach involved a [2 + 2] reductive coupling protocol
resulting in either symmetrically or asymmetrically substituted
calixarenes, with pronounced selectivity for the tetrameric
cyclooligomers. In this paper, we report novel synthetic routes
enabling introduction of different functionalities at the intra- and
extraannular positions of homoselenacalix[n]arene macrocycles,
including methods which afford bicyclic analogues. The confor-
mational features of the homoselenacalix[4]arene derivatives in
solution and in the solid state have been analyzed. Moreover, we
have also explored the metallosupramolecular complexation
ability of the homoselenacalix[4]arene scaffold, focusing on
Ag-mediated self-assembly in the solid state.
Results and discussion
Synthesis and characterization
We envisioned that the introduction of specific functional moi-
eties on the upper and lower rim of the homoselenacalix[4]arene
framework could alter the conformational preference and tune
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acetate moieties are employed as inner substituents. On the other
hand, such a tendency was not observed for the synthesis of the
di- and tetrasubstituted homothiacalix[4]arene analogues (via
reaction of 9 with a bismercapto precursor) either.7g,13 Optimiz-
ation of the procedure, affording a maximum amount of cyclo-
tetramer 10, was achieved by repeating the reaction at an enhanced
concentration (10.4 mM) of the building blocks. Thus, dropwise
addition of NaBH4 to a mixture of 9 and 2 in a 1 : 1 ratio at a
concentration of 10 mM in THF afforded homoselenacalix[4]-
arene 10 in 38% yield, while homoselenacalix[6]arene 11 was
additionally obtained in 22% yield (Scheme 2). Polymer/oligo-
mer formation significantly increased at an even higher concen-
tration (26 mM) of the building blocks.
The 1H NMR spectrum of A2B2-type homoselenacalix[4]-
arene 10 in CDCl3 at room temperature (rt) displayed broadened,
partly separated signals for several protons (e.g. the methoxy and
methylene groups), in contrast to the sharp singlet signals
observed for A4-type homoselenacalix[4]arene 4.8 From this
observation, it seems that the inner-rim tert-butyl acetate moi-
eties impart restricted mobility to the calixarene framework. The
broad multiplets were converted to singlet signals at 328 K due
to the enhanced conformational flexibility of the macrocycle at
this temperature (see the ESI†). For the corresponding thia ana-
logue, geminal coupling of the methylene protons was still
observed at 328 K and sharp signals were only seen upon
heating at or above 350 K.7g This observation can be correlated
to the larger size of the Se atom (and hence longer C–Se bonds,
vide infra), which in turn results in higher conformational flexi-
bility. The shielding effect experienced by the protons of the two
inner methoxy groups (at δ 3.19/3.14 ppm at 300 K) points to a
small (if any) contribution of cone-type conformations in sol-
ution. On the other hand, a sharp singlet signal was observed for
the methylene groups of the enlarged [3 + 3] coupling product
11, indicating its fast conformational interconversion at ambient
temperature.
Outer-rim functionalized homoselenacalix[4]arenes were
obtained by a similar pre-macrocyclization functionalization
strategy. This involved the use of building blocks already
bearing the desired functional groups, which then underwent
macrocyclization by a reductive coupling protocol (Scheme 3).
Dibromo precursor 14 was obtained by methylation of ethyl
4-hydroxy-3,5-bis(hydroxymethyl)benzoate (12), followed by
bromination under Appel reaction conditions. Homoselenacalix[4]-
arene 15, bearing alternate ethyl ester and tert-butyl groups at
the extraannular positions, was obtained in an isolated yield of
42% via the optimized procedure used for the synthesis of 4.8
Higher cyclic oligomers were also observed, but these could not
efficiently be purified chromatographically. The bis(hydroxy-
methyl)-substituted cyclotetramer 16 was obtained in 87% yield
by reduction of the diester with LiBH4 in THF at rt. This com-
pound may be easily modified further on for the preparation of
more sophisticated homoselenacalixarene receptors. The 1H
NMR spectra of 15 and 16 showed similar trends as observed in
the case of parent homoselenacalix[4]arene 4.8 The shielded
signals for the methoxy protons (at δ 3.47/3.36 ppm for 15 and
3.59/3.31 ppm for 16 at rt) indicated once more the preference
for non-cone conformations in solution.
Scheme 3 Synthesis of outer-rim functionalized homoselenacalix[4]-
arenes 15 and 16.
have particular advantages in host–guest chemistry due to their
restricted flexibility.3c,g,5b,6f We have recently reported on the
synthesis of a bicyclic analogue of a homothiacalix[4]arene
using a one-pot reaction.7g We have chosen the same monomer,
1,3,5-tris(bromomethyl)-2,4,6-trimethoxybenzene
(17),
to
prepare a similar bicyclohomoselenacalixarene. The methoxy
groups were introduced as it was shown that they play a crucial
role for the selective formation of the cyclic tetramer.8 Thus, a
three-fold ring-closing substitution reaction (under reductive
conditions) between bisselenocyanate 2 and electrophilic com-
ponent 17, in a 3 : 2 molar ratio, furnished bicyclohomoselena-
calixarene 19 in 23% yield (Scheme 4). A significant reduction
in the yield was observed upon repeating the reaction at a higher
concentration of the monomers. An attempt to prepare a similar
cage compound in a stepwise manner starting from homoselena-
calix[4]arene 16 was unsuccessful due to the failure to obtain the
Bicyclic “cage” (homo)heteracalixarene structures, in which
all macrocyclic ring systems have a calixarene structure, may
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coupling product.7g,8 Bis(selenacyclophane) 20 also shows a
strongly deviating 77Se NMR signal (at δ 259 ppm vs.
312–325 ppm for the homoselenacalix[4]arenes), which might
be used as a signature of [1 + 1] product formation.
