Synthesis and structural characterisation of the aggregates of benzo-1,2-chalcogenazole 2-oxides

Article abstract of DOI:10.1039/c7dt00612h

Iodine oxidation of bis[2-(hydroxyiminomethyl)phenyl] dichalcogenides yields benzo-1,2-chalcogenazole 2-oxides. Annulated derivatives of iso-tellurazole N-oxides spontaneously aggregate into cyclic tetra- and hexamers through Te?O chalcogen bonding; the s

Full text of DOI:10.1039/c7dt00612h

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Rafique, J. Lee, M. L. Lee, H. A. Jenkins, J. F. Britten, A. L. Braga and I. Vargas-Baca, Dalton Trans., 2017,
DOI: 10.1039/C7DT00612H.
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Synthesis and Structural Characterisation of the Aggregates of
Benzo-1,2-Chalcogenazole 2-Oxides
Peter C. Ho,a Jamal Rafique,b Jiwon Lee,a Lucia M. Lee,a Hilary A. Jenkins,a James F. Britten,a
Antonio L. Braga,b* Ignacio Vargas-Bacaa*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Abstract. Iodine oxidation of bis[2-(hydroxyiminomethyl)phenyl] dichalcogenides yields benzo-1,2-chalcogenazole 2-
oxides. The annulated derivative of the iso-tellurazole N-oxide spontaneously aggregates into cyclic tetra- and hexamers
trough Te…O chalcogen bonding; the structures of the co-crystals with benzene and CH2Cl2 illustrate the ability of these
macrocycles to interact with small guest molecules. The selenium congener crystallizes forming a supramolecular polymer.
VT NMR indicates that both compounds aggregate in solution but only at low temperature in the selenium case. The
different abilities of these molecules to engage in supramolecular interactions is interpreted on the basis of their
electronic properties evaluated with DFT-D3 calculations.
www.rsc.org/
heterocycles and their aggregates are remarkably stable in
ambient conditions and are tolerant of water. Mineral acids
such as HCl and HBr protonate the oxygen atom while the
Introduction
The remarkable success of halogen bonding1,2
in
halide binds the chalcogen; the process is reversible providing
a means to switch on and off the self-assembly of these
molecular building blocks.17
supramolecular chemistry has sparked great interest in the
analogous secondary bonds3 formed by other heavy main-
group elements. Organic derivatives of the chalcogens (sulfur,
selenium and tellurium) form molecules that often engage in
this type of interaction. For instance, dichalcogena alkynes
form tubular structures in crystalline lattices,4-6 telluradiazoles
are well-known for their abilities to bind Lewis bases7-11 and to
form infinite ribbons in the solid state.7,12 These concepts have
recently been extended to the construction of benzo-
tellurazole chains,13 the development of tellurophenes capable
of anion recognition in solution14 and catalysis of the reduction
of quinolines and imines by dithienothiophenes.15
A unique development in this area, with no equivalent in
halogen bonding, is the reversible autoassociation of 1,2-
tellurazole 2-oxides (Scheme 1,
1
) through Te…O interactions
forming annular structures (14, 16) that are persistent in
solution and display chemical properties of actual macrocycles
such as binding transition metal ions, forming fullerene
adducts, and hosting small molecules.16 Although the
preparation of these compounds requires several steps that
must be carried out under an inert atmosphere, the
Scheme 1. Iso-tellurazole oxides and their macrocyclic aggregates.
In search for a synthetic method which could grant easier
access to this type of compounds, we considered annulated
derivatives such as benzo-1,2-tellurazole 2-oxide (Scheme 2,
2a). As long as the autoassociation of the heterocycles is
preserved, annulation of the 1,2-tellurazole 2-oxide to a benzo
ring would confer advantages such as increased stability, four
positions that in principle are available for functionalization
and an increased van der Waals surface that would likely
enhance the interaction of the macrocycles with aromatic
molecules. Here we report the preparation of such compound,
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demonstrate its ability to form supramolecular aggregates, and reasoned that its reaction with I2 would give in first instance
show that the synthetic method is readily applicable to the 4a, an analogue of the products of reaction of 1a with HCl
selenium congener 2b and HBr, thus addition of a base would generate 2a
,
b
.
.
The steps along this route proceed with good yields and inert
atmosphere is only required for the initial lithiation and
subsequent reaction with elemental tellurium. The pure
dioxime 3a or its bis(2-formylphenyl) ditelluride precursor can
be conveniently stored as stable intermediate products.
However,
be promptly transformed into the target compound 2a. The
equivalent sequence of steps led to 1,2-selenazole 2-oxide 2b
Analytically pure benzotellurazole N-oxide, 2a can be
4 is unstable, it is best prepared in situ and should
.
(
)
obtained from the crude product by recrystallization from a
1:1 mixture of dichloromethane and pyridine.
Crystal Structures. Pure 2a forms plate-like crystals that
belong to the P-1 space group. They contain 2a4 in a chair
conformation (Figure 1) analogous to the structure previously
16,18
observed for 1b4
.
Given the Ci symmetry, the tetramer is
generated from two crystallographically independent units of
2a. Adjacent heterocycles subtend an interplanar angle of
72.34° (cf. 60.16° in 1b4). The two trans-annular Te-Te
distances, 3.6990(2) and 4.3638(4) Å, are much shorter than
the 5.5895(2) and 5.3043(2) Å of 1b4. Packing (Figure 2) of the
2a4 macrocycles along the a and b axes is driven by π-stacking.
Scheme 2. Synthesis of benzo-1,2-chalcogenazole 2-oxides, 2a,b.
