Modulation of Reduction Potentials of Bis(pyridinium)alkane Dications through Encapsulation within Cucurbit[7]uril

Article abstract of DOI:10.1021/acs.joc.9b01049

Supramolecular modulation of reduction potentials of two series of bis(pyridinium)alkane salts is described. Study of the encapsulation of bis(pyridinium)alkane guests within the CB[7] cavity revealed the critical influence of the linker length and the position of the heteroatom on the reduction potentials of encapsulated guests. CB[7] complexation of pyridinium salts induced reduction potential changes ranging between +50 and -430 mV. Noncovalent modulation of the electron-accepting ability of organic cations can be utilized in electron-transfer-initiated reactions.

Full text of DOI:10.1021/acs.joc.9b01049

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Note
Modulation of Reduction Potentials of Bis(pyridinium)alkane
Dications Through Encapsulation Within Cucurbit[7]uril
Nikolai A. Tcyrulnikov, Ramkumar Varadharajan, Anastasiia A. Tikhomirova,
Mahesh Pattabiraman, Vaidhyanathan Ramamurthy, and Robert Marshall Wilson
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01049 • Publication Date (Web): 12 Jun 2019
Downloaded from http://pubs.acs.org on June 12, 2019
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The Journal of Organic Chemistry
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†
‡
†
Nikolai A. Tcyrulnikov , Ramkumar Varadharajan , Anastasiia A. Tikhomirova , Mahesh Pattabi-
,
§
, ‡
, †
raman* , Vaidhyanathan Ramamurthy* , and R. Marshall Wilson*
†Center for Photochemical Sciences and Chemistry Department, Bowling Green State University, Ohio 43403, United States
‡Department of Chemistry, University of Miami, Coral Gables, Florida 33146, United States
§Department of Chemistry, University of Nebraska Kearney, Nebraska 68849, United States
Supporting Information Placeholder
the most species, pyridinium nitrogen resides adjacent to the polar
ABSTRACT: Supramolecular modulation of reduction poten-
carbonyl portals, while hydrophobic linker is included within the
CB[7] cavity. These electron acceptor compounds are of interest
not only as photo- and electro- chemically induced electron delo-
tials of two series of bis(pyridinium)alkane salts is described.
Study of the encapsulation of bis(pyridinium)alkane guests within
CB[7] cavity revealed the critical influence of the linker length
and the position of the heteroatom on the reduction potentials of
encapsulated guests. CB[7] complexation of pyridinium salts
induced reduction potential changes ranging between +50 mV and
2
5
26, 27
calizing molecules but also as antimicrobial agents.
In this
work, we studied two series of bis(pyridinium)alkane guests (Fig-
ure 1). We have demonstrated that CB[7] encapsulation and fa-
vorable ion-dipole interaction between pyridinium nitrogens and
carbonyl rims influences the reduction potentials of
bis(pyridinium)alkane dications. Results of this study highlight
that although the irreversibility of the reduction cannot be altered,
the reduction potentials of bis(pyridinium)alkanes in aqueous
media can be supramolecularly varied over a wide range (between
-
430 mV. Non-covalent modulation of the electron accepting
ability of organic cations can be utilized in electron transfer initi-
ated reactions.
+50 mV and -430 mV) and that slight structural variations in the
length of the linker and the position of N-atom can impart signifi-
cant changes in redox properties of bis(pyridinium)alkane CB[7]
complexes. Recently we
Cucurbit[n]urils (CB[n], n = 5-10) are a family of macrocyclic
molecular containers containing two polar carbonyl hydrophilic
1
-3
portals decorating the relatively hydrophobic inner cavity.
These features are responsible for the unique binding properties
4
,5
and widespread use of CBs in self-assembly , molecular recogni-
6-8
9-11
12,13
tion , catalysis , drug delivery
, and design of molecular
14,15
16
17
machines
. Since the reports by Kaifer and Kim describing
2
+
CB[7] encapsulation of redox active methyl viologens (MV )
there has been significant interest in using CBs to modulate phys-
icochemical properties of MVs.
