Synthetic and structural investigations of bis(N -alkyl-benzoselenadiazolium) cations

Article abstract of DOI:10.1039/c9dt02311a

The synthesis, and spectroscopic and structural characterization of bridged dicationic derivatives of benzo-2,1,3-selenadiazoles are reported. The chloride salt of [H₄C₆NSeN-CH₂-CH₂-NSeNC₆H₄

Full text of DOI:10.1039/c9dt02311a

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DOI: 10.1039/C9DT02311A.
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14 March 2017
Pages 3073-3412
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Synthetic and Structural Investigations of
Bis(N-alkyl-benzoselenadiazolium) cations
Lucia Myongwon Lee, Victoria Corless, Helen Luu, Allan He, Hilary Jenkins, James F. Britten,
Faisal Adam Pani and Ignacio Vargas-Baca*
McMaster University, Department of Chemistry and Chemical Biology,
1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1.
*To whom correspondence should be addressed. E-mail: vargas@chemistry.mcmaster.ca
TOC entry
A variety of supramolecular structures is formed by selenadiazolium cations linked by
hydrocarbon bridges
Abstract
The synthesis, spectroscopic and structural characterization of bridged dicationic derivatives of
benzo-2,1,3-selenadiazoles are reported. The chloride salt of [H4C6NSeN-CH2-CH2-NSeNC6H4]2+
crystallized forming a macrocyclic structure in which two cations are bridged by Se…Cl chalcogen
bonds (ChBs), with a third chloride at the centre of the macrocycle. The structure of [1,2-
(H4C6NSeN)2-C6H10]Cl2 consists of two selenadiazolium cations linked by a chiral cyclohexane
and capped by Se…Cl ChBs. The tetrafluoroborate salts of a xylene bridge crystallized in two
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pseudopolymorphs in which the cations form Se…F ChBs in anti or syn conformations. The triflate
salt of ethylene bridged cations dimerize through the formation of the [Se-N]2 supramolecular
synthon with Se…O ChBs capping the second selenium atom. In contrast, [H4C6NSeN-CH2-CH2-
CH2-NSeNC6H4](CF3SO3)2 only forms Se…O ChBs.
Introduction
The attractive interaction between positively polarized atoms of p-block elements and
electron-rich Lewis bases, has emerged as an interesting alternative to the ubiquitous hydrogen
bonding in supramolecular chemistry. By analogy to halogen bonding1, the term chalcogen
bonding (ChB) is now commonly used to denote such interactions when centred on heavy group-
16 elements (E= S, Se, Te). Recent advances on chalcogen bonding research2,3 encompass a wide
range of applications in crystal engineering4-7, catalysis7-10, anion transport8,9, anion
recognition10,11, and the assembly of supramolecular capsules12, polymers13-15, and macrocycles.16-
20 A particularly interesting example is the development of new organic semiconductors through
the formation of S/Se…N ChBs.21
The molecules of 1,2,5-chalcogenadiazoles (1, 2 in Scheme 1) have been of special interest
due to their propensity to associate with Lewis bases, neutral and anionic molecules and
themselves through the formation of Ch…N (Ch = S, Se, Te) ChBs.5,22,23 Within the series, the
telluradiazoles form the strongest Ch…N ChBs. These building blocks assemble supramolecular
ribbons or dimers, depending on the steric hindrance, thanks to the [TeN]2 supramolecular
synthon.5 The autoassociation of derivatives of 2c enables potentially useful optical properties
such as second-harmonic generation24 and chromotropism25. However, their moisture sensitivity
hampers wide-spread application of the tellurium compounds.
2

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Scheme 1. Chalcogenadiazoles and their N-alkyl cations.
The selenium congeners (1b, 2b) form weaker Se…N ChBs but these can be strengthened
by increasing the electron-withdrawing ability of the nitrogen atom in the antipodal position.26
This can be achieved by attachment of Lewis acidic groups such as electron-deficient boranes27,
transition metal ions28,29, or alkyl groups (formally carbocations).30,31 In the first two cases, the
lability of the bond between the nitrogen and the acidic group limits the application of this
approach as a general strategy in the construction of supramolecular structures. On the other hand,
nitrogen-carbon bonds usually are kinetically stable. Furthermore, the stability towards hydrolysis
of the cationic derivatives makes them very attractive as supramolecular building blocks.30
In comparison to 1c and 2c, the auto-association of 3a is limited to dimers in the best case.
