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From poly(dialkylstannane)s to poly(diarylstannane)s comparison of synthesis methods and resulting polymers.

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Full Paper
Received: 22 February 2011
Revised: 17 July 2011
Accepted: 17 July 2011
Published online in Wiley Online Library: 6 September 2011
( DOI 10.1002/aoc.1836
From poly(dialkylstannane)s to poly(diarylstannane)s: comparison of synthesis
methods and resulting polymers
Marie-Luise Lechnera∗ , Markus Trummerb , Irene Bräunlichb , Paul Smithb ,
Walter Caserib and Frank Uhligb
The efficiency and applicability of three different methods to synthesize polystannanes with different side chains are described.
By means of dehydrogenative coupling utilizing the transition metal catalyst RhCl(PPh3 )3 (Wilkinson’s catalyst), n-Bu2 SnH2
reached the highest molar masses. Dehydrogenetive coupling in the presence of tetramethylethylenediamine could be best
employed for (4-n-BuPh)2 SnH2 . Wurtz coupling using sodium in liquid ammonia was best suited for Ph2 SnCl2 . Next to the
above-mentioned educts, n-Bu(Ph)SnX2 (X = H or Cl (as appropriate for the particular route) was used for polymerization
c 2011 John Wiley
resulting in one of so far rare example of asymmetric polystannanes with high molecular masses. Copyright & Sons, Ltd.
Keywords: poly(dialkylstannane); poly(diarylstannane); Wilkinson’s catalyst; TMEDA; Wurtz coupling
Appl. Organometal. Chem. 2011, 25, 769–776
Diorganostannanes and dichloridodiorganostannanes were used
as starting materials for the synthesis of poly(diphenylstannane) 1, poly[bis(4-n-butylphenyl)stannane] 2, poly[n-butyl
(phenyl)stannane] 3 and poly(di-n-butylstannane) 4. The monomers, when not commercially available, were synthesized by Grignard reaction of tetrachloridostannane with the corresponding
Correspondence to: Marie-Luise Lechner, Institute of Inorganic Chemistry, Graz
University of Technology, Stremayrgasse 9, A-8010 Graz, Austria.
a Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse
9, A-8010 Graz, Austria
b Department of Materials, Eidgenössische Technische Hochschule (ETH) Zurich,
Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
c 2011 John Wiley & Sons, Ltd.
Copyright 769
Polystannanes are organometallic polymers which comprise
a linear polymer backbone of covalently interconnected
metal atoms. Recently, facile synthesis routes were developed
for poly(dialkylstannane)s[1] and poly[bis-(ω-phenylalkyl)stannane]s.[2] Thereby, dialkylstannanes are polymerized in the
presence of a transition metal catalyst. Using chloridotris(triphenylphosphine)rhodium(I) by dehydrogenation we
received linear polymers that can be isolated in high yields.
Depending on the side groups, uncommon thermal behavior (e.g.
liquid crystallinity below room temperature) was observed. Further, owing to σ -delocalization of the electrons along the polymer
main chain, electric semiconductivity was anticipated and indeed
demonstrated for poly(di-n-butylstannane).[3] Interesting properties are expected for polymers with extended σ -π -delocalization
of the electrons along the main chain and the side groups, as reported for poly(diarylsilane)s[4] and poly(diarylstannane)s.[5] These
aspects, together with the fact that polystannanes can be oriented
by various techniques to yield materials with anisotropic behavior, such as dichroism, attracting significant attention to such
Besides catalytic polymerization of dialkylstannanes, other
methods have been advanced to synthesize poly(diorganostannane)s, in particular Wurtz reactions,[6 – 9] electrochemical
reactions[10 – 12] and hydrostannylation reactions.[13,14] However,
most of these reactions suffered from drawbacks such as
pronounced formation of cyclic stannanes as byproducts,
low yields, low molecular weights or poor reproducibility. In
addition, while poly(dialkylstannane)s have been extensively
studied,[1,3,6 – 8,10 – 12,15 – 18] the synthesis of poly(diarylstannane)s
has been little considered owing to the insolubility of typical
representatives like poly(diphenylstannane),[19] and therefore the
material properties of well-defined poly(diarylstannane)s have still
been modestly explored.
Accordingly, in this study we compare the efficiency and
applicability, respectively, of polystannanes prepared by catalytic
dehydropolymerization with two new methods, i.e. polymerization
of diorganostannanes under the action of tetramethylethylenediamine (TMEDA) and polymerization of dichloridodiorganostannes
with sodium in liquid ammonia (Fig. 1). All methods were applied
to monomers of the type R2 SnX2 , with X = H or Cl (as appropriate
for the particular route) and R = n-butyl, phenyl, 4-n-butylphenyl,
as well as to n-Bu(Ph)SnX2 . This permitted systematic investigation
of the influence of alkyl or aryl groups, respectively, on the polymerization and properties of the resulting polymers. For instance,
the presence of flexible chains bound directly or via aryl groups to
the polymer backbone may increase the solubility,[20 – 26] while the
presence of aryl groups might increase the stability towards light,
which has been reported to be low for dissolved and moderate for
solid poly(di-n-butylstannane).[18]
M.-L. Lechner et al.
