Syntheses, structures, and reactions of heptacoordinate trihalogermanes bearing a triarylmethyl-type tetradentate ligand

Article abstract of DOI:10.1021/om060031o

Trichloro[tris(3-tert-butyl-6-methoxyphenyl)methyl]germane (3), containing a tetradentate ligand with three methoxy groups as coordinating sites, was synthesized by the reaction of the corresponding (triarylmethyl)lithium species with tetrachlorogermane. In contrast to the case for the previously reported trichlorosilane analogue, 3 slowly decomposed during column chromatography on silica gel, although it was quite stable against moisture. The corresponding trifluoro-, tribromo-, and triiodogermanes 4-6 were prepared from the trichlorogermane 3. X-ray crystallographic analyses of 3-6 showed heptacoordinate structures with interatomic distances between the oxygen atom and the central germanium atom shorter than the sum of van der Waals radii. By systematic comparisons of these intramolecular interactions based on the interatomic distances, it was found that they strongly depend on the Lewis acidity of the trihalogenated germanium atom. An Atoms-in-Molecules (AIM) analysis of the model compound 4′, in which three tert-butyl groups of trifluorogermane 4 were omitted, showed the existence of weak and ionic bonding between oxygen and germanium atoms. Reactions of these trihalogermanes with aqueous NaOH, LiAlH₄, and BX₃ were also investigated. Alkaline hydrolysis of trihalogermanes resulted in the cleavage of the carbon-germanium bond. LiAlH₄ also caused the same kind of bond cleavage, together with nucleophilic attack on the germanium atom, giving the trihydrogermane 8. Reaction of the trihalogermanes with trihaloboranes was found to be an efficient procedure to give other trihalogermanes through a halogen exchange reaction.

Full text of DOI:10.1021/om060031o

3388
Organometallics 2006, 25, 3388-3393
Syntheses, Structures, and Reactions of Heptacoordinate
Trihalogermanes Bearing a Triarylmethyl-Type Tetradentate
Ligand
Kohei Iwanaga,† Junji Kobayashi,† Takayuki Kawashima,*,† Nozomi Takagi,‡ and
Shigeru Nagase‡
Department of Chemistry, Graduate School of Science, The UniVersity of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-0033, Japan, and Department of Theoretical Molecular Science, Institute for Molecular
Science, Myodaiji, Okazaki 444-8585, Japan
ReceiVed January 10, 2006
Trichloro[tris(3-tert-butyl-6-methoxyphenyl)methyl]germane (3), containing a tetradentate ligand with
three methoxy groups as coordinating sites, was synthesized by the reaction of the corresponding
(triarylmethyl)lithium species with tetrachlorogermane. In contrast to the case for the previously reported
trichlorosilane analogue, 3 slowly decomposed during column chromatography on silica gel, although it
was quite stable against moisture. The corresponding trifluoro-, tribromo-, and triiodogermanes 4-6
were prepared from the trichlorogermane 3. X-ray crystallographic analyses of 3-6 showed heptacoordinate
structures with interatomic distances between the oxygen atom and the central germanium atom shorter
than the sum of van der Waals radii. By systematic comparisons of these intramolecular interactions
based on the interatomic distances, it was found that they strongly depend on the Lewis acidity of the
trihalogenated germanium atom. An Atoms-in-Molecules (AIM) analysis of the model compound 4′, in
which three tert-butyl groups of trifluorogermane 4 were omitted, showed the existence of weak and
ionic bonding between oxygen and germanium atoms. Reactions of these trihalogermanes with aqueous
NaOH, LiAlH4, and BX3 were also investigated. Alkaline hydrolysis of trihalogermanes resulted in the
cleavage of the carbon-germanium bond. LiAlH4 also caused the same kind of bond cleavage, together
with nucleophilic attack on the germanium atom, giving the trihydrogermane 8. Reaction of the
trihalogermanes with trihaloboranes was found to be an efficient procedure to give other trihalogermanes
through a halogen exchange reaction.
Introduction
Hypercoordinated main-group-element compounds have been
extensively studied because of their interesting structures and
reactivities and also as models of the transition state or the
intermediate of SN2 reactions. Among group 14 element
compounds, hypercoordinated organogermanium compounds
have been rather less studied, while organosilicon compounds
have been investigated intensively and widely used in synthetic
applications.1 Ionic penta-, hexa-, and heptacoordinate group
14 element compounds have been synthesized by nucleophilic
attack by anions at a neutral central atom. Bidentate ligands
such as the Martin ligand2 were well-known to stabilize these
highly coordinated species. In contrast, the syntheses of neutral
group 14 element compounds with high coordination numbers
have been achieved by the introduction of intramolecular dative
bonds provided by bidentate or tridentate ligands such as van
Koten type ligands.3
Figure 1.