However, pseudo-trimers (e.g. [3a.2b.3a]I2), can be formed with the introduction of the neutral
heterocycles.30,32 In order to favor the crystallization supramolecular polymers, we investigated
dicationic molecules built by linking two N-alkyl selenadiazolium cations (Scheme 2). Here we
report the use of hydrocarbon bridges, including a chiral 1,2-cyclohexane bridge, in such dicationic
supramolecular building blocks.
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N
N
N
N
Se
Se
Se
Se
N
N
N
N
Scheme 2. Proposed supramolecular polymers assembled by of bis(benzo-2,1,3-selenadiazolium)
cations.
Results and Discussion
Scheme 3. General approach for the syntheses of bis(benzo-2,1,3-selenadiazolium) cations 4a-d.
The synthetic methods previously developed for the N-alkyl benzo-2,1,3-selenadiazolium
cations25 were adapted to the preparation of bridged cations (4a-d, Scheme 3). The most flexible
approach is based on the condensation of N-alkylated aromatic ortho-diamines with selenous acid.
For the synthesis of dications, the key precursors are bridged bis(ortho-phenylene diamines). Some
of those reagents can be prepared by the reaction of phenylenediamine with organo-dihalides, but
the most efficient procedures are based on nucleophilic aromatic substitution of 1,2-
fluoronitrobenzene with diamines followed by catalytic hydrogenation.33 The latter method was
employed with ethylene diamine, 1,3-diaminopropane, and R,R-1,2-diaminocyclohexane; the first
method was used to create a 1,4-xylylenyl-bridged tetraamine. The precursor tetraamines prepared
4

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with these procedures are vulnerable to oxidization upon exposure to air and ambient light; they
were most conveniently isolated and purified as their hydrochlorides by treatment with anhydrous
hydrogen chloride. To minimize contamination by their oxidation products, these intermediates
were not usually stored, instead they were immediately used to produce salts of the
bis(selenadiazolium) cations 4a-d.
The reactions of the diamines with H2SeO3 require an acidic medium; aqueous HCl was used in
first instance because the organic reagents were prepared as hydrochlorides. However, as
discussed below, halides easily compete with neutral nitrogen atoms to form chalcogen bonds.
-
-
Salts of the less coordinating BF4 and CF3CO2 were obtained using the corresponding acid or
by anion exchange. However, not all bridge-anion combinations yielded well-defined products.
Only the species that could be conclusively identified and properly characterized are described in
this report.
Preparation and spectroscopic characterization of chloride salts. In a typical example, the
hydrochloride salt of 1,2-di(o-aminophenylamino)ethane reacted with a warm solution of selenous
acid in aqueous HCl to yield a dark red precipitate. Recrystallization from ethanol gave analytically
.
pure [4a]Cl2 4H2O. The R,R-1,2-cyclohexanediyl and 1,4-xylylenyl bridged molecules were used
to synthesize chloride salts of 4c and 4d. The identity of the products was verified by X-ray
diffraction of their single crystals, the homogeneity of [4a]Cl2 and [4c]Cl2 samples was established
by combustion elemental analysis. However, the low solubility of [4d]Cl2 precluded satisfactory
purification by recrystallization.
The 1H NMR spectrum of the dications 4a-d is characterized by resonances of the aromatic protons
of the benzoselenadiazolium that range from 7.49–7.96 ppm. The positions of these resonances
are comparable to those of the N-methyl cations, and appear at slightly lower frequency than
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observed for the isopropyl, tert-butyl monocations.30 The same aromatic protons are shifted upfield
by 0.15 ppm from that of 2b. The ESI mass spectra clearly displays the isotopic patterns expected
for the 2+ cations (Figure 1).
Figure 1. Experimental ESI-HR mass spectrum (blue) and calculated isotropic pattern (red) for:
.
.
(a) [C14H12N4Se]2+ (4a) from [4a]Cl2 4H2O; (b) [C18H16N4Se]2+ (4c) from [4c]Cl2 H2O.
