Preparation, Structure, and 73Ge NMR Spectroscopy of Arylgermanes ArGeH3, Ar2GeH2, and Ar3GeH

Article abstract of DOI:10.1021/om990349z

Arylgermanes of the types ArGeH₃, At₂GeH₂, and Ar₃GeH are important precursors for the preparation of oligo- and polygermanes. These precursors are readily prepared in good yields via an in situ Grignard reaction employing tetra(ethoxy)germane, an aryl halide, and magnesium metal in tetrahydrofuran as the reaction medium. The aryl-tri(ethoxy)germanes obtained were reduced to the germane hydrides with LiAIH₄. This method is also applicable for aryl groups with sensitive substituents, as demonstrated for (4-methoxyphenyl)germane (p-anisylgermane, MeOC₆H₄GeHa). With modified stoichiometry, bis(p-anisyl)gennane is also available. The insertion of GeCI₂ into the C-Br bond of arylbromides using catalytic amounts of anhydrous Aids proved to be an efficient alternative if the reaction was carried out in the absence of a solvent. After LiAlH₄ reduction of the aryltrihalogermanes, phenyl-,p-tolyl-, and mesitylgermane were obtained in good yields. The arylgermanes have been identified by their analytical and spectroscopic data, including ⁷³Ge (s = 9/2) NMR spectroscopy. Very surprisingly, sharp multiplet signals were observed with well-resolved ¹J(Ge,H) couplings. The molecular structure of p-MeOC₆H₄GeH₃ was determined from low-temperature X-ray diffraction data collected from a single-crystal grown "in situ" from the melt (mp: 15 °C). The significant distortions observed in the anisyl part of the structure and the conformation of the molecule are in excellent agreement with results of ab initio quantum chemical calculations (MP2/6-31G) of this compound.

Full text of DOI:10.1021/om990349z

Organometallics 1999, 18, 4317-4324
4317
P r ep a r a tion , Str u ctu r e, a n d 73Ge NMR Sp ectr oscop y of
Ar ylger m a n es Ar GeH3, Ar 2GeH2, a n d Ar 3GeH
Frank Riedmiller, Gerald L. Wegner, Alexander J ockisch, and
Hubert Schmidbaur*
Anorganisch-chemisches Institut der Technischen Universita¨t Mu¨nchen, Lichtenbergstrasse 4,
D-85747 Garching, Germany
Received May 10, 1999
Arylgermanes of the types ArGeH3, Ar2GeH2, and Ar3GeH are important precursors for
the preparation of oligo- and polygermanes. These precursors are readily prepared in good
yields via an in situ Grignard reaction employing tetra(ethoxy)germane, an aryl halide, and
magnesium metal in tetrahydrofuran as the reaction medium. The aryl-tri(ethoxy)germanes
obtained were reduced to the germane hydrides with LiAlH4. This method is also applicable
for aryl groups with sensitive substituents, as demonstrated for (4-methoxyphenyl)germane
(p-anisylgermane, MeOC6H4GeH3). With modified stoichiometry, bis(p-anisyl)germane is also
available. The insertion of GeCl2 into the C-Br bond of arylbromides using catalytic amounts
of anhydrous AlCl3 proved to be an efficient alternative if the reaction was carried out in
the absence of a solvent. After LiAlH4 reduction of the aryltrihalogermanes, phenyl-, p-tolyl-,
and mesitylgermane were obtained in good yields. The arylgermanes have been identified
by their analytical and spectroscopic data, including 73Ge (s ) 9/2) NMR spectroscopy. Very
1
surprisingly, sharp multiplet signals were observed with well-resolved J (Ge,H) couplings.
The molecular structure of p-MeOC6H4GeH3 was determined from low-temperature X-ray
diffraction data collected from a single-crystal grown “in situ” from the melt (mp: 15 °C).
The significant distortions observed in the anisyl part of the structure and the conformation
of the molecule are in excellent agreement with results of ab initio quantum chemical
calculations (MP2/6-31G*) of this compound.
In tr od u ction
Silicon hydrides have also attracted considerable
interest as precursors for optoelectronic and nonlinear
optical materials, which can be generated through new
techniques including, e.g., dehydrogenative or desilana-
tive coupling of arylsilanes.2-6 These silicon-based
polymers feature conjugated di/polysilane and arene
units with enhanced absorption in the UV-Vis region,
which has advantages for the production of photoresist
and related materials.7 This synthetic potential has led
to increasing interest in tailored arylsilane molecules
with various specific photochemical properties associ-
ated with the substitution pattern.8
Arylgermanes ArmGeH4-m have received only very
limited attention.1d,9 However, very recently two im-
portant contributions showed that oligomerization of
phenylgermanes by dehydrogenative as well as demeth-
anative coupling are facile, easily controlled, high-yield
For a long time germanium hydrides have been a
largely neglected area in preparative and structural
chemistry owing to a very limited range of applications.
The demand for high-purity germanium and germanium
alloys in modern microelectronics has changed this
situation very rapidly and there is now a steady growth
of pertinent research and development.1 Application of
volatile germanium compounds for the production of
thin film devices, in particular by epitaxial growth, has
focused renewed attention to germanium hydrides and
their derivatives.1d,2 The development thus follows, with
some delay, the enormous activities in the chemistry
and physics of silicon hydrides in the last four decades.2b,c
* To whom correspondence should be addressed.
(1) (a) Katz, S. M.; Reichl, J . A.; Berry, D. H. J . Am. Chem. Soc.
1998, 120, 9844. (b) J oseph, A. J .; Cresler, J . D.; Richey, D. M.; Hasame,
D. L. Technol. Dig.-Int. Electron. Devices Meet. 1996, 253. (c) Tanaka,
H.; Sadamoto, M.; Ishiguro, N.; Yanagana, N.; Fukuda, S. J pn. Kokai
Tokyo Koho Patent 09,191,117 [97,191,117] Chem. Abstr. 127, 193056v.
(d) Lesbre, M.; Mazerolles, P.; Satge´, J . The Organic Compounds of
Germanium; Seyferth, D., Ed.; Wiley-Interscience: New York, 1971.
(e) Riviere, P.; Riviere-Baudet, M.; Satge´, J . Comprehensive Organo-
metallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.;
Pergamon Press: Oxford 1982, Vol. 2; Chapter 10. (f) Comprehensive
Organometallic Chemistry II; Wilkinson, G., Stone, F. G. A., Abel, E.
