New small-ring cyclogermanes: syntheses and X-ray crystal structures

Article abstract of DOI:10.1021/ic970833z

Reaction of GeCl₂·dioxane with 2 equiv of Li(THF)_2.5Ge(SiMe₃)₃ in hexane afforded moderate yields of two cyclopolygermanes. A cyclotrigermane, (Ge(SiMe₃)₂)₃, was characterized by NMR spectra, elemental analyses, and an X-ray crystal structure determination. It crystallized from pentane in the R3?c space group (rhombohedral) with a = 19.294(3) A?, α = 31.89(1)°, V= 1781 A°₃, and Z = 2. The Ge₃ core consisted of an equilateral triangle with a Ge-Ge distance of 2.460(1) A°, the shortest so far measured in cyclotrigermanes. The second product was tentatively identified by its NMR spectra as a cyclotetragermane, ((Me₃Si)₃GeGeCl)₄, and this was confirmed by elemental analyses and an X-ray structure determination on the yellow crystals formed from pentane. The product was found to crystallize as a complex with two molecules of Ge(SiMe₃)₄ in the F2₃ (cubic) space group with a = 22.7731(3) A?, V = 11 810.5 A?³, and Z = 8. The Ge₄ core consisted of a nonplanar four-membered ring (fold angle = 18.7°) disordered over three positions related by 3-fold symmetry. In the assumed ordered structure, ring Ge-Ge distances averaged 2.503 A?. When the reaction was repeated with GeCl₂·dioxane and 2 equiv of Li(THF)₃Si(SiMe₃)₃, the known disilagermirane, (Me₃Si)₂Ge(Si(SiMe₃)₂)₂, was isolated (66% yield) along with a small yield of the known cyclotetragermane, ((Me₃Si)₃SiGeCl)₄. Reaction of GeI₂ with Li(THF)_2.5Ge(SiMe₃)₃ gave only traces of the cyclotrigermane.

Full text of DOI:10.1021/ic970833z

Inorg. Chem. 1997, 36, 6247-6250
6247
New Small-Ring Cyclogermanes: Syntheses and X-ray Crystal Structures
Siva P. Mallela,* Sven Hill, and R. A. Geanangel*
Department of Chemistry, University of Houston, Houston, Texas 77204-5641
ReceiVed July 3, 1997X
Reaction of GeCl2‚dioxane with 2 equiv of Li(THF)2.5Ge(SiMe3)3 in hexane afforded moderate yields of two
cyclopolygermanes. A cyclotrigermane, (Ge(SiMe3)2)3, was characterized by NMR spectra, elemental analyses,
and an X-ray crystal structure determination. It crystallized from pentane in the R3hc space group (rhombohedral)
with a ) 19.294(3) Å, R ) 31.89(1)°, V ) 1781 Å3, and Z ) 2. The Ge3 core consisted of an equilateral triangle
with a Ge-Ge distance of 2.460(1) Å, the shortest so far measured in cyclotrigermanes. The second product was
tentatively identified by its NMR spectra as a cyclotetragermane, ((Me3Si)3GeGeCl)4, and this was confirmed by
elemental analyses and an X-ray structure determination on the yellow crystals formed from pentane. The product
was found to crystallize as a complex with two molecules of Ge(SiMe3)4 in the F23 (cubic) space group with a
) 22.7731(3) Å, V ) 11 810.5 Å3, and Z ) 8. The Ge4 core consisted of a nonplanar four-membered ring (fold
angle ) 18.7°) disordered over three positions related by 3-fold symmetry. In the assumed ordered structure,
ring Ge-Ge distances averaged 2.503 Å. When the reaction was repeated with GeCl2‚dioxane and 2 equiv of
Li(THF)3Si(SiMe3)3, the known disilagermirane, (Me3Si)2Ge(Si(SiMe3)2)2, was isolated (66% yield) along with
a small yield of the known cyclotetragermane, ((Me3Si)3SiGeCl)4. Reaction of GeI2 with Li(THF)2.5Ge(SiMe3)3
gave only traces of the cyclotrigermane.
Introduction
tures9 incorporating -E(SiMe3)3 (E ) Si, Ge) groups. As a
part of a comparative study of Ge(SiMe3)3 and Si(SiMe3)3
Compounds with three- and four-membered rings involving
group 14 elements have attracted considerable interest.1,2
Cyclotrigermanes are useful photochemical precursors for
germylenes and digermenes. Bulky ligands have served to
stabilize such small cyclic systems by protecting reactive centers
with an organic “layer” that also prevents dimerization reactions.