1
8-21
However, to our knowledge,
1
there is no comprehensive study correlating redox behavior with
the structural features of the redox-active guests included within
CB. Information on the ability of CBs to manipulate electron
transfer processes would expand the utility of CBs in afore-
mentioned areas. Binding of various N-heterocyclic cations was
Figure 1. CB[7] complexation induced H NMR chemical shifts
(CIS, ppm) of bis(pyridinium)alkane guests; maximum CIS val-
ues from titration to up to 4:1 host-guest ratio are shown (for de-
tails, see SI); blue – upfield shift, red – downfield shift, * –
2
merged with H O, x – merged with CB[7].
2
2-24
studied by Macartney and co-workers.
They suggested that for
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reported the oxidation of 1a under aerobic conditions.28 This ef-
fect is noticeable only upon prolonged exposure and did not affect
the measurements in this work.
solution, and the length of the pentylene linker which allows sim-
ultaneous binding to two CB[7] without significant steric hin-
drance between them.
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1
We have employed H NMR to infer the inclusion of guests with-
Host-guest structures inferred from the H NMR data are in line
2
3, 29
in CB[7] cavity.
Hydrogens of guests located within the hy-
with the computationally-generated structures optimized at the
HF/3-21G level (Figure 4, Figures S85-87). As expected, guests
1-3 in their extended conformation were mostly encapsulated
within the CB[7] cavity. In the case of 5, the predicted structure
shown in Figure 4 is consistent with the NMR data. In this case,
the aromatic rings are extended well outside the portals of CB[7].
drophobic cavity of CB[n] typically exhibit an upfield shift (Δδ
comp. – free < 0) and those remaining adjacent to carbonyl portals
display a zero or downfield shifts (Δδ comp. – free > 0). Figures 2 and
3
reveal that the inclusion of 1 and 5 within CB[7] results in the
upfield shift of both methylene and aromatic protons. Neither
broadening of the signals nor separate resonances were observed
indicating that CB[7] is sliding fast over both alkyl chain and
aromatic rings in the NMR timescale. Similar features were
noted for 2, 3 and 4 (Figures S4, S7, S11).
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Figure 4. Computationally-generated structures of 1:1 complexes
of 1 and 5 with CB[7].
1
Figure 2. Variation in H chemical shifts for titration of 1mM
CB[7] with 30 mM 1 in D
spectrum – free host.
Guests 1a-3a exhibited different behavior from 1-5 in the pres-
ence of CB[7]. Two independent H NMR signals for free and
bound guests indicated a slow or lack of chemical exchange (in
the NMR time scale) between these two types of guests. 1a-3a
displayed much larger upfield shifts for the methylene protons
than 1-5, and a downfield shift of the N-methylpyridinium CH
groups. H NMR titration experiments confirmed the formation of
1:1 complexes.
2
O. Top spectrum – free guest, bottom
1
1H NMR titration experiments confirmed that 1-5 formed 1:1
complex (Figures S3, S6, S10, S14, S18). Of the five guests, 1-3
experienced upfield shifts in the range from -0.3 to -0.6 ppm for
aliphatic and from -0.2 to -0.7 ppm for aromatic protons. These
are much greater than the ones experienced by 4 and 5. In fact,
para and meta protons (a and b) of 4 and 5 showed only a small
shift (Figure 3). We believe the small shifts indicate the proximity
of the aromatic rings to the carbonyl portals.
3
1
To ascertain the host to guest ratio and to estimate the thermody-
namic parameters of binding, the isothermal calorimetric meas-
urements (ITC) were performed (Table 1).