W., Davies A. G., Eds.; Pergamon Press: Oxford 1995; Vol. 2, Chapter
5.
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10.1021/om990349z CCC: $18.00 © 1999 American Chemical Society
Publication on Web 09/14/1999

4318 Organometallics, Vol. 18, No. 21, 1999
Riedmiller et al.
processes which lead to interesting di- and polyger-
manes.1a,10 Dimethyltitanocene and tetrakis(trimeth-
ylphosphine)ruthenium are employed as catalyst pre-
cursors, respectively.
In modifications of these early preparations we used
tetra(ethoxy)germane as starting material and subjected
it to an “in situ Grignard” reaction (in analogy to the
well-known synthetic concept for polysilyl-arenes via Si-
(OR)423) employing magnesium metal and aryl halides
in boiling tetrahydrofuran (THF) (eq 1).
Following some earlier work on alkylgermanes11 we,
therefore, revisited the chemistry of arylgermanes.1 The
program was started with an effort to find new or
improved pathways to simple representatives, to deter-
mine their molecular structure, and to provide a set of
fundamental spectroscopic data. Previous spectroscopic
investigations had not employed 73Ge NMR methods.
The few attempts gave only poorly resolved spectra or
no results at all.12-14 Recent improvements in the
equipment and techniques have now made such studies
possible.11 Structural studies of arylgermanes were
limited to gas-phase investigations by microwave spec-
troscopy, supplemented by vibrational and electronic
spectroscopy, and by quantum chemical calculations.15-17
P r ep a r a tion of Ar ylger m a n es. The few arylger-
manes described in the literature were prepared by
treatment of germanium tetrachloride with aryl Grig-
nard, aryllithium, or arylmercury reagents to give
aryltrichlorogermanes.18-20 The first two mentioned
reactions are not very selective and give a range of
products in low yields. Reduction of the chlorogermanes
with lithium aluminum hydride affords the correspond-
ing hydrides. Arylhalogermane precursors were also
obtained by the insertion of germanium dihalides into
the aryl-halogen bond of aryl halides, but the procedure
(1)
(2)
This reaction can also be carried out with substituted
aryl halides as demonstrated with anisyl bromide (1-
bromo-4-methoxybenzene). The anisyl group has proved
to be an important substituent in the chemistry of
arylsilanes because of its excellent leaving group prop-
erties in protodearylation reactions.24 The primary
products, aryl(ethoxy)germanes, can be reduced with
LiAlH4 and have been found to give better yields (86%)
than the halogenogermanes (29 and 32%, respec-
tively).18 Equation 2 shows the preparation of 4-meth-
oxyphenylgermane (1) as a representative example.
Diarylgermanes such as bis(4-methoxyphenyl)germane
(2) can be synthesized following the same sequence of
reactions with modified stoichiometry (eq 3).
21
in its original form was limited either to GeI2 or to
pressurized reactions with GeCl2(L) adducts22 and thus
was not very satisfactory.
(8) (a) Schro¨ck, R.; Angermair, K.; Sladek, A.; Schmidbaur, H.
Organometallics 1994, 13, 3399. (b) Schro¨ck, R.; Sladek, A.; Schmid-
baur, H. Z. Naturforsch. 1994, 49b, 1036. (c) Schro¨ck, R.; Angermair,
K.; Sladek, A.; Schmidbaur, H. J . Organomet. Chem. 1996, 509, 85.
(d) Ishikawa, M.; Nate, K. Inorganic and organometallic Polymers;
Zeldin, M., Wynne, K. J ., Allcock, H. R., Eds.; ACS Symposium Series
360; American Chemical Society: Washington, DC, 1988; Chapter 16.
(9) (a) Trefonas, P.; West, R. J . Polym. Sci., Polym. Chem. Ed. 1985,
23, 2099. (b) Kodaira, T.; Watanabe, A.; Ito, O.; Matsuda, M.; Tokura,
S.; Kira, M.; Nagano, S.; Mochida, K. Adv. Mater. 1995, 7, 917.
(10) Aitken, C.; Harrod, J . F.; Malek A.; Samuel, E. J . Organomet.
Chem. 1988, 349, 285.
(3)
(11) (a) Schmidbaur, H.; Rott, J . Z. Naturforsch. 1990, 45b, 961. (b)
Schmidbaur, H.; Rott, J . Z. Naturforsch. 1989, 44b, 285. (c) Schmid-
baur, H.; Rott, J .; Reber, G.; Mu¨ller, G. Z. Naturforsch. 1988, 43b, 727.
(12) (a) Mackay, K. M.; Watkinson, P. J .; Wilkins, A. L. J . Chem.
Soc., Dalton Trans. 1984, 133. (b) Wilkins, A. L.; Watkinson, P. J .,
Mackay, K. M. J . Chem. Soc., Dalton Trans. 1987, 2365.
(13) Kidd, R. G.; Spinney, H. G. J . Am. Chem. Soc. 1973, 95, 88.
(14) (a) Liepins, E.; Zicmane, J .; Lukevics, E. J . Organomet. Chem.
1988, 341, 315. (b) Liepins, E.; Zicmane, J .; Ignatovich, L. M.; Lukevics,
E. J . Organomet. Chem. 1990, 389, 23.
(15) Caminati, W.; Damiani, D.; Dakkouri, M.; Zeeb, S. J . Mol.
Struct. 1993, 296, 79.
(16) (a) Sennikov, P. G.; Skobeleva, S. E.; Kuznetsov, V. A.; Egoroch-
kin, A. N.; Riviere, P.; Satge´, J .; Richelme, S. J . Organomet. Chem.
1980, 201, 213. (b) Skobeleva, S. E.; Egorochkin, A. N.; Khorshev, S.
Ya.; Ratushnaya, S. Kh.; Riviere P.; Satge´, J .; Richelme, S.; Cazes, A.
J . Organomet. Chem. 1979, 182, 1.
As an alternative synthetic pathway, the insertion of
GeX2 molecules into the C-halogen bond of haloben-
zenes has been revisited.24e The reaction conditions have
been optimized to allow the process to be carried out
(a) under convenient experimental conditions (no pres-
sure, only slightly elevated temperature), (b) with the
most readily available germylene reagent GeCl2(dioxane),
(c) with halobenzenes bearing sensitive substituents,
and (d) in high yields.
It was found that 4-bromotoluene (as a reagent and
as a solvent) reacts with GeCl2(dioxane) in the presence
of small amounts of anhydrous AlCl3 as a catalyst
already below the reflux temperature of the dioxane
(17) Basch, H. Inorg. Chim. Acta 1996, 242, 191.
