Facile synthesis of an unsaturated spiro germane by hydroalumination and intramolecular 1,1-carbalumination

Article abstract of DOI:10.1021/om100359k

Treatment of the tetraethynylgermanium compound Ge(C≡CC ₆H₅)₄ 4 with 2 equiv of H-Al[CH(SiMe ₃)₂]₂ yielded the addition product Ge(C≡CC₆H₅)₂[C{AlR₂}=C(H) C₆H₅]₂ (5, R = CH(SiMe₃) ₂) by reduction of two of its C≡C triple bonds. Heating of 5 to 260 °C for 10 min gave a unique rearrangement reaction which via intramolecular 1,1-carbalumination afforded the spiro germane 6 (a 3,7-bis[1-phenylmeth-(Z)-ylidene]-4-germaspiro[3,3]hepta-1,5-diene derivative). The molecular structure of 6 comprises two unsaturated 1-germacyclobut-2-ene heterocycles with a joint germanium atom and two exocyclic C=C double bonds.

Full text of DOI:10.1021/om100359k

5236 Organometallics 2010, 29, 5236–5240
DOI: 10.1021/om100359k
Facile Synthesis of an Unsaturated Spiro Germane by Hydroalumination
and Intramolecular 1,1-Carbalumination†
,†
†
‡
‡
€
Werner Uhl,* Martina Rohling, Ernst-Ulrich Wurthwein, Nugzar Ghavtadze, and
Klaus Bergander‡
†
€
Institut fu€r Anorganische und Analytische Chemie der Universitat Munster, Corrensstrasse 30,
D-48149 Mu€nster, Germany, and Organisch-chemisches Institut der Universitat Munster,
€
‡
€
€
Corrensstrasse 40, D-48149 Mu€nster, Germany
Received April 28, 2010
Treatment of the tetraethynylgermanium compound Ge(CtCC6H5)4 4 with 2 equiv of H-Al-
[CH(SiMe3)2]2 yielded the addition product Ge(CtCC6H5)2[C{AlR2}dC(H)C6H5]2 (5, R = CH-
(SiMe3)2) by reduction of two of its CtC triple bonds. Heating of 5 to 260 °C for 10 min gave a unique
rearrangement reaction which via intramolecular 1,1-carbalumination afforded the spiro germane 6
(a 3,7-bis[1-phenylmeth-(Z)-ylidene]-4-germaspiro[3,3]hepta-1,5-diene derivative). The molecular
structure of 6 comprises two unsaturated 1-germacyclobut-2-ene heterocycles with a joint germa-
nium atom and two exocyclic CdC double bonds.
Introduction
treatment of bis- or tris(tert-butylethynyl)benzenes with
dialkylaluminum or -gallium hydrides.4 Relatively stable
addition products have been obtained by the corresponding
reactions of ((trimethylsilyl)ethynyl)benzenes.5 In only a few
of the latter reactions release of trialkylelement compounds
took place, which as a particularly important class of com-
pounds yielded molecular capsules.5,6 Di-tert-butylbuta-
diyne afforded unique carbocationic species by C-H bond
activation and chelating coordination of hydride anions.7
Recently we started investigations into the hydroalumination of
phosphorus-, silicon-, or germanium-centered oligoalkynes.8,9
The partially reduced compounds show a remarkable activa-
tion of the P-C, Si-C, or Ge-C bonds by intramolecu-
lar interactions of the coordinatively unsaturated alumi-
num atoms with the R-carbon atoms of remaining ethynyl
Hydroalumination1 and hydrogallation reactions are
powerful methods for the reduction of unsaturated organic
compounds. Furthermore, they are suitable to generate a
broad variety of unusual oligoaluminum or -gallium com-
pounds when oligoalkynes were employed as starting
materials.2 Different reaction courses occurred, depending
on the substituents attached to the CtC triple bonds.
Alkynylaluminum or -gallium compounds gave carbaalane
clusters or heteroadamantane cages by the release of the
corresponding trialkylelement derivatives.3 Similar conden-
sation reactions yielded cyclophane-type molecules by the
† Part of the Dietmar Seyferth Festschrift. Dedicated to Dietmar Seyferth.
