Selective synthesis of stannoles by 1,1-carboboration of bis(trimethylsilylethynyl)tin compounds using weakly and strongly electrophilic triorganoboranes: Characterization of a zwitterionic intermediate

Article abstract of DOI:10.1002/ejic.201400028

The triorganoboranes BEt₃, BPh₃, and B(C₆F₅)₃ were allowed to react with bis(trimethylsilylethynyl)diorganotin compounds [R¹₂Sn(C≡C-SiMe₃)₂; R¹₂ = -(CH₂)₅- (a), R¹ = nBu (b), ⁿOct (c), Ph (d)] to give selectively and quantitatively stannoles. The reactions proceeded by 1,1-carboboration in two consecutive steps (inter- and intramolecular) and intermediates were detected by NMR spectroscopy. In one case, using the strongly electrophilic B(C₆F₅)₃, a zwitterionic intermediate was isolated and structurally characterized by X-ray diffraction analysis. The question of reversibility of the 1,1-carboboration is addressed. Multinuclear magnetic resonance spectroscopy (¹H, ¹¹B, ¹³C, ¹⁹F, ²⁹Si, ¹¹⁹Sn NMR) was used to characterize the intermediates and the stannoles as the final products. Some of the NMR parameters (¹¹B, ¹³C, ²⁹Si) of the intermediates were calculated by DFT methods using the optimized gas-phase geometries. The most important intermediates in the synthesis of stannoles by the reaction of bis(trimethylsilylethynyl)tin compounds with triorganoboranes have been detected, isolated, and structurally characterized.

Full text of DOI:10.1002/ejic.201400028

FULL PAPER
DOI:10.1002/ejic.201400028
Selective Synthesis of Stannoles by 1,1-Carboboration of
Bis(trimethylsilylethynyl)tin Compounds Using Weakly
and Strongly Electrophilic Triorganoboranes:
Characterization of a Zwitterionic Intermediate
Bernd Wrackmeyer,*[a] Peter Thoma,[a] Simone Marx,[a]
Tobias Bauer,[a] and Rhett Kempe[a]
Keywords: Tin / Tin heterocycles / Boron / Carboboration / Alkynes / Zwitterions
The triorganoboranes BEt3, BPh3, and B(C6F5)3 were allowed
to react with bis(trimethylsilylethynyl)diorganotin com-
mediate was isolated and structurally characterized by X-ray
diffraction analysis. The question of reversibility of the 1,1-
carboboration is addressed. Multinuclear magnetic reso-
nance spectroscopy (1H, 11B, 13C, 19F, 29Si, 119Sn NMR) was
used to characterize the intermediates and the stannoles as
the final products. Some of the NMR parameters (11B, 13C,
29Si) of the intermediates were calculated by DFT methods
using the optimized gas-phase geometries.
pounds [R12Sn(CϵC–SiMe3)2; R1 = –(CH2)5– (a), R1 = nBu
2
(b), nOct (c), Ph (d)] to give selectively and quantitatively
stannoles. The reactions proceeded by 1,1-carboboration in
two consecutive steps (inter- and intramolecular) and inter-
mediates were detected by NMR spectroscopy. In one case,
using the strongly electrophilic B(C6F5)3, a zwitterionic inter-
stannabora-cyclohexa-2,5-diene derivatives instead of
stannoles.[9]
Introduction
The properties of the π system in 1-heterocyclo-2,4-
dienes are a complex function of the heteroatom as well as
of substituents at the 1–5 positions. There is increasing
interest in metalloles because of their photophysical proper-
ties related to the tuneable band gap of the π system.[1,2]
In this context, stannoles deserve attention as electron-rich
cyclic dienes and potential starting materials for the synthe-
sis of other metalloles. However, there are rather few
straightforward routes available for their preparation,[3] and
the majority of the more convenient synthetic strategies ap-
pear to be limited to aryl groups at the 2–5 positions.[3,4]
This situation has been considerably improved by 1,1-
carboboration because the reactions of diethynyl(dimethyl)-
tin or bis(trimethylsilylethynyl)dimethyltin with trialkylbor-
anes afford stannoles (e.g., Scheme 1).[5,6] In this manner,
stannoles 1 and 2 were obtained in essentially quantitative
yields under mild conditions.[7,8] In the same way, stannoles
can be obtained selectively by using trialkylboranes and
other diethynyltin compounds.[9] In contrast, 1,1-carbobor-
ation using triphenylborane, BPh3, has led to mixtures of
stannoles and 1,4-stannaboracyclohexa-2,5-diene deriva-
tives.[9] In addition, the use of tris(pentafluorophenyl)bor-
Scheme 1. Two examples[5,6] of 1,1-carboboration reactions as a vi-
able route to stannoles.
In this work, we studied the 1,1-carboboration reactions
of four bis(trimethylsilylethynyl)diorganotin compounds 3
[R1 Sn(CϵC-SiMe3)2 with R1 = -(CH2)5-, (a); R1 = nBu,
2
2
(b), nOct (c), Ph (d)] with triorganoboranes BEt3, BPh3, and
B(C6F5)3, which differ greatly in their electrophilic charac-
ter. Previous work on the synthesis of 2 and related stann-
oles with Me3Si groups[6,8] had revealed no evidence for re-
active intermediates, and it was hoped that more electro-
philic triorganoboranes could be helpful in this respect. All
the reactions were studied by multinuclear magnetic reso-
nance methods (1H, 11B, 13C, 29Si, and 119Sn NMR spec-
troscopy) to elucidate mechanistic aspects of the 1,1-carbo-
boration reactions.
ane, B(C6F5)3, for the 1,1-carboboration of R1 Sn(CϵC-
2
R)2 (R1 = alkyl, Ph; R = H, nBu) selectively affords 1,4-
[a] Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
E-mail: b.wrack@uni-bayreuth.de
http://www.ac2.uni-bayreuth.de/catalyst-design.php
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Table 1. 13C, 119Sn, and 29Si NMR parameters[a] for the bis(tri-
methylsilylethynyl)diorganotin compounds.
Results and Discussion
Bis(trimethylsilylethynyl)tin Compounds
δ [ppm]
δC
δC
δC
δC
δSn
δSi
The bis(trimethylsilylethynyl)tin compounds 3a–d were
obtained (Scheme 2) in high yields as colorless solids or as
an oil (3b), and are slightly sensitive to moisture. Before use,
the purity of 3 was verified by NMR spectroscopy (Table 1).
Only limited NMR spectroscopic data have been reported
for 3b so far[10] and the NMR spectra for 3d in Figure 1
show the purity that can be achieved. In the case of 3a, the
molecular structure was established by X-ray crystallogra-
phy (Figure 2).
R1
Sn–Cϵ ϵC–Si SiMe3
Me2Sn(CϵC- –5.8
109.4
[542.0] [89.1]
|11.2|
118.6
0.1
|56.2|
–167.4 –19.1
[12.4]
SiMe3)2
(C6D6)
3a
[491.0]
|76.3|
119.3
14.1 [444.3], 107.5
27.0 [34.2]
0.0
|56.1|
–216.1 –19.4
[11.8]
R1
=
[516.9] [80.6]
2
-(CH2)5-
(CDCl3)
3b
30.8 [70.1]
13.2 [477.9], 109.4
28.5 [27.5], [468.8] [71.1]
26.5 [67.8]
13.6
|10.8|
|76.8|
119.0
0.1
|56.2|
–167.3 –20.0
[11.4]
R1 = nBu
(CDCl3)
|11.1|
|76.9|
3c
13.8 [475.9], 109.8
26.5 [27.4], [459.4] [70.6]
119.4
0.0
|56.0|
–168–0 –20.0
[11.0]
n
R1 = Oct
(CDCl3)
33.7 [65.7], |11.0|
29.6 [18.9],
|76.3|
29.5, 32.2,
23.0, 14.3
135.5
Scheme 2. Synthesis of bis(trimethylsilylethynyl)diorganotin com-
pounds.
