Germanium-containing ferrocenes and ferrocenophanes. Potential precursors for ring-opening polymerizations and 'germaferrocenes'

Article abstract of DOI:10.1016/s0020-1693(99)00133-4

The new germanium-containing ferrocene and ferrocenophane derivatives (2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-germa-[1]ferrocenophane (2), 2-(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-1,3-dithia-2-germa-[3] ferrocenophane (3), 1,1′-bis(1-ethoxy-2,3,4,5-tetramethyl-1-germacyclopenta-2,4-dienyl)- ferrocene (6), 1,3-bis(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-1,3-digerma-2-oxo-[3] ferrocenophane (7), 1,1′-bis(1-hydrido-2,3,4,5-tetramethyl-1-germacyclopenta-2,4-dienyl)- ferrocene (8) and 1,2-bis(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-digerma-[2]ferrocenophane (9) have been prepared starting from the dichlorogermol 1. The synthesis of the known ferrocenophanes dichloro-(ferrocene-1,1′-dithiolato)-germane (10a) and dichloro-(ferrocene-1,1′-dithiolato)-stannane (10b) was improved. X-ray crystal structural studies of 2 (C₁₈H₂₀FeGe, a=10.907(4), b=11.040(4), c=13.771(5) ?, β=110.87°, monoclinic, C2/c (No. 15), Z=4), 3 (C₁₈H₂₀FeGeS₂, a=8.104(3), b=8.593(4), c=13.177(6) ?, α=70.79(4), β=77.56(3), γ=85.80(3) ? triclinic, P1? (No. 2), Z=2), 7 (C₂₆H₃₂FeGe₂O, a=18.95(2), b=8.557(6), c=16.69(6) ?, β=110.65(6)°, monoclinic, C2/c (No. 15), Z=4), 9 (C₂₆H₃₂FeGe₂, a=11.209(6), b=10.839(5), c=19.819(10) ?, β=92.89(2), γ=90°, monoclinic, P2₁/n (No. 14), Z=4), 10a (C₁₀H₈FeGeS₂, a=10.873(5), b=7.417(4), c=16.415(10) ?, orthorhombic, Pca2₁ (No. 29), Z=4), 12a (C₂₀H₁₆Fe₂GeS₄, a=7.459(4), b=10.921(5), c=23.552(12) ?, orthorhombic, Pbcn (No. 60), Z=4) and 12b (C₂₀H₁₆Fe₂SnS₄, a=7.484(4), b=10.953(6), c=23.917(12) ?, orthorhombic, Pbcn (No. 60), Z=4) and cyclovoltammetric characterizations for all ferrocene-containing compounds have been carried out.

Full text of DOI:10.1016/s0020-1693(99)00133-4

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Inorganica Chimica Acta 291 (1999) 355–364
Germanium-containing ferrocenes and ferrocenophanes. Potential
precursors for ring-opening polymerizations and ‘germaferrocenes’
Stefan Zu¨rcher, Volker Gramlich, Antonio Togni *
Laboratory of Inorganic Chemistry, ETH Zentrum, Swiss Federal Institute of Technology, CH-8092 Zu¨rich, Switzerland
Received 8 January 1999; accepted 26 February 1999
Abstract
The new germanium-containing ferrocene and ferrocenophane derivatives (2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-germa-
[1]ferrocenophane (2), 2-(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-1,3-dithia-2-germa-[3]ferrocenophane (3), 1,1%-bis(1-ethoxy-
2,3,4,5-tetramethyl-1-germacyclopenta-2,4-dienyl)-ferrocene (6), 1,3-bis(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-1,3-digerma-2-
oxo-[3]ferrocenophane (7), 1,1%-bis(1-hydrido-2,3,4,5-tetramethyl-1-germacyclopenta-2,4-dienyl)-ferrocene (8) and 1,2-bis(2,3,4,5-
tetramethylbuta-1,3-dien-1,4-diyl)-digerma-[2]ferrocenophane (9) have been prepared starting from the dichlorogermol 1. The
synthesis of the known ferrocenophanes dichloro-(ferrocene-1,1%-dithiolato)-germane (10a) and dichloro-(ferrocene-1,1%-dithio-
lato)-stannane (10b) was improved. X-ray crystal structural studies of 2 (C18H20FeGe, a=10.907(4), b=11.040(4), c=13.771(5)
,
,
A, i=110.87°, monoclinic, C2/c (No. 15), Z=4), 3 (C18H20FeGeS2, a=8.104(3), b=8.593(4), c=13.177(6) A, h=70.79(4),
,
(
,
i=77.56(3), k=85.80(3) A triclinic, P1 (No. 2), Z=2), 7 (C26H32FeGe2O, a=18.95(2), b=8.557(6), c=16.69(6) A, i=
,
110.65(6)°, monoclinic, C2/c (No. 15), Z=4), 9 (C26H32FeGe2, a=11.209(6), b=10.839(5), c=19.819(10) A, i=92.89(2),
k=90°, monoclinic, P21/n (No. 14), Z=4), 10a (C10H8FeGeS2, a=10.873(5), b=7.417(4), c=16.415(10) A, orthorhombic,
Pca21 (No. 29), Z=4), 12a (C20H16Fe2GeS4, a=7.459(4), b=10.921(5), c=23.552(12) A, orthorhombic, Pbcn (No. 60), Z=4)
and 12b (C20H16Fe2SnS4, a=7.484(4), b=10.953(6), c=23.917(12) A, orthorhombic, Pbcn (No. 60), Z=4) and cyclovoltammet-
,
,
,
ric characterizations for all ferrocene-containing compounds have been carried out. © 1999 Elsevier Science S.A. All rights
reserved.
