Synthesis and Characterization of Readily Modified Poly(aryl)(alkoxy)stannanes by use of Hypercoordinated Sn Monomers

Article abstract of DOI:10.1002/chem.201804145

The synthesis and solid-state molecular structures of two dichlorido(aryl)(alkyl) tin compounds, 5 and 8, both key intermediates to tunable polystannane architectures, are reported. The materials were further investigated by single-crystal XRD and a DFT a

Full text of DOI:10.1002/chem.201804145

A Journal of
Accepted Article
Title: Synthesis and Characterization of Readily Modified Poly(aryl)
(alkoxy)stannanes by use of Hypercoordinate Sn Monomers
Authors: Jeffrey A Pau, Gloria M D'Amaral, R. Stephen A Wylie, Alan J
Lough, and Daniel Alain Foucher
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To be cited as: Chem. Eur. J. 10.1002/chem.201804145
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DOI: 10.1002/marc.((insert number)) ((or ppap., mabi., macp., mame., mren., mats.))
Article
Synthesis and
Characterization of Readily
Modified
Poly(aryl)(alkoxy)stannanes by use of Hypercoordinate Sn
Monomers
Jeffrey Pau, Gloria M. D’Amaral, Alan J. Lough†, R. Stephen Wylie, and Daniel A. Foucher *
–––––––––
J. Pau, G. M. D’Amaral, Prof. R. S. Wylie, Prof. D. A. Foucher
Advanced Materials Laboratory,
Department of Chemistry and Biology,
Ryerson University
350 Victoria Street, Toronto, ON, Canada, M5B 2K3
E-mail: daniel.foucher@ryerson.ca
Dr. A. J. Lough
X-ray Laboratory
Department of Chemistry
University of Toronto, Toronto, ON, Canada M5H 3H6
–––––––––
The synthesis and solid-state molecular structures of two dichlorido(aryl)(alkyl) tin compounds,
5 and 8, both key intermediates to tunable polystannane architectures, is reported. The materials
are further investigated by single-crystal XRD and a DFT analysis of their preferential “open
and closed” geometries. Conversion of said compounds to their dihydride analogues was
undertaken followed by their application as monomers for polystannane polymer synthesis. The
properties of two asymmetrical polystannanes thus prepared by transition metal-catalyzed
dehydropolymerization of dihydrido(aryl)alkylstannanes (6 and 9) were investigated. The first
is the structurally simple, modest molecular weight, semi-crystalline light and moisture stable
polystannane (10) with NMR (119Sn) evidence of prominent SnO hypercoordination along
the polymer backbone. The second is a lower molecular weight, functionally tosylated four
coordinate polystannane (11) with no evidence of hypercoordination. Thermal analysis (DSC)
of polymer 10 reveal a reversible semi-crystalline nature, while only amorphous behavior was
detected for polymer 11. Polystannane 10 was also found to be exceptionally stable to both
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moisture and light (> 6 months) and a promising candidate for the design of readily modified
(i.e. tunable) polystannane materials.
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1. Introduction
Dialkyl or diaryl linear polystannanes are main group polymers constructed of a backbone of
covalently bound tin atoms.[1–3] There are a multitude of ways to prepare polystannanes. The
first well characterized examples were reported by Tilley and co-workers in 1993 and were
prepared by dehydrogenative coupling of diorganostannanes in the presence of an early
transition metal catalyst.[4–6] More recently, Caseri et al. have demonstrated the successful
dehydrocoupling of dialkylstannanes to yield cyclic-free high molecular weight (105 Da)
polystannanes, such as 1, in the presence of a late transition metal complex (i.e. Wilkinson’s
Catalyst).[7,8] This Rh compound was identifed by Caseri and coworkers as the most efficient
dehydropolymerization catalyst for dialkyltin dihydrides from the testing of over thirty
transition metal complexes.[7,9] Earlier work by Molloy et al. had also shown that high
molecular weight (105 Da) polystannanes can be prepared via a low-temperature (60 °C) Na-
mediated Wurtz coupling of dialkyltin dichlorides[10] or alkylaryltin dibromides[11] in toluene
in the presence of 15-crown-5. Lower molecular weight (103 Da) polystannanes were more
recently obtained by Caseri and coworkers from the Wurtz coupling of dialkyltin dichlorides in
liquid ammonia.[8,12] Electrochemical coupling of dialkyltin dichlorides to low molecular
weight polymers (103 Da) has also been demonstrated by Okano and coworkers.[13,14] In 2015,
Harrypersad and Foucher described the preparation of moderate molecular weight (104-105 Da)
alternating polystannanes from the condensation polymerization of diaryl or dialkyl tin
dihydrides with appropriately chosen dialkyltin diamides.[15]
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Figure 1: Relative solution stability of different polystannane backbones to visible light.[5,16,17]
Characteristic of polystannanes is their unusual electronic properties which are derived
from the  overlap of diffuse formally 5sp3 hybridised tin orbitals that translate into a
detectable visible absorption in the 390-450 nm range. Unfortunately, these intriguing low
band gap intrinsic semi-conducting materials (2-4 eV) suffer from acute sensitivity to both light
and moisture. The origins of this sensitivity has been correlated to the presence of long, weak
Sn-Sn bonds of the Lewis acidic tin centres along the polymer backbone that are susceptible to
radical cleavage and nucleophilic attack. Extensive efforts by Caseri and co-workers have
shown that light induced degradation of polystannanes proceeds by an "unzipping" mechanism.
