The hydroalumination of diethynes with di(tert-butyl)aluminium hydride: A facile method for the synthesis of organometallic dialuminium compounds

Article abstract of DOI:10.1016/S0022-328X(00)00364-8

Di(tert-butyl)aluminium hydride reacted with the diynes 1,4-bis(trimethylsilyl)-1,3-butadiyne and 1,4-bis(trimethylsilyl-ethynyl)benzene by hydroalumination and addition of one Al-H bond to each C≡C triple bond. A selective cis addition was observed in bo

Full text of DOI:10.1016/S0022-328X(00)00364-8

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Journal of Organometallic Chemistry 608 (2000) 54–59
The hydroalumination of diethynes with di(tert-butyl)aluminium
hydride: a facile method for the synthesis of organometallic
dialuminium compounds
Werner Uhl *, Frank Breher
Fachbereich Chemie der Philipps-Uni6ersita¨t, Hans-Meerwein-Strasse, D-35032 Marburg, Germany
Received 3 April 2000; accepted 16 May 2000
Abstract
Di(tert-butyl)aluminium hydride reacted with the diynes 1,4-bis(trimethylsilyl)-1,3-butadiyne and 1,4-bis(trimethylsilyl-
ethynyl)benzene by hydroalumination and addition of one Al–H bond to each CꢀC triple bond. A selective cis addition was
observed in both cases to yield alkenes with Z configuration exclusively. The aluminium atoms were attached to those carbon
atoms which bear the trimethylsilyl groups. While the butadiyne product (1) decomposed upon heating in benzene solution, the
diene (2), obtained by the twofold hydroalumination of 1,4-bis(trimethylsilylethynyl)benzene, showed a remarkable rearrangement
and gave the thermodynamically favoured product (4) almost quantitatively, which has two alkenes in E configuration. All
products were characterized by crystal structure determinations. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Aluminium; Hydroalumination; Rearrangement
described by the trans addition of the Al–H bonds to
the CꢀC triple bonds. The further substituents attached
to the CꢁC double bonds of the products have a strong
influence on the rate of the rearrangements, and
the trimethylsilyl substituted compound H5C6–
(H)CꢁC(SiMe3)(Ali-Bu2) gave the completely rear-
ranged trans product already at a low temperature
(−10°C) [4]. The position of the alkylaluminium group
in the product was determined by the kind of the
further substituents of the starting alkyne R–CꢀC–E
(R=C6H5). If E was a tert-butyl group, the dialkylalu-
minium substituent was attached to that carbon atom
which was further bonded to the phenyl group. In the
1. Introduction
The addition of Al–H bonds to alkenes or alkynes is
an important method for the syntheses of alkylalu-
minium derivatives and found technical application in
the ‘Ziegler–Direktverfahren’ [1]. Preparative organic
chemistry employed hydroalumination in several reac-
tions in order to synthesize alkenes or to form cyclic
compounds from unsaturated chain molecules [2], for
instance. In most of these cases the organoaluminium
compounds were not isolated and characterized but
were hydrolyzed in situ to release the organic compo-
nent. Thus, only poor information is available from the
literature about the constitution of the organoalu-
minium intermediates. The groups of Eisch and Wilke
investigated the selectivity of hydroalumination reac-
tions and found that under kinetic control the cis
addition is preferred [3–5]. Upon heating or addition of
catalysts these products isomerize to the thermodynam-
ically more favoured products, which formally may be
cases of E=trimethylsilyl or trimethylgermyl,
a
product was formed almost quantitatively in which
aluminium and silicon or germanium were bonded to
the same carbon atom of the CꢁC double bond [4]. The
preferred formation of geminal silyl or germyl alu-
minium compounds may be caused by the better stabi-
lization of the negative charge at this position owing to
a hyperconjugative interaction with the silyl groups,
while alkyl groups may influence the course of the
reaction and the structure of the products mainly by
steric reasons.
* Corresponding author. Tel.: +49-6421-2825751; fax: +49-6421-
2725653.
