A Facile, Palladium-Catalyzed Synthesis of 1,1'Bi(cyclo[1.1.1]pentanes)

Article abstract of DOI:10.1002/1099-0690(200103)2001:6<1049::AID-EJOC1049>3.0.CO;2-V

Symmetrically 3,3'-disubstituted 1,1'-bi(bicyclo[1.1.1]pentanes) were synthesized in a four-step procedure, using commercially available starting materials, in fair overall yields (51-60%).In this synthesis the final step is an unexpected bridgehead-t-bridgehead homocoupling of bicyclo[1.1.1]pent-1-ylmagnesium halide catalyzed by palladium(II). Only 1.1 mol percent of bis(acetonitrile)palladium(II) chloride and two equivalents of bromoethane were necessary to accomplish this reaction. the bromoethane is essential to convert Pd⁰ into Pd^II. The X-ray structure of the C1-C3-distance of 1.907 Angstroem in the bicyclo[1.1.1]pentyl subunit.

Full text of DOI:10.1002/1099-0690(200103)2001:6<1049::AID-EJOC1049>3.0.CO;2-V

FULL PAPER
A Facile, Palladium-Catalyzed Synthesis of 1,1Ј-Bi(bicyclo[1.1.1]pentanes)
J. D. Daniel Rehm,[a] Burkhard Ziemer,[a] and Günter Szeimies*[a]
Keywords: CϪC coupling / Cage compounds / Strained molecules / Palladium
Symmetrically 3,3Ј-disubstituted 1,1Ј-bi(bicyclo[1.1.1]pent- 1.1 mol percent of bis(acetonitrile)palladium(II) chloride and
anes) were synthesized in a four-step procedure, using com- two equivalents of bromomethane were necessary to accom-
mercially available starting materials, in fair overall yields
plish this reaction. The bromomethane is essential to convert
(51−60%). In this synthesis the final step is an unexpected Pd0 into PdII. The X-ray structure of the [2]staffane 1c has
bridgehead-to-bridgehead homocoupling of bicyclo[1.1.1]- been determined and shows a nonbonded C1−C3 distance of
˚
pent-1-ylmagnesium halide catalyzed by palladium(II). Only
1.907 A in the bicyclo[1.1.1]pentyl subunit.
Introduction
one-pot reaction furnishing 1 with overall yields ranging
from 51 to 60% (based on the Grignard reagent RMgX).
Although a few methods have been developed for Bromomethane, which is a by-product in the synthesis of
the synthesis of 1,1Ј-bi(bicyclo[1.1.1]pentanes) or [2]- [1.1.1]propellane 2, and which is also present in the reaction
staffanes 1 (for structures see Scheme 1)[1,2] a straightfor- mixture, acts as an oxidant for palladium(0).
ward efficient synthetic route to 1 is still lacking. Recently,
Michl and co-workers[3] published the results of a copper-
Results and Discussion
mediated bridgehead-to-bridgehead coupling of 3-substi-
tuted bicyclo[1.1.1]pent-1-yllithium that yields some bi(bi-
cyclo[1.1.1]pentanes) 1 in reasonable yields. However, at-
tempts by the same authors to homocouple this compound
with 50 mol percent of palladium or nickel reagents gave
the staffanes 1 in yields of 26% and 38%, respectively.
The Grignard reagents 3 were obtained by the addition
of the corresponding organomagnesium halides to 2 as de-
scribed previously.[4Ϫ6] The propellane 2 was generated
from 5 with two equivalents of MeLi in ether.[7,8] The two
equivalents of bromomethane that were formed from MeLi
by lithium-bromine exchange with 5 and 6, respectively,
were not removed. The Grignard reagents 3 were then
treated with 1.1 mol-% of [PdCl2(CH3CN)2] and main-
tained for 48 hours at room temperature under an atmo-
sphere of nitrogen. A conventional workup afforded the
staffanes 1 in the isolated yields given in Table 1. The reac-
tions leading to 1aϪd were performed in ether. The addi-
tion of the arylmagnesium halides to 2 with diethoxy-
methane (DEM) as the solvent has been found to give satis-
factory results (reactions leading to 1eϪg).[5]
Table 1. Yields of 1 obtained from the palladium-catalyzed coup-
ling reaction of 3
1, 3
R
Yields of 1 (%)
Scheme 1
a
b
c
d
e
f
tert-Butyl
57
Cyclohexyl
Isopropyl
51
We have shown that alkyl or aryl Grignard reagents add
to the [1.1.1]propellane 2 to give the bicyclo[1.1.1]pent-1-
ylmagnesium halides 3.[4,5] The bicyclo[1.1.1]pent-1-ylmag-
nesium halides 3 can be cross-coupled with bromoarenes
using [dppf]PdCl2 as the catalyst to afford the 1,3-disubsti-
tuted bicyclo[1.1.1]pentanes 4 in good yields.[6] Here we
show that 3 can also be homocoupled to yield 1 by using a
catalytic amount of bis(acetonitrile)palladium(II) chloride
[(CH3CN)2PdCl2]. The three steps were carried out in a
57
Cyclopentyl
Ph
60
53[a]
59
p-CH3-C6H4
p-Si(CH3)3-C6H4
g
59
[a]
By-product: 3-methyl-1-phenylbicyclo[1.1.1]pentane (7) (42%).