The addition of light stabilizers that absorb in the visible range can dramatically increase the
stablity of dialkylstannanes.[18,19] Diaryl containing polystannanes also show inherently
improved stablity in comparison to the dialkyl analogues, likely due to the increased 
mixing of the ligand orbitals when directly bound[20] to tin, or as a light absorbing moiety
incorporated into the Sn containing skeleton.[21] One exception to this is the extreme light
sensitivity observed for polystannanes bearing strong electron-withdrawing substituents, such
as aryl groups containing CF3 functionalities (2), which presumably increase the Lewis acidic
nature of tin.[22] In addition to the pronounced sensitivity to light of these polystannanes, poor
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stability to ambient moisture also leads to the formation of stannoxane degradation products
likely via nucleophilic attack by H2O on the Sn atoms.[5]
A new approach to address the light and moisture stability concerns of polystannanes
was recently investigated by Foucher et al. who proposed the use of hypercoordinate
architectures at tin centers to provide both an electronic and steric solution to address these
stability issues.[17] The use of light absorbing azo-containing propyloxy substituents on the
metal centers revealed strong hypercoordination in small molecule species, with evidence of
two well separated distinct tin signals in the 119Sn NMR of the polystannane 3 (Figure 1)
assigned to both open and closed configurations within the polymer. This homopolymer proved
to be indefinitelty stable to ambient conditions for > 2 years and is the first example of a truly
stable polystannane.
To understand the "design rules" for constructing stable polystannanes more broadly,
the role of the ligand in hypercoordination must be understood. Synergistic push-pull
interactions, such as those defined by 3-center-4-electron hypercoordination arrangements have
been known for at least 50 years between the later Group 14 elements (Si, Ge, Sn, Pb), electron
rich N, P, O and S donor atoms and axially coordinated electron-withdrawing substituents (Cl-,
Br-, I-).[23,24] X-ray structural data for several of these Sn species reveals additional donor ligand
coordination to the Group 14 element along with an elongation of the ligand-metal bond trans
to the donating group.[25–32] Hypercoordination to a Sn center is theorized to be the result of a
2e donation from the formal p-orbital of the donating ligand into an empty non-bonding orbital
of Sn, which then simultaneously transfers electron density on to an antibonding p-orbital of
the electron-withdrawing substituent.[33] Facile hypercoordination in these species is likely a
result of the high formal oxidation state at Sn and hence pronounced Lewis acidic character of
the Sn(IV) center. The role of the Sn atom in such 3c-4e interactions for the most part is
unknown, but it appears to function as an efficient electron shuttle. If the electron withdrawing
substituent(s) are replaced with one or two equally deficient electron Sn atom(s), such as those
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present in hypercoordinated polystannanes, the opportunity to deploy additional electron
density to the Sn backbone could result in stronger Sn-Sn bonds. This would, in turn, possibly
make the metal-metal bonds less susceptible to undergo cleavage in the presence of
nucleophiles such as H2O.[5,34,35]
Herein, we describe the preparation of a semi-crystalline, moderate molecular weight
hypercoordinated polystannane (i.e., 10). This asymmetrical polystannane also possesses
exceptional light and moisture stability over several months of exposure to ambient atmosphere,
with no observed changes in molecular weight, nor NMR and UV-Vis spectroscopic behaviour.
Using similar methodology, we have also prepared a liable tosyl-containing macromolecular
derivative 11 that can be employed to yield tailored light and moisture stable aryl/alkylalkoxy
substituted materials following replacement of the tosyl group.
2. Results and Discussion
2.1 Preparation and Characterization of Monomers
Compound 4 (Scheme 1) was prepared via a hydrostannylation reaction of allyl alcohol with
Ph3SnH in the presence of AIBN, and after washing the resulting solids with hexanes, isolated
as a white coloured powder in an 82% yield. The NMR (1H, 13C) spectroscopic data obtained
for 4 was comparable to values previously reported by Wardell et al.[36] In addition, the 119Sn
NMR (CDCl3) spectrum of 4 shows a single resonance at δ = -99.2 ppm, which is similar to
that of other previously reported propyloxy triphenylstannanes.[11,17]
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Scheme 1: Preparation of functional stannane monomers 6 and 9 via 4.