*To whom correspondence should be addressed. Fax: þ49-251-
8336660. E-mail: uhlw@uni-muenster.de.
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r
pubs.acs.org/Organometallics
Published on Web 06/24/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 21, 2010 5237
dialkylaluminum hydride. Similar results have been ob-
tained with boron compounds.10
Results and Discussion
Reaction of Tetra(phenylethynyl)germane with H-Al[CH-
(SiMe3)2]2. Treatment of 2 equiv of the sterically encumbered
dialkylaluminum hydride H-Al[CH(SiMe3)2]2 with a solu-
tion of tetrakis(phenylethynyl)germane (4) at room tempera-
ture led to the complete consumption of the starting com-
pounds in less than 4 h (eq 1). Colorless crystals of compound
5 were isolated from these reaction mixtures after crystal-
lization from cyclopentane in 86% yield. A crystal structure
determination (Figure 1) revealed the expected product of
the addition of Al-H bonds to two of the CtC triple bonds
of 4. Despite the bulkiness of the bis(trimethylsilyl)methyl
groups the aluminum atoms attacked selectively the R-car-
bon atoms of the ethynyl groups which are attached to the
germanium atoms and bear a partial negative charge. Alumi-
num and hydrogen atoms occupy cis positions at the result-
ing CdC double bonds, which reflect the initial step of these
addition processes. Cis/trans isomerization to afford the
thermodynamically favored trans product is prevented in
this case by steric shielding.5 The lengths of the CdC double
Figure 1. Molecular structure of 5. The thermal ellipsoids are
drawn at the 40% probability level. Hydrogen atoms (with the
exception of the vinylic hydrogen atoms) and methyl groups of
˚
SiMe3 substituents are omitted. Important bond lengths (A) and
angles (deg) [values of the second molecule in brackets]: Ge(1)-
C(11) = 1.949(2) [1.958(2)], Ge(1)-C(21) = 1.952(2) [1.952(2)],
Ge(1)-C(31) = 1.929(2) [1.919(2)], Ge(1)-C(41) = 1.921(2)
[1.919(2)], C(11)-C(12) = 1.351(2) [1.348(3)], C(21)-C(22) =
1.347(3) [1.351(3)], C(31)-C(32) = 1.203(3) [1.207(3)], C(41)-
C(42) = 1.203(3) [1.205(3)], Al(11)-C(11) = 1.966(2) [1.976(2)],
Al(12)-C(21) = 1.978(2) [1.973(2)]; C(11)-Ge(1)-C(21) =
127.31(8) [127.77(8)], C(31)-Ge(1)-C(41) = 106.31(8) [104.15-
(9)], Ge(1)-C(11)-Al(11) = 122.67(9) [125.1(1)], Ge(1)-C(21)-
Al(12) = 126.1(1) [123.4(1)], Ge(1)-C(31)-C(32) = 170.4(2)
[172.6(2)], C(31)-C(32)-C(33) = 176.7(2) [176.8(2)], Ge(1)-
C(41)-C(42)=164.3(2) [173.4(2)], C(41)-C(42)-C(43)=176.5(2)
[177.1(2)].
11
˚
bonds (1.349 A on average) correspond to standard values.
The germanium atom has a distorted-tetrahedral environ-
ment with a relatively large angle between the alkenyl carbon
atoms (127.5°) which may be caused by a strong steric repul-
sion between the bulky dialkylaluminum substituents. The
different Ge-C bond lengths correlate to the different hybridiza-
2
˚
tion of the carbon atoms (Ge-C(sp )=1.953 A; Ge-C(sp) =
˚
1.920 A). Two C-C triple bonds remained intact and possess
the expected lengths of 1.205 A on average.
˚
Scheme 1
moieties (1; Scheme 1). In the case of the phosphorus
compounds these interactions resulted in the spontaneous
elimination of dialkylethynylaluminum and the formation of
novel mono- or bicyclic AlP2C2 (2) or AlP2C4 ring systems
(3).8 As reported in this article, we observed another type
of secondary reaction when we treated a tetraethynyl-
germanium compound with 2 equiv of a sterically shielded
The NMR data are in accordance with the molecular
structure in the solid state. We observed the expected
resonances for the carbon atoms of the CdC double bonds

5238 Organometallics, Vol. 29, No. 21, 2010
Uhl et al.