Table 1. Numbering scheme of the various compounds mentioned
in this work
R :
(RR Sn)n
RR SnCl2
Figure 1. Overview of the reaction types investigated in this work for the
preparation of polystannanes.
have not been able to prove this by any experimental means
until now, and that with Na in liquid ammonia via stannide
ions.[32,33] The four polystannanes indicated above could indeed
be synthesized; yet the schematic overview in Fig. 2 shows that,
in fact, each polymerization method is favorable for polymers
with particular substitutents. While polymerization in NH3 /Na was
especially appropriate for poly(diarylstannane)s, the qualification
of Wilkinson’s catalyst was quite complementary to that of TMEDA
for the compounds explored. Obviously, phenyl (including nbutylphenyl) groups restrict the efficiency of the former and
promote the performance of the latter method. In the following,
we will refer to characteristics of the individual reactions. Note
that molar masses of the polystannanes reported in this work were
estimated by GPC analyses (see Experimental section and Table 2),
as discussed elsewhere.[17]
Polymerization of Diorganostannanes with Wilkinson’s
Figure 2. Polymerization methods for the preparation of polystannanes.
Symbols: ++, MW above 8 × 103 g mol−1 , no cyclic byproducts; the
presence of poly(diphenylstannane) (not accessible to GPC analysis owing
to insolubility) was deduced from other methods (elemental analysis,
UV–vis spectra); +, molar masses below 8 × 103 g mol−1 or cyclic
byproducts; −, very slow reaction or absence of polymeric product.
organo magnesium halide to obtain the tetraorganostannane,
which was subsequently converted by a Kozeschkow reaction
with tetrachloridostannane to dichloridodiorganostannane.[27,28]
Diorganotin dihydrides were synthesized by reduction of dichloridodiorganostannanes with an excess of LiAlH4 .[29,30] A numbering
scheme of the various compounds is shown in table 1.
Three different polymerization methods were employed (Fig. 1).
The reaction with Wilkinson’s catalyst, RhCl(PPh3 )3 , probably
proceeds via oxidative addition of Sn–H bonds to Rh(I) centers;[17]
that with TMEDA proceeds most likely via radicals as described
for the reaction of R2 XSnH with pyridine.[31] However, we
Wilkinson’s catalyst is suited mainly to the polymerization
of di-n-butylstannane 4a. The reaction proceeded rapidly in
toluene at room temperature, and poly(di-n-butylstannane) 4
was subsequently precipitated by pouring the reaction mixture
in methanol at −78 ◦ C. 119 Sn NMR spectra showed one signal at
−190 ppm, in agreement with the literature value for 4,[18] while
signals of cyclic byproducts were absent in the spectra.
Poly[n-butyl(phenyl)stannane] 3 also formed under the action of
Wilkinson’s catalyst; however, precipitation in methanol or other
solvents was not successful, even at −78 ◦ C. Thus, the solvent
was evaporated to leave the reaction products. The resulting
compounds featured a broad molar mass distribution (cf. Table 2).
119 Sn NMR spectra showed a broad signal at −197 ppm, in the
common range of polystannanes.
Polymers containing two aromatic substituents per tin atom essentially could not be obtained with Wilkinson’s catalyst, apart from
a minor fraction of poly(diphenylstannane) 1 when the reaction
was performed at 70 ◦ C. The reaction mixtures showed the complete disappearance of Sn–H vibrations at 1854 cm−1 in IR spectra
Table 2. Weight average molar mass (Mw , in 103 g mol−1 ) and polydispersity index of polystannanes prepared by different synthetic methods
Wilkinson’s catalyst
(n-Bu2 Sn)n 4
[n-Bu(Ph)Sn]n 3
[(4-n-BuPh)2 Sn]n 2
– a
– a
No polymer obtained
NH3 /Na
No polymer obtained
Broad molar mass distribution with the highest value detected at about 30 × 103 g mol−1 and a high fraction of low molar mass products as low as
1.5 × 103 g mol−1 .
b Contains cyclic oligomers.
c Bimodal molar mass distribution; the value only refers to that of the high molar mass fraction.
c 2011 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2011, 25, 769–776
From poly(dialkylstannane)s to poly(diarylstannane)s
and of the signals associated with Ph2 SnH2 1a in 1 H and 119 Sn NMR
spectra, but red or brown solids or viscous oils arose as the main
products. These products featured no signal in 119 Sn NMR spectra
and we failed to consistently interpret the results of other analyses.
Polymerization of Diorganostannanes with TMEDA
Reactions in the presence of TMEDA were performed in diethyl
ether at room temperature. While the conversion of di-nbutylstannane 4a was not efficient (see Experimental section),
the reaction of diphenylstannane 1a with TMEDA led to a
yellow precipitate. Elemental analysis revealed few impurities
in the poly(diphenylstannane) 1. As this polymer was insoluble
in all solvents tested, the molar mass could not be determined.
Extraction of the products with a small quantity of CH2 Cl2 did
not give rise to any signal in 119 Sn NMR spectra, which indicated
that cyclic oligo(diphenylstannane)s did not form in significant
quantities since those species are soluble in that solvent.
n-Butyl(phenyl)stannane 3a and bis(4-n-butylphenyl)stannane
2a polymerized to highly viscous oils which were soluble in
CH2 Cl2 , toluene, hexane, tetrahydrofuran (THF) and diethyl ether.