Preparation and spectroscopic characterization of the tetrafluoroborateand trifluoromethyl
sulfonate salts. Given the strength of binding of halide anions to the chalcogen atom in
selenadiazolium cations,30 it was anticipated that Se…Cl- ChBs would strongly compete with the
Se…N ChBs. Attempts were thus made to replace chloride in the initial products with less
-
-
coordinating species such as BF4 and CF3SO3 . Preliminary precipitation attempts with AgBF4
failed to produce any solid AgCl, this is likely due to coordination of Ag+ in spite of the 2+ charge
of the cation. Coordination of transition metal ions to cations is rare but has been observed with
organic ligands that contain nitrogen donors.34 Successful anion replacement was first achieved in
the reaction of [4a]Cl2 with NOBF4 under anhydrous conditions. The by-product, NOCl, is a gas
in ambient conditions, which obviates the need for purification workup. The reactions with NOBF4
1
produced yellow precipitates which were collected and characterized by H and 19F NMR
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spectroscopy. The aromatic proton resonances observed for the tetrafluoroborate salts appear at
higher frequency (7.85-8.12 ppm) than those for the chloride salts (7.69-7.96 ppm). The
resonances of the protons on the ethylene bridge are found at 5.54 ppm, which is 0.09 ppm above
the resonance of that in the chloride salt.
The above anion replacement method is efficient but the overall yield is low. Better results were
achieved by adding the tetraamine to a stoichiometric amount of HBF4 and H2SeO3 in solution.
The resulting red-orange precipitate was washed with a saturated solution of NaBF4 in ethanol
until the remaining acid was removed. The 1,4-xylylenyl derivative [4d](BF4)2, was prepared in
the same way. Recrystallization of this material from acetonitrile gave two polymorphs of
[4d](BF4)2, depending on the concentration of the solution.
-
As discussed below, because Se…F- ChBs were observed in the structures of the BF4 salts,
trifluoromethanesulfonate salts of the dications were prepared with an analogous procedure. The
reaction of 1,2-di(o-aminophenylamino)ethane and selenous acid in ethanolic
trifluoromethanesulfonic acid yielded [4a](CF3SO3)2; 1,2-di(o-aminophenylamino)propane
yielded [4b](CF3SO3)2. The resonances of the aromatic protons of [4a](CF3SO3)2 range from 7.87
to 8.15 ppm, which are slightly higher in frequency than those of the chloride and tetrafluoroborate
salts. The chemical shifts of the same aromatic protons in [4b](CF3SO3)2 appear in the same region
77
(7.83 to 8.07 ppm). Because of their modest solubility in DMSO, the Se NMR chemical shifts
were measured through 1H – 77Se heteronuclear multiple bond correlation (HMBC) experiments.
The 77Se values of [4a](CF3SO3)2 and [4a](BF4)2 (1490 and 1482 ppm respectively) appear at 40
.
ppm higher than that for [4a]Cl2 4H2O (1445 ppm).
Crystal Structures. Full crystallographic data for all new structures are compiled in Table S1 and
selected bond distances and angles are compiled in Tables 1 and 2. Although compound [4a]Cl2
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was obtained in pure from the synthesis, single-crystal growth yielded a tetrahydrate. The crystal
.
of [4a]Cl2 4H2O displays a unique molecular arrangement. The dications feature the heterocycles
in a syn orientation and are organized in pairs bridged by Se…Cl ChBs (2.803, 2.682 Å) conforming
a macrocycle-like structure with a third chloride anion at the centre making longer (3.313 and
3.647 Å) contacts with the four chalcogens (Figure 2). The fourth chloride anion sits in the lattice
without making any meaningful interatomic contacts.
Figure 2. ORTEP and numbering scheme for the asymmetric unit in the crystal structure of
.
[4a]Cl2 4H2O. Displacement ellipsoids are shown at the 50 % probability level.
.
.
Table 1. Selected distances (Å) and angles (˚) for [4a]Cl2 4H2O and [4c]Cl2 H2O.
.
.
Compound
Se1-N2
Se1-N1
Se2-N4
Se2-N3
N2-C6
[4a]Cl2 4H2O
[4c]Cl2 H2O
1.879 (6)
1.793 (6)
1.867 (6)
1.778 (6)
1.341 (8)
1.456 (8)
1.330 (9)
88.4 (2)
1.888 (2)
1.768 (2)
1.893 (2)
1.768 (2)
1.332 (3)
1.480 (3)
1.330 (4)
88.55 (1)
110.6 (6)
111.2 (2)
N2-C7
N1-C1
N2-Se1-N1
Se1-N2-C6
Se1-N1-C1
110.6 (4)
111.8 (4)
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.