(δ 160.7 and 151.8 (AlC)) and CtC triple bonds (δ 109.3 and
1
96.9 (GeC)) in the 13C NMR spectrum. In the H NMR
spectrum the vinylic hydrogen atoms gave a singlet at δ 7.89
in the normal range.5 A further two singlets were observed
for the trimethylsilyl groups and the AlCH protons. The
latter exhibit an unusual chemical shift of δ 0.53 compared to
the expected value of about δ -0.312 (see for comparison
compound 6 below). In the solid-state structure these hydro-
gen atoms are almost ideally in the nodal plane of the CdC
double bonds and their chemical shift may be influenced by
this particular position. The dihedral angles C-Al-CdC
are 14.5° on average and indicate an almost coplanar ar-
rangement of the CdC bonds and the AlC3 planes and hence
a parallel orientation of the CdC π orbitals and the empty
p orbitals of the aluminum atoms. The dihedral angles C-
Al-C-H, including the C-H groups of the CH(SiMe3)2
substituents and the R-carbon atoms of the CdC double
bonds, are close to the ideal value of 0° (4.8° on average). A
similar correlation between molecular conformation and
chemical shift of Al-C-H hydrogen atoms has previously
been observed in a few bis(trimethylsilyl)methylaluminum
compounds.13 These NMR data may indicate that the mole-
cular conformation of 5 in the solid state predominates also
in solution.
Figure 2. Molecular structure of 6. The thermal ellipsoids are
drawn at the 40% probability level. Hydrogen atoms (with the
exception of the vinylic hydrogen atoms) and methyl groups of
˚
SiMe3 substituents are omitted. Important bond lengths (A) and
angles (deg) [values of the second molecule in brackets]: Ge(1)-
C(11) = 1.975(4) [1.977(4)], Ge(1)-C(21) = 1.981(4) [1.976(4)],
Ge(1)-C(32) = 1.974(4) [1.966(4)], Ge(1)-C(42) = 1.971(4)
[1.972(4)], C(11)-C(12) = 1.348(6) [1.335(6)], C(11)-C(31) =
1.488(6) [1.492(6)], C(31)-C(32) = 1.368(6) [1.374(6)], C(21)-
C(22) = 1.343(6) [1.338(6)], C(21)-C(41) = 1.484(6) [1.491(6)],
C(41)-C(42) = 1.365(6) [1.367(6)], Al(11)-C(31) = 2.001(4)
[1.985(4)], Al(12)-C(41) = 1.994(4) [1.998(4)]; C(11)-Ge(1)-
C(32) = 70.2(2) [70.7(2)], C(21)-Ge(1)-C(42) = 70.5(2)
[70.2(2)], C(11)-C(31)-C(32) = 105.1(4) [105.4(4)], C(21)-
C(41)-C(42) = 106.4(4) [105.2(4)].
Thermal Rearrangement of 5 and Formation of the Spiro
Compound 6. Compound 5 decomposed at 215 °C to give a
red, highly viscous liquid. We conducted this experiment on a
preparative scale and heated compound 5 without a solvent
to 260 °C for 10 min (eq 1). Dissolution of the product in
cyclopentane and slow evaporation of the solvent at room
temperature yielded colorless crystals of 6 in 81% yield.
Crystal structure determination (Figure 2) showed that a
remarkable rearrangement reaction had taken place. A spiro
compound was formed in which a joint germanium atom is
part of two electronically unsaturated germacyclobutene hetero-
cycles. These planar four-membered rings (maximum devia-
broken, and a new bond has been formed between germa-
nium and the original β-carbon atom of the alkynyl group.