E-mail address: uhl@chemie.uni-marburg.de (W. Uhl).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00364-8

W. Uhl, F. Breher / Journal of Organometallic Chemistry 608 (2000) 54–59
55
In a few cases only, hydroalumination was employed
for the synthesis of dialuminium compounds, and once
again the organoaluminium intermediates were not iso-
lated and characterized [2,3,5,6]. Only recently, we em-
ployed the reaction of dialkylaluminium hydrides with
dialkylaluminium ethynides for the preparation of car-
baalanes such as arachno-(AlMe)8(CCH2C6H5)5H or
closo-(AlMe)7(CCH2CH3)4H2 [7]. These compounds
contain polyhedral clusters of aluminium and carbon
atoms and may be described as analogues of carbabo-
ranes [8]. By the hydroalumination of polyalkynes we
hope to synthesize polyaluminium compounds contain-
ing coordinatively unsaturated aluminium atoms, which
may be useful as chelating Lewis acids in phase transfer
processes or in anion recognition. The suitability of the
dialuminium compound R2Al–CH2–AlR2 [R=
CH(SiMe3)2] [9] to act as a chelating Lewis acid for the
coordination of anions such as nitrite or nitrate was
verified by our group in some recently published inves-
tigations [10,11]. Much more compounds are required,
however, for a systematic approach to this type of
chemistry, and the hydroalumination of alkynes seems
to be a facile method for the synthesis of a broad
variety of polyaluminium compounds containing two,
three or even more aluminium atoms. We started our
investigations with the hydroalumination of diynes, in
order to get a better insight into the rate and the course
of these reactions and to obtain detailed information
about the structure and stability of those products.
(1)
(2)
2. Reactions of di(tert-butyl)aluminium hydride with
diynes
The starting diynes 1,4-bis(trimethylsilyl)-1,3-bu-
tadiyne and 1,4-bis(trimethylsilylethynyl)benzene were
dissolved in n-pentane and treated with two equivalents
of di(tert-butyl)aluminium hydride at room tempera-
ture. The components were consumed completely after
a reaction time of 15 and 3 h, respectively. After
filtration, the solvent was removed in vacuum, and the
residue was recrystallized from n-pentane to obtain pale
yellow (1; Eq. (1)) or colourless crystals (2; Eq. (2)) of
the products in a yield of 40–63%. Both products were
obtained in high purity; they are air sensitive and have
low melting points of 92 and 108°C, respectively. Their
constitution was solved by crystal structure determina-
tions (see below) and by spectroscopic characterization.
Besides singlets of the trimethylsilyl and tert-butyl
groups in an intensity ratio of 1 to 2, both compounds
3. Thermal behaviour of compounds 1 and 2
As discussed below and schematically shown in Eqs.
(1) and (2), both products 1 and 2 have Z configura-
tions at all CꢁC double bonds. The aluminium atoms
and the hydrogen atoms are on the same side, in
agreement with the cis addition of the Al–H bonds. As
discussed above, these products are usually formed
under kinetically controlled conditions, while the trans
products are thermodynamically favoured. Therefore,
we heated solutions of 1 and 2 in benzene to 60°C. The
butadiene product gave only a mixture of several un-
known products, of which none could be isolated in a
1
showed very characteristic resonances in the H-NMR
spectra with chemical shifts of l=7.47 (1) and l=7.72
(2), which are in the normal range [12] of CꢁC(H)R
groups possessing single hydrogen atoms and verify the
successful hydroalumination reactions and the addition
of only one Al–H bond per CꢀC triple bond.

56
W. Uhl, F. Breher / Journal of Organometallic Chemistry 608 (2000) 54–59
original constitution with the hydrogen and the alu-
minium atom in a cis position, while the second one has
the thermodynamically favoured trans arrangement of
both atoms. Upon longer heating, complete rearrange-
ment occurred with both alkenyl groups in a trans
configuration and an inversion centre in the middle of
the phenyl ring (4). The proposed constitution of the
final product 4 was verified by a crystal structure
determination. The symmetric structure of 4 led to the
pure form by recrystallization. In contrast, heating of
the benzene derivative 2 gave a clearly resolved sec-
ondary reaction, which is summarized in Eq. (2).
