Pd-catalysed reactions of alkynes with model distannanes and poly[di-(n-butyl)]stannane

Article abstract of DOI:10.1039/c2dt31999c

A reinvestigation of Pd-catalysed alkyne (R′-C≡CH; R′ = H, Ph) insertion chemistry involving R₃SnSnR₃ (3a: R = Me; 3b: R = n-Bu) was undertaken. Model distannyl ethylenes 4a-b (Me ₃SnCHCR′SnMe₃) and 5a-b ((n-Bu) ₃SnCHCR′Sn(n-Bu)₃) were reproduced and further characterized by NMR (¹¹⁹Sn, ¹³C, ¹H) and UV-Vis spectroscopy. In the presence of an excess of phenylacetylene, dimerization-carbostannylation of compound 4b yielded the new conjugated butadiene, (Z,Z)-1,4-bis(trimethylstannyl)-1,4-diphenyl-buta-1,3-diene (9). An X-ray structure determination of 9 reveals a symmetrical double-bond Z confirmation. Compound 9 was further characterized by NMR, UV-Vis spectroscopy, and MS. A DFT analysis of model compounds (4a-b, 5a-b, 9) and the experimental and theoretical λ_max values from the UV-Vis spectra were also compared. Acetylene and phenylacetylene Pd-catalysed insertion into the backbone of poly[di-(n-butyl)]stannane 12 resulted in new, modest molecular weight, partially inserted alkene tin polymers (13a-b) that were also characterized by GPC, NMR, UV-Vis spectroscopy and elemental analysis.

Full text of DOI:10.1039/c2dt31999c

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Pd-catalysed reactions of alkynes with model
distannanes and poly[di-(n-butyl)]stannane†
Cite this: Dalton Trans., 2013, 42, 2469
Aman Khan,a Alan J. Lough,b Robert A. Gossagea and Daniel A. Foucher*a
A reinvestigation of Pd-catalysed alkyne (R’–CuCH; R’ = H, Ph) insertion chemistry involving R3SnSnR3 (3a:
R = Me; 3b: R = n-Bu) was undertaken. Model distannyl ethylenes 4a–b (Me3SnCHvCR’SnMe3) and 5a–b
((n-Bu)3SnCHvCR’Sn(n-Bu)3) were reproduced and further characterized by NMR (119Sn, 13C, 1H) and
UV-Vis spectroscopy. In the presence of an excess of phenylacetylene, dimerization–carbostannylation of
compound 4b yielded the new conjugated butadiene, (Z,Z)-1,4-bis(trimethylstannyl)-1,4-diphenyl-buta-1,3-
diene (9). An X-ray structure determination of 9 reveals a symmetrical double-bond Z confirmation. Com-
pound 9 was further characterized by NMR, UV-Vis spectroscopy, and MS. A DFT analysis of model com-
pounds (4a–b, 5a–b, 9) and the experimental and theoretical λmax values from the UV-Vis spectra were also
compared. Acetylene and phenylacetylene Pd-catalysed insertion into the backbone of poly[di-(n-butyl)]
stannane 12 resulted in new, modest molecular weight, partially inserted alkene tin polymers (13a–b) that
were also characterized by GPC, NMR, UV-Vis spectroscopy and elemental analysis.
Received 2nd August 2012,
Accepted 15th November 2012
DOI: 10.1039/c2dt31999c
www.rsc.org/dalton
Metal-catalysed insertion of alkynes into Group 14 di-
silanes8 and digermanes9 (Fig. 1) was successfully demon-
Introduction
Polystannanes are unique conductive main group polymers strated by Tanaka et al. In these reactions, Pd-catalysed
comprised entirely of a backbone of tin atoms.1 While gener- insertion of alkynes into Si or Ge dimers or trimers (C6H6;
ally more stable in their solid form, in solution these soluble, 120 °C: sealed tube) leads to formation of disilalkenes (1),
film forming materials2 display an extreme sensitivity to light digermalkenes or trigermadialkene (2) derivatives. Metal-cata-
and moisture and hence readily depolymerize to yield cyclic lysed alkyne insertion into hexalkyldistannanes (3) was first
stannanes.3 Our interest in these polymers is focused on the attempted in the early 1970s.10 Using Pd(PPh3)4 as catalyst
tailoring of such polystannanes to improve their stability and (neat; 50–85 °C), Mitchell was able to prepare more than 20
also to explore their utility as conductive, one-dimensional varieties of distannylalkenes (4, 5) from the addition of
polymeric wires.4 We are currently investigating strategies alkynes to distannanes.11 Characteristic of many of these dis-
towards more stable polystannanes including the attachment tannylalkenes is the facile photoinduced transformation from
of light absorbing groups5 (e.g. ultra violet absorbers, UVA’s) to Z to E isomers when such molecules are irradiated with UV
the tin centers to protect sensitive Sn–Sn bonds, the prep- light. In the 1990s, Piers and Skerlij investigated the Pd-
aration of 5- and 6-coordinate tin centers that moderate the
Lewis acidic nature of Sn(IV)6,7 and the chemistry of alkyne
insertion into the weak Sn–Sn backbones of polystannanes to
produce potentially stable polycarbostannanes, a new class of
Group 14 conjugated polymers. The work reported herein
deals with this latter approach.
