Synthesis and reactivity of η5-germacyclopentadienyl complexes of iron

Article abstract of DOI:10.1021/om0110991

Reaction of 2 equiv of the previously reported germolyl anion Li[C₄Me₄GeSi(SiMe₃)₃] with FeCl₂(THT)_1.5 (THT = tetrahydrothiophene) at low temperature gave the new bis-η⁵-germolyl

Full text of DOI:10.1021/om0110991

1734
Organometallics 2002, 21, 1734-1738
Syn th esis a n d Rea ctivity of η5-Ger m a cyclop en ta d ien yl
Com p lexes of Ir on
William P. Freeman, J effrey M. Dysard, and T. Don Tilley*
Department of Chemistry, University of California at Berkeley,
Berkeley, California 94720-1460
Arnold L. Rheingold*
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received December 28, 2001
Reaction of 2 equiv of the previously reported germolyl anion Li[C4Me4GeSi(SiMe3)3] with
FeCl2(THT)1.5 (THT ) tetrahydrothiophene) at low temperature gave the new bis-η5-germolyl
complex [η5-C4Me4GeSi(SiMe3)3]2Fe (1), which was characterized by X-ray crystallography.
Reaction of 1 with I2 resulted in loss of the germolyl ligand as C4Me4Ge(I)[Si(SiMe3)3], while
the reaction with MeLi produced the ferrocenophane ansa-(Me3Si)2Si(η5-GeC4Me4)2Fe (4).
X-ray crystallographic analysis of this compound revealed that the Ge atoms are displaced
significantly out of the C4 plane. Attempts to induce the ring-opening polymerization of 4
were unsuccessful.
In tr od u ction
Cp*Ru[η5-C4Me4GeSi(SiMe3)3] (Cp* ) η5-C5Me5) sug-
gested that the germolyl ligand might be significantly
more electron donating than Cp*, and studies on a
related Hf system have shown that these ligands
possess a rich reaction chemistry.3c,d These factors have
compelled us to further explore the coordination chem-
istry of these interesting new ligands to more fully
understand their chemistry.
Recently, considerable attention has focused on the
nature of potentially aromatic rings containing silicon
and germanium.1,2 Our work in this area has produced
examples of delocalized sila- and germacyclopentadienyl
anions which are stabilized via coordination to a transi-
tion metal fragment.3 Electrochemical studies on the
ruthenium germacyclopentadienyl (or germolyl) complex
The chemistry of the group 15 element diheterofer-
rocenes has been well established, with isolation of
numerous examples of complexes of the type (C4R4E)2-
Fe, (E ) P, As, Sb, or Bi; R ) H, alkyl, or silyl).4 These
complexes exhibit a variety of structural motifs and
have been valuable in studies of aromaticity and π-bond-
ing between carbon and heavier main group elements.
It therefore seemed that it should be possible to obtain
complexes involving the heavier congeners of the group
14 elements. In this contribution we report on the
synthesis and structural characterization of the first
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1980, 19, 52. (l) Nakadaira, Y.; Sato, R.; Sakurai, H. Organometallics
1991, 10, 435. (m) Rich, J . D.; West, R. J . Am. Chem. Soc. 1982, 104,
6884. (n) J utzi, P.; Meyer, M.; Dias, H. V. R.; Power, P. P. J . Am. Chem.
Soc. 1990, 112, 4841. (o) Hong, J .-H.; Boudjouk, P.; Castellino, S.
Organometallics 1994, 13, 3387. (p) West, R.; Sohn, H.; Bankwitz, U.;
Calabrese, J .; Apeloig Y.; Mu¨ller, T. J . Am. Chem. Soc. 1995, 117,
11608. (q) Goldfuss, B.; Schleyer, P. v. R. Organometallics 1997, 16,
1543. (r) Tokitoh, N.; Wakita, K.; Okazaki, R.; Nagase, S.; Schleyer,
P. v. R.; J iao, H. J . Am. Chem. Soc. 1997, 119, 6951. (s) Wakita, K.;
Tokitoh, N.; Okazaki, R.; Nagase, S. Angew. Chem., Int. Ed. 2000, 39,
634. (t) Wakita, K.; Tokitoh, N.; Okazaki, R.; Nagase, S.; Schleyer, P.
v.; J iao, H. J . J . Am. Chem. Soc. 1999, 121, 11336. (u) Freeman, W.
