Highly luminescent 4-pyridyl-extended dithieno[3,2-b:2′,3′-d]phospholes

Article abstract of DOI:10.1021/acs.joc.0c01369

The unexpectedly challenging synthesis of 4-pyridyl-extended dithieno[3,2-b:2′,3′-d]phospholes via Stille cross-coupling is reported. The optical and electrochemical properties of the phosphoryl-bridged species were studied experimentally and computationa

Full text of DOI:10.1021/acs.joc.0c01369

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Article
Highly Luminescent 4‑Pyridyl-Extended
Dithieno[3,2‑b:2′,3′‑d]phospholes
Paul Demay-Drouhard and Thomas Baumgartner*
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ABSTRACT: The unexpectedly challenging synthesis of 4-pyridyl-
extended dithieno[3,2-b:2′,3′-d]phospholes via Stille cross-coupling is
reported. The optical and electrochemical properties of the phosphoryl-
bridged species were studied experimentally and computationally, and
their properties were compared with those of their non-P-bridged
congeners. The 4-pyridyl-extended dithienophospholes display quanti-
tative luminescence quantum yields in solution and reversible reduction
features upon methylation of the pyridine rings. Because of their very
high brightness, even in water, 4-pyridyl-extended dithienophospholes
are highly promising candidates for new fluorescent probes.
properties that can be easily tuned by functionalizing the two-
and six-positions with aromatic moieties, resulting in an
effectively tailorable HOMO−LUMO gap.16 The resulting
compounds display high luminescence quantum yields of up to
80%, and their emissions cover the entire visible spectrum.17
On the basis of the outstanding properties of these two
scaffolds, we were interested to see how the material properties
would potentially evolve in a system that combines the
favorable electrochemical behavior of phosphaviologens with
the exciting photophysical properties of dithienophospholes
(Figure 1). It should be mentioned in this context that
thienoviologens have been successfully used as electro-
fluorochromic materials.18−20 Our target species, which can
be seen as a hybrid of pyridyl-extended dithienophosphole
oxides and phosphorus-bridged thienoviologens, are the
subject of this Article, which has also been deposited on
ChemRxiv prior to submission.21 Their synthesis, optical
properties, and electrochemical behavior will be discussed and
further evaluated through theoretical calculations.
INTRODUCTION
■
Over the past decades, there has been a surge in the
development of new organic building blocks with useful
optoelectronic properties for practical applications in a variety
of organic electronics.1−5 Some representative molecular
platforms include oligothiophenes due to their outstanding
charge-transport properties6 and viologens for their reversible
redox behavior.7 Tuning the properties of these systems via
main-group elements is an interesting strategy because it can
result in unique changes in terms of the luminescence,
supramolecular organization, and electrochemistry.8−10 We
have been focusing our attention on phosphorus-containing π-
conjugated species,11 especially the highly luminescent
dithieno[3,2-b:2′,3′-d]phosphole12 and the related redox-
active phosphaviologen13 scaffolds (Figure 1). In these
systems, the addition of phosphorus reduces the energy of
the LUMO level via negative hyperconjugation from
endocyclic σ* orbitals with the π* system.11
Phosphaviologens are strong electron-accepting materials
displaying two reversible reduction processes that could
RESULTS AND DISCUSSION
successfully be leveraged for photoinduced charge separation14
■
and in hybrid batteries.15 On the contrary, the dithienophosp-
Synthesis. The first strategy toward pyridyl-functionalized
dithienophosphole (PyrDTP, 2) relied on a Suzuki cross-
coupling between the commercially available 4-pyridylboronic
acid and dibromophosphole 1, synthesized from 2,2′-
bithiophene according to literature procedures (Scheme
hole oxide scaffold possesses prominent photoluminescence
Special Issue: The New Golden Age of Organo-
phosphorus Chemistry
Received: June 9, 2020
Figure 1. Conjugated fused phospholes and viologens.
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© XXXX American Chemical Society
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A

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Scheme 1. Synthesis of the Targeted Compounds
Figure 2. UV−vis (left) and fluorescence (right) spectra of compounds 2, 4, and 7 (in CH2Cl2) and compounds 6 and 8 (in H2O).