aDepartment of Chemistry and Biology, Ryerson University, 350 Victoria Street,
Toronto, Ontario, Canada, M5B-2K3. E-mail: daniel.foucher@ryerson.ca;
Fax: +1 416-979-5044; Tel: +1 416-979-5000 ext 2260
bDepartment of Chemistry, University of Toronto, 80 St. George Street, Toronto,
Ontario, Canada, M5S-3H6. E-mail: alough@chem.utoronto.ca;
Fax: +1 416-978-8775; Tel: +1 416-978-6275
†Electronic supplementary information (ESI) available. CCDC 833176. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2dt31999c
Fig. 1 Group 14 dimers and alkyne inserted dimers and trimers.
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impact of this chemistry on the light stability of the resulting
polycarbostannanes (13a, 13b).
Results and discussion
Pd-catalysed alkyne insertion into distannanes and X-ray
structure of 9
The Pd-catalysed insertion reactions of alkynes into hexalkyl-
distannanes was first reported by Notles10 and later by Mit-
chell.11a–d These reactions proceed via cis-addition of the alkyne
into the Sn–Sn bond, which will then readily convert to the
more stable trans product upon exposure to light. In particular,
insertion of acetylene or phenylacetylene with 3a (R = Me)
proceed to near completion (4a and 4b); in contrast incom-
plete addition is observed in the case of 3b (R = n-Bu) yielding
the products 5a or 5b. As shown in Scheme 1 for 4b, the reac-
tions likely proceed through an initial oxidative-addition of the
distannane by Pd, followed by insertion of the alkyne, result-
ing in the cis-Pd intermediate and reductive elimination of the
product that generates the distannylalkene 4b. Characterization
data (NMR: 119Sn, 1H, 13C; C6D6) for both 4a and 4b agreed with
the reported chemical shifts and coupling constants for these
products.11b Insertion of acetylene into 3b was reported by
Mitchell,11b but no characterization data for the product 5a was
provided. Compound 5a has previously been prepared by non-
insertion routes15 and the reported chemical shift data (1H
NMR) is in good agreement with this work. The related Pd-cata-
lysed insertion of phenylacetylene into 3b leads to the pre-
viously prepared, but uncharacterized, distannylalkene 5b.
In the presence of an excess of phenylacetylene (>2.0
equiv.), we have observed the formal insertion of one
additional unit of phenylacetylene (presumably by cis inser-
tion) into the cis-Pd intermediate (Me3Sn)(PPh3)2Pd–
CHvC(Ph)(SnMe3), which leads to the photochemically and
Fig. 2 Alkyne and diene containing tin and silicon species.
catalysed insertion of alkynoates into distannanes and fol-
lowed their thermal conversions from Z to E isomers.12 Similar
metal-catalysed insertions of alkynes into [2]ferrocenophanes
with disilane13 or distannane14 (6) bridges (Fig. 2) were carried
out independently in both the Manners and Heberhold labora-
tories, respectively. Alternative, non-catalysed routes to alkene
(5a) and diene (7) materials of this type was previously demon-
strated by Corey,15 Seitz16 and Ashe.17 The utility of these dis-
tannylalkenes species in both cross-coupling1h,18 chemistry
and transmetallation19 strategies is well established.
The insertion chemistry of Group 14 polymers is not,
however, extensively explored. The Pd-catalysed insertion of
alkynes into the backbones of polysilanes, polycarbodisilanes
and oligogermanes was demonstrated in work largely carried
out by both Tanaka20 and Mochida.9 This insertion chemistry
rarely goes to completion and therefore results in random
block copolymers with repeating units that contain both
alkene units between two of the Group 14 elements and those
in which the Si–Si8 or Ge–Ge9 bonds remain undisturbed. The
electrochemical and spectroscopic properties of these alkyne
inserted systems have also not been extensively investigated.
Tanaka reported that the UV-Vis spectra of partially (80%)
alkyne inserted polycarbosilanes (8) showed nearly identical
λmax values to that of the parent polymer but doped conduc-
tivity values (3–10 × 10−4 S cm−1) that are far superior to the
unmodified polymer.20 As polysilanes inherently behave as
positive photoresists,21 the potential to enhance the light stab-
ility of these polymers is desirable. Unfortunately, the improve-
ment of the light stability following insertion within this
system was not mentioned.20
We describe herein our efforts to re-investigate the Pd-cata-
lysed alkyne insertion reactions of distannanes and provide
further characterization of the resulting products by NMR
(
119Sn, 1H, 13C) and UV-Vis spectroscopies. Gas phase struc-
tures of model compounds (4a–b, 5a–b) and novel compound
9 were examined by density functional theory (DFT) at the
B3LYP 6-31G* level. Additionally, we report on our attempts to
insert acetylene and phenylacetylene into the backbone of a
light sensitive poly[di-(butyl)]stannane (12) and detail the
Scheme 1 Proposed reaction pathway for the formation of 4b and 9.