Thus, by carefully choosing the monomers a bridged homo-
selenacalix[4]arene analogue 19 with a compact π-cavity was
synthesized in a one-pot approach, composed of three phenyl
rings as “walls” and two extra phenyl rings as “top” and “bottom
caps”. The enriched π-donor environment produced by the six
three-dimensionally preorganized aryl groups of the bicyclic
ligand may provide a nice steric fit for specific cations such as
alkali metals and ammonium ions.
Solid-state structural elucidation
To confirm the structure and analyze the conformation of the
synthesized macrocycles in the solid state, single crystals of
compounds 10 and 19 were grown from saturated solutions in
chloroform. Compound 10 crystallized in the monoclinic P2/n
space group as a chloroform solvate (Fig. 1). There are one half
of the homoselena[4]calixarene (the other half is generated by an
inversion centre) and one molecule of CHCl3 present in the
asymmetric unit. The calixarene adopts a 1,2-alternate confor-
mation, as observed earlier for its sulfur isologue.7g Neverthe-
less, the overall geometry of both molecules differs significantly.
Choosing the mean plane defined by the Se atoms as a reference
plane, the dihedral angles with the aromatic rings span between
56.7° (for the rings with the ester substituents on the lower rim)
and 58.1° (for the rings with the methoxy groups on the lower
rim), whereas the corresponding values for the related homothia-
calix[4]arene were 73.1° and 25.7°, respectively.7g The geome-
tries around the dimethylene–Se/S bridges are also dissimilar. In
10, Se atoms are alternatingly pointing outside and inside of the
macrocycle, whereas in the previous compound all S atoms were
pointing towards the inside (see Fig. S1†). The two C–C–Se–C
torsion angles defined by each bridge are associated with anti
Scheme 4 Synthetic pathway towards bicyclic selenacyclophanes 19
and 20.
dibrominated analogue in pure form from diverse bromination
trials (Br2/HBr, PPh3/CBr4, PPh3/NBS). The cage-type molecule
19 exhibits a symmetrical structure in solution, as evidenced
1
from its simple H NMR spectrum. The methoxy protons of the
nucleophilic component (at δ 3.29 ppm) were shifted up-field
considerably in comparison to the methoxy protons of the elec-
trophilic component (at δ 3.74 ppm), suggesting that they are
pointing more directly into the formed cavity. This observation
is comparable to the case of the structurally analogous bicyclo-
homothiacalixarene, which suggests that the conformations of
these molecules in solution are similar.7g
Treatment of bisnucleophile 2 with an alternative capping
component,
1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene
(18), under the same coupling conditions and at the same ratio,
provided a compound with a molecular mass (ESI-MS) matching
the analogous cage product (in 27% yield). However, the 1H
NMR spectrum was considerably more complicated. Doublets
were observed for the geminal protons of the bridging methylene
groups. Moreover, one of the methyl groups of the electrophilic
moieties showed an unusual upfield shift (at δ 1.29 ppm) as
compared to the other methyl groups (at δ 2.42 ppm). These
observations pointed towards the formation of a product with
restricted rotation, as in the [1 + 1] selenacyclophane pro-
ducts.8,14 Single crystal X-ray diffraction analysis allowed us to
identify the formation of bis(selenacyclophane) molecule 20 (see
Fig. S5†), as presented in Scheme 4, which explains the exten-
sive splitting and shielding noticed for the bridging methylene
and methyl groups, respectively. This observation once more
confirms the profound effect of the intraannular substituents on
the macrocyclization outcome, i.e. the absence of an interior
methoxy group on either of the monomers favours the [1 + 1]
Fig. 1 Molecular structure of the chloroform solvate of homoselena-
calix[4]arene 10 with an atom labelling scheme (thermal ellipsoids are
drawn at 50% probability). Unlabeled atoms are related to labelled atoms
by the symmetry operation 1 − x, 1 − y, −z. Disorder on the tert-butyl
group C26 is omitted for clarity.
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angles with values of 175.7(2)° and −167.8(2)° around Se1 and
gauche angles of 62.4(2)° and 50.3(2)° around Se2. As the
C–Se–C bridges are very flexible, the presence of weak C32–
H32⋯O32 hydrogen bonds between the cyclophane ring and the
solvent molecule (with a C⋯O bond length of 3.171(5) Å and a
C–H–O angle of 162°) could be the cause of the adopted geome-
try. The C–Se bond lengths are in the range 1.949(3)–1.969(3) Å
and the angles vary from 94.5(1)–97.4(1)°. These values are
comparable with previous reports.8 Additionally, there is a
network of weak C–H⋯π interactions which further stabilize the
adopted conformation. Further intramolecular interactions, such
as C7–H7B⋯Cg1 (where Cg1 is the centroid of C19–C24) and
C25–H25A⋯Cg2 (where Cg2 is the centroid of C1–C6), with
C⋯Cg distances of 3.616(4) and 3.707(5) Å, involve ester and
methoxy groups, respectively, whereas intermolecular ones such
as C17–H17B⋯Cg2 and C30–H30A⋯Cg1 (with C⋯Cg dis-
tances of 3.598(3) and 3.339(3) Å, respectively) involve
dimethyleneselena bridges.
Bicyclohomoselenacalix[4]arene 19 crystallized as a chloro-
form solvate in the triclinic P1 space group with one calixarene
molecule and two CHCl3 molecules in the asymmetric unit
(Fig. 2). The bicyclic molecule consists of five aryl moieties.