The formation of 1e was accompanied by 3-methyl-1-
phenylbicyclo[1.1.1]pentane (7) in 28% yield. It is unlikely
that this by-product is formed by the methylation of the
Grignard reagent 3e with bromomethane. In a control ex-
periment, a solution of 3e, which also contained bromo-
[a]
Institut für Chemie, Humboldt Universität zu Berlin,
Hessische Straße 1Ϫ2, 10115 Berlin, Germany
Eur. J. Org. Chem. 2001, 1049Ϫ1052
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ193X/01/0306Ϫ1049 $ 17.50ϩ.50/0
1049

J. D. D. Rehm, B. Ziemer, G. Szeimies
FULL PAPER
methane, was maintained for six days at room temperature. Table 2. Yields of 1a from 3a with different catalysts
An aqueous workup afforded 1-phenylbicyclo[1.1.1]pentane
Entry
Catalyst[a]
% Yield[b] of 1a
as the sole product. Inspection of the NMR spectra of the
crude products of 1aϪd and 1f and 1g showed the presence
of trace impurities of the corresponding 3-methylbicyclo-
[1.1.1]pentanes 4 (R1 as indicated in Table 1).
1
2
3
4
5
6
PdCl2(CH3CN)2
PdCl2(PPh3)2
Pd(dba)2
63
Ϫ
47
Pd/C
41
The essential role of the bromomethane in this reaction
was shown by initially removing the bromomethane and the
ether solvent in vacuo. The residual Grignard reagent 3a
was then dissolved in pure anhydrous ether, 1.1 mol-% of
NiCl2
Ϫ
(NH4)2PtCl6
traces[c]
[a]
Conditions: 3a (16.8 mmol), catalyst (0.18 mmol), diethyl ether
[b]
[c]
(25 mL), 72 h at 20 °C. Ϫ
Isolated yields. Ϫ Determined by
[PdCl2(CH3CN)2] was added and after 48 hours a standard 1H NMR spectroscopy.
workup yielded the crude product. The 1H NMR spectrum
of the product showed that 1a was not present. In a second
reaction satisfactorily. The use of a nickel or platinum cata-
lyst proved to be ineffective.
experiment, a bromomethane-free solution of 3a was
charged with two equivalents of bromomethane and again
maintained for two days at room temperature. In this case
1a was isolated in a yield of 54%.
X-ray Structure of 1c
The structure of compound 1c (Figure 1) has been deter-
Concerning the mechanism of this reaction, the precursor
of 1 should be the bis(organo)palladium complex 8, which
decomposes to 1 and Pd0. Oxidative addition of bromo-
methane to Pd0 would lead to 9. We propose that 9 un-
dergoes a symmetrization reaction leading to 10 and 11 (see
Scheme 2). Structurally related gold or platinum com-
pounds are known to show this type of reaction.[9] Trans-
metallation of 10 with the Grignard reagent 3 will furnish
the intermediate 8, whereas 11 is expected to decompose to
ethane and Pd0. Obviously, the symmetrization process of
9 should be considerably faster than the transmetallation of
9 to give 12, the decomposition of which would lead to 3-
methylbicyclo[1.1.1]pentanes of type 7.