Compound [4c]Cl2 also crystallized as a hydrate. The asymmetric unit of [4c]Cl2 H2O consists of
two heterocycles bridged by a 1-(R),2-(R)-substituted cyclohexane ring featuring Se…Cl ChBs
with distances of 2.731 Å, which are shorter than found in the monocation (N-hydro-benzo-2,1,3-
selenadiazolium chloride) (2.901(1) and 3.075(1) Å). The chirality of the cyclohexane bridge leads
to the formation of helical assemblies with a 9° deviation from the normal of the C1, C2, C3, C4
plane in the cyclohexane. (Figure 3) The angle between the two heterocycle planes is much larger
(25.5°) than that in the ethylene-bridged dication (4.36°).
Figure 3. (a) ORTEP and numbering scheme for the asymmetric unit and (b) packing in the crystal
.
structure of [4c]Cl2 H2O. Displacement ellipsoids are shown at the 50 % probability level.
In the case of the chloride salt of the 1,4-xylylenyl-bridged dication [4d]Cl2, it was not possible to
obtain single crystals of the compound because of its low solubility. Attempts to grow crystals by
diffusion under several conditions only yielded dendrites that scattered X-rays poorly and thus
were unsuitable for a structural determination.
The first polymorph of [4d](BF4)2 belongs to the P121/n1 space group and was obtained from
acetonitrile. Its asymmetric unit features the dication with an anti conformation. Each selenium
-
atom is engaged in a short contact with a BF4 anion (Figure 4) the shortest Se…F distance
(2.769(1) Å) is shorter than the sum of the van der Waals radii (3.37 Å). A second crystalline phase
from this salt, a pseudopolymorph, was obtained from a dilute solution in acetonitrile and includes
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.
solvent in the lattice ([4d](BF4)2 CH3CN). The sample deteriorated likely due to loss of the solvent
and only 85% of the collected data was processed. In this case, the molecular dication structure
-
displays a syn conformation that appears to chelate the BF4 anion. The Se…F distances are
3.005(8), and 2.914(7) Å.
.
Figure 4. Molecular structures in the crystals of (a) [4d](BF4)2 and (b) [4d](BF4)2 CH3CN.
Hydrogen atoms are omitted for clarity and displacement ellipsoids are shown at 50 % probability
level.
The asymmetric unit of [4a](CF3SO3)2 (Figure 5) includes two heterocycles bridged by one
ethylene molecule and two units of trifluoromethanesulfonate anions. Selected distances and
angles are compiled in Table 3. One heterocycle in the dication forms the [SeN]2 supramolecular
synthon with a neighbouring cationic heterocycle with Se-N distances of 2.588(2) Å. The same
selenium atom also has close contacts with the oxygen atoms of the trifluoromethanesulfonate
anions which are sitting above and below the plane of the cationic ring. (3.295(3), 3.319(3),
3.357(3) Å) The selenium atom of [4b](CF3SO3)2 features much shorter Se…O ChBs (2.665(1),
2.808(2), 3.137(2) Å) and does not form Se…N ChBs as the trifluoromethanesulfonate anion blocks
this site.
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Figure 5. ORTEP and numbering scheme for the asymmetric unit in the crystal structure of
[4a](CF3SO3)2. Displacement ellipsoids are shown at the 50 % probability level.
.
Table 2. Selected distances (Å) and angles (°) for [4d](BF4)2, [4d](BF4)2 CH3CN, [4a](CF3SO3)2
and [4b](CF3SO3)2.
.