This transformation may be considered as a special case of
the well-known carbalumination reactions14 which, how-
ever, usually proceed via an 1,2-addition of the Al-C bond
to the unsaturated organic system. In contrast, the corre-
sponding 1,1-carbaboration is quite common10 and leads to
the formation of unsaturated heterocyclic compounds, in-
cluding spiro silanes similar to 6.15 The reaction mechanism
based on quantum chemical calculations is discussed in detail
below. Some spiro germanes with a germanium atom in the
bridging position are reported in the literature, but they do
not contain four-membered unsaturated heterocycles.16,17
Resonances of two different CdC double bonds were
observed in the 13C NMR spectrum (δ 158.4 and 132.4;
˚
tion of an atom 0.036 A for C31) have an almost ideally
perpendicular arrangement with an angle between the nor-
mals of their planes of 87°. One carbon atom of the endo-
cyclic CdC double bonds is bonded to a phenyl group; the
second one bears the dialkylaluminum group with a coordi-
natively unsaturated aluminum atom. The third carbon
atom of the GeC3 rings is part of an exocyclic CdC double
bond. The germanium atom has a strongly distorted tetra-
hedral environment with acute endocyclic C-Ge-C angles
of 70.4° on average. The exocyclic CdC double bonds have
˚
normal lengths of 1.341 A on average, while the endocyclic
˚
ones are slightly lengthened to 1.369 A. The Al-C distances
to the alkenyl carbon atoms (1.995 A) are slightly lengthened
˚
(14) Eisch, J. J.; Amtmann, R. J. Org. Chem. 1972, 37, 3410.
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Chem. 2008, 22, 383. (b) Wrackmeyer, B.; Maisel, H. E.; Molla, E.; Mottalib,
A.; Badshah, A.; Bhatti, M. H.; Ali, S. Appl. Organomet. Chem. 2003, 17,
465. (c) Khan, E.; Wrackmeyer, B.; Kempe, R. Eur. J. Inorg. Chem. 2008,
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2009, 23, 124.
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Y.; Akkerman, O. S.; Bickelhaupt, F. J. Organomet. Chem. 1986, 316,
51. (b) Bajer, F. J.; Post, H. W. J. Organomet. Chem. 1968, 11, 187.
(c) Andriamizaka, J.-D.; Couret, C.; Escudie, J.; Laporterie, A.; Manuel, G.;
Regitz, M. J. Organomet. Chem. 1991, 419, 57. (d) Laurent, C.; Mazerolles,
P. Synth. React. Inorg. Met.-Org. Chem. 1992, 22, 1183. (e) Mazerolles, P.;
Laurent, C. J. Organomet. Chem. 1992, 439, 115. (f) Ogawa, K.; Takeuchi,
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(g) Boo, B. H.; Park, J.; Yeo, H. G.; Lee, S. Y.; Park, C. J.; Kim, J. H. J. Phys.
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compared to the corresponding bond lengths in the starting
compound 5. This lengthening may indicate some steric
stress in the molecule. The formation of 6 may be described
by the insertion of the R-carbon atoms of the CtC triple
bonds of 5 into the Al-C bonds of the aluminum-alkenyl
units (1,1-carbalumination). Hence, a Ge-C bond has to be
(9) (a) Uhl, W.; Heller, D. Z. Anorg. Allg. Chem. 2010, 636, 581.
€
(b) Uhl, W.; Rohling, M.; Kosters, J. New J. Chem. DOI:10.1039/
c0nj00050.g.
(10) Wrackmeyer, B. Coord. Chem. Rev. 1995, 145, 125.
(11) March, J. Advanced Organic Chemistry, 3rd ed.; Wiley: New York,
1985; p 19.
€
(12) Uhl, W.; Er, E.; Hepp, A.; Kosters, J.; Grunenberg, J. Organo-
metallics 2008, 27, 3346and references cited therein..
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(13) (a) Uhl, W.; Karsch, H. H.; Schutz, U.; Vester, A. Chem. Ber.