(18) (a) Meyer, J . M.; Allred, A. L. J . Phys. Chem. 1968, 72, 3043.
(b) Durig, J . R.; Sink, C. W.; Turner, J . B. J . Chem. Phys. 1968, 49,
3422. (c) J ohnson, O. H.; Harris, D. M. J . Am. Chem. Soc. 1950, 72,
5564. (d) Seyferth, D.; Hetflejs, J . J . Organomet. Chem. 1968, 11, 253.
(19) (a) Clark, K. B.; Griller, D. Organometallics 1991, 10, 746. (b)
Kuivila, H. G.; Beumel, O. F., J r. J . Am. Chem. Soc. 1961, 83, 1246.
(c) Stang, P. J .; White, M. R. J . Am. Chem. Soc. 1981, 103, 5429. (d)
Cross, R. J .; Glocking, F. J . Organomet. Chem. 1965, 3, 146.
(20) (a) Gyane, M. J .; Lappert, M. F.; Riviere, P.; Riviere-Baudet,
M. J . Organomet. Chem. 1977, 142, C9. (b) Riviere, P.; Riviere-Baudet,
M.; Satge´, J . Organometallic Synthesis; King, R. B., Eisch, J . J ., Eds.;
1988; Vol. 4, p 545.
(22) Kolesnikov, S. P.; Perl’mutter, B. L.; Nefedov, O. M. Dokl. Akad.
Nauk SSSR 1971, 196, 594.
(23) (a) Shea, K. J .; Loy, D. A.; Webster, O. J . Am. Chem. Soc. 1992,
114, 6700. (b) Shea, K. J .; Loy, D. A. Chem. Mater. 1989, 1, 572.
(24) (a) Ru¨dinger, C.; Beruda, H.; Schmidbaur, H. Chem. Ber. 1992,
125, 5, 1401. (b) Ru¨dinger, C.; Bissinger, P.; Beruda, H.; Schmidbaur,
H. Organometallics 1992, 11, 2867. (c) Schro¨ck, R.; Angermaier, K.;
Sladek, A.; Schmidbaur, H. Z. Naturforsch. 1995, 50b, 613. (d) So¨ldner,
M.; Schier, A.; Schmidbaur, H. Inorg. Chem. 1997, 36, 1758. (e) Wegner,
G. L. Dissertation, TU Mu¨nchen 1997.
(21) Lesbre, M.; Mazerolles, P.; Manuel, G. C. R. Hebd. Seances
Acad. Sci. 1963, 2303.

Analysis of Arylgermanes
Organometallics, Vol. 18, No. 21, 1999 4319
liberated in the process (80 °C) to give a mixture of
p-tolyltrichloro- and -tribromogermane (3a ,b) in almost
quantitative yield (98%, eq 4).
The products were identified by their physical con-
stants, and IR and mass spectra. UV spectra of several
arylgermanes were reported in a very early study.18 The
conclusions drawn from these preliminary results were
based only on a comparison with data of related methyl-
and silylarenes, and on a crude model separating
inductive and conjugative effects. Ge atoms were thus
assumed to be weak σ-donors and strong π-electron
acceptors, allegedly owing to their empty d-orbitals. In
light of advanced quantum chemical calculations this
assumption must be considered untenable.
1
Where H and 13C NMR spectra of the arylgermanes
had been recorded previously,19,27 the data were con-
firmed and complemented. There were no obvious
anomalies. However, in the absence of any reliable
results regarding 73Ge NMR spectroscopy, several
ArGeH3 prototypes have now been investigated in
greater detail using state-of-the-art facilities.
(4)
According to NMR spectroscopic and mass spectro-
metric data, this product is not a random distribution
of mixed p-tolylchloro/bromogermanes [4-MeC6H4Ge-
ClnBr3-n] and is free of the 2-Me- and 3-Me-isomers.
Only the two compounds with either three chlorine or
three bromine atoms (molar ratio 2:1) at a given
germanium atom are present, and the methyl groups
remain in the p-position. Note that the thermal and
catalyzed redistribution reactions between GeCl4 and
(p-Tol)4Ge probed for the synthesis of p-tolyltrichloro-
germane lead to extensive rearrangements to give
complex mixtures of o/ m/ p-tolylchlorogermanes with
different substitution patterns.25
Also note that the insertion of GeI2 into PhI requires
reaction temperatures of 160 °C (sealed tube, 32% yield
after reduction to the germane), and that of GeCl2 into
chloro- or bromobenzene requires even higher reaction
temperatures of 250 °C (under pressure), the latter
proceeding in 37 and 88% yield, respectively.26
The mixture of the two primary products is readily
reduced by LiAlH4 in diethyl ether to give good yields
of p-tolylgermane (3) (76%).
73Ge NMR Sp ectr oscop y. Among the various ger-
manium isotopes only the 73Ge nucleus is amenable to
high-resolution NMR spectroscopy. Yet its high nuclear
spin (s ) 9/2) and high quadrupole moment suggest
extensive line broadening and efficient quenching of
spin-spin coupling with neighboring nuclei. Therefore,
it was not a surprise that most germanium compounds
investigated to date showed either broad resonances
with no discernible multiplicity, or no signal at all.
Exceptions to this rule are molecules with high
symmetry securing a zero field gradient at the germa-
nium nucleus. Thus, solutions of monogermane GeH4
in solvents of low polarity show the famous 10-line
1H NMR signal from which the coupling constant
1J (Ge,H) ) 97.6 Hz can be extracted.28 Apart from Et3-
GeH,12 there is also a series of simple germa/sila-
alkanes for which 73Ge NMR spectra of surprisingly
good resolution have been obtained.11 1J (Ge,H) couplings
range from 88 to 99 Hz. Tetramethylgermane, GeMe4,
also shows rather sharp resonances, but with no split-
ting. As a convention, this compound has been used as
the standard of 73Ge NMR spectroscopy (δ ) 0.0 ppm).
Owing to their low molecular symmetry (point groups
Cs, C2, or C3), arylgermanes are not expected to give
high quality 73Ge NMR spectra, and, in fact, for several
series of aryl- and heteroarylgermanes only broad
resonances (w1/2 15-600 Hz) have been reported.14 The
chemical shift data show certain correlations with
electronegativity increments of the substituent pattern
of a given set of molecules.