3d
107.1
121.0
–0.2
–239.6 –18.9
[13.4]
[735.4],
Few structural data are available for dialkynyl(diorgano)-
tin compounds,[12,13] and 3a is the first example with tri-
methylsilylethynyl groups. All the bond lengths are in the
usual range, but the bond angles at tin are of interest be-
cause in 3a, as a consequence of the six-membered ring, the
endocyclic bond angle C5–Sn–C9 is fairly small [100.97(8)°]
R1 = Ph
(CDCl3)
136.5 [50.3], [632.3] [99.9]
|56.1|
129.2 [68.6], |10.7|
130.1 [13.9]
|74.5|
[a] Coupling constants J(119Sn,X) (X = 13C, 29Si) in Hz in [], and
n
nJ(29Si,13C) in Hz in ||.
when compared with the corresponding angles in other cyclic dialkynyl(diorgano)tin compounds (103–108°). The
noncyclic examples (Ͼ115 and Յ129°). However, the bond six-membered ring in 3a deviates slightly from the ideal
angle C1–Sn–C3 in 3a [108.98(8)°] is similar to that in non- chair conformation.
Figure 1. 100.6 MHz 13C{1H}, 79.47 MHz 29Si{1H} (refocused INEPT[11]), and 149.2 MHz 119Sn{1H} NMR spectra (refocused INEPT,[11]
measured at 296 K, in C6D6) of 3d showing numerous satellite signals for the various isotopomers. In the expanded regions of the 13C
NMR spectrum, 117/119Sn and 29Si satellites are marked by asterisks and crosses, respectively.
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Figure 2. Molecular structure of 3a (ORTEP, ellipsoids drawn at
the 40% probability level; hydrogen atoms have been omitted for
clarity). Selected bond lengths [pm] and angles [°]: Sn1–C1
209.66(18), Sn1–C3 209.80(17), Sn1–C5 213.29(17), Sn1–C9
213.88(18), C1–C2 120.4(2), C3–C4 120.4(2), Si1–C2 185.30(18),
Si2–C4 184.91(19), C2–C1–Sn1 173.55(15), C1–C2–Si1 177.17(15),
C4–C3–Sn1 177.82(15), C3–C4–Si2 174.54(16), C1–Sn1–C3
106.98(8), C1–Sn1–C5 108.83(7), C3–Sn1–C5 108.83(7), C1–Sn1–
C9 111.12(7), C3–Sn1–C9 113.09(7), C5–Sn1–C9 100.95(8).
Scheme 3. 1,1-Carboboration of bis(trimethylsilylethynyl)dior-
ganotin compounds.
stannoles 7. Although some evidence has been collected
previously for derivatives of type 4,[15,16] species such as 5
and 6 with Me3Si groups appeared to be too short-lived,
and their intermediacy was proposed to explain the forma-
tion of the stannoles with this particular pattern of substit-
uents.
1,1-Carboboration of Bis(trimethylsilylethynyl)diorganotin
Compounds Ϫ General Remarks
As for other dialkynyltin compounds, the 1,1-carbobor-
ation of 3 proceeds in two major steps (Scheme 3). The first
step is the intermolecular 1,1-carboboration, which may
lead to the alkenyl(alkynyl)tin compounds 4 or 5. The
1,1-Carboboration Using BEt3, and BPh3
In the cases of trialkylboranes such as BEt3, monitoring
stereochemistry of 4 precludes ring closure, however, 1,1- the 1,1-carboboration reactions by 29Si NMR spectroscopy
carboboration is readily reversible for such alkenes[8,14] (see proved successful for detecting intermediates of type 4(Et),
also below). Therefore the equilibrium is driven towards 5, readily identified by their characteristic NMR spectroscopic
in which the Sn–Cϵ bond is activated owing to vicinity of data (Table 2; see also Figure 3). Typically, mixtures of
the electron-deficient boron atom in the BR2 group. This 4(Et) and 7(Et) were present after warming the reaction
leads to migration of the alkynyl group from tin to boron mixtures to room temperature. However, 29Si NMR signals
and the formation of the zwitterionic intermediate 6. Fi- of the species 5 or 6 could not be observed. After 1 or
nally, irreversible rearrangement of 6 selectively affords the 2 days at room temperature, the stannoles 7(Et) were the
Table 2. 13C, 11B, 29Si, and 119Sn NMR parameters[a] for the alkenyl(alkynyl)tin compunds 4a–c(Et).
δ [ppm]
δC
δSi
δB
δSn
Sn–C=
=C–B
Sn–Cϵ
ϵC–Si
Et/BEt2
SiMe3
(alkene)
SiMe3
(alkyne)
(h1/2)
4a[b]
4b[c]
4c[d]
136.8
[321.4]
|60.0|
139.2
[229.6]
183.1
(br.)
115.9
[275.1]
|11.1|
116.7
[284.1]
117.9
[34.6]
|77.4|
119.2
[35.5]
35.2 [135.7],
14.1/
21.2 (br.), 9.3
36.7 [137.9],
14.0/
21.9 (br.), 9.5
33.7, 13.8/
22.0 (br.), 9.6
–5.5
[95.5]
–20.9
[7.8]
85.7
85.4
n.o.
–180.5
(39)
181.9
(br.)
–6.2
[80.7]
–21.0
[8.5]
–135.7
(31)
139.2
[312.3]
182.0
(br.)
116.8
[266.4]
119.4
[34.5]
–6.2
[80.7]
–21.0
[8.4]
–136.0
(13)
n
[a] Measured at 296 K in CDCl3 (4a) or C6D6 (4b, 4c), line widths h1/2 in () in Hz, coupling constants J(119Sn,X) (X = 29Si, 13C) and
nJ(29Si,13C) in [] and ||, respectively, in Hz, br. denotes the broadened 13C NMR signal of a carbon linked to boron; n.o. means not
observed. [b] Other 13C NMR spectroscopic data: δC = 0.2 |55.7| (Me3Si-alkyne), 1.3 [13.0] |50.5| (Me3Si-alkene), 16.5 [334.3] (SnCH2),
27.8 [34.8] (CH2), 31.7 [46.2] (CH2) ppm. [c] Other 13C NMR spectroscopic data: δC = 0.2 |55.6| (Me3Si-alkyne), 1.8 |49.8| (Me3Si-alkene),
15.6 [363.9] (Sn-CH2), 29.5 [24.0] SnCH2-CH2, 27.3 [62.4] (-CH2-), 13.9 (CH3) ppm. [d] Other 13C NMR spectroscopic data: δC = 0.1
|55.4| (Me3Si-alkyne), 1.9 |50.8| (Me3Si·alkene) ppm, other 13C NMR signals were not assigned because of overlap with signals for the
stannole 7c(Et).