Results and discussion
Synthesis. As shown in Scheme 2, the proposed approach for
the synthesis of 2a consists of the lithiation of ketal-protected
2-bromo benzaldehyde followed by reaction with elemental
tellurium. Aerobic oxidation yields a ditelluride which is
deprotected and condensed with hydroxyl amine to produce
Additional Te⋅⋅⋅O short contacts (3.151(2) Å, cf. ΣrvdW = 3.58 Å)
are formed between neighbouring macrocycles; but the
C-Te⋅⋅⋅O angle (145.2°) strongly deviates from the ideal linear
geometry of
σ
-hole interactions.
bis[2-(hydroxyiminomethyl)phenyl] ditelluride
(3a). We
Table 1. Crystallographic and refinement parameters for all characterized polymorphs of 2a and 2b
.
Crystal Composition
6(2a)• 1.78(CH2Cl2)• 0.22(H2O)
4(2a
1507754
)
4(2a)• C6H6
1507755
2b∞
1530647
C7H5NOSe
Orthorhombic
P212121
7.3324(9)
8.0016(10)
11.8324(15)
90
CCDC
Empirical formula
Crystal system,
Space group
a [Å]
1507753
C43.78H34Cl3.56N6O6.22Te6
Trigonal
C28H20N4O4Te4
Triclinic
P-1
C34H26N4O4Te4
Monoclinic
C2/c
18.646(3)
17.433(2)
10.6572(15)
90
95.384(2)
90
3448.9(8)
4, 2.051
296.15
P31
14.4246(7)
14.4246(7)
21.3472(12)
90
90
120
3846.6(4)
3, 2.118
100.15
7.2250(2)
8.7915(3)
12.1257(4)
106.411(2)
102.489(2)
90.001(2)
719.81(4)
1, 2.277
b [Å]
c [Å]
α [°]
90
90
β [°]
γ [°]
V [Å3]
694.22(15)
4, 1.895
100.15
5.327
6.146 to 56.782
Z,
ρ
(calc.) [g. cm–3
T [K]
]
100.15
4.054
5.788 to 66.262
ꢀ [ꢀꢀꢁꢂ
range [°]
]
3.604
5.02 to 67.072
3.393
6.412 to
56.598
2
θ
Limiting indices
-22 ≤ h ≤ 22,
-22 ≤ k ≤ 22,
-33 ≤ l ≤ 33
131669/ 20091
0.0477
-11 ≤ h ≤ 11,
-13 ≤ k ≤ 13,
-18 ≤ l ≤ 18
23510/ 5456
0.0239
-24 ≤ h ≤ 24,
-22 ≤ k ≤ 23,
-14 ≤ l ≤ 14
13318/ 4255
0.0276
208
0.0410/
0.0820
-9 ≤ h ≤ 9,
-10 ≤ k ≤ 10,
-15 ≤ l ≤ 15
7086/ 7086
0.1164
Refl. collected/ unique
R(int.)
No. of parameters
602
0.0330/ 0.0709
181
0.0238/ 0.0637
93
0.0351/ 0.0859
R1* / wR2* (I>2σ(I))
R1* / wR2* for all data
0.0435/ 0.0759
0.0299/ 0.0677
0.0697/
0.0917
1.036
0.0400/ 0.0876
Goodness-of-fit on F2
Largest difference
peak/hole [e.Å-3]
1.005
1.76/ -0.68
1.009
1.42/ -0.55
1.059
1.62/ -0.49
0.97/ -1.51
2 | J. Name., 2012, 00, 1-3
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in the case of 2a4
,
π
-stacking is the predominant interaction
between the macrocycles in each layer. Crystallographic
refinement of the CH2Cl2 population showed a loss of only 3%
in a sample held at 0.3 Torr during 12 hours.
Figure 1. ORTEP (75%) plot of the tetrameric aggregate of benzotellurazole N-oxide (2a)
as observed in a crystal of the pure compound. Te…O 2.235(2), 2.245(2) Å; Te-N
2.235(2), 2.197(2) Å; N-O 1.357(3), 1.355(3) Å; N-Te-O 162.37(7), 164.45(7)°; Te-N-O
126.3(1), 122.7(1)°; Te-O-N, 111.6(1), 115.5(1)°; Te-O-N-Te 89.4(1), 19.0(2)°.
Figure 3. ORTEP (75%) plot of the hexameric aggregate of benzotellurazole N-oxide as
observed in the crystal of composition 2a6(CH2Cl2)1.78(H2O)0.22. Te…O 2.201(6), 2.178(5),
2.187(4), 2.188(6), 2.188(5), 2.189(4) Å; Te-N 2.262(5), 2.268(4), 2.261(6), 2.262(5),
2.268(5), 2.267(6) Å; N-O 1.374(6), 1.365(9), 1.370(7), 1.361(6), 1.369(7), 1.361(9) Å; N-
Te-O 164.6(2), 164.7(2), 163.6(2), 163.9(2), 164.0(2), 164.5(2); Te-N-O 127.1(4),
126.8(4), 127.1(4), 127.1(4), 126.6(4), 127.2(4); Te-O-N 114.4(4), 114.5(4), 115.2(4),
115.3(4), 116.1(4), 116.4(4)°; Te-O-N-Te 11.2(6), 12.5(6), 2.2(7), 6.4(6), 15.1(7), 5.4(6)°.
Figure 2. Detail of packing in the crystal of 2a4 highlighting the interactions between
macrocyclic tetramers.