Bromomesitylene can be converted similarly into
mesitylgermane (4) (76% yield) via mesityltrichloro/
bromogermane (4a ,b) (80% yield, eq 5).
With this background, it was very surprising that
73Ge NMR spectra of excellent quality (Figures 1-4)
were obtained for all arylgermanes reported in this
work.
(5)
As a representative example, phenylgermane (5)
shows a well-resolved 1:3:3:1 quartet at δ ) -190 ppm
[1J (Ge,H) ) 98 Hz]. The same pattern is found for
p-tolyl-, mesityl-, and even p-anisylgermane as sum-
marized in Table 1.
Accordingly, diphenyl- and triphenylgermane (6,7)
show triplet and doublet signals, respectively, at -108.5
[J ) 94 Hz] and -55.4 ppm [J ) 98 Hz]. Conversely,
Phenyl-, diphenyl-, and triphenyl-germane (5-7) were
synthesized by LiAlH4 reduction of the corresponding
chlorogermanes which are commercially available. All
arylgermanes prepared in this work are colorless, dis-
tillable liquids as described in the literature: PhGeH3,18
Ph2GeH2,19 Ph3GeH,19 p-TolGeH3,20 MesGeH3,20 p-Me-
OC6H4GeH3,18 (p-MeOC6H4)2GeH2.18
(27) Birchall, T.; Drummond, I. J . Chem. Soc., Inorg. Phys. Theor.
1970, 1401.
(28) Ebsworth, E. A. V.; Rankin, D. W. H.; Cradock, S. Structural
Methods in Inorganic Chemistry, 2nd ed.; Blackwell Scientific Publica-
tion: Oxford, 1987.
(25) Ku¨hlein, K.; Neumann, W. P. Liebigs Ann. Chem. 1967, 702,
17.
(26) Mironov, V. F.; Gar, T. G. Organic Compounds of Germanium
[in Russian]; Nauka, 1967; pp 164, 173, 181.

4320 Organometallics, Vol. 18, No. 21, 1999
Riedmiller et al.
F igu r e 1. 73Ge NMR spectrum of Ph3GeH (in C6D6 at
20 °C).
F igu r e 2. 73Ge NMR spectrum of Ph2GeH2 (in C6D6 at
20 °C).
Ta ble 1. 73Ge NMR Da ta [p p m , Hz] of
Ar ylger m a n es Ar n GeH4-n (n ) 1, 2, 3)
compound
multiplicity
[ppm]
1J GeH [Hz]
p-anisylgermane (1)
bis(p-anisyl)germane (2) broad singlet -112.0
quartet
-189.9
97
-
p-tolylgermane (3)
mesitylgermane (4)
phenylgermane (5)
diphenylgermane (6)
triphenylgermane (7)
quartet
quartet
quartet
triplet
-190.6
-234.3
-190.0
-108.8
-55.4
96
95
98
94
98
doublet
1
none of these J (Ge,H) couplings was observed in the
1H NMR spectra of the compounds. It thus appears that
73Ge NMR spectroscopy is in fact a very helpful tool for
the identification and for a more detailed study of alkyl-
and arylgermanes. We can offer several suggestions
which help to explain this phenomenon: (1) Because of
the discontinuities in the electronegativity sequence of
group 14 elements, the Ge-C bond has an inherently
low polarity. (2) It is known from microwave and
vibrational spectroscopy that H3Ge-R bonds have very
low barriers of rotation, and this is, of course, particu-
larly true for bonds to sp2 and sp carbon atoms.
Virtually free rotation can be assumed. (3) The line
width factor l is a function of both the quadrupole
moment Q (73Ge: 0.18 × 10-28 m2, -0.22 barn) and the
nuclear spin I of the isotope under observation (9/2).
Apparently, an internal compensation of the two con-
tributions according to l ) (2I + 3)Q2/[I2(2I - 1)] )
2.4 × 10-59 m4 leads to an appreciable sharpness of the
lines generated in the spin-spin coupling.29
F igu r e 3. 73Ge NMR spectrum of PhGeH3 (in C6D6 at
20 °C).
Note that the sensitivity of the 73Ge nucleus (1.1 ×
10-4 rel 1H) is close to that of frequently observed nuclei
such as 29Si (3.7 × 10-4), but the frequency range is one
of the lowest of all nuclei [3.49 MHz, rel. 1H (100 MHz)].
Str u ctu r a l Stu d ies. Of all the arylgermanes pre-
pared in this work, only p-anisylgermane (1) could be
obtained in the form of single crystals suitable for X-ray
(29) Harris, R. K. Proceedings of the NATO Advanced Study on the
Multinuclear Approach to NMR-Spectroscopy; Lambert, J . P., Ridell,
F. G., Reidel, D., Eds.; Publishing Company: Dordrecht, 1987.

Analysis of Arylgermanes
Organometallics, Vol. 18, No. 21, 1999 4321
F igu r e 6. Packing diagram of 1.
Ta ble 2. Cr ysta l Da ta , Da ta Collection , a n d
Str u ctu r e Refin em en t for p-An isylger m a n e 1
Crystal Data
empirical formula
fw
C7H10GeO
182.74
cryst syst
space group
a, Å
orthorhombic
Pca21
6.386(1)
7.339(1)
17.011(3)
797.3(2)
1.522
b, Å
c, Å
V, Å3
D
Z
calcd, g cm-3
4
F(000), e
368
37.63
1.0 × 0.4 × 0.4
µ (Mo KR), cm-1
cryst dimens, mm
Data Collection
temp, K
203(2)
scan mode
hkl range
measured reflns
unique reflns
reflns used for refinement
ω
F igu r e 4. 73Ge-NMR spectrum of MesGeH3 (in C6D6 at
20 °C).
-8f8; -9f9; -21f21
3440
1723 (Rint ) 0.0693)
1723
Refinement
least-squares parameters
final R values [I > 2σ(I)]:
R1a
103
0.0345
0.0754
1.124
0.868/-0.370
wR2b
goodness-of-fit on F2
F
fin(max/min), e Å-3
R1 ) ∑(||Fo|| - ||Fc||)/∑|Fo|. wR2 ) {[∑w(Fo2-Fc2)2]/∑[w-
a
b
(Fo2)2]}1/2; w ) 1/[σ2(Fo2)+(ap)2+bp]; p ) (Fo2+2Fc2)/3; a ) 0.0476;
b ) 0.0000.