Dichlorido compound 5 was synthesized via a stepwise chlorination of 4 using 2 equivalents of
HCl (1.0 M in Et2O) in C6H6 over a 1 h (Scheme 1) time period. After the initial addition, the
impure monochlorido (solid) intermediate was isolated but not fully characterized. This crude
monochlorido was thereafter dissolved in DCM to separate it from the insoluble by-products
prior to further chlorination. Identical reaction conditions were then used to generate the
dichlorido 5. The crude product was washed with hexanes (3 × 20 mL) to give 5 as pale yellow
coloured solid in a 72% yield. NMR spectroscopic analysis of 5 (1H, 13C: C6D6) is fully
consistent with the expected structure. The 119Sn NMR (CDCl3) resonance for 5 is slightly
downfield (δ = -80.4 ppm) in comparison to that of 4. Crystals of 5 suitable for X-ray diffraction
were grown from a DCM solution containing 5 layered with hexanes (Figure 2a). The surmised
3c-4e sharing motif between the tin, chlorine, and oxygen atoms can be discerned from the
molecular configuration.[17] The propyl oxygen atom is found in a position strongly suggesting
dative bonding to the Sn center with a notably shorter bond length (2.40 Å) when compared to
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other previously reported five-coordinate Sn-O dichlorido species bearing either a propylazo or
propylphenyl substituent (2.73 Å or 2.82 Å).[17,37] The Sn-O bond length of 5 is about 17%
larger than those reported for tin complexes (2.05[38]-2.14 Å[39]) with truly covalent Sn-O bonds.
In the hypercoordinated geometry of 5, the axial Sn-Cl bond is notably elongated in comparison
to the equatorial Sn-Cl bond (~0.09 Å) as expected (vide supra).
Figure 2a Left: ORTEP representation of 5 found in the unit cell and selected bond lengths (Å)
and bond angles (˚). Thermal ellipsoids drawn at the 30% level. Sn-O 2.400(3), Sn-Cl1
2.3766(14), Sn-Cl2 2.4509(12), Cl1-Sn-Cl2, 94.20(5), C1-Sn-C4 143.79(18), O-Sn-Cl2
173.88(9). 2b Right: ORTEP representation of 8 found in the unit cell and selected bond lengths
(Å) and bond angles (˚). Thermal ellipsoids drawn at the 30% level. Sn-O 5.418(3), Sn-Cl1
2.3660(6), Sn-Cl2 2.3776(6), Cl1-Sn-Cl2, 98.73(2), C1-Sn-C7 138.24(8), O1-S1-Cl0
105.88(9).
Compound 6 (Scheme 1) was synthesized through a standard hydrogenation of 5 with LiAlH4
in Et2O at 0ºC for 4 h, after which the reaction was quenched with degassed distilled water.
The desired compound was isolated in a 92% yield as a pale-yellow colored, translucent gel
(Scheme 1). NMR spectroscopic analysis of 6 (1H, 13C: CDCl3) is consistent with the expected
structure, including the large 117/119Sn-H satellite coupling resonances (1J = 1841 and 1926 Hz)
centered on the hydrido signal (δH = 5.51 ppm). The 119Sn NMR spectrum of 6 (C6D6) displayed
a single resonance at δ = -214.9 ppm, a value typical for other known tin dihydrides.[40] This
thermally sensitive monomer was stored in the dark at -30 ºC, and could be kept in this way for
up to 30 days without substantial decomposition. The tosyl-containing triphenyl tin species 7
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was prepared as previously described.[17] Chlorination of 7 with HCl to give 8 proceeded in a
single step in a nearly quantitative yield. Conversion of the tosylated tin dichlorido 8 to the
dihydrido 9 was carried out with NaBH4 and isolated after work up (see Experimental) in the
form of a colourless liquid in a 62% yield. The hydrido resonance of 9 (δH = 5.31 ppm) was
found slightly upfield in comparison to 6, with the 117/119Sn-H couplings (1J = 1764, 1852 Hz),
smaller by about 70-80 Hz. Crystals of 8 suitable for X-ray diffraction were also grown from
DCM solution containing the material layered with hexanes (Figure 2b). An intramolecular
hypercoordinate interaction is clearly absent here, with the Sn-O distance of ~5.4 Å. The lack
of an intramolecular dative interaction is likely related to the electron withdrawing strength of
the tosyl substituent. There is no evidence of intermolecular interactions of the propyl oxygen
with neighbouring tin centers in the unit cell, but one of the tosyl O atoms (O3) is oriented
towards the Sn center of another molecule of 8 with an Sn-O distance of 2.776 Å and a O3-Sn-
Cl2 angle of 176.3°. The geometry of the Sn center and near equivalence of the Sn-Cl bond
lengths suggest however a relatively weak intermolecular interaction without substantial
hypercoordinate character.
2.2 Computational studies of monomers
DFT calculations of monomers 5 and 8 were carried out for comparison with solid-state
structural data to gain some insights into substituent effects. Such calculations are necessarily
approximate: DFT optimized geometries are dependent on both the basis set and the functional
used in the calculation and, once corrected for zero-point energy, correspond an isolated (gas-
phase) molecule at 0 K. Calculation of thermodynamic properties is non-trivial, even for the
gas phase, and especially for flexible molecules where Boltzmann conformational averaging is
required. Despite these limitations, DFT calculations can be useful in comparisons between
molecules or conformations, where relative differences are typically more accurately
determined than absolute energies.
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Due to the many possible conformations of the flexible monomers 5 and 8, attention was
restricted to the most stable of the non-hypercoordinate conformers, the trans-planar “open”
conformer, and the hypercoordinate “closed” structures with phenyl and chlorido ligands
respectively trans to a propyl oxygen atom (Figure 3). Dispersion-corrected B3LYP-GD3BJ
geometry optimizations of each conformer were verified by frequency calculations. Table 2
presents energies for the hypercoordinate conformers relative to the respective “open”
conformers.