Three of these building blocks, originating from precursor 2
(with methoxy and tert-butyl groups in the p-position of each
other), are alternating with two building blocks derived from pre-
cursor 17 (with three methoxy groups in positions 1, 3 and 5),
with each cycle containing four aromatic units. As mentioned
above, the molecule showed a similar conformation in solution
as reported earlier for the analogous bicyclohomothiacalix[4]-
arene.7g In the solid state, the conformation of the molecules
also remained more or less the same (see Fig. S2†). The most
striking differences concern the geometry of one of the dimethy-
lene–Se/S bridges and the orientation of one of the methoxy
groups on the arene bearing three methoxy substituents. Both of
them can be the result of the location of solvent molecules (C79)
in the crystal lattice. Weak C79–H79⋯Se16i interactions, with a
C–Se distance of 3.556(5) Å (symmetry operation: (i) x, −1 + y,
1 + z), probably cause the change in angular geometry of the Se
bridge as well as the ‘self-inclusion’ of the O11–C12 methoxy
group, which in this case is pointing towards the macrocyclic
ring. This indicates once again the flexibility of the C–Se–C
bridges of the macrocycle, whose geometry can be easily
influenced.
Metallosupramolecular chemistry
Metallosupramolecular architectures based on Se-bridged macro-
cycles have been investigated by a number of groups around the
world.9 The discovery of selenacoronands by Pinto and co-
workers in 1989 has initiated research on the formation of metal
complexes having unexpected electronic structures and redox
properties different from those of the corresponding oxa and thia
counterparts.9a Metal complexation for a wide range of middle
and late transition metals has been studied over the last
decade.9g,t Metallocomplexes composed of macrocyclic seleno-
ether ligands and p-block ions of group 15 (As, Sb and Bi) were
recently studied by Reid and co-workers.9d–f These ions often
showed strong binding and were stabilized by a combination of
primary interactions with the halogen counter ions and second-
ary interactions with Se. On the other hand, unsaturated selena-
crown ethers, which are conformationally more restricted and
possess different electronegativity for the Se atoms as compared
to the corresponding saturated systems, exhibited different com-
plexation behaviour and showed excellent inclusion features for
Ag(I) ions.9m Mixed donor macrocycles having harder donor
atoms such as N or O and softer Se atoms within the same mol-
ecular cavity are reported to behave as heterodinuclear macro-
cyclic ligands able to coordinate both hard and soft guest ions
or molecules. Panda and co-workers synthesized Se/N macro-
cycles of varying ring size and their coordination complexes with
Ni(II), Pd(II), Pt(II) and Hg(II) have been reported.9k,l,n The encapsu-
lation of transition metals like Cu(I), Ag(I), Pd(II) and Pt(II) in
mixed Se/O macrocycles has also been reported recently.9b,c,i
From the above examples, it is clear that homoselenacalix-
arenes possess the intrinsic potential to complex metal cations.
The binding potential of the novel macrocycles was initially
evaluated using homoselenacalix[4]arene 4 and Ag(I) salts.15,16
Mixing of 4 in THF or CHCl3 with one equivalent of
AgCF3SO3 or AgPF6 in MeOH at rt resulted in the formation of
monomeric complexes [Ag-4]CF3SO3 (21) and [Ag-4]PF6 (22)
as off-white solids in high yields (Scheme 5). ESI-MS analysis
showed an intense peak at m/z 1184, which corresponds to the
monomer of the [Ag-4]+ ionic species in agreement with the
existence of a 1 : 1 complex in solution. The 1H NMR spectra of
complexes 21 and 22 showed broadened signals with only negli-
gible chemical shift differences compared to precursor 4.
We successfully determined the crystal structures of the Ag(I)
cationic calixarene complexes mentioned above, i.e. with triflate
(21) and hexafluorophosphate (22) counter ions. Compound 21
crystallized in the monoclinic P21/c space group with two calix-
arene Ag(I) complexes of approximately the same conformation
and two disordered triflate counter ions in the asymmetric unit.
On the other hand, 22 crystallized (from THF) in the tetragonal
P4n2 space group with one quarter of the calixarene’s Ag(I)
Fig. 2 Molecular structure of the chloroform solvate of bicyclohomo-
selenacalixarene 19 with an atom labelling scheme (thermal ellipsoids at
50% probability). Hydrogen atoms as well as the disordered tert-butyl
group on C70 are omitted for clarity. The C–C–Se–C angles around the
Se atoms are as follows: Se1 174.0(4)° and −76.5(4)°, Se16 −175.5(4)°
and 117.0(5)°, Se31 176.4(4)° and 55.2(4)°, Se46 −160.8(4)° and
73.6(4)°, Se62 −177.6(4)° and 63.1(4)°, Se77 177.9(4)° and −66.6(5)°.
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Fig. 4 Overlay of homoselenacalix[4]arene 4·THF (red) with its Ag(I)
complex 22 (grey); the silver ion is represented as a ball. The C–C–Se–
C torsion angles have alternating gauche/anti geometry. For crystallo-
graphic information on 4·THF, see the ESI.†
of 124.51(2)° and 82.35(4)° for 21 and angles varying from
125.98(4)° (Ag1) and 126.29(4)° (Ag2) to 82.61(3)° (Ag1) and
81.70(3)° (Ag2) for 22. One pair of Ag–Se distances in 22
seems to be quite long, i.e. 3.244(2) Å (Ag1)/3.203(2) Å (Ag2),
but taking into account the similarity between complexes 21 and
22 (Fig. S4†), we can conclude that coordination nevertheless
takes place. The remaining Ag–Se distances with values of
2.950(1) Å for 21 and in the range of 2.773(1)–2.869(1) Å for
22 are in good agreement with previous reports.9h,m
Scheme 5 Synthesis of Ag(I) complexes 21 and 22.
cationic complex, with the silver ion located on a special pos-
ition with fourfold rotational symmetry (Wyckoff position 2a),
−
and half of the PF6 counter ion, with P15 and F17 located on
The difference between the crystal structures of 21 and 22 was
more noticeable at the supramolecular level. In both structures
the Ag(I) calixarene complexes are forming layers which are sep-
arated by the counter ions they interact with. As the shape and
the size of the counter ions differ, this results in different
special positions (Wyckoff positions 2c and 4h, respectively), in
the asymmetric unit (Fig. 3). The cationic complexes in 21 and
22 do not differ much (see Fig. S4†). The calixarene moieties in
21 and 22 keep the 1,3-alternate conformation as in the parent
homoselenacalix[4]arene 4,8 but because the Se atoms are
approaching the metal centers, a slight tilting of the aromatic
rings is observed, as well as a change in the orientation of the
methoxy groups which in this case are pointing outwards of the
macrocycle to create the space needed for encapsulation of the
Ag+ ion (Fig. 4).