Ta ble 3. Selected Bon d Len gth s [Å] a n d An gles
[d eg] of p-An isylger m a n e 1 (XRD a n d MP 2/6-31G*)
1 (XRD, crystal data)
1 (ab initio MP2/6-31 G*)
Ge-C1: 1.939(4)
1.929
1.551(2*1.554)
1.406
1.399
1.388
1.402
1.369
1.425
1.089
Ge-H: 1.400 fixed
C1-C2: 1.398(5)
C1-C6: 1.399(5)
C2-C3: 1.378(6)
F igu r e 5. (a and b) Molecular structure of 1 (ORTEP
drawing with 50% probability ellipsoids). Projection per-
pendicular and parallel to the plane of the arene ring.
C3-C4: 1.392(5)
C4-O: 1.370(5)
O-C7: 1.416(6)
C7-H(7A): 0.9506
C7-H(7B): 0.9506
C7-H(7C): 0.9506
C6-C1-Ge: 122.4(3)
C2-C1-Ge: 120.1(3)
C6-C1-C2: 117.5(4)
C3-C4-C5: 119.9(4)
O-C4-C5: 124.4(3)
O-C4-C3: 115.7(3)
C4-O-C7: 117.8(3)
O-C7-H71(av): 109 (4)
1.095
1.095
diffraction studies. Crystals of 4-MeO-C6H4-GeH3 (mp
15 °C, grown from the melt by “in situ” low-temperature
crystallization methods in a sealed capillary on the
diffractometer) are orthorhombic, space group Pca21,
with Z ) 4 molecules in the unit cell. An individual mol-
ecule is shown in projections perpendicular and parallel
to the molecular plane in Figures 5a and b, and the
packing of the molecules is presented in Figure 6. Se-
lected bond distances and angles are given in Table 3.
Figure 5b shows that all non-hydrogen atoms are
virtually coplanar, which places the methyl carbon atom
121.27
120.90
117.83
119.89
124.98
115.12
116.83
-
also in the molecular plane, with the dihedral angle C3-
C4-O-C7 close to 0°. The distance Ge-C1 ) 1.939(4)
Å is a new benchmark value for X-ray data of arylger-

4322 Organometallics, Vol. 18, No. 21, 1999
Riedmiller et al.
manes. A previous reference value was obtained from
gas-phase microwave studies (MW) of phenylgermane
(Ge-C ) 1.9423 Å). As expected, an ab initio calculation
(4.21G*) for PhGeH3 gave a much shorter distance of
only 1.9054 Å which refers to the position of the nuclei
and not of electron density maxima.15 Solid-state Ge-C
distances in polyphenylated germanes, such as Ph4Ge,
are all significantly longer owing to steric congestion
at the germanium atoms. For the structure refinement
of 1, the Ge-H bond lengths (constrained to idealized
tetrahedral geometry) were fixed at Ge-H ) 1.40 Å.
For the reason mentioned above, the reference value
from MW data of phenylgermane is larger at 1.520 Å,
and the calculated value (4.21G* with corrections) at
1.516 Å.15
The H3Ge group is positioned almost symmetrically
between the two ortho carbon atoms with angles Ge-
C1-C2 and Ge-C1-C6 at 120.2(3)° and 122.3(3)°,
respectively. The small difference between the two
angles is probably due to the orientation of the germyl
hydrogen atoms.
F igu r e 7. (a and b) Molecular structure of 1 as calculated
by ab initio quantum chemical methods (MP2/6-31G*). For
geometrical dimensions see Table 3. Projection perpen-
dicular and parallel to the plane of the arene ring.
By contrast, the methoxy oxygen atom is in a position
which strongly deviates from the line bisecting the angle
C3-C4-C5, as best illustrated by the angles O-C4-
C3 ) 115.6(3)° and O-C4-C5 ) 124.5(3)°. The “ethereal
angle” C4-O-C7 ) 118.2(4)° is not unusual, but
together with the aforementioned deformation it is large
enough that a close contact of the methyl group and the
arene ring is avoided. In unsubstituted phenol PhOH
and thiophenol PhSH, where no crowding is expected,
only much smaller differences in the two angles C-C-
O/S were found [PhOH by MW spectroscopy: 117.01-
(2)° and 122.14(2)°; PhSH: 120.9° and 121.0°].30a,b For
methyl phenyl sulfide groups, C6H5SMe, the deviations
from 120° are again much larger, mostly in the range
from 117° to 125°.30c
Sch em e 1
According to a MW study,31 gaseous anisole features
angles O-C-C of 113.7° and 126.3° (imposed planarity;
no error limits given), whereas electron diffraction (ED)
data give a deviation of 4° from 120°.32 The latter of the
two results is in excellent agreement with the data of
the present study [4.4(3)°]. Our data also confirm the
in-plane (coplanar) orientation of the methoxy group
(torsional angle 0°) proposed from MW and ED studies.
In conclusion, therefore, both the phenylgermyl (part
A) and the anisyl part (part B) of the p-anisylgermane
molecule show standard structural patterns with very
little, if any, mutual influence.
The packing of the molecules in the lattice shows a
parallel stacking of the arenes (Figure 6). Contacts
between these stacks are not very intimate, but it is
obvious that the methoxy oxygen atoms are oriented
toward the germyl groups of molecules in neighboring
stacks. The atom sequence C1-Ge-O is almost linear
(172.5°) with a distance Ge-O ) 3.396 Å. These
parameters may indicate a weak donor-acceptor or
dipole-dipole interaction, initiating a trigonal bipyra-
midal configuration at the germanium atom. These
interactions are probably responsible for the rather high
melting point of p-anisylgermane as compared to phen-
yl-, p-tolyl-, or mesitylgermanes.
A nonplanar structure had been considered on the
basis of earlier dipole moment and Kerr constant data
(torsional angle C-C-O-C ) 18°).33 Extended Hu¨ckel
calculations also seemed to indicate an even larger
torsional angle (75°),34 but CNDO/2 studies clearly
favored the planar structure (0°),35 and, finally, most
recent ab initio calculations (STO-3G) gave angles
O-C-C of 113.7° and 126.3° (for C-O-C ) 115.2°) for
a fully planar structure (Scheme 1).36
Ab In it io Qu a n t u m -Ch em ica l Ca lcu la t ion s of
p-An isylger m a n e. Ab initio quantum chemical calcu-
lations on the MP2/6-31G* level lead to a molecular
structure for p-anisylgermane (1) which is in excellent
agreement with the experimental data (Figures 7a and
b, and Table 3). Interestingly, the only significant
difference between the two structures is the conforma-
tion of the GeH3 group relative to the ring. The
calculated structure has the higher symmetry of point
group Cs as compared to C1 (but virtually Cs) for the
experimental data. The calculated energy differences
(30) (a) Larsen, N. W. J . Mol. Struct. 1979, 51, 175. (b) Byrn, M. P.;
Curtis, C. J .; Goldberg, I.; Hsiou, Yu.; Khan, S. I.; Sawin, P. A.; Tendick,
S. K.; Strouse, C. E. J . Am. Chem. Soc. 1991, 113, 6549. (c) Parfony,
A.; Tinant, B.; Declercq, J . P.; Van Meenche, M.; Klein, J .; Merenyi,
R.; Viehe, H. G. Bull. Soc. Chim. Belg. 1987, 96, 89.