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sole products (see Table 3 for the NMR spectroscopic data). 1,1-Carboboration Using B(C6F5)3
The 119Sn NMR spectra of the reaction mixtures were less
The enhanced electrophilic character of B(C6F5)3 can be
usefully exploited in 1,1-carboboration reactions when
compared with other triorganoboranes.[19] For instance, di-
alkynyl(dimethyl)silanes are converted quickly and selec-
tively into siloles under mild reaction conditions,[20] whereas
the analogous reaction with triethylborane requires heating
at 100–110 °C for several days.[21] The first attempts at using
B(C6F5)3 for the 1,1-carboboration of dialkynyl(diorgano)-
tin compounds other than 3 gave zwitterionic intermediates
similar to 6(C6F5) followed by the formation of 1,4-stanna-
boracyclohexa-2,5-dienes instead of stannoles.[9] Appar-
ently, the Lewis acid strength of the B(C6F5)2 group in the
elusive intermediates 5(C6F5) has two functions: 1) It accel-
erates the migration of the alkynyl group from tin to boron
to give 6(C6F5) and 2) it stabilizes the zwitterionic interme-
diates 6(C6F5) because of the relatively favored alkynylbor-
ate moiety (see Table 4 for relevant NMR spectroscopic
data). The presence of 6(C6F5) is already evident by moni-
toring the reaction progress using 11B and 29Si NMR spec-
troscopy (see Figure 6). The original 29Si(ϵC-Si) NMR sig-
nal of 3 vanishes and two new signals are observed, one
broadened signal accompanied by 117/119Sn satellites, corre-
n
informative because the 29Si satellites due to J(119Sn,29Si)
are not always well resolved, in contrast to 117/119Sn satel-
lites in the 29Si NMR spectra.
2
sponding to J(119Sn,29Si) across an olefinic carbon atom.
The broadening can be traced to unresolved vicinal 29Si–
11B spin–spin coupling.[17] The sharper 29Si NMR signal at
higher frequency belongs to the silicon atom attached to
the bridging CϵC unit. Apparently, this silicon atom is no
longer linked to a typical alkynyl carbon atom (as in alk-
ynylsilanes) and therefore its nuclear magnetic shielding is
similar to that in alkenylsilanes.[22] This is to be expected
for a bond angle CϵC–Si of 155.1°, as determined for solid
Figure 3. 79.47 MHz 29Si{1H} NMR spectra (at 296 K, in C6D6;
refocused INEPT[11]) for the reaction of 3b with triethylborane. Up-
per trace: Recorded after warming the reaction mixture to room
temp., removal of volatile materials, and dissolving in C6D6. Lower
trace: The same mixture after 24 h at room temp.
The reactions of 3a and 3b with triphenylborane were 6a(C6F5) (see below), which is in excellent agreement with
already complete (Ͼ95%) by the time the samples had the value of 155.4° for the calculated optimized geometry
reached ambient temperature. In the case of 3a, in one ex- [B3LYP/6-311G(d,p)[23] and Sn (LANL2DZ)[24] level of
periment, a weak broadened 119Sn NMR signal was de- theory]. The δSi values and the assignments were confirmed
tected at δSn = –177 ppm, tentatively assigned to 4a(Ph), by calculation of the 29Si nuclear magnetic shielding.[25] The
which was no longer visible after 12 h. The stannoles 7a(Ph) characteristic 13C(Si-Cϵ) NMR signal is accompanied by
and 7b(Ph) were formed quantitatively (see Figures 4 and 117/119Sn satellites [1J(119Sn,13Cϵ) ≈ 102–105 Hz], which in-
5).
dicates significant Sn-C(Si)ϵ bonding interactions.
Figure 4. 79.47 MHz 29Si{1H} NMR (refocused INEPT[11]) and 149.2 MHz 119Sn{1H} NMR spectra (at 296 K, in C6D6) for the reaction
2
of 3a with triphenylborane, which selectively leads to the stannole 7a(Ph). In the 29Si NMR spectrum, satellite signals for J(119Sn,29Si)
and 1J(29Si,13C) are marked by asterisks and crosses, respectively. The 119Sn NMR spectrum shows a broadened signal (h1/2 = 26 Hz)
2
because of unresolved vicinal 119Sn–11B spin–spin coupling.[17] The 29Si satellites for J(119Sn29Si) are barely visible at the bottom of the
119Sn NMR signal.
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Table 3. 13C, 11B, 19F, 29Si, and 119Sn NMR parameters[a] for the stannoles 7(Et, Ph, C5F5).
δ [ppm]
δC
δSi
δB
(h1/2
δSn
C2
C3
C4
C5
R/BR2
2-SiMe3
5-SiMe3
)
(h1/2)
7a(Et)[b]
7b(Et)[c]
7c(Et)[d]
7d(Et)[e]
7a(Ph)[f]
144.5
[167.6]
|65.2|
145.5
[166.0]
|65.0|
145.5
[166.5]
|64.7|
142.8
[200.0]
{64.7}
152.5
[161.8]
|63.6|
181.7
(br.)
166.7
[89.4]
|11.8|
168.5
[83.9]
|11.3|
168.5
[83.7]
|11.9|
169.8
[103.3]
{10.9}
167.7
[94.7]
|11.4|
138.3
[231.8]
|63.8|
139.5
[229.3]
|64.1|
139.5
[228.7]
|64.0|
136.8
[273.5]
{71.8}
143.4
[214.1]
|62.6|
31.5 [89.6],
16.1 [10.7]/
22.3 (br.), 9.4
32.1 [83.9],
16.2 [9.8]/
22.7 (br.), 9.7
34.6 [49.9],
16.2 [10.1]/
22.7 (br.), 9.8
31.8 [97.4],
16.1 [10.3]/
22.3 (br.), 9.5
146.5 [96.1] (i),
129.1, 127.6, 126.4/
142.1 (br.) (i), 138.1 (o),
127.7 (m), 131.4 (p)
146.5 [92.2] (i),
129.2, 127.5,
126.3/142.2 (br.)
(i) 138.2 (o),
–9.7
[100.2]
(0.5)
–10.5
[96.0]
(1.2)
–10.5
[96.0]
(1.2)
–8.2
[100.4]
(0.5)
–9.2
[96.2]
(1.2)
–9.1
[96.2]
(1.2)
–7.2
86.5
(1400)
83.1
(33.8)
183.7
(br.)
87.0
(1450)
141.8
(36.7)
183.8
(br.)
87.7
(1840)
141.6
(13.7)
184.0
(br.)
–8.7
[95.5]
87.1
(2200)
50.4
(24.5)
[96.9]
179.4
(br.)
–8.3
[99.0]
|51.7|
–6.9
[95.7]
|52.2|
70.0
(3200)
79.6
(25.2)
7b(Ph)[g]
153.7
[160.9]
|63.1|
181.0
(br.)
168.8
[88.8]
|11.7|
144.5
[210.7]
|62.1|
–9.0
[94.5]
|51.9|
–7.7
[91.5]
|52.1|
70.0
(2500)
138.1
(24.0)
127.7 (m), 131.4 (p)
[h]
7a(C6F5)[h]
7b(C6F5)[i]
7d(C6F5)[j]
163.8
[144.6]
|61.5|
165.5
[139.2]
|59.7|
162.3
[179.8]
|60.1|
172.0
(br.)
144.8
[n.o.]
156.3
[184.4]
|57.7|
158.0
[178.2]
|57.7|
155.2
[227.3]
|57.4|
–8.3
[81.1]
–6.6
[78.1]
62.0
(4000)
94.2
(30.0)
[i]
[j]
173.8
(br.)
146.1
[96.9]
–9.0
[73.7]
–7.6
[76.2]
63.5
(5000)
151.6
(24.8)
174.6
(br.)
147.3
[n.o.]
–7.4
[75.7]
–5.9
[75.4],
61.0
(5400)
45.8
(27.0)
n
n
n
[a] Measured at 296 K in C6D6, line widths h1/2 in () in Hz, coupling constants J(119Sn,X) (X = 29Si, 13C), J(29Si,13C), and J(19F,13C)
in [], ||, and {}, respectively, in Hz, br. denotes the broadened 13C NMR signal of a carbon linked to boron, n.o means not observed.