−
arrangements (Fig. 5). The smaller and spherically shaped PF6
ion in 22 facilitates the formation of a more complementary
packing, whereas in 21 the presence of the bigger elongated
−
CF3SO3 ion led to the occurrence of solvent accessible voids
(PLATON estimates the accessible space at 10.1% of the total
cell volume),17 which could have originally been occupied by
MeOH molecules (the solvent used during synthesis and crystal-
lization). As the crystals got dry, the solvent molecules left and
the space remained as a molecular shift was partially precluded
by the counter ions. This could explain the bad quality of the
crystal and the resulting poor data set.
The Ag(I) atoms in both complexes are coordinated by Se
atoms pointing towards the ring interior, to form a distorted tetra-
hedral geometry around the metal centre, with Se–Ag–Se angles
Conclusions
In the presented study, we have reported efficient and flexible
methods for the synthesis and functionalization (at the upper and
lower rim) of homoselenacalix[4]arenes through a [2 + 2] reduc-
1
tive coupling protocol. H NMR studies revealed a great simi-
larity in the up-field shift of the intraannular methoxy protons of
all homoselenacalix[4]arenes, pointing towards the preference
for non-cone conformations in solution. Furthermore, we have
extended our studies to the successful single-step synthesis of a
three-dimensionally preorganized bicyclohomoselenacalixarene.
The methoxy groups in the building blocks were proven to be
essential to obtain high selectivity for the formation of the
(bicyclo)homoselenacalix[4]arenes. In addition, the ability of the
Fig. 3 Molecular structure of 22 with an atom labelling scheme of the
asymmetric unit (thermal ellipsoids at 50% probability).
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Fig. 5 Representation of the packing down the a axis (21 on the left and 22 on the right). Counter ions are shown in space-filling representation.
Disorder is not shown for clarity.
parent homoselenacalix[4]arene ligand to form a metallosupra-
molecular architecture through coordination of a Ag(I) ion by the
bridging Se atoms is demonstrated. This work clearly illustrates
the structural diversity that can be achieved for Se-bridged calix-
arenes by carefully optimized reaction conditions and shows the
potential benefits of the introduction of soft Se atoms towards
host–guest chemistry. Further supramolecular features of this
class of expanded homoheteracalixarenes are currently actively
being pursued within our group.
of NaSeH without the necessity of generating dangerously toxic
H2Se. NaSeH is an unstable compound and decomposes in
moist air with the formation of polyselenides and precipitation of
Se. It should be used directly as prepared (in a fume hood) in
solution or suspension without isolation.20
Experimental and characterization data
5-tert-Butyl-2-methoxy-1,3-bis(selenocyanatomethyl)benzene
(2). Experimental and characterization data can be retrieved
from one of our previous manuscripts.8 Material identity and
purity were confirmed by mp, MS, 1H and 13C NMR.
Experimental section
General experimental methods
7,15,23,31-Tetra-tert-butyl-33,34,35,36-tetramethoxy-2,3,10,11,18,
19,26,27-octahomo-3,11,19,27-tetraselenacalix[4]arene (4). Experi-
mental and characterization data can be retrieved from one of our
previous manuscripts.8 Material identity and purity were
confirmed by mp, MS, 1H and 13C NMR.
NMR spectra were acquired on commercial instruments (Bruker
Avance 300 MHz, Bruker AMX 400 MHz or Bruker Avance II+
600 MHz) and chemical shifts (δ) are reported in parts per
million (ppm) referenced to tetramethylsilane (1H) or the internal
(NMR) solvent signals (13C).18 J values are given in Hz. The
77Se NMR spectra were recorded using Ph2Se2 in CDCl3 as an
external reference (δ 463 ppm).19 Mass spectra were run using
an HP5989A apparatus (CI and EI, 70 eV ionisation energy)
with an Apollo 300 data system or a Thermo Finnigan LCQ
Advantage apparatus (ESI). Exact mass measurements were
acquired on a Bruker Daltonics Apex2 FT-ICR instrument (per-
formed in the ESI mode at a resolution of 60 000). Melting
points (not corrected) were determined using a Reichert Thermo-
var apparatus. For column chromatography 70–230 mesh silica
60 (E. M. Merck) was used as the stationary phase. Chemicals
received from commercial sources were used without further
purification. Reaction solvents (THF, ethanol, methanol) were
used as received from commercial sources. Additions in (high-
dilution) macrocyclization reactions were performed at a constant
rate with the aid of an infusion pump.
tert-Butyl 2-[2,6-bis(bromomethyl)-4-tert-butylphenoxy]acetate
(9). Experimental and characterization data can be retrieved
from one of our previous manuscripts.7g Material identity and
purity were confirmed by mp, MS, 1H and 13C NMR.