(31) Onda, M.; Toda, A.; Mori, S.; Yamaguchi, I. J . Mol. Struct. 1986,
144, 47.
(32) Seip, H. M.; Seip, R. Acta Chem. Scand. 1973, 27, 4025.
(33) Aroney, M. J .; Le Fevre, R. J . W.; Pierens, R. K.; The, M. C. N.
J . Chem. Soc. B 1969, 666.
(34) Tylli, H. Suom. Kemistiseuran Tied. 1970, 79, 22.
(35) Tylli, H. Suom. Kemistiseuran Tied. 1972, 81, 19.
(36) Konschin, H. J . Mol. Struct. 1983, 105, 213.

Analysis of Arylgermanes
Organometallics, Vol. 18, No. 21, 1999 4323
triethoxygermane (1a ) was used with 2 equiv of p-bromoani-
sole (5.92 g, 4.0 mL, 31.7 mmol) and 1 molar equiv of
tetra(ethoxy)germane (4.00 g, 15.8 mmol). After a reaction time
of 1.5 h (with the formation of the product monitored by GC-
MS analysis), the product (2a ) was separated by extraction of
the oily residue with pentane. A slightly yellow oil was
obtained (27%, 1.62 g). 1H NMR (20 °C): δ ) 1.32 (t, 3J HH ) 7
between C1 and Cs are very small, however, which
suggests that the deviations may indeed be due only to
the above-discussed intermolecular contacts between
the germanium atom and the oxygen atom of the
neighboring molecule in the crystal.
3
Exp er im en ta l Section
Hz, 6H, CH3), 3.56 (s, 6H, OCH3), 4.28 (q, J HH ) 7 Hz, 4H,
3
3
CH2), 6.98 (d, J HH ) 8.5 Hz, 4H, H3,5), 7.64 (d, J HH ) 8.5 Hz,
4H, H2,6). 13C{1H} NMR (20 °C): δ ) 26.2 (CH3), 59.6 (OCH3),
67.9 (CH2), 129.3 (C2,6), 131.3 (C3,5), 135.2 (C1ipso), 167.8 (C4ipso).
Gen er a l Meth od s. All experiments were carried out under
an atmosphere of dry nitrogen using Schlenk techniques.
Germanium dichloride‚dioxane was prepared and purified
according to published procedures.2 Solvents were appropri-
ately dried, distilled, and saturated with dry nitrogen; glass-
ware was dried in an oven and filled with nitrogen. All NMR
spectra were recorded at 20 °C on a J EOL-J NM-LA 400
spectrometer (1H at 400.05 MHz, 13C at 100.50 MHz, 73Ge at
13.83 MHz) in sealed tubes with predried C6D6 as solvent
except where indicated otherwise. Mass spectra were recorded
with an analytical gas-liquid chromatography (GLC)-MS
Hewlett-Packard 5890 Series II chromatograph (column HP1,
cross-linked methylsilicone gum 12 m/0.2 mm, thickness of film
0.33 µm) with a mass-selective detector HP MS 5971 A
(electron ionization (EI)-MS 70 eV). Microanalyses were
performed in-house by combustion.
MS (EI, 70 eV): m/z ) 378 [M+], 333 [M+ - OEt], 289 [M+
-
2 OEt], 270 [M+ - CH3OC6H4], 226 [M+ - CH3OC6H4 - OEt],
181[100%, M+ - CH3OC6H4 - 2 OEt], 152 [M+ - CH3OC6-
H4 - OEt - Et], 108 [M+ - CH3OC6H4 - Ge(OEt)2], 89, 64.
Calcd for C18H24GeO4 (376.8): C, 57.38; H, 6.37. Found: C,
57.12; H, 6.33.
Bis(4-m eth oxyph en yl)ger m an e, [Bis(p-an isyl)ger m an e]
(2). Bis(4-methoxyphenyl)diethoxygermane (2a ) (1.62 g, 4.3
mmol) was reduced to bis(4-methoxyphenyl)germane (2) as
described for 1 with lithium aluminum hydride (90 mg, 2.4
mmol) in ethereal solution at -78 °C. After fractional trap-
to-trap condensation (0 °C, -10 °C) the product was isolated
1
as a colorless liquid in the 0 °C trap (51.8%, 0.64 g). H NMR
(21 °C): δ ) 3.29 (s, 6H, OCH3), 5.20 (s, 2H, GeH2), 6.78 (d,
4H, 3J HH ) 8.7 Hz, H3,5), 7.40 (d, 4H, 3J HH ) 8.8 Hz, H2,6). 13C-
{1H} NMR (21 °C): δ ) 54.3 (OCH3), 115.1 (C2,6), 120.9 (C1ipso),
137.0 (C3,5), 160.8 (C4ipso). 73Ge NMR (21 °C): δ ) -112.0 (bs,
GeH2). MS (EI, 70 eV): m/z ) 290 [M+ + H], 289 [M+], 273
[M+ - CH3], 240 [M+ - OCH3-CH3], 181 [100%, M+ - C6H5-
(4-Meth oxyp h en yl)tr ieth oxyger m a n e (1a ). A suspen-
sion of magnesium chips (0.72 g, 29.7 mmol) in 5 mL of dry
THF was stirred for about 10 min and activated with 1,2-
dibromoethane. Freshly distilled tetra(ethoxy)germane (5.00
g, 19.8 mmol) in 20 mL of THF was added and the mixture
heated to 60 °C with stirring. Ten percent of a solution of
4-bromoanisole (3.70 g, 2.5 mL, 19.8 mmol) in 15 mL of THF
was then added slowly, and stirring continued until a mild
exothermic reaction commenced. The addition was slowly
continued to maintain reflux of the solvent. Afterward, the
mixture was refluxed for 2 h. After the mixture cooled to room
temperature, 20 mL of pentane was added, the white precipi-
tate was filtered, and the volatile products were removed in
vacuo. The residue was extracted with pentane and the solvent
OCH3], 167 [M+ - CH3 - C6H5OCH3], 151 [M+ - OCH3
-
C6H5OCH3], 108 [M+ - C6H5OCH3 - GeH2], 77 [M+ - C6H5-
OCH3 - GeH2 - OCH3], 138, 65. Calcd for C14H16GeO2
(288.8): C, 58.23; H, 5.54. Found: C, 58.16; H, 5.50.