[b] Other 13C NMR spectroscopic data: δC = 1.9 [10.8] |51.5| (5-SiMe3), 2.2 [9.8] |51.7| (2-SiMe3), 14.3 [248.4] (Sn-CH2), 27.6 [29.1] (CH2),
31.8 [55.9] (CH2) ppm. [c] Other 13C NMR spectroscopic data: δC = 2.1 [10.0] |51.6| (2-SiMe3), 2.2 [9.3] |51.8| (5-SiMe3), 15.3 [272.5] (Sn-
CH2), 29.9 [18.6] (CH2), 27.4 [51.7] (CH2), 14.0 (CH3) ppm. [d] Other 13C NMR spectroscopic data: δC = 2.1 [10.6] |51.7| (2-SiMe3), 2.2
[9.3] |51.8| (5-SiMe3), 15.7 [272.8] (Sn-CH2), 27.8 [18.7] (CH2), 23.1 (CH2), 29.7 (CH2), 32.3 (CH2). 14.3 (CH3) ppm. [e] Other 13C NMR
spectroscopic data: δC = 2.0 [11.2] |52.1| (2-SiMe3), 1.9 [10.6] |52.1| (5-SiMe3), 141.5 [409.3] (Sn-C-i), 137.0 [39.0] (C-o), 128.5 [46.9] (C-
m), 128.7 [5.9] (C-p) ppm. [f] Other 13C NMR spectroscopic data: δC = 0.3 [7.6] |52.2| (5-SiMe3), 2.4 [9.5] |51.7| (2-SiMe3), 14.5 [251.4]
(Sn-CH2), 27.9 [29.3] (CH2), 32.1 [55.7] (CH2) ppm. [g] Other 13C NMR spectroscopic data: δC = 2.3 [10.3] |51.9| (2-SiMe3), 1.9 [7.7]
|52.1| (C5-SiMe3), 15.6 [275.7] (Sn-CH2), 30.3 [19.9] (CH2), 27.6 [49.4] (CH2), 14.2 (CH3) ppm. [h] Other 13C NMR spectroscopic data:
–0.26 |52.6| (SiMe3), 2.0 |52.3| (SiMe3), 14.9 [269.2] (Sn-CH2), 27.5 [30.7] (CH2), 31.7 [61.4] (CH2), 120.5 t {22.6} (C-i), 114.4 t {20.9}
(C-i) ppm, other 13C(C6F5) NMR signals were not assigned. 19F NMR spectroscopic data ([D8]toluene, 193 K): δF = –140.0, –140.3 (o-
F), –154.6 (p-F), –161.4 to –163.2 (m-F) for C6F5, –119.8, –126.4 (o-F), –128.0, –132.0 (o-F), –138.3 (p-F), –146.7 (p-F), –159.1, –160.2
(m-F), –160.7, –163.3 (m-F) for B(C6F5)2. [i] Other 13C NMR spectroscopic data: δC = 0.0 |53.0| (SiMe3), 1.7 |52.0| (SiMe3) 16.6 [207.0]
(Sn-CH2), 29.8 [22.7] (CH2), 27.5 [51.2] (CH2), 13.8 (CH3), 120.2 t {22.0} (C-i), 114.0 t {20.8} (C-i) ppm, other 13C(C6F5) NMR signals
were not assigned. 19F NMR spectroscopic data ([D8]toluene, 193 K): δF = –138.9, –140.4 (o-F), –154.4 (p-F), –161.5, –163.6 (m-F) for
C6F5, –119.9, –126.6 (o-F), –127.7, –132.2 (o-F), –138.4 (p-F), –147.0 (p-F), –160.5, –160.8 (m-F), –159.6, –163.3 (m-F) ppm for
B(C6F5)2. [j] Other 13C NMR spectroscopic data: δC = 0.2 |53.2| (SiMe3), 2.0 |55.2| (SiMe3), 139.2 (Sn-C-i), 137.1 [40.9] (C-o), 128.5 [43.2]
(C-m), 130.1 (C-p), 120.5 t {21.7} (C-i), 114.0 t {20.3} (C-i) ppm, other 13C(C6F5) NMR signals were not assigned. 19F NMR spectroscopic
data ([D8]toluene, 193 K): δF = –138.3, –140.3 (o-F), –153.7 (p-F), –160.9, –162.9 (m-F) for C6F5, –120.0, –126.3 (o-F), –127.8, –131.5
(o-F), –137.9 (p-F), –145.8 (p-F), –158.4, –160.3 (m-F), –159.6, –162.9 (m-F) ppm for B(C6F5)2.
After several days in C6D6 or toluene at room temp., the than that for the corresponding intermediate. The pattern
intermediates 6(C6F5) rearrange completely into the stann- typical for the olefinic C-2–5 of the 3-borylated stannoles
oles 7(C6F5). This process is indicated by the 11B NMR is observed in the 13C NMR spectra[6] (Table 3). The tem-
spectra in which the relatively sharp 11B NMR signal in the perature-dependent complex 19F NMR spectra of 7(C6F5)
borate region disappears and the typically broad 11B NMR can partially be analyzed[27] with respect to hindered rota-
signal for the trigonal-planar boron atom grows.[26] Simi- tion about the C–C6F5 and all B–C bonds (ΔG# at coalesc-
larly, two new 29Si NMR signals emerge, both accompanied ence = 11.5Ϯ0.5 kcal/mol). The stannoles 7(C6F5) do not
by 117/119Sn satellites for 2J(117/119Sn,29Si),[6] and a new rearrange upon irradiation with Pyrex-filtered UV light[28a]
broadened 119Sn NMR signal appears at lower frequencies as has been found for comparable siloles.[28b]
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Figure 5. 100.6 MHz 13C{1H} NMR spectrum of the stannole 7a(Ph), obtained from the reaction mixture without further purification.
Expansions are shown for the C-2,3,4,5 and C-ipso signals with 117/119Sn (asterisks) and 29Si satellites (crosses). The latter correspond to
the 13C satellites in the 29Si NMR spectrum (Figure 2) and confirm the assignment for Si-2 and Si-5. Note the typically[18] broadened C-
3 signals for the boron-bonded carbon atom.
Table 4. 13C, 11B, 19F, 29Si, and 119Sn NMR parameters[a] for the zwitterionic intermediates 6(C5F5).
δ [ppm]
δSi
δC
δC
δC
δF
δF
B(C6F5)2
–130.5 m (o),
–157.9 t ||20.9|| (p), –158.7 t ||20.9|| (p),
δB
δSn
Si-C= Si-Cϵ B-Cϵ
Si-Cϵ
RЈ2Sn
C6F5
–140.0 m (o),
(h1/2
)
(h1/2)
6a(C6F5)[b]
6b(C6F5)[d]
6d(C6F5)[e]
–7.8
–5.9 175.0
116.5
[102.5]
22.9 [242.4] (Sn-CH2),
27.2 [29.0] (CH2),
30.2 [74.2] (CH2)
–12.8
(97)
200.6
(124)
[143.0]
[Ͻ2] (br.)[c]
–164.2 m ||7.6||
||20.9|| (m)
–165.2 m ||8.5||
||20.9|| (m)
–9.3
[145.0]
–6.8 175.0
124.3
[n.o.]