2470 | Dalton Trans., 2013, 42, 2469–2476
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Fig. 3 Structures of related tin alkenes.
Fig. 4 ORTEP representation of a molecule of 9 with thermal ellipsoids drawn
at the 30% probability level. Selected bond lengths (Å) and angles (°). Sn(1)–
C(4) 2.189(13), Sn(2)–C(1) 2.148(14), C(1)–C(2) 1.37(2), C(1)–C(5) 1.481(19),
C(2)–C(3) 1.445(18), C(3)–C(4) 1.343(19),C(4)–C(11) 1.501(18), C(3)–C(4)–Sn(1)
120.4(10), C(1)–C(2)–C(3) 125.2(12), C(4)–C(3)–C(2) 128.0(12).
thermally stable (Z,Z)-1,4-bis(trimethylstannyl)-1,4-diphenyl-
buta-1,3-diene (9). A single δ
observed for 9.
resonance at −44 ppm was
119Sn
We propose that
a second phenylacetylene insertion
between the remaining Sn–Pd bond (see Scheme 1) occurs, fol-
lowed by reductive elimination and a concomitant C–C bond
forming step leading to 9. This process is similar to the dimer-
ization–carbostannylation products first reported by Tsuji
et al.22 (10) and later by Hiyama and co-workers (11).23 As with
9, compounds 10 and 11 (Fig. 3) are very likely the result of
regio- and stereo-selective reactions to yield the (E,E)-1,4
adduct and the (E,E)-conjugated α,-ω pentacenes, respectively.
Surprisingly, despite an excess of acetylene, a similar reaction
is not observed in the case of acetylene insertion with 3a. This
may be the result of the difference in reaction conditions (i.e.,
bubbling acetylene in to dioxane together with 3a, rather than
the neat reaction of phenylacetylene with 3a). The formation of
the 2 : 1 insertion product 9 may be thermodynamically
favoured, and will only occur in the presence of an additional
equivalent of phenylacetylene.
Compound 9 was further examined in the solid-state by
single crystal X-ray diffraction (Fig. 4; Table 1). The crystallo-
graphic data of 9 confirm that a second phenylacetylene unit
has inserted in a head-to-head fashion, with the molecule crys-
tallizing in the double Z conformation. The lengths of the
single and double bonds of 9 are inequivalent at 1.445 and
1.355 Å, a situation that has been previously observed in the
repeat unit of the backbone in t-butyl terminated trans-dodeca-
hexaene24 (avg. values 1.44 and 1.34 Å, respectively).
Table 1 Crystal data and structure refinement for 9
Empirical formula
Formula weight
Crystal colour
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C22H30Sn2
531.84
Yellow
150(1)
0.71073
Orthorhombic
Pca21
16.1862(3)
b (Å)
c (Å)
6.2126(6) Å
22.2214(11) Å
α (°)
β (°)
90
90
γ (°)
90
2234.5(2)
4
1.581
2.236
1048
Volume (Å3)
Z
Dcalc (Mg m−3
)
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm3)
θ range (°)
0.16 × 0.10 × 0.10
2.68 to 27.46.
−20 ≤ h ≤ 21, −8 ≤ k ≤ 8,
−22 ≤ l ≤ 28
Index ranges
Reflections collected
13 220
Independent reflections
Completeness to θ (%)
Absorption correction
Max. and min. transmission
Refinement method
4024 [Rint = 0.0906]
99.3% (θ = 27.46°)
Semi-empirical from equivalents
0.767 and 0.658
Full-matrix least-squares on F2
4024/1/222
Data/restraints/parameters
Goodness-of-fit on F2
1.036
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0590, wR2 = 0.1328
R1 = 0.1033, wR2 = 0.1620
0.58(9)
UV-Vis and DFT analysis of distannylethylenes
Absolute structure parameter
Solution UV-Vis spectroscopy (THF) of compounds 3a, 4b and
9 (Table 2) show a noticeable redshift in the observed λmax fol-
lowing alkyne insertion. This is consistent with the structure
of 9 as a model for a conjugated polyene.26 A DFT analysis
(B3LYP 6-31G* level) of stannanes and distannylalkenes (4a,
4b, 5a, 5b) and the distannyldiene (9) were also undertaken to
investigate the impact of introducing π-bridging units into the
Sn–Sn σ-bond. Calculated λmax values for these compounds
(Table 2) agree well with the experimental data and suggest
that insertion of the phenylacetylene into a Sn–Sn bond leads
Largest diff. peak and hole (e Å−3
)
2.028 and −1.675
to a destabilization of the HOMO and stabilization of the
LUMO orbitals (3a: ΔEHOMO–LUMO = 6.66 eV vs. 9: 4.07 eV),
resulting in a redshift. This is consistent with a conjugated σ–π
overlap. The frontier orbitals suggest that this σ–π overlap is
unhindred by the nodes centered on the p orbitals. A compari-
son of selected bond lengths and bond angles of 9 as
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Table 2 119Sn NMR (C6D6) chemical shifts and experimental (THF) and calcu-
lated UV-Vis λmax values of distannanes (3a and 3b) and model distannylalkenes
(4a, 4b, 5a, 5b and 9)
Table 3 119Sn (C6D6) chemical shifts, molecular weight data and experimental
UV-Vis (THF) λmax values of polystannane 12 and polycarbostannanes 13a and
13b
Calc. (λmax
nm
)
Exp. (λmax) nm,
Exp. (λmax) nm,
Compound
δ
119Sn (ppm)
(ε/dm3 mol−1 cm−1
)
Compound
δ
119Sn (ppm)
Mw (abs), PDI
(ε/dm3 mol−1 cm−1
)
3a
3b
4a
4b
−109
−83
206
214
210a
12
13a
13b
−190
1.2 × 104, 1.6
5.3 × 103, 1.8
1.3 × 104, 1.5
380, (760)
320, (80)
370, (970)
245b, (75 930)
237b, (67 200)
234b, (26 250)
−66.5
[E, −54.7, Z, −61.4] 197
[E, −45.7, −59.6, Z, 223
−39.0, −62.0]
−66.1, −190.6
5a
5b
−68.3
216
244b, (81 400)
235b
[E, −54.7, −66.5, Z, 223
−53.5, −66.1]
7
9
[Z, −53.6, E, −35.2] 236
249c
−44.0
312
309b, (1400)
a Ref. 25. b This work. c Ref. 17.