Upon heating a solution of compound 2 to 60°C for
some hours, the signals of two new products (3 and 4)
were detected by NMR spectroscopy besides the char-
acteristic resonances of the starting compound 2. One
of these products (3) disappeared as soon as 2 was
completely consumed after about seven days, thus it is
only an intermediate in the rearrangement process (Eq.
(2)). 3 has two different resonances of tert-butyl and
trimethylsilyl groups. Furthermore, two resonances
were observed for the hydrogen atoms attached to the
CꢁC double bond, and the hydrogen atoms bonded to
the aromatic ring gave two doublets in accordance with
two chemically different molecular halves. We suppose
that 3 is the product of a partial rearrangement of the
alkenylaluminium groups. One alkene group has the
1
observation of a quite simple H-NMR spectrum simi-
lar to that of compound 2 with singlets for the CMe3,
SiMe3 and phenyl protons.
4. Crystal structures of 1, 2, and 4
The molecular structure of compound 1 in the solid
state is depicted in Fig. 1. It results from a cis addition
of Al–H groups to both CꢀC triple bonds of the
starting diyne and has a trans butadiene core in its
molecular centre, which is located on a crystallographic
centre of symmetry. As expected (see Section 1), the
aluminium atoms are bonded to the terminal carbon
atoms, which are further attached to trimethylsilyl
groups. The bond distances in the electronically delo-
calized molecular center (CꢁC 134.1 pm; C–C 145.8
pm) are similar to those of free butadiene C4H6 (CꢁC
134 pm; C–C 148 pm) [13,14] and thus they are only
slightly affected by the dialkylaluminium substituents.
The Al1–C1 distances (196.5 pm) are as usual, and the
Al atoms have an almost ideally planar coordination
sphere (sum of the angles 359.4°). The atoms in the
molecular centre C1, C2, H2, Al1, Si1 and their equiva-
lents generated by the centre of symmetry form a
perfect plane, the maximum derivation of which is
observed for the hydrogen atom H2 with only 0.47 pm.
That plane is almost perpendicular to the plane around
the Al atom, their normals include an angle of 94.7°.
Compared to butadiene, some deformations of bond
angles in the molecular centre of 1 are observed which
may be caused by strong steric interactions. A small
angle of 112.1° is found between the dialkylaluminium
and trimethylsilyl substituents at the carbon atom C1,
while the angles C2–C1–Al1 and C2–C1–Si1 are en-
larged to 123.7 and 124.2°, respectively. In butadiene,
all angles of the terminal carbon atoms are close to the
ideal value of 120° [13]. The angle at the inner carbon
atom is enlarged from 122.4° in butadiene to 127.4° in
1.
Fig. 1. Molecular structure and numbering scheme of 1; the thermal
ellipsoids are drawn at the 40% probability level. Selected bond
lengths (pm) and angles (°): C1–C2 134.1(3), C2–C2% 145.8(4), C1–
Si1 187.5(2), C1–Al1 196.5(2), Al1–Ct1 198.6(3), Al1–Ct2 197.6(3),
C1–C2–C2% 127.4(3), C1–C2–H2 116.3(1), C2%–C2–H2 116.3(2),
C2–C1–Si1 124.2(2), C2–C1–Al1 123.7(2), Si1–C1–Al1 112.1(1),
C1–Al1–Ct1 119.2(1), C1–Al1–Ct2 117.3(1), Ct1–Al1–Ct2 122.9(1)
(C2% generated by −x, −y+1, −z+1).