The monomer concentration was varied between 10 and 40 g l−1
and the reaction time between 10 min and 45 h. Suitable conditions were found at a concentration of 10 g l−1 and a reaction
time of 30 min for the polymerization of 2a when the disappearance of the Sn–H vibration at 1850 cm−1 in IR spectra of reaction
mixtures indicated complete conversion of this monomer. For the
polymerization of 3a a concentration of 10 g l−1 and a longer reaction time of 40 min led to the highest molar masses. Under these
conditions, the weight average molar masses (Mw ) of 46 × 103 and
13 × 103 g mol−1 , respectively, were found for the polystannanes
(Table 2). The polydispersity index (PDI) varied from values as low as
1.8–2.1 to much broader values (3.2–3.3). It appears that the molar
mass at least of 3 decreased upon increase of the reaction time beyond 30 min. Higher concentrations also led to lower molar masses;
3 at a concentration of 20 g l−1 did not yield significant amounts of
polymer. At −80 ◦ C, monomer conversion was completed within
3 h, and the molar masses did not change significantly compared
to reactions at room temperature with same reaction time.
Both 2 and 3 featured a signal in 119 Sn NMR spectra at −197 ppm,
i.e. in the typical region of polystannanes. Again there was no
evidence for formation of cyclic oligomers in 119 Sn NMR spectra.
Polymerization of Dichloridodiorganostannanes with Sodium
in Liquid Ammonia
Appl. Organometal. Chem. 2011, 25, 769–776
revealed a broad signal at −197 ppm and did not show any
indication of the presence of cyclic byproducts.
Treatment of dichloridodi-n-butylstannane 4b with two molar
equivalents of sodium in liquid ammonia caused immediate
precipitation of a yellow product. Yet 119 Sn NMR spectra in CD2 Cl2
disclosed not only a broad signal at −190 ppm representing linear
polystannane but also signals of cyclic oligostannanes at −202
and −203 ppm. Notably, the liquid crystalline phase transition
of poly(di-n-butylstannane) 4[2] was not observed by differential
scanning calorimetry (DSC), probably owing to the presence of
cyclic byproducts and the lower molar mass of the products
obtained in liquid ammonia.
Comparison of Molar Masses
Table 2 shows molar masses determined for the soluble polymers by gel permeation chromatography (GPC) analysis. The
respective values (Mw between 5 × 103 and 60 × 103 g mol−1 )
and polydispersity indices (around 2–3, Table 2) of the polystannanes obtained in this work were in the range of those reported
previously.[2] Clearly, the polymerization method can influence
the molar mass, as reflected by the GPC traces shown in Fig. 3. The
c 2011 John Wiley & Sons, Ltd.
The two dichloridodiarylstannane monomers were better suited
to polymerization in liquid ammonia than the other two alkyl substituted monomers. Conversion of dichloridodiphenylstannane
1b with two molar equivalents of sodium resulted in immediate
precipitation of a shiny yellow product. The material obtained was
insoluble even at elevated temperatures in CH2 Cl2 , hexane, decalin
and p-xylene. The solids were extracted with hot CH2 Cl2 to analyze
soluble reaction byproducts such as cyclic oligostannanes by 119 Sn
NMR analysis. Concentration of the extracts indicated that no cyclic
byproducts were formed. Elemental analysis of the material was
in agreement with the composition of poly(diphenylstannane) 1.
Polymerization of dichloridobis(4-n-butylphenyl)stannane 2b
resulted in a polymer with a bimodal molar mass distribution, an
unsatisfactory elemental analysis, but a single 119 Sn NMR signal at
−197 ppm indicating the presence of polystannane. Also in the
case of poly[n-butyl(phenyl)stannane] 3, 119 Sn NMR spectroscopy
Figure 3. GPC traces of the products of the reactions intended to generate
(a) poly(di-n-butylstannane) 4, (b) poly[n-butyl(phenyl)stannane] 3 and
(c) poly[bis(4-n-butylphenyl)stannane] 2, synthesized with Wilkinson’s
Catalyst (solid line), TMEDA (dashed line) and sodium in liquid ammonia
(dotted line).
M.-L. Lechner et al.
Table 3. Selected material properties of polystannanes
Synthesized with
Molar mass (g mol−1 )
Degradation temperature (◦ C)
Thermal phase transitions (◦ C)
Relative stability at ambient
Absorption maximum UV–vis (nm)
Dichroic ratio after shearing
(n-Bu2 Sn)n 4
[n-Bu(Ph)Sn]n 3
Wilkinson’s catalyst
57 × 103
13 × 103
[(4-n-BuPh)2 Sn]n 2
46 × 103
No phase transition observed
Common organic solventsa
(Ph2 Sn)n 1
NH3 /Na
Not solublea
For example, CH2 Cl2 , toluene, hexane, diethyl ether, THF.
first derivative) increased markedly from 250 ◦ C for poly(di-nbutylstannane) 4 to 350 ◦ C for poly(diphenylstannane) 1.