Keywords: Crystal structures; Ferrocene complexes; Germanium complexes; Ferrocenophane complexes
1. Introduction
complexes containing the cyclopentadienyl anion; how-
ever, only very few where one carbon atom is replaced
by silicon or germanium [30–33]. In order to obtain
new data that would provide insight into the theoretical
aspects, and would additionally afford a new class of
donor molecules for charge-transfer (CT) complexes,
we have investigated the synthesis of ferrocene deriva-
Cyclopentadienes, where a heteroatom replaces one
of the ring carbons, are an interesting topic from a
theoretical point of view, as to the question of aro-
maticity of such five-membered rings [1–6]. Also, many
experimental studies towards the synthesis of such hete-
rocycles and their coordination chemistry have been
reported [4,7–20]. With cyclopentadienes containing a
Group 15 element (N, P, As, Sb, Bi), ferrocene-like
compounds do exist [21–29], implying that these rings
display at least some aromaticity. For the elements of
Group 14, there exists an extremely large number of
tives containing
a germacyclopentadienyl (germol)
fragment. We reported previously synthesis and charac-
terizations of CT complexes of ferrocenes bearing sulfur
substituents [34–37]. The large germanium atom should
enhance intermolecular interactions in CT complexes,
thus possibly improving, e.g. magnetic cooperativity
effects. Therefore, we were planning not to use very
large protecting groups at the Ge atom, such as
tris(trimethylsilyl)silyl, introduced and successfully ap-
plied by Tilley and co-workers [30,31].
* Corresponding author. Tel.: +41-1-632 22 36; fax: +41-1-632
10 90.
E-mail address: togni@inorg.chem.ethz.ch (A. Togni)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00133-4

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S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
2. Experimental
(62.895 MHz, CDCl3): 13.85 (CH3), 14.83 (CH3), 69.44
(CH Cp), 75.20 (CH Cp), 84.45 (Cipso Cp), 117.63
(C–Me), 145.56 (C–Me). MS: m/z 430 (M+., 100),
334, 322, 290, 226, 184, 108, 84, 56. Anal. Calc. for
C18H20FeGeS2: C, 50.40; H, 4.70; S, 14.95. Found: C,
50.24; H, 4.65; S, 14.86% IR (KBr): 3086, 2904, 2846,
1553, 1401, 1386, 1364, 1161, 1056, 1020, 892, 817, 800,
760, 525, 504.
2.1. Synthesis. General considerations
General experimental techniques were reported ear-
lier [34]. 1,1-Dichloro-2,3,4,5-tetramethyl-1-germacy-
clopenta-2,4-diene (1) was prepared as described in Ref.
[11].
2.4. Synthesis of 1-chloro-1-ethoxy-2,3,4,5-
tetramethyl-1-germacyclopenta-2,4-diene (4)
2.2. Synthesis of
(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-germa-[1]
ferrocenophane (2)
To 0.53 ml (9.1 mmol) of ethanol in 20 ml of THF
were added 5.7 ml (9.1 mmol; 1.6 M in hexane) of
methyllithium. The resulting solution was transferred to
2.3 g (9.1 mmol) of 1,1-dichloro-2,3,4,5-tetramethyl-1-
germacyclopenta-2,4-diene (1) and stirred for 30 min.
The solvent was distilled off and the oily residue was
distilled by a bulb-to-bulb distillation (100°C, 10−1
mbar). Yield: 1.91 g (80%) of a colourless liquid. In
solution, the product is in equilibrium with the corre-
sponding 1,1-dichloro- and 1,1-diethoxy-derivatives, as
A total of 1.18 g (3.798 mmol) of the 1,1%-dilithium-
ferrocene-TMEDA complex [38], suspended in 20 ml of
hexane and 956 mg (3.798 mmol) of 1,1%-dichloro-
2,3,4,5-tetramethyl-1-germacyclopenta-2,4-diene (1) dis-
solved in 5 ml of hexane were cooled separately to
−20°C. The latter solution was then added slowly to
the suspension of the dilithiated ferrocene. The reaction
mixture was stirred for 6 h at room temperature and
filtered. The solvent was removed under reduced pres-
sure until crystallization started. Yield after one night
at −20°C: 518 mg (37%) dark red crystals. M.p.:
1
shown by NMR spectroscopy. H NMR (250.13 MHz,
CDCl3): l 1.2–2.2 (m complex, ca. 15H), 3.85–4.15 (m
complex, 2H). 13C NMR (62.895 MHz, C6D6) 12.24,
13.04, 13.32, 13.48, 13.51, 13.97, 14.31, 19.06, 19.46,
59.98, 60.31, 61.25, 121.71, 122.84, 124.26, 145.24,
1
170°C. H NMR (250.13 MHz, CDCl3): l 1.93 (s, 6H,
CH3), 2.19 (s, 6H, CH3), 4.38 (t, J=1.6, 4H, CH Cp),
4.48 (t, J=1.6, 4H, CH Cp). 13C NMR (62.895 MHz,
CDCl3): 14.14 (CH3), 16.32 (CH3), 27.08 (Cipso Cp),
75.69 (CH Cp), 76.54 (CH Cp), 128.994 (C–Me),
147.07 (C–Me). MS: m/z 366 (M+, 80), 351, 292, 277,
259, 245 (100), 229, 203, 193, 139. Anal. Calc. for
C18H20FeGe: C, 59.26; H, 5.53. Found: C, 59.26; H,
5.73% IR (KBr): 3086, 3085, 3069, 2939, 2901, 2846,
1559, 1437, 1372, 1362, 1288, 1213, 1175, 1111, 1058,
1017, 902, 877, 857, 845, 806, 763, 677, 651, 591, 528,
507, 478, 406.