(4-Met h ylp h en yl)t r ich lor o-/(4-Met h ylp h en yl)t r ib r o-
m oger m a n e (2:1) (3a ,b). A mixture of 250 mL of p-bromo-
toluene (347.50 g, 2.03 mol), 10 g of GeCl2‚dioxane (43.2 mmol),
and 0.29 g of anhydrous AlCl3 (2.17 mmol) was heated to 80
°C for 24 h with continuous stirring. After the mixture was
cooled to room temperature, it was filtered, the dioxane
removed in vacuo, and the unreacted p-bromotoluene removed
by vacuum distillation (43 °C/0.5 mbar) to leave a white solid
(13.33 g, 98% altogether).
1
was removed in vacuo to give a colorless oil (36%, 2.20 g). H
3
NMR (20 °C): δ ) 1.25 (t, J HH ) 7 Hz, 9H, CH3), 3.53 (s, 3H,
OCH3), 4.25 (q, 3J HH ) 7 Hz, 6H, CH2), 6.96 (d, 3J HH ) 8.5 Hz,
3
2 H, H3,5), 7.60 (d, J HH ) 8.5 Hz, 2H, H2,6). 13C{1H} NMR (20
°C): δ ) 25.8 (CH3), 59.3 (OCH3), 67.2 (CH2), 129.0 (C2,6), 130.7
(C3,5), 133.4 (C1ipso), 167.5 (C4ipso). MS (EI, 70 eV): m/z ) 316
[M+ + H], 315 [M+], 301 [M+ - CH3], 271 [M+ - OEt], 257
[M+ - CH3-OEt], 225 [M+ - 2 OEt + H], 181[M+ - 3 OEt],
151 [M+ - 3 OEt-OCH3], 108 [M+ - Ge(OEt)3 + H, 100%],
p-Tolyltr ich lor oger m a n e: MS (GC-coupled, EI 70 eV,
64%): m/z ) 270 [M+], 235 [M+ - Cl], 126 [M+ - GeCl2], 109
[GeCl+], 91 [C7H7+], 65 [C5H5+].
p-Tolyltr ibr om oger m a n e: MS (GC-coupled, EI 70 eV,
32%): m/z ) 403 [M+], 322 [M+ - Br], 153 [GeBr+], 91 [C7H7+],
65 [C5H5+]. Calcd for C7H7GeCl3 (270.1)/C7H7GeBr3 (403.1) )
2:1 ratio: C, 26.93; H, 2.24. Found: C, 26.89; H, 2.20.
91 [M+ - Ge(OEt)3 - CH3], 78 [C6H4+], 51. Calcd for C13H22
GeO4 (314.8): C, 49.61; H, 6.99. Found: C, 49.43; H, 6.96.
-
(4-Meth oxyp h en yl)ger m a n e, [p-An isylger m a n e] (1). To
a stirred suspension of lithium aluminum hydride (222 mg,
5.9 mmol) in 25 mL of diethyl ether at -78 °C, a solution of
(4-methoxyphenyl)triethoxygermane (1a ) (2.20 g, 7.1 mmol)
in diethyl ether was added dropwise with vigorous stirring.
Stirring was continued for 1 h and the mixture was allowed
to warm to room temperature. The formation of a white
precipitate was observed. Pentane (30 mL) was added and the
precipitate was filtered. The filtrate was fractionized to give
a colorless liquid (1.1 g, 86.4%, bp 68 °C at 0.05 mbar, mp
15 °C). 1H NMR (20 °C): δ ) 3.27 (s, 3H, OCH3), 4.27 (s,
(4-Met h ylp h en yl)ger m a n e, [p -Tolylger m a n e] (3). A
portion of the product 3a ,b from the preceding experiment
(5.85 g, 18.33 mmol) was dissolved in 15 mL of diethyl ether
and slowly added to a slurry of 1.54 g of LiAlH4 (41.64 mmol)
in 25 mL of diethyl ether. The reaction mixture was refluxed
for 2 h. After the solvent was removed under reduced pressure,
20 mL of pentane was added to the residue. Subsequent
filtration and vacuum distillation gave a colorless liquid (yield
1
2.26 g, 74%, bp 40 °C/2 mbar). H NMR (C6D6, 25 °C) 2.08 [s,
3
3
3H, CH3], 4.77 [s, 3 H, GeH3], 6.93 [d, 2H, J HH ) 8.04 Hz,
3H, GeH3), 6.72 (d, 2H, J HH ) 8.8 Hz, H3,5), 7.25 (d, 2H,
3
2/6], 7.28 [d, 2H, J HH ) 8.04, H3/5]. 13C NMR: 21.3 [CH3],
3J HH ) 8.8 Hz, H2,6). 13C{1H} NMR (20 °C): δ ) 54.5 (OCH3),
H
114.6 (C2,6), 121.3 (C4ipso), 136.9 (C3,5), 161.0 (C1ipso). 73Ge NMR
127.4 [C-GeH3], 129.4 [C2/6], 135.7 [C3/5], 138.8 [C-CH3].
1
73Ge-NMR: -190.57 [q, J GeH ) 95.6 Hz, GeH3]. MS (GC-
2
(20 °C): δ ) -189.9 (q, J Ge-H ) 97 Hz, GeH3). MS (EI,
coupled, EI 70 eV): m/z ) 166 [M+], 91 [C7H7], 77 [GeH3]. Calcd
for C7H10Ge (166.2): C, 50.42; H, 6.04. Found: C, 50.31; H,
6.03.
70 eV): m/z ) 184 [M+ + H], 183 [M+], 167 [M+ - CH3], 152
[M+ - OCH3], 108 [M+ - GeH3 + H, 100%], 77 [M+ - GeH3 -
OCH3], 138, 123, 65. Calcd for C7H10GeO (182.7): C, 46.02;
H, 5.47. Found: C, 45.92; H, 5.30.