P.; Tilley, T. D.; Liable-Sands, L. M.; Rheingold, A. L. J . Am. Chem.
Soc. 1996, 118, 10457. (v) Hong, J .-H.; Pan, Y.; Boudjouk, P. Angew.
Chem., Int. Ed. Engl. 1996, 35, 186.
(3) (a) Freeman, W. P.; Tilley, T. D.; Rheingold, A. L. J . Am. Chem.
Soc. 1994, 116, 8428. (b) Dysard, J . M.; Tilley, T. D. J . Am. Chem.
Soc. 1998, 120, 8245. (c) Dysard, J . M.; Tilley, T. D. J . Am. Chem. Soc.
2000, 122, 3097. (d) Freeman, W. P.; Tilley, T. D.; Rheingold, A. L.;
Ostrander, R. L. Angew. Chem., Int. Ed. Engl. 1993, 32, 1744. (e)
Dysard, J . M.; Tilley, T. D. Organometallics 2000, 19, 2671.
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Acta Crystallogr. 1980, B36, 1344. (g) Ashe, A. J ., III; Mahmoud, S.;
Elschenbroich, C.; Wu¨nsch, M. Angew. Chem., Int. Ed. Engl. 1987, 26,
229. (h) Ashe, A. J ., III; Kampf, J . W.; Pilotek, S.; Rousseau, R.
Organometallics 1994, 13, 4067. (i) Ashe, A. J ., III; Diephouse, T. R.
J . Organomet. Chem. 1980, 202, C95. (j) Ashe, A. J ., III; Diephouse,
T. R.; Kampf, J . W.; Al-Taweel, S. M. Organometallics 1991, 10, 2068.
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1992, 11, 1491. (l) Ashe, A. J ., III; Kampf, J . W.; Puranik, D. B.; Al-
Taweel, S. M. Organometallics 1992, 11, 2743. (m) Sava, X.; Ricard,
L.; Mathey, F.; Le Floch, P. Organometallics 2000, 19, 4899.
(2) For reviews on silaaromatic compounds see: (a) Brook, A. G.;
Brook, M. A. Adv. Organomet. Chem. 1996, 39, 71. (b) Raabe, G.; Michl,
J . Chem. Rev. 1985, 85, 419. (c) Raabe, G.; Michl, J . In The Chemistry
of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley:
New York, 1989; p 1102. (d) Apeloig, Y. In The Chemistry of Organic
Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York,
1989; p 151. (e) Apeloig, Y.; Karni, M. In The Chemistry of Organic
Silicon Compounds, Part II; Rappoport, Z., Apeloig, Y., Eds.; Wiley:
New York, 1998; Vol. 2, Chapter 1.
10.1021/om0110991 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/21/2002

η5-Germacyclopentadienyl Complexes of Iron
Organometallics, Vol. 21, No. 8, 2002 1735
examples of diheteroferrocenes possessing germacyclo-
pentadienyl ligands.
Resu lts a n d Discu ssion
Several years ago we reported the synthesis of the
germacyclopentadienyl anion Li[C4Me4GeSi(SiMe3)3]
and its reaction with 0.25 equiv of [Cp*RuCl]4 to give
the η5-germacylopentadienyl complex Cp*Ru[η5-C4Me4-
GeSi(SiMe3)3].3d Our initial synthetic strategy for the
formation of a ferrocene derivative also relied on this
methodology. Reaction of 2 equiv of Li[C4Me4GeSi-
(SiMe3)3], generated in situ from the treatment of C4-
Me4Ge(H)Si(SiMe3)3 with nBuLi, with FeCl2(THT)1.5
(THT ) tetrahydrothiophene) at -80 °C in THF re-
sulted in formation of a deep red solution from which
Fe[η5-C4Me4GeSi(SiMe3)3]2 (1) was isolated in 65% yield
(eq 1).