mined by X-ray diffraction analysis. The bridgehead-to-
bridgehead distance CϪC3 in 1c is 1.9068(21) A and is typ-
˚
ical for bicyclo[1.1.1]pentanes. The distance between the
˚
two bicyclo[1.1.1]pentyl cages is 1.5002(27) A and this is
significantly shorter than the bond distance between
two tertiary carbon atoms in other compounds, such as
[10]
˚
1,1Ј-bi(adamantane) (1.58 A),
but is in agreement with
structurally related molecules.[1,11,12]
Figure 1. ORTEP Plot of 1c (50% probability ellipsoids); selected
˚
bond lengths [A] and angles [°]: C1ϪC3 1.907(3); C1ϪC2 1.552(3);
C1ϪC1Ј 1.500(3); C3ϪC6 1.525(3); C1ϪC2ϪC3 75.43(10);
C2ϪC3ϪC4 87.23(12); C2ϪC3ϪC5 85.62(11)
Experimental Section
General: 1,1-Dibromo-2,2-bis(chloromethyl)cyclopropane (5) and
[1.1.1]propellane (2) were prepared by literature methods.[7,8]
Methyllithium in DEM was purchased from Chemetall AG. 3-
Chloro-2-(chloromethyl)-1-propene, tert-butylmagnesium chloride
and cyclopentylmagnesium bromide were purchased from Aldrich;
isopropylmagnesium chloride and cyclohexylmagnesium chloride
were purchased from Fluka. All the reactions were carried out un-
der an atmosphere of nitrogen. Melting points were determined on
Scheme 2
The rate-determining steps in our postulated mechanism
will strongly depend on the ligand L of the palladium cata-
lyst. We have therefore investigated the influence of the
catalyst on the yield of 1a for the reaction of 3a and bromo-
methane. The results are summarized in Table 2.
Remarkably, the presence of triphenylphosphane inhib-
ited the reaction completely (entry 2, Table 2), presumably
because the decomposition of the triphenylphosphane com-
plex of 11 is rather slow at 20 °C.[9c] There is no significant
difference between a PdII or a Pd0 catalyst and even palla-
1
a Büchi 530 and are uncorrected. H (at 300 MHz) and 13C NMR
spectra (at 75 MHz) were measured in CDCl3 on a Bruker DPX300
with TMS as an internal standard. IR spectra were recorded on a
PerkinϪElmer 881 spectrometer. MS spectra were taken on a MSI
Concept 1H. Elemental analyses were carried out by the Analy-
tisches Labor des Instituts für Chemie der Humboldt-Universität
zu Berlin.
General Procedure for the Preparation of 3a؊g
a) Preparation of the Grignard Reagents 3a؊d: 1,1-Dibromo-2,2-
bis(chloromethyl)cyclopropane (5) was reacted with 2.00 equiv. of
dium on charcoal (entry 4, Table 2) is able to catalyze the MeLi[7,8] to yield the [1.1.1]propellane 2 (in an assumed yield of
1050
Eur. J. Org. Chem. 2001, 1049Ϫ1052

A Facile, Palladium-Catalyzed Synthesis of 1,1Ј-Bi(bicyclo[1.1.1]pentanes)
FULL PAPER
70%, based on 5). To a solution of [1.1.1]propellane 2 in diethyl
benzylideneacetone)palladium(0) [Pd(dba)2, 115 mg, 0.20 mmol],
ether was added the Grignard reagent (0.95 equivalents based on palladium (10%) on charcoal (180 mg), bis(triphenylphosphane)-
2; a: tert-butylmagnesium chloride; b: cyclohexylmagnesium chlor-
ide; c: 2-propylmagnesium chloride, d: cyclopentylmagnesium
chloride) at 0 °C and the solution was stirred for 48 h at room
temperature. After this time, the propellane 2 had disappeared and
the Grignard reagents 3aϪd had formed quantitatively.
palladium dichloride [(Ph3P)2PdCl2, 126 mg, 0.18 mmol], NiCl2
(23 mg, 0.18 mmol), or ammonium hexachloroplatinate
[(NH4)2PtCl6, 64 mg, 0.14 mmol]. After 72 h at room temperature
a standard workup afforded 1a in the yields given in Table 2.