compounds.4,5 The syntheses of these compounds have been
achieved by using more than two multidentate ligands in which
coordination sites are connected to the central atom (Figure 1,
type I). This type of compound can have only one functional
group, and each dative bond is opposite to one of the covalent
bonds with the central atom and another ligand. In contrast,
compounds using another type of interaction (Figure 1, type
II), in which coordination sites are connected to the atom
adjacent to the central atom, are rare despite their advantages;
more than two functional groups can be introduced, and each
coordination site is located at the opposite side of the functional
group, which makes possible a direct effect on its coordinating
nature by altering the functional groups. We have reported the
synthesis of a novel type of heptacoordinate trichlorosilane, 1,
with a type II interaction based on a tris(3-tert-butyl-6-
In comparison to the number of penta- and hexacoordinate
compounds, neutral heptacoordinate silicon compounds are rare
and only a few examples are known of germanium and tin
† The University of Tokyo.
‡ Institute for Molecular Science.
(1) Kost, D.; Kalikhman, I. In The Chemistry of Organic Silicon
Compounds; Wiley: New York, 1998; Vol. 2, p 1339.
(4) (a) Brelie`re, C.; Carre´, F.; Corriu, R. J. P.; Royo, G. Organometallics
1988, 7, 1006. (b) Brelie`re, C.; Carre´, F.; Corriu, R. J. P.; Royo, G.; Man,
M. W. C. Organometallics 1994, 13, 307. (c) Carre´, F.; Chuit, C.; Corriu,
R. J. P.; Fanta, A.; Mehdi, A.; Reye´, C. Organometallics 1995, 14, 194.
(d) Kano, N.; Nakagawa, N.; Kawashima, T. Angew. Chem., Int. Ed. 2001,
40, 3450.
(5) (a) Kawachi, A.; Tanaka, Y.; Tamao, K. Organometallics 1997, 16,
5102. (b) Dostal, S.; Stoudt, S. J.; Fanwick, P.; Sereatan, W. F.; Kahr, B.;
Jackson, J. E. Organometallics 1993, 12, 2284.
(2) A bidentate ligand (-(C6H4)-2-C(CF3)2O-): (a) Martin, J. C.;
Perozzi, E. F. Science 1976, 191, 154. (b) Perozzi, E. F.; Michalak, R. S.;
Figuly, G. D.; Stevenson, W. H., III; Dess, D. B.; Ross, M. R. Martin, J.
C. J. Org. Chem. 1981, 46, 1049. (c) Martin, J. C. Science 1983, 221, 509.
(3) A bidentate ligand (-(C6H4)-2-(CH2NMe2)): van Koten, G.; Schaap,
C. A.; Noltes, J. G. J. Organomet. Chem. 1975, 99, 157. A tridentate ligand
(-(C6H3)-2,6-(CH2NMe2)2): van Koten, G.; Jastrzebski, J. T. B. H.; Noltes,
J. G.; Spek, A. L.; Schoone, J. C. J. Organomet. Chem. 1978, 148, 233.
10.1021/om060031o CCC: $33.50 © 2006 American Chemical Society
Publication on Web 05/28/2006

Heptacoordinate Trihalogermanes
Organometallics, Vol. 25, No. 14, 2006 3389
mane 4. Although the fluorination reaction proceeded more
rapidly in polar solvents such as chloroform and acetonitrile,
side reactions also occurred, so that a complex mixture of 4
and unidentified products was obtained. The reaction of 3 with
3 equiv of bromotrimethylsilane and iodotrimethylsilane yielded
the tribromogermane 5 and the triiodogermane 6, respectively.
5 was also synthesized by treatment of 3 with an excess of
tribromoborane at -78 °C (vide infra). The reaction at higher
temperature caused decomposition to give a complex mixture,
in marked contrast to the previous report that trichlorosilane 1
underwent demethylation followed by Si-O bond formation.8
These results indicate that the present halogen exchange reaction
on the central atom proceeds more readily than demethylation
in the germanium derivative 3 compared to the silicon derivative
1.
X-ray Crystallographic Analyses and Spectroscopic Prop-
erties of Trihalogermanes. Single crystals of 3-6 suitable for
X-ray analysis were obtained in each case by slow evaporation
from a hexane solution for 3, a hexane/ether solution for 4, a
benzene/THF solution for 5, and a benzene/CHCl3 solution for
6, respectively. The crystal structures of 3-6 were determined
by X-ray crystallographic analysis, and ORTEP drawings of 4
are shown in Figure 3. Selected bond lengths, interatomic
distances, and bond angles are given in Table 2. All have
approximate C3 symmetrical propeller-like structures, as had
been found in the previously reported trichlorosilane 16 and
trichlorogermane 3′.7 The oxygen ligands adopt positions anti
to the halogen atoms (O‚‚‚Ge-X angles are 170-178°), while
the three aryl rings have similar twists out of their common
coordination plane with the germanium atom.