Compound
Se-N1
[4d](BF4)2
[4d](BF4)2 CH3CN
[4a](CF3SO3)2
[4b](CF3SO3)2
1.768 (2)
1.757 (3)
1.768 (2)
1.760 (2)
Se-N2
Se-N4
1.833 (1)
1.833 (1)
1.767 (1)
1.341 (2)
1.485 (2)
1.332 (2)
90.4 (6)
1.821 (4)
1.835 (3)
1.756 (4)
1.330 (6)
1.474 (5)
1.342 (6)
90.5 (2)
1.854 (2)
1.838 (2)
1.777 (2)
1.337 (3)
1.469 (3)
1.326 (3)
89.44 (8)
110.7 (2)
110.8 (2)
1.843 (2)
1.836 (1)
1.768 (2)
1.349 (2)
1.482 (2)
1.336 (3)
89.84 (7)
110.6 (1)
110.6 (2)
Se-N3
N2-C6
N2-C7
N1-C1
N2-Se1-N1
Se1-N2-C6
Se1-N1-C1
110.4 (1)
109.9 (1)
111.3 (3)
109.8 (3)
The asymmetric unit of [4b](CF3SO3)2 contains a two selenadiazolium heterocycles linked by a –
(CH2)3– chain. The trifluoromethanesulfonate anions are bound to the chalcogen, precluding the
formation of Se…N ChBs. The oxygen atoms display short distances to Se (2.685(1), 2.808(2) and
3.137(2) Å), all shorter than the sum of Se and O van der Waals radii (3.47 Å). Similar Se…O ChB
distances were observed in the dimer of the N-methyl-benzoselenadiazolium cation (2.823(8) Å).30
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Figure 6. ORTEP and numbering scheme for the asymmetric unit in the crystal structure of (a)
[4b](CF3SO3)2. Displacement ellipsoids are shown at the 50 % probability level.
Experimental
Materials. Selenium dioxide, fluoro-2-nitrobenzene, diamines and other reagents were used as
received from commercial suppliers. Anhydrous-grade solvents were used without further
purification.
Instrumentation. 1H, 13C and 77Se NMR spectra were recorded on Bruker 200 and Bruker
600 spectrometers at ambient temperature. Chemical shifts are reported in δ values (parts
1
13
per million) with respect to the resonances of tetramethylsilane for H and C and with
77
respect to the line of Me2Se for the chemical shift of Se. In the last case, spectra were
1
obtained using H-77Se HMBC unless otherwise stated. All vibrational spectra were
measured neat by Diffuse Reflectance Infrared Fourier Transform Spectroscopy in a Bio-
Rad FTS40 spectrometer with a resolution of 4 cm-1 in the 4000–40 cm-1 region. Low- and
high-resolution electrospray spectral analyses were performed using Micromass GCT
spectrometer and a Micromass Quattro Ultima for electron ionization spectra. In each case,
the sample was introduced into the ionization chamber in a shortened borosilicate glass
capillary on a probe rod. The samples were then heated and the temperature range that
displayed the most intense parent ion peaks was used for spectral acquisition. A 70 eV
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electron stream ionized the sample and the positively charged ions were identified by a
time-of-flight detector. Elemental analyses were performed by the Science Centre of
London Metropolitan University, 29 Hornsey Road, London, UK, N77DD. No melting
points are gives as all dication salts decomposed without melting by heating able 150 C.
All single crystal X-ray diffraction samples were mounted with paratone oil at the tip of a
glass fibre installed on a MiTeGen goniometer head and kept under a cold stream of nitrogen while
on the diffractometer. Data were collected at 100 K on a Bruker APEX2 diffractometer, using Mo
K α radiation (λ = 0.71073 Å) and outfitted with an Oxford cryostream low-temperature accessory.
Ω and ϕ scans were collected in 0.5° steps with a crystal to detector distance of 4.954 cm. The
preliminary unit cell parameters were determined using a minimum of 50 frames from three
different orientations, and final cell refinement after integration in SAINT.35 Data were corrected
for absorption and scaled using face-indices as well as redundant data in SADABS.36 Crystal
structures were solved using SHELXL and most structures were refined by full-matrix least square
of all F2 values with the WinGX package.
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Syntheses of chloride salts
.