145.61, 146.28, 146.40, 147.23. GC-MS: m/z 262 (M+.
,
43), 227, 218, 181, 163, 123, 109 (100), 93, 77, 67 59.
Anal. Calc. for C10H17OClGe: C, 45.97; H, 6.56.
Found: C, 46.24; H, 6.72%.
2.5. Synthesis of
1,1%-bis(1-ethoxy-2,3,4,5-tetramethyl-1-germ-
acyclopenta-2,4-dienyl)-ferrocene (6)
A total of 732 mg (2.8 mmol) of 1-chloro-1-ethoxy-
2,3,4,5-tetramethyl-1-germacyclopenta-2,4-diene
(4)
2.3. Synthesis of
were dissolved in 2 ml of THF and cooled to −78°C.
440 mg (1.4 mmol) of 1,1%-dilithioferrocene TMEDA
complex [38] were dissolved in 10 ml of THF and added
slowly to the germacyclopentadiene solution dropwise.
After slowly warming up the solution to room tempera-
ture, the solvent was evaporated under reduced pres-
sure. The product was extracted with 20 ml of dry
hexane, filtered over celite. After partial evaporation to
a volume of about 5 ml, the product crystallized
overnight at −20°C. Yield: 347 mg (39%) of a yellow
product. 1H NMR (250.13 MHz, CDCl3): l 1.14 (t,
J=6.9, 6H, CH3), 1.92 (s, 12H, CH3), 2.03 (s, 12H,
CH3), 3.59 (q, J=6.9, 4H, CH2), 4.16 (t, 4H, CH Cp),
4.23 (t, 4H). 13C NMR (62.895 MHz, CDCl3) 14.07
(CH3), 15.26 (CH3), 19.30 (CH3), 60.60 (CH2), 65.92
(Cipso Cp), 71.72 (CH Cp), 73.36 (CH Cp), 125.97
(C–Me), 147.32 (C–Me). MS: m/z 636 (M+., 100),
2-(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-
1,3-dithia-2-germa-[3]ferrocenophane (3)
1.5 g (31 mmol) of sodium hydride dispersion in oil
(ꢀ50%) were washed three times with hexane and
suspended in 30 ml of THF. 948 mg (3.79 mmol) of
1,1%-ferrocenedithiol [38] were added and the reaction
mixture was stirred until evolution of hydrogen ceased.
A solution of 955 mg (3.79 mmol) of 1,1-dichloro-
2,3,4,5-tetramethyl-1-germacyclopenta-2,4-dien (1) in
10 ml of hexane was added dropwise. The resulting
yellow solution containing a white solid was filtered
and evaporated to dryness. Yield: 1.12 g (69%) of a
1
yellow microcrystalline powder. M.p.: 238–240°C. H
NMR (250.13 MHz, CDCl3): l 1.88 (d, J=0.75, 6H,
CH3), 2.07 (d, J=0.75, 6H, CH3), 4.11 (t, J=1.9, 4H,
CH Cp), 4.26 (t, J=1.9, 4H, CH Cp). 13C NMR

S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
357
562, 544, 365, 299, 180. Anal. Calc. for C30H42O2FeGe2:
C, 56.68; H, 6.66. Found: C, 56.71; H. 6.73% IR (KBr):
3080, 2968, 2919, 2853, 1560, 1478, 1438, 1383, 1214,
1159, 1099, 1061, 1033, 908, 829, 762, 663, 613, 482,
372, 285, 226, 210.
n-BuLi were added. The reaction mixture was allowed
to warm up to room temperature and was stirred
overnight. The mixture was then cooled to −78°C, 30
mg (0.23 mmol) of anhydrous iron(II) chloride were
added in one portion and the mixture was warmed up
slowly to room temperature. At −20°C, the solution
darkened and became a black suspension at room
temperature (probably because of the formation of
elemental iron). The solvent was evaporated under re-
duced pressure and the product extracted with hexane.