F igu r e 1. ORTEP diagram for Fe[η5-C4Me4GeSi(SiMe3)3]2
(1).
same values in Cp*Ru[η5-C4Me4GeSi(SiMe3)3] are 0.02
Å and 12.9°, respectively.3d Further evidence for sp2
hybridization at germanium is given in the sum of the
bond angles about Ge (358.1°). Finally, the Fe-Ge bond
lengths of 2.415(1) Å fall in the range for typical Fe-
Ge single bonds (2.340(1)-2.484(1) Å).7
Interestingly, it seems that use of the bulky Si(SiMe3)3
group on the germanium atom is necessary for the
formation of the digermaferrocene complexes, as similar
reactions with the germolyl anions Li[C4Me4GeSiMe3],1u
K[C4Me4GeSiMe3],1u Li[C4Me4GeMe],1u Li[C4Me4GePh],8
and Li[C4Me4GeMes]1u (Mes ) 2,4,6-trimethylphenyl)
did not result in the clean formation of new compounds.
Furthermore, reactions of the silolyl anion reagents Li-
[C4Me4SiSiMe3]1u and Mg[C4Me4SiSiMe3]23c with FeCl2,
FeCl2(THT), or FeBr2 (THF, Et2O, benzene; room tem-
perature and -80 °C) did not result in formation of the
corresponding bis-η5-silolyl ferrocenes.
The 1H NMR spectrum for 1 is consistent with C2
symmetry on the NMR time scale, as indicated by three
single resonances for the germolyl ligands at δ 0.36,
1.74, and 2.50 for the Si(SiMe3)3 and ring methyl groups,
respectively. In addition, the 13C{1H} NMR spectrum
of 1 exhibits resonances at δ 79.51 and 89.86 for the
carbon atoms of the coordinated germolyl ring. For
comparison, the corresponding carbon atoms in the
bond-localized germolyl anion Li[C4Me4GeSi(SiMe3)3]
resonate at δ 132.89 and 146.45, while in the η5-
germolyl complex Cp*Ru[η5-C4Me4GeSi(SiMe3)3] the
analogous carbon shifts are δ 80.23 and 87.82.3d An
irreversible oxidation wave was observed for 1 at E1/2
) -0.45 V (vs SCE) by cyclic voltammetry (dichlo-
romethane, 0.1 M [N(nBu)4]ClO4 as the supporting
electrolyte). These data suggest that the germacylopen-
tadienyl ligands in 1 are more electron donating than
Cp*, as decamethylferrocene exhibits an oxidation wave
at 0.28 V (vs SCE) under similar conditions.5
Initial reactivity studies of 1 focused on functional-
ization of the germanium center upon cleavage of the
bulky Si(SiMe3)3 substituent. Reaction of 1 with I2
(THF-d8, room temperature) did not result in cleavage
of the Ge-Si linkage but rather proceeded with quan-
titative loss of the germolyl ligand to give C4Me4Ge(I)-
1
Si(SiMe3)3 (2; eq 2; by H NMR spectroscopy).
X-ray-quality crystals of 1 were grown from a con-
centrated pentane solution cooled to -40 °C. The
molecular structure of 1 (Figure 1) consists of two
coplanar η5-germolyl rings bound in a “sandwich”
fashion to the iron center. The angle between the least-
squares planes of these rings is 5°, and they both lie
1.69 Å from the iron center. For comparison, the
germolyl ring in Cp*Ru[η5-C4Me4GeSi(SiMe3)3] lies 1.81
Å from the ruthenium center, and the analogous dis-
tance in decamethylferrocene is 1.657 Å.3d,6 The ger-
manium atoms deviate by only 0.04 Å from the C4Ge
least-squares planes, and the bulky Si(SiMe3)3 group is
bent out of these planes by 12.4°. For comparison, these
(5) Gassman, P. G.; Winter, C. H. J . Am. Chem. Soc. 1988, 110, 6130.
