Tuning the Optoelectronic Properties of Stannoles by the Judicious Choice of the Organic Substituents

Article abstract of DOI:10.1021/acs.inorgchem.8b01649

Stannoles are organometallic rings in which the heteroatom is involved in a form of conjugation that is called σ?-π? conjugation. Only very little is known about how the substituents on the Sn atom or substituents on the stannole ring determine the optoelectronic properties of these heterocycles. In this work, this question has been studied experimentally and theoretically. Calculations of optimized equilibrium geometries, energy gaps between the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs), and of the absorption spectra of a wide range of compounds were performed. The computational data showed that the substituents on the Sn atom influence the optoelectronic properties to a lower extent than the substituents in the 2 and 5 positions of the ring. These substituents in the 2 and 5 positions of the stannole ring can also have a strong influence on the overall planarity of the structure, in which mesomeric effects can play a substantial role only if the structure is planar. Thus, only structures with a planar backbone are of interest in the context of tuning the optoelectronic properties. These were selected for the experimental studies. On the basis of this information, a series of six novel stannoles was synthesized by the formation of a zirconium intermediate and subsequent transmetalation to obtain the tin compound. The calculated electronic HOMO-LUMO energy gaps varied between 2.94 and 2.68 eV. The measured absorption maxima were located between 415 and 448 nm compared to theoretically calculated values ranging from 447 nm (2.77 eV) to 482 nm (2.57 eV). In addition to these optical measurements, cyclic voltammetry data could be obtained, which show two reversible oxidation processes for three of the six stannoles. With this study, it could be demonstrated how the judicious choice of the substituents can lead to large and predictable bathochromic shifts in the absorption spectra.

Full text of DOI:10.1021/acs.inorgchem.8b01649

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Tuning the Optoelectronic Properties of Stannoles by the Judicious
Choice of the Organic Substituents
†
,‡
‡,§
†,‡
‡,||
‡,||
Isabel-Maria Ramirez y Medina, Markus Rohdenburg, Farzin Mostaghimi, Simon Grabowsky,
Petra Swiderek,‡,§ Jens Beckmann,
‡,||
Jonas Hoffmann, Vincent Dorcet, Muriel Hissler,
⊥
⊥
,†,‡,¶
and Anne Staubitz*
†
Institute for Organic and Analytical Chemistry, University of Bremen, Leobener Straße 7, 28359 Bremen, Germany
Institute for Applied and Physical Chemistry, University of Bremen, Leobener Straße 5, 28359 Bremen, Germany
MAPEX Center for Materials and Processes, University of Bremen, Bibliothekstraße 1, 28359 Bremen, Germany
§
‡
|
|
Institute of Inorganic Chemistry and Crystallography, University of Bremen, Leobener Straße 3 and 7, 28359 Bremen, Germany
⊥
Universite Rennes, CNRS, ISCR, UMR 6226, Campus de Beaulieu, 263 Av. du General Leclerc, 35042 Rennes France
́ ́ ́
Otto-Diels-Institute for Organic Chemistry, University of Kiel, Otto-Hahn-Platz 4, 24118 Kiel, Germany
¶
*
S Supporting Information
ABSTRACT: Stannoles are organometallic rings in which the
heteroatom is involved in a form of conjugation that is called
σ*−π* conjugation. Only very little is known about how the
substituents on the Sn atom or substituents on the stannole
ring determine the optoelectronic properties of these hetero-
cycles. In this work, this question has been studied experi-
mentally and theoretically. Calculations of optimized equili-
brium geometries, energy gaps between the highest occupied
molecular orbitals (HOMOs) and lowest unoccupied molecu-
lar orbitals (LUMOs), and of the absorption spectra of a wide
range of compounds were performed. The computational data
showed that the substituents on the Sn atom influence the
optoelectronic properties to a lower extent than the sub-
stituents in the 2 and 5 positions of the ring. These substituents in the 2 and 5 positions of the stannole ring can also have a
strong influence on the overall planarity of the structure, in which mesomeric effects can play a substantial role only if the
structure is planar. Thus, only structures with a planar backbone are of interest in the context of tuning the optoelectronic
properties. These were selected for the experimental studies. On the basis of this information, a series of six novel stannoles was
synthesized by the formation of a zirconium intermediate and subsequent transmetalation to obtain the tin compound. The
calculated electronic HOMO−LUMO energy gaps varied between 2.94 and 2.68 eV. The measured absorption maxima were
located between 415 and 448 nm compared to theoretically calculated values ranging from 447 nm (2.77 eV) to 482 nm
(
2.57 eV). In addition to these optical measurements, cyclic voltammetry data could be obtained, which show two reversible
oxidation processes for three of the six stannoles. With this study, it could be demonstrated how the judicious choice of the
substituents can lead to large and predictable bathochromic shifts in the absorption spectra.
6−8
INTRODUCTION
on opposite ends of the molecule. In semiconducting polymers,
■
often two different heterocycles, one electron-rich and one
Heterocycles with a conjugated π system that contain a Sn
atom in the ring are of fundamental interest because the Sn
atom changes the electronic structure of the overall system
substantially. Although there are examples of systems where
the Sn atom is involved in a classic aromatic system that obeys
9
−12
electron-deficient, are coupled.
When other main-group
elements are introduced, the range of possibilities to lower this
gap becomes larger: Strategies involve formally antiaromatic
13
compounds such as boroles or phosphole oxides (for the
latter of which the antiaromaticity is due to σ*−π* conju-
the Hu
̈
ckel rule, a different, nonaromatic form of conju-
14,15
16,17
1
−5
gation).
B−N substitution of (poly)aromatic rings
gation, σ*−π* conjugation, plays a more dominant role.
results in compounds that are formally aromatic but whose
charge delocalization around the ring is severely impeded by
In the context of attempts to lower the highest occupied
molecular orbital (HOMO)−lowest unoccupied molecular
orbital (LUMO) gaps in materials, bathochromic shifts often
are achieved by creating push−pull systems (acceptor−donor
systems) by introducing electron-donating and -accepting groups
Received: June 17, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01649
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Article
the very polar B−N substitution, which may aide long-range
delocalization of electrons.
However, using σ*−π* conjugation as a means for lowering
the HOMO−LUMO gap is much less common; this
phenomenon can be observed by formally substituting the
tetracoordinated C atom in cyclopentadienes by heavy group
have been reported, but systematic studies of the effects of
changing the substituents on stannoles on their optoelectronic
22,23
properties do not exist.
However, such a study is needed
because it could already be demonstrated that stannoles
can serve as monomers for conjugated polymers with a strong
47,48
bathochromic shift compared to polythiophenes.
With
1
4 and 15 heteroelements.
a thorough understanding of the electronic characteristics of
stannoles, desired characteristics may be achievable. In this
work, optimized equilibrium geometries of stannoles with
different substituents R and R (Figure 2), their synthesis, and
a comparison of the theoretical and experimental absorption
maxima are reported. In addition, the electrochemical behavior
of six stannoles was analyzed by cyclic voltammetry (CV)
measurements. On the basis of these results, the change in the
optoelectronic properties by changing the substituents on the Sn
or the periphery of the molecule can be predicted.
Tin-containing metalloles (Figure 1) are part of heavy group
4 (Si, Ge, Sn, and Pb) cyclopentadiene analogues and were
1
18
1
2
first synthesized in 1959.
Figure 1. Cyclopentadienes and the related group 14 metalloles.