(2,4,6-Tr im e t h ylp h e n yl)t r ich lor o-/(2,4,6-Tr im e t h yl-
p h en yl)tr ibr om oger m a n e (2:1) (4a ,b). As described for
3a ,b, a mixture of 60 mL of bromomesitylene (0.4 mol), 5.2 g
Bis(4-m eth oxyp h en yl)d ieth oxyger m a n e (2a ). A proce-
dure analogous to that described for (4-methoxyphenyl)-

4324 Organometallics, Vol. 18, No. 21, 1999
Riedmiller et al.
of GeCl2‚dioxane (22.5 mmol), and 0.15 g of anhydrous AlCl3
(1.2 mmol) was heated to 80 °C for 4 days. The workup
procedure was the same as described above, the excess of
bromomesitylene being collected at 43 °C/0.05 mbar. The
residue was a white solid (yield 7.21 g, 80% altogether).
Mesityltr ich lor oger m a n e: MS (GC-coupled, EI 70 eV,
53%): m/z ) 298 [M+], 262 [M+ - Cl], 153 [M+ - GeCl2], 118
[M+ - GeCl3].
bonds. The germyl group was refined as a rigid group with
tetrahedral angles and Ge-H distances fixed at 1.4000 Å.
Further information on crystal data, data collection, and
structure refinement are summarized in Table 2. Important
interatomic distances and angles are given in Table 3. For
further details, see the Supporting Information. Anisotropic
thermal parameters, tables of distances and angles, and atomic
coordinates have been deposited at Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
U.K. The data are available on request by quoting CCDC No.
129255.
Ab In itio Ca lcu la tion s. Ab initio molecular orbital calcu-
lations were carried out using the Gaussian 94 program.39
Geometry optimizations (self-consistent field (SCF) and MP2
level of theory) and vibrational frequency calculations (up to
SCF/6-31 G*) were performed from analytical first and second
derivatives. Calculations were undertaken at the SCF level
using the standard 3-21G*40,41 and 6-31G*42-44 basis sets, the
larger basis sets being used for calculations at the MP2 level
of theory.
Mesityltr ibr om oger m a n e: MS (GC-coupled, EI 70 eV,
27%): 432 [M+], 353 [M+ - Br], 198 [M+ - GeBr2], 118 [M+
-
GeBr3]. Calcd for C9H11GeCl3 (298.1)/C9H11GeBr3 (431.5) ) 2:1
ratio: C, 31.55; H, 3.23. Found: C, 31.53; H, 3.26.
(2,4,6-Tr im eth ylph en yl)ger m an e, [Mesitylger m an e] (4).
A 5.20 g (15.2 mmol) sample of the above product mixture
(4a ,b) in 15 mL of diethyl ether was added to a slurry of 1.3
g of LiAlH4 (34.2 mmol) in 20 mL of diethyl ether. After 2 h at
reflux, volatiles were distilled in vacuo. Extraction with 20 mL
of pentane and vacuum distillation yielded a colorless liquid
1
(2.25 g, 76%, bp 85 °C/4 mbar). H NMR (C6D6, 25 °C): 2.22
[s, 3H, p-CH3], 2.32 [s, 6H, o-CH3], 4.15 [s, 3H, GeH3], 6.74 [s,
2H, m-CH]. 13C NMR: 21.45 [p-CH3], 24.47 [o-CH3], 127.19
[C1], 128.90 [C3], 138.37 [C4], 144.08 [C2]. 73Ge NMR: -234.32
Ack n ow led gm en t. This work was supported by
Fonds der Chemischen Industrie and by Deutsche
Forschungsgemeinschaft. The authors are grateful to
Dr. Norbert Mitzel for help with the crystal growth and
data collection.
1
ppm [q, J GeH ) 95.0 Hz, GeH3]. MS (GC-coupled, EI 70 eV):
194 [M+], 179 [M+ - CH3], 118 [M+ - GeH3]. Calcd for C9H14
Ge (194.4): C, 55.49; H, 7.24. Found: C, 55.47; H, 7.26.
-
For phenylgermane (5), diphenylgermane (6), and triphen-
ylgermane (7), the syntheses followed the literature proce-
dures.18,19
Su p p or tin g In for m a tion Ava ila ble: Details of crystal
data, data collection, and structure refinement and tables of
atomic coordinates, isotropic and anisotropic thermal param-
eters, and all bond lengths and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
Cr ysta l Str u ctu r e Deter m in a tion s. A solid-liquid equi-
librium was established at 258 K in a sample of compound 1
held in a capillary. Single crystals grew on cooling at 1 K h-1
.
The specimens were used for measurement of precise cell
constants and intensity data collection on an Enraf-Nonius
CAD4 diffractometer (graphite-monochromated Mo KR radia-
tion, λ(Mo KR) ) 0.71073 Å). During data collection, three
standard reflections were measured periodically as a general
check of crystal and instrument stability. No significant
changes were observed. The structure was solved by direct
methods (SHELXTL-NT37) and completed by full-matrix least-
squares techniques against F2 (SHELXL-9738). The thermal
motion of all non-hydrogen atoms was treated anisotropically.
The hydrogen atoms of the phenyl ring were found and refined
with isotropic contributions. The methyl group was refined as
an idealized group with tetrahedral angles and C-H distances
that may vary, the same shift being applied along all C-H
OM990349Z
(39) Calculations were performed using standard methods imple-
mented in Gaussian 94: Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.;
Gill, P. M. W.; J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith,
T.; Petersson, G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham,
M. A.; Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople J . A. GAUSSIAN
94, Revision C.3; Gaussian, Inc.: Pittsburgh, PA, 1995.
(40) Pietro, W. J .; Francl, M. M.; Hehre, W. J .; Defrees, D. J .; Pople,
J . A.; Binkley, J . S. J . Am. Chem. Soc. 1982, 104, 5039.
(41) Hehre, W. J .; Ditchfield, R.; Pople, J . A. J . Chem. Phys. 1972,
56, 2257.
(42) Hariharan, P. C.; Pople, J . A. Theor. Chim. Acta 1973, 28, 213.
(43) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163.
(44) Krishnan, R.; Binkley, J . S.; Seeger, R.; Pople, J . A. J . Chem.
Phys. 1980, 72, 650.
(37) SHELXTL-NT V5.1; Bruker AXS Inc.: Madison, WI, 1997.
(38) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen: Gottingen, FRC, 1997.