Yield after crystallization at −20°C: 6 mg (5%) of
2.6. Synthesis of
1,3-bis(2,3,4,5-tetramethylbuta-1,3-dien-1,4-diyl)-
1,3-digerma-2-oxa-[3]ferrocenophane (7)
A total of 105 mg (0.165 mmol) 1,1%-bis(1-ethoxy-
2,3,4,5-tetramethyl-1-germacyclopenta-2,4-dienyl)-ferr-
ocene (6) were dissolved in 10 ml of hexane, 4 drops of
a 2N HCl solution were added and the solution was
stirred overnight. The organic phase was dried over
Na2SO4 and evaporated to dryness. Yield: 40 mg (43%)
of a yellow, crystalline product. 1H NMR (250.13
MHz, CDCl3): l 1.80 (s, 12H, CH3), 2.02 (s, 12H,
CH3), 4.30–4.35 (t, J=1.6, 4H, CH Cp), 4.40–4.43 (t,
J=1.6, 4H, CH Cp). 13C NMR (75.47 MHz, CDCl3)
13.6 (CH3), 14.7 (CH3), 68.6 (Cipso Cp), 71.2 (CH Cp),
72.4 (CH Cp), 126.7 (C–Me), 146.2 (C–Me). MS: m/z
562 (M+., 100), 459, 365, 302, 292, 245, 194, 107, 91,
77. Anal. Calc. for C26H32OFeGe2: C, 55.61; H, 5.74.
Found: C, 55.81; H, 5.71.
1
orange crystals. H NMR (250.13 MHz, CDCl3): l 1.80
(s, 12H, CH3), 2.24 (s, 12H, CH3), 4.20–4.30 (q, 4H,
1
CH Cp), 4.70–4.75 (q, 4H, CH Cp). H NMR (300.13
MHz, C6D6): l 1.70 (s, 12H), 2.39 (s, 12H), 4.25–4.31
(q, 4HCp), 4.80–4.90 (q, 4H-Cp). 13C NMR (75.47
MHz, C6D6) 13.7 (CH3), 16.5 (CH3), 69.6 (CH Cp),
74.0 (CH Cp), 77.4 (Cipso Cp), 130.5 (C–Me), 145.1
(C–Me). MS: m/z 446 (M+., 100), 438, 365, 292, 245.
Anal. Calc. for C26H32FeGe2: C, 57.24; H, 5.91. Found:
C, 56.98; H, 5.93.
(b) 100 mg (0.157 mmol) of 1,1%-bis(1-ethoxy-2,3,4,5-
tetramethyl-1-germacyclopenta2,4-dienyl)-ferrocene (6)
and 3.6 mg (0.52 mmol) of lithium in 5 ml of THF were
refluxed for 2 h. The solvent was removed under re-
duced pressure and the residue recrystallized from hex-
ane. Yield: 12 mg (14%) of orange crystals with the
same analytical data as the product obtained under a).
A second but less clean crop of product (28 mg (32%))
was obtained by flash chromatography on silica with
dichloromethane as eluent.
2.7. Synthesis of
1,1%-bis(1-hydrido-2,3,4,5-tetramethyl-1-
germacyclopenta-2,4-dienyl)-ferrocene (8)
A total of 173.4 mg (0.27 mmol) of 1,1%-bis(1-ethoxy-
2,3,4,5-tetramethyl-1-germacyclopenta-2,4-dienyl)-ferro-
cene (6) were dissolved in 15 ml of THF and cooled to
0°C. 0.27 ml (0.27 mmol, 1 M in THF) of LiAlH4
solution were added. The reaction mixture was stirred
at room temperature for 18 h. The solvent was removed
under reduced pressure, the product dissolved in hexane
and filtered twice over celite. Yield: 111 mg (75%) of an
2.9. Synthesis of
dichloro-( ferrocene-1,1%-dithiolato)-germane [39] (10a)
A total of 2.32 g (9.25 mmol) of ferrocene-1,1%-dithiol
[38] and 1.6 ml (13.9 mmol) of germanium tetrachloride
were refluxed for 2 h in benzene until no evolution of
HCl gas could be detected. The resulting orange solu-
tion was evaporated to dryness and the product dried
under high vacuum. Yield: 3.31 g (90%). 1H NMR
(250.13 MHz, CDCl3): l 4.18–4.23 (m, 4H, CH Cp),
4.43–4.45 (m, 4H, CH Cp). 13C NMR (62.895 MHz,
CDCl3): 71.29 (CH Cp), 75.01 (CH Cp), 76.00 (Cipso
Cp). MS: m/z 392 (M+., 100), 357, 261, 248, 214, 170,
152, 126, 64, 56, 40. Anal. Calc. for C10H8FeGeS2Cl2:
C, 30.67; H, 2.06; S, 16.37. Found: C, 30.85; H, 1.98; S,
16.43. IR (KBr): 3099, 1654, 1636, 1407, 1389, 1163,
1056, 1028, 1020, 890, 858, 825, 523, 497, 441, 412.
1
orange oil. H NMR (250.13 MHz, CDCl3): l 1.85 (s,
12H, CH3), 2.16 (s, 12H, CH3), 4.27–4.30 (t, 4H, CH
Cp), 4.30–4.40 (t, 4H, CH Cp), 5.54 (s, 2H, Ge-H). 13C
NMR (62.895 MHz, CDCl3) 14.10 (CH3), 15.95 (CH3),
67.21 (Cipso Cp), 71.30 (CH Cp), 73.62 (CH Cp), 129.24
(C–Me), 146.97 (CMe). MS: m/z 548 (M+., 100), 438,
367, 330, 2912, 259, 245, 186, 139. Anal. Calc. for
C26H34FeGe2: C, 57.03; H, 6.26. Found: C, 57.22; H,
6.28.