Table 1. Binding constant (Ka), molar ratio (n) enthalpy
(ΔH), and entropy (ΔS) for compounds 1-5 and 1a-3a with
CB[7] at 25°C
Kaa
nb
ΔHc
ΔSd
6
-1
(J/mol∙K)
x 10 M
(kJ/mol)
1
1.53 ± 0.02 1.11 ± 0.01 -16.66 ± 0.08
0.95 ± 0.09 1.16 ± 0.01 -27.01 ± 0.41
3.17 ± 0.17 0.93 ± 0.02 -21.60 ± 0.15
3.06 ± 0.53 0.97 ± 0.06 -19.03 ± 0.62
1.19 ± 0.15 0.91 ± 0.00 -29.21 ± 0.11
3.86 ± 0.06 0.98 ± 0.04 -27.57 ± 0.10
2.54 ± 0.01 1.04 ± 0.05 -29.64 ± 0.33
62.54 ± 0.18
23.81 ± 0.54
52.02 ± 0.03
60.22 ± 0.64
18.32 ± 0.69
33.63 ± 0.21
23.41 ± 0.80
2
3
4
1a
2
a
1
Figure 3. Complexation-induced shifts in H NMR signals of 5
upon addition to CB[7] (1mM) in D
phatic (bottom) region of the spectra are presented.
2
O. Aromatic (top) and ali-
3a
a
Mean value measured from two isothermal titration calorime-
b, c & d
Length and hydrophobicity of the methylene chain suggest that it
would prefer the interior of the CB than the hydrophilic rim.
Consistent with this, aliphatic protons of 4 and 5 experience the
largest upfield shifts in the series, indicating that CB[7] slides
over alkyl chains in both molecules. Unlike 1-4, 5 showed binding
induced NMR changes in the presence of excess CB[7], suggest-
ing the formation of 2:1 host-guest complex and fast exchange
between 1:1 and 2:1 complex (in this manuscript the ratio is men-
tioned as host to guest). The reversal in direction of CIS (signal
a, Figure 3) for 5 beyond one equivalence of CB[7], and its satu-
ration beyond two equivalents suggests ability of 5 to form higher
order complex in a stepwise equilibrium. This could be attributed
to the optimal concentration (mM) of the host and guest in the
try experiments at 25°C in DI water.
Molar Ratio, Enthalpy
and Entropy values measured by ITC. We could not obtain relia-
ble binding characteristics for 5, possibly due its ability to form a
higher order complex in addition to 1:1 complex.
Table 1 reveals that the host-guest ratio (n) in all cases is one
which is consistent with NMR titration results. Except for 2, all
other guests exhibited a trend in their ΔH and ΔS values. Guests
1
, 3 and 4 have a lower (-) ΔH and higher (+) ΔS than 1a-3a.
2
2
These suggest that 1a-3a are bound more tightly than 1, 3, and 4.
Clearly, the presence of two independent peaks in NMR spectrum
and larger influence of CB on the reduction potentials of 1a-3a
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(
see later section) must be a consequence of the stronger binding
move closer to electron rich portals. Favorable ion-dipole interac-
tion between the portals of CB and the guest positive charges
1
2
3
4
5
6
7
8
9
of these guests to CB[7].
“
shields” the electron acceptor pyridinium rings and leads to the
Next, we proceeded to examine the influence of CB[7] on the
electrochemical properties of 1-5 and 1a-3a. Absence of the re-
verse oxidation wave or its large separation from the reduction
peaks, and dependence of the reduction potential on the scan rate
confirmed the irreversibility of the electrochemical reduction of 1-
4
2
negative shift of their reduction potential.
3
0
5
and 1a-3a (Figure 5, C). This is consistent with the irreversi-
bility of N-methylpyridinium and bis(pyridinium)alkanes reduc-
tion leadingto 4,4’-coupled σ-dimers and cyclomers, correspond-
3
1-34
ingly (Figure 5, A).
Interestingly, irreversibility is not affected
by CB[7], suggesting that cyclomerization and/or σ-dimerization
is not prevented by inclusion within CB[7]. This is likely to be
the result of neutral diradical intermediates, generated upon two-
electron reduction, exiting the CB host. Thus, we believe that the
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35
cyclomerization occurs outside the CB[7] host.