1).12,16 Because all Suzuki coupling attempts failed, even under
a vast range of conditions (see the Supporting Information),
we turned our attention to compound 5, which would be a
direct precursor of PyrDTP, as shown for related com-
pounds.22 Pyridyl-substituted bithiophene (PT)2 (4) was
synthesized from dibromobithiophene 3 according to Osadnik
either coupling reaction previously mentioned. (See the
Supporting Information.)
Unfortunately, the lithiation of compound 5 followed by the
reaction with PhPCl2 toward dithienophosphole oxide 2
according to our established protocols12 was not effective,
possibly due to the very low solubility of bithiophene 5 in the
common solvents used for lithiation. (See the Supporting
Information.)
With these unforeseen setbacks, we moved back to our
initial strategy but using a different type of cross-coupling. To
our satisfaction, Stille coupling between 1 and 4-
(trimethylstannyl)pyridine using standard conditions (Pd-
(PPh3)4, refluxing toluene) afforded PyrDTP 2, albeit in low
yield (24%). The yield of 2 could be optimized to 37% using
tri(2-furyl)phosphine and Pd2(dba)3 as a catalytic system
(Scheme 1).31 PyrDTP was fully characterized by multinuclear
NMR spectroscopy and elemental analysis. In particular, its 31P
NMR spectrum exhibits a single peak at 18.4 ppm character-
istic of a π-extended dithieno[3,2-b:2′,3′-d]phosphole oxide
species.16
and Lu
̈
tzen23 but employing a modified purification procedure.
The bromination of 4 was accomplished using N-bromosucci-
nimide (NBS) in AcOH at 110 °C in 42% yield. Other solvents
(CHCl3, DMF) or bromide sources (Br2) gave only traces of
product. Although the yield of compound 5 is moderate, the
bromination of 4 is selective for the 3,3′-positions, as observed
for bithiophenes similar to 4 but possessing alkyl chains at the
5,5′-positions.24,25 A definitive proof of the structure of
compound 5 was provided by preliminary single-crystal X-ray
diffraction. (See the Supporting Information.)
It should be noted that the synthesis of bithiophene 5 was
also attempted by means of a Suzuki cross-coupling between
3,3′,5,5′-tetrabromo-2,2′-bithiophene or 3,3′-dibromo-5,5′-
diiodo-2,2′-bithiophene and 4-pyridylboronic acid, as this
route seemed effective for other arylboronic acids,22,26−28 but
no coupling product could be obtained in our case.
Unfortunately, a Stille cross-coupling protocol using 4-
(trimethylstannyl)pyridine29 did not prove efficient either,
nor did the oxidative dehydro C−H coupling of 4-(4-
bromothiophen-2-yl)pyridine.30 Moreover, the use of pyr-
idine-N-oxides also did not result in any improvements for
The methylation of the nitrogen centers was accomplished
with MeOTf to give [PyrDTPMe2]2+[OTf−]2 (6) in 71% yield
as its triflate salt. Salient structural features include a singlet at
4.22 ppm for the methyl groups in the 1H NMR spectrum and
a singlet at −79.3 ppm in the 19F NMR spectrum for the
triflate anion. For comparison purposes, 4 was also methylated
B
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Table 1. Photophysical Data of the Studied Compounds (c = 2.5 × 10−5 M)
a
b
c
d
e
compound
solvent
λmax (nm)
εmax (L mol−1 cm−1
)
λem (nm)
Stokes shift (cm−1
)
ΦPL
B (L mol−1 cm−1
)
2
4
7
6
CH2Cl2
CH2Cl2
CH2Cl2
H2O
MeCN
H2O
276, 288 (sh), 327, 415
259 (sh), 381
271, 317, 414
289, 305 (sh), 352, 440, 455 (sh)
292, 305 (sh), 351, 443, 457 (sh)
256, 284, 431
27 900
36 300
11 300
49 900
50 100
57 900
507
455
497
504
510
501
501
4400
4300
4000
2900
2300
3200
3400
0.99
0.22
0.81
0.99
0.98
0.59
0.60
27 600
8000
9200
49 400
49 100
34 200
8
MeCN
257, 282, 429
58 400
35 000
a
b
c
UV/vis absorption peaks; bold values correspond to the π−π* transition. Extinction coefficient associated with the π−π* transition. Emission
d
maxima, excitation at the π−π* transition absorption maximum. Absolute luminescence quantum yield, determined using an integrating sphere.
e
Brightness, defined as B = ΦPL × εmax
.
under the same conditions to afford [(PT)2Me2]2+[OTf−]2 (8)
in 82% yield.
theory (TD-DFT) calculations via increased oscillator
strengths for the respective transitions (vide infra). These
values are considerably superior to commonly used fluoro-
phores (including most coumarins, naphthalimides, cyanines,
and BODIPY-based dyes) and are comparable to xanthene-
based fluorophores (rhodamine and fluorescein derivatives, B
usually in the 20 000−90 000 range).35,36
Electrochemical Properties. The redox properties of
pyridyl-functionalized dithienophospholes were assessed using
cyclic voltammetry (Figure 3).