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Article
Organometallics, Vol. 29, No. 21, 2010 5239
δ 181.5 and 177.0). The signals at lower field belong to the
endocyclic CdC bond. The vinylic hydrogen atoms resonate
at δ 7.43 in the 1H NMR spectrum. The hydrogen atoms of
the AlCH groups have a chemical shift of δ -0.24, which in
contrast to the corresponding resonance of compound 5 is in
the range normally observed for bis(trimethylsilyl)methyla-
luminum compounds with tricoordinated aluminum atoms.11
Probably due to steric interactions, the endocyclic CdC
bond and the AlC3 plane are not coplanar as in 5 but are
almost perpendicularly arranged with dihedral angles
C-Al-CdC (including the central carbon atom of the CH-
(SiMe3)2 substituents) of about 68°. Hence, in contrast to 5
the C-H bonds of the AlCH groups are not in the nodal
planes of the π orbital of the CdC bond. Molecular sym-
metry gives rise to chemically different trimethylsilyl groups,
and a temperature-independent splitting of the correspond-
ing resonances into two singlets in the 1H, 13C, and 29Si NMR
spectra is observed.
Quantum Chemical Calculations and Rearrangement Me-
chanism. Quantum chemical calculations using the Gaussian
09 suite of programs18 have been performed on the simplified
model system 7, in which the germanium atom is bonded to
two methyl groups and alkynyl and alkenyl substituents. The
rearrangement reaction of 7 to give 8 proceeds synchro-
nously via the transition structure TS7f8 shown in Figure 3.
The calculations for the sterically relatively poorly shielded
model compound result in a significant direct interaction
Figure 3. Calculated structures and relative energies (kcal/mol)
for the conversion of the model compound 7 to 8.
˚
is weakened (2.00 to 2.21 A). It is completely opened in the
final product 8. The C-C bond length C(1)-C(2) increases
continuously from 1.22 A for the triple bond in 7 to 1.31 A
˚
˚
˚
(transition state) and 1.38 A in 8, which is slightly lengthened
compared to the standard value of a CdC double bond. The
bond lengths calculated for the germacyclobutene hetero-
cycle of 8 are in excellent agreement with the experimental
data of the spiro compound 6 (Figure 2). The NBO charges
calculated for 8 are -0.36 (C(1)), -0.62 (C(2)), -0.34 (C(4)),
þ1.41 (Ge(3)), and þ1.97 (Al(5)). The activation barrier is
calculated to be 34.9 kcal/mol, which is in accordance with
the relatively drastic reaction conditions (260 °C) required
for the formation of 6. The complete reaction is slightly
exothermic (-2.8 kcal/mol). The bond forming process
mainly proceeds in the HOMO-1 and HOMO-2 (see Sup-
porting Information). A dissociation of the starting com-
pound 7 into dimethyl(2-phenylethenylidene)germane and
di-tert-butylphenylethynylaluminum and subsequent cyclo-
addition seems to be unlikely, as this system is 57.4 kcal/mol
higher in energy compared to 7.
˚
between the carbon atom C(2) and Al(5) (Al(5)-C(2) = 2.60 A)
in the ground state of the molecule. This interaction is
favored by the relatively high negative charge at C(2) (NBO:
-0.49; Al, þ1.96). In the transition state the Al(5)-C(2)
˚
distance is shortened to 1.93 A and corresponds to a normal
Al-C bond. Simultaneously the Ge(3)-C(2) distance in-
creases from 1.98 to 2.58 A, and a new bond is formed
˚
˚
between Ge(3) and the carbon atom C(1) (2.00 A), which
represents the β-carbon atom of the intact ethynyl moiety of
the starting compound 7. A transannular approach of the
˚
carbon atoms C(2) and C(4) (2.19 A) may reflect the first step
of the C-C bond formation to give the GeC3 heterocycle
˚
(1.48 A in 8). The Al-C bond to the vinylic carbon atom C(4)
€
€
€
(17) (a) Koster, R.; Seidel, G.; Klopp, I.; Kruger, C.; Kehr, G.; Suss,
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Y. J. Organomet. Chem. 2010, 695, 740. (g) Chen., X.; Yamamoto, Y.;
Akiba, K. Heteroat. Chem. 1995, 6, 293. (h) Weatherhead, R. A.; Carducci,
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Castle, S. L. J. Org. Chem. 2009, 74, 9082.