(6) (a) Struchkov, Y. T.; Andrianov, V. G.; Sal’nikova, T. N.; Lyatifov,
I. R.; Materikova, R. B. J . Organomet. Chem. 1978, 145, 213. (b)
Freyberg, D. P.; Robbins, J . L.; Raymond, K. N.; Smart, J . C. J . Am.
Chem. Soc. 1979, 101, 892.
The characterization of 2 is based only on comparison
of NMR spectroscopic data with the known chloride
derivative, as attempts to isolate it in pure form were

1736 Organometallics, Vol. 21, No. 8, 2002
Freeman et al.
unsuccessful.1u The SiMe3 protons in 2 resonate at δ
0.12, while the ring methyl protons appear as singlets
at δ 1.53 and 1.87. In addition, the ring carbon atoms
in 2 give rise to two singlets in the 13C NMR spectrum
at δ 141.5 and 148.52, which are similar to the same
values found for the analogous chloride derivative (δ
133.63 and 146.02) but quite different from those for
an η5-germolyl ligand bound to a late transition metal.3d
We have previously shown that nucleophilic cleavage
of Ge-Si bonds in certain germole derivatives leads to
the formation of germolyl anions.1u It seemed that such
reactions might be useful for the generation of the bis-
(germolyl) dianion 3. However, treatment of 1 with MeLi
(THF, 0 °C) did not lead to the expected product (3, eq
3) but instead gave the novel bis(germolyl) ferro-
cenophane derivative ansa-Fe(η5-C4Me4Ge)2Si(SiMe3)2
in 55% isolated yield (4, eq 3).
F igu r e 2. ORTEP diagram for ansa-Fe(η5-C4Me4Ge)2Si-
(SiMe3)2 (4).
2.867(2) Å in the related germole complex [η4-C4Ph4Ge-
(F)Me]Fe(CO)3.10 Also, the structure of 4 is related to
that of a lithocenophane derivative of a trisgermole
dianion, reported by the group of Boudjouk.1v
One possible mechanism for the formation of 4 is
shown in Scheme 1. Presumably, the first step in this
reaction is nucleophilic cleavage of a Si-Si bond in 1 to
produce a silyl anion (A, Scheme 1). The resulting
anionic silicon center could then attack the other
germolyl ring via nucleophilic displacement of LiSi-
(SiMe3)3 to produce 4. This mechanism is supported by
the observed reactivity of 1 with LiCH2Ph (THF-d8,
room temperature), which cleanly produced Me3SiCH2-
Ph, 4, and Li[Si(SiMe3)3] as the only products observed
1
The H NMR spectrum of 4 exhibits three resonances
at δ 1.58, 1.49, and 0.50 for the two sets of ring methyl
groups and the SiMe3 groups, respectively. Interest-
ingly, the 13C{1H} NMR resonances for the germolyl ring
carbon atoms (δ 101.08 and 126.62) are quite shifted
from those in 1, suggesting that the germolyl ligand is
bound in more of a “diene-like” fashion to the iron
center. Finally, the 29Si{1H} NMR spectrum for 4
exhibits two distinct resonances for the bridging silicon
atom (δ 17.56) and trimethylsilyl groups (δ -7.50).
Slow evaporation of a concentrated benzene-d6 solu-
tion resulted in X-ray quality crystals of 4, and the
molecular structure is shown in Figure 2. Complex 4
possesses approximate C2v symmetry and can best be
described as an ansa-ferrocene with two eclipsed ger-
molyl rings bridged by an Si(SiMe3)2 group. Interest-
ingly, that the Ge atoms in 4 lie 0.42 Å above the C4
least-squares planes and the sum of the angles about
Ge (296.1°) both suggest that this center is sp3-hybrid-
ized. Presumably this bending of the Ge atoms away
from one another is the result of an electrostatic
repulsion between the two, formally negatively charged
Ge atoms. This is not seen for 1, as the Ge atoms are
not required to reside in an eclipsed conformation and
can avoid close contacts with one another by rotation
about the metal-ring bond. Finally, the Fe-Ge bond
lengths in 4 (2.536(3) and 2.539(3) Å) are somewhat
longer than the corresponding values in 1 (2.415(1) Å)
but are much shorter than the analogous distance of
1
by H NMR spectroscopy.