1
9−21
Since then, investigations of different synthetic routes
22,23
and studies of the (opto)electronic properties,
aromatic-
2
4
25−27
ity, and reactivity were conducted for the related siloles,
2
8,29
30
31,32
but germoles,
stannoles, and plumboles
are much
33
less well investigated. However, the study of such hetero-
cycles is of great interest because they themselves or their ring-
3
4−40
fused analogues
devices.
show great potential in organic electronic
The formal replacement of the methylene C atom
4
1−46
by Si, Ge, Sn, or Pb in cyclopentadiene and its derivatives leads
to unique optoelectronic properties in comparison to their
carbon analogues. These heteroles show smaller energy gaps
between the HOMO and LUMO and a broad bathochromi-
cally shifted absorption maximum. Therefore, they are pro-
mising building blocks for the development of semiconducting
47,48
polymers used in organic electronics.
The origin of these
interesting properties has been well studied by Tamao and
22,49
co-workers in 1998 and 1996, respectively.
On the basis of
quantum-chemical calculations, they showed that the replace-
ment of the C atom of the methylene group in cyclopentadiene
by E = Si, Ge, or Sn lowers the energy of the σ* orbital of the
two exocyclic E−R bonds. This observation results in efficient
interactions of the σ* and π* orbitals of the butadiene moiety
1
2
Figure 2. Stannoles with different substituents R and R that were
investigated by quantum-chemical calculations. The compounds indicated
with asterisks were also synthesized and analyzed experimentally.
(
strong σ*−π* conjugation) compared to the negligibly small
σ*−π* conjugation in cyclopentadiene. This strong σ*−π*
22,50
RESULTS AND DISCUSSION
conjugation leads to a remarkable lowering of E
.
A com-
■
LUMO
plementary electronic analysis has been provided by Ottosson
Initially, a wide range of stannoles were studied theoretically to
gain insight into the influence of the different substituents on
the Sn and in the periphery on the optoelectronic properties
(Figure 2). All of those stannoles were substituted with aromatic
groups on the Sn atom. To draw valid comparisons with the
cyclopentadiene analogues, two further stannoles and analogous
cyclopentadienes were calculated (Figure 3); in those cases, the
24
and co-workers on the related siloles. In this view, the group
4 heteroles can be depicted in several mesomeric forms
1
including ionic forms, where the substituent on the Sn atom
can be anionic or cationic combined with a cationic or anionic
heterole counterpart. Depending on the electron-withdrawing
or -donating nature of the substituents on the group 14 hetero-
atom, these mesomeric forms have a higher or lower contri-
bution to the overall energy, leading to a bathochromic shift
compared to electronically neutral substituents.
3
substituents on the sp atom in the ring were methyl groups
because the aromatic groups were sterically too large for the
cyclopentadienes. On the basis of these results, a set of six stan-
noles was selected and synthesized, showing that the theoretical
calculations were indeed predictive for the experiments.
Until today, only comparisons of the optoelectronic charac-
teristics of tailored siloles, germoles, and their carbon analogues
B
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Article
same substituent in the periphery, both HOMO and LUMO
are affected. The energy levels of the HOMO and LUMO
decrease by ca. 0.5 eV (2 and 1 as opposed to 3) because
electron-withdrawing groups stabilize the HOMO and LUMO.
The same trend can be observed for the series 5-4-6 where the
energy levels of the HOMO and LUMO decrease also by ca.
0
.5 eV (5 and 4 as opposed to 6). The HOMO−LUMO
Figure 3. Stannoles and the corresponding cyclopentadiene derivatives
with methyl substituents on the tetracoordinated atom of the ring.
energy gap for compounds 1−6 is the lowest in compound 6,
where the butadienyl system is particularly electron-rich
because of the attached TphOMe groups and the R on the
2
Optimization of the Selected Structures. The inves-
tigated stannoles fall into two categories: those with a thiophenyl
derivate in the 2 and 5 positions and those with a six-membered
aromatic ring in the 2 and 5 positions (for two representative
structures, see Figure 4; for all other structures, see the
Sn is particularly electron-deficient, creating a push−pull
system that operates across the tetracoordinated Sn atom.
Although the influence of the substituents on the Sn atom
on the overall system is smaller than the π system going
through the dienyl part of the stannole, the substituents on the
Sn atom modulate both the HOMO and LUMO. The energy
of the HOMO level decreases when there are electron-
withdrawing substituents on the Sn atom (e.g., perfluorinated
phenyl rings, stannoles 3 and 6), but the HOMO energy level
decreases to a higher extent if the electron-withdrawing group
is in the periphery (nitro group at the thiophene or perfluori-
nated phenyl ring, stannoles 7 and 10).
Electron-withdrawing six-membered rings do contribute
substantially to decreasing the HOMO and LUMO energy,
presumably mainly by inductive effects. However, a surprising
degree of delocalization is found. Because EHOMO is decreased
much more than ELUMO (compared to 1), the energy gap
between the frontier molecular orbitals is large. If there is a six-
membered ring with an electron-donating group in the peri-
phery, for example, 16, the HOMO energy level is increased
slightly, but the LUMO energy level is increased much more
strongly. In general, the HOMO−LUMO energy gaps for the
compounds with six-membered rings in the 2 and 5 positions
are strongly increased in comparison to the compounds with
thiophenes in the 2 and 5 positions but are still smaller than
those for the unsubstituted stannole 38 (Table 1). The origin
of this observation is likely to be that these substituents are
tilted because of steric hindrance with respect to the plane of
the stannole (Figure 4).
The isosurface representations of the frontier molecular orbitals
show that the HOMO and LUMO are delocalized over the
whole backbone (for representative examples, see Figure 5a).
The substituents on the Sn atom are not involved in the
HOMO and only marginally involved in the LUMO. If there
are perfluorinated rings on the Sn atom as in 3 and 6, the
substituents on the Sn atom are more involved in the LUMO
(see the SI). The shapes of the isosurfaces of the HOMOs and
LUMOs for compounds 1−3, on the one hand, and 4−6, on
the other hand, are similar (see Figure 5a and the SI). If there
are six-membered aromatic rings in the 2 and 5 positions, the
distribution of the HOMO is much more concentrated on the
stannole; the peripheral rings play a smaller role for efficient
π conjugation compared to the thiophene rings because of the
ring tilt (Figure 5a).
Figure 4. Optimized geometries of 1 and 10.
Supporting Information, SI). We found that the stannoles with
thiophenyl derivatives in the 2 and 5 positions have an overall
planar backbone (anticoplanar arrangement of the thiophenes
with respect to the stannole ring), whereas the stannoles with
six-membered rings in those positions display a twisted backbone
(
Figure 4). The calculated torsion angle between the thiophenyl
substituent and stannole ring is −174.0° for compound 1,
whereas in the twisted compound 10, the torsion angle between
the fluorinated phenyl group and stannole is −123°. The
stannole ring is planar in all cases, and the substituents on the
Sn atom are twisted from this plane so that the Sn atom has a
distorted tetrahedral arrangement.
Because the electronic influence for a π-conjugated system
must be much larger for planar backbones than for twisted
species, we turned the focus to those stannoles that contain a
(
substituted) thiophene in the 2 and 5 positions.
Molecular Orbital Calculations. For the theoretical
studies of the electronic properties, the orbital energies of
the HOMO and LUMO and the resulting energy gaps can be
compared (Table 1).
If we take the unsubstituted stannole 38 as a point of
reference, the energy gap between the HOMO and LUMO is
much larger than those for any of the peripherally substituted
stannoles. This gives a first indication that extension of the
conjugated dienyl moiety plays an important role in stannoles.
1
If R is changed to a thienyl group (compound 1), E
There is one type of stannole in our study where the Sn
atom is not at all involved in the LUMO: The stannoles 7−9
with a nitro group attached to the thiophenyl group in the
periphery have the narrowest HOMO−LUMO energy gaps.