[4a]Cl2 4H2O. A neat mixture of fluoro-2-nitrobenzene (1.42 mL, 3.5 mmol) and ethylenediamine
(0.5g, 1.7 mmol) was stirred vigorously for 1 hour at 100C in 25 mL of ethanol. A crystalline
solid formed on cooling to room temperature and was separated by filtration. This nitro compound
(0.5g, 1.66 mmol) was dissolved in absolute ethanol (30 mL) and Pd/C 10% (50 mg) was added
to the solution with stirring. The mixture was placed in a stainless-steel reactor and held under
1 atm of pure H2. Progress of the reduction reaction was monitored by TLC on silica with an eluent
mixture of 10% ethyl acetate in hexanes. Once the starting material was completely consumed,
the mixture was filtered through celite and concentrated under vacuum to yield the crude N,N’-
bis(2-aminophenyl)ethylenediamine as a brown thick oil. This intermediate was dissolved in
anhydrous THF and treated with HCl gas at 0 °C. After 15 minutes, the pale purple solid product
was filtered, washed with hexanes and dried under vacuum for 3 h. The hydrochloride salt purified
in this way was dissolved in 5 mL HClconc and mixed with a solution of SeO2 (2.19 mmol. 4 equiv.)
in ethanol A dark red solid formed within minutes and was recrystallized from HClconc yielding
.
needles of [4a]Cl2 4H2O. Yield 46 %. 1H NMR (d6-DMSO): δ (ppm) 7.96(2H, Ar-CH), 7.85(2H,
Ar-CH), 7.83 (2H, Ar-CH), 7.69 (2H, Ar-CH), 5.45 (4H, CH2). 1H-77Se HMBC NMR (d6-DMSO,
600 MHz): δ (ppm) 1444.9. 13C NMR (d6-DMSO): δ (ppm) 156.97, 149.52,138.34, 136.69,
129.31,128.30, 116.68(Ar-CH), 52.60 (CH2). E.A. % calcd. for C14H12Cl2N4Se2: C 36.15, H 2.60,
N 12.05, found C 36.3, H 2.68, N 12.25.
.
[4c]Cl2. Prepared following the procedure described above for [4a]Cl2 4H2O. Yield 27 %. 1H NMR
(d6-DMSO): δ (ppm) 7.84 (m, 1H, Ar-CH), 7.63 (m, 1H, Ar-CH), 7.43 (m, 1H, Ar-CH ), 6.21(m,
1H, Ar-CH, 3.46 (m, 2H, CH2-cycl) 2.38 (m, 2H, CH2-cycl), 1.97(m, 2H, CH2-cycl), 1.83(m, 2H,
13
CH2-cycl). C NMR (d6-DMSO): δ (ppm) 156.25, 150.52, 136.43, 128.82, 125.00, 117.28 (Ar-
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CH), 66.33, 24.12, 36.49 ((CH2)3). E.A. % calcd. for C18H18Cl2N4Se2: C 41.64, H 3.49, N 10.79,
found C 41.40, H 3.35, N 10.57.
[4d]Cl2. 1,4-Bis(bromomethyl)benzene (1 g, 3.79 mmol) was dissolved in 35 mL of CH3CN with
o-phenylenediamine (2.05 g, 18.9 mmol) and refluxed 4 hours under N2, after which a white
precipitate formed. The solvent was removed under reduced pressure and a 10-5 M solution of
NaOH was added, this was followed by extraction with CH2Cl2 until the pH of the aqueous layer
remained constant. The organic layer was dried using Na2SO4 and concentrated. The crude
material was sublimed at 100°C under reduced pressure to yield (N,N’-bis(2-aminophenyl)-p-
xylylenediamine) as a dark orange viscous oil. Yield 82 %. 1H NMR (CD3D, 200MHz): ( ppm)
7.36 (s, 4H, Ar-H), 6.61, 6.55 (m, 4H, Ar-H), 4.32 (s, 4H, CH2) ppm. LR ESI-MS: m/z 319.2
(M+H) (Cf. calc. for C20H22N4 319.2). The tetraamine (0.989 g, 3.11 mmol) was dissolved in 20
mL of anhydrous CH2Cl2 under N2 and treated with HCl(g) for 15 min until precipitation of a
pale-purple solid was complete. Titration with 0.05 M NaOH established that the product obtained
.