Figure 6. Black – reduction potentials (Volts) of free 1-5 (E
1, 2) and their 1:1 CB[7] complexes (red) vs linker length. Inset –
ΔE (bound – free, mV) for 1-5 (green), 1a-3a (blue); E used for
1
for
1
1
, 2, 1a, 2a. Fit applied to aid in visualization.
1
a-3a displayed much larger negative shifts than 1-3. This is con-
sistent with the stronger binding as noted from the NMR and ITC
data. In these cases, for a given linker length, positive charges are
located closer to carbonyl rims than in 1-3. This result is best
illustrated by comparing 3 and 3a (Figure 7). While 3 exhibited a
small shift of -40 mV, isomeric 3a showed the largest shift among
all studied compounds of -430 mV. Since the reduction potential
of 3a with CB[7] falls outside the electrochemical window of
water, we performed the measurements in non-aqueous media.
Figure 5. Irreversible electrochemical reduction (A); Reduction
of 1:1 complex of 1 with CB[7] at different scan rates (B); Reduc-
tion potentials of 1 (E ) and 3 vs the scan rate (C).
1
2
Reliability of comparison between H O and DMSO solutions is
illustrated in Figure 7 (A vs B, also Figures S41-43, S47-50).
Molecules listed in Figure 1 could undergo either a single step or
stepwise reduction. We believe that the stepwise reduction is
favored when the radical cation formed upon one electron reduc-
36-38
tion can be delocalized over both rings.
For this to occur, face-
to-face interaction is required, which is only possible in the cisoid
2
conformation of a bispyridyl system. Figure 5 B (E and E )
1
shows that in the case of 1 stepwise reduction is favored (Figure
S46 for 1a). In this case, the energetically favorable radical cation
intermediate leads to a positive shift of the first reduction poten-
3
9
tial (compared to N-methylpyridinium (-1.45 V vs Ag/AgCl).
According to quantum chemical (QC) calculations, CB[7] encap-
sulation favors the transoid conformation for the longer chain
guests. In such a conformer, direct electronic communication
between aromatic units would decrease resulting in their inde-
pendent reduction at potentials close to that of N-
methylpyridinium. This should favor a single reduction peak.
This is the case for CB[7]-included 2 and 2a and longer chain
systems (Figures S40, S41, S44, S45, S47-50).
Figure 6 shows the reduction potentials of free and CB[7] com-
plexed guests 1-5 and 1a-3a. Upon inclusion within CB[7], 1 and
2
showed a small positive shift of the reduction potential which
could be due to the low polarizability and electron density of the
4
0,41
CB[7] inner cavity.
Upon increasing the linker length (3-5), a
gradual negative shift is observed. This is consistent with binding
modes observed by NMR titration and QC calculations discussed
above. Extension of the hydrophobic linker leads to its placement
in the inner cavity, while positive charges of pyridinium rings
Figure 7. Voltammograms of free guests (black), 1:2 (red; 2x
excess of guest), and 1:1 (blue) complex of 3 and 3a with CB[7]
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in aqueous (A, D), and non-aqueous media (B,C); computational-
ly generated structures of 1:1 complexes of 3 and 3a with CB[7].
dilution was corrected by injecting the bis(pyridinium)alkane
guests solution into deionized water and subtracting these data
from those of the host-guest titration. Data were analyzed and
fitted in the NanoAnalyze software.
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A final note relates to the formation of 2:1 complex of 5 with CB.
Cyclic voltammetry suggested the formation of 2:1 complex (see
SI, Figure S45) in addition to 1:1 complex. In the presence of
excess CB[7], additional reduction (-1.23 V) was observed. This
is consistent with the NMR titration spectra shown in Figures
S15-S17 in the SI. However, ITC data did not reveal the presence
of the 2:1 complex (Figure S33). The discrepancy between the
NMR and ITC could be due to the different concentrations re-
quired for these experiments. Also, the limitations of the ITC
software hindered the analysis of the ITC curve with two expo-
nentials and we did our best to fit the curve into a single exponen-
tial. Except for 5, no other guests showed the presence of 2:1
complex.