Fig. 2. Molecular structure and numbering scheme of 2; the thermal
ellipsoids are drawn at the 40% probability level; methyl groups are
omitted for clarity. Selected bond lengths (pm) and angles (°): C21–
C2 148.0(3), C1–C2 133.9(3), C1–Si1 185.9(2), C1–Al1 196.0(2),
Al1–Ct1 198.0(3), Al1–Ct2 197.9(3), C21–C2–H2 114.0(1), C21–
C2–C1 132.0(2), C1–C2–H2 114.0(1), C2–C1–Si1 132.7(2), C2–
C1–Al1 117.6(2), Si1–C1–Al1 109.7(1), C1–Al1–Ct1 117.8(1),
C1–Al1–Ct2 117.9(1), Ct1–Al1–Ct2 123.3(1) (equivalent atoms gen-
erated by −x, −y, −z).
Figs. 2 and 3 show the molecular structures of com-
pounds 2 and 4; both molecules are located on crystal-
lographic centres of symmetry. 2 is the product of a cis
addition of two Al–H bonds to the ethyne groups of
the starting 1,4-bis(trimethylsilylethynyl)benzene, 4 is

W. Uhl, F. Breher / Journal of Organometallic Chemistry 608 (2000) 54–59
57
of the aromatic ring and of the ethene groups compris-
ing the atoms C1, C2, H2, Si, Al are tilted by 39.7°, and
the plane formed by the aluminium atom and its sub-
stituents deviates from an ideal perpendicular arrange-
ment (74.2°). The aluminium atom is 14 pm above the
a carbon atoms of its substituents. Owing to the partic-
ular conformation of the molecule, the Al atoms are
situated 193 pm above the plane of the benzene ring
and in particular above the C–H bond C23–H23. A
narrow contact exists between this bond and the coor-
dinatively unsaturated Al atoms (Al···C23 276.6 pm;
Al···H23 234.5 pm), which may indicate some weak
donor–acceptor interaction.
Fig. 3. Molecular structure and numbering scheme of 4; the thermal
ellipsoids are drawn at the 40% probability level; methyl groups are
omitted for clarity. Selected bond lengths (pm) and angles (°): C21–
C2 147.7(2), C1–C2 134.7(2), C1–Si 186.3(2), C1–Al 197.1(2), Al–
Ct1 199.4(2), Al–Ct2 199.6(2), C21–C2–H2 118.4, C21–C2–C1
123.3(1), C1–C2–H2 118.4, C2–C1–Si 119.1(1), C2–C1–Al
114.1(1), Si–C1–Al 126.10(8), C1–Al–Ct1 120.59(7), C1–Al–Ct2
115.82(8), Ct1–Al–Ct2 122.18(8) (equivalent atoms generated by
−x+1, −y+2, −z+2).
5. Experimental
All procedures were carried out under purified argon
in dried solvents (n-pentane and n-hexane over LiAlH4;
benzene over Na/benzophenone). Di(tert-butyl)-
aluminium hydride was synthesized as described in Ref.
[15], commercially available 1,4-bis(trimethylsilyl)-1,3-
butadiyne and 1,4-bis(trimethylsilylethynyl)benzene
(Lancaster) were thoroughly evacuated at room tem-
perature and used without further purification.