Figure 3. Optimized structures for conformations of 5 (B3LYP-GD3BJ/6-31+(d,p):H,C,O,Cl;
LANL08d:Sn).
Table 2. B3LYP-GD3BJ calculated energies for “closedˮ hypercoordinate conformers relative
to the respective “open” conformers.
Hypercoordinate
conformer
Relative electronic
Relative electronic and
zero-point energies
[kJ mol-1]
energy [kJ mol-1]
5: trans-phenyl
-18.4
-40.6
-13.0
-37.1
-15.8
-36.4
-11.5
-35.1
5: trans-chlorido
8: trans-phenyl
8: trans-chlorido
Hypercoordinate conformers are more stable than the “open” conformers in each case.
Comparing the effect of the ligand trans to the hypercoordinate propyl oxygen shows
significantly lower relative energies for conformers with the electronegative chlorido ligand (by
~ 21 – 24 kJ mol-1). Hypercoordinate conformers of 5 are somewhat more stable than 8 (by ~
3 – 5 kJ mol-1), presumably due to greater electron density on the hypercoordinating O atom
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with a H substituent in comparison with the more electron-withdrawing tosyl substituent.
Comparisons of calculated Sn-O distances support these observations. For the trans-phenyl
conformer of 5, the Sn-O separation is 2.656 Å, while for the trans-chlorido conformer it is
2.572 Å. The hypercoordinate conformers of 8 have longer Sn-O distances in each case: 2.952
Å for the trans-phenyl conformer and 2.795 Å for the trans-chlorido conformer, but with the
same trend with respect to the specific trans-ligand. Comparison of bond angles in the
calculated structures of the hypercoordinated conformers with those of the open conformers
show the expected shift towards trigonal bipyramidal geometries at Sn in the former, and to a
greater degree with 5 than 8. In the two cases where comparisons of calculated and
crystallographic structural parameters can be made, there is generally reasonable agreement.
The calculated Sn-O separation distance is very similar for the “open” conformer of 8 and the
somewhat different crystallographic conformer (5.418 Å (exp.), 5.444 Å (calc.)). In contrast,
the “closed” trans-chlorido 5 crystallographic Sn-O distance is significantly shorter (2.400 Å)
than the calculated one (2.572 Å), as has been noted previously for hypercoordinate Sn
complexes.[17] There are two other notable discrepancies in the calculated structures. The Cl-
Sn-Cl bond angles are overestimated in the calculated “open” conformer of 8 by about 9°,
possibly due to the intermolecular hypercoordinate interaction in the solid state noted above.
Secondly, the calculated structure of 5 does not reproduce the long Sn-Cl bond length of the Cl
trans to the hypercoordinate propyl O atom, a feature also noted previously.[17] It is unclear
whether this is a crystal packing effect or reflects an inadequacy in the computational model.
This question remains an active area of investigation within our research group.
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2.3 Polymerization and Characterization of Homopolymers 10 and 11
Scheme 2. Transition metal-catalyzed dehydropolymerization of tin dihydrides.
Homopolymers 10 and 11 were prepared via dehydropolymerization reactions of 6 and 9
involving the application of Wilkinson’s catalyst in toluene at RT for 4 h (Scheme 2). Volatiles
were thereafter removed in vacuo and the crude materials of 10 or 11 were then re-dissolved in
a minimal volume of THF (3 mL) and added slowly, dropwise, to 100 mL of a stirring, cold
hexanes mixture. The resulting yellow-coloured solids that formed were recovered by filtration,
and after drying in vacuo, yellow coloured powders of purified 10 or 11 were recovered in a
78% and 63% yields, respectively. In the case of 10, (Figure 4) a molecular weight
determination (GPC) revealed a narrowly dispersed, modest molecular weight polymer (42
kDa; PDI 1.16). A lower molecular weight was found for 11 (31 kDa, PDI 1.20).
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Polymer 10
Polymer 11
Figure 4. GPC chromatogram (RI, THF) of polystannanes 10 and 11.
1H NMR (C6D6) analysis of 10 shows surprisingly well-resolved resonances for the aromatic
1
and alkyl portions of the polymer; by contrast the H NMR signals of purified 11 are notably
broad. Interestingly, the 119Sn NMR spectrum of 10 in C6D6 displays two nearly equal intensity
resonances (δSn = -113.4 ppm and -176.0 ppm) (Figure 5b).
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Polymer 11
Polymer 11
Polymer 10
Polymer 10
Figure 5. 119Sn NMR spectra of 10 and 11 in two deuterated solvents.
We attribute this to the presence of both an open (lower field) configuration, where
propylhydroxy or propylalkoxy ligand is untethered to the tetrahedral tin centre, and a closed
(higher field) motif where the –OH group is datively bound to the tin, making it formally 5-
coordinate (Figure 6).
Figure 6. Proposed partially “openˮ and “closedˮ random structure of 10.
Interestingly, only a single sharp downfield resonance at -108 ppm was observed for polymer
10 when run in d8-THF (Figure 5a). The 119Sn NMR spectrum of 11 (Figures 5c, 5d) in either
d8-THF or C6D6 are similar and reveal a broad spilt resonance centred near -202 ppm, which is
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typical of chemical shifts of other polystannanes bearing propyloxy linkages.[17,40] The
differences in the 119Sn NMR between C6D6 and d8-THF are consistent with the relative
coordinating ability of the related non-deutrated solvents as described by Alvarez et al.[41] In
the case of 10, the d8-THF solvent likely overwhelms and displaces the intramolecular
hypercoordinate bonding in the polymer so all propyloxy ligands lie in the open position.