Compound 2 could also be selectively modified at the
phosphorus center by converting it to sulfide PyrDTPsulf (7)
using Lawesson’s reagent. Compared with 6, compound 7
shows a downfield shift of 8.0 ppm in the 31P NMR spectrum,
correlating well with related phosphole sulfide species.17,32
Optical Properties. The optical properties of compounds
2, 4, and 6−8 were investigated in different solvents; the
results are shown in Figure 2 and are listed in Table 1. All
pyridyl-extended phospholes are strongly luminescent in the
blue-green to green region of the optical spectrum (λem = 497
to 510 nm) and show a significant red shift compared with
phosphole 1, as previously observed for phospholes with
extended π-conjugation.16 The maximum emission of 2 (λem
=
507 nm) is very similar to the emission of a related 2-picolyl-
extended dithienophosphole (λem = 511 nm).16 Compound 4
and its viologen congener 8 are also luminescent, as previously
reported.18,19,33,34 The tethering of the thiophene rings with an
oxyphosphoryl moiety has a strong influence on the optical
properties: A red shift of Δλ = 34 nm (absorption) and Δλ =
52 nm (emission) is observed between 4 and 2. This effect is
much less pronounced for the methylviologen analogs 6 and 8
(Δλ = 9 to 14 nm in absorption and 3 to 9 nm in emission,
depending on the solvent). The absorption coefficients for the
phospholes are in the typical range of 11 000−50 000 L·mol−1·
cm−1, which is slightly lower compared with the nonphosphole
analogs 4 and 8. Stokes shifts vary from 2200 to 4400 cm−1,
similar to previously reported dithienophospholes,16 and a
lowering of 1000−1400 cm−1 is observed upon methylation.
The most striking features of pyridyl-extended phosphole
oxides, N-quaternized or not, are their very pronounced
emission properties. Compound 2 displays a quantitative
luminescence quantum yield in CH2Cl2. Upon N-methylation
of the pyridine rings, the quantum yield remains quantitative in
MeCN and even in water, in sharp contrast with the quantum
yields of 4 (ΦPL = 0.22 in CH2Cl2, 0.10 in 40% aq MeOH,33
and 0.11 in DMF34) and thienoviologen 8 (ΦPL = 0.60 in H2O
compared with 0.52 for diprotonated 4 in 40% aq MeOH33).
Compared with P-oxide 2, the quantum yield of sulfide
analogue 7 is lower (ΦPL = 0.81 in CH2Cl2) but is still quite
high. As a result, the pyridyl-extended dithienophospholes
display very high brightness values (up to 50 000 L·mol−1·
cm−1), with the viologen species 6 having the highest observed
value in this series. Given that both phosphole-oxide-based
compounds 2 and 6 have quantum yields near unity, the
doubling of the brightness from 2 to 6 can only be attributed
to the significantly larger extinction coefficient for the latter
that is also supported by time-dependent density functional
Figure 3. Cyclic voltammograms (referenced vs Ag/AgCl) of
compounds 2, 4, and 6−8 in DMF containing 0.1 M [NBu4][PF6]
as the supporting electrolyte (c = 1 to 2 mg·mL−1, scan rate: 100 mV·
s−1). For cyclic voltammograms at different scan rates, see the
Supporting Information.