A closer inspection of the electronic structure revealed that
these systems have different electronic structures in compar-
ison to stannoles 1−6. In the case of compounds 7−9, the
LUMO orbital coefficients are nearly zero on the Sn atom,
which appears not to be involved in the LUMO (Figure 5a).
HOMO
increases but ELUMO decreases, which results in an overall
reduction of the HOMO−LUMO energy gap by 1.66 eV.
A decrease of the HOMO−LUMO energy gap with exten-
sion of the π system is very typical and warrants little discus-
sion. However, modulation of this effect by the attached Sn
3
sp atom with its different substituents is interesting and insightful.
For example, in the series 2−1−3, where the substituent on
the Sn atom becomes increasingly electron-deficient with the
C
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Table 1. Molecular Orbital Energies (EHOMO−1, EHOMO, ELUMO, and ELUMO+1) and HOMO−LUMO Energy Gaps (eV)
molecule
E
R1
Tph
Tph
Tph
TphOMe
TphOMe
TphOMe
TphNO2
TphNO2
TphNO2
PFB
PFB
PFB
Py
Py
Py
A
A
A
R2
Ph
EHOMO−1/eV
EHOMO/eV
ELUMO/eV
ELUMO+1/eV
Egap(HOMO−LUMO)/eV
1
2
3
4
5
6
7
8
9
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
C
−6.38
−6.11
−6.87
−5.79
−5.74
−6.21
−7.45
−6.69
−7.98
−7.09
−6.37
−7.97
−6.16
−6.24
−5.00
−4.93
−5.53
−4.58
−4.52
−5.05
−6.18
−6.10
−6.67
−6.71
−6.37
−7.33
−6.00
−5.91
−2.07
−2.00
−2.64
−1.78
−1.72
−2.37
−3.85
−3.78
−4.23
−2.54
−2.42
−3.19
−2.15
−2.05
−0.82
−0.54
−2.20
−0.73
−0.46
−2.09
−3.17
−3.10
−3.51
−1.78
−1.74
−2.45
−0.64
−0.89
2.93
2.93
2.89
2.80
2.80
2.68
2.33
2.32
2.44
4.17
3.95
4.14
3.85
3.86
A
PFB
Ph
A
PFB
Ph
A
PFB
Ph
A
PFB
Ph
A
PFB
Ph
A
PFB
Me
Me
Me
Me
Ph
10
11
12
13
14
15
16
17
18
19
20
21
22
38
a
−5.71
−5.62
−6.09
−7.60
−7.71
−6.38
−6.46
−6.62
−5.07
−5.03
−5.63
−6.23
−6.25
−4.99
−4.94
−5.83
−1.44
−1.36
−2.15
−3.90
−3.87
−2.02
−1.81
−1.24
−0.59
−0.39
−1.89
−3.23
−3.24
−0.55
−0.50
−0.59
3.63
3.66
3.48
2.33
2.38
2.97
3.13
4.59
TphNO2
TphNO2
Tph
Tph
H
Sn
C
Sn
a
Geometry optimization did not converge so that no minimum geometry could be obtained.
This means that there is no longer the characteristic lobe on
calculations (Table 1), these levels contribute only to a minor
extent to the intensities of the electronic spectra of the
stannoles discussed.
the Sn, which is responsible for any σ*−π* conjugation and
49
thus lowering of the LUMO energy level; therefore, there
should be no difference in the HOMO−LUMO energy gap
between the stannole and its carbon analogue. To confirm this
hypothesis, we also performed calculations for simplified stannoles
In summary, the HOMO−LUMO energy gaps appear to be
dominated by the substituents in the periphery through
π conjugation; however, inductive effects play a very important
role, which are again higher for the substituents in the
periphery. The electronic properties of the molecule may then
be fine-tuned by the substituents on the Sn atom. It could also
be demonstrated for the stannoles that the Sn atom is involved
in the LUMO and is the origin of the lowered energy level of the
LUMO. For these general findings, there is a notable exception:
compounds 7−9, which have different electronic structures.
Nucleus-Independent Chemical Shifts (NICSs).
In stannoles, σ*−π* conjugation is known, and although
19 and 21 and carbon analogues 20 and 22 (Table 1 and
Figure 3). The simplification of using a methyl group instead
of a phenyl group on the Sn or C atom was necessary because
the C atom in such cyclopentadienes is too small to accom-
modate phenyl groups. For the tin compound 19, the isosur-
face representation of the LUMO confirms that the Sn atom is
no longer involved when there is a nitro group in the 5 posi-
tion of the thiophene (Figure 5b), and the electronic structure
is changed. The tin compound 21 that contains peripheral
thiophenyl groups clearly shows a lobe on the Sn atom and
therefore an involvement of the Sn atom in the LUMO.
In addition, the energy levels of the HOMO and LUMO of
the nitrothiophenyl-substituted compounds 19 (tin com-
pound) and 20 (carbon compound) are almost the same,
confirming that the tetracoordinated element in the ring is not
part of the π system (Table 1). When there are thiophenyl
groups in the periphery, the LUMO is lower in energy for the
stannole because of the strong, effective σ*−π* conjugation,
resulting in a lower HOMO−LUMO energy gap. The carbon
24
Ottosson and co-workers describe the possibility of some
aromatic resonance structures, stannoles are not considered to
be aromatic compounds. The calculated NICS(1) values of the
stannoles range from −2.74 for compound 2 to −3.25 for
molecule 4. For comparison, the NICS(1) value for benzene
was determined with the same computational method and was
found to be −11.26. Therefore, the stannoles 1−6 only display
weak-to-no aromaticity. Furthermore, only a slight dependence
of the NICS(1) values on the substitution pattern of the
stannole was observed, which fits with the other experiments
reported herein. For a list of all values, refer to the SI.
3
analogue has no lobe on the C sp atom and therefore only a
negligibly small σ*−π* conjugation (Figure 6).
Syntheses. For the experimental studies, we decided to
synthesize the stannoles that have the narrowest HOMO−
LUMO energy gaps and planar backbones because these are
beneficial properties for further potential applications in
The energy levels of the frontier orbitals ±1 allow for addi-
tional low-energy electronic excitations if they are energetically
close to the HOMO/LUMO levels. However, according to our
D
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Article
Figure 5. (a) Isosurface representations of the HOMOs and LUMOs for the stannoles 1, 4, 7, and 10. (b) Isosurface representations of the
LUMOs of two stannoles and their carbon analogues.
semiconducting polymers. Although the stannoles 7−9 also
exhibit these characteristics, they were not of our interest for
this particular study because the Sn atom appears to not be
involved in the electronic structure (Figure 5a,b).
The overall synthetic strategy for the stannoles was to form
an intermediary zirconium precursor from an adequately
substituted octadiyne, followed by transmetalation by diaryl-
dichlorostannane.
Lithiation of pentafluorobenzene (PFB-H) or 4-bromoanisole
(Br-A) and transmetalation to the Sn atom using tin(IV)
chloride gave the tetraarylstannanes 30 and 31 in yields of 85%
5,53
and 97%, respectively. A synproportionation reaction of the
tetraarylstannanes 30 and 31 at 220−250 °C for 1−7 days with
tin(IV) chloride led to compounds 32 (44%) and 33 (38%)
53,54
(Scheme 2).