Thermal analysis of 10 and 11 was conducted by DSC. Compound 10 was run through
three consecutive heating/cooling cycles and showed no evidence of decomposition below
200 °C. A weak, reversible glass transition temperature (Tg) was detected at 49.3°C and a
strong reversible melt temperature (Tm) was observed at 110.1 °C (Figure 7). These results
suggest a semi-crystalline nature for polymer 10. In the case of 11, only a weak Tg (65.9 °C)
was detected and is more typical of amorphous polymers (Figure B1).
10
Figure 7. DSC spectra for homopolymer 10.
An understanding of the morphology of polystannanes is of great interest because of the impact
that hypercoordination in the solid state may have on the degree of crystallinity, and conjugation
in the backbone. The suspected semi-crystalline polymer 10 was found to be both air and
moisture stable. Analysis of the polymer morphology of 10 by PXRD without prior annealing,
suggests some level of long range order, revealed by two broad peaks centered at 2 = 7.1° and
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2 = 19.7 (Figure 8). This corresponds to possible interchain d-spacings of 4.51 Å and 12.5 Å
respectively. The larger d-spacing is similar to that reported earlier by Caseri et al. (11.2-13.2
Å) for polymer 1. Further work to explore the nature of these d-spacings is now ongoing.
Figure 8: The PXRD diffractogram of polymer 10.
3. Conclusions
The asymmetrical polystannane macromolecular intermediate 10 was prepared from the
transition metal catalyzed dehydropolymerization of dihydrido 9 in a 78% yield.
Characterization of 10 by 119Sn NMR spectroscopy in C6D6 revealed the presence of two equal
intensity resonances at  -117 and -175 ppm attributed to hyper and non-hypercoordinated Sn-
--O interactions along the polymer backbone. GPC analysis confirmed a narrowly dispersed
high molecular weight polymer. Further analysis by DSC and PXRD revealed a semi-crystalline
nature of 10. Polymer 10 showed no evidence of decomposition after exposure to both ambient
light and moist air for > 6 months. Polymer 11 bearing a tosyl substituent was also prepared by
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dehydropolymerization, and could become an important macromolecular intermediate to a
number of stable, asymmetrical polystannanes. These materials have obvious merit in the
design of functional molecular wires containing polystannanes.
4.0 Experimental Section
Material and Methods. Syntheses were carried out using standard Schlenk and glove box
protocols. 1H NMR (400 MHz), 13C NMR (100.6 MHz), and 119Sn NMR (79.5 MHz) spectra
for small molecules were recorded on a Bruker Avance 400 MHz NMR spectrometer with a
BBFO 5 mm direct probe. A 1H pulse width of 30° was used, acquiring a spectral window of
8223 Hz (20 ppm) using a relaxation delay of 1 s, acquisition time of 3.98 s, and 32k points (16
scans). The 1H 90° pulse width was 10.4 μs. A 13C pulse width of 1H 30° pulse width was used
acquiring a spectral window of 24,038 Hz (239 ppm) using a relaxation delay of 2 s, acquisition
time of 1.36 s, and 32k points (4096 scans). The 13C 90° pulse width was 8.7 μs. A 119Sn pulse
width of 30° was used, 8.75 μs, acquiring a spectral window of 100,000 Hz (670 ppm) using a
relaxation delay of 1 s, acquisition time of 0.33 s, and 32k points (15,360 scans) with inverse
1
gated proton decoupling. H and 13C were referenced internally to the deuterated solvent
resonances. All chemical shifts are given in δ (ppm) relative to the solvent and assigned to
atoms. All J coupling values are reported as absolute values. Additional 1D 13C and 119Sn NMR
data for polymers were acquired at the CSICOMP NMR facility at the University of Toronto.
1D 13C spectra were acquired using an Agilent DD2 spectrometer (n(13C); 125.653 MHz, n(1H);
499.663 MHz) equipped with either a 5 mm XSens 13C-sensitive Cold Probe (Agilent
Technologies, Inc., Santa Clara, USA). The 1D 13C{1H} spectra were acquired with a standard
CARBON pulse sequence at 25 ºC, over a 30487.8 Hz spectral window with a 30° pulse width,
121952 points, a 0.2 s recycle delay, and 3200 transients. 1D 119Sn spectra were acquired using
an Agilent DD2 spectrometer (n(119Sn); 186.378 MHz, n(1H); 499.875 MHz) equipped with a
OneNMR probe (Agilent Technologies, Inc., Santa Clara, USA). The 1D 119Sn{1H} spectra
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were acquired with an s2pul pulse sequence at 25 ºC, over a 56818.2 Hz spectral window with
a 45° pulse width, 113636 points, a 1.0 s recycle delay, and 5000 transients. Inverse gated
proton decoupling was applied. Elemental analysis was performed by Atlantic Microlab, Inc.