A second polymorph was isolated when the solvent mixture
used for crystallization contained a small amount (15 % v/v) of
pyridine. This hexagonal R-3c phase is built from 2a6
macrocycles (Figure 3) arranged in layers, similar those
observed in the crystal of 1b6.2THF. However, in this case the
layers pack in an ABC pattern, not AB, and the macrocycle
cavities conform isolated pockets instead of pores (Figure 4).
The voids are occupied by water and dichloromethane
molecules, the relative occupations of which were determined
Figure 4. Detail of packing in the crystal of 2a6(CH2Cl2)1.78(H2O)0.22. Void surfaces are
from the structural refinement affording
a composition
calculated with a 1 Å probe.
2a6(CH2Cl2)1.78(H2O)0.22 which is consistent with the results of
combustion analysis. In addition, the 3 vibrational modes of
the water molecule are well resolved in the infrared spectrum
(Figure S2). All the heterocycles in the structure of 2a6 are
crystallographically distinct and, of all the tellurazole N-oxide
aggregates characterized until now, they are the closest to
being truly orthogonal to each other (interplanar angles range
from 80.03 to 88.79°). In these macrocycles the trans-annular
Te-Te distances (7.1297(8), 7.3407(8) and 7.3589(5) Å) are
slightly shorter than the 7.638(2) Å observed in 1b6.2THF.15 As
Acicular crystals grown from benzene belong to the C2/c space
group and feature the tetramer 2a4 in a hitherto not observed
twist-boat conformation (Figure 5) which sits on a two-fold
axis. There are two distinct trans-annular Te-Te distances
(5.2164(8) and 5.2172(8) Å) in this ring. The macrocycles align
along the c-axis forming tubular channels which are occupied
by benzene molecules (Figure 6) giving an overall
stoichiometry 2a4•C6H6. Combustion analysis was satisfactory
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for freshly grown crystals, but the loss of benzene became While all the polymorphs of 2a that could be identified
apparent after a few days of dry storage.
contained macrocyclic aggregates, attempts to grow crystals of
2b in different conditions yielded only one crystalline phase
that belongs to the P212121 space group. In this case the
molecules are linked by 2.412(5) Å, cf. ΣrvdW = 3.42 Å) Se…O
chalcogen bonds (Figure 7) forming infinite chains that lay
along the b axis of the unit cell. This arrangement is
reminiscent of the packing in the crystals of 1b grown in the
presence of trifluoroacetic acid.17
Solution NMR spectroscopy. As in the case of 1a and 1b 16
, the
1H NMR spectrum of 2a in solution (Figure 8) is indicative of
aggregation. For a 2 mM solution in CD2Cl2, significant
broadening of the resonances is observed at room
temperature. Upon cooling, peak width increases and new
resonances appear creating an intricate pattern that is not
completely resolved at 190 K in the 500 MHz instrument. The
8.86 ppm singlet that at 298 K arises from the hydrogen atom
on the heterocycle (H3) splits into at least 7 separate
resonances that spread from 8.7 to 9.1 ppm and have different
intensities. The low solubility of 2a precludes a thorough study
but the ratio of intensities of the singlets at 8.87 and 8.93 ppm
at 190 K is dependent on concentration (2mM: 1:1.3; 0.4 mM:
1:0.9), which indicates that these resonances arise from two
structures related by aggregation. Such behaviour is observed
in the spectrum of 1b at 190 K due to the equilibrium between
tetramers and hexamers.
Figure 5. ORTEP (50%) plot of the tetrameric aggregate of benzotellurazole N-oxide as
observed in
a
crystal of composition 2a4⋅C6H6. Te…O, 2.201(4), 2.213(4) Å; Te-N
2.244(5), 2.250(4) Å; N-O 1.361(7), 1.368(5) Å; N-Te-O 161.3(2), 164.6(1)°; Te-N-O
125.4(3), 127.2(3)°; Te-O-N 110.0(3), 115.7(3)°; Te-O-N-Te 1.4(5), 42.6(4) °.
Figure 6. a) Detail of the crystalline structure of 2a4⋅C6H6 highlighting the channels
occupied by benzene molecules.
The observed ranges of Te…O (2.178(5) to 2.245(2) Å), and
Te—N (2.198(2) to 2.274(7) Å) distances as well as the average
N-Te-O (163.4°), N-Te-C (75.8°) and O-N-Te (126.4°) angle
values are comparable to those measured in the crystal
structures of 1a and 1b 18
stable.
,
suggesting that they are equally
Figure 8. VT 1HNMR spectrum of 2a in CD2Cl2. a) 2 mM, 298 K; b) 2 mM, 190 K;
c) 0.4 mM 190 K.
The complex VT 1H NMR spectra of 2a are in sharp contrast
with those of 2b (Figure 9). No significant broadening is
observed between 190 and 298 K, however, the frequencies of
two resonances (H3 and H7) strongly depend on temperature,
following a sigmoidal trajectory. A third resonance (from H4)
displays the same behaviour, albeit within a much narrower
range. Such profiles are characteristic of fast supramolecular
aggregation equilibria, thus the observed frequencies are
averaged. The data was analysed assuming that all aggregation
steps have the same equilibrium constant (K), with an
isodesmic model.19 The temperature dependency of δ(H3)
served as the basis to model the degree of aggregation (
with eq. 1 where Tm is the melting temperature, i.e. T for
which = 0.5, and H is the molar change of enthalpy.
α)
Figure 7. ORTEP (75%) depicting the organization of the molecules in the crystal of 2b.
Se…O 2.412(5) Å; Se-N 1.938(5) Å; N-O 1.315(6) Å; N-Se-O 172.3(2)°; Se-N-O 118.8(4)°;
Se-O-N, 108.1(3)°; Se-O-N-Se 86.3(4)°.