Fig. 5 Comparison of UV-Visible spectra (THF) of alkyne inserted and non-
inserted tin products.
Attempts to insert phenylacetylene into 12 under reaction
conditions similar to the synthesis of 13a were unsuccessful.
Insertion was carried out from the neat reaction of 12 with
phenylacetylene in the presence of Pd catalyst at elevated
temperatures (5d: 85 °C). Analysis by GPC revealed the resul-
tant polymer (13b) to be of a slightly higher molecular weight
(Table 3), indicative of the insertion of the phenylacetylene.
Scheme 2 Insertion of acetylene and phenylacetylene in to the backbone of
poly[di-(butyl)]stannane (12) to produce the copolymer (13a) and the random
copolymer (13b).
measured (X-ray) and calculated by DFT are given in the ESI:†
Table S-1.‡
Analysis (NMR) showed two δ
resonances at −66.1 and
119Sn
−190.6 ppm suggestive of a more random structure. The reson-
ance at −190.6 ppm, which is similar to the parent polymer
12, indicates that there is likely only a partial substitution of
the backbone.
UV-Vis analysis of the new polycarbostannanes 13a and 13b
in THF show λmax absorbances that extend into the visible, but
are slightly blue shifted from the parent polystannane 12
(Table 3, Fig. 5).
Similar to the properties reported by Tanaka and co-
workers8 for the polycarbosilane 8, insertion into Sn–Sn bonds
by alkynes does not seem to disrupt conjugation in the mole-
cular backbone. The UV stability of 13a and 13b was evaluated
by multiple (>50) UV-Vis scans over a 1 h time period. Both
13a and 13b show remarkable stability, with virtually no
change in their UV-Vis characteristics compared to the parent
polymer 12, which completely decomposes after only ten con-
secutive scans.
Pd-catalysed insertion of alkynes into polystannane 12
Insertion reactions of alkynes into polystannane 12 (Scheme 2)
were also attempted. Using conditions similar to those for the
insertion of alkynes into distannanes, two new polymers 13a
and 13b were produced. Pd-catalysed insertion of acetylene
into 12 (1,4-dioxane) yields (4d: 85 °C) an orange-coloured, pre-
sumably polymeric, product (13a). Analysis of the crude
material by NMR (119Sn) shows at least five new resonances
but no evidence for 12. Precipitation into cold methanol and
recovery reveals (NMR) a single δ
resonance (−66.5 ppm),
119Sn
in a similar chemical shift range for that of 3b inserted with
1
acetylene (5a). H NMR of 13a suggests that the insertion pro-
ceeds to approximately 50% of the Sn–Sn bonds, leaving on
average all of the Sn centers with a single acetylene carbon
bond and one Sn–Sn bond. Elemental analysis of 13a supports
the proposed structure shown in Scheme 2. This polymer
appears to be indefinitely stable to ambient light and was iso-
lated as an orange powder. GPC analysis (Table 3) shows
evidence of some depolymerization, with a significant weight
loss (≈45%) from the parent polymer 12.
Conclusion
We have carried out a reinvestigation of the Pd-catalysed inser-
tion chemistry of acetylene and phenylacetylene into distan-
nanes (3a, 3b) to yield the mono-inserted products 4a, 4b, 5a
and 5b. In the case of 3a, reaction with excess phenylacetylene
‡Resolution of 119Sn–13C and 117Sn–13C couplings in some instances could not
be made.
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results in an unusual dimerization–carbostannylation (vide brown in colour during this time period. The solvent was then
supra) product 9. An X-ray analysis of 9 reveals a head-to-head removed under reduced pressure and the product 4a recovered
1
arrangement of phenylacetylene units. Pd-catalysed alkyne as a red brown semi-solid. The NMR (119Sn, 13C, and H) data
insertions into polystannane 12 results in new, modest mo- in C6D6 was in good agreement for the exclusive initial for-
lecular weight polycarbostannanes 13a and 13b which show mation of the Z isomer with the data reported by Mitchell
improved light stability relative to the parent polymer. Further et al.11b and provided here for completeness. Yield = 0.96 g
investigations into polymeric materials of this type are (85%).