1
. To 4ml of distilled water, 23 mg of NaCl (anhydrous, ACS
Reagent, ≥ 99%) was added to achieve 0.1 M concentration of the
supporting electrolyte (0.1 M TBAP (tetrabutylammonium per-
chlorate, Sigma-Aldrich, for electrochemical analysis, ≥99.0%) in
dry DMSO was used for non-aqueous systems). A solution was
transferred to a single compartment glass electrochemical cell
equipped with a Teflon cap (3 electrode setup) and a nitrogen inlet
Teflon tube. Typically the cell was fitted with a glassy carbon
0
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(GC) working electrode, Pt wire auxiliary electrode and Ag/AgCl
reference electrode (Ag/AgNO for non-aqueous solutions, the
3
In conclusion, we investigated CB[7] encapsulation of two series
of bis(pyridinium)alkane dications and its effects on the electron
accepting ability of pyridinium units. Our studies bring out the
importance of the linker length and the position of nitrogen atoms
in aromatic rings on the reduction potential of CB[7] complexes.
The difference in electrochemical responses of the isomeric hosts
(internal vs external N positioning) despite the same length of the
linker provided specific insights into the structural sensitivity of
the CB[7] complexation. We demonstrated that the reduction
potentials of pyridinium salts can be non-covalently manipulated
over a wide range of values by means of supramolecular chemis-
try. Conclusions drawn here could find potential applications in
the supramolecular control of electron acceptor ability of organic
molecules in catalytic and electron transfer reactions.
Fc/Fc+ redox couple was used as an internal standard). Nitrogen
was bubbled through the solution for 20 min to remove the dis-
solved oxygen. During the measurements, the Teflon tube was
removed from the solution and kept above the liquid to prevent
oxygen from redissolving.
2
. The working electrode was polished on a microcloth using
polishing alumina. Electrode was sonicated in deionized water to
remove any alumina left after polishing, rinsed with distilled wa-
ter and dried using KimWipe. The electrode was polished before
each measurement.
3. Baseline was measured in the 0-(–1600 mV) and 0-(–1800 mV)
regions to ensure that no oxygen or other impurities are present in
the solution.
4
. Solid pyridinium salt was added to the above solution to
achieve 0.7 mM (or 0.45 mM for less soluble compounds) con-
centration of a solute. The solution was sonicated for 10 sec to aid
in dissolving. Tetrafluoroborate salts were used for CV measure-
ments.
All commercially available materials were used as supplied with-
out further purification, unless otherwise noted. Proton and carbon
NMR characterization, and NMR titration studies of 1-5 and 1a-
3a were performed on Bruker Avance 500 spectrometer equipped
with cryoprobe. Chemical shifts are reported in parts-per-million
5
6
. The solution was further purged with nitrogen for 10 min.
. Reduction peaks were recorded in 0-(–1600 mV) or 0-(–1800
mV) regions at 100 mV/sec.
7
. To the above solution solid CB[7] was added to achieve the
(ppm). Deuterated solvent was used as a lock and residual protiat-
desired ratio (2:1 or 1:1 host-guest complexes).
ed solvent peak was used as reference. FIDs are available upon
request. UV–Vis spectra were recorded in 1 cm Starna Cells cu-
vette on Agilent 8453 UV–Vis spectrometer. Mass spectrometry
characterization of 1-5 and 1a-3a was performed usinga Thermo
Scientific LTQ-FT, a hybrid mass spectrometer consisting of a
linear ion trap (the LTQ portion) and a Fourier transform ion cy-
clotron resonance mass spectrometer, FT-ICR. IR spectra were
recorded on Thermo Scientific Nicolet iS5 ATR IR Spectrometer.