α
ꢁ
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ꢂ
ꢃ ꢄ
(1)
ꢌꢇꢌ
ꢎ ꢌ
ꢍ
ꢍ
ꢇꢈ.ꢉꢈꢊ ∆ꢋ
ꢏ
ꢂꢅꢆ
The fitted model (Figure 10) was then used to estimate the
aggregation number (AN, Figure 11). At 190 K, the AN value of
4.8 at 190 K suggests that hexamers and tetramers are present
in solution. In fact, the most NMR sensitive hydrogen atoms
would be brought close to each other by the assembly of
annular aggregates. The structures of the crystals that contain
2a4 and 2a6 are useful examples in this regard, they feature
2.9-3.2 Å distances between the H3 and H7 of neighbouring
molecules. Similar distances would be obtained in the
selenium case.
At each measured temperature, the equilibrium constant was
evaluated with eq. 2, all points were used to extract the
thermodynamic parameters with
(Figure 12).
a
Van’t Hoff analysis
ꢂ
½
ꢐꢑ ꢄ ꢒ
ꢄ ½ ꢖ ½ꢒ4 K Cꢔ ꢖ 1ꢕ
(2)
½
ꢕ
ꢂꢁꢓꢒꢔꢕ
Figure 9. VT 1H NMR of 2b in CD2Cl2 (15 mM). 1H-13C HMBC assignments are labelled
using standard IUPAC numbering.
Figure 12. Van’t Hoff plot for the autoassociation equilibrium of 2b in CD2Cl2. Fitting
parameters: ꢁH = -14.0 ± 0.4 kJ mol-1, ꢁS = -46 ± 2 J mol-1 K-1, r2 = 0.999.
The negative entropy change is consistent with aggregation.
Although the fitted enthalpy change confirms the exothermic
character of the process, its magnitude is different from the
value obtained from the degree of aggregation plot. Such
disagreements are not uncommon19 as the model contains
approximations, therefore these values must be used with
caution.
Figure 10. Degree of aggregation (a) of 2b as a function of temperature modelled for
the resonance of H3. The dotted line corresponds to the model with fitted parameters
Tm = 239 K and ꢁH = -33 kJ/mol.
DFT calculations. GGA (PBE-D3, ZORA, TZ2P) calculations were
performed to assess the relative strengths of the Se…O and
Te…O chalcogen bonds formed by the benzo-1,2-
Chalcogenazole 2-Oxides. Because previous investigations16
have shown that the energies of such interactions are
approximately additive, modelling was based on the individual
molecules and dimers of 2a and 2b. Consistent with the
crystallographic observations, the minimized dimers are not
planar, the optimized angles between the molecular planes are
71.2° and 66.3° in 2a2 and 2b2, respectively. Optimized
intramolecular distances in the dimers differ by less than
0.11 Å with respect to the crystallographic determinations and
by less than 0.07 Å from the optimized individual molecules.
Deviations in the E…O (E = Te, Se) distances are 0.165(4) Å for
Figure 11. Aggregation number (AN) of 2b as a function of temperature,
calculated from the resonance of H3.
2a2 and 0.206(5) Å for 2b2
.
The binding energy of the chalcogen bonds (EE…O, E = Te, Se)
was evaluated and analysed using the Ziegler-Rauk transition-
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state approach,20-22 which assumes a hypothetical stepwise Each of the energy terms is larger in magnitude for the
process. In the first stage, the individual molecules are tellurium case. The most important stabilising contributions
calculated in the geometries optimized for the dimers but are Eelstat and EOrbital, the former being slightly larger in
without orbital mixing. Calculation of this transition-state magnitude. The difference of Eelstat is related to the
yields the electrostatic interaction (Eelstat) and Pauli repulsion magnitudes of Vmax at the
σ hole of each molecule (2a: 139.62
(EPauli) between the molecules. Combined, the electrostatic and kJ mol-1, 0.053 e bohr-3; 2b: 118.15 kJ mol-1, 0.045 e bohr-3, for
Pauli repulsion energies are termed the total steric interaction 2b). As the energies of the HOMOs (O centred lone pairs) are
(ESteric). The second stage consists of the mixing of orbitals of similar (-5.328 eV for 2a and -5.410 eV for 2b), the EOrbital
the interacting molecules, here relaxation of the system by values reflect the LUMO heights (-3.303 eV for 2a and -2.884
polarization gives the orbital interaction (EOrbital). Combination eV for 2b) and different overlap abilities of the Te and Se
of those contributions and the dispersion correction (EDispersion
)
orbitals with those of oxygen. Electrostatic potential maps and
give the total EE…O. However, there is an energetic cost LUMOs are displayed in Figure 13.
(EPreparation) for the geometric distortion of the molecules from Vibrational calculations were carried out to demonstrate that
their non-associated structures. Combination with EE…O gives each optimized geometry is an actual minimum on the
the total electronic bonding energy (ETotal
contributions are compiled in Table 2.
,
eq. 3). All respective potential energy surface and to derive the
corresponding standard thermodynamic parameters in gas-
phase. The results in Table
2 show that while the
ETotal = Eelstat + EPauli + EOrbital + EDispersion + EPreparation
= ESteric + EOrbital + EDispersion + EPreparation
= EE…O + EPreparation
autoassociation of 2a is a spontaneous process, the Se…O
interaction is too weak to compensate for the entropic cost of
the dimerization of 2b at ambient temperature. As calculated,
the differences in the stability of the aggregates of these
molecules are consistent with the behaviour of their NMR
spectra in solution as a function of temperature.