was 4-(2-NH2-C6H4-NH-CH2)-C6H4 3HCl. Yield 93%. IR: 3377.21, 2871.60, 2603.85, 2090.36,
2011.76, 1633.05, 1561.82, 1510.17, 1461.45, 1322.50, 1155.30, 1137.52 cm-1. HR ESI-MS: m/z
319.1923 (M+H) (Cf. calc. for C20H22N4 319.1916). The hydrochloride salt (0.409 g, 0.96 mmol)
was dissolved in 40mL 1:1 v/v 10% HCl/EtOH. H2SeO3 (0.308 g, 2.39 mmol) was dissolved in
4 mL of the same solvent and added to the mixture. The solution turned red and produced a yellow
precipitate. The solid product, [4d]Cl2, was isolated by filtration and dehydrated by suspending it
in an ethanol-toluene mixture and heating to reflux though a column of activated alumina. Yield
61 %. 1H NMR (d6-DMSO, 600MHz): ( ppm) 7.95 (d, 2H, Ar-H), 7.83 (m, 4H, Ar-H), 7.67 (m,
2H, Ar-H), 7.48 (s, 4H, Ar-H), 6.14 (s, 4H, CH2) ppm. 13C NMR (d6-DMSO, 600MHz): ( ppm)
158.98, 149.53, 136.69, 136.32, 129.31, 128.73, 125.40, 116.68, (Ar-CH) 53.60 (CH2) ppm. 1H-
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77Se HMBC NMR (d6-DMSO, 600MHz): ( ppm) 1445.8. IR: 3055.60, 2970.40, 2937.30,
2793.36, 2721.35, 2637.11, 1977.05, 1955.18, 1837.26, 1810.53, 1714.29, 1607.43, 1530.10,
1504.74, 1423.52, 1323.22, 1163.82 cm-1. LR ESI-MS: m/z 235.7 (M2+) (Cf. calc. for
2+
C20H16N4Se2 236.5), 506.9 (M-Cl) (Cf. calc. for C20H16N4Se2Cl+ 506.9). No satisfactory
combustion elemental analysis could be obtained for this product.
Syntheses of tetrafluoroborate salts
[4a](BF4)2: (a) A small sample of [4a]Cl2 (0.03g, 0.06 mmol) was treated with NOBF4 (0.015g,
0.12 mmol) in anhydrous acetonitrile under N2. The reaction mixture was stirred for 2 hours and
the solvent was removed under vacuum to give yellow powder. Yield 6%. (b) Prepared in a
.
polypropylene test tube following the procedure described above for [4a]Cl2 4H2O, with 48% wt.
HBF4 in water instead of HClconc. Yield30 % 1H NMR (d6-DMSO): δ (ppm) 8.05 (m, 1H, Ar-CH),
77
7.94 (m, 1H, Ar-CH), 7.77(m, 1H, Ar-CH), 7.50(m, 1H, Ar-CH), 6.26 (d, 2H, CH2). Se NMR
(d6-DMSO, 600 MHz) δ (ppm): 1481.6. 13C NMR (d6-DMSO): δ (ppm) 156.93, 150.07, 137.93,
130.29, 125.57, 116.42(Ar-CH), 53.5 (CH2). No satisfactory combustion elemental analysis could
be obtained for this product.
[4d](BF4)2. (N,N’-bis(2-aminophenyl)-p-xylylenediamine) (0.234 g, 0.735 mmol) was suspended
in 9 mL of CH3OH in a polypropylene test tube. 48% wt. HBF4 in water (1.15 mL, 7.17 mmol)
was added to the suspension, dissolving immediately all solids to form a brown solution. H2SeO3
(0.235 g, 0.185 mmol) was dissolved in 2 mL of CH3OH and added to the solution. The mixture
turned red and a redish-orange precipitate was formed. After 1 hour, the mixture was centrifuged,
the liquid was decanted, and the solid was washed with a saturated solution of NaBF4 in EtOH
until the pH of the solution was no longer acidic. This was followed by a wash with EtOH, then a
final wash with anhydrous ether and allowed to dry under atmosphere. The resulting orange
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powder was recrystallized from CH3CN and the final product consisted of orange needle-like
crystals. Yield 66 %. 1H NMR (d6-DMSO, 600 MHz): δ (ppm) 8.05 (d, 2H, Ar-H), 7.93 (m, 4H,
13
Ar-H), 7.77 (m, 2H, Ar-H), 7.50 (s, 4H, Ar- H), 6.26 (s, 4H, CH2) ppm. C NMR (d6-DMSO,
600MHz) ( ppm): 53.45, 116.42, 125.57, 128.64, 130.29, 135.91, 137.39, 150.08, 156.93 (Ar-
1
CH). H-77Se HMBC NMR (d6-DMSO, 600MHz): δ (ppm) 1481.5. 19F NMR (d6-DMSO,
200MHz) ( ppm): -151.5 ppm. IR: 3606.23, 3519.00, 3104.46, 2045.80, 3022.69, 2384.48,
2106.00, 1969.36, 1822.20, 1606.87, 1532.31, 1396.54, 1319.03, 1115.62 cm-1. LR ESI-MS: m/z
2+
+
236.2 (M2+) (Cf. calc. for C20H16N4Se2 236.5), 559.3 (M-BF4) (Cf. calc. for C20H16N4Se2BF4
559.0). E.A. % calcd. for C20H16B2F8N4Se2: C 37.31, H 2.50, N 8.70, found C 37.13, H 2.85, N
.