3,3Ј-Dicyclohexyl-1,1Ј-bi(bicyclo[1.1.1]pentane) (1b): Tetrahalide 5
(5.00 g, 16.8 mmol) was converted into 3b which, following the
standard procedure, gave rise to 1b (850 mg, 51%) as a colorless
b) Preparation of the Grignard Reagents 3e؊g: 1,1-Dibromo-2,2-
bis(chloromethyl)cyclopropane (5) was reacted with 2.00 equiv. of
MeLi[7,8] to yield the [1.1.1]propellane 2 (in an assumed yield of
70%, based on 5). To a solution of the [1.1.1]propellane 2 in di-
ethoxymethane was added the Grignard reagent [0.95 equiv. based
on 2; e: phenylmagnesium bromide; f: p-methylphenylmagnesium
bromide; g: p-(trimethylsilyl)phenylmagnesium bromide] at 0 °C
and the solution was stirred for 6 days at room temperature. After
this time the propellane 2 had disappeared and the Grignard re-
agents 3e؊g had formed quantitatively.
1
solid, m.p. 222 °C. Ϫ H NMR: δ ϭ 0.70Ϫ1.75 (m, 22 H), 1.33 (s,
12 H). Ϫ 13C NMR: δ ϭ 26.2 (t, 2 C), 26.4 (t, 4 C), 29.3 (t, 4 C),
38.3 (d, 2 C), 38.2 (s, 2 C), 42.2 (s, 2 C), 46.6 (t, 6 C). Ϫ IR (KBr):
ν˜ ϭ 2957, 2956, 2920, 2903, 2864, 2850, 1445, 1203 cmϪ1. Ϫ MS
(EI): m/z (%) ϭ 215 (10), 133 (50), 121 (30), 105 (62), 93 (60), 91
(64), 81 (50), 67 (87), 55 (100), 41 (84). Ϫ C22H34 (298.5): calcd. C
88.52, H 11.48; found C 88.17, H 11.54.
3,3Ј-Diisopropyl-1,1Ј-bi(bicyclo[1.1.1]pentane) (1c): Tetrahalide 5
(5.00 g, 16.8 mmol) was converted into 3c which, following the
standard procedure, gave rise to 1c (700 mg, 57%) as a colorless
General Procedure for the Palladium-Catalyzed Reaction:
[PdCl2(CH3CN)2] (1.1 mol-%, based on 2) was added to a solution
of 3a؊g. The solution turned brown and was then stirred for 48 h
at room temperature. For the workup, aqueous NH4Cl was added,
the organic layer was separated and the aqueous layer was ex-
tracted with pentane (2 ϫ 50 mL). The combined organic layers
were washed twice with water, dried with MgSO4, and the solvent
removed in vacuo. The crude coupling product 1 was purified by
flash chromatography with silica gel using pentane as the solvent.
The yields of 1 are based on the Grignard reagent RMgX, which
amounted to 64Ϫ67% of the starting tetrahalide 5.
1
solid, m.p. 35 °C. Ϫ H NMR: δ ϭ 0.79 (d, 12 H), 1.34 (s, 12 H),
1.62 (sp, 2 H). Ϫ 13C NMR: δ ϭ 18.8 (q, 4 C), 28.6 (d, 2 C), 37.9
(s, 2 C), 43.3 (s, 2 C), 46.3 (t, 6 C). Ϫ IR (KBr): ν˜ ϭ 2956, 2904,
2868, 1465, 1363, 1274, 1202, 893 cmϪ1. Ϫ MS (EI): m/z (%) ϭ
133 (28), 119 (65), 105 (58), 93 (64), 91 (100), 79 (54), 69 (66), 55
(50), 41 (94). Ϫ C16H26 (218.4): calcd. C 88.00, H 12.00; found C
87.98, H 11.67.