2.8. Synthesis of 1,2-bis(2,3,4,5-tetramethylbuta-
1,3-dien-1,4-diyl)-digerma-[2] ferrocenophane (9)
2.10. Synthesis of dichloro-( ferrocene-1,1%-
dithiolato)-stannane [39] (10b)
(a) 111 mg (0.203 mmol) of 1,1%-bis(1-hydrido-2,3,4,
5-tetramethyl-1-germacyclopenta-2,4-dienyl)-ferrocene
(8) were dissolved in 10 ml of THF and cooled to
−78°C. 0.25 ml (0.23 mmol, 1.6 M in hexane) of
A total of 525 mg (2.1 mmol) ferrocen-1,1%-dithiol
[38] were dissolved in 50 ml of benzene and 0.37 ml

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S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
(3.15 mmol) of tin tetrachloride were added. The result-
ing dark violet solution was refluxed for 1 h and
evaporated to dryness. Yield: 772 mg (84%). A very
clean fraction for elemental analysis could be obtained
by sublimation. 1H NMR (250.13 MHz, CDCl3): l
3.60–3.76 (m, 4H, CH Cp), 3.85–3.40 (m, 4H, CH Cp).
13C NMR (62.895 MHz. CDCl3): 71.17 (CH Cp), 75.33
(CH Cp). MS: m/z 435 (M+., 100), 402, 341, 306, 259,
248, 223, 152, 120, 56. Anal. Calc. for C10H8FeSnS2Cl2:
C, 27.44; H, 1.84; S, 14.65. Found: C, 27.58; H, 2.08; S,
14.68. IR (KBr): 3099, 1654, 1407, 1388, 1362, 1162,
1052, 1028, 887, 849, 823, 517, 496, 415, 390, 360, 343,
321.
solution was evaporated to dryness. A mass spectrum
of the residue showed it to be a mixture of at least three
products (bis(ferrocene-1,1%-dithiolato)germanium (12a),
bis(tolyl-3,4-dithiolato)germanium (13a) and (ferro-
cene - 1,1% - dithiolato - tolyl - 3,4 - dithiolato)germanium
(11a)). The residue was extracted with dichloromethane
and recrystallized from 1,2-dichloroethane. 62 mg
(68%) of 12a were obtained as yellow crystals, which
could be used directly for X-ray analysis. 1H NMR
(250.13 MHz, CDCl3): l 4.3–4.7 (m, 8H, CH Cp),
4.2–4.7 (m, 8H, CH Cp). 13C NMR (62.895 MHz,
CDCl3): 70.11 (CH Cp), 74.83 (CH Cp). MS: m/z 569
(M+., 100), 377, 322, 304, 272. Anal. Calc. for
C20H16Fe2S4Ge: C, 42.22; H, 2.83; S, 22.55. Found: C,
41.98; H, 2.71; S, 22.65. IR (KBr): 3098, 3087, 1407,
1385, 1360, 1162, 1052, 1024, 890, 848, 830.
2.11. Synthesis of bis( ferrocene-1,1%-dithiolato)-
germane [39] (12a)
To 50.6 mg (0.32 mmol) of toluene-3,4-dithiol dis-
solved in 4 ml of THF were added 0.4 ml (0.64 mmol)
of n-BuLi (1.6 M in hexane). The resulting solution was
transferred at 0°C to a solution containing 1,1%-(1,3-
dithia-2,2-dichlorogermyl)-[3]ferrocenophane (10a) in
20 ml of THF, stirred for 5 min at 0°C and for an
additional hour at room temperature. Subsequently, the
2.12. Synthesis of
bis( ferrocene-1,1%-dithiolato)-stannane [39,40] (12b)
A similar procedure as for the synthesis of 12a was
followed. Recrystallization from chloroform yielded a
few red platelets.
Table 1a
Experimental data for the X-ray diffraction studies of 2, 3, 7 and 9
2
3
7
9
Empirical formula
Formula weight
C18H20FeGe
364.8
C18H20FeGeS2
428.9
C26H32FeGe2O
561.5
C26H32FeGe2
545.5
Crystal dimensions (mm)
Crystal system
Space group (No.)
0.3×0.1×0.1
monoclinic
C2/c (15)
10.907(4)
11.040(4)
13.771(5)
90
110.87(3)
90
1549.4(10)
4
0.8×0.7×0.2
triclinic
0.5×0.2×0.2
monoclinic
C2/c (15)
18.95(2)
8.557(6)
16.69(6)
90
110.65(6)
90
2533(5)
4
0.22×0.20×0.16
monoclinic
P21/n (14)
11.209(6)
10.839(5)
19.819(10)
90
92.89(2)
90
2405(2)
4
(
P1 (2)
,
a (A)
8.104(3)
8.953(4)
13.177(6)
70.79(4)
77.56(3)
85.80(3)
881.6(7)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
z(calc)r (g cm−3
)
1.564
2.863
744
1.616
2.757
436
1.472
7.429
1144
1.507
7.774
1112
v (mm−1
F(000)
)
Diffractometer
Wavelength u (A)
q Range (°)
Syntex P21
Mo Ka, u=0.71073
2.72–20.04
787
737
109
0.0639
0.0236
0.573
Syntex P21
Mo Ka, u=0.71073
1.67–20.03
1803
1645
232
0.091
0.030
1.095
Picker STOE
Cu Ka, u=1.54178
4.99–49.93
1428
1314
138
0.0889
0.0347
1.106
Picker STOE
Cu Ka, u=1.54178
4.4–50.00
2474
2474
271
0.0882
0.0324
0.991
,
Measured reflections
Reflections observed (n) a
Parameters refined (p)
wR2 [1\2|(I)] b
R1 [1\2|(I)] c
GOF on F2 d
2
2
a (ꢀFo ꢀ=4.0 |(ꢀFꢀ )).
b wR2=[|(w(Fo2−Fc2)2]/|[w(Fo2)2]1/2
c R1=|ꢀꢀFoꢀ−ꢀFcꢀꢀ/|ꢀFoꢀ.