The formation of zirconium intermediates was carried out
Different thiophene-flanked octadiynes functioned as precursors
for these zirconacyclopentadienes (Scheme 1). Electrophilic aro-
matic substitution of 2-methoxythiophene led to compound
by reaction of the precursor 26 or 27 with Rosenthal and co-
55,56
workers’ zirconocene 34
in toluene at 20 °C for 18 h
57
1
(Scheme 3). Full conversion was proven by H NMR spec-
troscopy under inert conditions. The zirconocene interme-
diate was directly transformed into the stannole within 3−6 h
by a consecutive Zr−Cu−Sn exchange reaction with copper(I)
chloride as the catalyst and the diaryltin dichlorides 32 and 33
or diphenyltin dichloride as reagents (Scheme 3). In total, six
novel stannoles could be provided for the experimental
51,52
2
(
5.
24) or 2-iodo-5-methoxythiophene (25) with 1,7-octadiyne gave
compounds 26 and 27 with yields of 65% and 37%, respectively
Scheme 1).
Twofold Sonogashira cross couplings of 2-iodothiophene
(
Diphenyltin dichloride was obtained commercially, but the
diaryltin dichlorides 32 and 33 had to be synthesized (Scheme 2).
E
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Scheme 2. Synthesis of Diaryltin Dichlorides
Figure 6. Comparison of the energy levels of the HOMO and LUMO
between the cyclopentadiene derivative 22 and the stannole 21, based
on the B3LYP/LanL2DZ level of theory. The representation of the
49
orbital levels is simplified based on work by Tamao and co-workers.
a
Scheme 1. Synthesis of Thiophene-Flanked Octadiynes
Scheme 3. Synthesis of Different Stannoles via a
Zirconocene Intermediate
a
dppf = 1,1′-bis(diphenylphosphino)ferrocene.
analyses of the theoretical predictions. The stannoles
1
19
1
all showed Sn{ H} NMR signals in the range of −82.4 to
−
152.7 ppm.
Structures in the Solid State. The molecular structures
of 1, 4, and 5 are shown in Figure 8 and confirm the identity of
the compounds. Compounds 2, 3, and 6 were oily products,
and therefore no crystal structures could be obtained.
The reaction to form the stannole 2 led not only to the
desired product but also to the byproduct 37, which we could
isolate by crystallization. It was identified as a spirostannole
derivative (Figure 7). The amount in which this byproduct was
formed was very low (<2%), and it is not certain how this
compound is formed. Formally, disproportionation of bis(p-
methoxyphenyl)dichlorostannane to SnCl4 and tetrakis(p-
methoxyphenyl)stannane and the subsequent reaction of
Figure 7. Spirostannole 37.
Nagase et al., where they reacted a double-lithiated diene with
dichlorodiorganoplumbane.
60
In all compounds, the Sn atoms were found to be in a
tetracoordinated distorted tetrahedral arrangement. The Sn
atoms are incorporated into almost planar five-membered
central rings, whereas the annulated six-membered rings (the
C H tethers) comprise also puckered confirmations. Selected
SnCl with 2 equiv of the zirconium intermediate 35 seem
4
likely. However, this would involve a reverse Kocheshkov
reaction. While these reactions do take place, they typically
4
8
bond lengths and angles are collected in Table 2. The torsion
angles of the planes of the stannoles against the aromatic side
groups in the 2 and 5 postions of 1, 4, and 5 are also compared
58,59
require coordinating solvents.
A method to synthesize
metalloles with a spirocenter is also described in the work of
F
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Inorganic Chemistry
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Figure 8. ORTEP drawings of the molecular structures of 1, 4, 5, and 37 showing 50% probability ellipsoids and the crystallographic numbering scheme.
with those of the optimized geometries obtained by density
functional theory (DFT) calculations. While the structures 1,
intensities are shown without applying Gaussian curve fitting
as part of the SI. It can be seen that the maxima just show the
main electronic transition and no further transitions near this
maximum; therefore, we think that the additional shoulders
arise from vibrational broadening.
4
, and 37 show an overall planarity of the thiophene−stannole
backbone with torsion angles (C2−C1−C10−C11) of
77.8(2)°, −177.3(3)°, and −176.5(5)°, respectively, the thio-
1
phenes of compound 5 are slightly twisted with respect to the
stannole ring with an angle of −161.3(3)°. The torsion angles
of 1 and 4 agree with those of the optimized geometries, but
the angle of the optimized geometry 5 differs slightly, with an
angle of −175.6°.
Theoretical and Experimental Absorption Spectra.
Computational information on the absorption spectrum was
obtained for an isolated molecule in the gas phase, while the
experimental absorption spectra were measured in chloroform
Both the experimental and theoretical data show the same
tendency for λmax. The change of the substituent on the Sn
atom of the stannole (Figure 1) leads only to a relatively small
effect. λmax is slightly bathochromically shifted by about 8−12 nm.
When the thiophene substituent in the 2 and 5 positions
(Figure 1) is 5-methoxythiophenyl instead of thiophenyl, λmax
is more strongly bathochromically shifted by about 21−25 nm.
The experimentally measured molar extinction coefficients
2
decrease for both 1−3 and 4−6 with the substituents R :A >
(
for calculated and measured spectra of stannoles 1−3 and
Ph > PFB. All of the optical characteristics are consistent with
the information of the molecular orbital calculations (Table 1).
The absorption spectra for the peripherally nitrothiophenyl-
substituted compound 7 and the peripherally pentafluor-
ophenyl-substituted stannole 10 were also calculated for
comparative purposes because their electronic structures
(Figure 5) and the HOMO−LUMO energy gaps (Table 1)
were significantly different from those of all other stannoles
under investigation. Stannole 7 has a theoretical λmax of
544 nm, which is the strongest bathochromically shifted peak
in the series, while 10 has a theoretical λmax of 337 nm, which
is remarkably hypsochromically shifted in comparison to
the other stannoles. This confirms that the substituents in the
2 and 5 positions have a much stronger influence on the
electronic structure of the molecule than the substituents on
the Sn atom on both the HOMO−LUMO energy gap and the
absorption maxima, certainly for large substituents.
4
−6, see Figure 9). In general, all theoretical absorption
spectra are slightly bathochromically shifted compared to the
experimental ones by about Δλ = 26−32 nm (Table 3).
max
The shape of the experimental absorption maxima is different
from that of the theoretical ones; the experimental spectra
display a shoulder on each side of the maximum. This differ-
ence most likely arises because the TD-DFT calculations do
not consider vibrational fine structures but only pure electronic
transitions. However, the vibrational transitions will also play a
role for the characteristic form of absorption bands.