Figure 2.
methoxyphenyl)methyl unit (Figure 2), and found that 1 is
unusually stable to nucleophilic substitutions.6 Despite several
reports on syntheses of heptacoordinate compounds with type
II interactions,5-7 there have been few systematic studies on
group 14 element compounds with varying functional groups
using the same ligand. We report here the syntheses of
heptacoordinate trihalogermanes substituted with the tris(3-tert-
butyl-6-methoxyphenyl)methyl group, and we compare their
structures and reactivities.
Results and Discussion
Synthesis of the Trichlorogermane 3 and Its Derivatization
to the Corresponding Trifluoro-, Tribromo-, and Tri-
iodogermanes. In a way similar to that previously reported by
us and Takeuchi et al. for the trichlorosilane 16 and trichloro-
germane 3′,7 respectively, the trichlorogermane 3 was synthe-
sized by the lithiation of tris(3-tert-butyl-6-methoxyphenyl)-
methane (2) by an excess of n-butyllithium followed by reaction
of the lithium reagent thus formed with tetrachlorogermane (eq
1). An increase in the yield of 3 was achieved when DME was
Interatomic distances between the oxygen atom and the
germanium atom are 16-23% shorter than the sum of van der
Waals radii (3.40 Å).9 The ratio of O‚‚‚Ge distances to the sum
of van der Waals radii is gradually increased as the halogen
atom on the germanium atom becomes less electronegative: 4
(2.622 Å; 77%) < 3 (2.769 Å; 81%) < 5 (2.821 Å; 83%) < 6
(2.853 Å; 84%). The averaged X-Ge-X angles also widen
with 4 (98.93°) < 3 (101.25°) < 5 (101.78°) < 6 (102.55°),
and the averaged torsion angles of the propellers Ge-C1-C2-
C3 (see Figure 4) increase except for 6: 4 (47.8°) < 3 (51.5°)
< 5 (55.3°) ≈ 6 (54.7°). Because the Lewis acidity of the
germanium atom was generally enhanced by the introduction
of more electronegative groups, these results indicate that all
of these compounds have a heptacoordinate structure with
“tricapped tetrahedral” geometry, by the coordination of three
oxygen atoms from the side opposite to the halogen atoms. The
Ge-X bond lengths of 3-6 are slightly elongated compared to
the average Ge-X bond lengths of tetracoordinate organotri-
halogermanes without coordination, as shown in the Cambridge
Structural Database (CSD).
The changes in the NMR spectra between trihalogermanes
can be rationalized by the structural changes. The 13C NMR
chemical shift of the methoxy groups was shifted to lower field
with a decrease in the distances between the oxygen atom and
the central germanium atom, as shown in the X-ray structures.
When the oxygen-germanium interaction is increased, the
neighboring carbon atom is more deshielded. When the 13C
NMR chemical shifts of the methoxy group were plotted against
the interatomic distances between the oxygen atom and the
used as a solvent in the presence of HMPA, which is well-
known to activate the lithium reagent by solvation to the lithium
cation. Once isolated, 3 was quite stable compared with the usual
trichlorogermanes and could be stored in the air. However, 3
was slightly less stable than 1 and slowly decomposed during
column chromatography on silica gel, thus resulting in isolation
in only low yield (30%).
The trifluoro-, tribromo-, and triiodogermanes 4-6 were
obtained by halogen exchange reactions with the trichloroger-
mane 3 (eqs 2-4; the yields of 5 and 6 were quantitative, as
estimated by 1H NMR). 3 was allowed to react slowly with an
AgF
Ar3CGeCl3
Ar CGeF
4 (50%)
8
(2)
(3)
3
3
3
Me3SiX
Ar3CGeCl3
Ar CGeX
8
3
3
3
5 (X ) Br)
6 (X ) I)
(6) Kobayashi, J.; Ishida, K.; Kawashima, T. Silicon Chem. 2002, 1, 351.
(7) Takeuchi, Y.; Takase, Y. J. Organomet. Chem. 2004, 689, 3275.
(8) Kobayashi, J.; Kawaguchi, K.; Kawashima, T. J. Am. Chem. Soc.
2004, 126, 16318.
BBr3
Ar3CGeCl3
Ar CGeBr
5 (98%)
8
(4)
3
3
3
(9) For the van der Waals radii of Ge: Bondi, A. J. Phys. Chem. 1964,
68, 441.
excess of silver(I) fluoride in benzene to give the trifluoroger-

3390 Organometallics, Vol. 25, No. 14, 2006
Iwanaga et al.
Figure 3. ORTEP drawings of 4 (50% probability): (left) side view; (right) top view.
Table 1. Crystallographic Data for the
Trihalo[tris(3-tert-butyl-6-methoxyphenyl)methyl]germanes
3-6
3
4
5
6
formula
C34H45Cl3-
GeO3
153(2)
monoclinic
C2/c
35.665(15)
10.282(4)
20.270(9)
C34H45F3-
GeO3
120(2)
triclinic
P1h
10.093(3)
11.968(4)
14.947(5)
97.379(4)
C34H45Br3- C34H45Ge-
GeO3
120(2)
cubic
I3O3
120(2)
cubic
Pa3h
temp/K
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
Pa3
Figure 4.