2
ongoing.
1H NMR (C6D6) δ (ppm): 0.28 (s, 18H, J
(Sn–CH3) =
119Sn–H
53.98 Hz, 2J
(Sn–CH3) = 52.74 Hz), 7.39 (s, 2H, JHH
3
117Sn–H
(vCH) = 17.1 Hz, 2J
(vCH–Sn) = 102.4 Hz, 2J
119Sn–H
117Sn–H
(vCH–Sn) = 97.60 Hz, 3J
(CHvCH–Sn) = 216.6 Hz,
119Sn–H
Experimental
3J
(CHvCH–Sn) = 207.6 Hz), 13C{1H} NMR (C6D6) δ
117Sn–H
General procedures
(ppm): −8.8 (s, –Sn–CH3), 154.7 (s,vCH–Sn), 119Sn{1H} NMR
All manipulations of air and/or moisture-sensitive compounds
were performed under N2(g) atmosphere in a glovebox or
using standard Schlenk techniques. Me6Sn2 (3a) and (n-
Bu)6Sn2 (3b) were purchased from Strem and used as received.
(n-Bu)2SnH2 used to prepare the polystannane [(n-Bu)2Sn]n (12)
was prepared from (n-Bu)2SnCl2 and LiAlH4 according to a lit-
erature preparation.1b,2a Solvents were dried by standard pro-
(C6D6) δ (ppm): −61.37 (J
= 470.2 Hz). UV-VIS:
119Sn–117Sn
λmax(THF)/nm 237 (ε/dm3 mol−1 cm−1 67 200).
COMPOUND 5A: REACTION OF 3B WITH ACETYLENE. The distannane
3b (1.2 g, 2.06 mmol) and Pd(PPh3)4 (40 mg, 3.5 × 10−2 mmol)
were added to a reaction flask in a glove box. The reaction
mixture was diluted with 20 mL of 1,4-dioxane, warmed to
85 °C, and acetylene gas was thereafter bubbled into the flask
for 100 h. The contents of the flask turned brown in colour
during this period. The solvent was then removed under
reduced pressure and the product 5a recovered as a moisture-
sensitive, red coloured oil. Analysis of the crude reaction
product by 119Sn NMR (C6D6) revealed only one signal for the
acetylene inserted product 5a. Yield = 0.3 g (24%).
1
cedures prior to use. H, 13C{1H} and 119Sn{1H} NMR spectra
were recorded on a Bruker Avance 400 MHz NMR spec-
trometer. 1H spectra were referenced to the residual solvent
peaks in the deuterated solvents (in turn referenced to external
TMS) while the 13C spectra are referenced internally to the
deuterated solvent resonances which are also in turn refer-
enced to TMS (δ = 0.00 ppm). 119Sn resonances were referenced
to external SnMe4 (δ = 0.00 ppm). UV-Vis measurements were
carried out in THF solutions using a Perkin Elmer Lamda 40
spectrometer. 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 (λ0 =
670 nm) and a low angle (7°) 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 the eluent. GPC samples were
prepared using 3–10 mg of polymers per mL THF, and filtered
using a 0.45 μm filter. High resolution mass spectrometry
experiments were carried out using an accuTOF DART-MS at
the University of Toronto. Elemental analyses were performed
by Atlantic Microlab of Norcross Georgia. The gas phase mo-
lecular calculations (DFT) of model compounds (4a–b, 5a–b)
and novel compound 9 were performed by using Spartan 10.0
V1.1.0 software program at the B3LYP 6-31G* level.
1H NMR (C6D6) δ (ppm): 0.95 (t, 3H, JHH = 14.6 Hz,
CH3CH2CH2CH2–Sn), 1.07 (m, 2H, CH3CH2CH2CH2–Sn), 1.41
3
(m, 2H, CH3CH2CH2CH2–Sn), 1.64 (m, 2H, CH3CH2CH2CH2–
3
Sn), 7.59 (s, 2H, JHH (vCH) = 17.7 Hz, 2J
(vCH–Sn) =
(CHvCH–Sn) =
119Sn–H
119Sn–H
2
3
93.3 Hz, J
(vCH–Sn) = 87.3 Hz, J
117Sn–H
3
201 Hz, J
(CHvCH–Sn) = 194 Hz), 13C{1H} NMR (C6D6)
117Sn–H
δ (ppm): 10.77 (1J
(CH3CH2CH2CH2–Sn) = 330 Hz, J
1
119Sn–C
117Sn–C
(CH3CH2CH2CH2–Sn) = 315 Hz), 13.99 (CH3CH2CH2CH2–Sn),
27.91 (3J
(CH3CH2CH2CH2–Sn) =
56.0 Hz, 3J
119Sn–C
117Sn–C
(2J
119Sn–C
(CH3CH2CH2CH2–Sn)
=
55.0
Hz),
29.75
2
(CH3CH2CH2CH2–Sn) = 19.7 Hz, J
(CH3CH2CH2CH2–Sn)
117Sn–C
= 19.7 Hz), 154.24 (1J119Sn–C (–Sn–CHv) = 428 Hz, 1J117Sn–C (–Sn–
2
2
CHv) = 410 Hz, J
(–Sn–CHv) = 34.3 Hz, J
(–Sn–
117Sn–C
119Sn–C
CHv) = 34.3 Hz), 119Sn{1H} NMR (C6D6) δ (ppm): −68.3
(3J
–
= 342.0 Hz).‡ UV-VIS: λmax(THF)/nm 244 (ε/dm3
119Sn 117Sn
mol−1 cm−1 81 400).