(3)
Table 2. Energy decomposition analysis for dimerization of 2a and 2b. All DFT
calculations were done with GGA (PBE-D3, ZORA, TZ2P). All values are given in kJ mol–1
unless otherwise noted.
2a2, E=Te
2b2, E=Se
Experimental
Eelstat
-269.54
418.08
148.54
-229.83
-11.68
-92.97
-81.55
118.94
37.38
-62.11
-9.85
Materials and methods
EPauli
ESteric
Air sensitive materials were handled using an atmosphere of
nitrogen. Organic solvents were purified either by distillation
over the appropriate dehydrating agents under nitrogen or
using an Innovative Technologies purification system. The
following chemicals were used as received from the
commercial suppliers: dichloromethane-d2 (Aldrich), DMSO-d6
(Aldrich), 2-bromobenzaldehyde (Aldrich), 2.5 M n-butyllithium
solution in hexanes (Aldrich), Hydroxylamine hydrochloride
(Fisher), sodium hydroxide (EMD), ethylene glycol (Fisher),
sodium bicarbonate (Sigma), sodium sulphate (EMD), silica gel
(EM, 230-400 mesh), elemental tellurium (CERAC), iodine
(AnalaR), and p-Toluenesulfonic acid (Eastern).
EOrbital
EDispersion
EE…O
-34.58
EPreparation
17.98
-74.99
2.14
3.04
-31.54
1.81
ETotal
ΔZPE × 10-2 [eV]
ΔH
ΔS [J mol-1K-1]
-72.68
-29.21
-186.74
-17.01
-171.85
22.03
ΔG273.15K
V (kJ/mol)
136
a)
b)
Nuclear Magnetic Resonance. All spectra were measured in
solution with a deuterated solvent. Spectra were obtained
using Bruker AVANCE 500MHz (Bruker 5-mm Broad Band
Inverse probe) or Bruker AVANCE 600MHz (Bruker 5-mm
BROAD BAND OBSERVE probe) Spectrometers at 287.5 K. The
1H, 13C and 125Te spectra were processed using Bruker TopSpin
2.1 or 3.2 software packages. The 1H and 13C spectra were
referenced to tetramethyl silane using the deuterated solvent
signal as a secondary reference. The 125Te and 77Se chemical
shifts are reported respect to the room-temperature
14
-108
resonance of TeMe2 and SeMe2 respectively (
were measured using a secondary reference of diphenyl
ditelluride 420.36 ppm) and diphenyldiselenide
= 462.99 ppm) in CD2Cl2.
δ=0.00 ppm) but
2a
2b
(
δ
=
Figure 13. DFT analysis of the electronic structure of 2a and 2b. a) Electrostatic
(
δ
potential maps plotted on the 0.001 a.u. isodensity surfaces; b) LUMOs plotted at 0.04
a.u.
Electrospray Ionization Mass spectrometry. Mass spectra
were acquired in positive ion mode on a Waters/Micromass
Quattro Ultima Global TOF mass spectrometer functioning in
6 | J. Name., 2012, 00, 1-3
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W Mode. Pure samples were dissolved in dichloromethane mL) and tellurium power (26.5 mmol) was added all at once
followed by dilution with methanol. High resolution Mass while maintaining a 0°C temperature. The mixture was stirred
spectra were obtained in a Waters Global and Ultima (ES Q- at room temperature for 2 h. The reaction was quenched with
TOF) Mass Spectrometer (capillary = 3.20 V, cone= 100 V, distilled water (60 mL) at 0°C and stirred for 30 min. The
source temp= 80
℃
and resolving power= 10000).
product was extracted with dichloromethane, washed with
Single-Crystal X-ray Diffraction All crystals were mounted on distilled water, dehydrated over anhydrous Na2SO4 and
nylon loops (Hampton, California) or MiTeGen micromounts concentrated under vacuum to yield a dark yellow crystalline
(Ithaca, New York) with Paratone-N oil. Data were collected at material. No further purification was necessary before the next
100 K or 173.15 K using Mo-K
Bruker APEX2 diffractometer. The CCD area detector was column with a hexane-EtOAc gradient from 95:5 to 80:20. Yield
equipped with
low-temperature accessory (Oxford 75%. Mp 118-120°C. 1H NMR (600 MHz, CD2Cl2) δ 7.98-7.96 (m,
ꢃ radiation (ꢗ = 0.71073 Å) with a step, but it can be achieved by chromatography on a silica gel
a
cryostream). A minimum of 50 frames from three different 2H), 7.37-7.36 (m, 2H), 7.26-7.23 (m, 2H), 7.16-7.13 (m, 2H),
orientations were used for the determination of the 5.83 (s, 2H), 4.21-4.15 (m, 4H), 4.08-4.03 (m, 4H). 13C NMR
precursory unit cell parameters and final cell advancement (600 MHz, CD2Cl2) δ 140.2, 139.2, 130.8, 127.8, 126.3, 108.0,
after integration in SAINT.23 The absorption was corrected for 105.7, 65.6. 125Te NMR (600 MHz, CD2Cl2) δ 318.3. IR (KBr, ꢘꢙ):
each data set in SADABS.24 Direct methods were used to solve 3052, 2971, 2885, 1582, 1565, 1462, 1446, 1390, 1285, 1213,
all structures and then refined by the full-matrix least-squares 1119, 1083, 1043, 1016, 966, 942, 874, 754, 734, 654, 440.
techniques on F2 using SHELXL.25 All non-hydrogen atoms HRMS-ESI+: m/z [M+H]+ calcd. for C18H18O4129Te2H: 558.9408;
were assigned anisotropic thermal parameters. Appropriate found: 558.9426.
riding models were used to place hydrogen atoms in idealized Bis(2-formylphenyl)
ditelluride
.