3,3Ј-Dicyclopentyl-1,1Ј-bi(bicyclo[1.1.1]pentane) (1d): Tetrahalide 5
(5.00 g, 16.8 mmol) was converted into 3d which, following the
standard procedure, gave rise to 1d (910 mg, 60%) as a colorless
3,3Ј-Di-tert-butyl-1,1Ј-bi(bicyclo[1.1.1]pentane) (1a): a) 3a and
[PdCl2(CH3CN)2]: The general procedures for the preparation of
3a from 5 and the subsequent reaction of 3a with [PdCl2(CH3CN)2]
were followed. Tetrahalide 5 (5.00 g, 16.8 mmol) was converted into
3a and then reacted with [PdCl2(CH3CN)2] to yield a crude prod-
uct. A standard workup and purification yielded 1a (778 mg, 57%)
1
solid, m.p. 122 °C. Ϫ H NMR: δ ϭ 1.20 (m, 4 H), 1.35 (s, 12 H),
1.51 (m, 12 H), 1.86 (m, 2 H). Ϫ 13C NMR: δ ϭ 25.7 (t, 4 C), 29.0
(t, 4 C), 39.0 (d, 2 C), 40.5 (s, 2 C), 41.2 (s, 2 C), 47.3 (t, 6 C). Ϫ
IR (KBr): ν˜ ϭ 2954, 2901, 2863, 1445, 1270, 1199 cmϪ1. Ϫ MS
(EI): m/z (%) ϭ 159 (11), 145 (18), 133 (30), 119 (65), 105 (38), 93
(50), 91 (100), 79 (59), 55 (33), 41 (97). Ϫ C20H30 (270.5): calcd. C
88.82, H 11.18; found C 88.42, H 10.85.
1
as a colorless solid, m.p. 180 °C. Ϫ H NMR: δ ϭ 0.80 (s, 18 H),
1.35 (s, 12 H). Ϫ 13C NMR: δ ϭ 25.9 (q, 6 C), 29.4 (s, 2 C), 36.3
(s, 2 C), 46.5 (s, 2 C) 45.2 (t, 6 C). Ϫ IR (KBr): ν˜ ϭ 2958, 2953,
2927, 2902, 2864, 1358, 1210, 697 cmϪ1. Ϫ MS (EI): m/z (%) ϭ
133 (38), 119 (28), 105 (33), 91 (46), 83 (27), 67 (22), 57 (100), 55
(52), 41 (77). Ϫ C18H30 (246.4): calcd. C 87.73, H 12.27; found C
87.56, H 11.92.
3,3Ј-Diphenyl-1,1Ј-bi(bicyclo[1.1.1]pentane) (1e) and 3-Methyl-1-
phenylbicyclo[1.1.1]pentane (7): Tetrahalide 5 (5.00 g, 16.8 mmol)
was converted into 3e which, following the standard procedure,
gave rise to a mixture of 1d (850 mg, 53%; the analytical data match
the previously published data[2]) and 7 (750 mg, 42%) as a colorless
liquid, b.p. 80Ϫ85 °C (0.1 Torr). Ϫ 1H NMR: δ ϭ 1.27 (s, 3 H),
1.93 (s, 6 H), 7.25 (m, 5 H). Ϫ 13C NMR: δ ϭ 18.2 (q), 35.3 (s),
38.68 (s), 53.89 (t, 3 C), 126.0 (d, 1 C), 128.0 (d, 5 C), 141.5 (s). Ϫ
IR (KBr): ν˜ ϭ 2958, 2918, 2905, 2865, 1277, 1153, 739 cmϪ1. Ϫ
MS (EI): m/z (%) ϭ 154 (37), 91 (48), 77 (50), 55 (38), 43 (76), 41
(53), 39 (78), 29 (74), 18 (100). Ϫ C12H14 (158.2): calcd. C 91.08,
H 8.92; found C 90.98, H 8.70.
b) 3a and [PdCl2(CH3CN)2] without Bromomethane: Tetrahalide 5
(5.00 g, 16.8 mmol) was reacted with methyllithium (1.4 ,
24.0 mL, 33.6 mmol) and then with tert-butylmagnesium chloride
(2.0  in diethyl ether, 5.40 mL, 10.80 mmol) to yield a solution of
3a. The volatile materials were removed in vacuo and anhydrous
diethyl ether was added. This solution was then charged with
[PdCl2(CH3CN)2] (50 mg, 0.19 mmol). A standard workup and
purification of the crude product yielded only traces of 1a (as deter-
1
mined by H NMR spectroscopy).