Steric hindrance by bulky -Si[C(CH3)3]3 groups help stabilize
a free germanyl cation.3 In some cases, silyl and germyl anionic
reagents were employed in the synthesis of cyclotrigermanes,4
however, Masmune and others5 obtained cyclotrigermanes by
reductive cyclization of dichlorodiorganogermanes with lithium
naphthalide, while Ando and co-workers6 used Mg-MgBr2 for
reductive coupling. Recently, the first mixed group 14, three-
membered ring compounds were reported.7 Using a different
approach, we prepared a cyclotetragermane8 and related struc-
substituents, we now report the sytheses and structures of
hexakis(trimethylsilyl)cyclotrigermane and tetrachlorotetrakis-
(tris(trimethylsilyl)germyl)cyclotetragermane.
Experimental Section
Materials. The germanium(II) chloride-dioxane complex was
prepared as described in the literature,10 and GeI2 was purchased from
Gelest and used as received. The lithium silyl and germyl reagents
Li(THF)3Si(SiMe3)3 (1a) and Li(THF)2.5Ge(SiMe3)3 (1b) were prepared
according to published procedures.11,12 Hexane and pentane were
distilled just prior to use from Na/benzophenone under argon. THF
and ether were distilled from LiAlH4 under argon.
Procedures. All synthetic reactions were conducted using Schlenk
techniques under argon. Elemental analyses were performed by Atlantic
Microlabs, Norcross, GA. NMR spectra were obtained and other
manipulations and characterizations were carried out as described
earlier.13 Infrared spectra were recorded as Nujol mulls between AgBr
windows.
X Abstract published in AdVance ACS Abstracts, December 15, 1997.
(1) Masamune, S.; Hanzawa, Y.; Williams, D. J. J. Am. Chem. Soc. 1982,
104, 6136. (b) Snow, J. T.; Murakami, S.; Masamune, S.; Williams,
D. J. Tetrahedron Lett. 1984, 25, 4191. (c) Collins, S.; Murakami, S.;
Snow, J. T.; Masamune, S. Tetrahedron Lett. 1985, 26, 1281. (d)
Batcheller, S. A.; Masamune, S. Tetrahedron Lett. 1988, 29, 3383.
(e) Masamune, S.; Batcheller, S. H.; Park, J.; Davis, W. M.;
Yamaguchi, O.; Ohta, Y.; Kabe, Y. J. Am. Chem. Soc. 1989, 111,
1888. (f) Tsumuraya, S. A.; Batcheller, S. A.; Masamune, S. Angew.
Chem., Int. Ed. Engl. 1991, 30, 902. (g) Baines, K. H.; Cook, J. A.;
Payne, N. C.; Vittal, J. J. Organometallics 1992, 11, 1408.
(2) Ross, L.; Drager, M. J. Organomet. Chem. 1980, 199, 195. (b)
Sekiguchi, A.; Yatabe, T.; Naito, H.; Kabuto, C.; Sakurai, H. Chem.
Lett. 1992, 1697. (c) Mochida, K.; Kawajiri, Y.; Goto, M. Bull. Chem.
Soc. Jpn. 1993, 66, 2773.
(3) Sekiguchi, A.; Tsukmoto, M.; Ichinohe, M. Science 1997, 275, 60.
(4) Sekiguchi, A.; Yamazaki, H.; Kabuto, C.; Sakurai, H. J. Am. Chem.
Soc. 1995, 117, 8025.
(5) Masamune, S.; Sita, L. R.; Williams, D. J. J. Am. Chem. Soc. 1983,
105, 630. (b) Masamune, S.; Hanzawa, Y.; Murakami, S.; Bally, T.;
Blount, J. J. J. Am. Chem. Soc. 1982, 104, 1150. (c) Weidenbruch,
M.; Grimm, F. T.; Herndorf, M.; Schaa¨fer, A.; Peters, K.; Vonschmer-
ing, H. G. J. Organomet. Chem. 1988, 341, 335.
Hexakis(trimethylsilyl)cyclotrigermane, [Ge(SiMe3)2]3 (2).