Experimental Section
All procedures were carried out under purified argon. n-
Pentane, n-hexane, and cyclopentane were dried over LiAlH4,
toluene, and diethyl ether over Na/benzophenone. The dialkyl-
aluminum hydride R2Al-H (R = CH(SiMe3)2) was obtained
according to a literature procedure.19 Tetrakis(phenylethynyl)-
germane was synthesized in high yield by a slight modification of
a method described by Wrackmeyer.17 Germanium tetrachlor-
ide and phenylethyne were employed as purchased. The assign-
ment of the NMR spectra is based on HMBC, HSQC, ROESY,
and DEPT135 data. Only the most intensive masses of the mass
spectra are given; the complete isotopic patterns are in accor-
dance with the calculated ones.
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.;
Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.;
Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.;Staroverov, V. N.;Kobayashi, R.;Normand, J.;Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.;
Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,
A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannen-
berg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.;
Ortiz, J. V.; Cioslowski, J.; , Fox, D. J. Gaussian 09, Revision A.02;
Gaussian, Inc., Wallingford, CT, 2009. Details of the quantum chemical
calculations (Gaussian archive entries) may be obtained from E.-U.W. upon
request.
Synthesis of Tetrakis(phenylethynyl)germane (4).17 A solution
of n-butyllithium in n-hexane (1.6 M, 58.2 mL, 93.2 mmol) was
added dropwise to a solution of phenylethyne (9.51 g, 10.2 mL,
93.2 mmol) in 100 mL of diethyl ether at -78 °C. After 2 h
a solution of germanium tetrachloride (5.00 g, 2.7 mL, 23.3
mmol) in 50 mL of diethyl ether was added dropwise at the
(19) (a) Uhl, W.; Cuypers, L.; Graupner, R.; Molter, J.; Vester, A.;
€
Neumuller, B. Z. Anorg. Allg. Chem. 2001, 627, 607. (b) Uhl, W.; Matar,
M. Z. Naturforsch. 2004, 59b, 1214.

5240 Organometallics, Vol. 29, No. 21, 2010
Uhl et al.
same temperature. Stirring was continued at -78 °C for 2 h. The
solution was warmed to room temperature and stirred for a
further 14 h. The mixture was treated with dilute HCl (10%,
100 mL) and additional diethyl ether (50 mL). The organic layer
was separated, and the aqueous phase was extracted three times
with 20 mL of diethyl ether. The combined organic layers were
dried over MgSO4 and filtered. The solvent was removed under
vacuum, and compound 4 was obtained as a colorless solid after
crystallization from n-pentane at -30 °C. Yield: 7.65 g (69%).
Mp (argon, sealed capillary): 186 °C. Anal. Calcd for C32H20Ge
(477.2): C, 80.5; H, 4.2. Found: C, 80.1; H, 4.1. 1H NMR (C6D6,
400 MHz): δ 7.35 (8 H, m, o-H), 6.89 (4 H, m, p-H), 6.83 (8 H, m,
m-H). 13C NMR (C6D6, 100 MHz): δ 132.7 (o-C), 129.4 (p-C),
128.4 (m-C), 122.3 (ipso-C), 105.8 (CtCPh), 85.2 (CtCPh).
IR (KBr plates, paraffin, cm-1): 2164 m (ν(CtC)); 2031 vw,
1954 vw, 1906 vw, 1884 vw, 1807 vw, 1701 vw, 1686 vw, 1595 vw
(phenyl); 1456 vs, 1377 vs (paraffin); 1300 w, 1277 vw, 1240 vw,
1215 w, 1155 w, 1067 vw, 1051 vw, 1024 w, 966 vw, 916 w, 843
vw, 814 m, 754 s (ν(CC), δ(CH), δ(CC)); 723 s (paraffin); 687 m,
590 m, 532 s, 463 w (ν(GeC)). MS (EI, 20 eV, 120 °C): m/z (%)
478 (92) [M]þ, 404 (100), 276 (18) [Ge(CCPh)2]þ.