2,2'-(ditellurodi-2,1-
positions. phenylene)bis-1,3-Dioxolane (1 g, 1.8 mmol) and p-
Other Instrumental Methods. Infrared vibrational spectra Toluenesulfonic acid (0.190 g, 1.1 mmol) were dissolved in a
were measured in a Bio-Rad FTS-40 FT-IR spectrometer or a mixture of distilled water/acetone/distilled THF (60:60:30 mL)
Thermo Scientific Nicolet 6700 FT-IR spectrometer. Melting then refluxed for 2 h. After cooling to room temperature,
points were measured with Uni-Melt Thomas Hoover capillary distilled water (300 mL) was added to the yellow solution; the
melting point apparatus and are reported uncorrected. product was extracted with CH2Cl2, washed with distilled water
Combustion elemental analyses were carried out by the then brine. The yellow solution was dehydrated over
London Metropolitan University elemental analysis service anhydrous Na2SO4 and concentrated under vacuum to yield a
(London, United Kingdom).
dark yellow crystalline material. No further purification was
necessary before the next step, but it can be achieved by
precipitation in hexanes from a concentrated solution of
CH2Cl2. (93%). Mp 141-143°C. 1H NMR (600 MHz, CD2Cl2) δ
10.14 (s, 2H), 8.02 (d, 2H), 7.85-7.84 (m, 2H), 7.48-7.45 (m,
2H), 7.34-7.31 (m, 2H). 13C NMR (600 MHz, CD2Cl2) δ 193.7,
140.8, 137.3, 137.2, 134.8, 127.5, 112.8. 125Te NMR (600 MHz,
CD2Cl2) δ 414.4. IR (KBr, ꢘꢙ): 2835, 2742, 1654, 1577, 1551,
1447, 1436, 1386, 1298, 1255, 1205, 1163, 1112, 1019, 840,
760, 745, 700, 657, 435. HRMS-ESI+: m/z [M+H]+ calcd. for
C18H18O4129Te2H: 470.8884; found: 470.8889.
Syntheses
2-(2-bromophenyl)-1,3-dioxolane. Ethylene glycol (6 g, 96.7
mmol) and p-Toluenesulfonic acid (0.616 g, 3.24 mmol) were
added to 2-bromobenzaldehyde (12 g, 64.9 mmol) in 150 mL
of toluene. The solution was heated to reflux with a Dean-
Stark trap during 19 hours. The slightly cloudy yellow solution
was cooled then washed with a NaHCO3 solution (1 M) until
the organic phase was no longer acidic. This treatment was
followed by washings, first with distilled water and later with
brine. The organic layer was dehydrated with Na2SO4 and
concentrated. The crude product, a yellow liquid, was purified
by chromatography on a silica gel column with a hexane/EtOAc
95:5 mixture. The product was obtained as a clear colourless
2,2'-ditellurobis-benzaldehyde dioxime (3a). A solution of
hydroxylamine hydrochloride (0.063 g, 0.9 mmol) and sodium
hydroxide (0.036 g, 0.9 mmol) in distilled water (1.6 mL) was
added dropwise into bis(2-formylphenyl) ditelluride (0.093 g,
0.2 mmol) dissolved in pyridine (1.6 mL) at 0°C under a
nitrogen atmosphere. The solution was stirred at room
temperature for 2 h, then diluted with 10 mL of CH2Cl2, then
washed with distilled water. The yellow solution was
dehydrated over anhydrous Na2SO4 and concentrated under
vacuum to yield a yellow solid. The moist crude was
suspended in CHCl3 (freshly-filtered through activated neutral
alumina) and filtered to yield a light-yellow crystalline powder.
Yield 73%. Mp 166°C (d). 1H NMR (600 MHz, DMSO-d6) δ
11.83 (s, 2H), 8.45 (s, 2H), 7.90 (d, 2H), 7.49-7.47 (m, 2H), 7.32-
7.29 (m, 2H), 7.17-7.14 (m, 2H). 13C and 125Te NMR could not
be recorded due to the low solubility of this compound. IR
(KBr, ꢘꢙ): 3356, 3250, 1581, 1523, 1458, 1432, 1342, 1301,
1254, 1204, 1161, 1122, 1042, 1034, 1020, 970, 943, 904, 880,
1
liquid after solvent evaporation. Yield 90%. H NMR (600 MHz,
CD2Cl2) δ 7.60-7.56 (m, 2H), 7.37-7.34 (m, 1H), 7.26-7.23 (m,
1H), 6.05 (s, 1H), 4.16-4.01 (m, 4H). 13C NMR (600 MHz,
CD2Cl2) δ 133, 131, 128, 128, 123, 103, 66. HRMS-ESI+: m/z
[M+H]+ calcd. for C9H9O2BrH: 228.9864; found: 228.9863.
2,2'-(ditellurodi-2,1-phenylene)bis-1,3-Dioxolane
. A 2.5 M
solution n-butyllithium in hexanes (11.7 mL, 29.2 mmol) was
added dropwise to 2-(2-bromophenyl)-1,3-dioxolane (6.08 g,
26.5 mmol) in anhydrous diethyl ether (80 mL) at 0°C, the
solution developed a brown colour and a pale pink solid
precipitated. The mixture was stirred for 1 h at room
temperature; the precipitate was filtered under argon and
washed with anhydrous diethyl ether. The precipitate was
dissolved under argon with freshly-distilled anhydrous THF (80
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750, 730, 713, 663, 652, 562, 527, 453, 432. HRMS-ESI+: m/z (600 MHz, CDCl3) δ 136.8, 132.5, 130.3, 130.1, 127.2, 127.1,
[M+H]+ calcd. for C14H12N2O2129Te2H: 500.9142; found: 103.6, 65.4. 77Se NMR (600 MHz, CDCl3) δ 411.3. HRMS-
500.9144. Elemental anal. % calcd. C14H12N2O2Te2: C 33.94, H TOFEI+: m/z [M]+ calcd. for C18H18O480Se2: 457.9535; found:
2.44, N 5.65; found: C 34.07, H 2.52, N 5.54.