of Norcross, GA, USA. Time-of-flight mass spectrometry analyses were performed using a
JMS-T1000LC mass spectrometer (JEOL Inc., Peabody, MA, USA) equipped with a direct
analysis in real time (DART) ionization source (DART-SVP, Ionsense Inc., Saugus, MA, USA)
at University of Toronto. The DART source was operated with He gas, and the temperature was
adjusted in the range 100−400 °C. Isotopic distributions for the observed ionic species were
calculated using the Mass Center utility (JEOL) and were in good agreement with the measured
mass spectra. All reagents and solvents were obtained from Sigma-Aldrich and used as
received. Triphenyl tin chloride was purchased from Sigma-Aldrich. Triphenylstannane was
prepared and characterized according to published routes. All column chromatography was
carried out on Silica gel or 60 aluminum backed plates, eluting with the solvent system indicated
below for each compound. Melting points were measured in open air using a Fischer Scientific
melting point apparatus. Molecular weights of polymers were determined by gel permeation
chromatography (GPC) using a Viscotek Triple Model 302 Detector system equipped with a
Refractive Index Detector (RI), a four capillary differential viscometer (VISC), a right angle
(90) laser light scattering detector. GPC columns were calibrated versus polystyrene standards
(American Polymer Standards). A flow rate of 1.0 mL min-1 was used with ACS grade THF as
eluent. GPC sample were prepared using 10-15 mg of polymers per mL THF, and filtered using
a 0.45 m filter. All UV-VIS spectroscopy were carried out using a Perkin Elmer Lambda 40
UV/Vis system. The University of Toronto X-ray Crystallography Lab was used to obtain X-
ray information for compounds 5 and 8. Data was collected on a Bruker Kappa APEXDUO
diffractometer using monochromated Mo-Kα radiation (Bruker Triumph) and were measured
using a combination of φ scans and ω scans. The data was processed using APEX2 and
SAINT1. Absorption corrections were carried out using SADABS.1. The structures were
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solved using SHELXT2 and refined using SHELXL-20132 for full-matrix least-squares
refinement that was based on F2. For all structures, H atoms were included in calculated
positions and allowed to refine in a riding-motion approximation with U~iso~ tied to the carrier
atom. All geometric optimizations and frequency calculations were carried out with the
Gaussian 09 suite of programs[42] using the B3LYP level of theory[43] supplemented with
Grimme’s D3 empirical dispersion function and Becke-Johnson damping.[44] The LANL08d
basis set was used for Sn[45] and the 6-31+G(d,p) basis set for all other atoms, as a reasonable
compromise between accuracy and computational cost.[46,47] Tight convergence criteria and an
ultrafine integration grid were employed for all geometry optimizations. Frequency
calculations were performed in each case to verify that a minimum in the potential energy
surface had been located.
Synthesis of 3-(Triphenylstannyl)propan-1-ol (4)
Propa-2-ene-1-ol (0.8 mL, 13.7 mmol) was added to a dry 50 mL Schlenk flask via syringe.
Ph3SnH (1.46 g, 4.15 mmol) and 2% mole AIBN (0.045 g, 0.274 mmol) was added to the allyl
alcohol. The flask was heated to 80°C for 3 h. A white colored solid formed when the solution
cooled. The crude sample was washed with hexanes (3 × 10 mL) and the white colored solid
was isolated by vacuum filtration. Synthesis was previously reported by Wardell et al.[36] Yield
82.2% (1.39 g); m.p. 105°C. 1H NMR (400 MHz, C6D6, δ): 7.60-7.54 (m, 6H, H6), 7.39-7.35
(m, 9H, H7 & H8), 3.64 (t, 2H, H2, 3J = 6.6 Hz), 2.01-1.94 (m, 2H, H3), 1.55-1.49 (m, 2H, H4)
ppm, 1.29 (s, 1H, H1). 13C{1H} NMR (100 MHz, C6D6, δ): 138.99 (C5), 137.04 (C6), 128.84
(C8), 65.66 (C2) 29.36 (C3), 6.67 (C4) ppm. 119Sn NMR (149 MHz, CDCl3, δ): -99.16 ppm.
Synthesis of 3-(dichloro(phenyl)stannyl)propan-1-ol (5)
In a 100 mL dry Schlenk flask, 1.0 M HCl/Et2O (2.45 mL) was added to a solution of 4 in C6H6
(25 mL). This was repeated for a second time for full conversion. The mixture was stirred at
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RT for 1 h and the solvent removed in vacuo to obtain a pale yellow colored powder of 5. The
crude product was washed with hexanes (3 × 20 mL) and brought to dryness. Yield 72.1%
1
(0.919 g); m.p. 96.5°C. H NMR (400 MHz, C6D6, δ): 7.89-7.70 (m, 2H, H6), 7.55-7.36 (m,
3H, H7 & H8), 3.85 (s, 2H, H2), 2.86 (s, 1H, H1), 2.17-2.14 (m, H3, 2H), 1.87 (t, 2H, H4, 3J =
6.9 Hz) ppm. 13C{1H} NMR (100 MHz, C6D6, δ): 141.27 (C5), 135.27 (C6), 130.79 (C7),
129.10 (C8), 129.10 (C8), 62.57 (C2). 119Sn NMR (149 MHz, CDCl3, δ): -80.48 ppm. HRMS-
1
35
DART (m/z) = 290.9599 (M-Cl) calculated for 12C9 H1216O1 Cl2120Sn1; found 290.9588.