3,3Ј-Bis(4-methylphenyl)-1,1Ј-bi(bicyclo[1.1.1]pentane) (1f): Tetra-
halide 5 (5.00 g, 16.8 mmol) was converted into 3f which, following
the standard procedure, afforded 1f (1.04 g, 59%) as a colorless
c) 3a, Purified, and [PdCl2(CH3CN)2] with Bromomethane: Tetra-
halide 5 (5.00 g, 16.8 mmol), methyllithium (24.00 mL, 33.6 mmol)
1
solid, m.p. 214 °C: H NMR: δ ϭ 1.90 (s, 12 H) 2.32 (s, 6 H) 7.15
and tert-butylmagnesium chloride (2.0
 in diethyl ether,
(s, 8 H). Ϫ 13C NMR: δ ϭ 21.1 (q, 2 C), 38.2 (s, 2 C), 40.5 (s, 2
C), 51.1 (t, 6 C) 125.9 (d, 4 C), 128.8 (d, 4 C), 135.8 (s, 2 C), 138.6
(s, 2 C). Ϫ IR (KBr): ν˜ ϭ 2992, 2964, 2918, 1904, 2867, 2851, 1520,
1443, 1333, 1208, 1110, 823 cmϪ1. Ϫ MS (EI): m/z (%) ϭ 314 [Mϩ]
(1), 299 (15), 209 (39), 196 (95), 183 (49), 181 (61), 167 (50), 115
(57), 105 (100), 91 (64), 51 (17). Ϫ C24H26 (314.5): calcd. C 91.67,
H 8.33; found C 91.43, H 8.16.
5.40 mL,10.80 mmol) were treated according to the procedure de-
scribed in b). The volatile materials were removed in vacuo and the
residue was dissolved in anhydrous diethyl ether to yield a solution
of 3a. Bromomethane (about 5 mL) and [PdCl2(CH3CN)2] (50 mg,
0.19 mmol) were added to the solution of 3a and the reaction mix-
ture was maintained at room temperature for 48 h. A standard
workup and purification yielded 1a (739 mg, 54%)
d) 3a and Several Catalysts: Individual solutions of 3a in ether,
prepared by the procedure described in a) were charged with bis(di-
3,3Ј-Bis[3-(trimethylsilyl)phenyl]-1,1Ј-bi(bicyclo[1.1.1]pentane) (1g):
Tetrahalide 5 (5.00 g, 16.8 mmol) was converted into 3g which, fol-
Eur. J. Org. Chem. 2001, 1049Ϫ1052
1051

J. D. D. Rehm, B. Ziemer, G. Szeimies
FULL PAPER
(6.72° Ͻ 2θ Ͻ 50.48°). Intensities were measured by -oscillation
scans. The structure was solved by direct methods and refined an-
isotropically on F2 (SHELX-97).[13] Hydrogen atoms were isotrop-
ically included into the full-matrix least-squares refinement.[14]
Table 3. Crystal data and structure refinement for compound 1c
1c
Empirical formula
C16H26
218.37
Mr
Acknowledgments
We thank the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie for the financial support for this investi-
gation.
˚
a [A]
12.119(3)
5.805(2)
10.248(2)
90
˚
b [A]
˚
c [A]
α [°]
β [°]
91.16(3)
90
γ [°]
[1]
Z
2
U. Bunz, K. Polborn, H.-U. Wagner, G. Szeimies, Chem. Ber.
Dx [Mg/cm3]
Crystal system
Space group
Crystal size [mm]
θ range [°]
1.006
1988, 121, 1785Ϫ1790.
monoclinic
P21/c
[2] [2a]
P. Kaszynski, A. C. Friedli, J. Michl, J. Am. Chem. Soc.
[2b]
1992, 114, 601Ϫ620. Ϫ
Y. S. Obeng, M. E. Liang, A. C.
0.57 ϫ 0.38 ϫ 0.15
3.36Ϫ25.24
4252
Friedli, H. C. Yang, D. Wang, E. W. Thulstrupp, A. J. Bard, J.
Michl, J. Am. Chem. Soc. 1992, 114, 9943Ϫ9952.
C. Mazal, A. J. Paraskos, J. Michl, J. Org. Chem. 1998, 63,
2116Ϫ2119.
A. Godt, Diploma Thesis, Universität München, 1988; see
also: G. Szeimies, in Strain and Its Implications in Organic Syn-
thesis (Eds.: A. de Meijere, S. Blechert), Kluwer Academic Pub-
lishers, Dordrecht, 1989, pp 361Ϫ381.
S. Guffler, Dissertation, Humboldt-Universität 1998.
J. D. D. Rehm, B. Ziemer, G. Szeimies, Eur. J. Org. Chem 1999,
2079Ϫ2085; see also: M. Messner, S. I. Kozhushkov, A. de Mei-
jere, Eur. J. Org. Chem 2000, 1137Ϫ1155.