.
d GOF=S=[|(w(Fo2−Fc2)2]/(n−p)]1/2
.

S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
359
Table 1b
Experimental data for the X-ray diffraction studies of 10a, 12a and 12b
10a
12a
12b
Empirical formula
Molecular weight
Crystal dimensions (mm)
Crystal system
C10H8FeGeS2
391.6
C
568.9
20H16FeGeS4
C20H16Fe2SnS4
615.0
0.2×0.2×0.14
orthorhombic
Pca21 (29)
10.873(5)
7.417(4)
16.415(10)
90
0.6×0.5×0.1
orthorhombic
Pbcn (60)
7.459(4)
10.921(5)
23.552(12)
90
0.3×0.3×0.06
orthorhombic
Pbcn (60)
7.484(4)
10.953(6)
23.917(12)
90
90
90
1961(2)
4
2.083
Space group (No.)
,
a (A)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
90
90
90
90
3
,
V (A )
Z
1323.8(12)
4
1.965
4.052
768
1918.5(17)
4
1.969
17.905
1136
z(calc)r (g cm−3
)
v (mm−1
F(000)
)
25.766
1208
Diffractometer
Wavelength u (A)
q Range (°)
Syntex P21
Mo Ka, u=0.71073
2.48–20.0
650
650
144
0.1192
0.0522
1.222
Picker STOE
Cu Ka, u=1.54178
3.75–49.99
1196
989
124
0.0795
0.0294
1.117
Picker STOE
Cu Ka, u=1.54178
3.70–49.98
1006
1006
,
Measured reflections
Reflections observed (n) a
Parameters refined (p)
wR2 [1\2 |(I)] b
R1 [1\2 |(I)] c
124
0.1142
0.0493
1.044
GOF on F2 d
2
2
a (ꢀFo ꢀ\4.0 |(ꢀFꢀ )).
b wR2=[|(w(Fo2−Fc2)2]/|[w(Fo2)2]1/2
c R1=|ꢀꢀFoꢀ−ꢀFcꢀꢀ/|ꢀFoꢀ.
.
d GOF=S=[| (w(Fo2−Fc2)2]/(n−p)]1/2
.
2.13. X-ray crystallographic studies of 2, 3, 7, 9, 10a,
12a and 12b
3. Results and discussion
3.1. Synthesis
Suitable crystals for an X-ray analysis of all these
compounds were obtained by cooling hot saturated
hexane solutions to −20°C. Selected crystallographic
and relevant data collection parameters are listed in
Tables 1a and 1b. Data were measured at room temper-
ature (293(2) K) with variable scan speed to ensure
constant statistical precision on the collected intensities.
One standard reflection was measured every 120 reflec-
tions and no significant variation was detected. The
structures were solved by Direct or Patterson Methods
and refined by full-matrix least squares using an-
isotropic displacement parameters for all non hydrogen
atoms. The contribution of the hydrogen atoms in their
The starting idea was to introduce two germol frag-
ments onto ferrocene, and to use them subsequently as
ligands for the construction of a second metallocene,
thus leading to a biferrocene-like structure.
For all germacyclopentadiene-containing ferrocenes
reported here, 1,1-dichloro-1-germa-2,3,4,5-tetramethyl-
cyclopentadiene (1) (dichlorogermol) (see Scheme 1)
was used as starting material as obtained following a
reported procedure [11]. By the direct reaction of
dichlorogermol
1
with the dilithiated ferrocene-
TMEDA complex [38,41,42] [1]ferrocenophane 2 was
obtained as main product (40% yield) together with
oligomeric by-products that were not further character-
ized. Compound 2 should be a useful precursor for ring
opening polymerizations (ROP) [43]. Even if an excess
of 1 was used, no disubstituted ferrocene could be
idealized position (Riding model with fixed isotropic
2
,
U=0.080 A ) was taken into account but not refined.
All calculations were carried out by using the Siemens
SHELX93 (VMS) system.

360
S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
rocene. A 2D 1H NMR experiment (proton–proton
correlation) of the observed intermediate formed by the
addition of 1 equiv. of LiOEt to 1 showed that an
equilibrium mixture of the desired 1-chloro-1-ethoxy-
germol 4, the dichlorogermol 1 and the diethoxygermol
5 is formed. By reacting this mixture with the dilithi-
ated ferrocene-TMEDA complex, the disubstituted
compound 6 could be isolated in 39% yield together
with oligomers and the [1]ferrocenophane 2. By an
attempt to recrystallize 6 from chloroform, a small
amount of yellow crystals were obtained. This com-
pound turned out to be the oxygen bridged
[3]ferrocenophane 7. The same compound was obtained
in moderate yield by the reaction of 6 with 2N aq HCl
in hexane. The reduction of the diethoxy compound 6
with LiAlH4 produced 8 in good yield (75%) as an
orange oil. When 8 was reacted with n-BuLi and
iron(II) chloride, the expected diferrocene-like com-
pound could not be isolated but the [2]ferrocenophane
9 was isolated in a very low yield of 5%. This was
accompanied by a significant amount of a black residue
(probably elemental iron). A better yield of 46% could
be obtained by the direct reduction of the diethoxy
compound 6 with lithium in THF. The formation of 9
from either 6 or 8 is at first sight quite surprising.