the completely rearranged product, in which the hydro-
gen atoms and the dialkylaluminium substituents are
on opposite sides of the CꢁC double bonds. Once
again, aluminium and silicon atoms are attached to the
same terminal carbon atoms in both cases. Despite their
different configurations, both compounds show almost
indistinguishable bond lengths. The CꢁC double bonds
(C1–C2 133.9 and 134.7 pm, respectively), the bonds to
the phenyl ring (C2–C21 148.0 and 147.7 pm), the
Al–C bonds (C1–Al1 196.0 and 197.1 pm, Al–Ct1/2
198.0 and 199.5 pm) and the Si–C bonds (C1–Si1 185.9
and 186.3 pm) are in an expected range and need no
further discussion. In contrast, the bond angles differ
significantly between both compounds with a strong
deformation of the angles at the CꢁC double bonds in
the cis product 2. While the angles C2–C1–Al and
C2–C1–Si are quite normal in the trans product 4
(114.1 and 119.1°, respectively), the C2–C1–Si1 angle
of 2 is enlarged to 132.7° (C2–C1–Al1 117.6°) indicat-
ing a considerable steric stress in the molecule, which
may be caused by a steric repulsion between the phenyl
group and the trimethylsilyl substituents. The molecular
centre of 2 comprising the benzene ring, the CꢁC
double bonds and the atoms attached to the ethene
groups is almost planar. The angle between the normals
of benzene (C21 to C23) and the alkenyl group (C21,
C2, C1, H2, Si1, Al1) is only 6.4°. The coordination
sphere of the aluminium atom deviates slightly from
planarity, and Al1 is located 11 pm above the plane
spanned by the carbon atoms C1, Ct1 and Ct2. This
plane is perpendicular to the diethenylbenzene group,
and their normals enclose an angle of 87.2°. The trans
product 4 deviates strongly from planarity. The planes
5.1. Synthesis of s-trans-[Z,Z]-1,4-bis{di(tert-
butyl)aluminium}-1,4-bis(trimethylsilyl)-1,3-butadiene
1: A solution of 0.951 g (6.70 mmol) of di(tert-bu-
tyl)alane in 25 ml of n-pentane was added dropwise to
a solution of 0.641 g (3.30 mmol) of 1,4-bis(trimethylsi-
lyl)-1,3-butadiyne in 25 ml of n-pentane at room tem-
perature. The mixture was stirred for 15 h, and the
solution adopted a yellow colour. All volatile compo-
nents were removed in vacuum, and the orange crys-
talline residue was dissolved in n-pentane. Product 1
crystallized in pale yellow, air sensitive crystals upon
cooling of the solution to −50°C. Yield: 0.632 g (40%).
M.p. (argon, sealed capillary): 92–93°C. 1H-NMR
(C6D6, 300 MHz): l=0.27 (s, 18 H, SiMe3), 1.12 (s, 36
H, Al–CMe3), 7.47 (s, 2 H, Al(Si)CꢁCH). 13C-NMR
(C6D6, 75.5 MHz): l=1.5 (SiMe3), 19.4 (Al–CMe3),
29.5 (Al–CMe3), 154.5 (Al(Si)CꢁCH–R); the second
alkene carbon atom was not detected. IR (CsBr plates,
paraffin, cm−1): w=1534 w wCꢁC; 1462 vs, 1377 s
paraffin; 1306 w, 1246 s, 1221 w lCH3; 1069 w, 1042 w,
1007 w, 936 w wCC; 882 sh, 856 vs zCH3; 837 vs, 814
sh wC3C; 766 m, 745 m, 723 w zCH3; 689 w, 678 w
wasSiC; 656 vw, 629 m, 596 m, 548 w, 529 w, 478 w
wAlC; 451 m, 424 w lC3C, lSiC3. Molar mass
(cryoscopically in benzene, g mol−1): calc. 478.86;
found 514.

58
W. Uhl, F. Breher / Journal of Organometallic Chemistry 608 (2000) 54–59
Table 1
Crystal data, data collection parameters and structure refinement for 1, 2 and 4a
1
2
4
Formula
C26H56Al2Si2
C32H60Al2Si2
Monoclinic
P21/n; no. 14
2
C32H60Al2Si2
Monoclinic
P21/n; no. 14
2
Crystal system
Space group [16]
Z
Monoclinic
P21/n; no. 14
2
Temperature (K)
213(2)
0.956
213(2)
0.976
213(2)
0.991
Dcalc (g cm−3
)
Unit cell parameters
a (pm)
b (pm)
950.0(1)
1031.1(2)
1231.1(2)
1546.7(3)
105.89(3)
1888.3(6)
0.157
878.26(6)
1156.03(9)
1533.9(2)
99.10(1)
1663.4(3)
0.170
1614.67(8)
1364.04(9)
105.917(8)
1860.2(2)
c (pm)
i (°)
V (10−30 m3)
v (mm−1
)
0.159
Crystal size (mm)
Diffractometer
Radiation
0.30×0.40×0.35
Stoe-IPDS
Mo–Ka; graphite monochromator
1.00×0.47×0.46
0.47×0.37×0.36
Exposure; D€ (°)
2q range (°)
Index ranges
207; 1.5
140; 1.5
158; 1.2
4.452q552.1
−115h511
−135k513
−185l518
3214
4.352q552.1
−115h511
−155k515
−195l518
3444
5.052q552.0
−105h510
−195k519
−165l516
3613
Independent reflections
Reflections F\4|(F)
Parameters
2492
145
2712
172
3005
172
R=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFo (F\4|(F))
0.0578
0.1220
0.665/−0.341
0.0525
0.1121
0.462/−0.253
0.0421
0.1323
0.379/−0.320
2
2 2
wR2={ꢀw(ꢁFoꢁ −ꢁFcꢁ ) /Sw(F2o )2}1/2 (all data)
Maximum/minimum residual electron density (1030 e m−3
)
a Programs SHELXL-97, SHELXTL-Plus [17]; solutions by direct methods, full matrix refinement with all independent structure factors.