COMPOUND 4B: REACTION OF 3A WITH PHENYLACETYLENE. The distan-
nane 3a (1.55 g, 4.7 mmol), phenylacetylene (483 mg,
4.7 mmol) and Pd(PPh3)4 (10 mg, 8.6 × 10−3 mmol) were
weighed into a reaction flask in a glove box. The neat reaction
mixture was heated (80 °C) for 72 h. Analysis by 119Sn NMR
(C6D6) initially revealed resonances for both the cis and trans
Insertion of alkynes into Sn–Sn bonds
Compounds 4a, 4b, 5a, and 5b were prepared according to the isomers of 4b, as previously reported,11b with full conversion
method previously described by Mitchell et al.11b
to the trans isomer of 4b occurring under ambient light con-
COMPOUND 4A: REACTION OF 3A WITH ACETYLENE. The distannane ditions in 1 week. Yield = 1.1 g (55%).
2
3a (1.05 g, 3.2 mmol) and Pd(PPh3)4 (10 mg, 8.6 × 10−3 mmol)
1H NMR (C6D6) δ (ppm): 0.20 (s, 9H, JSn–H (Sn–CH3) = 53.8
3
were weighed and transferred to a reaction flask in a glove box. Hz), 0.23 (s, 9H, JSn–H (C6H5–C–Sn–CH3) = 51.9 Hz), 7.03–7.18
The reaction mixture was then diluted with 20 mL of 1,4- (m, 5H, C6H5–), 6.92 [7.37] (br m, 1H,vCH), 13C{1H} NMR
dioxane, warmed to 60 °C, and acetylene gas was thereafter (C6D6) δ (ppm): −7.39 [−7.42] (1J
(HC–Sn–CH3) = 333 Hz,
119Sn–C
bubbled into the flask for 4 h. The contents of the flask turned 1J
(HC–Sn–CH3) = 319 Hz), −6.56 [−6.58] (1J
(C6H5–
119Sn–C
117Sn–C
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C–Sn–CH3) = 343 Hz, 1J
(C6H5–C–Sn–CH3) = 328 Hz), −44.01 ppm. The crystal structure of this product reveals two
117Sn–C
126.25 (p-C6H5), 128.52 (m-C6H5), 132.40 (o-C6H5), 148.9 phenylacetylene units inserted between two tin atoms. The
2
(1J
C6H5–CvCH–Sn = 491 Hz, J
117Sn–C
C6H5–CvCH–Sn = crystalline product contained a carbon backbone that was
119Sn–C
119Sn–C
69 Hz, 1J
C6H5–CvCH–Sn = 468 Hz, 2J
C6H5– entirely the cis isomer, i.e., (Z,Z)-1,4-bis(trimethylstannyl)-1,4-
117Sn–C
CvCH–Sn = 66 Hz), 150.82 (1J
i-C6H5–Sn = 98 Hz, J
i-C6H5–Sn = 94 Hz, J
C6H5–CvCH–Sn = 497 Hz, J
diphenyl-buta-1,3-diene, 9. Yield = 1.07 g (43%).
2
119Sn–C
119Sn–C
1
2
2
i-C6H5–Sn = 56 Hz, J
i-C6H5–
1H NMR (C6D6) δ (ppm): 0.25 (s, 18H, J
(Sn–CH3) =
119Sn–H
(Sn–CH3) = 52 Hz), 7.02–7.31 (m, 10H, C6H5–),
117Sn–C
117Sn–C
Sn = 54 Hz), 169.0 (1J
54 Hz, J
2
2
119Sn–C
119Sn–C
117Sn–H
C6H5–CvCH–Sn = 40 Hz, 1J
C6H5–CvCH–Sn = 456 Hz, 7.41 (s, 2H, J
(vCH–Sn) = 21 Hz, J (vCH–Sn) =
117Sn–H
2
2
117Sn–C
119Sn–H
2J
C6H5–CvCH–Sn = 40 Hz), 119Sn{1H} NMR (C6D6) δ 21 Hz, 13C{1H} NMR (C6D6) δ (ppm): −7.28 (C6H5–C–Sn–CH3),
117Sn–C
(ppm): −45.7 [−38.97], −59.62 [62.00].§ UV-VIS: λmax(THF)/nm 126.32 (p-C6H5), 126.88 (m-C6H5), 128.60 (o-C6H5), 143.48
234 (ε/dm3 mol−1 cm−1 26 250).