It has been shown that silicon-bridged ferrocenophanes
are very good precursors for the preparation of high
molecular weight polyferrocenes.11 This chemistry relies
on the high ring strain in metallocenophane monomers
that possess a single silicon atom bridge between the
two cyclopentadienyl ligands. These silicon-bridged fer-
rocenophanes can be polymerized thermally or via
anion-initiated or transition-metal-catalyzed ring-open-
ing polymerizations.11 Given the similarity between
these ferrocenophanes and our ansa-bis(germolyl) fer-
rocene complex, it seemed that 4 might be a precursor
to iron-germolyl-containing polymers. However, ther-
molysis of solid 4 up to 260 °C in an evacuated sealable
reaction vessel for 18 h did not result in the formation
of any polymeric materials, and only unreacted 4 was
recovered. The anionic polymerization of 4 was at-
tempted using either (Et2O)LiCH2Ph or nBuLi as an
initiator (in THF or benzene, room temperature). Un-
fortunately, no polymeric materials were detected in
either of these reactions (by gel permeation chromatog-
raphy; THF solvent). Presumably, the presence of the
germanium atoms in 4, and their displacements out of
their respective germolyl C4 planes, relieves ring strain
that might otherwise exist.
In this contribution we have shown that it is possible
to form bis-η5-germolyl transition metal complexes.
(7) (a) Tobita, H.; Ishiyama, K.; Kawano, Y.; Inomata, S.; Ogino, H.
Organometallics 1998, 17, 789. (b) Elder, M.; Hutcheon, W. L. J . Chem.
Soc., Dalton Trans. 1972, 175. (c) Barsuaskas, G.; Lei, D.; Hampden-
Smith, M. J .; Duesler, E. N. Polyhedron 1990, 9, 773. (d) Lei, D.;
Hampden-Smith, M. J .; Duesler, E. N.; Huffman, J . C. Inorg. Chem.
1990, 29, 795.
(9) (a) Alcock, N. W. Adv. Inorg. Chem. Radiochem. 1972, 15, 1. (b)
Ashe, A. J ., III. Adv. Organomet. Chem. 1990, 30, 77.
(10) J utzi, P.; Karl, A.; Burschka, C. J . Organomet. Chem. 1981,
215, 27.
(11) For a recent review of the polymerization of silicon-bridged
ferrocenophanes see: Nguyen, P.; Go´mez-Elipe, P.; Manners, I. Chem.
Rev. 1999, 99, 1515.
(8) Dufour, P.; Dubac, J .; Dartiguenave, M.; Dartiguenave, Y.
Organometallics 1990, 9, 3001.

η5-Germacyclopentadienyl Complexes of Iron
Organometallics, Vol. 21, No. 8, 2002 1737
Sch em e 1
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p ou n d s 1
a n d 4
Structural, as well as NMR spectroscopic, analyses of
the bisgermolyl ferrocene complex Fe[η5-C4Me4GeSi-
(SiMe3)3]2 (1) indicate that the η5-germolyl rings possess
a significant amount of aromatic character. In addition,
this compound was shown to be reactive toward nucleo-
philes, which cleave a Si-Si bond to form the novel
ferrocenophane derivative ansa-Fe(η5-C4Me4Ge)2Si-
(SiMe3)2 (4). Structural characterization of this complex
revealed severe perturbations in the aromaticity of the
germolyl rings. We are currently exploring the reactivity
of these complexes in the hopes of establishing novel
reactivity patterns and structural motifs for this class
of heterole ligands.