631 m, 596 w, 523 w, 465 vw wAlC; 446 vw, 419 w
lC3C, lSiC3. Molar mass (cryoscopically in benzene, g
mol−1): calc. 554.96; found 495.
5.2. Synthesis of s-trans-[Z,Z]-1,4-bis{2-di(tert-
butyl)aluminium-2-trimethylsilyl-ethenyl}benzene
2: A solution of 0.274 g (1.93 mmol) of di(tert-bu-
tyl)alane in 15 ml of n-pentane was added dropwise to
a solution of 0.262 g (0.97 mmol) of 1,4-bis(trimethylsi-
lylethynyl)benzene in 30 ml of n-pentane at room tem-
perature. The mixture was stirred for 3 h. The
yellow-brown suspension was filtered, and all volatile
components were removed in vacuum. The oily brown
residue was dissolved in a small quantity of n-pentane
and cooled to −50°C to yield compound 2 as colour-
less, air sensitive crystals. Yield: 0.340 g (63%). M.p.
1
5.3. H-NMR data of the intermediate compound
s-trans-[E,Z]-1,4-bis{2-di(tert-
butyl)aluminium-2-trimethylsilyl-ethenyl}benzene (3)
1H-NMR (C6D6, 300 MHz): l=0.20 and 0.28 (each
s, 9 H, SiMe3), 1.05 and 1.15 (each s, 18 H, Al–CMe3),
7.07 and 7.39 (each d, 2 H, JHH=7.9 Hz, C6H4), 7.65
and 7.92 (s, 1 H, Al(Si)CꢁCH).
3
1
(argon, sealed capillary): 107–109°C. H-NMR (C6D6,
5.4. Synthesis of s-trans-[E,E]-1,4-bis{2-di(tert-butyl)-
aluminium-2-trimethylsilyl-ethenyl}benzene
300 MHz): l=0.19 (s, 18 H, SiMe3), 1.17 (s, 36 H,
Al–CMe3), 7.30 (s, 4 H, C6H4), 7.72 (s, 2 H,
Al(Si)CꢁCH). 13C-NMR (C6D6, 125.8 MHz): l=1.5
(SiMe3), 19.2 (Al–CMe3), 29.8 (Al–CMe3), 141.9 (ipso-
C of benzene), the other resonance of the benzene ring
was covered by the C6D6 signal, 153.9 (Al(Si)CꢁCH–
C6H4), 158.7 (Al(Si)CꢁCH–C6H4). IR (CsBr plates,
paraffin, cm−1): w=1593 w, 1551 w, 1501 w aryl,
wCꢁC; 1464 vs, 1377 s paraffin; 1314 vw, 1262 sh, 1246
m lCH3; 1221 vw, 1175 w, 1107 vw, 1076 vw, 1044 w,
1038 w, 1018 w, 1006 w, 934 w wCC; 854 vs, 841 vs
zCH3, wC3C; 812 m, 762 m, 721 w zCH3; 691 w wasSiC;
4: A solution of 1.210 g (2.18 mmol) of 2 in 25 ml of
benzene was heated to 60°C in a closed glass vessel for
7 days. The colour changed from colourless to yellow.