Compound 4 shows two successive quasi-reversible
reduction events in DMF (Ered,1 = −1.58 V and Ered,2
−1.80 V). The same behavior is observed for P-oxide 2 and its
sulfide congener 7 (Ered,1 = −1.22 and −1.21 V and Ered,2
=
=
−1.53 and −1.52 V, respectively). The shift toward lower
potentials for compounds 2 and 7 compared with compound 4
was also observed for phosphaviologens compared with
viologens and can be attributed to the σ*−π* interaction in
the phosphoryl-bridged species.13 Notably, the reversibility was
found to depend strongly on the solvent: In CH2Cl2, only
irreversible reductions were found for compound 4, whereas
for phospholes 2 and 7, the second reduction peak became
irreversible. (See the Supporting Information.) This points
toward solubility issues and deposition on the electrode in this
solvent. When the nitrogen atoms are methylated, only one
reduction event is detected (Ered = −0.75 V for 8 and −0.59 V
for 6) in addition to a considerable shift toward lower
potentials. Whereas most viologen derivatives exhibit two
distinct reduction peaks, such behavior was already observed
for closely related derivatives of compound 8.37 This single-
C
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Figure 4. Calculated HOMO and LUMO energy levels (B3LYP/6-31G(d) level of theory)35 of dithienophospholes, thienoviologens, and
phosphaviologens. Calculations were performed in a vacuum for neutral species and in H2O for cationic species.
Figure 5. Frontier orbitals of 2, 4, 7 (PCM in CH2Cl2), 6, and 8 (cations only; PCM in MeCN). Isovalue is 0.02. The TD-DFT-derived
contribution of the HOMO−LUMO transition to the lowest excited state is indicated beside the arrows.
step two-electron reduction event may also consist of two very
close one-electron reduction peaks. Viologen 8 displays a
quasi-reversible behavior, whereas phosphole 6 exhibits
complete electrochemical reversibility for scan rates between
10 and 200 mV·s−1, as shown by the constant peak potential
within this range, making it a promising species for battery
applications.15
Density Functional Theory Calculations. The electronic
properties of pyridyl-extended dithienophospholes were
investigated by DFT calculations (B3LYP/6-31G(d) level of
theory)38 and were compared with related dithienophosphole
oxides, phosphaviologens, and thienoviologens. Calculations
were performed in a vacuum and DMF and in a CH2Cl2
environment for neutral species as well as in H2O and MeCN
for cationic species. The polarization continuum model
(PCM) was employed to simulate solvation effects. Compared
with the 2,6-diphenyl-substituted dithienophosphole 9,16 the
replacement with a 4-pyridyl moiety results in a lowering of
both HOMO and LUMO levels by the same extent, resulting
in a similar energy gap but a stabilized LUMO level (Figure 4).
A smaller stabilization of the LUMO level of 2 compared with
that of 4 is observed, along with a small reduction of the energy
gap. This can be explained by the additional rigidification of
the scaffold provided by the bridging phosphorus. No
significant difference in terms of the energy levels was seen
between P-oxide 2 and P-sulfide 7. On the contrary, N-
D
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Table 2. Calculated Transitions of the Studied Compounds and Comparison between Experimental and DFT Values
a
b
c
d
e
compound
solvent
λmax,exp (nm)
λmax,DFT (nm)
f
ELUMO,exp (eV)
ELUMO,DFT (eV)
2
4
7
6
CH2Cl2
CH2Cl2
CH2Cl2
H2O
MeCN
H2O
415
381
414
440
443
431
429
442
409
442
497
498
481
0.889
1.319
0.783
1.371
1.374
1.645
1.649
−2.80
−2.44
−2.81
−2.53
−2.26
−2.55
−3.40
−3.22
−3.57
−3.43
8
MeCN
482
a
b
c
d
Absorption maximum from UV/vis spectroscopy. (See Table 1.) Absorption maximum from TD-DFT calculations. Oscillator strength. Energy
of the LUMO level found from the onset of the first reduction potential in cyclic voltammetry (in DMF) and calculated by referencing it to the
e
energy level of Ag (−3.91 eV). Energy of the LUMO level found through DFT calculations (PCM in DMF).
methylation led to a further stabilization of the HOMO and
LUMO levels as well as to an important reduction of the
energy gap, showcasing the strong electron-accepting character
of viologens 6 and 8. Finally, compared with the phosphaviol-
ogen series (10 and 11), the LUMO level is less stabilized, but
the energy gap is smaller (Figure 4).