22.9 [272.9] (Sn-CH2),
28.3 [60.1] (Sn-CH2–CH2), –157.9 t ||20.9|| (p), –159.1 t ||20.4|| (p),
–139.3 m (o),
–130.2 m (o),
–12.9
(140)
247.7
(99)
[Ͻ2] (br.)[c]
27.1 [73.8] (CH2),
13.4 (CH3)
135.5 [448.5],
136.2 [48.1],
129.3 [62.5],
131.6 [12.1]
–164.2 m
||7.5|| ||20.9|| (m)
–138.9 m (o),
–156.9 t ||21.2|| (p), –158.2 t ||21.2|| (p),
–163.7 m
–165.3 m
||8.3|| ||20.4|| (m)
–129.7 m (o),
–7.2
[149.0]
–5.6 173.0
116.9
[105.0]
–12.7
(90)
76.3
(55)
[Ͻ2] (br.)[c]
–164.7 m ||7.9||
||21.2|| (m)
||7.9|| ||21.2|| (m)
n
n
n
[a] Measured at 296 K in C6D6, linewidths h1/2 in () in Hz, coupling constants J(119Sn,X) (X = 29Si, 13C), J(29Si,13C), J(19F,13C), and
nJ(19F,19F) in [], ||, and ||||, respectively, in Hz, br. denotes the broadened 13C NMR signal of a carbon linked to boron, n.o means not
observed. [b] δSi(Si-C =)calcd. = –4.4 ppm, δSi(Si-C≈)calcd. = –3.7 ppm; other 13C NMR spectroscopic data: δC = –0.3 (SiMe3), 0.1 (SiMe3),
119.1 br. (B-C6F5, i), 121.8 t {21.7} (C6F5, i), 152.1 (Sn-C=), 175.0 br. (=C-B) ppm. [c] Assignment uncertain, because of overlap with
13C(=C-B) NMR signal. [d] Other 13C NMR spectroscopic data: δC = –0.5 (SiMe3), 0.1 (SiMe3), 119.7 br. (B-C6F5, i), 122.4 t {21.8}
(C6F5, i), 157.4 (Sn-CH=), 175.0 br. (=C-B) ppm. [e] Other 13C NMR spectroscopic data: δC = –1.1 (SiMe3), 0.2 (SiMe3), 119.2 br. (B-
C6F5, i), 122.2 t {21.5} (C6F5, i), 155.8 (Sn-CH=), 180.0 br. (=C-B) ppm.
Zwitterionic Intermediates in the Course of 1,1-
Carboboration
stannoles 7 via the elusive alkene 5. There is evidence
(Scheme 4) that this particular Z/E isomerization takes
place by 1,1-decarboboration, a process in which not only
As shown in Scheme 3, among the first products formed notoriously labile Sn–C but also C–C bonds are cleaved un-
in the intermolecular 1,1-carboboration reactions are the der mild conditions. This can be concluded from earlier ob-
alkene derivatives 4, unsuitable for further intramolecular servations by Hagelee and Köster using rather forcing con-
1,1-carboboration. Apparently, Z/E isomerization readily ditions [Scheme 4 (a)],[29] and later on from our work under
takes place to give zwitterionic intermediates 6 and finally much milder conditions [Scheme 4 (b,c)].[7,8,14]
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Scheme 4. Examples of organometallic-substituted alkenylboranes known to undergo 1,1-decarboboration.
The 1,1-decarboboration requires the formation of a bor-
ate-like intermediate by charge separation (A, B, or C,
Scheme 4) when the Me3Sn or Me3M groups move along
the C=C bond. The relative contributions of the respective
structures A, B, or C may be reflected in the 11B and 13C
chemical shifts and, in favorable cases, by structural param-
eters such as Sn–C bond lengths (Figure 7). Given the
shortcomings of the theoretical model (e.g., by using the
LAN[24] data set for the heavy atom Sn), the trends in the
experimental data are fairly well reproduced by the calcula-
tions. Particularly noteworthy are the strongly deshielded
13C(B-Cϵ) nuclei in 6(C6F5) (Figure 7 and Table 4), which
indicate significant contributions of structure A (Scheme 4).
Such a structure, similar to a β-metal-stabilized carbo-
cation,[30] can be considered as a prerequisite for the final
intramolecular 1,1-carboboration. This process is usually
fast for 6(Et) and 6(Ph), and becomes moderately slow in
6(C6F5) because the C6F5 groups on the boron lead to an
increase in the Lewis acidity of boron to favor a longer-
lived borate structure.
Figure 6. 79.47 MHz 29Si{1H} NMR (at 296 K, in C6D6; refosused
INEPT[11]) for the reaction of 3d with B(C6F5)3 leading at first
almost selectively to the zwitterionic intermediate 6d(C6F5). The
2
satellite signals for J(119Sn,29Si) are marked by asterisks.
Figure 7. Comparison of the experimental and calculated structural parameters and chemicals shifts δC and δB of some zwitterionic
intermediates 6a(C6F5), 8(C6F5),[9] 9(Et),[31] 10(Et),[32] and 11(Et).[33]
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The isolated and characterized intermediates 6(C6F5) are mechanism of 1,1-carboboration by the characterization of
the first examples in which a stannyl group is side-on coor- zwitterionic intermediates prior to stannole formation, both
dinated to the CϵC bond of an alkynylborate bearing a in the solid state and in solution.
Me3Si group. Previously, such intermediates with CϵC-
SiMe3 units were not observed at all, except when the cat-
Experimental Section
ionic stannyl group was stabilized by a coordinative Sn–N
bond, although direct structural evidence was missing.[16]
General: All preparative work, as well as handling of the samples,
Now we have succeeded in isolating and structurally char- was carried out observing precautions to exclude traces of air and
moisture. Carefully dried solvents and oven-dried glassware were
used throughout. Diphenyltin, di-n-butyltin, and di-n-octyltin di-
chlorides, trimethylsilylethyne, and triethylborane were commer-
cially available and used as received. 1,1-Dibromo-1-stannacy-
clohexane was prepared as described in the literature.[34] 1H, 11B,
13C, 19F, 29Si, and 119Sn NMR spectra were recorded in CDCl3,
C6D6, and [D8]toluene (concentration ca. 5–10%) with samples in
5 mm tubes at 23Ϯ1 °C by using Varian Inova 300 and 400 MHz
spectrometers; chemical shifts are given relative to Me4Si [δH
(CHCl3) = 7.24, δC (CDCl3) = 77.0, δH (C6HD5) = 7.15, δC (C6D6)
acterizing 6a(C6F5) (Figure 8). The unit B–C1–C33 is close
to linear [178.9(5)°], whereas the unit C1–C33–Si1 is mark-
edly bent [155.1(4)°], and both Sn–C1 and Sn–C33 dis-
tances are somewhat shorter than in the related derivative
8(C6F5).[9] All other bond lengths and angles of 6a(C6F5)
are in the expected ranges. The tetracoordinate boron atom
is typically at the center of a slightly distorted tetrahedron.
The surroundings of the tin atom deviate from trigonal
planarity (sum of the bond angles 347.3°) as a result of
bonding interactions with the CϵC bond. The sum of the = 128.0, δH (C6D5CHD2) = 2.03, δC (C6D5CD3) = 20.4, δSi
=
=
=
bond angles at tin is larger in both 8(C6F5) (354.4°)[9] and
9(Et) (351.1°),[31] which suggests stronger additional bond-
ing interactions in 6a(C6F5). The atoms B1, Sn1, C8, C9,
C1, and C33 form a plane within experimental error.