A
suspension of GeCl2‚dioxane (1755 mg, 7.58 mmol) in hexane (30 mL)
was cooled to -78 °C and treated with 170 mL of a hexane solution
of 1b (7274 mg, 15.17 mmol). The orange-yellow reaction mixture
was stirred at -78 °C for 9 h and then allowed to warm to ambient
temperature and stirred 15 h, giving a dark brown solution with a fine
gray precipitate. Hexane was removed in vacuo, and the residue was
stirred with pentane (100 mL) for 1 h. The brown pentane solution
obtained after filteration was concentrated to about 50 mL and held at
-78 °C for 6 h, affording 1026 mg of colorless, transparent, hexagonal
slab crystals. Further concentration and recooling of the filtrate to -78
°C for 6 h gave 300 mg more product for a total yield of 1326 mg
(26.6% based on germanium dichloride). The mother liquor was
retained for further work-up. In a sealed capillary under argon, crystals
of 2 decompose at 135 °C, becoming orange, and melt at 185 °C. Anal.
(9) Mallela, S. P.; Schwan, F.; Geanangel, R. A. Inorg. Chem. 1996, 35,
745. (b) Schwan, F.; Mallela, S. P.; Geanangel, R. A. J. Chem. Soc.,
Dalton Trans. 1996, 4183.
(6) Tsumuraya, T.; Yoshio, K.; Ando, W. J. Organomet. Chem. 1994,
482, 131. (b) Ando, W.; Tsumuraya, T. J. Chem. Soc., Chem. Commun.
1987, 1514.
(7) Baines, K. H.; Cook, J. A. Organometallics 1991, 10, 3419. (b) Heine,
A.; Stalke, D. Angew. Chem., Int. Ed. Engl. 1994, 33, 113.
(8) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1994, 33, 1115.
(10) Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert, M. F.; Thorne,
A. J. J. Chem. Soc., Dalton Trans. 1986, 1551.
(11) Gutekunst, G.; Brook, A. G. J. Organomet. Chem. 1982, 225, 1.
(12) Brook, A. G.; Abdesaken, B.; So¨rall, H. S. J. Organomet. Chem. 1986,
299, 9.
(13) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1993, 32, 602.
S0020-1669(97)00833-1 CCC: $14.00 © 1997 American Chemical Society

6248 Inorganic Chemistry, Vol. 36, No. 27, 1997
Mallela et al.
Calcd for C18H54Ge3Si6: C, 32.9; H, 8.28. Found: C, 32.2; H, 8.10.
NMR (C6D6): 1H δ 0.466; 13C{1H} δ 5.06. IR (cm-1): 2700 (vw),
1910 (vw), 1845 (vw), 1320 (m), 1260 (vs), 1035 (sh), 1080 (vs), 860
(vs), 1790 (w), 520 (s), 650 (m), 590 (sh), 450 (w), 390 (m).
Table 1. Data Collection and Processing Parameters for 2 and 3
2
3
empirical formula
fw
C18H54Si6Ge3
657.03
C30H90Cl2Ge5Si10
1165.77
Tetrachlorotetrakis(tris(trimethylsilyl)germyl)cyclotetra-
germane Adduct with Tetrakis(trimethylsilyl)germane, [(Me3Si)3-
GeGeCl]4‚2Ge(SiMe3)4 (3). After crystallization of 2, the brown
pentane mother liquor was further concentrated and held at -10 °C
for 3 days, affording 3 as bright yellow rectangular crystals (274 mg).
The remaining solution was kept at -78 °C overnight and gave an
additional 124 mg of yellow crystals for a total isolated yield of 18.0%
based on starting germanium dichloride (24.5% based on the remaining
germanium dichloride). In a sealed capillary under argon, crystals of
3 turned red at 125 °C, decomposed at 151 °C, and melted to a brown
liquid at 171 °C. Anal. Calcd for C30H90Cl2Ge5Si10: C, 30.9; H, 7.78.
Found: C, 30.76; H, 7.38. NMR (C6D6): 1H NMR δ 0.569 (27 H,
(Me3Si)3GeGeCl), 0.298 (18 H, Ge(SiMe3)4); 13C{1H} NMR δ 5.27
((Me3Si)3GeGeCl), 3.44 (Ge(SiMe3)4). IR (cm-1): 2700 (vw), 1850
(vw), 1720 (w), 1320 (w), 1255 (vs), 1180 (vw), 1140 (vw), 1050 (w),
985 (m), 855 (vs), 790 (s), 725 (ms), 655 (s), 645 (sh), 370 (s). The
mother liquor still exhibited several NMR signals: 1H/13C NMR (major)
δ 0.291/3.48 (Ge(SiMe3)4), 0.278/3.54 (HGe(SiMe3)3), 0.270/3.57;
(minor) 0.208/1.13, 0.368/4.40, 0.385/4.90 (Ge2(SiMe3)6), 0.436 (m).