Synthesis of 5. A solution of 4 (0.203 g, 0.425 mmol) in 10 mL
of toluene was added dropwise to a solution of bis[bis-
(trimethylsilyl)methyl]aluminum hydride (0.296 g, 0.855 mmol)
in 15 mL of toluene at room temperature. The colorless solution
was stirred for 4 h. The solvent was removed under vacuum, and
the residue was recrystallized from cyclopentane (þ20 to -15 °C)
to yield colorless crystals of 5. Yield: 0.421 g (86%). Mp (argon,
sealed capillary): 215 °C dec (formation of 6). Anal. Calcd for
C60H98Al2Si8Ge (1170.7): C, 61.6; H, 8.4. Found: C, 61.8; H 8.2.
1H NMR (C6D6, 400 MHz): δ 7.89 (2 H, s, CdCHPh), 7.63 (4 H,
m, o-H of alkynyl-Ph), 7.26 (4 H, m, o-H of alkenyl-Ph), 7.19 (4
H, m, m-H of alkenyl-Ph), 7.10 (2 H, m, p-H of alkenyl-Ph), 7.07
(4 H, m, m-H of alkynyl-Ph), 7.00 (2 H, m, p-H of alkynyl-Ph),
0.53 (4 H, s, CHSi2), 0.31 (72 H, s, SiMe3). 13C NMR (C6D6,
100 MHz): δ 160.7 (CdCHPh), 151.8 (CdCHPh), 140.6 (ipso-C
of alkenyl-Ph), 132.6 (o-C of alkynyl-Ph), 129.1 (o-C of alkenyl-
Ph), 128.9 (p-C of alkynyl-Ph), 128.5 (m-C of alkynyl-Ph), 128.2
(m-C of alkenyl-Ph), 128.1 (p-C of alkenyl-Ph), 124.3 (ipso-C of
alkynyl-Ph), 109.3 (CtCPh), 96.9 (CtCPh), 10.1 (AlCHSi2),
5.0 (SiMe3). 29Si NMR (C6D6, 79.5 MHz): δ -3.1. IR (KBr
plates, paraffin, cm-1): 2164 m, 2151 m (ν(CtC)); 1944 vw,
1802 vw, 1699 vw, 1597 w, 1576 vw, 1543 m (ν(CdC), phenyl);
1466 vs, 1377 vs (paraffin); 1300 w, 1248 s (δ(CH3)); 1215 m,
1155 w, 1072 w (ν(CC), δ(CH), δ(CC)); 1015 m (δ(CHSi2)); 947 m,
927 m, 845 vs, 777 w, 754 m (F(CH3(Si))); 723 m (paraffin);
689 m, 671 m (νas(SiC)); 633 vw, 614 vw, 601 vw (νs(SiC)); 575 w,
532 m, 498 w, 470 w, 428 w (ν(GeC), ν(AlC)). MS (EI, 20 eV,
180 °C): m/z 1170 (1) [M]þ, 1155 (1) [M - CH3]þ, 1011 (3) [M -
CH(SiMe3)2]þ, 622 (43) [Ge(CtCPh)(CAlR2=CHPh)]þ.