For the sake of clarity and readability, the calculated
absorption wavelengths of the electronic transitions including
singlet and triplet states were not directly included in the
graphics of the calculated UV/vis spectra shown as the sum of
the Gaussian curves or in the experimental spectra. Despite
this, all calculated wavelengths and relative absorption
G
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Table 2. Selected Interatomic Distances (Å) and Angles (deg) of 1, 4, 5, and 37 and a Comparison of Torsion Angles with
Those of the Calculated Structures
1
4
5
37
Bond Lengths (Å) and Angles (deg)
Sn1−C1
Sn1−C30
C1−C2
C1−C10
C2−C7
2.149(3)
2.013(3)
1.314(3)
1.498(3)
1.561(3)
2.130(2)
2.128(2)
1.368(3)
1.442(3)
1.489(3)
2.133(2)
2.123(2)
1.362(3)
1.446(2)
2.133(4)
1.366(5)
1.441(5)
1.496(5)
C2−C2a
1.499(3)
C1−Sn1−C30
C1−Sn1−C1a
C1−Sn1−C40
C1−Sn1−C30a
C1−Sn1−C8a
C30−Sn1−C40
C30−Sn1−C30a
Sn1−C1−C2
C1−Sn1−C8
C1−Sn1−C1a
C1−C2−C7
110.73(8)
122.90(7)
118.30(8)
112.99(8)
118.87(5)
124.0(3)
122.8(2)
112.42(5)
111.38(7)
110.55(9)
109.33(7)
108.93(9)
103.2(2)
89.44(7)
108.4(2)
83.78(9)
108.0(3)
84.0(3)
83.32(7)
121.6(2)
119.4(2)
119.7(3)
C1−C2−C2a
119.33(8)
−161.3(3)
Torsion Angles (deg)
−177.3(3)
C2−C1−C10−C11
C1−C2−C7−C8
177.8(2)
8.6(3)
−176.5(5)
6.3(7)
−1.0(4)
C1−C2−C2a−C1a
C10−C11−C12−C13
5.2(3)
1.7(3)
0.3(4)
0.2(4)
0.7(7)
Torsion Angles (Calculated, deg)
C2−C1−C10−C11
C1−C2−C7−C8
−174.0
−2.9
−174.7
−3.0
−175.6
C1−C2−C2a−C1a
C10−C11−C12−C13
−3.2
0.5
0.6
0.5
Figure 9. (a) Calculated absorption spectra of stannoles 1−3. (b) Calculated absorption spectra of stannoles 4−6. (c) Experimental absorption
spectra of stannoles 1−3. (d) Experimental absorption spectra of stannoles 4−6. All calculated spectra were arbitrarily broadened to approximately
fit the experimental resolution. The peak width at half-height of the main maximum for stannoles 1, 2, 4, and 5 is 68 nm, and that for stannoles 3
and 6 is 84 nm.
Electrochemical Data. The electrochemical behavior of
the synthesized stannoles was studied by CV measurements
Table 4 and Figure 10). The stannoles with unsubstituted
thienyl substituents in the periphery display one irreversible
oxidation step with no corresponding reduction step (see
Table 4, entries 1−3). It appears that the unsubstituted thienyl
groups are reactive under CV conditions. The oxidation
processes for compounds 4−6, on the other hand, are
reversible; in this case, the flanking thienyl groups all bear a
methoxy group. This suggests that, in the case of 1−3, this
(
H
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Article
Table 3. Theoretical and Experimental Absorption Maxima
5 and 6 with rising potential for the first oxidation. The
differences, however, are very small and may result from
interactions of the molecule with the solvent and electrodes. We
could also observe experimentally that the electrodes were
quickly contaminated by the substances.
(Molar Extinction Coefficient)
theory
experiment
ε/L·mol−1·cm−1
molecule
λmax/nm
λmax/nm
1
2
3
4
5
6
7
448
447
452
472
470
481
544
337
418
415
427
440
440
448
a
20146
13963
7296
28156
26590
7081
a
The electrochemical behaviors of stannoles 4 and 5 are very
similar, which is in accordance with the findings from the
calculations and absorption spectra. Whether the substituent
on the Sn atom is phenyl or the much electron-richer anisole
motif only leads to a small shift in the first oxidation wave
(Δ E
= 0.07 V) and the second oxidation wave (Δ E
4
,5 p1/2
4,5 p1/2
= 0.09 V). Calculations of the singly occupied molecular
orbitals (SOMOs; see the SI) of the monooxidized species
shows qualitatively very similar electronic structures and offers
no further explanations of why the cyclovoltammogram of 6
looks somewhat different from those of 4 and 5.
1
0
a
a
a
These molecules were not prepared and were only analyzed
theoretically.
Table 4. Electrochemical Data for Stannoles 1−3
CONCLUSIONS
■
molecule
Epa/V (vs ferrocene)
Epc/V (vs ferrocene)
a
Calculations of the geometries, energy gaps between the
HOMOs and LUMOs, and absorption spectra of a wide range
of stannoles were performed to understand the factors that
govern the optoelectronic properties of these materials. Out of
those, the most interesting compounds were selected for
synthesis: a series of stannoles with different substituents in the
periphery and on the Sn atom. The influence of these substi-
tuents on the optical properties and electrochemical behavior
was studied experimentally. The crystal structures of the indi-
vidual products were measured, and the torsion angles were
compared to those obtained for the optimized geometries.
These proved that the extended π system comprised of the
stannole and different thienyl groups in the 2 and 5 positions is
planar. This π system has a larger influence on the HOMO−
LUMO energy gaps than the substituents on the Sn atom;
however, it is clear that the absolute energy of the HOMO and
LUMO levels is substantially influenced by the substituents on
the Sn atom although the influence on the overall energy gap is
somewhat smaller. Therefore, the absorption maxima are only
a little affected; however, the stability toward the oxidation
processes can be increased by introducing electron-with-
drawing groups on the Sn atom. Because of the dominance of
the conjugated π system, any peripheral π-aromatic group
whose plane is tilted against the dienyl system of the stannole
has a reduced effect. Therefore, five-membered heterocycles
are preferable compared to six-membered heterocycles.
1
+0.37
+0.15
+1.02
-
-
-
b
2
a
3
a
−1
b
−1
The scan rate was 0.1 V·s . The scan rate was 0.2 V·s .
position might be involved in oxidation reactions. Stannoles 4
and 5 exhibited two reversible oxidation processes. At first
glance, compound 6 only seemed to show one reversible
oxidation process (Table 5). However, looking at the data very
closely, a shoulder could be seen in the oxidation and
reduction peaks. This suggests that both oxidation events are
almost independent of each other in compound 6, whereas in
compounds 4 and 5, the electrons are removed from the same
delocalized system, making the second removal energetically
less favorable and, hence, leading to a larger gap between the
two oxidation events. For stannoles 4−6, also the adiabatic
ionization energies were calculated (Table 5). From the DFT
calculations, compound 5 should be oxidized at the lowest
oxidation potential, then compound 4, and at the highest
oxidation potential stannole 6 (Table 5, column 5). However,
the CV measurements show the order of oxidation as 4 before
Because of their small HOMO−LUMO energy gaps and the
broad long-wavelength absorption spectra, stannoles with
substituted thiophenes in the periphery or electron-with-
drawing groups on the Sn atom are promising building blocks
in polymers for electronical devices like solar cells, provided
they show reversible redox processes. From the CV studies, we
can assume that the molecules may have to be protected in the
periphery of the thiophenes if electropolymerization processes
−
1
Figure 10. Reversible redox processes of stannoles 4 (5.2 mg·mL ),
−1
−1
5
(5.5 mg·mL ), and 6 (5.6 mg·mL ). Conducting salt: 0.1 M
Bu NPF in dichloromethane.
4
6
Table 5. Electrochemical Data for Stannoles 4−6
a
a
molecule
Ep1/2/V (versus Fc)
Eonset(ox)/V
−0.35
calcd EHOMO(CV) /eV
−4.05
calcd EHOMO(DFT)/eV
−4.58
1.IE/eV
5.55
2.IE/eV
8.79
4
−0.22
−
0.02
−0.15
0.07
−0.09
0.09
5
6
−0.30
−0.30
−4.10
−4.10
−4.52
−5.05
5.47
6.02
8.66
9.21
+
−
a
−1
61
All scan rates were 0.1 V·s . The HOMO energy was calculated using Eonset for the first oxidation with the equation EHOMO = −[4.4 + Eonset(ox)] eV.
I
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are not desired. We are currently conducting research in our
laboratories to elucidate the potential of stannoles for electro-
polymerization.
chloroform. All melting points were measured with a melting point
apparatus by the company Gallenkamp and are uncorrected.
Crystallography. The intensity data of 1, 4, 5, and 37 were col-
lected on a Bruker Venture D8 diffractometer at 100 K with graphite-
monochromated Mo Kα (0.7107 Å) radiation. All structures were
2
EXPERIMENTAL SECTION
solved by direct methods and refined based on F by using the SHELX
■
71,72
program package, as implemented in WinGX.