Reaction of GeCl2‚dioxane with (THF)3LiSi(SiMe3)3. GeCl2‚
dioxane (734.2 mg, 3.17 mmol) and 1a (2986.2 mg, 6.34 mmol) were
allowed to react in hexane as decribed for 2, followed by work-up
affording 1191 mg (66%) of disilagermirane, (Me3Si)2Ge(Si(SiMe3)2)2
(4). NMR (C6D6): 1H NMR δ 0.423 (Si(SiMe3)2), 0.452 (Ge(SiMe3)2)
(lit.7b δ 0.43, 0.45); 13C{1H} NMR δ 4.51 (Si(SiMe3)2), 5.26 (Ge-
(SiMe3)2). After 4 was separated by crystallizations (3×), the mother
liquor was concentrated and held at -10 °C for 14 days, yielding a
small batch of yellow crystals identified as tetrachlorotetrakis(tris-
(trimethylsilyl)silyl)cyclotetragermane, ((Me3Si)3Si)GeCl)4.8 NMR
(C6D6): 1H NMR δ 0.531; 13C{1H} NMR δ 4.89 (lit.8 δ 0.533, 4.85).
Reaction of GeI2 with (THF)2.5LiGe(SiMe3)3. A hexane (50 mL)
suspension of GeI2 (1322.6 mg, 4.05 mmol) and 150 mL of a hexane
solution of 1b (3885 mg, 8.1 mmol) were combined and worked up in
pentane as described for 2. The resulting red-brown solution, held at
-10 °C for 20 h, afforded 147.4 mg of a crude product mixture. NMR
(C6D6) 1H δ 0.461 (minor, 2), 0.285 (trace, HGe(SiMe3)3), 0.296 (major,
Ge(SiMe3)4), 0.391 (major, Ge2(SiMe3)6). Repeating the GeI2 reaction
in diethyl ether gave comparable results with only a small amount of
the cyclotrigermane product.
X-ray Structure Determination of 2. A colorless block having
approximate dimensions of 0.25 × 0.50 × 0.60 mm was cut from a
large hexagonal slab and mounted in a random orientation on a Nicolet
R3m/V automatic diffractometer. The sample was held in a stream of
dry nitrogen gas at -50 °C, and the radiation used was Mo KR
monochromatized by a highly ordered graphite crystal. Final cell
constants, as well as other information pertinent to data collection and
refinement, are listed in Table 1. The Laue symmetry was determined
to be 3hm, and from systematic absences, the space group was shown
to be R3c or R3hc. Intensities were measured using the ω-scan
technique, with the scan rate depending on the count obtained in rapid
prescans of each reflection. Two standard reflections were monitored
every 2 h or every 100 data collected, and these showed no significant
change. During data reduction, Lorentz and polarization corrections
were applied, as well as a semiempirical absorption correction based
on ψ scans of 10 reflections having ø values between 70 and 90°.
Since the unitary structure factors displayed centric statistics, space
group R3hc was chosen from the outset. The structure was solved by
the SHELXTL direct-methods program which revealed the positions
of all of the atoms in the asymmetric unit, consisting of 1/6 of a molecule
situated about a crystallographic 32 site. In Scho¨nflies notation, the
molecule possesses D3 symmetry. The usual sequence of isotropic and
anisotropic refinement was followed, after which all hydrogens were
entered in ideal calculated positions and constrained to riding motion,
with a single variable isotropic temperature factor for all of them. After
all shift/esd ratios were less than 0.1, convergence was reached at the
agreement factors listed in Table 1. No unusually high correlations
were noted between any of the variables in the last cycle of full-matrix
least-squares refinement, and the final difference density map showed
space group
a, Å
R3hc (rhombohedral) F23
19.294(3)
31.89(1)
1781
a ) b ) c ) 22.7731(3)
R, deg
V, Å3
Z
R ) â ) γ ) 90
11810.5(3)
8
2
F
calc, g cm-3
1.23
26.9
1.311
28.28
µ, cm-1
T, °C
-50
-100(2)
0.710 73
1.55 < 2θ < 24.95
25 664
λ, Å (Mo KR)
0.710 73
collection range, deg 4 < 2θ < 50
no. of total data
collected
1262
818
no. of indep data,
I > 3σ(I)
1759 (Rint ) 0.0336)
no. of total variables 43
83
Ra
0.026
R1 ) 0.0849
(I > 2θ(I) ) 1561)
wR2c ) 0.2208
b
Rw
0.027
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc| /∑w|Fo| ]1/2, w )
2
2
2
σ(F)-2
.