Synthesis of 3-(phenylstannyl)propan-1-ol (6)
A solution of 5 (0.73 g, 2.24 mmol) in Et2O (5 mL) was added to a solution of 1 M LiAlH4/Et2O
(2.24 mL) in Et2O (10 mL) in 100 mL Schlenk flask at 0°C. After 4 h, the reaction was warmed
to room temperature and distilled degassed water (12 mL) was added to the solution to quench
the reaction. The organic layer was removed, and the solvent was removed under reduced
pressure to obtain a pale-yellow colored, translucent gel of 6. Yield 92.1% (0.53 g). 1H NMR
(400 MHz, C6D6, δ): 7.47-7.39 (m, 2H, H6), 7.17-7.11 (m, 3H, H7 & H8), 5.51 (s, 2H, H9,
117Sn-HJ = 1841 Hz, 119Sn-HJ = 1926 Hz), 3.35 (t, 2H, H2, 3J = 6.27 Hz), 2.60 (s, 1H, H1), 1.71-
13
1.64 (m, 2H, H3), 1.08-1.00 (m, 2H, H4) ppm. C{1H} NMR (100 MHz, C6D6, δ): 137.44
(C6), 128.52 (C7 & C8), 64.76 (C2), 30.12 (C3), 4.41 (C4, 117/119Sn-CJ = 401.3 Hz) ppm. 119Sn
NMR (149 MHz, C6D6, δ): -214.89 ppm. HRMS-DART (m/z) = 256.9988 (M+H) calculated
1
for 12C9 H1416O1120Sn1; found 256.9991.
Synthesis of (Triphenylstannyl)butyl 4-methylbenzenesulfonate (7)
Compound 7 was prepared as previously reported.[17]
Synthesis of 4-(dichloro(phenyl)stannyl)butyl 4-methylbenzenesulfonate (8)
3-(Triphenylstannyl)propyl 4-methylbenzenesulfonate, 7, (0.1 g, 0.178 mmol) in C6H6 (≈ 20
mL) was added 1.0 M HCl/Et2O (0.18 mL, 0.178 mmol) by syringe and stirred at 0°C for 1 h.
The pure product was then precipitated in to a large volume of hexane (100 mL) with stirring.
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After decanting, the residual solvent was removed in vacuo to obtain a white colored solid of 8
in near quantitative yield. Yield 99 % (0.20 g); m.p. 102 °C. 1H NMR (400 MHz, CDCl3, δ):
7.80-7.74 (m, 2H, H8), 7.74-7.73 (m, 2H, H7), 7.72-7.52 (m, 3H, H6 & H5), 7.34-7.32 (m, 2H,
H9), 4.15-4.13 (t, 3J = 5.5 Hz, 2H, H4), 2.44 (s, 3H, H3), 2.26-2.23 (t, 3J = 12.5 Hz, 2H, H2),
3
13
1.97-1.94 (t, J = 7.6 Hz, 2H, H1) ppm; C{1H} NMR (100 MHz, CDCl3, δ): 145.18 (C10),
138.73 (C12), 134.88 (C11), 132.55 (C7), 131.60 (C9), 130.02-129.56 (C5 & C6), 128.02 (C8),
71.18 (C4), 24.57 (C3), 21.71 (C2), 21.07 (C1) ppm; 119Sn NMR (79.5 MHz, CDCl3, δ): 30.1
ppm. EA Ccalc/found: 40.04/41.40, Hcalc/found: 3.78/3.87
Synthesis of 3-(phenylstannyl)propyl 4-methylbenzenesulfonate (9)
An EtOH solution (10 mL) containing 8 (0.21 g, 0.438 mmol) was added to a solution of NaBH4
(0.150 g, 4.38 mmol) in EtOH (8 mL) in a 100 mL Schlenk flask, and stirred at 0 °C for 1 h. 20
mL of 5°C degassed distilled water was added to the solution containing crude 9 over 30 min
and stirred. The solution was then extracted with hexanes (3 × 20 mL) and dried over MgSO4.
The mixture containing 9 was filtered, and solvent removed under reduced pressure to obtain a
transparent colorless liquid. Yield 62 % (0.111 g). 1H NMR (400 MHz, C6D6, δ): 1H NMR (400
MHz, CDCl3, δ): 7.75-7.73 (m, 2H, H8), 7.40-7.31 (m, 2H, H7), 7.14-7.13 (m, 3H, H6 & H5),
6.73-6.71 (m, 2H, H9), 5.31 (s, 117Sn-HJ = 1764 Hz, 119Sn-HJ = 1851.6 Hz, 2H, H13), 3.74-3.71
(t, 3J = 6.3 Hz, 2H, H4), 1.85 (s, 3H, H3), 1.54-1.47 (q, 2J= 13.9 Hz, 1J= 7.2 Hz, 2H, H2), 0.74-
13
0.70 (t, 3J = 8.2 Hz, 2H, H1) ppm; C{1H} NMR (100 MHz, C6D6, δ): 143.87 (C10), 137.32
(C12), 135.39 (C11), 134.22 (C7), 129.43 (C9), 128.67-128.42 (C5 & C6), 127.81 (C8), 71.85
(C4), 26.81 (C3), 20.76 (C2), 3.17 (C1) ppm; 119Sn NMR (79.5 MHz, C6D6, δ): -216.2 ppm.