All non-H atoms
Computational Details. The calculations were performed with
62
were refined using anisotropic displacement parameters. H atoms
attached to C atoms were included in geometrically calculated posi-
tions using a riding model. Crystal and refinement data are collected
the Gaussian 09 package. The optimized geometries of the stannoles
(
Figure 2) for the ground state, the adiabatic ionization energies, and
the SOMOs were calculated on the B3LYP/LanL2DZ level of
theory.
73
63−66
in Table S1. Figures were created using DIAMOND. Compounds 1
and 37 comprise three and two crystallographically independent, yet
similar conformers. Disorder was resolved for the atoms S6/S6′ and
C81/C81′ of 37 and refined with split occupancies of 60:40. Crystal-
lographic data for the structural analyses have been deposited with the
Cambridge Crystallographic Data Centre.
This level of theory has been used for organotin
compounds, as reported in the literature, because the LanL2DZ basis
includes definitions both for heavy metals like Sn [effective core
potential and double-ζ (DZ)-quality valence basis set] and for light
67
elements (all-electron basis set D95V for H−Ne). Frequency ana-
lyses were performed in all cases to confirm the absence of imaginary
frequencies and thus prove that the obtained geometries correspond
to minima on the potential energy surface. The isodensity value for
the molecular orbital isosurface representations was set to 0.02 in all
cases. The Cartesian coordinates of each geometry, and the respective
energies are listed as part of the SI. The absorption spectra were
calculated based on the electronic structure information using time-
dependent DFT (TD-DFT) with the B3LYP functional and
Synthesis of Thiophenyl-Flanked Stannoles 1−3. General
procedure for the synthesis of the thiophenyl-flanked stannoles: 1,
8-Bis(thiophen-2-yl)octa-1,7-diyne (150 mg, 550 μmol) and Rosen-
thal’s zirconocene (259 mg, 550 μmol) were dissolved in toluene (8 mL).
The dark-red solution was stirred for 18 h at 20 °C under a nitrogen
atmosphere. The diaryldichlorostannanes and copper(I) chloride
(5.4 mg, 60 μmol) in toluene (2 mL) were added to the dark solution.
6
2−66
The reaction mixture was stirred at 20 °C for a further 6 h. The reac-
tions were quenched with water (1 × 50 mL) and extracted with
dichloromethane (3 × 50 mL). The combined organic layers were
dried over magnesium sulfate, filtered, and concentrated in vacuo.
The crude product was purified by column chromatography (silica gel
LanL2DZ as the basis set.
considered. NICS calculations (CSGT-B3LYP/LanL2DZ)
performed, whereby the NICS values were determined to be 1 Å
Both singlet and triplet states were
63−66
were
68−70
above the geometric center of the respective ring.
Materials and Methods. All reactions were carried out using
standard Schlenk techniques under a dry, inert nitrogen atmosphere
or inside a nitrogen-filled glovebox from Inert, Innovative Tech-
nology, Inc. Co. (<0.1 ppm of O and <0.1 ppm of H O) unless noted
1
5 μm grain size, n-hexane).
,2′-(2,2-Diphenyl-4,5,6,7-tetrahydro-2H-benzo[c]stannole-1,
-diyl)dithiophene (1). Diphenyltin dichloride (189 mg, 0.55 mmol)
2
3
2
2
was used to give the product as a yellow solid (95 mg, 32%); R =
f
otherwise. All dry solvents were taken from the solvent purification
system, degassed by three freeze−pump−thaw cycles, and stored
under a nitrogen atmosphere unless noted otherwise. Copper and
palladium catalysts were stored in the glovebox. All chemicals were
commercially available and were used without further purification
unless noted otherwise.
1
0
.36. Mp: 156 °C. H NMR (500 MHz, CDCl ; signals that show
satellites due to coupling with Sn are marked with asterisks): δ 7.63
3
(
(
m, 4H, H-12, H-12′)*, 7.37 (m, 6H, H-13, H-14, H-13′), 7.26
m, 2H, H-9; the integral of that peak is not exact because the signal is
overlapping with the peak of CDCl ), 6.95 (m, 4H, H-7, H-8), 2.91
3
13
1
(
m, 4H, H-4), 1.82 (m, 4H, H-5). C{ H} NMR (126 MHz, CDCl ;
3
1
13
1
19
119
1
H, C{ H}, F, and Sn{ H} NMR spectra were recorded on a
signals that show satellites due to coupling with Sn are marked with
asterisks): δ 149.7 (C-3)*, 145.9 (C-11)*, 138.2 (C-6), 137.4 (C-12,
C-12′)*, 130.2 (C-9), 129.5 (C-2)*, 129.3 (C-14)*, 129.0 (C-13,
1
13
1
Bruker DRX 500 at 300 K. All H and C{ H} NMR spectra were
referenced against the solvent residual proton signals ( H) or the
solvent itself ( C). Sn{ H} NMR spectra were calculated based on
the H NMR spectrum of tetramethylsilane. F NMR spectra were
referenced against BF ·Et O. All chemical δ shifts are given in parts
1
13
119
1
119
1
C-13′)*, 127.1 (C-8), 125.9 (C-7), 31.9 (C-4), 23.4 (C-5). Sn{ H}
1
19
NMR (187 MHz, CDCl ): δ −82.4. IR (ATR): ν 3060 (w), 2935 (w),
3
3
2
2359 (w), 1633 (w), 1515 (w), 1493 (w), 1478 (m), 1428 (m),
per million (ppm) and all coupling constants J in hertz (Hz).
Column chromatography was carried out by using the column
machine PuriFlash 4250 from Interchim. Silica gel columns of the
type PF-15SiHP-F00125 (PuriFlash with the grain size in microns,
silica gel high performance, grams), PF-15SiHP-F0025, PF-50SiHP-
JP-F0080, PF-50SiHP-JP-F0120, and PF-50SiHP-JP-F0220 were used.
The sample was applied using a dry loading method. The column
material of the dry load was Celite 503 from Macherey-Nagel.
CV measurements were carried out with a Metrohm Autolab
PGSTAT101 potentiostat. The material of the working and counter
electrodes was platinum. The material of the reference electrode was
silver; all spectra were referenced against ferrocene. The scan rate was
1
1
9
6
5
411 (w), 1381 (w), 1348 (w), 1329 (w), 1283 (w), 1250 (w),
211 (m), 1189 (w), 1134 (w), 1074 (m), 1059 (m), 1020 (w),
96 (w), 966 (w), 924 (w), 848 (m), 801 (m), 781 (w), 723 (m),
−1
116
86 (s) cm . HR-MS (EI, C H S Sn; R = 10000). Calcd:
2
8
24 2
40.03314. Found: 540.03303. MS (EI, 70 eV, direct inlet, 200 °C):
•
+
m/z (% relative intensity) = 544 (63) ([M] ), 270 (100) ([M −
•+
2
−1
(C H ) Sn] ); λ = 418 nm (chloroform, ε = 2014.6 cm ·mmol ).