(C6H5–CvCH–), 147.13 (i-C6H5), 153.63 (C6H5–CvCH–Sn),
COMPOUND 5B: REACTION OF 3B WITH PHENYLACETYLENE. The distan- 119Sn{1H} NMR (C6D6) δ (ppm): −44.01. UV-VIS: λmax(THF)/nm
nane 3b (1.0 g, 3.0 mmol), phenylacetylene (352 mg, 309 (ε/dm3 mol−1 cm−1 1400). HRMS (70 eV): m/z calc. for
3.4 mmol) and Pd(PPh3)4 (10 mg, 8.6 × 10−3 mmol) were C22H30Sn2 534.2041, not observed, calc. m/z 519.1841 (M+
weighed into a reaction flask in a glove box. The neat reaction CH3), found m/z 519.2036.
−
mixture was heated (80 °C) for 72 h. Analysis by 119Sn NMR
COMPOUND 12: PREPARATION OF [(n-Bu)2Sn]n. The parent poly-
(C6D6) revealed resonances for the cis isomer along with a reso- stannane, [(n-Bu)2Sn]n, 12 was prepared according to the
nance at −83.6 ppm for the unreacted starting material (3b). method described by Caseri et al.1f in good yield (>90%).
The reaction proceed to only 35% conversion to 5b as Polymer 12 was recovered from dehydropolymerization of (n-
1
measured by H NMR. No attempt to isolate the product was Bu)2SnH2 in CH2Cl2 using Wilkinson’s catalyst. 119Sn{1H}
made. This was a similar result observed earlier by Mitchell NMR (C6D6) δ (ppm): −190.7. λmax(THF)/nm 380 (ε/dm3 mol−1
et al. for this compound.11a
1H NMR (C6D6)
cm−1 760).
δ
(ppm): 0.92–1.7 (m, 54H,
COMPOUND 13A: REACTION OF 12 WITH ACETYLENE. Under an inert
CH3CH2CH2CH2–Sn), 6.94 (br m, 1H,vCH), 7.00–7.52 (m, 5H, atmosphere (N2(g)) and protected from ambient light sources,
C6H5–), 13C{1H} NMR (C6D6)
(ppm): 10.29 (s, the yellow coloured polymer 12 (1 g, 4.3 mmol) and Pd(PPh3)4
CH3CH2CH2CH2–Sn–CHv), 10.68 (s, CH3CH2CH2CH2–Sn– (40 mg, 3.5 × 10−2 mmol) were dissolved in 20 mL of 1,4-
CPhv), 13.95 (CH3CH2CH2CH2–Sn–CHv), 13.98 dioxane and transferred to a 3-neck flask equipped with septa
δ
(CH3CH2CH2CH2–Sn–CPhv), 27.67 (CH3CH2CH2CH2–Sn– and two gas inlets. Acetylene gas was passed through the reac-
CHv), 29.74 (CH3CH2CH2CH2–Sn–CPhv), 126.37 (p-C6H5), tion mixture and the contents heated to reflux temperature
128.45 (m-C6H5), 132.50 (o-C6H5), 148.0 (1J119Sn–C C6H5–CvCH– (85 °C) for 100 h. A small amount of the reaction mixture was
2
1
Sn = 421 Hz, J
C6H5–CvCH–Sn = 65 Hz, J
117Sn–C
C6H5– sampled from the reaction flask. The 119Sn NMR spectrum
117Sn–C
119Sn–C
2
CvCH–Sn = 401 Hz, J
C6H5–CvCH–Sn = 62 Hz), 152.2 revealed new resonances at 68.51, −50.23, −66.60 and
117Sn–C
i-C6H5–Sn = 53 Hz), 169.5 (1J
119Sn–C
(1J119Sn–C i-C6H5–Sn = 91 Hz, 2J119Sn–C i-C6H5–Sn = 53 Hz, 1J
−176.83 ppm, and the absence of a resonance at −190 ppm for
the parent polymer (12). The solvent was removed under
2
i-C6H5–Sn = 94 Hz, J
117Sn–C
C6H5–CvCH–Sn = 415 Hz, 2J
C6H5–CvCH–Sn = 37 Hz, reduced pressure, redissolved in a small amount of CH2Cl2
C6H5–CvCH–Sn = and then triturated with excess dry methanol. The opaque
117Sn–C
119Sn–C
1J
C6H5–CvCH–Sn = 379 Hz, J
2
117Sn–C
37 Hz), 119Sn{1H} NMR (C6D6) δ (ppm): E −54.45, −66.35, solution was placed in a glove box freezer (−33 °C) overnight
Z −49.39, 65.91, −83.59 (unreacted 3b).‡
and thereafter a yellow solid was recovered. The 119Sn NMR
COMPOUND 9: REACTION OF 3A WITH 2 EQUIV. OF PHENYLACETYLENE. revealed a single peak at −66.5 ppm for the new polymer
The experiment to prepare 4b was repeated with a 1 : 2 ratio of (13a).¶
the distannane 3a and phenylacetylene and the reaction
1H NMR (C6D6) δ (ppm): 0.8–2.0 (m, 54H, CH3CH2CH2CH2–
Sn, CH3CH2CH2CH2–Sn, CH3CH2CH2CH2–Sn), 7.40 (br s, 2H,
mixture analyzed after 72 h.