19.7087(5) 19.9244(5)
103.1143(17) 98.341(4)
105.019(4)
7239(5)
1699.2(10) 7655.5(3)
2
1.234
9622
7909.6(3)
8
Z
D
8
8
calcd/g cm-3
1.249
19 977
1.742
36 618
1.670
39 716
no. of rflns
collected
no. of unique
rflns
5852
5135
1894
2151
goodness of fit 1.099
1.140
1.173
1.073
R1
wR2
0.0734
0.1896
0.0330
0.0866
0.0392
0.0983
0.0536
0.1634
Table 2. Selected Bond Lengths, Interatomic Distances, and
Anglesa
Figure 5. Plots of oxygen-germanium interatomic distances vs
NMR chemical shifts.
omitted, was performed at the B3PW91/6-311+G(d)[Ge]:6-
31+G(d)[O,F]:6-31G(d)[C,H] level. The optimized geometry
of 4′ reproduced well that of 4, and the O‚‚‚Ge distance of 4′
(2.638 Å) was close to those (2.521, 2.658, and 2.685 Å) of 4.
As the bond critical points were found on the bond paths
between the oxygen atoms and the germanium atom, bonding
between oxygen and germanium should be considered to exist.
E-X in O‚‚‚E-X/
E
X
R
rw/Åb O‚‚‚E/Å E-X/Å CSD/Åc
deg
1d Si Cl t-Bu 3.39 2.80 (83)e
Ge Cl t-Bu 3.40 2.77 (81)
3′ Ge Cl 3.40 2.78 (81)
t-Bu 3.40 2.62 (77)
Ge Br t-Bu 3.40 2.82 (83)
Ge t-Bu 2.85 (84)
2.07
2.16
2.16
1.78
2.32
2.52
2.02 (-)d
2.13 (18)
2.13 (18)
f
2.28 (3)
2.52 (2)
176
176
3
H
4
5
6
Ge
F
171
177
178
3
The small value of the electron density (F(r): 0.0229 e/ao ) and
2
5
the small positive Laplacian value (∇ F(r): 0.0598 e/ao ) at the
bond critical point indicate that the corresponding bonds are
weak and have ionic character.11
I
a Values are the average of the symmetric parts of the compounds. b The
sum of van der Waals radii of O‚‚‚E. c Average E-X bond lengths of
trichlorosilane or trihalogermanes without any coordination. Values in
parentheses represent the number of compounds from the CSD. d Reference
6. e Values in parentheses represent (O‚‚‚E)/(sum of VDW radii) in percent.
f There are no crystal data for organotrifluorogermanes in the CSD.
Reactivity of Trihalogermanes. To obtain further insight
into the properties of these trihalogermanes, reactions of 3-5
with some reagents were performed. Unfortunately, the reac-
tivities of triiodogermane 6 could not be examined properly
germanium atom, they showed a good linear correlation (Figure
5), and this result indicates that trihalogermanes have a
“tricapped tetrahedral” heptacoordinate structure with oxygen-
germanium interactions in solution as well as in the solid state.
To clarify the properties of the interatomic interaction of
trihalogermanes, AIM analysis10 of the model compound 4′, in
which three tert-butyl groups of trifluorogermane 4 were
(10) (a) Bader, R. F. W. Atoms in Molecules-A Quantum Theory; Oxford
University Press: Oxford, U.K., 1990. (b) Bader, R. F. W. Chem. ReV.
1991, 91, 893. (c) Bader, R. F. W.; Slee, T. S.; Cremer, D.; Kraka, E. J.
Am. Chem. Soc. 1983, 105, 5061. (d) Bader, R. F. W. J. Phys. Chem. A
1998, 102, 7314.
(11) For similar values, see: Yamashita, M.; Yamamoto, Y.; Akiba, K.-
y.; Hashizume, D.; Iwasaki, F.; Takagi, N.; Nagase, S. J. Am. Chem. Soc.
2005, 127, 4354.

Heptacoordinate Trihalogermanes
Organometallics, Vol. 25, No. 14, 2006 3391
Table 3. Ratios of the Products for the Reactions of 3-5
Table 4. Reaction Conditions and Products for the
a
with LiAlH4
Reactions of 3-5 with Trihaloboranes
X
2b
8b
X
reagent (amt/equiv)
conditions
producta
3
4
5
Cl
F
Br
29
0
23
16
100
77
3
4
4
5
Cl
F
F
BBr3 (10)
BBr3 (10)
BCl3 (6)
BCl3 (6)
-78 °C, 1 h
-78 °C, 1 h
0 °C, 3 h
5 (98)
5 (quant)
3 (quant)
3 (31)b
Br
room temp, 17 h
a Reactions were carried out for 4 h at room temperature, with 3 equiv
of LiAlH4. b Estimated by H NMR.
a Estimated by 1H NMR; percentage yields are given in parentheses.