However, it is known that germanides, here both
formed from 6 and 8, respectively, as intermediates,
readily couple affording digermanes [1a].
With the aim of preparing Ge (and Sn) spiro com-
pounds, the known dichlorides 10 were needed. Thus,
the dichloro [3]ferrocenophane 10a was formed in ex-
cellent yield upon reaction of ferrocene dithiol and
germanium tetrachloride in boiling benzene. The origi-
nal synthesis reported by Osborne [39], in which a
10-fold excess of germanium tetrachloride and triethyl-
amine as a base were used (yield 61%), could be im-
proved. The analogous tin derivative 10b was obtained
by the same procedure. The reaction of this compound
with a second different dithiol ligand, such as toluene-
3,4-dithiol, did not allow us to isolate the desired mixed
ligand compounds 11a or 11b but the bis(ferrocene-1,1%-
dithiolato)germanium (12a) and the analogous tin
derivative 12b, respectively. Thus, ligand scrambling
leading to the homoleptic derivatives is the major path-
way under the reported conditions. Therefore, we did
not pursue the synthesis of compounds 11 any further
(Scheme 2).
Scheme 1. Synthesis of germacyclopentadiene-containing ferrocenes,
starting from 1,1-dichloro-2,3,4,5-tetramethyl-1-germacyclopentadi-
ene (1).
obtained. Similarly, the [3]ferrocenophane 3 was ob-
tained in good yields (70%) by deprotonation of fer-
rocene-1,1%-dithiol with NaH and reaction with
dichlorogermol 1.
Since the desired disubstituted ferrocene was not
accessible by the above route, one chloride of the
dichlorogermol was replaced by an ethoxy group, in
order to ensure different reactivity of the two leaving
groups, favouring a disubstitution reaction of fer-
3.2. Solid-state structure of germanium substituted
ferrocenes
For seven of the obtained products, single crystal
X-ray studies were carried out. Tables 1a and 1b give
the relevant crystal and data collection parameters.
Bond distances and angles of each asymmetric unit
were found to fall in the expected ranges and will not
Scheme 2. Attempted synthesis of germanium and tin complexes with
two different chelating sulfur ligands.

S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
361
Fig. 1. ORTEP plots and atom numbering schemes of the seven compounds 2, 3, 7, 9, 10a, 12a, and 12b. Thermal ellipsoids are drawn at the 30%
probability level at 293 K.
be discussed in detail (they are provided as Supplemen-
tary Material). ORTEP representations of the seven
molecules are depicted in Fig. 1 and relevant structural
features are shown in the schematic plot of Fig. 2.
[1]Ferrocenophane 2 crystallizes in the monoclinic
space group C2/c, with iron and germanium on the
2-fold axes. The bridging germanium shows a relatively
quite small angles of 92° for C(1)–Ge–C(1A) and
C(6)–Ge–C(6A). The two Cp rings span an angle of
18.9°, which is comparable to angles found in other
[1]ferrocenophanes with silicon or germanium bridges
[44,45]. The bond Ge–C(1) is bent by 36.7° out of the
Cp plane.
The [3]ferrocenophane 3 crystallizes in the triclinic
,
(
short distance of 2.80 A to iron. The two different
space group P1. The two Cp rings are eclipsed and
,
Ge–C distances are in the normal range (1.93 A for
parallel (interplanar angle: 1°). The geometry of the
bridge is comparable to the one found in similar SES-
[3]ferrocenophanes (E=C, S, Si, Ge, Sn, and others)
,
Ge–Cp and 1.97 A for the germol ring). The coordina-
tion sphere at germanium is tetrahedrally distorted with

362
S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
[38,40] where the two sulfur atoms are always eclipsed
and the central bridging atom is out of the plane of the
four atoms S(1), C(1), C(1%), and S(2). The correspond-
ing interplanar angle is 53.6°. The two sulfur atoms are
slightly above the respective Cp planes and the S–S
2-fold axes. The two Cp rings are parallel (interplanar
angle 0.32°) but rotated against each other by 11.8°.
The two germacyclopentadienyl rings span a mutual
angle of 74.3 and of 52.8° with the Cp rings, respec-
tively. The germanium atom lies almost perfectly in the
plane of the respective Cp ring (distance to this plane is
,
distance is 3.64 A whereas the distance C(1)–C(1%) is
,
,
only 3.33 A The two sulfur atoms form an angle with
0.05 A). Because of the 2-fold axes, the six-membered
germanium of 109°, corresponding to the angle in a
tetrahedron. The distance germanium–iron is quite
ring, constituted by iron, the two Cipso-carbon atoms,
the two germanium atoms and oxygen shows a twist
conformation.
,
large (3.85 A).
The [3]ferrocenophane 7 crystallizes in the mono-
clinic space group C2/c with oxygen and iron on the
The [2]ferrocenophane 9 crystallizes in the mono-
clinic space group P21/n. The two Cp rings are bent
Fig. 2. Schematic drawings of the seven compounds 2, 3, 7, 9, 10a, 12a, and 12b with the most important angles and bond distances.