c w ) [s2(Fo ) + (AP)2 + (BP)-1, where P ) (Fo2 + 2Fc2)/3, A
) 0.1344, B ) 187.6490.
a maximum peak of about 0.25 e/Å3. All calculations were made using
Nicolet’s SHELXTL PLUS (1987) series of crystallographic programs.
X-ray Structure Determination of 3. A crystal of 3 was attached
to a glass fiber and mounted on the Siemens SMART system for a
data collection at 173(2) K. An initial set of cell constants was
calculated from reflections harvested from three sets of 20 frames. These
initial sets of frames are oriented such that orthogonal wedges of
reciprocal space were surveyed. This produces orientation matrices
determined from 211 reflections. Final cell constants were calculated
from a set of 4306 strong reflections from the actual data collection.
Table 1 contains crystal and refinement information. The space group
F23 was determined based on systematic absences and intensity
statistics. A successful direct-methods solution was calculated which
provided most non-hydrogen atoms from the E-map. Several full-
matrix least-squares/difference Fourier cycles were performed, which
located the remainder of the non-hydrogen atoms. All non-hydrogen
atoms were refined with anisotropic displacement parameters unless
stated otherwise. All hydrogen atoms were placed in ideal positions
and refined as riding atoms with group isotropic displacement
parameters. Two molecules of Ge(SiMe3)4 were found in addition to
the cyclotetragermane. The central Ge4 core of the complex is
disordered over three positions related by 3-fold symmetry. (Ge(1) is
pulled off the crystallographic 31 axis.) It is this statistical disorder
which likely results in the higher than expected residuals (Rint ) 0.0336).
The largest difference feature was located in the vicinity of Si(1). A
second data set collected from a different sample did not yield a better
result (R1 for that refinement was 10.36%). Because of the disorder,
the fold angle and some bond distances and angles were determined
by importing the atomic coordinates of the skeleton atoms of the
assumed ordered structure of 3 into the CAChe program and measuring
them graphically. Data collection and structure solution were conducted
at the X-Ray Crystallographic Laboratory, 160 Kolthoff Hall, Chemistry
Department, The University of Minnesota. All calculations were
preformed using SGI INDY R4400-SC or Pentium computers using
the SHELXTL V5.0 suite of programs.
Results and Discussion
Consideration of the size and electronic properties suggests
that -Si(SiMe3)3 and -Ge(Me3)3 groups should exhibit similar
effects on compounds in which they are substituents. The
slightly larger Ge atom (radius of 122 vs 118 pm for Si14) should
lead to a smaller cone angle15 for M-Ge(SiMe3)3 compared to
(14) Huheey, J. E. Inorganic Chemistry, 3rd ed.; Harper & Row: New
York, 1983; p 258.
(15) Aggarwal, M.; Ghuman, M. A.; Geanangel, R. A. Main Group Met.
Chem. 1991, 14, 263.

Small-Ring Cyclogermanes
Inorganic Chemistry, Vol. 36, No. 27, 1997 6249
Scheme 1
Figure 1. View of the molecular structure of 2 showing the labeling
scheme. Hydrogens are omitted for clarity.