1
b 69% of 5 was observed.
because it was difficult to isolate from the byproducts formed
in its preparation and also it was relatively unstable compared
with the other trihalogermane derivatives.
Alkaline hydrolysis of both the trichlorogermane 3 and the
tribromogermane 5 with aqueous NaOH gave the triarylmethanol
species 712 (eq 5). This result indicates that these trihalogermanes
trichloroborane, the reactions of trifluoro- and tribromogermanes
4 and 5 gave trichlorogermane 3. In contrast to the reactions
with tribromoborane, the halogen exchange reactions of 4 and
5 with trichloroborane proceeded without formation of byprod-
ucts at 0 °C or at room temperature. The desirable halogen
exchange reactions of the tribromogermane 5 with trichlorobo-
rane proceeded slowly (31% for 17 h at room temperature). On
the other hand, the reaction of trifluorogermane 4 proceeded
much more quickly. Apparently, the more electronegative
fluorine accelerates the halogen exchange reaction. Trifluo-
roborane etherate did not react with any of these trihaloger-
manes, and reactions with triiodoborane resulted in a complex
decomposition of substrates. To obtain further insight into these
reactions, theoretical calculations of the free energy differences
of the reaction of trihalomethylgermanes with trihaloboranes
were performed at the B3LYP/6-31G*//B3LYP/6-31G* level.13
Equations 9-11 are energetically favorable, which can be
aq NaOH
Ar3CGeX3
Ar COH
8
(5)
3
THF
3, 5
7
tend to be attacked by nucleophiles (in this case, OH-) at their
triarylmethyl carbon position, resulting in carbon-germanium
bond cleavage. For 4 h at room temperature, only 31% of 7
was obtained from trichlorogermane 3, in contrast to quantitative
conversion in the case of tribromogermane 5. The higher
reactivity of 5 may be caused by the great leaving ability of
GeBr3, which is bulkier than GeCl3.
Similar reactivity was also observed in the reaction of
trichlorogermane 3 with 3 equiv of LiAlH4. The triarylmethane
2 was the major product, and the trihydrogermane 8 was formed
in lower yield (eq 6 and Table 3). The origin of the hydrogen
MeGeF3 + BCl3 f MeGeCl3 + BF3
(9)
(10)
(11)
∆G ) -40 kcal mol-1
LiAlH4
MeGeF3 + BBr3 f MeGeBr3 + BF3
Ar3CGeX3
Ar CH Ar CGeH
+
3 3 3
8
(6)
THF
∆G ) -64 kcal mol-1
3-5
2
8
atom substituted on the triarylmethyl carbon was confirmed by
treatment with LiAlD4; triaryldeuteriomethane (2-d) was ob-
tained, suggesting direct nucleophilic attack by the hydride
(deuteride) anion. The trihydrogermane derivative 8 was very
likely formed by nucleophilic displacement of chlorine by
hydride. Both 2 and 8 were obtained in the reaction of
tribromogermane 5 with LiAlH4, but their ratio was reversed
and 8 was the major product. The reaction of trifluorogermane
4 with LiAlH4 yielded 8 quantitatively. These results indicate
that the ratio of 2 and 8 in the competing reactions is determined
by the difference in the halogen substituents of the trihaloger-
manes, their leaving abilities and steric factors, as well as the
Lewis acidity of the Ge atom in each case.
MeGeCl3 + BBr3 f MeGeBr3 + BCl3
∆G ) -23 kcal mol-1
rationalized by the quantitative conversion to products in the
corresponding reactions of trihalo(triarylmethyl)germanes with
trihaloboranes. The reverse reaction of eq 11 is energetically
disfavored, reflecting the low conversion yield in the reaction
of tribromogermane 5 with trichloroborane. Considering that
the reverse reactions of eqs 9 and 10 are thermodynamically
more unfavorable and trifluoroborane etherate was used in the
real system, it is quite reasonable that 3 and 5 did not react
with trifluoroborane etherate at all.
The reaction of trichlorogermane 3 with an excess (10 equiv)
of tribromoborane at -78 °C yielded tribromogermane 5
quantitatively. To obtain further insight, the reactions of
trihalogermanes 3-5 and BBr3 or BCl3 were investigated (eqs
7 and 8 and Table 4). Treatment with a large excess (10 equiv)
Experimental Section
Synthesis of Trichloro[tris(3-tert-butyl-6-methoxyphenyl)-
methyl]germane (3). To a solution of tris(3-tert-butyl-6-methoxy-
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; 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.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A.
G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, revision B.05; Gaussian, Inc.: Wallingford, CT, 2004.