Benzo-1,2-Tellurazole 2-Oxide (2a)
457.9557. All data were in agreement with literature values.22
.
2,2'-ditellurobis- Bis(2-formylphenyl) diselenide. Similar to Bis(2-formylphenyl)
benzaldehyde dioxime (0.1 g, 0.2 mmol) was suspended in ditelluride synthesis, 2,2'-(diselenadi-2,1-phenylene)bis-1,3-
methanol (5 mL). The solid was consumed as I2 (0.051 g, 0.2 dioxolane (1.60 g, 3.5 mmol) and p-Toluenesulfonic acid (0.41
mmol) was added. The red solution was stirred at room g, 2.13 mmol) were dissolved in a mixture of distilled
temperature for 2 h, period after which 0.1 M NaHCO3 (5 mL) water/acetone/distilled THF (120:120:60 mL) then refluxed for
was added and a light yellow solid precipitated. The crude 2 h. After cooling to room temperature, distilled water (600
product was re-dissolved and extracted with CH2Cl2. The mL) was added to the yellow solution; the product was
organic layer was washed with distilled water, dehydrated extracted with CH2Cl2, washed with distilled water then brine.
over anhydrous Na2SO4 and concentrate under reduced The yellow solution was dehydrated over anhydrous Na2SO4
pressure yielding a light-yellow precipitate. Yield 95%. Mp 221- and concentrated under vacuum to yield a dark yellow
222°C (d). 1H NMR (600 MHz, DMSO-d6) δ 9.28 (s, 1H), 7.98 (d, crystalline material. No further purification was necessary
1H), 7.91 (d, 1H), 7.52 (t, 1H), 7.45 (t, 1H). 13C and 125Te NMR before the next step, but it can be achieved by precipitation in
could not be recorded due to the low solubility of this hexanes from a concentrated solution of CH2Cl2. (90 %). Mp =
compound. HRMS-ESI+: m/z [M+H]+ calcd. for C7H5NO129TeH: 171.2-172.3
°
C (d). 1H NMR (600 MHz, CDCl3) δ 10.17 (s, 2H),
249.9512; found: 249.9505. IR (KBr, ꢘꢙ): 1582, 1568, 1523, 7.86-7.84 (m, 2H), 7.83-7.82 (m, 2H), 7.42-7.40 (m, 4H). 13C
1454, 1432, 1341, 1256, 1204, 1122, 1060, 1049, 1020, 899, NMR (600 MHz, CDCl3) δ 193.1, 136.0, 135.0, 134.8, 134.5,
880, 750, 713, 682, 664, 652, 559, 530, 453, 430. Elemental 131.2, 126.5. 77Se NMR (600 MHz, CDCl3) δ 456.4. HRMS-
anal. % calcd. C7H5NOTe: C 34.08, H 2.04, N 5.68; found: C TOFEI+: m/z [M]+ calcd. for C14H10O280Se2: 369.9014; found:
33.92, H 1.95, N 5.76. Single crystals of the polymorphs of 2a 369.8999. All data were in agreement with literature values.23
were grown as follows. (2a6)•(CH2Cl2)•(H2O): Slow evaporation 2,2'-diselenabis-benzaldehyde dioxime (3b). A solution of
from a 0.043 M dichloromethane solution with pyridine (15% hydroxylamine hydrochloride (0.968 g, 13.9 mmol) and sodium
v/v).
Elemental
anal.
%
calcd.
C42H30N6O6Te6• hydroxide (0.58 g, 13.9 mmol) in distilled water (25 mL) was
1.78(CH2Cl2)•0.22(H2O): C 32.15, H 2.10, N 5.14; found: C added dropwise into bis(2-formylphenyl) diselenide (1.14 g,
32.36, H 2.11, N 5.31. (2a4): Slow evaporation from a 0.043 M 3.10 mmol) dissolved in pyridine (25 mL) at 0°C under a
dichloromethane solution with equal volume pyridine. nitrogen atmosphere. The mixture was stirred at room
Elemental anal. % calcd. C7H5NOTe: C 34.08, H 2.04, N 5.68; temperature for 2 h, then diluted with 10 mL of CH2Cl2 and
found: C 33.90, H 2.03, N 5.55. (2a4)•(C6H6): Slow evaporation washed with distilled water. The yellow organic layer was
from
C34H26N4O4Te4: C 38.34, H 2.46, N 5.26; found: C 38.21, H 2.40, vacuum to yield an oily yellow crude product that can be
N 5.33. crystallized at room temperature from dichloromethane by
a
benzene solution. Elemental anal.