ITC measurements were performed on Nano ITC Standard vol-
ume instrument (TA). Cyclic Voltammograms were recorded on
Epsilon potentiostat/galvanostat (BASi).
8. After every CB[7] addition, the solution was sonicated for 10
sec and purged for 10 min with nitrogen.
9
. Reduction peaks were recorded in 0-(–1600 mV) or 0-(–1800
mV) regions at 100 mV/sec.
0. Additional CB[7] was added to a solution of 1:1 H:G complex
1
and reduction peaks were recorded in 0-(–1600 mV) or 0-(–1800
mV) regions to ensure that presence of excessive amount of Host
molecule does not change the electrochemical response with re-
spect to 1:1 complex.
Geometry optimization of individual hosts/guest and their inclu-
Typical procedure: 1 mM solution of CB[7] was dissolved in
D O, to this 30 mM of guest stock solution was added stepwise.
2
After each addition, NMR spectrum was collected to monitor the
changes of the Host and Guest proton resonances.
sion complexes were performed using Gaussian ’09 software on a
43
Windows desktop computer. Coordinates for CB[7] were im-
ported from the crystal structure of the compound (.cif file) as a
.pdb file, and that of the structure of guests were constructed in
the software. Geometry optimizations of complexes were per-
formed individually, and the inclusion complexes were assembled
using the optimized their coordinates. Semi-empirical calculations
were performed first (SE-PM6) and the optimized structures were
then used for performing the calculation at HF/3-21G level in the
gas phase. IR frequency calculations were performed on the opti-
mized structures and the vibrations were confirmed to be all posi-
tive values thereby validating the ground state structures.
The formation constants and thermodynamic parameters for the
inclusion of bis(pyridinium)alkane guests in CB[7] were deter-
mined by titration calorimetry using a Nano ITC standard volume
instrument from TA. All solutions were prepared in purified water
(Milli-Q,
Millipore).
A
solution
(0.1
mM)
of
bis(pyridinium)alkane guest was placed in the sample cell. As 1
mM solution of CB[7] was added in a series of 25-40 injections
(5-10 μL), the heat evolved was recorded at 25 °C. The heat of
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mmol) in 5mL of acetonitrile was added an excess of methyl io-
1
2
3
4
5
6
7
8
9
dide (240 mg, 1.6 mmol) and the stirred reaction mixture was
refluxed overnight. After cooling to room temperature, the pre-
cipitate was filtered, washed with 0.5 mL of acetonitrile, 2 X 5
mL of diethyl ether and dried in vacuo to afford 2a as a cream-
colored powder (78 mg, 84%). Mp = 127-130 ⁰C (decomp.) H
2
NMR (500 MHz, D O): δ 8.53 (d, 4H, J = 6.63 Hz), 7.77 (d, 4H, J
Compound 1a was synthesized according to the previously re-
28
ported procedure. The optimized synthetic procedure has been
1
-3
used to prepare CB[7].
To exchange counter ions to the tetrafluoroborate, aqueous solu-
tions of 1-5 and 1a-3a were treated with 2 equivalents of aqueous
1
AgBF
trated under reduced pressure to afford tetrafluoroborate salts.
,1-bis(pyridinium)methane Iodide (1). To a solution of diiodome-
4
. Silver halide precipitate was filtered and filtrate concen-
13
1
=
D
6.55 Hz), 4.21 (s, 6H), 3.28 (s, 4H). C{ H} NMR (125 MHz,
-
2 4
O): δ 159.96, 144.55, 127.66, 47.37, 34.00. IR (BF salt, ν =
cm ): 3066, 1647, 1479, 1191, 1021, 848, 814, 575. HRMS
-
1
1
+
+
thane (Sigma-Aldrich, 99%, 52 mg, 0.2 mmol) in 5 ml of acetoni-
trile was added an excess of pyridine (Sigma-Aldrich, 99.8%,
anhydrous, 64 mg, 0.8 mmol). Stirred solution was refluxed over-
night. After cooling to the room temperature, the precipitate was
filtered and washed with 1 mL of acetonitrile followed by 3 X 5
mL diethyl ether, and dried in vacuo to afford 1 as yellow powder
(ESI): calcd. for C14
301.1493.