At 400 ◦ C, decomposition appears to be complete for all
polystannanes. However, it is evident from Fig. 4 that the residual
mass is clearly below the mass fraction of tin in the polymer (4,
51%; 3, 47%; 1, 43%; 2, 31%); this can be explained by formation
of volatile organotin compounds at elevated temperatures.
Differential scanning calorimetry revealed the previously described phase transition of 4,[1] while no phase transition was
observed between −50 and 200 ◦ C for the other polymers.
Relative Stability at Ambient Temperature
Figure 4. Thermogravimetric analysis of poly(di-n-butylstannane) 4 (solid
line), poly[n-butyl(phenyl)stannane] 3 (dotted line), poly(diphenylstannane) 1 (dashed line), and poly[bis(4-n-butylphenyl)stannane] 2
(dashed–dotted line).
highest molar masses were obtained for poly(di-n-butylstannane)
4 synthesized with Wilkinson’s catalyst (57 × 103 g mol−1 ) and
poly[bis(4-n-butylphenyl)stannane] 2 prepared in the presence of
TMEDA (46 × 103 g mol−1 ). Rather low molar masses (with respect
to the soluble polymers) were obtained with the NH3 /Na synthetic
Comparison of Material Properties
In the case of poly(diphenylstannane) 1, material properties were
investigated for the polymer that featured the best elemental
analysis values, i.e. the polymer resulting from the NH3 /Na
synthesis method. For studies of the other polymers, those
obtained with the method that yielded the highest molar masses
were used. Degradation temperatures, relative stability in ambient,
wavelength at maximum absorption in UV–vis spectra (λmax ) and
dichroic ratio of polymer films produced by shearing, solubility and
phase transitions are summarized in Table 3, and discussed below.
Thermal Properties
Thermogravimetric analysis (TGA) of the polystannanes (Fig. 4)
clearly shows increasing thermal stability with increasing aromatic
content in the polymers. The decomposition temperature defined
by the maximum rate of decomposition (maximum of the
Visual examination of solutions and solid polymers showed again,
as in the case of thermal stability, that polystannanes with two
aryl groups bound to each tin atom were more stable at ambient
than polymers that contained Sn-alkyl bonds. Degradation, as
judged by the loss of the characteristic yellow color, was far slower
for the poly(diarylstannane)s than for poly(dialkylstannane)s and
poly(alkylarylstannane)s. Obviously, not only one but two aryl
groups are required to provide enhanced stability at ambient.
UV–vis Spectra and Dichroic Ratio after Shearing
Poly(di-n-butylstannane) 4 with pure σ -delocalization showed
an absorption maximum (λmax ) at 390 nm, i.e. in the range
convenient for polystannanes.[16,34] UV–vis absorption spectra
reveal that phenyl groups induce a bathochromic shift of the
wavelength at maximum absorbance (Table 3 and Fig. 5), which
might be associated with increasing delocalization of electrons
with increasing number of aromatic groups in the polymer. For
instance a bathochromic shift of 20 nm was found for poly[nbutyl(phenyl)stannane] 3 in comparison to 4. However, besides
the nature of the side chains, the conformation of the polystannane main chain may also influence λmax . This phenomenon is
well known for polysilanes[35] and was also described for polystannanes, where delocalization was found to be maximal for planar
zigzag structures[5,36] . Thus, part of the poly(diphenylstannane)
1 might be present in the planar zigzag conformation, leading
to a low band gap polymer with a pronounced bathochromic
shift of the absorption maximum. This resulted in an UV–vis
absorption spectrum displaying two maxima. For 1 synthesized in
the presence of TMEDA no bathochromic shift could be observed.
An alternative explanation could be that the NH3 /Na pathway
results in a bimodal molar weight distribution. However, UV–vis
absorption spectra of one type of polymer with various molar
masses did not show any significant shift of the absorption
c 2011 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2011, 25, 769–776
From poly(dialkylstannane)s to poly(diarylstannane)s
As already indicated above, poly(di-n-butylstannane) 4, poly[nbutyl(phenyl)stannane] 3 and poly[bis(4-n-butylphenyl)stannane]
2 were soluble in common organic solvents (e.g. CH2 Cl2 , toluene,
hexane, THF). In fact, it is not uncommon for alkyl groups to
provide solubility to polymers, mainly as a result of entropy
gain upon dissolution owing to an increase in mobility of alkyl
groups upon transition from the solid to the dissolved state. In
contrast, however, no solvent for poly(diphenylstannane) 1, the
only polymer without alkyl groups, could be found.
Figure 5. Optical absorption spectra of poly(diphenylstannane) 1
(dashed–dotted line), poly[bis(4-n-butylphenyl)stannane] 2 (dashed
line), poly[n-butyl(phenyl)stannane] 3 (dotted line) and poly(di-nbutylstannane) 4 (solid line) recorded for thin films on glass slides and
arbitrarily adjusted in intensity for facile comparison.
maximum. Therefore it can be assumed that there is little influence
of molar mass on the absorption maximum. However, as the
polymer is too insoluble for GPC measurements, there is no way
of knowing for certain.