Synthesis of homoselenacalix[n]arenes 10 and 11. A solution
of NaBH4 (0.039 g, 1.01 mmol, 2.2 equiv.) in ethanol (12 mL)
was added over 2 h to a stirred mixture of 2 (0.207 g,
0.51 mmol) and 9 (0.184 g, 0.51 mmol) in degassed THF
(50 mL) at rt. The mixture was subsequently stirred for 10 h and
then concentrated to 10 mL. CH2Cl2 (50 mL) was added and the
organic solution was washed with distilled water (3 × 50 mL),
dried over MgSO4, filtered, and then evaporated to dryness to
afford the crude product mixture. Purification by column chrom-
atography (silica, eluent CH2Cl2–heptane–diethyl ether
45 : 45 : 1) afforded 10 (0.123 g, 38%) and 11 (0.073g, 22%) as
off-white solids. 10: mp 70–72 °C; 1H NMR (400 MHz, CDCl3)
δH 7.22 (s, 4H; ArH), 7.04 (sbr, 4H; ArH), 4.58–4.40 (m, 4H;
OCH2), 4.15–4.05 (dbr, 4H; CH2), 3.95–3.60 (m, 12H; CH2),
3.22–3.07 (dbr, 6H; OCH3), 1.48 (s, 18H; t-Bu), 1.28 (s, 18H;
t-Bu) and 1.25 (s, 18H; t-Bu); 13C NMR (75 MHz, CDCl3) δC
Safety precautions
The most convenient procedure to prepare NaSeH involves
reduction of Se with NaBH4. It allows rapid and easy preparation
6532 | Org. Biomol. Chem., 2012, 10, 6526–6536
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168.5 (CO), 153.9, 153.8, 152.7, 147.0, 132.9, 132.8, 131.1,
127.2 (CH), 126.7 (CH; br), 82.1 (O-t-Bu), 71.3 (OCH2), 60.96
(OCH3), 60.86 (OCH3), 34.44, 34.38, 31.55 (CH3), 31.52
(CH3), 28.3 (CH3), 23.2 (CH2), 22.2 (CH2) and 22.1 (CH2);
77Se NMR (76.3 MHz, CDCl3) δSe 312; IR (ATR) νmax/cm−1
2959, 2950, 2926, 1750, 1729, 1479, 1460, 1363, 1214, 1153,
1095, 1053, 1007, 879, 836 and 580; MS (ESI+) m/z 1301.8
[M + Na]+; FTMS (ESI+) calcd for C62H88O8Se4Na [M + Na]+:
1301.3046; found: m/z 1301.3093.21
δH 8.06 (s, 2H; ArH), 4.56 (s, 4H; CH2), 4.38 (q, J = 7.1, 2H;
CH2), 4.07 (s, 3H; OCH3) and 1.40 (t, J = 7.1, 3H; CH3); 13C
NMR (75 MHz, CDCl3) δC 165.3 (CO), 160.4 (CO), 133.6
(CH), 132.4, 127.4, 62.6 (OCH3), 61.4 (OCH2), 26.9 (CH2) and
14.5 (CH3); IR (ATR) νmax/cm−1 3054, 2990, 2961, 2831, 1711,
1603, 1474, 1368, 1314, 1224, 1200, 1028, 989, 955, 767, 597
and 579; MS (ESI+) m/z 367 [M+H]+; FTMS (ESI+) calcd for
C12H14Br2O3 [M+]: 365.9289; found: m/z 365.9271.
1
11: mp 72–74 °C; H NMR (400 MHz, CDCl3) δH 7.16 (s,
7,23-Bis(ethoxycarbonyl)-15,31-di-tert-butyl-33,34,35,36-tetra-
methoxy-2,3,10,11,18,19,26,27-octahomo-3,11,19,27-tetraselena-
calix[4]arene (15). A solution of NaBH4 (0.031 g, 0.81 mmol, 3
equiv.) in ethanol (12 mL) was added over 3 h to a stirred
mixture of 2 (0.109 g, 0.27 mmol) and 14 (0.100 g, 0.27 mmol)
in degassed THF (200 mL) at rt. The mixture was subsequently
stirred for 1 h and then concentrated to 10 mL. CH2Cl2 (50 mL)
was added and the organic solution was washed with distilled
water (3 × 50 mL), dried over MgSO4, filtered, and then evapor-
ated to dryness to afford the crude product mixture. Purification
by column chromatography (silica, eluent CH2Cl2–heptane–
diethyl ether 46 : 30 : 24) afforded 15 (0.063 g, 42%) as an off-
6H; ArH), 7.12 (s, 6H; ArH), 4.55 (s, 6H; OCH2), 3.93 (s, 12H;
CH2), 3.87 (s, 12H; CH2), 3.79 (s, 9H; OCH3), 1.51 (s, 27H;
O-t-Bu), 1.27 (s, 27H; t-Bu) and 1.26 (s, 27H; t-Bu); 13C NMR
(75 MHz, CDCl3) δC 168.6 (CO), 153.9, 152.9, 147.4, 147.0,
132.3, 132.0, 126.9 (CH), 82.0 (O-t-Bu), 71.4 (OCH2), 61.7
(OCH3), 34.3, 31.56 (CH3), 31.51 (CH3), 28.4 (CH3), 23.2
(CH2) and 23.0 (CH2); 77Se NMR (76.3 MHz, CDCl3) δSe 313;
IR (ATR) νmax/cm−1 2967, 2949, 2926, 1749, 1733, 1478, 1419,
1364, 1214, 1154, 1103, 1053, 1004, 881, 844 and 582; MS
(ESI+) m/z 1938.3 [M + Na]+.