8.59. The pseudopolymorph [4d](BF4)2 CH3CN formed yellow crystals by slow evaporation of an
acetonitrile solution.
Preparation of trifluoromethylsulfonate salts. Triflic acid (0.5 M in EtOH) was added dropwise
to a mixture of the corresponding tetraamine and one equivalent of SeO2 in anhydrous ethanol.
Red powders formed over 24 hours, were recovered by filtration and recrystallized from
acetonitrile. The identity of the products was confirmed by single-crystal X-ray diffraction but
satisfactory elemental analyses could not be obtained after repeated attempts.
[4a](CF3SO3)2: Yield 38 % 1H NMR (d6-DMSO): δ (ppm) 8.15(m, 1H, Ar-CH) 8.08(m, 1H, Ar-
13
CH), 7.87 (m, 2H, Ar-CH). 5.18 (m, 4H, CH2) C NMR (d6-DMSO) δ (ppm): 156.57, 151.11,
1
137.35. 130.35, 125.53, 116.33 (Ar-CH), 51.30 (CH2). H-77Se HMBC NMR (d6-DMSO, 600
MHz): δ (ppm) 1490.0.
[4b](CF3SO3)2: Yield 30 % 1H NMR (d6-DMSO): δ (ppm) 8.07 (m, 3H, Ar-CH), 7.83 (m, 1H, Ar-
CH), 5.20 (t, 2H, CH2). 2.60 (p, 1H, CH2). 77Se NMR (d6-DMSO, 600 MHz) δ (ppm) 1486.3. 13C
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NMR (d6-DMSO) δ (ppm): 156.65, 150.63, 137.11, 130.23, 125.0 116.15, (Ar-CH), 48.68 (CH2),
33.77 (CH2), 30.06 (CH2).
Conclusions
The efficient synthetic route previously developed for the N-alkyl benzo-2,1,3-selenadiazolium
cations was readily adapted to the preparation of a variety of bis(benzoselenadiazolium) cations
linked by a variety of hydrocarbon groups that included alkyl chains, a 1,2-cyclohexanediyl, and
1,4-xylylenyl bridges. As anticipated, the dications have a strong affinity for anions; chloride is
strongly associated by chalcogen bonding in the solid state. The chlorides were replaced with less
coordinating anions such as tetrafluoroborate and trifluoromethanesulfonate in an attempt to
promote the formation of Se…N ChBs and the [Se-N]2 supramolecular synthon. The strategy
worked in part in the case of [4a](CF3SO3)2, with the formation of dimers in the crystal structure.
The selenium atom in the cations most frequently acted as a chalcogen-bond donor towards the
fluorine atoms of the tetrafluoroborate and oxygen atoms of the trifluoromethanesulfonate anions.
While these anions do interfere with the formation of Se…N ChBs, the resulting structures (e.g. the
.
macrocyclic formed by [4a]Cl2 4H2O) offer opportunities for the design of new supramolecular
architectures. Further, the crystal structures suggest that the chalcogen-bonding donor ability of
these dicationic species could also be applied in anion sensing and catalysis.
Electronic Supplementary Information (ESI) available: CCDC 1912322, 1912321, 1912323,
1912324, 1912325, 1914922.
Conflicts of Interest. There are no conflicts to declare.
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Acknowledgements. We gratefully acknowledge funding from the Natural Sciences and
Engineering Research Council of Canada (IVB: DGI, LML: PGSD).
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