1
4
(a) Crystal Parameters
FeGe2Si8C34H78
912.7
formula
fw
FeGe2Si3C22H42
591.9
size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.38 × 0.52 × 0.54 0.33 × 0.21 × 0.11
orthorhombic
Pbcn
triclinic
P1h
28.858(6)
11.277(2)
15.362(3)
90, 90, 90
10.256(3)
12.210(3)
13.786(6)
69.17(3), 64.94(3),
63.18(3)
1366(1)
2
R, â, γ (deg)
V (Å3)
4999.2(18)
4
Z
D
calc (g cm-3
)
1.213
1963
1.438
612
Exp er im en ta l Section
F000
(b) Data Collection
All manipulations were conducted under an atmosphere of
nitrogen using either standard Schlenk techniques or a glove-
box. Dry, deoxygenated solvents were employed for all ma-
nipulations. All solvents were distilled from Na/benzophenone
ketyl, except benzene-d6 and toluene-d8, which were purified
by vacuum distillation from Na/K alloy. C4Me4Ge(H)Si-
temp (°C)
-145.0
25.0
4803/5018
0.0156
no. of unique/total reflns 4409/5021
Rint
0.0476
na
T
max/Tmin
0.9986/0.6323
(c) Refinement
204
12.4
no. of variables
reflection/param ratio
R ) ∑||Fo| - |Fc||/
∑|Fo|
253
12.4
0.0364
3d
(SiMe3)3 was prepared according to literature procedures.
nButyllithium and methyllithium were purchased from Aldrich
Chemical Company and used without further purification.
Elemental analyses were performed by Desert Analytics and
by the College of Chemistry Microanalytical Laboratory, U.C.
Berkeley. NMR spectra were recorded on either a GE QE-300
or Bruker AMX-300 spectrometer at 300 MHz (1H), 75.5 MHz
(13C), or 59.6 MHz (29Si) or on a Bruker AMX-400 spectrometer
at 400 MHz (1H) and 100 MHz (13C). All IR absorptions are
reported in cm-1 and were recorded with a Perkin-Elmer 1330
spectrometer.
0.0409
Rw ) [∑w(|Fo| - |Fc|)2/
∑wFo2)]1/2
0.0490
1.00
0.0448
0.98
goodness of fit
([∑w(|Fo| -
|Fc|)2/(No - Nv)]1/2
)
max. and min. peaks in 0.37/-0.35
0.44/-0.41
final diff map (e-/Å3)
2.69 (s, Si(SiMe3)3. 29Si{1H} (benzene-d6): δ -9.3 (s, Si-
(SiMe3)3), -118.9 (s, Si(SiMe3)3. Anal. Calcd for C34H78FeGe2-
Si8: C, 44.73; H, 8.63. Found: C, 44.71; H, 8.67. IR (toluene,
NaCl): 2368 w, 1962 w, 1873, w, 1811, w, 1661 m, 1254 m,
1439 w, 865 sh, 847 s, 635 sh, 511 m.