The distannane 3a (1.55 g, 4.7 mmol), phenylacetylene (–Sn–CHv), 13C{1H} NMR (C6D6)
δ
(ppm): 11.18
(966 mg, 9.4 mmol) and Pd(PPh3)4 (10 mg, 8.6 × 10−3 mmol) (CH3CH2CH2CH2–Sn), 14.28 (CH3CH2CH2CH2–Sn), 29.33
were weighed into a reaction flask in a glove box. The neat (CH3CH2CH2CH2–Sn), 30.82 (CH3CH2CH2CH2–Sn, 167.60
reaction mixture was heated (80 °C) for 72 h. Initial 119Sn NMR (–Sn–CHv), 119Sn{1H} NMR (C6D6) δ (ppm): −66.5. UV-VIS:
(C6D6) revealed peaks identified as the cis and trans isomers of λmax(THF)/nm 320 (ε/dm3 mol−1 cm−1 80). Found: C, 48.41, H,
compound 4b along with unreacted 3a. The sample was 6.60. Calc. for C26H56Sn3: C, 47.64, H, 7.52%.
heated at 80 °C for an additional 72 h and again analyzed by
COMPOUND 13B: REACTION OF 12 WITH PHENYLACETYLENE. First
119Sn NMR, confirming all of the unreacted 3a was consumed. attempt: Under an inert atmosphere (N2(g)) and protected from
The crude brown semi-solid product was left in the NMR tube ambient light sources, the yellow coloured polymer 12
and crystals were formed after two weeks. Analysis of the crys- (500 mg, 2.2 mmol), phenylacetylene (150 mg, 1.5 mmol) and
talline product 9 (119Sn NMR) displays a single resonance at
¶Trace PPh3 and PPh3O were evident by NMR (1H and 13C) and could not be
§Values for trans isomer in square brackets. Sn–Sn couplings not resolved.
2474 | Dalton Trans., 2013, 42, 2469–2476
effectively removed due to the solubility of polymer 13a in almost all solvents.
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Pd(PPh3)4 (10 mg, 8.6 × 10−3 mmol) were dissolved in 20 mL of
1,4-dioxane and transferred to a Schlenk flask. The reaction
mixture was heated to reflux temperature (85 °C) for 100 h.
The 119Sn NMR spectrum revealed new resonances at
89.0 ppm, along with two small peaks at −190 ppm for the
parent polymer (12) and at −201 for cyclic oligomers.
Second attempt: Under an inert atmosphere (N2(g)) and pro-
tected from ambient light sources, the yellow coloured
polymer 12 (800 mg, 3.4 mmol) phenylacetylene (250 mg,
2.4 mmol) and Pd(PPh3)4 (15 mg, 1.3 × 10−2 mmol) were
reacted neat in a Schlenk flask. The reaction mixture was
heated to 85 °C for 100 h. The 119Sn NMR spectrum revealed
resonances at −66.1 ppm and −190.6 ppm.
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1H NMR (C6D6) δ (ppm): 0.8–2.0 (m, 54H, CH3CH2CH2CH2–
Sn, CH3CH2CH2CH2–Sn, CH3CH2CH2CH2–Sn), 6.94–7.40 (m,
5H, C6H5), 7.52 (m, 1H, (–Sn–CHv), 13C{1H} NMR (C6D6)
δ (ppm): 11.75 (CH3CH2CH2CH2–Sn), 14.05 (CH3CH2CH2CH2–
Sn), 28.68 (CH3CH2CH2CH2–Sn), 33.67 (CH3CH2CH2CH2–Sn,
126.65 (p-C6H5), 129.22 (m-C6H5), 131.70 (o-C6H5), 132.49
(C6H5–CvCH–Sn), 159.40 (–Sn–CHvCPh), 167.60 (–Sn–
CHvCPh), 119Sn{1H} NMR (C6D6) δ (ppm): −66.1, −190.6.
UV-VIS: λmax(THF)/nm 370 (ε/dm3 mol−1 cm−1 970). Found: C,
48.98, H, 6.62. Calc. for C32H60Sn3: C, 49.14, H, 8.01%.
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Crystal structure determination
Data for the X-ray structure determination of 9 was collected
on a Bruker-Nonius Kappa-CCD diffractometer using mono-
chromated Mo-Kα radiation (λ = 0.70926 Å) and were measured
using a combination of ϕ scans and ω scans with κ offsets, to
fill the Ewald sphere. The data were processed using the
Denzo-SMN package.27 Absorption corrections were carried
out using SORTAV.28 The structure was solved and refined
using SHELXTL V6.129 for full-matrix least-squares refinement
that was based on F2. All H atoms were included in calculated
positions and allowed to refine in riding-motion approxi-
mation with Uiso tied to the carrier atom.
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This work was supported with NSERC Discovery Grants (DAF,
RAG) and the Ryerson Dean’s Research Fund.
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