Contrary to 1, no pronounced bathochromic shift was observed
for poly[bis(4-n-butylphenyl)stannane], 2. Apparently the 4-nbutylphenyl side group inhibits the planar zigzag conformation
and therefore a more bathochromic shift. Furthermore no second
absorption maximum could be observed for either 3 nor 4.
When the polymers were sheared on a glass slide, optical
microscopy of samples placed between crossed polarizers revealed
that 4, 3 and 1 were readily oriented (Fig. 6). The preferred
orientation in the direction of shear was also evident from
UV–vis spectroscopy using polarized light. Light was preferentially
absorbed for a parallel position of the polarization plane and
orientation direction of the polymer, leading to dichroic ratios
around 2 at the absorption maximum (Table 3).
When subjected to shear, 2 featured hardly any alignment
(Fig. 6b; Table 3). Notably, in contrast to the other polymers that
exhibited the consistence of soft powder, 2 was a highly viscous
oil. Apparently the quasi-liquid state of this polymer allowed rapid
rearrangement of the polymer chains back into the isotropic state
during shearing.
Ammonia was purchased from PanGas (Dagmarsellen, Switzerland, 99.999%), dichloridodi-n-butylstannane from ABCR GmbH
(Karlsruhe, Germany) and dichloridodiphenylstannane from Sigma
Wavelength /nm
Each of the three polymerization methods explored here is particularly suited for the synthesis of specific polymers. The route
employing Wilkinson’s catalyst is most beneficial for the preparation of poly(di-n-butylstannane) 4, TMEDA for polystannanes
containing at least one aromatic group per Sn atom, and Na/NH3
for polystannanes with two aromatic groups per Sn atom. With
the most suitable method, polymers of weight average molar
masses in the range of roughly 10 × 103 to 60 × 103 g mol−1
were obtained, depending on the particular structure of the
macromolecules. Furthermore it is interesting to note that poly[nbutyl(phenyl)stannane] 3 represents one of the first examples for
asymmetrical high-molecular-weight polystannanes.
Not surprisingly, the material’s properties are strongly influenced by the substituents along the polymeric chains.
Poly(diarylstannane)s exhibited higher thermal stability and were
more resistant at ambient than the other two polystannanes, while
n-butyl groups (including 4-n-butylphenyl groups) improved solubility. Finally, phenyl groups led to a bathochromic shift, which
might be due to delocalization of electrons as well as the particular conformations of the polymer chains. Except in the case
of poly[bis(4-n-butylphenyl)stannane] 2, which was present in
a liquid-like state, the polystannanes could readily be oriented
simply by shearing of thin films on glass.
Wavelength /nm
Appl. Organometal. Chem. 2011, 25, 769–776
c 2011 John Wiley & Sons, Ltd.
Figure 6. Polarized optical absorption spectra of sheared films of poly[n-butyl(phenyl)stannane] 3 (a) and poly[bis(4-n-butylphenyl)stannane] 2 (b) at
different angles ϕ between the polarization plane of the light and the shearing direction (parallel, ϕ = 0◦ ; perpendicular, ϕ = 90◦ ). (c) Optical microscopy
images of sheared films taken between crossed polarizers at angles of 45◦ to the polarizers and 0◦ to one of the polarizers (i.e. 90◦ to the other polarizer).
The films were deposited on glass slides.
M.-L. Lechner et al.
Aldrich (Buchs, Switzerland). Both substances were recrystallized
twice by dissolving in boiling pentane and subsequent precipitation of the product at 250 K. CD2 Cl2 (99.9% D) was purchased from
Cambridge Isotope Laboratories (ReseaChem GmbH, Burgdorf,
Switzerland), and organic solvents from Fluka (Buchs, Switzerland). TMEDA was dried with a molar sieve; all other chemicals
were used as received from the respective chemical suppliers.
Thermal analysis was performed by DSC with a DSC822e
instrument (Mettler Toledo, Greifensee, Switzerland) equipped
with an intracooler, and TGA with a TGA/SDTA851e from Mettler
Toledo under nitrogen atmosphere. The heating rates (and the
cooling rate in the case of DSC) were 5 ◦ C min−1 .
Synthesis of the Starting Materials
NMR measurements
NMR spectra were recorded on a Bruker UltraShield
300 MHz/54 mm Fourier transform spectrometer and on a Varian Mercury 300 spectrometer. Standard 5 mm broad band probes
were employed. The samples were dissolved in CD2 Cl2 . For the
investigation of reaction solutions, a D2 O capillary was inserted
into the NMR tube. In order to inhibit decomposition of the samples by ambient light, the NMR tubes were wrapped in white
tissue and subsequently covered with aluminum foil, which was
only removed immediately before inserting the samples in the
Elemental analyses
Elemental analyses of the polymers were performed by the Microelemental Analysis Laboratory of the Department of Chemistry
at ETH Zürich. The elemental analysis of the educts was performed
with a Heraeus Vario Elementar EL analyzer.
Gel permeation chromatography
Gel permeation chromatography was performed with a GPC
instrument from Viscotek (VE7510) equipped with a degasser,
VE1121 solvent pump, VE520 autosampler and model 301 triple
detector array. A PL gel 5 µm Mixed-D column from Polymer
Laboratories Ltd (Shropshire, UK) was used. A preliminary test
showed that the refractive index detector revealed the most
reproducible values. Therefore, the reported data refer to molar
masses obtained with this detector. For calibration, atactic
poly(styrene) standards from Fluka were employed. Samples were
dissolved in THF with 2.5% v/v toluene, which served as marker.