1
Ethyl 4-hydroxy-3,5-bis(hydroxymethyl)benzoate (12). This
compound has been prepared according to the procedure
reported by Shabat et al.22 Material identity and purity were
confirmed by MS, 1H and 13C NMR.
white solid. mp 136–138 °C; H NMR (300 MHz, CDCl3) δH
7.85 (s, 4H; ArH), 7.11 (s, 4H; ArH), 4.34 (q, J = 7.1, 4H;
CH2), 3.79 (s, 8H; CH2), 3.77 (s, 8H; CH2), 3.47 (s, 6H; OCH3),
3.36 (s, 6H; OCH3), 1.38 (t, J = 7.1, 6H; CH3) and 1.27 (s, 18H;
t-Bu); 13C NMR (75 MHz, CDCl3) δC 165.9 (CO), 160.0 (CO),
153.7, 146.9, 133.0, 131.7, 131.2 (CH), 126.9 (CH), 126.1,
61.12 (OCH3), 61.05 (OCH2), 34.3, 31.5 (CH3), 22.6 (CH2),
21.6 (CH2) and 14.5 (CH3); 77Se NMR (76.3 MHz, CDCl3) δSe
324; IR (ATR) νmax/cm−1 2954, 2867, 1480, 1361, 1245, 1217,
1185, 1093, 1033, 1000, 897, 879 and 580; MS (ESI+) m/z =
1131.3 [M + Na]+.
Ethyl 3,5-bis(hydroxymethyl)-4-methoxybenzoate (13). To a
mixture of ethyl 4-hydroxy-3,5-bis(hydroxymethyl)benzoate
(12) (4.00 g, 17.7 mmol) and K2CO3 (12.26 g, 88.8 mmol, 5
equiv.) in acetone (100 mL), MeI (5.04 g, 35.4 mmol, 2 equiv.)
was added. The mixture was stirred at reflux temperature for
12 h and then concentrated under reduced pressure. CH2Cl2
(100 mL) was added and the organic solution was washed with
distilled water (3 × 50 mL), dried over MgSO4, filtered, and then
evaporated to dryness to afford the crude product mixture. Purifi-
cation by column chromatography (silica, eluent ethyl acetate–
CH2Cl2 80 : 20) afforded 13 (3.3 g, 77%) as an off-white solid.
mp 69–71 °C; 1H NMR (400 MHz, CDCl3) δH 8.00 (s, 2H;
ArH), 4.73 (s, 4H; CH2), 4.35 (q, J = 7.1, 2H; CH2), 3.86 (s,
3H; OCH3), 2.59 (sbr, 2H; OH) and 1.38 (t, J = 7.1, 3H; CH3);
13C NMR (75 MHz, CDCl3) δC 166.3 (CO), 159.9 (CO), 134.3,
130.4 (CH), 126.7, 62.4 (OCH3), 61.2 (CH2), 60.5 (CH2) and
14.4 (CH3); IR (ATR) νmax/cm−1 3363, 2959, 1696, 1308, 1204,
1102, 1081, 1009, 914, 770, 671 and 550; MS (ESI+) m/z 240
[M + H]+; FTMS (ESI+) calcd for C12H16O5Na [M + Na]+:
263.0895; found: m/z 263.0895.
7,23-Bis(hydroxymethyl)-15,31-di-tert-butyl-33,34,35,36-tetra-
methoxy-2,3,10,11,18,19,26,27-octahomo-3,11,19,27-tetraselenaca-
lix[4]arene (16). A solution of LiBH4 (1.6 mL, 2 M in THF) in
dry THF (10 mL) was added dropwise to a stirred mixture of 15
(0.109 g, 0.16 mmol) in dry THF (20 mL) at 0 °C. The tempera-
ture was gradually increased to rt. After stirring the resulting
mixture for 2 days, the reaction mixture was added to water
(40 mL). Ethyl acetate (30 mL) was added and the organic sol-
ution was washed with distilled water (3 × 30 mL), dried over
MgSO4, filtered, and then evaporated to dryness to afford the
crude product mixture. Purification by column chromatography
(silica, eluent CH2Cl2–ethyl acetate 90 : 10) afforded 16
1
(0.140 g, 87%) as an off-white solid. mp 140–142 °C; H NMR
Ethyl 3,5-bis(bromomethyl)-4-methoxybenzoate (14). A sol-
ution of 13 (2.00 g, 8.33 mmol) and CBr4 (4.08 g, 25 mmol, 3
equiv.) in CH2Cl2 (40 mL) was prepared in a 100 mL flask and
cooled down to 0 °C. A solution of PPh3 (3.27 g, 25 mmol, 3
equiv.) in CH2Cl2 (10 mL) was added and the temperature was
gradually increased to rt. After stirring the resulting mixture for
another 12 h, the reaction mixture was added to water (40 mL).
CH2Cl2 (70 mL) was added and the organic solution was
washed with distilled water (3 × 50 mL), dried over MgSO4,
filtered, and then evaporated to dryness to afford the crude
product mixture. Purification by column chromatography (silica,
eluent CH2Cl2–heptane 70 : 30) afforded 14 (2.37 g, 80%) as an
(400 MHz, CDCl3) δH 7.18 (s, 4H; ArH), 7.05 (s, 4H; ArH),
4.51 (s, 4H; CH2), 3.76 (s, 8H; CH2), 3.75 (s, 8H; CH2), 3.59 (s,
6H; OCH3), 3.31 (s, 6H; OCH3), 3.00 (sbr, 2H; OH) and 1.28 (s,
18H; t-Bu); 13C NMR (75 MHz, CDCl3) δC 155.5 (CO), 153.4,
147.4, 137.0, 133.1, 131.5, 128.6, 127.0 (CH), 64.8 (CH2OH),
61.6 (OCH3), 61.2 (OCH3), 34.4, 31.5 (CH3), 22.0 (CH2) and
21.8 (CH2); 77Se NMR (76.3 MHz, CDCl3) δSe 325; IR (ATR)
νmax/cm−1 3385, 2855, 1478, 1432, 1360, 1295, 1234, 1185,
1109, 1046, 998, 880, 856 and 592; MS (ESI+) m/z 1046.9
[M + Na]+.