%
calcd. dehydrated with anhydrous Na2SO4 and concentrated under
2,2'-(diselenadi-2,1-phenylene)bis-1,3-Dioxolane. Similar to slow addition of hexanes. Yield 86%. Mp 138.5-139.0 °C (d). 1H
2,2'-(ditellurodi-2,1-phenylene)bis-1,3-Dioxolane synthesis, a NMR (600 MHz, DMSO-d6) δ 11.74 (s, 2H), 8.44 (s, 2H), 7.69 (d,
2.5 M solution n-butyllithium in hexanes (6.28 mL, 15.7 mmol) 2H), 7.56 (d, 2H), 7.32-7.27 (m, 4H). 13C NMR (600 MHz, CDCl3)
was added dropwise to 2-(2-bromophenyl)-1,3-dioxolane (3.27 δ 149.0, 131.7, 130.7, 130.3, 129.5, 128.9, 126.6. 77Se NMR
g, 14.3 mmol) in anhydrous diethyl ether (40 mL) at 0°C, the (600 MHz, DMSO-d6) δ 446.3. IR (KBr, ꢘꢙ): 3317, 3039, 2836,
solution developed a brown colour and a pale pink solid 2729, 1584, 1556, 1471, 1436, 1300, 1256, 1208, 1025, 964,
precipitated. The mixture was stirred for 1 h at room 942, 931, 876, 866, 745, 711, 661, 642, 488, 443. Elemental
temperature; the precipitate was filtered under argon and anal. % calcd. C14H12N2O2Se2: C 42.23, H 3.04, N 7.04; found: C
washed with anhydrous diethyl ether. The precipitate was 42.38, H 2.96, N 7.06.
dissolved under argon with freshly-distilled anhydrous THF (40 Benzo-1,2-Selenazole
2-Oxide
(2b)
.
2,2'-diselenabis-
mL) and selenium power (1.13 g, 14.3 mmol) was added all at benzaldehyde dioxime (1.23 g, 3.11 mmol) was suspended in
once while maintaining a 0°C temperature. The mixture was methanol (80 mL). The solid was consumed as I2 (0.79 g, 3.11
stirred at room temperature for 2 h. The reaction was mmol) was added. The red mixture was stirred at room
quenched with distilled water (30 mL) at 0°C and stirred for 30 temperature for 2 h, period after which 0.1 M NaHCO3 (80 mL)
min. The product was extracted with dichloromethane, was added and a light yellow solid precipitated. The crude
washed with distilled water, dehydrated over anhydrous product was re-dissolved and extracted with CH2Cl2. The
Na2SO4 and concentrated under vacuum to yield a dark yellow organic layer was washed with distilled water, dehydrated
crystalline material. No further purification was necessary over anhydrous Na2SO4 and concentrate under reduced
before the next step, but it can be achieved by pressure yielding a light-yellow precipitate. Yield 95%. Mp
chromatography on a silica gel column with a hexane-EtOAc 108.0–112.0 °C (d). 1H NMR (600 MHz, DMSO-d6) δ 8.33 (s,
gradient from 95:5 to 90:10. Yield 70%. 1H NMR (600 MHz, 1H), 7.83-7.81 (m, 1H), 7.66-7.64 (m, 1H), 7.40-7.34 (m, 2H).
CDCl3) δ 7.79-7.77 (m, 2H), 7.48-7.46 (m, 2H), 7.25-7.24 (m, 13C NMR (600 MHz, DMSO-d6) δ 139.5, 134.6, 132.6, 127.0,
4H), 6.01 (s, 2H), 4.18-4.15 (m, 4H), 4.06-4.04 (m, 4H). 13C NMR 126.2, 124.8, 123.4. 77Se NMR (600 MHz, DMSO-d6) δ 1175.0.
8 | J. Name., 2012, 00, 1-3
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HRMS-TOFEI+: m/z [M]+ calcd. for C7H5NO80Se: 198.9536;
found: 198.9536. IR (KBr, ꢘꢙ): 3055, 3038, 2964, 2923, 2225,
1585, 1560, 1492, 1428, 1414, 1335, 1308, 1259, 1251, 1199,
1153, 1131, 1094, 1040, 1016, 877, 859, 756, 716. Elemental
anal. % calcd. C7H5NOSe: C 42.44, H 2.54, N 7.07; found: C
42.59, H 2.42, N 6.92.
6
7
8
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DFT Calculations. All calculations were performed using ADF
DFT package (Version 2013.01).26,27 Models for 2a
, 2b and their
9
respective dimers were optimized using the exchange-
correlation functionals of Perdew, Burke, and Ernzerhof28 and
corrected for dispersion29 with a triple-ζ all-electron basis set
with two polarization functions each and applying the Zeroth
Order Regular Approximation30-33 formalism with specially
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10
11
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16
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The procedures here described provide a more convenient
entry point to the supramolecular chemistry of iso-
chalcogenazole N-oxides. Compared to other methods for the
preparation of such heterocycles, the synthesis of the
benzoannulated derivatives is simpler because it only requires
two inert-atmosphere steps that can be carried out in
sequence without isolation and purification of the sensitive
intermediates. The crystal structures confirm that these
species retain the ability of the parent heterocycles to undergo
autoassociation. While self-assembled macrocyclic tetra- and
hexamers were obtained from the tellurium compound, a
supramolecular polymer was obtained from the selenium
heterocycle. DFT-D3 calculations indicate that the chalcogen
bonds formed by the selenium compound are much weaker;
however, VT NMR spectroscopy provides evidence of its
aggregation in solution at low temperature.
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Acknowledgements
We gratefully acknowledge funding from NSERC, OGS and
MITACS (Canada) as well as CAPES (Brazil). The conclusions
section should come in this section at the end of the article,
before the acknowledgements.
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This journal is © The Royal Society of Chemistry 20xx
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TOC Entry
Benzoannulated derivatives of the iso-tellurazole N-oxides retain their ability to spontaneously assemble functional
supramolecular macrocycles.
Table of Contents artwork
1