6
5
2
max
2
,2-Bis(4-methoxyphenyl)-1,3-bis(thiophen-2-yl)-4,5,6,7-tetrahy-
dro-2H-benzo[c]stannole (2). Di(p-methoxyphenyl)-
dichlorostannane (222 mg, 550 μmol) was used to give the product
as a yellow oil (109 mg, 33%); R = 0.16. H NMR (500 MHz,
CDCl ; signals that show satellites due to coupling with Sn are
1
f
3
−1
−1
0.1 V·s for stannoles 1 and 3−6 and 0.2 V·s for stannole 2. The sol-
marked with asterisks): δ 7.54 (m, 4H, H-12, H-12′)*, 7.24 (m, 2H,
vent was dichloromethane, and the conducting salt was 0.1 M tetra-
H-9; the integral of that peak is not exact because the signal is
butylammonium hexafluorophosphate (TBA[PF ]).
overlapping with the peak of CDCl ), 6.94 (m, 8H, H-13, H-13′, H-7,
6
3
High-resolution mass spectrometry (HR-MS) spectra were
recorded on the MAT 95+ double-focusing mass spectrometer from
Finnigan Mat. Precision weights were determined via the peak-matching
method. The reference substance was perfluorokerosene. The resolution
H-8)*, 3.79 (s, 6H, H-15), 2.91 (m, 4H, H-4), 1.82 (m, 4H, H-5).
1
3
1
C{ H} NMR (126 MHz, CDCl ; signals that show satellites due to
3
coupling with Sn are marked with asterisks): δ 160.8 (C-14)*,
149.5 (C-3)*, 146.0 (C-6)*, 138.5 (C-12, C-12′)*, 130.4 (C-11),
129.2 (C-2)*, 128.5 (C-9), 127.0 (C-8), 125.8 (C-7), 114.9 (C-13,
(R) of the peak-matching performance was 10000 or 12000. IR spectra
1
19
1
were recorded on a Nicolet Thermo iS10 Scientific IR spectrometer
with a diamond attenuated-total-reflectance (ATR) unit. The resolu-
C-13′)*, 55.1 (C-15), 31.9 (C-4), 23.4 (C-5).
Sn{ H} NMR
(187 MHz, CDCl ): δ −74.9. IR (ATR): ν = 2925 (w), 2858 (w),
3
−1
tion was 4 cm . The relative intensities of the IR bands were des-
cribed by s = strong, m = medium, or w = weak. UV/vis spectra were
recorded with a resolution of 0.1 nm on a UV-2700 spectrometer
from Shimadzu with a double monochromator. The solvent was
2832 (w), 1584 (m), 1563 (m), 1492 (m), 1455 (m), 1438 (w),
1411 (w), 1394 (w), 1347 (w), 1309 (w), 1278 (m), 1242 (m),
1211 (m), 1176 (m), 1090 (w), 1072 (m), 1025 (m), 924 (w),
−
1
901 (w), 851 (m), 807 (m), 787 (m), 787 (m), 687 (m) cm .
J
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HR-MS (EI, C H O S2116SnR = 10000). Calcd: 600.05426. Found:
126.9 (C-7), 114.8 (C-14, C-14′)*, 104.1 (C-8), 60.0 (C-11), 55.1
30
28
2
1
19
1
6
00.05475. MS (EI, 70 eV, direct inlet, 200 °C): m/z (% relative
(C-16), 31.6 (C-4), 23.5 (C-5). Sn{ H} NMR (187 MHz, CDCl ):
3
•
+
•+
intensity) = 604 (74) ([M] ), 270 (100) ([M − (C H O) Sn] );
δ −71.3. IR (ATR): ν = 3878 (w), 3851 (w), 3748 (w), 2584 (w),
2543 (w), 2472 (w), 2440 (w), 2323 (w), 2224 (w), 2120 (w),
1989 (w), 1947 (w), 1877 (w), 1843 (w), 1757 (w), 1251 (w), 1161 (w),
1123 (w), 1011 (w), 995 (w), 978 (w), 917 (w), 885 (w), 774 (w),
7
7
2
2
−1
λ
max
= 415 nm (chloroform, ε = 1396.3 cm ·mmol ).
2
,2′-(2,2-Bis(perfluorophenyl)-4,5,6,7-tetrahydro-2H-benzo[c]-
stannole-1,3-diyl)dithiophene (3). Di(pentafluorophenyl)-
−1
116
dichlorostannane (282 mg, 550 μmol) was used to give the product
765 (w) cm . HR-MS (EI, C H O S Sn; R = 10000). Calcd: 660.07539.
32 32 4 2
1
as an orange-yellow oil (23 mg, 6%); R = 0.13. H NMR (500 MHz,
Found: 660.07426. MS (EI, 70 eV, direct inlet, 200 °C): m/z (% relative
+
f
3
3
•+
CDCl ): δ 7.21 (d, J = 5.1 Hz, 2H, H-9), 6.88 (dd, J = 5.1 Hz,
J = 3.7 Hz, 2H, H-7), 6.82 (d, J = 3.7 Hz, 2H, H-8), 2.94 (m, 4H,
intensity) = 664 (36) ([M] ), 315 (100) ([M − (C H O) Sn − CH ] );
2 −1
3
7
7
2
3
3
3
λ
max
= 440 nm (chloroform, ε = 2659.0 cm ·mmol ).
1
3
1
13
19
H-4), 1.86 (m, 4H, H-5). C{ H} NMR ( C { F} NMR was not
possible to measure; therefore, the signal intensity was too low for
identification of the C atoms attached with F; 126 MHz, CDCl3;
signals that show satellites due to coupling with Sn are marked with
asterisks): δ 148.5 (C-3)*, 144.8 (C-6), 129.7 (C-2)*, 128.9 (C-9),
1,3-Bis(5-methoxythiophen-2-yl)-2,2-bis(perfluorophenyl)-
4,5,6,7-tetrahydro-2H-benzo[c]stannole (6). Di(pentafluorophenyl)-
dichlorostannane (236 mg, 450 mmol) was used to give the product
1
as an orange oil (27 mg, 8%); R
= 0.10. H NMR (500 MHz,
f
3
3
CDCl
): δ 6.56 (d, J = 4.0 Hz, 2H, H-7), 6.10 (d, J = 4.0 Hz,
3
1
19
1
1
(
(
27.0 (C-8), 125.9 (C-7), 31.5 (C-4), 23.1 (C-5). Sn{ H} NMR
2H, H-8), 3.89 (s, 6H, H-11), 2.81 (m, 4H, H-4), 1.77 (m, 4H, H-5).
1
9
13
1
13
19
187 MHz, CDCl ): δ −152.7. F NMR (471 MHz, CDCl ): −158.5
C{ H} NMR ( C{ F} NMR was not possible to measure;
therefore, the signal intensity was too low for identification of the
C atoms attached with F; 126 MHz, CDCl ): δ 167.5 (C-9), 145.5
(C-3), 130.0 (C-6), 127.5 (C-7), 125.9 (C-2), 104.0 (C-8), 59.9
3
3
3
3
3
dd, J = 19.3 Hz, J = 16.7 Hz, 4F, F-13, F-13′′), −147.1 (t, J =
3
1
9.3 Hz, 2F, F-14), −122.4 (d, J = 16.7 Hz, 4F, F-12, F-12′).
3
IR (ATR): ν = 3889 (w), 3850 (w), 3742 (w), 3695 (w), 2442 (w),
1
19
1
2
9
7
325 (w), 2226 (w), 2164 (w), 2124 (w), 1997 (w), 1951 (w),
(C-10), 31.2 (C-4), 22.9 (C-5). Sn{ H} NMR (187 MHz, CDCl
δ −145.2. F NMR (471 MHz, CDCl
F-14′), −150.0 (t, J = 19.7 Hz, 2F, F-15), −120.2 (d, J = 15.8 Hz,
4F, F-13, F-13′). IR (ATR): ν = 2928 (w), 2825 (w), 1716 (w), 1626
(w), 1469 (w), 1416 (m), 1313 (w), 1274 (w), 1230 (w),
1200 (m), 1149 (w), 1088 (w), 1039 (w), 989 (m), 875 (w), 765
3
):
−
1
116
19
75 (w) cm . HR-MS (EI, C H F S Sn; R = 10000). Calcd:
3
): δ −159.6 (m, 4F, F-14,
2
8
14 10 2
3
3
19.93892. Found: 719.93844. MS (EI, 70 eV, direct inlet, 200 °C):
•
+
m/z (% relative intensity) = 724 (30) ([M] ), 270 (100) ([M −
•+
2
−1
(C F ) Sn] ); λ = 427 nm (chloroform, ε = 729.6 cm ·mmol ).