H
18
N
2
BF
4
4
[M-BF ] , 301.1494, found
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
,3-bis(N-methylpyridin-4-ium)propane Iodide (3a). Using the
procedure given for the preparation of 2a, 4,4’-
trimethylenepyridine (Sigma-Aldrich, 98%, 39 mg, 0.2 mmol)
was reacted with an excess of methyl iodide (240 mg, 1.6 mmol).
To aid in the precipitation, after cooling down to the room tem-
perature, the reaction mixture was concentrated under reduced
pressure until the precipitate formed. Following the same steps
after the filtration as described for 2a, we obtained 3a as an off-
1
(20 mg, 23%). Mp = 227-230 ⁰C (decomp.) H NMR (500 MHz,
2
D O): δ 9.22 (d, 4H, J = 5.55 Hz), 8.72 (t, 2H, J = 7.89 Hz), 8.19
1
3
1
(
D
t, 4H, J = 7.02 Hz), 7.31 (s, 2H). C{ H} NMR (125 MHz,
-
1
2
O): δ 149.8, 145.1, 129.5, 78.0. IR (ν = cm ): 3472, 3430,
3
C
023, 2999, 1622, 1489, 1293, 765, 687. HRMS (ESI): calcd. for
H N BF [M-BF ] , 259.1024, found 259.1024.
11 12 2 4 4
1
white powder (78 mg, 51%). Mp = > 300 ⁰C (decomp.) H NMR
+
+
(500 MHz, D
2
O): δ 8.51 (d, 4H, J = 6.60 Hz), 7.77 (d, 4H, J =
1
,2-bis(pyridinium)ethane Bromide (2). Using the procedure giv-
6.42 Hz), 4.20 (s, 6H), 2,89 (t, 4H, J = 7.75 Hz), 2.06 (quint, 2H, J
13
1
en for the preparation of 1, 1,2-dibromoethane (Sigma-Aldrich,
98%, 37 mg, 0.2 mmol) was reacted with pyridine (64 mg, 0.8
2
= 7.84 Hz). C{ H} NMR (125 MHz, D O): δ 161.86, 144.29,
-
-1
127.58, 47.24, 34.10, 28.42. IR (BF
4
salt, ν = cm ): 3284, 3110,
mmol) to afford 2 as a light yellow powder (25 mg, 36%). Mp =
1645, 1519, 1476, 1287, 1028, 835. HRMS (ESI): calcd. for
1
+
+
2
78-280 ⁰C (decomp.) H NMR (500 MHz, D
2
O): δ 8.73 (d, 4H, J
15 20 2 4 4
C H N BF [M-BF ] , 315.1650, found 315.1650.
=
5.48 Hz), 8.58 (t, 2H, J = 7.89 Hz), 8.03 (t, 4H, J = 6.76 Hz),
1
3
1
5
1
7
2
.24 (s, 4H). C{ H} NMR (125 MHz, D
29.1, 60.1. IR (ν = cm ): 3022, 2996, 2942, 1633, 1487, 1194,
75, 677. HRMS (ESI): calcd. for C12
73.1181, found 273.1180.
2
O): δ 147.5, 144.6,
-
1
+
+
H
14
N
2
BF
4
4
[M-BF ] ,
The Supporting Information is available free of charge on the
ACS Publications website.