BBr3
Ar3CGeX3
8 Ar3CGeBr3
(7)
(8)
CH2Cl2
3, 4
5
BCl3
Ar3CGeX3
8 Ar3CGeCl3
CH2Cl2
4, 5
3
of tribromoborane at -78 °C also converted trifluorogermane
4 into tribromogermane 5 quantitatively, whereas reactions
carried out at 0 °C resulted in a complex mixture. With
(12) Kobayashi, J.; Goto, K.; Kawashima, T.; Schmidt, M. W.; Nagase,
S. J. Am. Chem. Soc. 2002, 124, 3703.

3392 Organometallics, Vol. 25, No. 14, 2006
Iwanaga et al.
phenyl)methane12 (5.00 g, 9.95 mmol) in benzene (250 mL) was
added n-BuLi (1.67 M hexane solution, 50.1 mmol) at 50 °C. The
mixture was stirred at 50 °C for 12 h. After removal of the solvent
under reduced pressure, DME (125 mL) and HMPA (6.90 mL, 39.7
mmol) were added to the residue. To the mixture was added
tetrachlorogermane (11.3 mL, 99.5 mmol) at 0 °C. The mixture
was stirred at 0 °C for 2 h and at room temperature for 12 h. After
removal of the solvent, the residue was treated with 200 mL of
EtOH and then 100 mL of H2O. The mixture was extracted with
CHCl3. After removal of the solvent under reduced pressure, the
residue was dissolved in ether and washed with 2% aqueous NaOH.
The extracts were combined and dried over anhydrous MgSO4, and
the solvent was removed under reduced pressure. The residue was
subjected to column chromatography on silica gel. Elution with
15/1 hexane/AcOEt gave 3, which was further purified by recrys-
tallization from hexane/CHCl3 to afford the pure product (2.02 g,
µL, 220 µmol) at room temperature in a 5 mm o.d. NMR tube.
After several freeze-pump-thaw cycles, the tube was evacuated
and sealed. The solution was heated at 75 °C for 8 h. After the
completion of the reaction was confirmed by 1H NMR spectroscopy,
the sealed tube was opened in a glovebox, and the solvent was
removed under reduced pressure. The residue was purified by
recrystallization from hexane/Et2O to afford 6 (16 mg, 23%). 6:
yellow crystal, mp 169.5-169.8 °C dec; 1H NMR (500 MHz,
CDCl3, 27 °C) δ 1.08 (s, 27H), 3.52 (s, 9H), 6.57 (d, 3H, J ) 1.8
Hz), 6.80 (d, 3H, J ) 8.5 Hz), 7.36 (dd, 3H, J ) 1.8, 8.5 Hz); 13
C
NMR (126 MHz, CDCl3, 27 °C) δ 31.3 (q), 33.9 (s), 52.5 (q), 69.7
(s), 109.8 (d), 125.2 (d), 126.6 (s), 128.4 (d), 143.1 (s), 154.3 (s).
Anal. Calcd for C34H45GeI3O3: C, 42.76; H, 4.75. Found: C, 42.95;
H, 5.00.
X-ray Structural Analysis. Single crystals of 3-6 were grown
from the appropriate solution (hexane solution for 3, hexane/ether
solution for 4, benzene/THF solution for 5, and benzene/CHCl3
solution for 6). The intensity data were collected at 120 K (except
for 3, at 153 K) on a Rigaku/MSC Mercury CCD with Mo KR
radiation (λ ) 0.710 69 Å). The structures were solved by direct
methods and refined by full-matrix least squares on F2 using
SHELXS97.14 Crystallographic data are given in Table 1. The
structures were refined anisotropically, except for hydrogen atoms.
Hydrogen atoms were idealized by using the riding models.
Alkaline Hydrolysis of Trichlorogermane 3. To a solution of
the trichlorogermane 3 (4.8 mg, 7.0 µmol) in THF (1 mL) was
added NaOH (0.7 mM aqueous solution, 0.7 mmol) at room
temperature. The mixture was stirred for 6 h and then was extracted
with CHCl3. The extracts were combined and dried over anhydrous
MgSO4, and the solvent was removed under reduced pressure. The
1
30%). 3: colorless crystal, mp 265.5-265.7 °C; H NMR (500
MHz, CDCl3, 27 °C) δ 1.06 (s, 27H), 3.63 (s, 9H), 6.37 (d, 3H, J
) 2.3 Hz), 6.80 (d, 3H, J ) 8.5 Hz), 7.31 (dd, 3H, J ) 2.3, 8.5
Hz); 13C NMR (126 MHz, CDCl3, 27 °C) δ 31.2 (q), 34.0 (s), 53.6
(q), 69.0 (s), 108.7 (d), 125.2 (d), 126.5 (s), 127.8 (d), 143.0 (s),
154.4 (s). Anal. Calcd for C34H45Cl3GeO3: C, 59.99; H, 6.66.
Found: C, 59.74; H, 6.74.
Synthesis of Trifluoro[tris(3-tert-butyl-6-methoxyphenyl)-
methyl]germane (4). To a solution of trichlorogermane 3 (500 mg,
735 µmol) in benzene (5 mL) was added silver(I) fluoride (467
mg, 3.68 mmol), and the mixture was heated at reflux for 4 days.