Scheme 2
Scheme 3
M-Si(SiMe3)3 and perhaps to less steric strain for the former
in crowded molecules. In ((Me3Si)3E)2SnCl2 (E ) Si, Ge),
however, the Si-Sn-Si and Ge-Sn-Ge angles and the
-E(SiMe3)3 cone angles are essentially the same.8,16 The
electronegativity of Ge slightly exceeds that of Si, indicative
of a small difference in the inductive effects of the E(SiMe3)3
substituents. The Taft inductivity parameter, σ*, of the SiMe3
group is reported as -0.95,17 consistent with moderate to strong
electropositive behavior. This suggests that both E(SiMe3)3
groups should be notably electropositive, and theoretical studies
indicate that this quality causes a marked relief of strain in small
rings of group 14 atoms with E(SiMe3)3 substituents.18 Both
LiE(SiMe3)3 reagents behave as strong reducing agents. Often,
substituting LiGe(SiMe3)3 for LiSi(SiMe3)3 causes no change
in the course of reactions, but in some instances differences do
occur, such as in the reaction shown in Scheme 1. Using 1a,
both digermane and cyclotetragermane products were isolated,
as shown in Scheme 1; however, 1b gave only the acyclic
tetragermane (Me3Si)3GeGeCl2GeCl2Ge(SiMe3)3, analogous to
the digermane in Scheme 1, despite our efforts to identify the
expected tetragermylcyclotetragermane.8
owing to the simultaneous formation of 3, the synthetic approach
is somewhat cleaner than the reductive coupling reactions
employing lithium napthalide or Mg-MgBr2 previously used
to prepare cyclotrimetallanes, (R2M)3 (M ) Si, Ge, and Sn).5-7
In an interesting variation on such reactions, silyl-substituted
cyclotrigermenes were obtained by treating GeCl2‚dioxane with
t-Bu3GeLi or t-Bu3SiNa in THF.3
The cyclotrigermane, 2, crystallizes as very hygroscopic,
transparent, hexagonal slabs that are stable in pentane solution
for months but decompose to a liquid mixture within 1 week,
even under argon at -10 °C. During the recording of its IR
spectrum, 2 reacted with the AgBr windows. From an X-ray
structure determination, 2 was found to be isomorphous with
4, crystallizing in the R3hc space group (Table 1). Each Ge in
the symmetrical ring exhibits approximately tetrahedral geom-
etry in the exocyclic bond angles (Figure 1). The Ge-Ge
distance, 2.460(1) Å, is the shortest yet reported for cyclo-
trigermanes, except for the computed value of 2.45 Å for the
parent, (GeH2)3.19 Since Ge-Ge bond lengths are considered
to increase with increasing steric congestion around the Ge3
ring,1f the short Ge-Ge bonds suggest that the Ge coordination
sphere in 2 is relatively uncrowded, probably owing to the longer
Ge-Si bonds (2.388 Å, Table 2) compared to the Ge-C links
(1.98-2.06 Å)1f in other structurally characterized cyclotriger-
manes. The fact that the Ge-Si-C angles average close to
the tetrahedral value (Table 2) is also consistent with minimal
steric crowding around Ge in 2.
The recent synthesis of the disilagermirane (4) shown in eq
1 represented an interesting case in which to compare the
behavior of the lithium silyl and germyl reagents.7b The report
As noted above, the investigators who prepared 4 from GeCl2
and 1a (eq 1) reported no other Ge-bearing products from the
reaction.7b Unidentified NMR peaks in the product mixture of
our similar reaction of GeCl2‚dioxane and 1b led us to carry
out further crystallizations from the concentrated pentane extract,
which afforded a moderate yield of bright yellow crystals. The
chemical shifts of the yellow compound, 1H NMR δ 0.569 and
13C NMR δ 5.27, supported a tentative identification of this
product as a cyclotetragermane with Ge(SiMe3)3 and Cl sub-
stituents on each ring Ge.20 Its identity was confirmed by an
X-ray structure determination that showed a disordered [(Me3-
Si)3GeGeCl]4 molecule accompanied in the lattice by two
molecules of Ge(SiMe3)4 (Table 1). The Ge4 core in 3 is
by Heine and Stalke led us to the expectation of a cyclotriger-
mane product in an analogous reaction using 1b. When that
reaction was carried out under literature conditions, except that
GeCl2‚dioxane was employed, the anticipated cyclotrigermane
was isolated in 26% yield (Scheme 2). Further crystallization
from the pentane extract of the reaction mixture residue also
afforded the cyclotetragermane, 3, described below. The
formation of 2 in the reaction shown in Scheme 2, thus, parallels
the previous results,7b but the simultaneous formation of a
cyclotetragermane was not observed earlier. The mechanism
of formation of the disilagermirane suggested by those inves-
tigators seems equally applicable to the formation of 2 (see
Scheme 3). Although the yield of 2 was moderately low, partly
(16) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1990, 29, 3525.
(17) Bu¨rger, H.; Kilian, W. J. Organomet. Chem. 1969, 18, 299.
(18) Nagase, S.; Kobayashi, K.; Nagashima, M. J. Chem. Soc., Chem.