1,3,5-Tris(bromomethyl)-2,4,6-trimethoxybenzene (17). This
compound has been prepared according to the procedure
1
off-white solid. mp 119–121 °C; H NMR (400 MHz, CDCl3)
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reported by Castellano et al.23 Material identity and purity were
confirmed by MS, 1H and 13C NMR.
222–224 °C; 1H NMR (400 MHz, CDCl3) δH 7.17 (s, 8H; ArH),
3.78 (sbr, 16H; CH2), 3.15 (sbr, 12H; OCH3) and 1.27 (s, 36H;
t-Bu); IR (ATR) νmax/cm−1 2950, 2938, 2232, 1488, 1290, 1226,
1153, 1101, 1022, 988, 937, 849, 629 and 574; MS (ESI+) m/z
1,3,5-Tris(bromomethyl)-2,4,6-trimethylbenzene
(18). This
1184.6 [M
−
CF3SO3]+; FTMS (ESI+) calcd for
compound has been prepared according to the procedure
reported by Van der Made and Van der Made.24 Material identity
and purity were confirmed by MS, 1H and 13C NMR.
C52H72AgO4Se4 [M − CF3SO3]+: 1185.1150; found: m/z
1
1185.1184. 22: mp 194–196 °C; H NMR (400 MHz, CDCl3)
δH 7.20 (s, 8H; ArH), 3.83 (sbr, 16H; CH2), 3.17 (sbr, 12H;
OCH3) and 1.28 (s, 36H; t-Bu); IR (ATR) νmax/cm−1 2956,
2935, 2225, 2204, 1993, 1484, 1289, 1248, 1132, 998, 1022,
842, 825, 656 and 570; MS (ESI+) m/z 1184.3 [M − PF6]+;
Synthesis of bicyclohomoselenacalix[4]arene 19. A solution of
NaBH4 (0.038 g, 1.01 mmol) in ethanol (12 mL) was added
over 2 h to a stirred mixture of 2 (0.135 g, 0.34 mmol) and 17
(0.100 g, 0.22 mmol) in degassed THF (150 mL) at rt. The
mixture was subsequently stirred for 3 h and then concentrated
to 10 mL. CH2Cl2 (50 mL) was added and the organic solution
was washed with distilled water (3 × 50 mL), dried over MgSO4,
filtered, and then evaporated to dryness to afford the crude
product mixture. Purification by column chromatography (silica,
eluent CH2Cl2–heptane–diethyl ether 67 : 26 : 7) afforded 19
FTMS (ESI+) calcd for C52H72AgO4Se4 [M
−
PF6]+:
1185.1150; found: m/z 1185.1207.
Crystal structure determination
X-ray crystallographic general experimental data are outlined in
the ESI.† In the case of bis(selenacyclophane) 20, the data were
limited and their quality was very poor. However, as all our
efforts to collect a better data set failed, we decided to mention
the structure in the text as we could prove formation of the pres-
ented molecule (see Fig. S5†). It crystallized as a dichloro-
methane solvate in the triclinic P1 space group with unit cell
parameters a = 9.774(5), b = 17.634(10), c = 18.839(10) Å, α =
77.619(10), β = 80.539(11), γ = 79.259(11)° and V = 3090(3)
Å3. For structure 21, the crystal quality was rather poor, which
could be caused by release of the solvent molecules.
1
(0.039 g, 23%) as an off-white solid. mp 216–218 °C; H NMR
(400 MHz, CDCl3) δH 7.17 (s, 6H; ArH), 3.83 (s, 12H; CH2),
3.78 (s, 12H; CH2), 3.74 (s, 18H; OCH3), 3.29 (s, 9H; OCH3)
and 1.27 (s, 27H; t-Bu); 13C NMR (75 MHz, CDCl3) δC 157.2,
153.9, 146.9, 131.6, 126.8 (CH), 123.2, 62.3 (OCH3), 61.1
(OCH3), 34.4, 31.5 (CH3), 22.8 (CH2) and 16.6 (CH2); 77Se
NMR (76.3 MHz, CDCl3) δSe 322; IR (ATR) νmax/cm−1 2955,
2877, 1570, 1487, 1463, 1428, 1258, 1193, 1167, 1087, 999,
895, 845 and 599; MS (ESI+) m/z 1483.1 [M + Na]+.
Synthesis of bis(selenacyclophane) 20. A solution of NaBH4
(0.038 g, 1.01 mmol) in ethanol (12 mL) was added over 2 h to
a stirred mixture of 2 (0.150 g, 0.38 mmol) and 18 (0.100 g,
0.25 mmol) in degassed THF (150 mL) at rt. The mixture was
subsequently stirred for 3 h and then concentrated to 10 mL.
CH2Cl2 (50 mL) was added and the organic solution was
washed with distilled water (3 × 50 mL), dried over MgSO4,
filtered, and then evaporated to dryness to afford the crude
product mixture. Purification by column chromatography (silica,
eluent CH2Cl2) afforded 20 (0.048 g, 27%) as an off-white solid.
Crystal data for 4. C52H72O4Se4·2(C4H8O), M = 1221.14,
colourless block, 0.32 × 0.18 × 0.09 mm3, tetragonal, space
group I41/a (No. 88), a = b = 28.310(4), c = 14.618(3) Å, V =
11 716(3) Å3, Z = 8, Dc = 1.385 g cm−3, F000 = 5056,
KM4CCD, MoKα radiation, λ = 0.71073 Å, T = 100(2) K,
2θmax = 52.8°, 94 873 reflections collected, 5998 unique (Rint
=
0.0597). Final GooF = 1.079, R1 = 0.0364, wR2 = 0.0844, R
indices based on 4733 reflections with I > 2σ(I) (refinement on
F2). Lp and absorption corrections applied, μ = 2.552 mm−1
.