EXPERIMENTAL SECTION
■
General Materials, Instruments, and Methods. All manipu-
lations were performed under an argon atmosphere using standard
Schlenk techniques. Solvents were dried with an MBraun Solvent
Purification System. An oil bath was used for reactions requiring
heating. Starting materials and reagents were purchased from Sigma-
Aldrich, Oakwood Chemical, or Strem Chemicals and used without
further purification. Compounds 1,12,16 3,43 and 4-(trimethylstannyl)-
pyridine29 were synthesized according to literature procedures. Flash
column chromatography was performed using a SiliaFlash M60 silica
gel (60−120 μm). Thin-layer chromatography was performed on
silica gel 60 F254 precoated plates. 1H, 13C{1H}, 31P{1H}, and 19F{1H}
NMR spectra were recorded on a Bruker Avance 400 MHz
spectrometer. Chemical shifts were referenced to residual non-
deuterated solvent peaks (CDCl3: 7.26 ppm for 1H and 77.16 ppm for
Time-dependent density functional theory (TD-DFT)
calculations were also performed at the B3LYP/6-31G(d)
level of theory;38 solvent effects were taken into account using
the PCM solvation model, and the results are shown in Figure
5 and Table 2. For all compounds, the main absorption band,
which corresponds to the π−π* transition (see the Supporting
Information), nearly exclusively stems from HOMO to LUMO
transitions, as observed for other fluorophores including
alizarin39 and coumarin derivatives.40 The trend in extinction
coefficients is quite well reflected by the corresponding
oscillator strength values. The >50% larger value for the
viologen species 6 (compared with that of 2) can be correlated
with the increased polarity of its scaffold that leads to a more
pronounced change in dipole moment between the ground and
excited states. The calculated absorption maxima are system-
atically overestimated by 27 to 28 nm for the neutral species
and 50−57 nm for the cationic species, but such discrepancies
are not uncommon for TD-DFT calculations involving
dyes.41,42 Finally, for all compounds, a good correlation is
observed between the LUMO levels obtained from cyclic
voltammetry and those obtained through DFT calculations,
with a systematic slight difference of ∼0.2 eV (Table 2).
1
13C, CD3CN: 1.94 ppm for H and 1.32 ppm for 13C). Elemental
analysis was performed using an Elementar vario EL cube.
Electrospray ionization (ESI) high-resolution mass spectrometry
(HRMS) was performed on a ThermoFisher Orbitrap Elite
spectrometer. Optical spectroscopy was performed on an Agilent
Cary 5000 UV−vis spectrophotometer. Fluorescence spectroscopy
was performed on an Edinburgh Instruments FS5 spectrofluorometer.
Cyclic voltammetry was performed on a Metrohm Autolab
PGSTAT204 potentiostat connected to a three-electrode cell with
glassy carbon as a working electrode, Pt wire as a counter electrode,
and Ag/AgCl as a reference electrode. Solvents were degassed with
argon, and the working electrode was polished with alumina before
each experiment. DFT calculations were performed with Gaussian
09.38 Vibrational harmonic frequency analysis was performed to
ensure that there were no imaginary frequencies.
Synthetic Procedure for (PT)2 (4). A mixture of 5,5′-dibromo-
2,2′-bithiophene (10.0 g, 30.9 mmol, 1.0 equiv), 4-pyridylboronic acid
(8.0 g, 64.9 mmol, 2.1 equiv), Pd(PPh3)4 (1.79 g, 1.55 mmol, 0.05
equiv), and K2CO3 (25.6 g, 185 mmol, 6.0 equiv) was stirred in
toluene/MeOH/H2O (500/250/80 mL) at 85 °C for 48 h. The
solvent was removed in vacuo, and the resulting solid was washed
with H2O and dried. Column chromatography (1:1 CH2Cl2/EtOAc,
then 4:1 CH2Cl2/MeOH) followed by washing with toluene (50 mL),
then acetone (50 mL) afforded 4 as a yellow solid (6.56 g, 20.5 mmol,
66%). Rf 0.66 (9:1 CH2Cl2/MeOH). 1H NMR (400 MHz, CDCl3) δ
8.62 (dd, J = 4.5, 1.7 Hz, 4H), 7.48−7.44 (m, 6H), 7.25 (s, 2H).