The THF eluent flow amounted to 1 ml min−1 .
Optical microscopy
A Leica DMRX polarizing microscope was used at 20-fold
UV–vis spectroscopy
UV–vis measurements were performed in transmission with a
Perkin Elmer Lambda 900 spectrophotometer equipped with
rotating polarizers. The polymers were applied as films on glass
IR spectroscopy
Infrared spectra were recorded with a Bruker Vertex 70 FTIR
spectrometer with the attenuated total reflection (ATR) technique
using a Si-crystal. The samples were directly deposited to the
crystal with a syringe or a spatula.
Thermogravimetric analysis and differential scanning calorimetry
A 42.6 g (0.2 mol) aliquot of 4-n-butylphenylbromide was treated
under nitrogen atmosphere with 5.8 g (0.24 mol) magnesium in a
Grignard reaction to form 4-n-butylphenylmagnesium bromide. A
300 ml aliquot of THF was used as solvent. The reaction mixture
was heated under reflux for 1 h.
The 4-n-butylphenylmagnesium bromide solution was added
to 4.7 ml (0.4 mol) SnCl4 suspended in 200 ml THF via a cannula
while cooling the suspended SnCl4 with ice. The reaction mixture
was heated under reflux for 1 h. Thereafter, the THF was removed
in vacuo. The product was extracted with hexane via a Soxhlet
extractor. Hexane was distilled off, and the resulting product was
dried in vacuo (about 0.1 mbar) overnight. The product was a
yellowish liquid. No melting point could be measured. Yield: 80%.
1 H NMR (299.948 MHz, CD Cl , in ppm): δ = 0.98 [t, 12 H, CH ,
2 2
3 J(1 H– 1 H) = 7.2 Hz], 1.38 [h, 8 H, CH , 3 J(1 H– 1 H) = 7.3 Hz], 1.64
[q, 8 H, CH2 , 3 J(1 H– 1 H) = 6.9 Hz], 2.61 [t, 8 H, CH2 , 3 J(1 H– 1 H) =
7.4 Hz], 7.26 [d, 8 H, meta-Ar-H, 3 J(1 H– 1 H) = 7.7 Hz, 4 J(1 H–Sn) =
20 Hz], 7.83 [d, 8 H, 3 J(1 H– 1 H) = 7.7 Hz, ortho-Ar-H, 3 J(1 H–Sn) =
47 Hz].
13 C NMR (75.50 MHz, CD Cl , in ppm): δ = 13.93 (s, 4C, CH ),
2 2
22.45 (s, 4C, CH2 ), 33.73 (s, 4C, CH2 ), 35.82 (s, 4C, CH2 ), 135.2 (s, 4C,
para-Ar), 129.0 [s, 8C, meta-Ar, 3 J(13 C– 119 /117 Sn) = 53.2/51.0 Hz],
137.5 [s, 8C, ortho-Ar, 2 J(13 C– 119 /117 Sn) = 39.1/37.5 Hz], 143.7 [s,
4C, ipso-Ar, 1 J(13 C– 119 Sn) = 11.2 Hz]. 119 Sn NMR (111.96 MHz,
CD2 Cl2 , in ppm): δ = −125. Elemental analysis (in percent w/w,
calculated values in brackets): C 73.70 (73.72); H 8.05 (8.04).
A 25.8 g (0.04 mol) aliquot of tetrakis-(4-n-butylphenyl)stannane
and 4.6 ml (0.04 mol) SnCl4 were placed under nitrogen atmosphere in a flask. A 200 ml aliquot of heptane was added and the
reaction mixture was heated under reflux for 4 h. The hot solution
was filtered in order to remove inorganic side products. Completeness of the reaction was monitored via 119 Sn NMR spectroscopy.
The solvent was removed in vacuo and the product was dried in
vacuo (about 0.1 mbar) over night. The product was a brownish
liquid. No melting point could be measured. Yield: 83%
1 H NMR (299.948 MHz, CDCl , in ppm): δ = 1.04 [t, 6 H, CH ,
3 J(1 H– 1 H) = 8.1 Hz], 1.46 [h, 4 H, CH , 3 J(1 H– 1 H) = 7.6 Hz], 1.71 [q,
4 H, CH2 , 3 J(1 H– 1 H) = 7.8 Hz]; 2.74 [t, 4 H,CH2 , 3 J(1 H– 1 H) = 7.8 Hz];
7.44 [d, 4 H, meta-ArH, 3 J(1 H– 1 H) = 8.1 Hz, 4 J(1 H–Sn) = 26 Hz];
7.71 [d, 4 H, ortho-ArH, 3 J(1 H– 1 H) = 7.5 Hz, 3 J(1 H– 119 /117 Sn) =
81/78 Hz].