12
1
32
HRMS-DART (m/z) = 411.00769 (M+H) calculated for C16 H2016O3 S1120Sn1; found
411.00809.
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Preparation of hydroxy homopolymer (10)
A solution of toluene (10 mL) and RhCl(PPh3)3 (0.076 g, 0.082 mmol) was added to a foil
wrapped 100 mL Schlenk flask. The solution mixture was stirred at RT for 10 min to activate
the catalyst. A solution of 6 (0.53 g, 2.06 mmol) in toluene (5 mL) was added to the catalyst
solution, and the reaction allowed to stir at RT for 4 h. The solvent was removed in vacuo and
the crude product was dissolved in minimal amount of THF (< 1 mL) and transferred dropwise
to a 100 mL flask containing a stirring solution of cold hexanes (50 mL). A yellow colored
precipitate formed immediately, and the solution was stirred for an additional 5 min and allowed
to settle. The hexane layer was removed with a Pasteur pipette. The solid was dried in vacuo to
obtain a dry yellow colored powder of 10. Yield = 78%. Mw = 42,000 Da, PDI = 1.16. 1H NMR
(400 MHz, C6D6, δ): 7.59-6.95 (m, 5H, H6-H8), 3.57-3.54 (m, 2H, H2), 1.28-1.22 (m, 2H, H3),
13
0.89-0.82 (m, 2H, H4) ppm. C{1H} NMR (100 MHz, C6D6, δ): 139.06 (C7), 133.25 (C8),
132.93 (C5), 130.02 (C6), 69.39 (C2), 31.64 (C3), 27.31 (C4) ppm. 119Sn NMR (149 MHz,
C6D6, δ): -113.42 & -176.13 ppm. EA Ccalc/found: 42.41/39.52, Hcalc/found: 4.75/4.54
Preparation of tosyl-polymer (11)
A toluene solution (9 mL) containing RhCl(PPh3)3 (0.0320 g, 0.0350 mmol) was added to a foil
wrapped 50 mL Schlenk flask and stirred at 0 °C (20 min) for activation. Thereafter, 9 in 9 mL
of toluene (0.360 g, 0.876 mmol) was added dropwise over 20 min to the catalyst solution. The
reaction was allowed to stir at 0 °C for 4 h. The mixture was then reduced in volume (in vacuo)
to roughly 5 mL and using a double tipped cannula, transferred to a 100 mL foil wrapped
Schlenk flask contained a stirring solution of cold hexanes (50 mL). An orange-yellow
precipitate formed immediately and the solution was stirred for additional 5 min and then
allowed to settle. The top layer of the solution was then extracted using a double tipped cannula
needle. The residues were dried in vacuo to obtain an orange yellow coloured solid. Yield 63 %
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1
(0.230 g). Mw = 31,000 Da, PDI = 1.20. H NMR (400 MHz, C6D6, δ): 7.91 (bm, 2H, H8),
7.76-7.37 (bm, 5H, H5-H7), 6.88-6.83 (bm, 2H, H9), 3.73 (bm, 2H, H4), 1.88-1.54 (bm, 5H,
H2 & H3), 1.23 (bm, 2H, H1) ppm; 13C{1H} NMR (100 MHz, C6D6, δ): 144.10 (C10), 138.15
(C12), 137.12 (C6), 133.84 (C11), 133.82 (C7), 131.96 (C9), 126.33 (C8), 72.98 (C4), 29.55
(C2), 21.17 (C1), 14.02 (C3) ppm; 119Sn NMR (79.5 MHz, C6D6, δ): -205 ppm. EA Ccalc/found
:
46.98/45.45, Hcalc/found: 4.44/4.30
Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.
Crystallographic data for compounds 5 (CCDC# 1843959) and 8 (CCDC# 1843959) were
deposited with the Cambridge Crystallographic Data Base.
Acknowledgements: This work was funded by the NSERC Discovery Grant Program. The
computational studies were made possible by the facilities of the Shared Hierarchical Academic
Research Computing Network (SHARCNET: www.sharcnet.ca) and Compute/Calcul Canada.
Thanks to Prof. Robert Gossage for his kind and timely editing of this manuscript.
Received: Month XX, XXXX; Revised: Month XX, XXXX; Published online:
Keywords: hypercoordinate, polystannanes, tin dihydrides, dehydropolymerization
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Table of Contents Entry
Synthesis
and
Characterization
of
Readily
Modified
Poly(aryl)(alkoxy)stannanes by use of Hypercoordinate Sn Monomers
Jeffrey Pau, Gloria M. D’Amaral, Alan J. Lough†, R. Stephen Wylie, and Daniel A. Foucher *
A simple light and moisture stable semi-crystalline hypercoordinate polystannane is
revealed. A key design feature for asymmetrical polystannanes is the use of strongly datively
bonded ligands that render a majority of tin(IV) centers of this main group inorganic polymer
5-coordinate, electron rich and protected from nucleophilic attack.
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