The solvent was removed in vacuum, and the pale
yellow residue was dissolved in n-pentane. After con-
centration to about 20 ml and cooling to −30°C the
product (4) was obtained as yellowish crystals. Yield:
1.150 g (95%). M.p. (argon, sealed capillary): 187°C.
1H-NMR (C6D6, 300 MHz): l=0.23 (s, 18 H, SiMe3),
1.04 (s, 36 H, Al–CMe3), 7.13 (s, 4 H, C6H4), 7.82 (s, 2

W. Uhl, F. Breher / Journal of Organometallic Chemistry 608 (2000) 54–59
59
H, Al(Si)CꢁCH). 13C-NMR (C6D6, 125.8 MHz): l=
0.3 (SiMe3), 18.8 (Al–CMe3), 30.0 (Al–CMe3), 125.8
(o-C of C6H4), 147.7 (ipso-C of C6H4), 153.0
(Al(Si)CꢁCHC6H4), 166.9 (Al(Si)CꢁCHC6H4). IR
(CsBr plates, paraffin, cm−1): w=1532 w, 1487 w aryl,
wCꢁC; 1460 vs, 1377 vs paraffin; 1316 w, 1260 sh, 1244
s lCH3; 1210 vw, 1171 vw, 1158 vw, 1105 w, 1079 vw,
1050 vw, 1007 w, 998 w, 982 vw, 959 w, 934 m, 916 s
wCC; 887 vs wC3C; 835 vs, 806 s, 743 s, 723 m zCH3;
687 m wasSiC; 625 w wsSiC; 592 m, 579 m, 542 m, 498 w,
466 vw wAlC; 434 s, 420 w, 403 w, 388 w, 370 w lC3C,
lSiC3.
Angew. Chem. 67 (1955) 424. (b) K. Ziegler, Angew. Chem. 68
(1956) 721. (c) K. Ziegler, H.-G. Gellert, H. Lehmkuhl, W.
Pfohl, K. Zosel, Justus Liebigs Ann. Chem. 629 (1960) 1.
[2] (a) E. Winterfeldt, Synthesis (1975) 617. (b) I. Marek, J.-F.
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5.5. Crystal structure determinations
Single crystals of compounds 1, 2 and 4 were ob-
tained by recrystallization from n-pentane. The crystals
of compound 1 were grown over a period of 4 weeks
from a dilute solution in n-pentane at −30°C. All
crystals of 1 were twinned, but the reflections of the
individuals could be detected separately. The refinement
of 1 was carried out with all but 12 reflections, which
were probably damaged by an overlap with those of the
second individual. Crystal data and structure refine-
ment parameters of all compounds are given in Table 1.
.
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Marder, Organometallics 17 (1998) 3557.
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Stoicheff, Tetrahedron 17 (1962) 163.
6. Supplementary material
The crystallographic data of compounds 1, 2 and 4
(excluding structure factors) were deposited with the
Cambridge Crystallographic Data Centre as supple-
mentary publication nos. CCDC 142062 (1), 142063 (2)
and 142064 (4). Copies of the data can be obtained free
of charge on application to The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
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Roth, O. Adamczak, R. Breuckmann, H.-W. Lennartz, R.
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Acknowledgements
We are grateful to the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie for
generous financial support.
[15] W. Uhl, Z. Anorg. Allg. Chem. 570 (1989) 37.
[16] T. Hahn (Ed.), International Tables for Crystallography, Space
Group Symmetry, vol. A, Kluwer Academic Publishers, Dor-
drecht, 1989.
[17] (a) SHELXTL-Plus REL. 4.1, Siemens Analytical X-Ray Instru-
ments Inc., Madison, WI, 1990. (b) G.M. Sheldrick, SHELXL-97,
Program for the refinement of structures, University of Go¨ttin-
gen, 1997.
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