13C{1H} NMR (101 MHz, CDCl3) δ 150.7, 140.9, 140.6, 138.5,
126.4, 125.6, 119.7. Characterization is in accordance with the
literature.23,33,34,44,45
Synthetic Procedure for Compound 5. Compound 4 (3.0 g,
9.36 mmol, 1.0 equiv) was dissolved in AcOH (150 mL). NBS (5.0 g,
28.1 mmol, 3.0 equiv) was added. The resulting mixture was stirred at
110 °C for 48 h. The solvent was removed in vacuo, and the resulting
solid was washed with H2O and dried. Column chromatography
(100:0 to 95:5 CH2Cl2/MeOH) afforded 5 as an orange solid (1.86 g,
3.89 mmol, 42%). Rf 0.70 (9:1 CH2Cl2/MeOH). 1H NMR (400
MHz, CDCl3) δ 8.61 (dd, J = 4.5, 1.7 Hz, 4H), 7.47−7.44 (m, 6H),
7.47 (dd, J = 4.5, 1.7 Hz, 4H). 13C{1H} NMR (101 MHz, CDCl3) δ
CONCLUSIONS
■
In conclusion, we have established a synthetic protocol toward
pyridyl-extended dithienophospholes in the hope of obtaining
a compound combining the electrochemical properties of
phosphaviologens with the optical properties of dithieno[3,2-
b:2′,3′-d]phospholes. Both properties are indeed combined in
this new scaffold, which displays electrochemically reversible
features upon methylation of the pyridine rings as well as
prominent optical properties including quantitative quantum
yields in organic and aqueous solvents in conjunction with
reasonably large Stokes shifts. This evolves the previously
established features of π-extended dithienophospholes and
makes pyridyl-extended dithienophospholes attractive candi-
dates for potential fluorescent (bio)probes, next to organic
batteries. In particular, modifications at the nitrogen center do
not seem to affect quantum yields, thus providing a convenient
grafting point for fluorescence labeling. Further developments
may reveal the potential of pyridine-extended dithienophosp-
holes in materials science and for imaging purposes. These
studies are ongoing in our laboratory.
E
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150.9, 142.7, 139.8, 129.9, 129.0, 119.7, 113.7. HRMS (ESI) m/z: [M
+ H]+ calcd for C18H11Br2N2S2 478.8710; found 478.8711.
ASSOCIATED CONTENT
■
sı
* Supporting Information
Synthetic Procedure for PyrDTP (2). A mixture of phosphole 1
(242 mg, 0.54 mmol, 1.0 equiv), 4-(trimethylstannyl)pyridine (392
mg, 1.62 mmol, 3.0 equiv), tri(2-furyl)phosphine (23 mg, 0.10 mmol,
0.18 equiv), and Pd2(dba)3 (30 mg, 0.03 mmol, 0.06 equiv) was
refluxed in toluene (10 mL) for 15 h. The solvent was removed in
vacuo. Column chromatography (95:5 to 88:12 EtOAc/MeOH)
afforded 2 as an orange solid (89 mg, 0.20 mmol, 37%). Rf 0.34 (4:1
EtOAc/MeOH). 1H NMR (400 MHz, CDCl3) δ 8.64 (dd, J = 4.6, 1.6
Hz, 4H), 7.80 (ddd, J = 13.6, 8.2, 1.2 Hz, 2H), 7.59 (td, J = 7.5, 1.7
Hz, 1H), 7.57 (d, J = 2.8 Hz, 2H) 7.48 (td, J = 7.6, 3.4 Hz, 2H), 7.42
(dd, J = 4.6, 1.6 Hz, 4H). 31P{1H} NMR (162 MHz, CDCl3) δ 18.4.
13C{1H} NMR (101 MHz, CDCl3) δ 150.9, 146.0 (d, J = 14.1 Hz),
145.9 (d, J = 22.9 Hz), 140.7 (d, J = 110.8 Hz), 140.3, 133.2 (d, J =
3.0 Hz), 131.0 (d, J = 11.6 Hz), 129.4 (d, J = 13.2 Hz), 128.8 (d, J =
109.1 Hz), 124.1 (d, J = 14.3 Hz), 119.7. Anal. Calcd for
C24H15N2OPS2: C, 65.14; H, 3.42; N, 6.33; S, 14.49. Found: C,
65.39; H, 3.05; N, 6.71; S, 14.53. HRMS (ESI) m/z: [M + H]+ calcd
for C24H16N2OPS2 443.0442; found 443.0442.
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.joc.0c01369.