S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
363
Table 2
Formal electrode potentials (vs. Fc/F+c ) for ferrocene derivatives in dichloromethane solutiona
Compound
E°0% /+% (V)
DEp% (mV)
i
pc/ipa
E°1% +/2+% (V)
(+0.77)(+1.23)
+0.58
DEp% (mV)
ipc/ipa
2
3
6
7
+0.15b
+0.25b
+0.26c
+0.44c
+0.24c
+0.43d
+0.42b
+0.26b
335
245
308
132
112
183
101
482
1.3
1.04
1.49
1.06
1.11
1.24
2.70
4.99
9
10a
12a
12b
94
1.1
a All experiments carried out in dry dichloromethane/0.1 M (NBu4)(BF4) versus 0.05 M Fc/F+c reference electrode with E°%=+0.042 V for
ferrocene, and a Pt working electrode (all values are corrected for 0 V). Values in brackets are Epa (anodic peak potential) only assigned to
irreversible oxidation steps. DEp is the difference between anodic and cathodic peak potential and ipc/ipa is a measure for the reversibility of the
redox process.
b Scan rate: 100 mV s−1
c Scan rate: 30 mV s−1
d Scan rate: 10 mV s−1
.
.
.
slightly by 4.9°. The planes of the two germacyclopen-
tadienyl rings are almost perpendicular to each other
(interplanar angle is 85.1°) and the two crystallographi-
cally independent angles between the Cp rings and the
germacyclopentadienyl rings are 41.0 and 49.0°. The
two Cp rings are not staggered perfectly. This is shown
by the torsion angle −11° of C(1)–Ge(1)–Ge(2)–C(1%)
or by the rotation of the two Cp rings against each
other by 7.8°, respectively. As in 2, the two CipsoꢀGe
bonds are bent slightly by about 9.5° out of the plane
of the Cp ring. The distances of germanium to iron are
these two compounds the bridges have a similar confor-
mation as in the other two [3]ferrocenophanes with
SES-bridges 3 and 10a.
3.3. Electrochemical characterization
In order to judge the ability of the new compounds
to act as electron donors in CT complexes, their oxida-
tion potentials were determined by means of cyclo-
voltammetric measurements. The redox potentials are
reported in Table 2. All derivatives turn out to be
relatively hard to oxidize, as they all display positive
E°%-values, as compared to non-substituted ferrocene.
Even the strong acceptor TCNQF4 (E°1% −/0= +0.14 V)
should not be able to oxidize one of these ferrocenes
under the typical conditions used for the formation of
CT complexes (e.g. in hot dichloromethane). As it is
expected for ferrocene compounds, the derivatives ex-
amined all show at least one reversible oxidation wave.
The diethoxy compound 8 displays two additional irre-
versible oxidation waves at higher potential, probably
connected with the oxidation of the germacyclopentadi-
enyl rings. The bisferrocene 12a can be reversibly oxi-
dized twice, meaning that the two iron atoms
communicate with each other through the sulfur–ger-
manium bridge. The analogous tin derivative, in the
contrary, shows only one irreversible oxidation wave.
,
3.39 and 3.40 A, and the Ge–Ge bond distance is 2.43
,
A.
The [3]ferrocenophane 10a crystallizes in the or-
thorhombic space group Pca21. The two Cp rings are
almost parallel with an interplanar angle of 3.4° and the
,
two sulfur atoms lie 0.15(1) A above the respective Cp
,
rings. The S–S distance is 3.76 A, whereas the distance
between the two Cipso carbon atoms is only 3.36 A The
iron–germanium distance is with 3.36 A a little shorter
,
,
than the corresponding distance in 3. The conformation
of the bridge is comparable to the one in ferro-
cenophane 3. The germanium atom displays an almost
perfect tetrahedral coordination sphere. Only the angle
S(1)–Ge(1)–S(1%) (118.5°) deviates more than by 9°
from the expected optimum value for a tetrahedral
,
geometry. The sulfur–germanium distances are 2.19 A
,
and the chloro–germanium distances 2.14 A.
The two compounds 12a and 12b, the crystal struc-
ture of which has not been reported before, are iso-
morphous and crystallize in the orthorhombic space
group Pbcn (values for the tin derivative in brackets).
The germanium (tin) lies on the 2-fold axes which
converts one of the ferrocene ligands into the other.
The single molecules are chiral. The two Cp rings are
not perfectly parallel (interplanar angle 2.2° (4.5°)) and
they are rotated against each other by 5.9° (6.7°). In
4. Conclusions
Some ferrocene derivatives containing Ge sub-
stituents were prepared. However, the final goal to
obtaining
a
biferrocene-like compound was not
achieved. Iron(II) behaves as an oxidating agent for the
germacyclopentadienyl anion, thus giving an oxidative
coupling of the germanium atoms. Further studies to-

364
S. Zu¨rcher et al. / Inorganica Chimica Acta 291 (1999) 355–364
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reactions.
2 towards ring-opening polymerization
5. Supplementary material
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Crystallographic data (excluding structure factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC
112439-CCDC 112445. Copies of the data can be ob-
tained free of charge on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: (+44)
1223 336-033; e-mail: deposit@ccdc.cam.ac.uk), or may
be obtained from the authors upon request.
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Acknowledgements
S.Z. is grateful to the Swiss National Science Foun-
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