6 5 2 max
Synthesis of Methoxythiophenyl-Flanked Stannoles 4−6.
−
1
120
General procedure for the synthesis of the methoxythiophenyl-flanked
(m), 713 (w), 694 (w) cm . HR-MS (EI, C30
H
18
F O
10
S
2
2
Sn; R =
stannoles: 1,8-Bis(5-methoxythiophen-2-yl)octa-1,7-diyne (150 mg,
10000). Calcd: 783.96050. Found: 783.96077. MS (EI, 70 eV, direct
•
+
450 μmol) and Rosenthal’s zirconocene (211 mg, 450 μmol) were
inlet, 200 °C): m/z (% relative intensity) = 784 (95) ([M] ), 315
+
(
100) ([M − (C F ) Sn − CH ] ); λ
= 448 nm (chloroform,
dissolved in toluene (8 mL). The dark-red solution was stirred for 18 h
at 20 °C under a nitrogen atmosphere. The diaryldichlorostannanes
and copper(I) chloride (5.0 mg, 50 μmol) in toluene (2 mL) were
added to the dark solution. The reaction mixture was stirred at 20 °C
for a further 6 h. The reactions were quenched with water (1 × 50 mL)
and extracted with dichloromethane (3 × 50 mL). The com-
bined organic layers were dried over magnesium sulfate, filtered, and
concentrated in vacuo. The crude product was purified by column
chromatography (silica gel 15 μm grain size, n-hexane).
6
5
2
3
max
2
−1
ε = 708.1 cm ·mmol ).
ASSOCIATED CONTENT
Supporting Information
■
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01649.
1
,3-Bis(5-methoxythiophen-2-yl)-2,2-diphenyl-4,5,6,7-tetrahy-
dro-2H-benzo[c]stannole (4). Diphenyltin dichloride (155 mg,
50 μmol) was used to give the product as an orange-yellow solid
Experimental and analytical details, NMR spectra, CV,
4
and absorption spectra (PDF)
All computational data (XYZ)
1
3
(
96 mg, 35%); R = 0.30. Mp: 178 °C. H NMR (500 MHz, CDCl ;
f
signals that show satellites due to coupling with Sn are marked with
asterisks): δ 7.63 (m, 4H, H-13, H-13′)*, 7.37 (m, 6H, H-14, H-15,
3
3
Accession Codes
H-14′), 6.59 (d, J = 4.0 Hz, 2H, H-7), 6.07 (d, J = 4.0 Hz, 2H, H-8),
1
3
1
CCDC 1560181−1560184 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
3
.86 (s, 6H, H-11), 2.80 (m, 4H, H-4), 1.77 (m, 4H, H-5). C{ H}
NMR (126 MHz, CDCl ; signals that show satellites due to coupling
3
with Sn are marked with asterisks): δ 166.8 (C-9), 146.3 (C-3), 138.6
(
(
(
C-12), 137.3 (C-13, C-13′)*, 132.6 (C-6)*, 130.1 (C-2)*, 129.4
C-15)*, 128.9 (C-14, C-14′)*, 127.0 (C-7), 104.1 (C-8), 60.0
1
19
1
C-11), 31.6 (C-4), 23.5 (C-5). Sn{ H} NMR (187 MHz, CDCl ):
3
δ −78.3. IR (ATR): ν = 3742 (w), 2439 (w), 2323 (w), 2220 (w),
2
9
6
6
118 (w), 1985 (w), 1952 (w), 1245 (w), 1177 (w), 1076 (w),
AUTHOR INFORMATION
94 (w), 978 (w), 949 (w), 806 (w), 790 (w), 762 (w), 692 (w),
■
−
1
116
73 (m) cm . HR-MS (EI, C H O S Sn; R = 10000). Calcd:
Corresponding Author
E-mail: staubitz@uni-bremen.de (A.S.).
3
0
28
2 2
00.05426. Found: 600.05402. MS (EI, 70 eV, direct inlet, 200 °C): m/z
*
•
+
(% relative intensity) = 604 (40) ([M] ), 315 (100) ([M − (C H )
6
5 2
+
2
−
1
ORCID
Sn − CH ] ); λ = 440 nm (chloroform, ε = 2815.6 cm ·mmol ).
3
max
2
,2-Bis(4-methoxyphenyl)-1,3-bis(5-methoxythiophen-2-yl)-
Simon Grabowsky: 0000-0002-3377-9474
Jens Beckmann: 0000-0002-8548-1821
Muriel Hissler: 0000-0003-1992-1814
Anne Staubitz: 0000-0002-9040-3297
4
,5,6,7-tetrahydro-2H-benzo[c]stannole (5). Di(p-methoxyphenyl)-
dichlorostannane (182 mg, 450 μmol) was used to give the product as
1
an orange solid (89 mg, 30%); R = 0.21. Mp: 160 °C. H NMR
f
(
500 MHz, CDCl ; signals that show satellites due to coupling with
Sn are marked with asterisks): δ 7.53 (d, J = 8.6 Hz, 4H, H-13,
3
3
Author Contributions
3
3
H-13′)*, 6.93 (d, J = 8.6 Hz, 4H, H-14, H-14′), 6.57 (d, J = 4.0 Hz,
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
3
2
H, H-7), 6.06 (d, J = 4.0 Hz, 2H, H-8), 3.86 (s, 6H, H-11), 3.79
(
(
s, 6H, H-16), 2.80 (m, 4H, H-4), 1.76 (m, 4H, H-5). 13C{ H} NMR
1
126 MHz, CDCl ; signals that show satellites due to coupling with Sn
3
Notes
are marked with asterisks): δ 166.7 (C-9), 160.77 (C-15), 146.1 (C-3),
138.5 (C-13, C-13′)*, 132.8 (C-12)*, 130.3 (C-6)*, 129.0 (C-2)*,
The authors declare no competing financial interest.
K
DOI: 10.1021/acs.inorgchem.8b01649
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
components with a great deal of potential. Chem. Soc. Rev. 2016,
ACKNOWLEDGMENTS
■
4
(
5, 5296−5310.
This research has been supported by the Institutional Strategy
of the University of Bremen, funded by the German Excellence
Initiative. We thank Mathias Gogolin for synthetic assistance
with compound 23. We thank Dr. Thomas Du
Kempken for measuring the mass spectra and Prof. Dr. Frank
Sonnichsen from Kiel University for measuring the NMR
16) Thiedemann, B.; Gliese, P. J.; Hoffmann, J.; Lawrence, P. G.;
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B-vinylazaborine) - a semi-inorganic B-N polystyrene analogue. Chem.
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Synthesis of Azaborine Oligomers and a Polymer with a syn
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samples. S.G. thanks the German Research Foundation (DFG)
for funding within the Emmy-Noether scheme (Project GR
(
18) Leavitt, F. C.; Manuel, T. A.; Johnson, F. Novel
4
451/1-1). J.H. acknowledges funding for a Short Term
Scientific Mission from the COST action COST 1302:
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work is supported by the Ministere de la Recherche et de
l’Enseignement Superieur, the CNRS, the Region Bretagne,
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(
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