Reflections measured
Independent reflections
[3]
[4]
1243
0.056
µ [mmϪ1
]
Max./min. transmission
Parameters
F(000)
0.9917/0.9690
126
244
0.979
GoF
[5]
[6]
Ϫ3
˚
Max./min ∆ρ [e A
R1[a]
]
0.225/Ϫ0.172
0.0482
wR2[b]
0.1335
[7] [7a]
[a]
[b]
J. Belzner, U. Bunz, G. Szeimies, K. Opitz, A.-D. Schlüter,
R1 ϭ Σ||Fo| Ϫ |Fc||/Σ|Fo| for reflections with I Ͼ 2σ(I). Ϫ
[7b]
wR2 ϭ {Σ[w(Fo Ϫ Fc ) ]/Σ[w(Fc ) ]}0·5 for all reflections; wϪ1
ϭ
2
2 2
2 2
Chem. Ber. 1989, 122, 397Ϫ398. Ϫ
K. Semmler, G. Szeim-
σ2(F2) ϩ (aP)2 ϩ bP, where P ϭ (2Fc ϩ Fo )/3 and a and b were
2
2
ies, J. Belzner, J. Am. Chem. Soc. 1985, 107, 6410Ϫ6411.
K. M. Lynch, W. P. Dailey, Org. Synth. 1997, 75, 98Ϫ105.
[8]
[9] [9a]
constants set by the program.
R. J. Puddephatt, P. J. Thompson, J. Chem. Soc., Dalton
[9b]
Trans. 1975, 1810Ϫ1814. Ϫ
P. J. Thompson, R. J. Pudde-
phatt, J. Chem. Soc., Chem. Commun. 1975, 841Ϫ843. Ϫ [9c] D.
Milstein, J. K. Stille, J. Am. Chem. Soc. 1979, 101, 4981Ϫ4991.
R. A. Alden, J. Kraut, T. G. Taylor, J. Am. Chem. Soc. 1968,
90, 74Ϫ82.
lowing the standard procedure, afforded 1g (1.41 g, 59%) as a col-
1
orless solid, m.p. 252 °C. Ϫ H NMR: δ ϭ 0.25 (s, 18 H), 1.93 (s,
[10]
[11]
[12]
12 H) 7.24 (d, 4 H), 7.46 (d, 4 H). Ϫ 13C NMR: δ ϭ Ϫ1.1 (q, 6
C), 38.3 (s, 2 C), 40.7 (s, 2 C), 51.1 (t, 6 C), 125.5 (d, 4 C), 133.2
(d, 4 C), 138.1 (s, 2 C), 124.0 (s, 2 C). Ϫ IR (KBr): ν˜ ϭ 3030, 3014,
2961, 2904, 2867, 1601, 1389, 1246, 1208, 1117, 1064, 852, 754
cmϪ1. Ϫ MS (EI): m/z (%) ϭ 430 [Mϩ] (1), 416 (27), 254 (46), 239
(32), 225 (26), 200 (40), 167 (7), 73 (100). Ϫ C28H38Si2 (430.8):
calcd. C 78.07, H 8.89; found C 77.87, H 8.84.
J. Schäfer, K. Polborn, G. Szeimies, Chem. Ber. 1988, 121,
2263Ϫ2265.
O. Ermer, P. Bell, J. Schäfer, G. Szeimies, Angew. Chem. 1989,
101, 503Ϫ506; Angew. Chem. Int. Ed. Engl. 1989, 28, 473Ϫ475.
G. M. Sheldrick, SHELX-97, University of Göttingen, 1997.
Crystallographic data (excluding structure factors) for the
structure reported in this paper has been deposited with the
Cambridge Crytallographic Data Centre as supplementary
publication no. CCDC-151584. Copies of the data can be ob-
tained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. [Fax: (internat.) ϩ44-1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
[13]
[14]
X-ray Crystal Structure Determination of 1c: The crystal data of 1c
are given in Table 3. Measurements were carried out on a STOE
Imaging Plate Diffraction System at 180 K using graphite-mono-
˚
chromated Mo-Kα radiation (λ ϭ 0.71073 A). Unit cell parameters
Received August 9, 2000
were determined from a least-squares analysis of 1243 reflections
[O00422]
1052
Eur. J. Org. Chem. 2001, 1049Ϫ1052