Insoluble silver salts were filtered off, and the solvent was removed
under reduced pressure. The residue was purified by recrystallization
from hexane to afford 4 (233 mg, 50%). 4: colorless crystal, mp
1
1
residue was analyzed by H NMR spectroscopy to give the ratio
263.3-263.7 °C dec; H NMR (500 MHz, CDCl3, 27 °C) δ 1.06
of 3 (69%) and tris(3-tert-butyl-6-methoxyphenyl)methanol (7;12
31%).
(s, 27H), 3.78 (s, 9H), 6.28 (d, 3H, J ) 2.4 Hz), 6.85 (d, 3H, J )
8.5 Hz), 7.28 (dd, 3H, J ) 2.4, 8.5 Hz); 13C NMR (126 MHz,
2
Alkaline Hydrolysis of Tribromogermane 5. To a solution of
the tribromogermane 5 (5.7 mg, 7.0 µmol) in THF (1 mL) was
added NaOH (0.7 mM aqueous solution, 0.7 mmol) at room
temperature. The mixture was stirred for 6 h and extracted with
CHCl3. The extracts were combined and dried over anhydrous
MgSO4, and the solvent was removed under reduced pressure. The
residue was analyzed by 1H NMR spectroscopy to show the
quantitative formation of tris(3-tert-butyl-6-methoxyphenyl)metha-
nol (7).12
CDCl3, 27 °C) δ 31.2 (q), 34.0 (s), 52.3 (q, JCF ) 6.5 Hz), 55.5
(q), 109.3 (d), 125.1 (d), 126.4 (d), 127.7 (s), 143.5 (s), 153.2 (s);
19F NMR (376 MHz, CDCl3, 27 °C) δ -25.45. Anal. Calcd for
C34H45F3GeO3: C, 64.68; H, 7.18. Found: C, 64.52; H, 7.22.
Synthesis of Tribromo[tris(3-tert-butyl-6-methoxyphenyl)-
methyl]germane (5) by Reaction of 3 with Bromotrimethyl-
silane. To a solution of the trichlorogermane 3 (50 mg, 73.5 µmol)
in CDCl3 (0.5 mL) was added bromotrimethylsilane (17.5 µL, 132
µmol) at room temperature in a 5 mm o.d. NMR tube. After several
freeze-pump-thaw cycles, the tube was evacuated and sealed. The
solution was heated at 75 °C for 2 weeks. After the completion of
Reaction of Trichlorogermane 3 with Lithium Aluminum
Hydride. To a solution of trichlorogermane 3 (50 mg, 74 µmol) in
THF (3 mL) was added LiAlH4 (9.0 mg, 237 µmol) at 0 °C. The
mixture was warmed to room temperature and stirred for 4 h. The
mixture was treated with aqueous NH4Cl and extracted with CHCl3.
The extracts were combined and dried over anhydrous MgSO4, and
the solvent was removed under reduced pressure. The residue was
1
the reaction was confirmed by H NMR spectroscopy, the sealed
tube was opened in a glovebox, and the solvent was removed under
reduced pressure. The residue was purified by recrystallization from
hexane/Et2O to afford 5 (31 mg, 53%). 5: yellow crystal, mp
1
181.9-182.3 °C dec; H NMR (500 MHz, CDCl3, 27 °C) δ 1.08
1
analyzed by H NMR spectroscopy to show that the ratio of 3 to
(s, 27H), 3.60 (s, 9H), 6.46 (d, 3H, J ) 2.3 Hz), 6.80 (d, 3H, J )
8.5 Hz), 7.34 (dd, 3H, J ) 2.3, 8.5 Hz); 13C NMR (126 MHz,
CDCl3, 27 °C) δ 31.2 (q), 34.0 (s), 53.2 (q), 72.2 (s), 108.9 (d),
125.3 (d), 126.3 (s), 128.2 (d), 142.9 (s), 154.5 (s). Anal. Calcd
for C34H45Br3GeO3: C, 50.16; H, 5.57. Found: C, 50.14; H, 5.72.
tris(3-tert-butyl-6-methoxyphenyl)methane (2) to trihydro[tris(3-
tert-butyl-6-methoxyphenyl)methyl]germane (8) was 55:29:16.
1
8: colorless crystal, mp 189.5-190.0 °C dec; H NMR (500
MHz, CDCl3, 27 °C) δ 1.04 (s, 27H), 3.63 (s, 9H), 4.33 (s, 3H),
6.33 (d, 3H, J ) 2.5 Hz), 6.78 (d, 3H, J ) 8.4 Hz), 7.15 (dd, 3H,
J ) 2.5, 8.4 Hz); 13C NMR (126 MHz, CDCl3, 27 °C) δ 31.3 (q),
33.9 (s), 54.5 (q), 55.9 (s), 109.6 (d), 122.7 (d), 127.2 (d), 134.4
(s), 142.4 (s), 155.1 (s); HR-MS (FAB+) m/z calcd for C34H47-
GeO3 ([M - H]+) 577.2737, found 577.2762. Anal. Calcd for
C34H48GeO3: C, 70.73; H, 8.38. Found: C, 70.59; H, 8.52.