1
mp 221–223 °C; H NMR (400 MHz, CDCl3) δH 7.33 (s, 6H;
Crystal data for 10. C62H88O8Se4·2(CHCl3), M = 1515.90,
colourless rod, 0.4 × 0.2 × 0.15 mm3, monoclinic, space group
P21/n (No. 14), a = 10.8677(13), b = 12.6155(10), c = 26.392(5)
ArH), 4.01 (s, 4H; CH2), 3.99 (s, 4H; CH2), 3.89 (s, 3H; OCH3),
3.78 (dd, J = 26.8/14.4, 8H; CH2), 3.65 (d, J = 18.2, 4H; CH2),
3.19 (d, J = 17.0, 4H; CH2), 3.11 (s, 6H; OCH3), 2.43 (s, 12H;
CH3), 1.36 (s, 9H; CH3) and 1.29 (s, 27H; t-Bu); 13C NMR
(75 MHz, CDCl3) δC 155.8, 154.0, 147.0, 146.5, 138.9, 136.7,
132.6, 132.3, 130.7, 128.9, 127.5 (CH), 126.8 (CH), 62.0
(OCH3), 61.6 (OCH3), 34.54, 34.48, 31.6 (CH3), 31.5 (CH3),
29.6, 25.4 (CH2), 22.9 (CH2), 21.6 (CH2), 18.3 (CH2), 16.1
(CH3) and 15.0 (CH3); 77Se NMR (76.3 MHz, CDCl3) δSe 258;
IR (ATR) νmax/cm−1 2819, 2726, 2672, 1692, 1479, 1460, 1246,
1184, 1169, 1010, 934, 876, 831, 619 and 576; MS (ESI+) m/z
1386.8 [M + Na]+.
Å, β = 95.784(8)°, V = 3600.0(9) Å3, Z = 2, Dc = 1.398 g cm−3
,
F000 = 1552, SMART 6000, CuKα radiation, λ = 1.54178 Å,
T = 100(2) K, 2θmax = 143.4°, 30 601 reflections collected, 6885
unique (Rint = 0.0777). Final GooF = 1.055, R1 = 0.0456, wR2 =
0.1082, R indices based on 5837 reflections with I > 2σ(I)
(refinement on F2). Lp and absorption corrections applied, μ =
4.871 mm−1
.
Crystal data for 19. C63H84O9Se6·2(CHCl3), M = 1697.80,
colourless plate, 0.4 × 0.2 × 0.1 mm3, triclinic, space group P1
(No. 2), a = 14.9433(4), b = 16.7585(4), c = 17.4804(4) Å, α =
109.7050(10), β = 98.3310(10), γ = 112.9910(10)°, V =
3595.47(16) Å3, Z = 2, Dc = 1.568 g cm−3, F000 = 1708, SMART
Synthesis of Ag(I) complexes 21 and 22. A solution of
Ag+CF3SO3 (0.007 g, 0.028 mmol) or Ag+PF6 (0.007 g,
0.028 mmol) in methanol (3 mL) was added to a solution of
homoselenacalix[4]arene 4 (0.030 g, 0.028 mmol) in THF
(10 mL) at rt and the mixture was stirred for 10 h. The resulting
solution was evaporated to dryness and washed with diethyl
ether to afford the monomeric complexes 21 (0.034 g; 91%) and
22, respectively (0.031 g; 86%), as off-white solids. 21: mp
−
−
6000, CuKα radiation, λ = 1.54178 Å, T = 100(2) K, 2θmax
=
141.6°, 70 888 reflections collected, 13 363 unique (Rint = 0.0980).
Final GooF = 1.033, R1 = 0.0497, wR2 = 0.1095, R indices
based on 10 164 reflections with I > 2σ(I) (refinement on F2). Lp
and absorption corrections applied, μ = 6.067 mm−1
.
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Crystal data for 21. C52H72AgO4Se4CF3SO3, M = 1333.89,
colourless rod, 0.4 × 0.2 × 0.1 mm3, monoclinic, space group
P21/c (No. 14), a = 13.801(7), b = 27.671(12), c = 31.568(16)
Å, β = 93.689(14)°, V = 12 030(10) Å3, Z = 8, Dc = 1.473 g cm−3
,
F000 = 5376, SMART 6000, CuKα radiation, λ = 1.54178 Å,
T = 100(2) K, 2θmax = 133.2°, 21 230 reflections collected,
21 230 unique (Rint = 0.0000). Final GooF = 1.071, R1 = 0.0837,
wR2 = 0.1718, R indices based on 18 418 reflections with
I > 2σ(I) (refinement on F2). Lp and absorption corrections
applied, μ = 6.225 mm−1
.
Crystal data for 22. C52H72AgO4Se4PF6, M = 1329.78, col-
ourless prism, 0.38 × 0.25 × 0.11 mm3, tetragonal, space group
P4n2 (No. 118), a = b = 13.994(2), c = 14.223(3) Å, V =
2785.4(8) Å3, Z = 2, Dc = 1.586 g cm−3, F000 = 1336,
KM4CCD, MoKα radiation, λ = 0.71073 Å, T = 100(2) K, 2θmax
=
52.7°, 11 491 reflections collected, 2855 unique (Rint = 0.0721).
Final GooF = 0.988, R1 = 0.0512, wR2 = 0.0887, R indices
based on 1461 reflections with I > 2σ(I) (refinement on F2). Lp
and absorption corrections applied, μ = 3.065 mm−1
.
CCDC 848952–848956 contain the supplementary crystallo-
graphic data for this paper (compounds 19, 4·THF, 21, 22 and
10, respectively).
Acknowledgements
We thank the FWO (Fund for Scientific Research – Flanders),
the KU Leuven and the Ministerie voor Wetenschapsbeleid for
continuing financial support.
Notes and references
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6536 | Org. Biomol. Chem., 2012, 10, 6526–6536
This journal is © The Royal Society of Chemistry 2012