Commun. 1992, 1302. (b) Nagase, S. Pure Appl. Chem. 1993, 65,
675.
(19) Nagase, S.; Nakano, M. J. Chem. Soc., Chem. Commun. 1988, 1077.
(20) On the basis of NMR shifts for its Si(SiMe3)3 counterpart (Scheme
1), the ∆δ relationship found for structurally characterized Si(SiMe3)3
and Ge(SiMe3)3 derivatives (ref 9b predicted 1H NMR δ 0.563 ( 0.007
and 13C NMR δ 5.41 ( 0.22 for 3).

6250 Inorganic Chemistry, Vol. 36, No. 27, 1997
Mallela et al.
Table 2. Selected Bond Lengths and Angles for 2
the corresponding (Ge-Si-Si) angle in 5, indicating that the
small distortion of the Ge(SiMe3)3 and Si(SiMe3)3 substituents
from the tetrahedral ideal is similar in the two molecules. The
“fold” angles in 3 and 5 are 18.7° and 17.1°, respectively. The
next closest analogue of 3, (t-BuGeCl)4, has shorter Ge-Ge
bonds (average 2.463 Å) and a smaller fold angle (14.6°).2b
Qualitatively, at least, there appears to be some lengthening of
ring Ge-Ge distances with increasing steric bulk of the
substituents in the Ge4 rings similar to the behavior described
for Ge3 rings.1f
Bond Lengths (Å)
Ge-Ge′
Ge-Si
Si-C(3)
2.460(1)
2.388(4)
1.879(4)
Si-C(1)
Si-C(2)
1.874(4)
1.882(5)
Bond Angles (deg)
Si-Ge-Ge′
120.7(1)
60.0
Si-Ge-Ge′′
121.9(1)
106.3(1)
109.7(4)
107.8(4)
108.3(2)
Ge′-Ge-Ge′′
Ge-Si-C(1)
C(1)-Si-C(2)
C(1)-Si-C(3)
Si-Ge-Si′
115.7(3)
104.8(4)
110.3(5)
Ge-Si-C(2)
Ge-Si-C(3)
C(2)-Si-C(3)
The formation of 3 in the reaction of GeCl2‚dioxane and 1b
led us to repeat the literature reaction7b using GeCl2‚dioxane,
instead of GeCl2, with 2 equiv of 1a to determine whether any
5 formed. Besides a 66% (lit.7b 48%) yield of the reported
disilagermirane (1H NMR δ 0.432 (Si(SiMe3)2), 0.452 (Ge-
(SiMe3)2), lit.7b δ 0.43, 0.45), we isolated a small yield of yellow
crystals identified by their NMR spectra (1H NMR 0.531, 13C
NMR δ 4.89, lit.8 δ 0.533, 4.85, respectively) as 5. Since the
reaction conditions closely followed those in the literature,7b it
appears that the presence of dioxane may influence the course
of the reaction, favoring the cyclotetragermane product. If so,
it may have also favored the formation of 3 in the reaction in
Scheme 2.
Torsion Angles (deg)
Ge′-Ge-Si-C1
Ge′-Ge-Si-C2
Ge′-Ge-Si-C3
Ge′′-Ge-Si-C1
Ge′′-Ge-Si-C2
Ge′′-Ge-Si-C3
Si′-Ge-Si-C1
60.8
179.1
Si′-Ge-Si-C3
81.3
-111.5
0.0
109.6
109.6
-111.5
-36.5
Ge′′-Ge′-Ge-Si
Ge′′-Ge′-Ge-Ge
Ge′′-Ge′-Ge-Si′
Ge′-Ge′′-Ge-Si
Ge′-Ge′′-Ge-Si′
Si′-Ge-Si-C2
-63.2
-10.8
107.5
-134.8
-154.8
The variety of products identified from the reaction of GeCl2‚
dioxane and 1b suggests that multiple pathways are active
(Scheme 3). Formation of 3 could reasonably be the result of
monosubstitution of GeCl2‚dioxane by Ge(SiMe3)3 followed by
cyclopolymerization and loss of dioxane. The origin of 2 may
involve the formation of a disubstituted germylene intermediate
that rearranges via SiMe3 migration, perhaps due to steric strain,
to yield 2. We did not detect the putative germylene or any
oligomer of it, although there were 1H NMR peaks in the mother
liquor that were not assigned. The presence of resonances for
HGe(SiMe3)3, Ge2(SiMe3)6, and Ge(SiMe3)4 is common for
reactions where 1b is oxidized, for example, by PbCl2.21
In summary, the reaction of GeCl2‚dioxane with 1b gives a
cyclotrigermane, 2, probably originating from rearrangement of
a sterically crowded Ge(GeR3)2 intermediate, paralleling the
behavior of GeCl2 with 1a, the SiR3 counterpart of 1b.