Synthesis of 6. Neat compound 5 (0.305 g, 0.261 mmol) was
melted and heated to 260 °C for 10 min. The product was cooled
to room temperature and dissolved in cyclopentane. Slow
evaporation of the solvent at room temperature afforded com-
pound 6 as colorless crystals. Yield: 0.246 g (81%). Mp (argon,
sealed capillary): color change to red occurred >210 °C;
sublimation of a colorless substance started >260 °C before
melting. Anal. Calcd for C60H98GeAl2Si8 (1170.7): C, 61.6; H,
8.4. Found: C, 62.0; H, 8.4. 1H NMR (C6D6, 400 MHz): δ 7.72
(4 H, m, o-H of CdC(H)-Ph), 7.47 (4 H, m, o-H of GeC-Ph), 7.43
(2 H, s, CdCHPh), 7.21 (4 H, m, m-H of CdC(H)-Ph), 7.14 (4 H,
m, m-H of GeC-Ph), 6.97 (2 H, m, p-H of C=CHPh), 6.94 (2 H,
m, p-H of GeC-Ph), 0.33 and 0.31 (each 36 H, s, SiMe3), -0.24
(4 H, s, AlCHSi2). 13C NMR (C6D6, 100 MHz): δ 181.5 (GeC3
ring, C-Al), 177.0 (GeC3 ring, C-Ph), 158.4 (GeC3 ring, exocyclic
CdC), 140.9 (ipso-C of GeC-Ph), 139.0 (ipso-C of CdC(H)Ph),
132.4 (CdCHPh), 129.4 (m-C of CdC(H)Ph), 129.2 (m-C of
GeC-Ph), 128.3 (p-C of GeC-Ph), 127.7 (m-C of CdC(H)Ph),
127.4 (o-C of GeC-Ph), 126.3 (o-C of CdC(H)Ph), 11.8
(AlCSi2), 4.7 and 4.6 (SiMe3). 29Si NMR (C6D6, 79.5 MHz):
δ -2.44 and -2.39. IR (KBr plates, Nujol, cm-1): 1951 vw, 1934
vw, 1595 m, 1574 w, 1526 vw, 1493 m (ν(CdC), phenyl); 1458 vs,
1377 vs (paraffin); 1248 vs (δ(CH3)); 1175 vw, 1153 w, 1051 s
(ν(CC), δ(CH), δ(CC)); 1012 s (δ(CHSi2)); 930 m, 914 w, 843 vs,
779 m, 750 s (F(CH3(Si))); 723 w (paraffin); 689 s, 673 m
(νas(SiC)); 633 w, 613 w (νs(SiC)); 565 m, 550 w, 505 w, 465 w
(ν(GeC), ν(AlC)).
Crystal Structure Determinations of Compounds 5 and 6.
Single crystals were obtained by crystallization from n-hexane
(5, þ20 to -15 °C) or by slow evaporation of a solution in n-
hexane at room temperature (6). The crystallographic data were
collected with a Bruker APEX diffractometer. The structures
were solved by direct methods and refined with the program
SHELXL-9720 bya full-matrix least-squares methodbased onF2.
Both compounds crystallize in the centrosymmetric triclinic
space group P1 with two independent molecules in the asym-
metric unit. A trimethylsilyl group (Si71) of compound 5 showed
disorder; the atoms of the methyl groups were refined on split
positions (0.61: 0.39). The crystals of 6 enclosed one n-hexane
molecule in the unit cell; it is located on a center of symmetry.
Further details of the crystal structure determinations are
available from the Cambridge Crystallographic Data Center
on quoting the depository numbers CCDC-774576 (5) and
CCDC-774577 (6 0.25C6H14).
3
Quantum Chemical Calculations.18 The B3LYP functional
with the 6-311G(d,p) basis set was used to compute the geome-
tries and the normal mode vibration frequencies of the struc-
tures. For single-point energy calculations on DFT-optimized
geometries the SCS-MP2 method was applied.21 All energies
discussed are 0 K energies including zero-point corrections. The
character of the stationary points was verified on the basis of
frequency analyses. The vibration related to the imaginary
frequency of the transition structure corresponds to the nuclear
motion along the reaction coordinate under study. An intrinsic
reaction coordinate (IRC) calculation was performed in order to
unambiguously connect the transition structure with the reac-
tant and the product. NBO charges were determined using the
Gaussian 09 program.22
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie (Frankfurt) for generous financial support.
Supporting Information Available: CIF files giving the crystal
data for compounds 5 and 6 0.25C6H14, a table of crystal data
3
and structure refinement details, and tables and figures giving
optimized geometries and MO plots of the calculated structures.
This material is available free of charge via the Internet at http://
pubs.acs.org.
(20) SHELXTL-Plus, release 4.1; Siemens Analytical X-Ray Instru-
ments, Inc., Madison, WI, 1990. Sheldrick, G. M. SHELXL-97, Program
€
€
€
for the Refinement of Structures; Universitat Gottingen, Gottingen,
Germany, 1997.
(21) Grimme, S. J. Chem. Phys. 2003, 118, 9095–9102.
(22) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys.
1985, 83, 735–746.