13 C NMR (75.50 MHz, CDCl , in ppm): δ = 13.9 (s, 2C, CH ), 22.2
(s, 2C, CH2 ), 33.3 (s, 2C, CH2 ), 35.6 (s, 2C, CH2 ), 133.6 [s, 2C, para-Ar,
4 13
J( C– 119 /117 Sn) = 801/760 Hz], 129.7 [s, 4C, meta-Ar, 3 J(13 C–Sn)
= 88 Hz], 134.0 [s, 4C, ortho-Ar, 2 J(13 C–Sn) = 66 Hz], 147.0 [s, 2C,
ipso-Ar, 1 J(13 C–Sn) = 17 Hz]. 119 Sn NMR (111.96 MHz, CDCl3 , in
ppm): δ = −19.6. Elemental analysis (in percent w/w, calculated
values in brackets): C 52.30 (52.68); H 5.48 (5.75).
c 2011 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2011, 25, 769–776
From poly(dialkylstannane)s to poly(diarylstannane)s
Diethyl ether was degassed: freezing with liquid nitrogen,
removing O2 in vacuo for 10 min. A 0.5 g (0.013 mol) aliquot
of LiAlH4 was suspended under nitrogen atmosphere in 150 ml
degassed diethyl ether. A 6 g (0.013 mol) aliquot of bis(4-nbutylphenyl)dichloridostannane was placed in a dropping funnel
and dissolved in 100 ml degassed diethyl ether. This solution
was added dropwise while cooling the reaction mixture to 0 ◦ C.
Subsequently, the reaction mixture was stirred for 1 h.
Unreacted LiAlH4 was neutralized by dropwise adding 100 ml
degassed water. The organic phase was separated with a cannula
and washed with 200 ml degassed saturated aqueous disodium
tatrate solution. Afterwards the organic phase was dried with CaCl2
for 30 min. The solution was filtered and the diethyl ether was removed in vacuo. The product was purified by drying in vacuo (about
0.1 mbar) for 1 h. The product was a colorless liquid. No melting
point could be measured. Owing to instability the compound was
finally stored in brown-colored septum vials at 4 ◦ C. Yield: 51%
1 H NMR (299.948 MHz, D O, in ppm): δ = 0.96 [t, 6 H, CH ,
3 J(1 H– 1 H) = 7.2 Hz], 1.35 [h, 4 H, CH , 3 J(1 H– 1 H) = 7.4 Hz], 1.59 [q,
4 H, CH2 , 3 J(1 H– 1 H) = 7.0 Hz]; 2.58 [t, 4 H, CH2 , 3 J(1 H– 1 H) = 7.6 Hz];
7.17 [d, 4 H, ArH, 3 J(1 H– 1 H) = 7.6 Hz, J(1 H–Sn) = 29 Hz]; 7.58 [d,
4 H, ArH, 3 J(1 H– 1 H) = 7.8 Hz, J(1 H–Sn) = 53 Hz], 6.26 [s, 2 H, SnH,
1 J(1 H– 119 /117 Sn) = 1907/1821 Hz]. 119 Sn NMR (111.96 MHz, D O,
in ppm): δ = −234.3.
The compound was synthesized according to Wardell et al.[37]
The compound was synthesized according to Kozeschkow and
co-workers.[38] 119 Sn NMR (CD2 Cl2 , 112 MHz, in ppm): 45.16.
The compound was synthesized according to Sonika.[39]
Reactions of Diorganostannanes with Chloridotris
(triphenylphosphine)rhodium(I) (Wilkinson’s Catalyst)
Appl. Organometal. Chem. 2011, 25, 769–776
Reactions of diorganostannanes with TMEDA
In a typical experiment 0.5 mmol monomer were placed under
nitrogen atmosphere in a Schlenk tube and dissolved in 10 ml
diethyl ether. The flask was wrapped with white tissue that was
then surrounded by aluminum foil before 0.5 mmol of TMEDA
were added with a syringe. After a given time (between 10 min
and 45 h) the solvent was evaporated. Polymers were dried in
vacuo (ca. 0.1 mbar).
Poly(di-n-butylstannane) 4: After stirring the reaction mixture
over night the polymer was obtained in 10% yield according to
119 Sn NMR spectroscopy. The rest of the starting material has not
reacted, so far. Because of the low conversion, the polymer was
not isolated.
Poly[n-butyl(phenyl)stannane] 3
Monomer concentrations between 39 mmol l−1 (10 g l−1 ) and
157 mmol l−1 (40 g l−1 ) were used. Elemental analysis (in percent
w/w, calculated values in brackets): C 46.85 (47.49); H 5.62
(5.58). Obtained molar masses: 13000 g mol−1 (corresponds to
approximately 51 n-BuPhSn units).
Poly(diphenylstannane) 1
Elemental analysis (in percent w/w, calculated values in brackets):
C 50.55 (52.81); H 3.90 (3.69).
Poly[bis(4-n-butylphenyl)stannane] 2
Monomer concentrations between 26 mmol l−1 (10 g l−1 ) and
103 mmol l−1 (40 g l−1 ) were used. Elemental analysis (in percent
w/w, calculated values in brackets): C 63.05 (62.37); H 6.92
(6.80). Obtained molar masses: 46 000 g mol−1 [corresponds to
approximately 120 (4-n-BuPh)2 Sn units].