0 ppm], external Me4Sn [δSn
=
0 ppm for Ξ(119Sn)
0 ppm for Ξ(19F)
37.290665 MHz], external CFCl3 [δF
=
94.094003 MHz], and external BF3·OEt2 [δB = 0 ppm for Ξ(11B) =
32.083971 MHz]. Chemical shifts are given to Ϯ0.1 ppm for δC, δF,
δSi, and δSn, and to Ϯ0.4 ppm for δB; coupling constants are given
to Ϯ0.4 Hz for J(119Sn,13C). 13C NMR signals were assigned by
the usual 2D methods (1H-13C HSQC and HMBC[35]). 19F NMR
spectra were assigned by 19F-19F COSY experiments.[35] 29Si NMR
spectra were recorded by using the refocused INEPT pulse se-
quence,[11] based on 2J(29Si,1HMe) = 7 Hz. 119Sn NMR spectra were
recorded directly by single pulse methods or also by the refocused
2
INEPT pulse sequence[11] based on J(119Sn,1H) (50–100 Hz) after
optimizing the delay times in the pulse sequence. EI mass spectra
(70 eV) were recorded by using a Finnigan MAT 8500 spectrometer
with a direct inlet or solutions (1H, 11B, 12C, 19F, 28Si, 120Sn). IR
spectra were recorded with a Perkin–Elmer Spectrum 100 FTIR
spectrometer equipped with an ATR unit. Melting points were de-
termined by using a Büchi 510 melting point apparatus. Elemental
analyses (C, H) were performed with a Vario Elementar EL III
instrument. All quantum chemical calculations were carried out by
using the Gaussian 09 program package.[36]
Figure 8. Molecular structure of the zwitterionic intermediate
6a(C6F5) (ORTEP, ellipsoids drawn at the 40% probability level,
hydrogen aroms have been omitted for clarity). Selected bond
lengths [pm] and angles (°): Sn1–C22 213.3(5), Sn1–C26 215.1(5),
Sn1–C9 215.4(4), Sn1–C33 247.5(5), Sn1–C1 247.8(4), Si2–C9
188.5(5), Si1–C33 188.1(5), C1–C33 122.7(6), C1–B1 161.1(7), C2–
B1 166.3(7), B1–C8 163.8(7), B1–C16 165.5(7), C8–C9 135.6(6),
C8–C10 150.9(6), C22–Sn1–C26 101.26(18), C22–Sn1–C9
121.94(19), C26–Sn1–C9 124.07(18), C9–Sn1–C33 105.63(16), C1–
Typical Procedure for the Synthesis of Bis(trimethylsilylethynyl)tin
Compounds 3a–d: A freshly prepared suspension of trimethylsilyl-
ethynyllithium [30 mmol; from trimethylsilylethyne and nBuLi
(1.6 m) in hexane] was cooled to –78 °C, and the respective dior-
ganotin dihalide (15 mmol) was added in one portion. The mixture
was stirred, warmed to room temp., and heated at reflux for 10 min.
Insoluble materials were removed by filtration and volatile materi-
C33–Sn1 75.8(3), C9–Sn1–C1 79.16(16), C33–Sn1–C1 28.69(14), als were removed under vacuum (10–2 Torr). The colorless residues
C33–C1–Sn1 75.5(3), C33–C1–B1 178.9(5), C1–B1–C8 107.5(4),
C1–B1–C16 108.8(4), C1–B1–C2 103.3(4), C8–B1–C2 115.8(4),
C16–B1–C2 112.6(4), C8–C9–Si2 130.5(3), C8–C9–Sn1 115.5(3),
Si2–C9–Sn1 113.8(2), C1–C33–Si1 155.1(4).
consisted of the pure compounds 3a–d (yields 80–95%). Crystals
of 3a were grown from concentrated solutions in hexane.
3a: 1H NMR (CDCl3): δH = 0.16 (s, 18 H, SiMe3), 1.31 [t,
2J(119Sn,1H) = 67.7 Hz, 6.7 Hz, 4 H, CH2], 1.36–1.49 (m, 2 H,
CH2), 1.84 [m, 3J(119Sn,1H) = 105.5 Hz, 4 H, CH2] ppm. IR (ATR,
hexane): ν = 2013 [ν(CϵC)] cm–1. C H Si Sn (382.9): calcd. C
˜
15 28
2
47.01, H 7.37; found C 46.8, H 7.3.
Conclusions
3b: B.p. 83–87 °C/10–3 Torr, colorless oil. 1H NMR ([D8]toluene):
δH = 0.0 (s, 18 H, SiMe3), 0.74 (t, 7.3 Hz, 6 H, CH3), 0.89 [t, J =
7.9 Hz, 2J(119Sn,1H) = 60.9 Hz, 4 H, CH2-Sn], 1.18 (4 H, CH2),
Confirming previous findings, it has been shown that the
1,1-carboboration of bis(trimethylsilylethynyl)tin com-
pounds, irrespective of the other substituents on tin, pro-
vides a general route to stannoles bearing trimethylsilyl
groups at the 2 and 5 positions. Moreover, the use of
1.48 [m, 3J(119Sn,1H) = 77.0 Hz, 4 H] ppm. IR (ATR, hexane): ν =
˜
2089 [ν(CϵC)] cm–1. MS (EI): m/z (%) = 370 (100) [M – Bu]+, 314
(8) [Sn(CCSiMe3)2]+, 216 (12) [Sn(CCSiMe3)]+, 97 (7) [CCSiMe3]+,
B(C6F5)3 has helped to establish firm evidence for the 73 (7) [SiMe3]+.
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1
3c: 1H NMR (C6D6, 399.81 MHz, 296 K): δH = 0.14 (s, 18 H, 7a(C6F5): H NMR (C6D6): δH = –0.07 (s, 9 H, SiMe3), 0.01 (s, 9
2
SiMe3), 0.89 (t, 6.7 Hz, 6 H, Me), 1.07 [m, J(119Sn,1H) = 61.0 Hz,
H, SiMe3), 1.25–1.49 (m, 6 H, CH2), 1.77–1.93 (m, 4 H, CH2) ppm.
3
4 H, CH2], 1.18–1.38 (m, 16 H), 1.67 [m, J(119Sn,1H) = 78.1 Hz,
1
6b(C6F5): H NMR (C6D6): δH = –0.12 (s, 9 H, SiMe3), –0.05 (s, 9
4 H, CH ] ppm. IR (ATR, hexane): ν = 2084 [ν(CϵC)] cm–1. MS
˜
2
H, SiMe3), 0.9 (t, 6 H, CH3), 1.21–1.67 (m, 12 H, CH2) ppm.
(EI): m/z (%)
=
525 (2) [M
–
Me]+, 427 (100) [OctSn-
1
(CCSiMe3)2]+, 314 (8) [Sn(CCSiMe3)2]+, 217 (19) [Sn(CCSiMe3)]+,
97 (9) [CCSiMe3]+, 73 (8) [SiMe3]+, 43 (17) [SiMe]+.
7b(C6F5): H NMR (C6D6): δH = –0.09 (s, 9 H, SiMe3), –0.03 (s, 9
H, SiMe3), 0.95 (t, 6 H, CH3), 1.21–1.37 (m, 8 H, CH2), 1.56–1.68
(m, 4 H, CH2) ppm.
3d: 1H NMR (C6D6): δH = 0.10 (s, 18 H, SiMe3), 7.07 (m, 6 H,
m/p-C6H5), 7.70 [m, 3J(119Sn,1H) = 66.3 Hz, , 4 H, o-C6H5] ppm.
C22H28Si2Sn (466.9): calcd. C 56.55, H 6.04; found C 56.8, H 6.1.
1
6d(C6F5): H NMR (C6D6): δH = –0.12 (s, 9 H, SiMe3), 0.02 (s, 9
H, SiMe3), 7.30–7.48 (m, 6 H, Ph), 7.93 (m, 4 H, Ph) ppm.