Details of attempted (unsuccessful) reactions toward
pyridyl-extended dithienophospholes, X-ray crystallo-
graphic data for 5, additional cyclic voltammetry data,
DFT computational data, and copies of NMR spectra of
all new compounds (PDF)
AUTHOR INFORMATION
■
Corresponding Author
Thomas Baumgartner − Department of Chemistry, York
University, Toronto, Ontario M3J 1P3, Canada; orcid.org/
0000-0001-8066-0559; Email: tbaumgar@yorku.ca
Author
Paul Demay-Drouhard − Department of Chemistry, York
University, Toronto, Ontario M3J 1P3, Canada; orcid.org/
0000-0003-2270-1177
Synthetic Procedure for [PyrDTPMe2]2+[2OTf−]2 (6). A
solution of 2 (80 mg, 0.18 mmol, 1.0 equiv) in DCM (15 mL) was
cooled to 0 °C. MeOTf (50 μL, 0.45 mmol, 2.5 equiv) was added.
The resulting mixture was allowed to warm to rt for 15 h. The
precipitate was filtered, washed with a small amount of cold MeCN,
and dried to afford 6 (99 mg, 0.13 mmol, 72%) as an orange solid. 1H
NMR (400 MHz, CD3CN) δ 8.53 (d, J = 6.6 Hz, 4H), 8.17 (d, J = 2.9
Hz, 2H), 8.10 (d, J = 6.6 Hz, 4H), 7.82 (dd, J = 13.9, 7.6 Hz, 2H),
7.67 (t, J = 7.2 Hz, 1H), 7.54 (td, J = 7.4, 2.9 Hz, 2H), 4.22 (s, 6H).
31P{1H} NMR (162 MHz, CD3CN) δ 15.7. 13C{1H} NMR (101
MHz, CD3CN) δ 150.1 (d, J = 21.8 Hz), 148.8, 146.4, 144.2 (d, J =
43.6 Hz), 143.6 (d, J = 50.8 Hz), 134.5 (d, J = 3.0 Hz), 131.9 (d, J =
11.7 Hz), 130.8 (d, J = 14.0 Hz), 130.4 (d, J = 13.6 Hz), 129.3 (d, J =
110.9 Hz), 123.7, 122.2 (q, J = 321.1 Hz, appears as a doublet due to
the low intensity), 48.5. 19F{1H} NMR (377 MHz, CD3CN) δ −79.3.
Anal. Calcd for C28H21F6N2O7PS4: C, 43.64; H, 2.75; N, 3.63; S,
16.64. Found: C, 43.48; H, 2.38; N, 3.75; S, 16.45. HRMS (ESI) m/z:
[M]2+ calcd for C26H21N2OPS2/2 236.0417; found 236.0412.
Synthetic Procedure for PyrDTPsulf (7). Compound 2 (56 mg,
0.13 mmol, 1.0 equiv) was partially dissolved in toluene (15 mL).
Lawesson’s reagent (26 mg, 0.06 mmol, 0.5 equiv) was added. The
resulting mixture was refluxed for 18 h. The solvent was removed in
vacuo. Column chromatography (100:0 to 85:15 EtOAc/MeOH)
afforded 7 as an orange solid (35 mg, 0.08 mmol, 62%). Rf 0.63 (4:1
EtOAc/MeOH). 1H NMR (400 MHz, CDCl3) δ 8.63 (dd, J = 4.6, 1.6
Hz, 4H), 7.86 (ddd, J = 15.4, 8.3, 1.1 Hz, 2H), 7.58 (d, J = 2.9 Hz,
2H), 7.55 (td, J = 7.6, 2.1 Hz, 1H), 7.47 (td, J = 7.8, 3.3 Hz, 2H), 7.44
(dd, J = 4.6, 1.6 Hz, 4H). 31P{1H} NMR (162 MHz, CDCl3) δ 26.7.
13C{1H} NMR (101 MHz, CDCl3) δ 150.7, 146.0 (d, J = 14.7 Hz),
144.3 (d, J = 19.0 Hz), 143.6 (d, J = 93.2 Hz), 140.4, 132.8 (d, J = 3.0
Hz), 130.9 (d, J = 12.6 Hz), 129.2 (d, J = 13.7 Hz), 128.8 (d, J = 85.7
Hz), 123.5 (d, J = 15.4 Hz), 119.6. HRMS (ESI) m/z: [M + H]+
calcd for C24H16N2PS3 459.0213; found 459.0217.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.joc.0c01369
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support by the Natural Sciences and Engineering
Research Council of Canada (NSERC) and the Canada
Foundation for Innovation is gratefully acknowledged. T.B.
thanks the Canada Research Chairs program for support. We
thank M. Rossato of the YSciCore Mass Spectrometry Facility
of York University for the HRMS measurements.
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F
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