Reactions of Dichloridodiorganostannanes with Sodium
in Liquid Ammonia
Sodium (8 mmol) was dissolved under nitrogen atmosphere in
90 ml of liquid ammonia at −78 ◦ C by stirring for 15 min. After
c 2011 John Wiley & Sons, Ltd.
In a typical reaction 0.04 mmol (3 mol% with respect to diorganostannane) Wilkinson’s catalyst was placed under nitrogen atmosphere in a Schlenk tube and dissolved in 10 ml of toluene. The
flask was wrapped with white tissue that was then surrounded
by aluminum foil before 1.3 mmol of the respective diorganostannane was added dropwise with a syringe through a septum.
Reaction mixtures with di-n-butylstannane 4a were stirred for
1 h before cooling to −78 C in an isopropanol/dry-ice bath and
then poured into 50 ml of precooled methanol at −78 ◦ C. Poly(din-butylstannane) 4 precipitated and was filtered off under nitrogen
atmosphere and dried in vacuo (24 h, 0.1 mbar). Elemental analysis
(in percent w/w, calculated values in brackets): C 40.82 (41.25), H
7.53 (7.79). Obtained molar masses: 57 000 g mol−1 (corresponds
to approximately 250 n-Bu2 Sn units).
Applying the above conditions to diphenylstannane 1a yielded
a red solid with an elemental composition well apart from that
of poly(diphenylstannane) 1. Elemental analysis (in percent w/w,
calculated values for 1 in brackets): C 43.86 (52.81), H 3.42 (3.69).
If the reaction solution was heated to 70 ◦ C for 1 h after adding 1a
and stirring for about 5 min at room temperature, a minor quantity of yellow precipitate formed that was filtered and dried under
reduced pressure (0.1 mbar). The composition of this product was
in the range of that of 1. Elemental analysis (in percent w/w, calculated values in brackets): C 51.89 (52.81), H 3.69 (3.69). When the filtrate was cooled to −78 ◦ C and poured into 100 ml methanol of the
same temperature, a light yellow solid precipitated that turned immediately red upon filtration. Elemental analysis (in percent w/w,
calculated values of 1 in brackets): C 43.82 (52.81), H 3.42 (3.69).
The reaction mixture of bis(4-n-butylphenyl)stannane 2a was
also warmed to 70 ◦ C after stirring for 1 h at room temperature.
Subsequently the solution was cooled to −78 ◦ C and poured
into 100 ml methanol No precipitate formed. The solvents were
removed completely in vacuo (0.1 mbar), resulting in a product
with an elemental analysis different from that of poly[bis(4-nbutylphenyl)stannane] 2. Elemental analysis (in percent w/w,
calculated values in brackets): C 52.69 (62.38), H 5.53 (6.80).
Catalytic dehydrogenation of n-butyl(phenyl)stannane 3a was
performed at room temperature. The reaction solution was stirred
for two h and subsequently cooled to −78 ◦ C and poured into 50 ml
methanol at the same temperature. The solvent was removed
and the product dried under reduced pressure (0.1 mbar, 24 h).
Elemental analysis [in percent w/w, calculated values in brackets
for poly(n-butylphenylstannane) 3]: C 46.05 (47.49), H 5.33 (5.58).
M.-L. Lechner et al.
the flask was wrapped with white soft tissue and surrounded
by aluminum foil, a quantity of dichloridodiorganostannane
(4 mmol) dissolved in 10 ml THF was added through a septum
under continuous stirring. The polymer precipitated after about
10–15 s and the solution was stirred for another 5 min before
the ammonia was evaporated by warming the reaction solution
to room temperature in a nitrogen stream. Thereafter the THF
was removed in vacuo (about 0.1 mbar). The resulting solids were
washed with 50 ml of a water–ethanol (9 : 1) mixture until no
chloride could be detected in the washing solution (usually three
to four times, until the addition of 5 ml saturated AgNO3 solution
did not lead to the visible formation of AgCl precipitates) and
thereafter three times with 50 ml CH2 Cl2 . Finally the product was
dried in vacuo (about 0.1 mbar, 24 h).
Poly(di-n-butylstannane) 4
Elemental analysis (in percent w/w, calculated values in brackets): C
40.754 (41.25), H 7.56 (7.79). Obtained molar masses: 5000 g mol−1
(corresponds to approximately 22 n-Bu2 Sn units).
Poly[n-butyl(phenyl)stannane] 3
Elemental analysis (in percent w/w, calculated values in brackets): C
44.90 (47.49); H 5.66 (5.58) Obtained molar masses: <5000 g mol−1
(corresponds to approximately <13 n-BuPhSn units).
Poly(diphenylstannane) 1
Elemental analysis (in percent w/w, calculated values in brackets):
C 51.98 (52.81); H 3.66 (3.69).
Poly[bis(4-n-butyl(phenyl)stannane)] 2
Elemental analysis (in percent w/w, calculated values in brackets):
C 59.22 (62.37); H 6.43 (6.80). Obtained molar masses: 8000 g mol−1
[corresponds to approximately 22 (4-n-BuPh)2 Sn units].
We thank the Swiss National Science Foundation and fForteWissenschaftlerinnenkolleg FreChe Materie for financial support.
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polymer, synthesis, method, dialkylstannane, poly, resulting, comparison, diarylstannane
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