1
,3-bis(pyridinium)propane Iodide (3). Using the procedure given
for the preparation of 1, 1,3-diodopropane (Sigma-Aldrich, 99%,
29 mg, 0.1 mmol) was reacted with pyridine (32 mg, 0.4 mmol) to
NMR and ITC titration data, cyclic voltammetry data, scan rate
experiments, quantum chemical calculations (PDF), Cartesian
coordinates.
afford 3 as an off-white powder (41 mg, 92%). Mp = 197-200 ⁰C
1
(
decomp.) H NMR (500 MHz, D
2
O): δ 8.80 (d, 4H, J = 5.60 Hz),
8
7
5
.49 (t, 2H, J = 7.87 Hz), 8.01 (t, 4H, 6.86 Hz), 2.71 (quint, J =
1
3
1
.72 Hz). C{ H} NMR (125 MHz, D
8.0, 31.7. IR (ν = cm ): 3027, 3007, 1631, 1479, 1170, 773, 677.
2
O): δ 146.3, 144.3, 128.6,
-1
+
+
HRMS (ESI): calcd. for C13
found 287.1337.
H
16
N
2
BF
4
4
[M-BF ] , 287.1337,
*E-mail:
rmw@bgsu.edu,
murthy1@miami.edu,
pattabi-
1
,4-bis(pyridinium)butane Iodide (4). Using the procedure given
for the preparation of 1, 1,4-diodobutane (Sigma-Aldrich, ≥ 99%,
1 mg, 0.1 mmol) was reacted with pyridine (32 mg, 0.4 mmol) to
afford 4 as an off-white powder (44 mg, 94%). Mp = 191-195 ⁰C
raman2@unk.edu
3
1
The authors declare no competing financial interests.
(decomp.) H NMR (500 MHz, D
2
O): δ 8.73 (d, 4H, J = 5.79 Hz),
8
2
1
.45 (t, 2H, J = 7.82 Hz), 7.97 (t, 4H, J = 6.95 Hz), 4.57 (m, 4H),
13
1
.57 (m, 4H). C{ H} NMR (125 MHz, D
28.3, 60.7, 27.2. IR (ν = cm ): 3046, 1627, 1479, 1447, 1146,
2
O): δ 145.9, 144.1,
-1
RMW thanks R. Marshall and Antonia G. Wilson Chemistry Fund
for financial support of this research. VR thanks the National
Science Foundation (CHE-1807729) for financial support. Re-
search activity at UNK was supported by Great Plains IDeA-CTR
Pilot Grant (NIGMS 1U54GM115458-01). NAT and AAT thank
Stefan Ilic (UIC) and Dr. Stephania Messersmith (BGSU) for CV
training. RMW thanks Dr. Larry Sallans (UC) for the mass spec-
tral analysis.
+
+
817, 763. HRMS (ESI): calcd. for C14
found 341,0509.
18 2
H N I [M-I] , 341.0509,
1,5-bis(pyridinium)pentane Iodide (5). Using the procedure given
for the preparation of 1, 1,5-diodopentane (Sigma-Aldrich, 97%,
3
2 mg, 0.1 mmol) was reacted with pyridine (32 mg, 0.4 mmol) to
afford 5 as a pale yellow powder (45 mg, 94%). Mp = 128-130 ⁰C
1
(
8
7
decomp.) H NMR (500 MHz, D
2
O): δ 8.72 (d, 4H, J = 5.58 Hz),
.44 (t, 2H, J = 7.86 Hz), 7.96 (t, 4H, J = 6.97 Hz), 4.51 (t, 4H, J =
.45 Hz), 1.98 (quint, 4H, J = 7.66 Hz), 1.32 (quint, 2H, J = 7.80
1
3
1
Hz). C{ H} NMR (125 MHz, D
29.9, 22.0. IR (ν = cm ): 3420, 3377, 3011, 1629, 1489, 1234,
163, 775, 683. HRMS (ESI): calcd. for C15
55.0666, found 355.0665.
2
O): δ 145.6, 144.1, 128.2, 61.3,
-
1
1. Behrend, R.; Meyer, E.; Rusche, F. Ueber Condensationsproducte
+
+
aus Glycoluril und Formaldehyd. Liebigs Annalen der Chemie
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3
20 2
H N I [M-I] ,
1
905, 339, 1–37.
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