Simultaneous formation of another product, the cyclotetrager-
mane, 3, appears to be associated with the use of GeCl2‚dioxane
instead of GeCl2 since 5, the SiR3 counterpart of 3, was present
when the literature 1a reaction was repeated using GeCl2‚
dioxane but not when the reaction was originally reported.
To study the influence of the halogen in GeX2, reactions of
GeI2 with 2 equiv of 1b in hexane and in ether were carried
out. Only traces of 2 were found along with the oxidation
products of 1b. Reactions of SnCl2 with 1a and 1b are currently
being investigated.
Figure 2. View of the (assumed ordered) molecular structure of 3
showing the labeling scheme. There are two molecules of Ge(SiMe3)4
that are not shown. Hydrogens are omitted for clarity.
Table 3. Selected Bond Lengths and Angles for 3
Bond Lengths (Å)
Ge(1)-Cl(1)
Ge(2)-Si(1)
Ge(4)-Si(3)
Si(1)-C(2)
2.367(5)
2.404(4)
2.378(6)
1.881(14)
Ge(1)-Ge(2)
Ge(3)-Si(2)
Si(1)-C(1)
Si(1)-C(3)
2.589(3)
2.392(7)
1.92(2)
1.870(14)
Bond Angles (deg)
Si(1)-Ge(2)-Ge(1) 94.15(11) Cl(1)-Ge(1)-Ge(2) 119.29(11)
C(3)-Si(1)-C(2)
C(2)-Si(1)-C(1)
104.5(8)
114.7(8)
C(2)-Si(1)-Ge(2) 110.5(5)
C(5)-Si(3)-Ge(4) 110.6(5)
C(3)-Si(1)-C(1)
112.6(8)
C(3)-Si(1)-Ge(2) 107.0(5)
C(1)-Si(1)-Ge(2) 107.3(6)
C(4)-Si(2)-Ge(3) 109.9(6)
Torsion Angles (deg)
Cl(1)-Ge(1)-Ge(2)-Si(1)
Ge(1)-Ge(2)-Si(1)-C(3)
Ge(1)-Ge(2)-Si(1)-C(2)
17.61(14)
167.7(6)
54.5(6)
Acknowledgment. The authors gratefully acknowledge the
support of this investigation by the Robert A. Welch Foundation
under Grant No. E-1105. We also thank James Korp for
determining the structure of 2 and Victor G. Young at the X-ray
Crystallographic Laboratory at the University of Minnesota for
determining the structure of 3. Thanks are also due the
Universita¨t des Saarlandes for partial support of S.H.
Supporting Information Available: Tables listing full data col-
lection and processing parameters, atomic coordinates, bond distances
and angles, anisotropic displacement parameters and H atom coordinates
and ORTEP and packing diagrams for 2 and 3 (28 pages). Ordering
information is given on any current masthead page. Observed and
calculated structure factors are available from the corresponding authors.
disordered over three positions related by 3-fold symmetry (i.e.,
Ge(1) is pulled off the crystallographic 31 axis). This statistical
disorder is the probable reason for the higher than expected
residuals (Rint ) 0.0336). A second data set collected from a
different sample did not yield an improved result.
Figure 2 shows an ORTEP view of the assumed ordered
structure of 3. The structure of 3 closely resembles that of its
tris(trimethylsilyl)silyl counterpart, [(Me3Si)3SiGeCl]4, 5.8 The
ring in 3 has Ge-Ge bond lengths (2.501 and 2.505 Å, Table
3) that average slightly shorter than those in 5 (2.509 and 2.558
Å), indicative of less steric crowding around the Ge4 core in 3.
This difference is likely due at least in part to the greater Ge-
Ge(exo) distance (2.589 Å) compared to Ge-Si (average 2.460
Å) in 5, moving the bulky substituents further from the ring.
The mean Ge-Ge-Si angle in 3 (111.4°) is nearly identical to
IC970833Z
(21) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1993, 32, 5623.