1
7d(C6F5): H NMR (C6D6): δH = –0.14 (s, 9 H, SiMe3), 0.00 (s, 9
Typical Procedure for the Ethyl- and Phenylboration of Bis(tri-
methylsilylethynyl)tin Compounds to Yield 7a–d(Et, Ph): A stirred
solution of the alkynyltin compound (0.7 mmol) in hexane (20 mL)
was cooled to –78 °C and an equimolar amount of triethylborane
(or triphenylborane as a solution in toluene) was added through
a syringe. After 1 h, the yellowish mixture was warmed to room
temperature, and after 3 d (BEt3) or 1 h (BPh3), all volatile materi-
als were removed under vacuum (10–2 Torr). Monitoring the reac-
tion by 29Si NMR spectroscopy showed for BEt3 the presence of
intermediates of the type 4(Et) (see Figure 1), which rearranged
completely into the stannoles 7(Et). The stannoles were left as
light-yellow oils or a waxy solid 7d(Et) and 7d(Ph) (Ͼ97% pure
according to NMR spectroscopy).
H, SiMe3), 7.30–7.46 (m, 6 H, Ph), 7.91 (m, 4 H, Ph) ppm.
Crystal Structure Determinations of 3a and 6a(C6F5): Details perti-
nent to the crystal structure determinations are listed in Table 5.[37]
Crystals of appropriate size were selected (in perfluorinated oil at
tom temperature)[38] and the data collections were carried out at
133 K using a STOE IPDS II system equipped with an Oxford
Cryostream low-temperature unit. Structure solutions and refine-
ments were accomplished by using SIR97,[39] SHELXL-97,[40] and
WinGX.[41]
)
Table 5. Crystallographic data[a] of 1,1-bis(trimethylsilylethynyl)-1-
stannacyclohexane (3a) and the zwitterionic intermediate 6a(C6F5).
1
7a(Et): H NMR (CDCl3): δH = 0.10 (s, 9 H, SiMe3), 0.21 (s, 9 H,
Parameters
3a
6a (R = C6F5)
SiMe3), 1.36, 0.94 (qt, 10 H, BEt2), 2.20 1.01 (qt, 5 H, 4-Et), 1.31
(t, 4 H, CH2), 1.42–1.62 (m, 6 H, CH2), 1.82 (m, 4 H, CH2) ppm.
Formula
C15H28Si2Sn
383.24
Colorless plate
0.33ϫ0.32ϫ0.28 0.33ϫ0.07ϫ0.06
monoclinic
C33H28BF15Si2Sn
895.23
Colorless plate
M [g/mol]
Crystal shape
Crystal size [mm3]
Crystal system
Space group
Lattice parameters
a [pm]
b [pm]
c [pm]
α [°]
β [°]
1
7b(Et): H NMR ([D8]toluene): δH = 0.10 (s, 9 H, SiMe3), 0.20 (s,
9 H, SiMe3), 2.17 (q, 2 H, 4-CH2) ppm; no assignment of other 1H
NMR signals because of severe overlap.
triclinic
¯
P21/c
P1
1
7c(Et): H NMR (C6D6): δH = 0.19 (s, 9 H, SiMe3), 0.29 (s, 9 H,
1825.7(1)
906.8(1)
1238.4(1)
90
108.336(3)
90
1090.8(3)
1126.3(3)
1682.3(5)
93.078(20)
108.074(19)
109.428(19)
2
1.630
888
1.67–25.615
0.867
133(2)
SiMe3), 1.79 (q, 4 H, CH2, BEt2), 1.82 (m, 4 H, CH2), 2.08 (q, 2
1
H, 4-CH2) ppm; no assignment of other H NMR signals because
of severe overlap.
1
7d(Et): H NMR (CDCl3): δH = –0.22 (s, 9 H, SiMe3), –0.10 (s, 9
γ [°]
Z
H, SiMe3), 1.30, 0.87 (qt, 10 H, BEt2), 2.16, 0.93 (qt, 5 H, 4-Et),
7.10–7.21 (m, 6 H, Ph), 7.43 (m, 2 H, Ph). C28H43BSi2Sn (565.3):
calcd. C 59.49, H 7.67; found C 59.3, H 7.4.
4
ρcalcd. [g/cm3]
F(000)
1.308
784
1.73–26.08
1.422
133(2)
7042
1
θ range [°]
7a(Ph): H NMR (CDCl3): δH = 0.09 (s, 9 H, SiMe3), 0.11 (s, 9 H,
μ [mm–1]
SiMe3), 1.51–1.72 (m, 6 H, CH2), 2.02–2.12 (m, 4 H, CH2), 6.63–
6.91 (m, 3 H, Ph), 7.02–7.26 (m, 5 H, Ph), 7.70 (m, 2 H, Ph) ppm.
T [K]
Reflections collected
Independent reflec-
tions [IՆ2σ(I)]
23275
4299
1
3199
7b(Ph): H NMR (CDCl3): δH = –0.03 (s, 9 H, SiMe3), –0.01 (s, 9
H, SiMe3), 1.01 (t, 6 H, CH3), 1.38 (m, 4 H, CH2), 1.46 (m, 4 H,
CH2), 1.82 (m, 4 H, CH2), 6.55–6.81 (m. 3 H, Ph), 7.07–7.22 (m,
5 H, Ph), 7.66 (m, 2 H, Ph) ppm.
[b]
Absorption correction numerical
–
Refined parameters
wR2/R1 [IՆ2σ(I)]
Max./min. residual
electron density
[10–6 epm–3]
163
0.0162/0.0384
0.482/–0.229
469
0.0427/0.0760
1.047/–0.443
Typical Procedure for the 1,1-Carboboration of Bis(trimethylsilyl-
ethynyl)tin Compounds with B(C6F5)3: A stirred solution of the re-
spective bis(trimethylsilylethynyl)tin compound (0.4 mmol) in hex-
ane (15 mL) was cooled to –78 °C and a solution of B(C6F5)3 in
toluene (0.096 m, 4.2 mL) was added. The mixture was stirred for
30 min, warmed to room temp., and after 15 min volatile materials
were removed under vacuum (10–2 Torr). The residue was taken up
in C6D6, in which the intermediates 6(C6F5) are less soluble than
the stannoles 7(C6F5). This enabled us to isolate pure samples of
6(C6F5). Crystals of 6a(C6F5) were grown from concentrated solu-
tions in toluene at –26 °C. In solution at room temp., the deriva-
tives 6(C6F5) rearranged completely after several days into the
stannoles 7(C6F5).
[a] Diffractometer: STOE IPDS II, Mo-Kα, λ = 71.073 pm, graphite
monochromator. [b] Absorption corrections did not improve the
parameter set.
Acknowledgments
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG). The authors thank the late Prof. Roland Köster for samples
1
6a(C6F5): H NMR (C6D6): δH = –0.14 (s, 9 H, SiMe3), –0.02 (s, 9 of BPh3, and Prof. Gerhard Erker and his group for a sample of
H, SiMe3), 0.75–1.88 (m,10 H, CH2) ppm.
pure B(C6F5)3.
Eur. J. Inorg. Chem. 2014, 2103–2112
2111
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[24] a) P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270–283; b)
W. R. Wadt, P. J. Hay, J. Chem. Phys. 1985, 82, 284–298; c) P. J.
Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299–310.
[25] K. Wolinski, J. F. Hinton, P. J. Pulay, J. Am. Chem. Soc. 1990,
112, 8251–8260.
[26] H. Nöth, B. Wrackmeyer, Nuclear Magnetic Resonance Spec-
troscopy of Boron Compounds, in: NMR - Basic Principles and
Progress (Eds.: P. Diehl, E. Fluck, R. Kosfeld), Springer,
Berlin, 1978, vol. 14.
[27] a) W. E. Piers, Adv. Organomet. Chem. 2005, 52, 1–76; b) T.