C4Me4Ge(I)Si(SiMe3)3 (2). To a solution of 1 (0.033 g, 0.036
mmol) in 0.35 mL of THF-d8 was added I2 (0.018 g, 0.072
mmol). The resulting solution was placed in an NMR tube,
F e[η5-C4Me4GeSi(SiMe3)3]2 (1). A hexane solution of n-
butyllithium (0.308 mL, 0.491 mmol) was slowly added to a
cold solution (-80 °C) of C4Me4Ge(H)Si(SiMe3)3 (0.201 g, 0.468
mmol) in 100 mL of THF. The reaction solution became yellow
and was stirred for 1 h at -80 °C. This solution was then added
via cannula to a 200 mL round-bottomed Schlenk flask
containing a precooled (-80 °C) solution of FeCl2(THT)1.5 (0.052
g, 0.234 mmol) in 50 mL of THF. The reaction solution became
amber and then deep red. After 5 min the cold bath was
removed and the reaction solution was allowed to slowly warm
over 1.5 h. After this time the volatile materials were removed
under dynamic vacuum and the residue was extracted with
pentane (3 × 25 mL). The combined pentane extracts were
reduced in volume (25 mL), and the resulting solution was
cooled to -80 °C to give red crystals of 1 in 65% yield (0.138
g, 0.152 mol). 1H NMR (benzene-d6): δ 2.50, 1.74 (s, 12 H,
C4Me4Ge), 0.36 (s, 54 H, Si(SiMe3)3). 13C{1H} NMR (benzene-
d6): δ 89.86, 79.51 (s, C4Me4Ge), 18.55, 17.68 (s, C4Me4Ge),
1
which was shaken for 10 min to give 2 exclusively. H NMR
(THF-d8): δ 1.87, 1.53 (s, 12 H, C4Me4Ge), 0.12 (s, 27 H, Si-
(SiMe3)3. 13C{1H} NMR (THF-d8): δ 148.52, 141.51 (s, C4Me4-
Ge), 21.92, 17.95 (s, C4Me4Ge), 5.93 (s, Si(SiMe3)3.
a n sa -F e(η5-C4Me4Ge)2Si(SiMe3)2 (4). An ethereal solution
of methyllithium (0.409 mL, 0.573 mmol) was added to a 200
mL round-bottomed Schlenk flask containing a cold (0 °C)
solution of 1 (0.498 g, 0.546 mmol) in 50 mL of THF. The cold
bath was removed, and the reaction solution was stirred for
90 min. The original red color of the reaction solution still
remained after this time. The volatile materials were then

1738 Organometallics, Vol. 21, No. 8, 2002
Freeman et al.
removed under dynamic vacuum, and the residue was ex-
tracted with pentane (3 × 40 mL). The combined extracts were
concentrated to 25 mL and cooled to -80 °C to afford 4 as black
crystals in 55% yield (0.178 g, 0.301 mmol). 1H NMR (benzene-
d6): δ 1.58, 1.49 (s, 12 H, C4Me4Ge), 0.50 (s, 18 H, Si(SiMe3)2).
13C{1H} NMR (benzene-d6): δ 126.62, 101.08 (s, C4Me4Ge),
18.45, 14.30 (s, C4Me4Ge), 4.44 (s, Si(SiMe3)2. 29Si{1H} NMR
(benzene-d6): δ 17.6 (s, Si(SiMe3)2), -7.5 (s, Si(SiMe3)2). Anal.
Calcd for C22H42FeGe2Si3: C, 44.64; H, 7.17. Found: C, 44.45;
H, 7.08. IR (toluene, NaCl): 2363 w, 1957 w, 1876 w, 1812 w,
1659 w, 1461 w, 1307 w, 1253 m, 1145 w, 1018 w, 937 w, 874
sh, 847 s, 585 m, 504 s.
much greater probability and subsequently affirmed by the
results of refinement. Both structures were corrected for
absorption by empirical methods, solved by direct methods,
refined with anisotropic thermal parameters for all non-
hydrogen atoms, and incorporated hydrogen atoms as idealized
contributions. All software was contained in versions of the
SHELXTL library of programs (G. Sheldrick, Siemens XRD,
Madison, WI).
Ack n ow led gm en t is made to the National Science
Foundation for their generous support of this work.
Cr ysta llogr a p h ic Str u ctu r a l Deter m in a tion s. Crystal-
lographic data are collected in Table 1. Crystals of both 1 and
4 were mounted in fine capillary tubes in an inert atmosphere
and studied on a Siemens P4 diffractometer. Crystals of 1 were
uniquely assigned to the orthorhombic space group Pbcn based
on diffraction symmetry and systematic absences in the data.
Crystals of 4 showed no symmetry higher than triclinic, and
the centrosymmetric option was selected on the basis of its
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data collection and refinement parameters, bond distances and
angles, and anisotropic displacement parameters for 1 and 4.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM0110991