Reaction of Tribromogermane 5 with Lithium Aluminum
Hydride. To a solution of the tribromogermane 5 (20 mg, 25 µmol)
in THF (1.5 mL) was added LiAlH4 (3.0 mg, 79 µmol) at 0 °C.
The mixture was warmed to room temperature and stirred for 4 h.
The mixture was treated with aqueous NH4Cl and extracted with
Synthesis of Tribromo[tris(3-tert-butyl-6-methoxyphenyl)-
methyl]germane (5) by Reaction of 3 with Tribromoborane. To
a solution of the trichlorogermane 3 (68 mg, 0.10 mmol) in CH2-
Cl2 (3 mL) was added tribromoborane (1.0 M CH2Cl2 solution,
1.0 mmol) at -78 °C. The mixture was stirred at -78 °C for 1 h.
Subsequently it was treated with EtOH and then H2O and extracted
with CHCl3. The extracts were combined and dried over anhydrous
MgSO4, the solvent was removed under reduced pressure, and the
residue was purified by recrystallization from hexane to afford 5
(80 mg, 98%).
Synthesis of Triiodo[tris(3-tert-butyl-6-methoxyphenyl)meth-
yl]germane (6). To a solution of the trichlorogermane 3 (50 mg,
73.5 µmol) in CDCl3 (0.5 mL) was added iodotrimethylsilane (32
(14) Sheldrick, G M. SHELXS-97: Program for Crystal Structure
Solution; University of Go¨ttingen, Go¨ttingen, Germany, 1997.

Heptacoordinate Trihalogermanes
Organometallics, Vol. 25, No. 14, 2006 3393
CHCl3. The extracts were combined and dried over anhydrous
MgSO4, and the solvent was removed under reduced pressure. The
residue was analyzed by H NMR spectroscopy to show that the
extracted with CHCl3. The extracts were combined and dried over
anhydrous MgSO4, and the solvent was removed under reduced
pressure. The residue was analyzed by H NMR spectroscopy to
1
1
ratio of tris(3-tert-butyl-6-methoxyphenyl)methane (2) to the tri-
hydrogermane 8 was 23:77.
show that the ratio of 5 to the trichlorogermane 3 was 69:31.
Reaction of Trifluorogermane 4 with Trichloroborane. To a
solution of the trifluorogermane 4 (14 mg, 22 µmol) in CH2Cl2 (2
mL) was added trichloroborane (1.0 M hexane solution, 130 µmol)
at 0 °C. The mixture was stirred at 0 °C for 3 h. The mixture was
treated with EtOH and then H2O and extracted with CHCl3. The
extracts were combined and dried over anhydrous MgSO4, and the
solvent was removed under reduced pressure. The residue was
analyzed by 1H NMR spectroscopy to show the quantitative
formation of the trichlorogermane 3.
Reaction of Trifluorogermane 4 with Lithium Aluminum
Hydride. To a solution of the trifluorogermane 4 (19 mg, 30 µmol)
in THF (3 mL) was added LiAlH4 (3.4 mg, 90 µmol) at 0 °C. The
mixture was warmed to room temperature and for 4 h. The mixture
was treated with aqueous NH4Cl and extracted with CHCl3. The
extracts were combined and dried over anhydrous MgSO4, and the
solvent was removed under reduced pressure. The residue was
analyzed by 1H NMR spectroscopy to show the quantitative
formation of the trihydrogermane 8.
Reaction of Trifluorogermane 4 with Tribromoborane. To a
solution of the trifluorogermane 4 (11 mg, 17 µmol) in CH2Cl2
(1.5 mL) was added tribromoborane (1.0 M CH2Cl2 solution, 170
µmol) at -78 °C. The mixture was stirred at -78 °C for 1 h. The
mixture was treated with EtOH and then H2O and extracted with
CHCl3. The extracts were combined and dried over anhydrous
MgSO4, and the solvent was removed under reduced pressure. The
residue was analyzed by 1H NMR spectroscopy to show the
quantitative formation of the tribromogermane 5.
Reaction of Tribromogermane 5 with Trichloroborane. To a
solution of the tribromogermane 5 (16 mg, 20 µmol) in CH2Cl2 (2
mL) was added trichloroborane (1.0 M hexane solution, 120 µmol)
at room temperature. The mixture was stirred at room temperature
for 17 h. The mixture was treated with EtOH and then H2O and
Acknowledgment. This study was supported by a Grant-
in-Aid for The 21st Century COE Program for Frontiers in
Fundamental Chemistry and a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science and Technology of Japan. We also thank Tosoh
Finechem Co., Ltd., and Shinetsu Chemicals for the generous
gifts of alkyllithiums and silicon compounds, respectively.
Supporting Information Available: CIF files giving crystal-
lographic data for 3-6 and figures giving ORTEP drawings of 3,
5, and 6. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM060031O