Beringhelli, D. Donghi, D. Maggioni, G. D’Alfonso, Coord.
Chem. Rev. 2008, 252, 2292–2313; c) J. Sandström, Dynamic
NMR Spectroscopy, Academic Press, New York, 1982, p. 95–
112.
[28] a) The authors thank Dr. J. Ugolotti, Institute of Organic
Chemistry, University of Münster, Germany for performing
these experiments; b) J. Ugolotti, G. Kehr, R. Fröhlich, G.
Erker, Chem. Commun. 2010, 46, 3016–3018.
[1]
a) C. Booker, X. Wang, S. Haroun, J. Zhou, M. Jennings, B. L.
Pagenkopf, Z. Ding, Angew. Chem. Int. Ed. 2008, 47, 7731–
7735; Angew. Chem. 2008, 120, 7845; b) L. Sambri, A. Baschi-
eri, Mini-Rev. Org. Chem. 2013, 10, 254–267.
A. Steffen, R. M. Ward, W. D. Jones, T. B. Marder, Coord.
Chem. Rev. 2010, 254, 1950–1976.
a) M. Saito, M. Yoshioka, Coord. Chem. Rev. 2005, 249, 765–
780; b) K. Tamao, S. Yamaguchi, M. Shiro, J. Am. Chem. Soc.
1994, 116, 11715–11722; c) V. Y. Lee, A. Sekiguchi, Inorg.
Chem. 2011, 50, 12303–12314.
B. Wrackmeyer, O. L. Tok, Comprehensive Heterocyclic Chem-
istry III (Eds.: A. R. Katritzky, C. A. Ramsden, E. F. V.
Scriven, R. J. K. Taylor), Elsevier, Oxford, UK, 2008, p. 1181–
1223.
L. Killian, B. Wrackmeyer, J. Organomet. Chem. 1977, 132,
213–221.
B. Wrackmeyer, J. Organomet. Chem. 1989, 364, 331–342.
a) B. Wrackmeyer, Revs. Silicon Germanium Tin Lead Compd.
1982, 6, 75–148; b) B. Wrackmeyer, Coord. Chem. Rev. 1995,
145, 125–156.
B. Wrackmeyer, Heteroat. Chem. 2006, 17, 188–206.
B. Wrackmeyer, P. Thoma, S. Marx, G. Glatz, R. Kempe, Z.
Anorg. Allg. Chem. 2013, 639, 1205–1213.
[2]
[3]
[4]
[5]
[29] L. A. Hagelee, R. Köster, Synth. React. Inorg. Met.-Org,.
Chem. 1977, 7, 53–67.
[30] H. U. Siehl, F. P. Kaufmann, Y. Apeloig, V. Braude, D. Danov-
ich, A. Berndt, N. Stammatis, Angew. Chem. Int. Ed. Engl.
1991, 30, 1479–1481; Angew. Chem. 1991, 103, 1546.
[31] B. Wrackmeyer, S. Kundler, R. Boese, Chem. Ber. 1993, 126,
1361–1370.
[6]
[7]
[8]
[9]
[32] B. Wrackmeyer, S. Kundler, W. Milius, R. Boese, Chem. Ber.
1994, 127, 333–342.
[10]
[11]
S. Lamande-Langle, M. Abarbri, J. Thibonnet, A. Duchene, J.
Organomet. Chem. 2009, 694, 2368–2374.
a) G. A. Morris, R. Freeman, J. Am. Chem. Soc. 1979, 101,
760–761; b) G. A. Morris, J. Am. Chem. Soc. 1980, 102, 428–
429.
[33] B. Wrackmeyer, G. Kehr, R. Boese, Angew. Chem. Int. Ed. Engl.
1991, 30, 1370–1372; Angew. Chem. 1991, 103, 1374.
[34] V. I. Shiryaev, E. M. Stepina, V. P. Kochergin, T. S. Kuptsova,
V. F. Mironov, Zh. Obshch. Khim. 1978, 48, 2627–2628.
[35] S. Braun, H.-O. Kalinowski, S. Berger, 150 and More Basic
NMR Experiments: A Practical Course - Second Expanded Edi-
tion, Verlag Chemie, Weinheim, Germany, 1999.
[12] B. Wrackmeyer, B. H. Kenner-Hofmann, W. Milius, P. Thoma,
O. L. Tok, M. Herberhold, Eur. J. Inorg. Chem. 2006, 101–108.
[13] B. Wrackmeyer, P. Thoma, R. Kempe, Eur. J. Inorg. Chem.
2009, 1469–1476.
[14] a) B. Wrackmeyer, Z. Naturforsch. B 1978, 33, 385–389; b) B.
Wrackmeyer, C. Bihlmayer, M. Schilling, Chem. Ber. 1983, 116,
3182–3192.
[36] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li,
H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-
nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-
gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M.
Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Starov-
erov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N.
Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Strat-
mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D.
Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski,
D. J. Fox, GAUSSIAN 09, revision A.02, Gaussian, Inc., Wall-
ingford, CT, 2010.
[15] B. Wrackmeyer, G. Kehr, R. Boese, Chem. Ber. 1992, 125, 643–
650.
[16] B. Wrackmeyer, K. Horchler von Locquenghien, S. Kundler, J.
Organomet. Chem. 1995, 503, 289–295.
[17] B. Wrackmeyer, Polyhedron 1986, 5, 1709–1721.
[18] B. Wrackmeyer, Prog. Nucl. Magn. Reson. Spectrosc. 1979, 12,
227–259.
[19] a) J. Chunfang, O. Blacque, H. Berke, Organometallics 2010,
29, 125–133; b) J. Yu, G. Kehr, C. G. Daniliuc, G. Erker, Inorg.
Chem. 2013, 52, 11661–11668; c) C. Chen, G. Kehr, R.
Fröhlich, G. Erker, J. Am. Chem. Soc. 2010, 132, 13594–13595;
d) C. Chen, T. Voss, R. Fröhlich, G. Kehr, G. Erker, Org. Lett.
2011, 13, 62–65; e) G. Fang, G. Kehr, G. D. Constantin, G.
Erker, J. Am. Chem. Soc. 2014, 136, 68–71.
[37] CCDC-975044 [for 6a(C6F5) at –133 K] and -975045 (for 3a at
133 K). contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[20] G. Dierker, J. Ugolotti, G. Kehr, R. Fröhlich, G. Erker, Adv.
Synth. Catal. 2009, 351, 1080–1088.
[21] R. Köster, G. Seidel, J. Süß, B. Wrackmeyer, Chem. Ber. 1993,
126, 1107–1114.
[22] B. Wrackmeyer, Annu. Rep. NMR Spectrosc. 2006, 57, 1–49.
[23] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) C. Lee,
W. Yang, R. G. Parr, Phys. Rev. B 1988, 41, 785–789; c) P. J.
Stevens, F. J. Devlin, C. F. Chablowski, M. J. Frisch, J. Phys.
Chem. 1994, 98, 11623–11627; d) D. McLean, D. G. S. Chan-
dler, J. Chem. Phys. 1980, 72, 5639–5648; e) R. Krishnan, J. S.
Blinkley, R. Seeger, J. A. Pople, J. Chem. Phys. 1980, 72, 650–
654.
[38] T. Kottke, D. Stalke, J. Appl. Crystallogr. 1993, 26, 615–619.
[39] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Crystallogr. 1999, 32, 115–119.
[40] G. M. Sheldrick, SHELX-97, Program for Crystal Structure
Analysis, rel. 97-2, University of Göttingen, Germany, 1998.
[41] L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837–838.
Received: January 9, 2014
Published Online: March 17, 2014
Eur. J. Inorg. Chem. 2014, 2103–2112
2112
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim