Reaction of bis(alkynyl)silanes with tris(pentafluorophenyl)-borane: Synthesis of bulky silole derivatives by means of 1,1-carboboration under mild reaction conditions

Article abstract of DOI:10.1002/adsc.200900029

The strong Lewis acid tris(pentafluorophe-nyl)borane [B(C₆F ₅)₃] reacts rapidly with dimethyl-bis(phenylethynyl)silane (1c) at room temperature in toluene by shift of a pentafluorophenyl (C ₆F₅) group

Full text of DOI:10.1002/adsc.200900029

FULL PAPERS
DOI: 10.1002/adsc.200900029
Reaction of Bis(alkynyl)silanes with Tris(pentafluorophenyl)-
G
A
1,1-Carboboration under Mild Reaction Conditions
Gereon Dierker,a Juri Ugolotti,a Gerald Kehr,a Roland Frçhlich,a,b
and Gerhard Erkera,*
a
Organisch-Chemisches Institut der Universitꢀt Mꢁnster, Corrensstrasse 40, 48149 Mꢁnster, Germany
Fax : (+49)-251-833-6503; e-mail: erker@uni-muenster.de
Address for correspondence concerning the X-ray crystal structure analyses.
b
Received: January 14, 2009; Revised: March 18, 2009; Published online: April 30, 2009
Dedicated to Professor Armin de Meijere on the occasion of his 70th birthday.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200900029.
Abstract: The strong Lewis acid tris(pentafluorophe-
nyl)borane [B(C6F5)3] reacts rapidly with dimethyl- borane gave the corresponding boryl-substituted
ACHTUNGTRENNUNGbis(phenylethynyl)silane (1c) at room temperature in silole derivative (7d) featuring six bulky substituents
ACHTUNGTRENyNUGN l)diphenylsilane (1d) with tris(pentafluorophenyl)-
ACHTUNGTRENNUNG
toluene by shift of a pentafluorophenyl (C6F5) group attached at the central heterocyclic framework. Both
and formation of a new carbon-bis(pentafluorophe- the starting materials (1c, 1d) and the products (7c,
ꢀ
nyl)boron linkage [C B
ACHTUNGTRENNUNG
carboboration
bis(pentafluoro
reactions
phenyl)boryl/3-pentafluorophenyl-
substituted 1,1-dimethyl-2,5-diphenylsilole derivative Keywords: boranes; 1,1-carboboration; Lewis acids;
7c. The analogous reaction of bis(trimethylsilylethyn- siloles
Introduction
an intramolecular ring closure of a bis-radical anion
intermediate (2) (see Scheme 1). This route has exten-
The synthetic chemistry of siloles has found increased sively been applied for the preparation of novel
interest lately.[1,2] This is mostly due to their use in silole-based electronic materials.[6,7a,b,d–f,h]
modern materials chemistry. Suitably substituted
In this context, boron- and silicon-containing sys-
silole derivatives have found extensive use due to tems have become of interest, and easy accesses to
their photoluminescent properties.[1b,c,3–7] Some deriva- specifically functionalized boryl-substituted siloles or
tives were used as sensor materials.[8]
similar compounds are becoming increasingly impor-
Early synthetic entries to siloles[9] include salt meta- tant.[17] Wrackmeyer et al. have developed and de-
thesis routes, e.g., by reacting substituted 1,4-dilithio- scribed a fascinating one-pot procedure for the prepa-
butadiene reagents with R2SiCl2 substrates.[10,11] A re- ration of boryl-substituted silole derivatives (7b) by
lated route was used more recently to prepare lithio- treatment of a bis
ACHTUNGTRENNUNG
ACHTUNGTRENN(UNG alkynyl)silane (1b) with, for exam-
siloles.[12] Other work reported in the last 15 years ple, triethylborane.[1a,2a,18,19] The unique reaction se-
makes use of the ready formation of the group 4 met- quence involves alkynyl abstraction/1,1-carboboration
allacyclopentadienes[13] and related complexes[14] fol- followed by a 1,1-alkenylboration step to directly lead
lowed by direct or indirect transmetallation from tita- to the boryl-functionalized silole derivative (see
nium or zirconium to silicon.[15]
Scheme 1).[20] Unfortunately, the reaction with simple
Tamao et al. developed an ingenious method of alkylboranes often requires elevated temperatures
silole formation from bis(alkynyl)silanes (1a) by treat- (ca. 1008C).
ment with Li/naphthalene.[16] The formation of the
When more reactive boranes were used (e.g., trial-
silole products (3) probably takes place by means of lylborane, 1-boraadamantane) the reaction conditions
AHCTUNGTRENNUNG
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Reaction of BisACHTUNGTRENNUNG(alkynyl)silanes with Tris(pentafluorophenyl)borane
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Scheme 1. (i): 1,1-ethylboration, (ii): 1,1-alkenylboration.
of the 1,1-organoboration reactions were milder but the phenylethynylsodium reagent in tetrahydrofuran.
sometimes the formation of side products took After filtering off the precipitated sodium chloride,
place.[21] We have now found that this general reaction the product (1c) was obtained as a colorless solid in
sequence can very favourably be used for the synthe- ca. 40% yield. The more bulky bis(trimethylsilyl-
sis of substituted siloles containing a combination of
C6F5 and B(C6F5)2 groups that are probably of great pared analogously by treatment of trimethylsilyl-
yl)diphenylsilane[23] (1d, see Scheme 2) was pre-
ACHUTGTNRENNUGethynACHTUTGNRENNUGN
ACHTUNGTRENNUNG
advantage in the respective areas of silole-derived ethynyllithium with Ph2SiCl2 (8d). The product (1d)
materials science. We describe two representative ex- was obtained as an oil which solidified upon stand-
amples in this article.
ing at ambient temperature. It was isolated in 77%
yield.
The identity of the known compounds 1c and 1d
was confirmed spectroscopically. In addition, the two
compounds were characterized by X-ray diffraction.
Results and Discussion
Following procedures reported in the literature, we Single crystals of both compounds suitable for the X-
have prepared the known dimethylbis(phenylethyn- ray crystal structure analysis were obtained from di-
ACHTUNGTRENNUNG
yl)silane (1c)[22] by treatment of Me2SiCl2 (8c) with ethyl ether. Compound 1c features a pseudotetrahe-
Scheme 2.
Adv. Synth. Catal. 2009, 351, 1080 – 1088
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Gereon Dierker et al.
FULL PAPERS
Figure 2. Molecular structure of 1d. Selected bond lengths
ꢀ
ꢀ
(ꢃ) and angles (8): Si1 C21 1.831(2), Si1 C31 1.831(2),
C21 C22 1.208(2), C31 C32 1.203(2), Si2 C22 1.846(2),
Figure 1. A view of the bis(phenylethynyl)dimethylsilane
compound 1c. Selected bond lengths (ꢃ) and angles (8): Si
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Si3 C32 1.847(2), Si1 C11A 1.867(2), Si1 C11B 1.870(2),
C21 Si1 C31 108.0(1), C22 C21 Si1 176.6(2), C21 C22
Si2 177.2(2).
ꢀ
ꢀ
ꢀ
C1 1.843(2), Si C2 1.848(2), Si C11 1.830(2), Si C21
1.835(2), C11 C12 1.201(3), C21 C22 1.204(2), C11 Si C21
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ
ꢀ
ꢀ
106.4(1), C1 Si C2 112.4(1), C12 C11 Si 177.7(2), C11
ꢀ
C12 C13 177.7(2).
Silole formation also takes place readily upon treat-
ment of the sterically more congested bis(trimethyl-
dral coordination geometry around the central silicon
ACHTUNGTRENNUNG
ꢀ
atom (see Figure 1). The Si C
G
N
ꢀ
slightly longer than the Si C(sp) bond lengths, as ex- temperature. After work-up and crystallization from
ꢀ ꢀ
ꢀ
pected. The C1 Si C2 angle between the methyl Si pentane the B
G
ꢀ ꢀ
vectors is markedly larger than the C11 Si C21 angle 7d was isolated in 35% yield (see Scheme 2).
of the acetylide substituents at silicon. Compound 1c
exhibits short C C bonds. The acetylide units are troscopically and by X-ray diffraction (single crystals
nearly linear, as expected. The planes of the terminal from pentane). The silole 7c shows a 29Si NMR signal
phenyl substituents form an angle of 92.68. The at d=+9.8, which occurs downfield from the corre-
phenyl groups are located close to in-plane with their sponding 29Si NMR resonance of the starting material
Both products 7c and 7d were characterized spec-
ꢁ
respective Si CH3 vectors [dihedral angles C1
1c (d=ꢀ39.4).[26] It features two sets of o-, p- and m-
ꢀ
ꢀ
Si···C23 C28: 26.68, C2 Si···C13 C14: ꢀ10.48)].
C6F5 19F NMR signals in a 2:1 ratio, namely of the
ꢀ
ꢀ
ꢀ
Compound 1d has a very similar structure (see Lewis acidic -BACHTUNGTRENNUNG
ꢀ
Figure 2). The Si C(sp) s-bond lengths of 1d are rather large DdACHTUNGTRENNUNG
ꢀ
ꢀ
responding C21 Si1 C31 angle amounts to 108.0(1)8. signals of the four “quarternary” ring carbon atoms
ꢁ
The C C triple bonds again are short, and the termi- C2 to C5 were located at d=152.3, 136.7, 161.9 (adja-
ꢀ
nal C(sp) Si bonds are slightly longer than the inter- cent to B), and 165.5. The UV/Vis spectrum of com-
ꢀ ꢁ ꢀ
nal ones. The Si C C Si units are nearly linear. The pound 7c shows absorptions at lmax (log e)=305
situation around the central silicon atom Si1 is rather (4.41) and 231 (4.27) nm and a corresponding feature
2
ꢀ
crowded. This leads to rather long Si C(sp , aryl) at lmax =390 nm in the emission spectrum. The more
bond lengths. The angle between the phenyl planes in bulky compound 7d features overlapping UV/Vis ab-
1d amounts to 50.68.
sorptions at lmax (log e)=234 (4.73), 262 (4.47) and
The reaction of compound 1c with one molar equiv- 274 (4.50) nm and emission bands at lmax =402 and
alent of tris(pentafluorophenyl)borane (9)[24] was per- 390 nm. The absorption data are similar to results ob-
formed in toluene at room temperature. In contrast to served previously in siloles carrying perfluorinated
the reactions of bisACTHNUTRGNEUNG
(alkynyl)silanes with the much less aryl groups in positions 2 and 5,[4c] whereas the emis-
Lewis acidic trialkylboranes (see above) rapid silole sion spectra show a shift to the ultraviolet region
formation takes place with the strong Lewis acid B- when compared to related systems.[6,7] Compound 7d
[25]
G
at ambient conditions. After work-up and shows three characteristic 29Si NMR resonances,
crystallization from pentane the product 7c was isolat- namely that of the ring silicon atom at d=+17.6 and
ed in 36% yield.
a pair of resonances at d=ꢀ9.0/ꢀ8.3 attributed to the
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Reaction of BisACHTUNGTRENNUNG(alkynyl)silanes with Tris(pentafluorophenyl)borane
FULL PAPERS
Figure 3. 19F NMR spectra (470 MHz, C7D8, CFCl3) of 7d at various temperatures.
chemically inequivalent SiMe3 substituents. The
13C NMR signals of the ring carbon atoms C2–C5 of
7d occur at d=154.9, 150.2, 176.8 and 161.5. At 298 K
there is one set of broad 19F NMR resonances of the
C6F5 substituent [d=ꢀ138.7 (2F, o), ꢀ154.3 (1F, p),
ꢀ161.9 (2F, m)], as well as another for the B
ACHTNUGRTEN(NGNU C6F5)2
group [d=ꢀ126.0 (4F, o), d=ꢀ142.8 (2F, p), d=
ꢀ160.7 (4F, m)]. Due to the steric congestion caused
by the presence of bulky vicinal SiMe3 and BACHTNURGTNEUNG(C6F5)2
substituents at the planar five-membered framework
the silole 7d features hindered rotation around the
[28]
¼
ꢀ1
ꢀ
ꢀ
C4 B vector
ipsoA
the
[DG ꢂ11.3ꢃ0.2 kcalmol ], the B
¼
C
(C6F5) vectors [DG ꢂ11.5ꢃ0.2 kcalmolꢀ1] and
¼
ꢀ
C3 CipsoA
(C6F5)
vector
[DG ꢂ11.4ꢃ
0.2 kcalmolꢀ1]. Consequently, pairwise decoalescence
of all o- and m-F 19F NMR signals, as well as the B-
ACHTUNGTRENNUNG
(C6F5)2 p-F 19F NMR signals was observed upon moni-
toring the 19F NMR spectrum of 7d in toluene-d8 at
213 K (see Figure 3, for details see the Supporting In-
formation).
The X-ray crystal structure analysis of compound
7c (see Figure 4) has revealed the presence of a
planar five-membered silole framework with an alter-
nating unsaturated C4 section. The Me2Si unit com-
Figure 4. Molecular geometry of compound 7c. Selected
bond lengths (ꢃ) and angles (8): C2 C3 1.353(3), C3 C4
ꢀ
ꢀ
ꢀ
ꢀ
pletes the silole framework. The C11A Si1 C11B
angle of the germinal dimethylsilylene unit is much
ꢀ
ꢀ
ꢀ
1.508(3), C4 C5 1.358(3), Si C2 1.888(3), Si C5 1.874(2),
Si C11A 1.866(3), Si C11B 1.851(3), C3 C31 1.497(3), C4
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
larger and the respective Si CH3 bonds are slightly
ꢀ
ꢀ
ꢀ
ꢀ
B1 1.554(4), C2 Si1 C5 91.5(1), C11A Si1 C11B 111.5(2),
shorter compared to the endocyclic Si(C2) unit. The
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
B1 C4 C3 122.6(2), C4 C3 C31 118.2(2), C4 B1 C41A
ꢀ
ꢀ
ꢀ
ꢀ
phenyl substituents attached at carbon atoms C2 and 122.6(2), C4 B1 C41B 116.8(2), C41A B1 C41B 120.6(2).
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Gereon Dierker et al.
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Conclusions
Our new variant of the “Wrackmeyer reaction”[1a,c,2a,18]
can apparently be used to construct highly substituted
and functionalized boryl-silole systems under mild re-
action conditions. Even the formation of the highly
sterically crowded derivative 7d proved to be unpro-
blematic. It is remarkable how easily these reactions
proceed to form products with an accumulation of
very bulky substituents all around the periphery of
the central five-membered silole framework.
We assume that the products 7c and 7d are formed
by means of a reaction pathway as it is schematically
depicted in Scheme 3. The rate enhancement upon
employing BACHTNUGTRNE(UNG C6F5)3 instead of, for example, Et3B may
be due to the markedly increased Lewis acidity of this
boron reagent,[25,29] resulting in a lowering of the bar-
rier of acetylide abstraction in the initial 1,1-carbobo-
ration step – actually an intermediate (12, see
Scheme 4) conceptually related to 4c/4d was recently
isolated by us from the reaction of a bis(acetylide)zir-
Figure 5. A projection of the molecular structure of com-
pound 7d in the crystal. Selected bond lengths (ꢃ) and
angles (8): C2 C3 1.345(3), C3 C4 1.515(3), C4 C5
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1.368(3), Si1 C2 1.879(2), Si1 C5 1.891(2), Si1 C11A
1.874(2), Si1 C11B 1.871(2), Si2 C2 1.885(2), Si5 C5
ꢀ
ꢀ
ꢀ
conocene complex (11) with HBACHTNUGRTNEUNG
(C6F5)2 (10).[30]
ꢀ
ꢀ
ꢀ
ꢀ
1.879(2), C3 C31 1.506(3), C4 B1 1.561(3), C2 Si1 C5
ꢀ
ꢀ
ꢀ
ꢀ
94.6(1), C11A Si1 C11B 112.4(1), C3 C2 Si2 128.6(2),
The X-ray crystal structure analyses and the NMR
spectra have revealed that there is no significant C-
ꢀ
ꢀ
C4 C5 Si5 128.5(1).
2
ꢀ
G
ent from remotely related five-membered group 4
metallacyclic compounds (e.g., 15, see Scheme 4) that
C5 are found markedly rotated from the central SiC4 were recently prepared by similar reaction sequen-
ring plane [dihedral angles: C3 C2 C21 C22 ces.[31,32]
ꢀ147.3(3)8, C4 C5 C51 C52: 57.2(4)8]. A single
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C6F5 substituent is attached at C3. It is rotated mark-
edly relative to the central silole plane [q C4 C3
ACHTNUGNERT(NGNU C6F5)2 group is
attached at the adjacent ring carbon atom C4 [dihe-
dral angle C31 C3 C4 B1: 11.9(3)8]. The electron-
deficient boron center is planar-tricoordinate (sum of
ꢀ
ꢀ
ꢀ
C31 C32: ꢀ122.9(2)8]. The bulky B
ꢀ
ꢀ
ꢀ
bond angles at boron: 360.08). The B
ACHTNUGTNER(NGNU C6F5)2 unit is ro-
tated markedly relative to the central silole plane [q
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C5 C4 B1 C41A:
ꢀ128.7(2)8] and the individual C6F5 groups are found
52.3(4)8,
C5 C4 B1 C41B:
ꢀ
ꢀ
ꢀ
in a propeller-like conformation [q C4 B1 C41A
C42A: 31.7(4)8, C4 B1 C41B C42B: 40.9(3)8].
In the crystal, compound 7d features a rather
crowded periphery of substituents around the central
five-membered ring core (see Figure 5). The frame-
work again shows bond alternation among the
carbon-carbon linkages, which is supplemented by a
pair of long Si1 C2/C5 endocyclic bonds. The exocy-
clic Si1 C
steric bulk appears in rather large C3 C2 Si2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(aryl) bonds are only slightly shorter. The
ꢀ
ꢀ
ꢀ
ꢀ
[128.6(2)8] and C4 C5 Si5 [128.5(1)8] bond angles.
The single C6F5 substituent at C3 is rotated toward a
perpendicular orientation to the central silole ring [q
ꢀ
ꢀ
ꢀ
C2 C3 C31 C32: ꢀ97.2(2)8] as is the coordination
plane of the B(C6F5)2 substituent at C4 [sum of bond
angles at B1: 359.8(2)8, q C5 C4 B1 C41A: 70.0(3)8,
ACHTUNGTRENNUNG
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C5 C4 B1 C41B: ꢀ115.7(2)8].
Scheme 3.
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Reaction of BisACHTUNGTRENNUNG(alkynyl)silanes with Tris(pentafluorophenyl)borane
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tion: GTC Waters Micromass (Manchester, UK). UV/Vis:
UV double-ray spectrometer Uvikon 923 (Kontron Instru-
ments, Zꢁrich, Switzerland), using SUPRASIL Quarz glass
(200–2500 nm). Fluorescence spectra: spectrofluorometer
AMINCO-Bowman Series 2 (AB2) (Thermo Fischer Scien-
tific Inc., Waltham, USA), with excitation at 350 nm, using
[23b]
SUPRASIL Quarz glass cuvette (200–2500 nm). BACHTNUTRGNEUNG(C6F5)3
was prepared according to procedures reported in the litera-
ture (caution: the intermediate involved is explosive). X-ray
crystal structure analyses: Data sets were collected with a
Nonius KappaCCD diffractometer. Programs used: data col-
lection COLLECT (Nonius B.V., 1998), data reduction
Denzo-SMN,[33] absorption correction Denzo,[34] structure so-
lution SHELXS-97,[35] structure refinement SHELXL-97,[36]
graphics SCHAKAL (E. Keller, Univ. Freiburg, 1997).
CCDC 715065, 715066, 715067 and 715068 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 [or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (in-
ternat.) +44-(1223)-336-033, E-mail: deposit@ccdc.cam.
ac.uk].
Dimethylbis(phenylethynyl)silane[22] (1c) and
Bis(trimethylsilylethynyl)diphenylsilane[23] (1d)
Scheme 4.
These compounds were prepared analogously as described
in the literature (for details see the Supporting Informa-
tion).
The use of boranes of enhanced Lewis acidities
seems to help carrying out the synthetic sequences
under mild conditions that include variants of the un-
usual 1,1-carboboration reaction. It might be worth-
while to investigate advanced variations of this inter-
esting reaction type for the preparation of new
heteroACHTUNGTRENNUNGcyclic systems, for example of interest for appli-
cations in materials chemistry on a broader scale.
X-ray crystal structure analysis of 1c (single crystals were
obtained from a diethyl ether solution): formula C18H16Si,
M=260.40, colourless crystal 0.55ꢄ0.15ꢄ0.10 mm, a=
14.709(1), b=11.454(1), c=18.613(1) ꢃ, V=3135.9(4) ꢃ3,
1calcd. =1.103 gcmꢀ3, m=1.173 mmꢀ1, empirical absorption
correction (0.565ꢄTꢄ0.892), Z=8, orthorhombic, space
group Pbca (No. 61), l=1.54178 ꢃ, T=223 K, w and f
scans, 12740 reflections collected (ꢃh, ꢃk, ꢃl), [(sinq)/l]=
0.58 ꢃꢀ1, 2475 independent (Rint =0.041) and 2179 observed
reflections [Iꢅ2 s(I)], 174 refined parameters, R=0.040,
wR2 =0.109, max. residual electron density 0.22 (ꢀ0.19)
eꢃꢀ3, hydrogen atoms calculated and refined as riding
atoms.
X-ray crystal structure analysis of 1d (single crystals were
obtained from a diethyl ether solution): formula C22H28Si3,
M=376.71, colourless crystal 0.50ꢄ0.45ꢄ0.40 mm, a=
18.706(1), b=10.077(1), c=12.444(1) ꢃ, b=90.78(1)8, V=
2345.5(3) ꢃ3, 1calcd. =1.067 gcmꢀ3, m=1.860 mmꢀ1, empirical
absorption correction (0.457ꢄTꢄ0.523), Z=4, monoclinic,
space group P21/c (No. 14), l=1.54178 ꢃ, T=293 K, w and
f scans, 19157 reflections collected (ꢃh, ꢃk, ꢃl), [(sinq)/
l]=0.60 ꢃꢀ1, 4111 independent (Rint =0.035) and 3823 ob-
served reflections [Iꢅ2 s(I)], 232 refined parameters, R=
0.040, wR2 =0.109, max. residual electron density 0.26
(ꢀ0.20) eꢃꢀ3, hydrogen atoms calculated and refined as
riding atoms.
Experimental Section
In all preparations, the air- and moisture-sensitive com-
pounds were synthesized and handled under an argon at-
mosphere using standard glove-box and Schlenk techniques.
Anhydrous solvents were used in all the preparations. The
solvents were passed through alumina columns under an
argon atmosphere, the deuterated solvents were distilled
from drying agents and stored under argon. For the NMR
experiments, C6D6 (room temperature measurements) and
toluene-d8 (variable temperature) were used. The physical
characterization of the products was performed using the
following instruments: NMR: Bruker AC 200 P-FT (11B:
64 MHz), Bruker ARX 300 (11B: 96 MHz), Varian Inova
500 (1H: 500 MHz; 13C: 126 MHz; 11B: 161 MHz; 19F:
470 MHz; 29Si: 99 MHz), Varian Unity Plus 600 (1H:
1
600 MHz; 13C: 151 MHz; 19F: 564). References: TMS for H,
13C and 29Si NMR, BF3·OEt2 for 11B NMR, CFCl3 for
19F NMR. Most NMR assignments were supported by addi-
tional 2D experiments. IR spectra: Varian 3100 FT-IR (EX-
CALIBUR Series) spectrometer. Elemental analyses: Foss-
Heraeus CHN-O-Rapid instrument. Exact mass determina-
4-[Bis(pentafluorophenyl)boryl]-3-pentafluorophenyl-
1,1-dimethyl-2,5-diphenylsilole (7c).
Dimethylbis(phenylethynyl)silane (1c) (100 mg, 0.384 mmol)
and tris(pentafluorophenyl)borane (9) (197 mg, 0.384 mmol)
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Gereon Dierker et al.
FULL PAPERS
were weighed in an argon-filled glove-box and put into a
100-mL Schlenk flask under argon. Toluene (70 mL) was
added to the flask at room temperature by cannula and the
resulting bright yellow solution was stirred overnight. The
volatiles were removed under vacuum, leaving a yellow oily
product. The product was crystallised at ꢀ308C from pen-
tane (2 mL) (107 mg, 36%). Crystals suitable for single-crys-
tal X-ray diffraction were obtained in a NMR tube by slow
Ph), 7.22 (m, 4H, m-Ph), 7.19 (m, 2H, p-Ph), ꢀ0.25 (s,
2
2JSi,H =6.5 Hz, 9H, 5-SiMe3), ꢀ0.30 (s, 9H, JSi,H =6.6 Hz, 2-
SiMe3); 13C{1H} NMR (126 MHz, C6D6, 298 K): d=176.8
1
(C4), 161.5 (C5), 154.9 (C2), 150.2 (C3), 148.9 (dm, JF,C
1
ꢂ254 Hz, 4ꢄCF), 145.1 (dm, JF,C ꢂ260 Hz, 2ꢄCF), 143.6
1
1
(dm, JF,C ꢂ245 Hz, 2ꢄCF), 141.0 (dm, JF,C ꢂ256 Hz, CF),
1
137.7 (dm, JF,C ꢂ254 Hz, 6ꢄCF) (C6F5), 135.7 (o-Ph), 131.0
(p-Ph), 130.6 (i-Ph), 128.8 (m-Ph), 118.7 (i-C6F5), 113.9 (br,
1
B
evaporation of C6D6. H NMR (500 MHz, C6D6, 298 K): d=
i-C6F5 ), 1.5 [1JSi,C =52.3 Hz, 5-Si
(CH3)3], ꢀ0.3 [1JSi,C
=
7.00 (m, 4-H, o,m-Ph2), 6.97 (m, 2H, o-Ph5), 6.93 (m, 1H, p-
Ph2), 6.85 (m, 2H, m-Ph5), 6.74 (m, 1H, p-Ph5), 0.22 (s,
2JSi,H =7.0 Hz, 6H, SiMe2); 13C{1H} NMR (126 MHz, C6D6,
298 K): d=165.5 (C5), 161.9 (br, C4), 152.3 (C2), 147.9 (dm,
52.7 Hz, 2-SiACTHNGUTERNNUG
(CH3)3]; 29Si{1H} NMR (99 MHz, C6D6, 298 K):
d=17.6 (SiPh2), ꢀ8.3 (2-Si), ꢀ9.0 (5-Si) [tentative assign-
ment for positions 2 and 5]; 19F NMR (470 MHz, C7D8,
298 K, CFCl3): d=ꢀ126.0 (br, 4F, o-F), ꢀ142.8 (br, 2F, p-F),
B
1
B
1JF,C ꢂ252 Hz, C6F5 ), 143.8 (dm, JF,C ꢂ 248 Hz, C6F5 ),
ꢀ160.7 (br, 4F, m-F) [B(C6F5)2], ꢀ138.7 (br, 2F, o-F),
N
143.8 (dm, JF,C ꢂ248 Hz, C6F5), 141.4 (i-Ph5), 140.7 (dm, JF,C
ꢀ154.3 (t, 3JF,F =20.8 Hz, 1F, p-F), ꢀ161.9 (br, 2F, m-F)
(C6F5); 19F NMR (470 MHz, C7D8, 213 K, CFCl3): d=
ꢀ119.9, ꢀ126.0 (each m, each 1F, o-F), ꢀ137.7 (br, 1F, p-F),
ꢀ159.4, ꢀ160.6 (each br, each 1F, m-F), ꢀ126.6, ꢀ130.7
(each m, each 1F, o-F), ꢀ144.9 (br, 1F, p-F), ꢀ158.1, ꢀ162.1
1
1
ꢂ257 Hz, C6F5), 138.7 (i-Ph2), 137.6 (dm, JF,C ꢂ253 Hz,
1
1
B
C6F5), 137.4 (dm, JF,C ꢂ253 Hz, C6F5 ), 136.7 (C3), 129.0 (m-
Ph2), 128.5 (m-Ph5), 128.5 (p-Ph5), 128.1 (o-Ph5), 127.6 (p-
Ph2), 127.1 (o-Ph2), 115.4 (i-C6F5), 114.5 (br, i-C6F5 ), ꢀ5.4
B
(1JSi,C =51.5 Hz, SiMe2) [tentative assignment for positions 2
and 5]; 19F NMR (470 MHz, C6D6, 298 K, CFCl3): d=ꢀ128.2
(each br, each 1F, m-F) [B
N
each 1F, o-F), ꢀ153.2 (br, 1F, p-F), ꢀ160.2, ꢀ162.3 (each br,
each 1F, m-F) (C6F5); 19F NMR (470 MHz, C7D8, 353 K,
CFCl3): d=ꢀ125.4 (br, 4F, o-F), ꢀ143.6 (br, 2F, p-F),
3
4
(br, 4 F, o-F), ꢀ145.7 (tt, JF,F =20.7 Hz, JF,F =5.7 Hz, 2F, p-
F), ꢀ161.5 (br, 41F, m-F) [B(C6F5)2], ꢀ138.3 (m, 2F, o-F),
R
ꢀ154.4 (t, 3JF,F =20.9 Hz, 1F, p-F), ꢀ161.9 (m, 2F, m-F)
ꢀ161.1 (m, 4F, m-F) [B(C6F5)2], ꢀ138.5 (m, 2F, o-F), ꢀ154.8
A
(C6F5).; 29Si
{DEPT} NMR (99 MHz, C6D6, 298 K): d=9.8;
(t, JF,F =20.3 Hz, 1F, p-F), ꢀ162.2 (m, 2F, m-F) (C6F5). UV/
Vis (CH2Cl2): lmax (e)=274 (31620), 262 (29500), 234
(53700) nm; fluorescence (CH2Cl2); lmax =390, 402 (sh) nm;
anal. calcd. for C40H28BF15Si3 (888.7): C 54.06, H 3.17;
found: C 53.99, H 3.37%.
3
UV/Vis (CH2Cl2): lmax (e)=305 (25700), 231 (18620) nm;
fluorescence (CH2Cl2); lmax =390 nm; anal. calcd. for
C36H16BF15Si (772.4): C 55.98, H 2.09; found: C 55.73, H
1.93%.
X-ray crystal structure analysis of 7c: formula
C36H16BF15Si, M=772.39, yellow crystal 0.20ꢄ0.15ꢄ
0.03 mm, a=15.928(1), b=9.076(1), c=23.222(1) ꢃ, b=
X-ray crystal structure analysis of 7d: formula
C40H28BF15Si3, M=888.70, colourless crystal 0.30ꢄ0.25ꢄ
0.25 mm, a=11.7473(3), b=37.8490(8), c=9.1945(2) ꢃ, b=
104.03(1)8,
V=3256.9(4) ꢃ3,
1calcd. =1.575 gcmꢀ3,
m=
92.531(1)8,
V=4084.1(2) ꢃ3,
1calcd. =1.445 gcmꢀ3,
m=
1.686 mmꢀ1, empirical absorption correction (0.729ꢄTꢄ
0.951), Z=4, monoclinic, space group P21/c (No. 14), l=
1.54178 ꢃ, T=223 K, w and f scans, 46761 reflections col-
lected (ꢃh, ꢃk, ꢃl), [(sinq)/l]=0.60 ꢃꢀ1, 5811 independent
(Rint =0.081) and 4504 observed reflections [I ꢅ 2 s(I)], 480
refined parameters, R=0.046, wR2 =0.107, max. residual
electron density 0.31 (ꢀ0.26) eꢃꢀ3, hydrogen atoms calcu-
lated and refined as riding atoms.
1.962 mmꢀ1, empirical absorption correction (0.591ꢄTꢄ
0.640), Z=4, monoclinic, space group P21/c (No. 14), l=
1.54178 ꢃ, T=223 K, w and f scans, 39467 reflections col-
lected (ꢃh, ꢃk, ꢃl), [(sinq)/l]=0.60 ꢃꢀ1, 7242 independent
(Rint =0.044) and 6708 observed reflections [Iꢅ2 s(I)], 538
refined parameters, R=0.043, wR2 =0.118, max. residual
electron density 0.30 (ꢀ0.25) eꢃꢀ3, hydrogen atoms calcu-
lated and refined as riding atoms.
4-[Bis(pentafluorophenyl)boryl]-3-pentafluorophenyl-
2,5-bis(trimethylsilyl)-1,1-diphenylsilole (7d)
Acknowledgements
Bis(trimethylsilylethynyl)diphenylsilane
(1d)
(0.88 g,
Financial support from the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie is gratefully ac-
knowledged.
2.34 mmol) and tris(pentafluorophenyl)borane (9) (1.20 g,
2.34 mmol) were weighed in an argon-filled glove-box and
placed into a 100-mL Schlenk flask. Toluene (30 mL) was
added at room temperature and the yellow solution was
stirred overnight. Then the volatiles were removed under
vacuum, leaving a yellow glue-like product. Pentane (4 mL) References
was added, and the product dissolved completely with stir-
ring under argon. After 30 min, the volume was reduced to
2 mL by reduced pressure, and the resulting yellow solution
was stored at ꢀ308C. Part of the product crystallised over-
night and was filtered off while kept at ꢀ308C, to avoid re-
dissolution. The filtrate was stored again at ꢀ308C, afford-
ing more crystalline product in 14 days; total yield: 0.721 g
(35%). Crystals suitable for single-crystal X-ray diffraction
were obtained at ꢀ308C from a concentrated pentane solu-
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1086
asc.wiley-vch.de
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2009, 351, 1080 – 1088

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Adv. Synth. Catal. 2009, 351, 1080 – 1088